Mass Customization in Building Envelope

#### **Chapter 4**

## Perspective Chapter: Prefabricated Building Envelope Modular Assemblies for Secure Facilities

*Hugh D. Lester and Andrew Schopp*

#### **Abstract**

Mid-rise and high-rise urban jails are subject to complex performance requirements at the building envelope. This case study examines the design of dual envelope systems—a unitized curtain wall system and a modular steel cell secure perimeter system—for thermal performance and security, emphasizing compliance with the New York City Energy Conservation Code (NYCECC) and ASTM F33 standards. These systems are designed through a design-build, design-assist collaboration with separate subcontractors under contract to the design-builder. Key considerations include the location, spacing, form, and dimensions of structural columns, spandrel beams, or intermediate hollow structural steel supports, and the overall size of unitized curtain wall elements. Additional factors range from the sequence of trades to fire-stopping. The well-being of persons in custody is a primary focus, as the design team aims to create normative environments. Prefabrication plays a crucial role in achieving project objectives. The case study delves into design considerations, the design process, and explores an alternative system approach and its implications.

**Keywords:** jail, building envelope, secure perimeter, prefabrication, energy conservation

#### **1. Introduction**

In the United States, each county within every state is overseen by a Sheriff responsible for detaining individuals awaiting their first court appearance, except in cases where citation and release apply. According to the 2010 census, there were a total of 50 states and 3143 counties in the United States, which includes the District of Columbia but excludes U.S. territories [1]. However, not every county maintains their own jail facility, leading those without one to house detainees in nearby jurisdictions at a negotiated cost. Nonetheless, jails represent substantial infrastructural investments, especially in highly urbanized areas where land is expensive, necessitating the construction of mid-rise or high-rise jails.

The urgency of addressing climate change has spurred regulatory initiatives aimed at enhancing building performance in many jurisdictions, with the New York City Energy Conservation Code (NYCECC) [2] serving as a pertinent example. This case study focuses on the Borough-Based Jail (BBJ) capital improvement program

[3], under which new jails will be constructed in four of New York City's five boroughs. Each of these boroughs corresponds to a county within the State of New York: Bronx (Bronx County), Brooklyn (Kings County), Manhattan (New York County), and Queens (Queens County) [4]. As per the approved Uniform Land Use Review Procedure (ULURP) for the BBJ program [5], the Bronx and Queens jails are limited to a height of less than 195 feet, while the Brooklyn and Manhattan jails are capped at less than 295 feet [6]. For our purposes, we classify the former as mid-rise and the latter as high-rise structures. The NYCECC mandates rigorous envelope design to mitigate infiltration or exfiltration [7] and thermal bridging, which is critical for both mid-rise and high-rise jail facilities.

Since the cell serves as the innermost security zone within a jail, and BBJ cells are required to provide natural light through a clear glazing area equaling 10% of the room floor area [8], the cell's exterior wall and glazing must meet or exceed regulatory standards for attack resistance at the secure perimeter. These standards include ASTM F2322-12(2019) Standard Test Methods for Physical Assault on Vertical Fixed Barriers for Detention and Correctional Facilities (60 min) [9], F1592-12(2019) Standard Test Methods for Detention Hollow Metal Vision Systems (60 min) [10], and ASTM F1915- 05(2019) Standard Test Methods for Glazing for Detention Facilities (60 min) [11].

This chapter addresses these complex requirements and explores additional factors, such as achieving a weather-tight enclosure promptly, construction trade sequencing, the role of prefabrication in reducing on-site labor and enhancing quality, critical path items related to enclosure within the overall delivery timeline, life cycle cost considerations, carbon footprint, return on investment, construction tolerances, fire-stopping, accommodating building movement, ensuring ongoing maintenance access, the potential for reflective interior surfaces inhibiting vision, and the possibility of a 'fishbowl' effect due to the separation of secure and non-secure glazing assemblies, among other considerations. This case study will provide insights into the design-build, design-assist process [12] and the nature of the proposed design. Sustainability is underpinned by the energy efficiency of the proposed design, while an alternative system to a dual systems approach will also be explored, along with its implications.

The final requirement of this case study is that the proposed dual systems or alternative system maintain compatibility with other perimeter conditions within the project and adhere to the Building Exterior Design Guidelines [13]. These guidelines require design-build teams to:


#### *Perspective Chapter: Prefabricated Building Envelope Modular Assemblies for Secure Facilities DOI: http://dx.doi.org/10.5772/intechopen.113959*

Design decisions were reached through a careful balancing act involving concerns for Request for Proposal (RFP) compliance, performance, and cost. Collaboration between the design and construction teams is intrinsic to the design-build project delivery method, and this collaboration intensifies during the in-market procurement phase. In this instance, the procurement takes the form of a design-build competition between two teams, advancing the design to approximately 20% of its development. The stakes are high, as all participants in the design-build competition—even those receiving a stipend when not selected—bear a financial impact if their firms are not selected. Following proposal review and selection of the preferred proposer, a contract is negotiated and registered by the City. Upon receipt of a notice to proceed (NTP), the design-build team begins to implement their proposal, which involves significant additional design alongside actual construction. This case study, however, only addresses the design process that occurred during the in-market procurement period, from RFP receipt to proposal submission.

The in-market period is characterized by highly restricted communication protocols, with the RFP, as amended by addenda, serving as the sole legal basis for generating a proposal. Although feedback sessions with the Program Management Consultant (PMC), the client, and user groups are informative, they are not legally binding. Only the RFP, as amended by addenda, holds legal significance. Design advances iteratively, guided by addenda-driven feedback. Eventually, all requests for information have been submitted and addressed via addenda, and the proposal is submitted by the established due date.

Throughout this process, the first author was a participant (named within the Request for Qualifications (RFQ ) response) on one of the competing teams for one of the four BBJ program sites. Thus, he has insights into the design efforts associated with the development of the building envelope conducted by the Architect of Record, the Design Architect, engineering subconsultants on the design team, and contractors and construction managers on the construction team. Recommendations and design decisions were arrived at based on the author's involvement and consensus-building efforts.

#### **1.1 Research methodology**

"Research methodology refers to the principles and procedures of logical thought which are applied to a scientific investigation; a system of methods" ([14], p. 31). The research process should aim to be an integrated, clear, and consistent process that, when rigorously applied, contributes to the advancement of knowledge. Qualitative research explores socially constructed 'truths,' emphasizing the complexity of a specific situation. Qualitative research methods include Narrative Research, Ethnographic Research, Grounded Theory, Case Research, Action Research, Interpretative Phenomenological Analysis, and Phenomenological Research. In our context, two of these methods apply: Ethnographic Research and Case Study Research.

#### **1.2 Ethnographic research**

Ethnography traces its origins back to the 1700s when researchers began studying social groups and cultures. Researchers typically immerse themselves in the social groups they investigate, actively engaging with subjects and creating detailed assessments from their perspective. Thus, ethnographic research is characterized by a more interpretive and naturalistic approach than traditional research, yielding highly detailed accounts that can range from objective and factual to subjective impressions

and explorations of constructed realities [15]. Given the first author's role, embedded within the design team during the in-market period, the case study research conducted exhibits distinct ethnographic characteristics.

#### **1.3 Case study research**

Case study research centers on examining events, individuals, organizations, groups, or change processes. This approach seeks to study the dynamics of a phenomenon leading to specific outcomes. It can incorporate quantitative, qualitative, or mixed methods, adopt inductive or deductive reasoning, and encompass single or multiple cases depending on the research objectives. In our case, a qualitative, inductive, and single-case approach has resulted in outcomes that can be generalized across the BBJ program. These outcomes are generally complex, providing empirical descriptions and defining what transpired, its consequences, and its implications for the future [15, 16]. This process, while limited to the in-market procurement phase, offers insights into the potential application of design-assist during subsequent phases.

#### **1.4 Validation**

Validation in qualitative research has been a complex and contested issue for years, with various approaches proposed, but no consensus emergent. At its core, validation aims to ensure the integrity of data collection methods, the collected data itself, and the analytic methods applied to derive outcomes that accurately reflect the data [17]. Alternative terms for internal and external validation, reliability, and objectivity have been proposed, but none have become widely accepted. Definitions of validation span from the broad—"a process of verifying research data, analysis and interpretation to establish their validity/credibility/authenticity" ([15], p. 206)—to the more specific—"an attempt to assess the 'accuracy' of the findings as best described by the researcher, the participants, and the readers (or reviewers)" ([18], p. 259).

Creswell and Poth [18] propose several validation strategies and recommend using at least two for study validation. The following validity methods were adopted for this research:


### **2. Results and discussion**

Performance in the context of building construction can be defined as "the level of service provided by a building material, component or system, in relation to an

#### *Perspective Chapter: Prefabricated Building Envelope Modular Assemblies for Secure Facilities DOI: http://dx.doi.org/10.5772/intechopen.113959*

intended, or expected threshold or quality," as described by Kesik [19]. Kesik goes on to delineate building envelope performance, including performance requirements and parameters (**Table 1**), which offer a comprehensive framework for addressing the considerations that our design-build team encountered. This framework will be further augmented with case-specific additions.



**Table 1.**

*Contemporary performance requirements and their corresponding assessment parameters [19].*

#### **2.1 Structural strength/rigidity**

The dual systems approach we adopted necessitated the consideration of distinct parameters for the unitized curtain wall system and the internal secure perimeter system. Central to the structural system's performance are factors such as the location, spacing, form factor, and dimensions of structural columns, spandrel beams, or intermediate hollow structural steel supports, as well as the selected size and span of unitized curtain wall elements. The latter are driven by vertical spans from slab edge to slab edge and can be substantial when floor-to-floor heights are significant, as in the case of two-tier housing, or when outdoor recreation spaces with 18′-0″ clear ceiling heights are required by American Correctional Association (ACA) performancebased standards for jails [20, 21].

The unitized curtain wall system, designed as non-loadbearing, accommodates seismic loading via its slab edge connections while simultaneously isolating the curtain wall from torsional forces. It is also designed to transmit wind loads through these connections and to adapt to expansion or contraction resulting from external temperatures fluctuations.

On the other hand, the internal secure perimeter system comprises steel cells, specifically the loadbearing rear wall of each cell. This wall bears the dead load of the ceiling/roof assembly as well as any other loads imposed on it, including live loads. As steel cells can be stacked, dead and live loads from upper cells are transmitted through the lower cells to the building structure via the structural slab at designated points, resulting in point loads rather than distributed loading. Furthermore, the structural slab must be designed to facilitate the rolling of steel cells into place during construction. Seismic loading is addressed as the steel cell accepts and redistributes applied horizontal forces. The rigid connections between the walls and the ceiling/roof assembly transform each plane of the 'five-sided box' into a diaphragm, enhancing the steel cell's rigidity and ability to disperse horizontal forces. The walls of the steel cells are welded to leveling plates, which, in turn, are welded to embeds in the structural slab at load application points. This rigid connection prevents movement between the steel cell walls and the structural slab. This system remains isolated from wind loads due to structural separation of the dual systems. Thermal effects are negligible since solar radiation is either reflected or absorbed by the unitized curtain wall system, shielding the inner secure perimeter system from most solar heat gain.

As delineated, the structural strength/rigidity parameters from **Table 1** manifest differently across the two systems. A similar analysis will be applied to each of the specified parameters.

*Perspective Chapter: Prefabricated Building Envelope Modular Assemblies for Secure Facilities DOI: http://dx.doi.org/10.5772/intechopen.113959*

#### **2.2 Control of heat flow**

The unitized curtain wall assembly is, by design, resistant to thermal influences. It consists of two primary elements: the structural frame and the infill panels, including glazed assemblies, glazed spandrel panels, or spandrel panels filled with other opaque finish materials. The structural frame comprises an outer wythe of extruded aluminum, an element providing thermal isolation between the outer and inner wythes, and an inner wythe of extruded aluminum. The temperature of the outer wythe can fluctuate due to external forces such as solar gain, convective cooling, or longwave radiation heat exchange with the night sky. While a temperature differential exists between the outer and inner wythes, and can be extreme, the substantial reduction in thermal bridging inherent in the system effectively mitigates against heat flow in either direction.

#### **2.3 Control of air flow**

The dual systems have varying interactions with each other and the internal air volumes within the building. The inner secure perimeter system constitutes a volumetric space, namely the interior of the cell. This air volume is subject to differential pressure compared to adjacent spaces. Within the steel cell, it is essential to maintain eight air changes per hour. This means that new ventilation air is introduced under mechanical pressure, while existing air is displaced through exhaust grilles or leaks in the perimeter of the assembly. Some elements are hermetically sealed, such as the solid metal walls and the pick-resistant sealant between the walls and the floor. Other elements inherently allow air leakage, including the ¾″ undercut of the door, the door perimeter at the jambs and head, and the glazing retention assembly around security glazed openings. Since the dayroom has fewer air changes per hour than the cells, the cells are slightly pressurized, leading to a net air loss to the dayroom. In contrast, the plenum space above, between, and behind the steel cells is not actively ventilated but freely exchanges air with the dayroom and, to a lesser extent, the cell. The physical assembly between the dayroom and the plenum space serves primarily as a security barrier but can also be used as a surface for acoustically absorptive materials, colors, graphics, or murals. It is not designed to resist air flow, resulting in pressure equalization between the dayroom and the plenum. However, the HVAC influences on the modular steel cell secure perimeter system are minor compared to the macro-level impacts on the unitized curtain wall system.

On a larger scale, mid- and high-rise buildings are influenced by the stack effect, a significant driver of air flow. This effect must be resisted by the unitized curtain wall system. Additionally, this system must contend with (positive) wind pressure or negative air pressure created by wind vortexes. Air infiltration or exfiltration is a major contributor to energy loss or gain, affecting heating and cooling loads and overall energy efficiency.

The interface between the systems is black EMSEAL QuietJoint® SSH, which is non-invasively anchored to the steel cell and mechanically compressed against the mullions of the unitized curtain wall system when the steel cells are positioned. A butted, non-sealed approach to the joints mitigates glare and dust infiltration and allows potential condensation to disperse within the pressure-equalized plenum while Brownian motion efficiently dissipates heat buildup. Reductions in glare due to the

absorptive black interface mitigate the 'fishbowl' effect, offering a more normalized experience of looking through two layers of glazing for persons in custody.

#### **2.4 Control of moisture flow**

The parameters for moisture flow, including rain penetration, air leakage, vapor diffusion, and the potential for condensation, all apply to the unitized curtain wall system. The HVAC system regulates interior air temperature and humidity while introducing fresh air and exhausting air at a similar rate. The inner secure perimeter system is surrounded by dayroom air, both within the dayroom and the plenum space over, between, and behind it. This isolation shields the inner secure perimeter system from humidity fluctuations, given the similar levels of humidity and temperature in the introduced ventilation air.

Conversely, the unitized curtain wall system serves as a mediator between the plenum's temperature, humidity, and pressure and exterior atmospheric conditions. Pressure differentials, humidity differentials, and levels of air leakage through this system challenge its performance. Perfect building envelopes are elusive, as they would be costly and maintenance intensive. They would lack the redundancy of critical control functions and would not drain water were it to penetrate. Therefore, our proposed pressure-equalized rain screen design for the unitized curtain wall system aims to eliminate most wind-driven, rain-based infiltration; pressure differentialinduced or air leakage-driven vapor diffusion; and capillary action through the system.

#### **2.5 Control of solar radiation**

The unitized curtain wall system's glazed panels consist of 1″ nominal insulated glazing units (IGU), often referred to as air gap units, featuring a low-e coating on the #2 surface that blocks 62% of solar energy while allowing 70% of visible light to pass through. When light interacts with any glass surface, some is transmitted, some is absorbed, and some is reflected. This phenomenon extends to the inner pane of the air gap unit, where an additional 13% of solar energy is reflected or absorbed. In aggregate, only 33% of the original potential solar heat gain contributes to heating the plenum air or the exterior surfaces of the inner secure perimeter system's rear wall. The security glazing within this wall is glass-clad polycarbonate (GCP) with a nominal 1″ thickness and a shading coefficient of .80, mitigating solar gain even further. Fritting is also applied to the IGU to meet bird safety requirements outlined in the Building Exterior Design Guidelines [13] and in more detail by the New York City Buildings Department [22].

A significant challenge of the dual systems approach lies in managing the solar gain-related heat buildup within or between the glazed assemblies of each system. Even with a low-e coating that mitigates a substantial portion of solar heat gain, some still passes through the outer IGU. Since the two wythes of the unitized curtain wall are joined by thermoset, a reinforced composite thermal break material that mitigates thermal wicking effectively, dissipation of unwanted heat must still be careful considered.

One concern arises at the glass laminate interlayer and the polyisobutylene (PIB) air spacer at the perimeter of an IGU. Manufacturers generally do not warrant their products above temperatures of approximately 80°C (176°F), with some extending to 100°C (212°F). Careful detailing of the assembly must facilitate venting of the sealed

*Perspective Chapter: Prefabricated Building Envelope Modular Assemblies for Secure Facilities DOI: http://dx.doi.org/10.5772/intechopen.113959*

cavity while managing dirt and dust infiltration. Proposed designs should be analyzed using thermal simulation software, predicting temperatures through transient or steady-state analysis to ensure continued performance of all components.

Unitized curtain wall system spandrel panels, irrespective of material, are opaque and insulated, effectively controlling solar radiation. While solar orientation and shading are vital considerations, we will assume an orientation equal to the median condition for the purposes of this generalized case study. We will also assume that shading devices are absent from the design.

#### **2.6 Control of sound transmission**

Sound transmission through the building envelope is a crucial aspect of design. The unitized curtain wall system is intentionally designed to mitigate environmental noise, considering the materials used for both its spandrel and glazed panels. The glazed panels are detailed as nominal 1″ IGUs with a Sound Transmission Class (STC) rating of 35. Additionally, the 4″ air gap between the systems contributes a STC of 6, and the GCP provides a STC of 27 for each 0.25″ pane of heat-strengthened or chemically strengthened glass and a STC of 34 for the ½″ monolithic polycarbonate core. The use of interlayers to bind these three layers further enhances performance. While the newer Outdoor/Indoor Transmission Class (OITC) rating system would provide a better estimate of sound attenuation through exterior wall assemblies, limited manufacturer testing restricts the use of this rating system.

In essence, the dual systems effectively attenuate sound and noise, even at their weakest point. While structure-borne vibration remains a possibility, specific measures to mitigate it will be determined as the design progresses beyond the in-market period for the BBJ.

#### **2.7 Control of fire**

The materials in the dual systems, such as aluminum, glass, open-cell foam with a fire-resistant, acrylic-based mass-loading agent, steel, and GCP, are generally noncombustible, except under extreme fire conditions. Several measures are in place to prevent such conditions from occurring. Firestopping at the slab edge isolates each floor, eliminating the vertical spread of fire via the stack effect. Each floor is subdivided into smoke zones, contributing to fire fighting and enabling the protect-inplace life safety paradigm typical in jails under I-3 conditions. Further elaboration on this parameter is unnecessary.

#### **2.8 Durability**

The durability parameters outlined in **Table 1** are largely mitigated or eliminated due to the design and materiality of the unitized curtain wall system. Less sophisticated curtain wall systems have evinced an effective design life of 50 years or more. Given more than 50 years of technological advancement and lessons learned, it is reasonable to assume a longer design life for this system.

For the inner secure perimeter, the materiality and construction of the steel cells are designed to mitigate intentional attempts to defeat or degrade their performance as a security barrier. Interior surfaces can be refurbished if vandalized or degraded, and if GCP is damaged, it is inside glazed to facilitate replacement.

#### **2.9 Security**

The BBJs are secure facilities, intrinsically able to mitigate blast effects, winddriven projectile impacts, and bullet penetration due to their design and materiality. Even though these parameters were not the primary design focus of the dual systems comprising the building envelope, they result from the attack resistant design.

Designers will continue to explore the performance of these designs as they are further developed post-selection.

#### **2.10 Economy**

Constructing the proposed dual systems is a significant investment, and these buildings are expected to be very expensive. In addition to their design, factors such as the global COVID-19 pandemic, supply chain disruptions, labor availability issues, and other externalities continue to impact costs and lead times. The design-build method used for project delivery aims to mitigate initial costs by enhancing efficiencies in design and construction coordination and informs approaches to schedule mitigation. These systems contribute significantly.

Operating costs, including utility costs, are expected to benefit from the high-performance envelope's reductions in heating and cooling loads. However, ongoing building maintenance and fine-tuning of complex interdependent systems through Building Management System monitoring and adjustment are essential to optimizing building operations and reducing overall life cycle costs over the extended life of these mission critical 24/7/365 buildings.

#### **2.11 Environmental impacts**

The scale and intensive use of these buildings will result in a significant carbon footprint. Additionally, the rated capacity of the BBJ system is constrained, and systemwide pressures are likely to require operating at or near the rated capacity throughout their design life, even with potential additional rated capacity being added to the jail system in response to population growth.

Constructed on city-owned sites within urban areas, these buildings are not expected to contribute to a reduction in biodiversity. In fact, their construction is anticipated to enhance the streetscape through thoughtful landscape design that improves upon existing uses and environments at these sites.

While several of the materials used contribute to significant carbon footprints, their durability and maintainability as well as the buildings' extreme design life of a minimum of 80 years or, given their historic precedent Rikers Island, potentially more than a century of continuous use will amortize these environmental costs over an extended timeframe. Typical institutional buildings of the same scale with more typical design lives contribute to cyclical demolition and replacement over the same timeframe at much higher cost to the environment.

#### **2.12 Buildability (ease of construction)**

These dual systems represent the most complex prefabricated assemblies in the project(s). Both are prefabricated to the greatest extent possible and erected on-site to enhance construction efficiency and reduce the intensity of and need for onsite labor at prevailing wages as required by the Project Labor Agreement (PLA). Sequencing

*Perspective Chapter: Prefabricated Building Envelope Modular Assemblies for Secure Facilities DOI: http://dx.doi.org/10.5772/intechopen.113959*

of trades, reductions in mobilization time, and reductions in general conditions and schedule duration are achievable through this approach. Prefabrication increases quality by ensuring factory-controlled conditions and assembly repetition. Construction tolerances are meticulously addressed through detailing that mitigates potential issues. Additionally, prefabrication accelerates "drying-in" via the rapid erection of the unitized curtain wall system, which allows earlier installation of finishes, accelerating the overall schedule.

#### **2.13 Esthetics**

The Building Exterior Design Guidelines [13] emphasize esthetics within the context of performative suitability within neighborhood contexts. However, the inclusion of Public Design Commission (PDC) review [23] in the overall process centralizes esthetic considerations and represents a series of significant hurdles to implementation. This multistage public process often involves substantial revisions to the proposed design at each stage. Esthetics thereby become critical not only for being selected as the preferred proposer, but also for successful implementation by the four contracted design-build teams.

#### **3. Alternative systems and their implications**

The most apparent alternative to the dual systems approach is to consolidate the performance requirements of both systems into a single-skinned system. This would require a unitized curtain wall design capable of meeting all envisioned performance requirements, including the energy performance mandated by the NYCECC, while simultaneously meeting or exceeding the forced entry standards for the secure perimeter of a jail.

Such a system would require several key characteristics:

In terms of the framing system, it would have to be constructed from aluminumclad steel and be thermally broken. Although U.S. manufacturers already offer such systems for punched openings, adapting this concept to a curtain wall is a significant and challenging leap.

Regarding the glazing system, the glazing assemblies would need to replicate those used in the dual systems examined in this case study. The external IGU would address thermal, solar, wildlife, and weather concerns, while the inboard security glazing would provide vandalism and attack resistance. These two assemblies would be retained by a system-spanning framing system, creating an air-filled cavity between them, which would be factory-sealed and carefully vented to avoid heat buildup. The inboard security glazing assembly and associated framing would anchor to available structural substrates. The unitized system would be pre-glazed in the factory for delivery but allow replacement of the glazing from both sides.

Considering structural design, the system would need to account for the maximum span between structural supports, likely requiring the inclusion of Hollow Structural Steel (HSS) columns between the ceiling/floor assemblies that the unitized curtain wall system vertically spans. The design of the curtain wall anchor system, which ties the loads from the curtain wall back to primary structure, is of particular concern. It would involve tying the steel inner wythe of the frame to the slab with steel elements, which is not commonplace in the curtain wall industry. These anchors, along with the fire-safing-filled slab edge gap, must remain inaccessible to persons in

custody and other building users. This would necessitate detailing that will mitigate thermal bridging while preserving constructability and erection speed.

As for testing, the notional single-skinned system would require rigorous laboratory testing to all relevant performance criteria. Each type of test necessitates the provision of an assembly, making testing expensive and time-consuming due to the limited number of testing laboratories. This adds to both cost and scheduling delays.

Despite the desirability of such a single-skinned system in an increasing number of urban jails, it is unlikely to materialize in time for the BBJ program. The program's delivery method and legislatively mandated schedule will make it challenging to accommodate this innovation [24].

#### **4. Conclusion**

The dual systems proposed in this design-build case study offers several advantages. They expedite the achievement of a weather-tight enclosure, improve the sequencing of trades, leverage prefabrication to reduce on-site labor and enhance quality, and decouple enclosure-related critical path items from the overall delivery timeline. They embody the best outcomes of a design-build, design-assist process given the technologies currently available.

Furthermore, these dual systems ensure that all the City's requirements, including sustainability supported by the energy efficiency of the proposed design over its lengthy anticipated design life, will be met or exceeded. This is achieved through inspired coordination and integration both within and external to the designbuild team, based on the level of design completed during the in-market phase of procurement.

#### **Acknowledgements**

Ellyn A. Lester, Ph.D. of Pennsylvania College of Technology, Williamsport, PA, USA, provided methodological guidance.

#### **Author details**

Hugh D. Lester\* and Andrew Schopp STV, New York, USA

\*Address all correspondence to: hugh.lester@stvinc.com

© 2023 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

*Perspective Chapter: Prefabricated Building Envelope Modular Assemblies for Secure Facilities DOI: http://dx.doi.org/10.5772/intechopen.113959*

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[2] City of New York. 2020 Energy Conservation Code. 2023. Available from: https://www.nyc.gov/site/buildings/ codes/2020-energy-conservation-code. page

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[18] Creswell J, Poth C. Qualitative Inquiry and Research Design: Choosing among Five Approaches. 4th ed. California: Sage Publications; 2018

[19] Kesik T. Differential durability and the life cycle of buildings. In: Proceedings of the ARCC/EAAE 2002 International Conference on Research. May 22-25, 2002. Montreal, Canada (CD-ROM): McGill University; 2002

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**Chapter 5**

## Shells as a Universal Structural Type in Nature and Design

*Miroslava Nadkova Petrova and Dobrina Zheleva-Martins Viana*

#### **Abstract**

Universal is this structure or construction which is ubiquitous in the world. It is encountered in living and non-living nature, implemented in various fields of human activity and interpreted appropriately according to the needs and the specifics of the context of use. The aim of the chapter is to verify the universal character of shells as a structural and constructive type. It is discerned that shells exist as a structural type in living and non-living nature. With the progress of civilization, humans have gained experience and mastered their deliberate use for the benefit of the individual and social existence. Therefore, it can be stipulated that research and formalization of shells in scientific and technological aspect will lead to an even wider range of applications in various design fields. In perspective are outlined the emerging formgeneration opportunities in engineering, architecture and design. To substantiate the universality, a comparative research method is adopted. The existence of various shells found in nature is compared with the same or similar types applied in design. If hitherto this has happened objectively without interdependence, we demonstrate the possibilities of conscious and purposeful impetus of ideas exchange between the form-finding process, scientific research and technological development of shell structures.

**Keywords:** universal structures, shells in living and non-living nature, shells in historical human experience, shell analogies, ideas exchange in design

#### **1. Introduction**

Universal is this structure or construction which is ubiquitous in the world. It is encountered in living and non-living nature, implemented in various fields of human activity and interpreted appropriately according to the needs and the specifics of the context of use. Universal constructions are the basis for every form-generation, both in nature and in human activity. This universality of constructions is predetermined by the imperative force of physical laws (gravity, symmetry, statics, dynamics, etc.), the properties of materials in which it is materialized and the environmental conditions where it originates or is implemented (wind, temperature, humidity, motion, light, way of life for organic constructions, etc.).

The aim of the chapter is to verify the universal character of shells in particular as a structural and constructive type.

The text will unfold in three directions:


To substantiate the universality, a comparative research method will be adopted the existence of various shells found in nature will be compared with the same or similar types applied in design. If hitherto this has happened objectively without interdependence, we will demonstrate the possibilities of conscious and purposeful impetus of ideas exchange in the form-finding process—the basis for which is the universality of shells.

It can be stipulated that research and formalization of shells in scientific and technological aspect will lead to an even wider range of applications in various design fields. In perspective, the emerging form-generation opportunities in engineering, architecture and design are outlined.

#### **2. Shell structures: definition and differentiation**

In our extensive teaching experience, we have used two terms—'structure' and 'construction' to differentiate two hierarchical concepts covering the semantic field of shells. 'Shells are a skeletal type of structure—with an external skeleton; The structure consists of a rigid, monolithic, peripheral shell or an elastic, firm skin (shell) this is the outer skeleton which covers an amorphous, mechanically unstable interior' [1]. From the point of view of geometry, the shell is a three-dimensional curvilinear structure that can resist loads due to its inherent curvature. Shells can perform different functions according to their expediency: enclosing, limiting, unifying, protecting, preserving, covering, load-bearing, constructive, etc. One and the same shell structure can be realized through different types of constructions and materials—monolithic, cast, adhesive, webbed, knitted, woven, reticulate, rod, ribbed, cable, folded, pneumatic, etc. [1].

However, the analysis of the definitions of the concept of 'shell' shows that there are no uniformly accepted meaning, terminology or definitions for this structural type. In the different languages and scientific circles, the name varies from envelopes, membranes and covers to shells, laminas, etc. Furthermore, shells are not unambiguously specified as typology. A wide range of varieties are included: convex, hanging, reticulate, membranous, folded, and all of these are referred to as shells.

Several definitions will be examined to derive the specific properties of shells and what differentiates them as structural systems.

'The most obvious definition of a shell might be through its geometry… A shell is a structure defined by a curved surface. It is thin in the direction perpendicular to the surface, but there is no absolute rule as to how thin it has to be. It might be curved in

two directions, like a dome, or a cooling tower, or it may be cylindrical and curved only in one direction' [2].

Another definition by the American Concrete Institute states:

'Three-dimensional spatial structures made up of one or more curved slabs or folded plates whose thicknesses are small compared to their other dimensions. Thin shells are characterized by their three-dimensional load-carrying behavior, which is determined by the geometry of their forms, by the manner in which they are supported, and by the nature of the applied load' [3].

Both definitions imply the importance of the geometry of shells, and their curved surface in particular, which predetermines the performance and the efficiency of the structure. This central characteristic of shells is considered by Pierre Luigi Nervi as 'work by form' or the principle of synthetic resistance of natural forms. Nervi writes that this capacity—resistance and structural strength according to or by the form, is common in nature, in flowers, reed, eggs, insects, crustacean, etc. [4]. The greatest success in achieving high resistance through the form can be obtained using spatial curvilinear systems such as shells. Spatiality and curvature of form are two inherent qualities in all living things in the world. Living systems can increase their size where needed and reduce the cross section of tissues, or save material while increasing their mechanical properties. Nature works primarily with curved surfaces, whose stability is based on their spatial curvature. Therefore, the strength achieved through the form is the most essential of all other means and is the most common in nature [4]. A significant lesson from nature is that natural shells are always double-curved—the most efficient form which avoids bending moments in the material and hence preserves the form regardless of the load condition [5]. E. Torroja also emphasizes the quality of shells to resist load due to its inherent curvature—the best structure is the one whose reliability is ensured by its form and not by the strength of the material [6]. Another specific of shells is that due to the even distribution of stresses through their surface, the thickness can be significantly smaller than the other two dimensions.

According to the above definitions, natural forms such as eggs and man-made concrete thin shells will be obvious representatives of the typology, but tension structures such as spider webs, balloons and tents will be included as well [2]. However, shells and tension structures display quite different properties and structural behaviour. Tension structures, as their name infers, transmit only tensile forces, while shells transmit the applied forces by compressive, tensile and sheer stresses. The first are force-active structures which are made of flexible materials and actively adjust their shape as a result of the applied loads. The latter are force-passive structures which are made of rigid materials, but because the applied forces are redirected through the surface of the structure, their shape is intrinsically related to the structural performance [7]. From the point of view of mechanics, 'shell structures carry the applied forces mostly by the so called membrane forces' [8]. F. Candela describes the mechanical behaviour of shells as follows: 'the external forces, the loads, are transformed into direct or membrane stresses, that is, stresses that at each point of the surface are contained in the plane tangent to it, excluding bending in the sheet and, in this way, the material works in the most efficient way possible' [9].

This load-resistance mechanism of shells determines their major advantages over the other structural types:


In addition, H. Isler adds that 'shell structures have an inherent capacity to express structural beauty' [11].

We can summarize that the advantages of shells consist of their economic, functional and constructive efficiency. For example, with minimal thickness and minimal use of materials, larger spaces can be covered and bigger distances can be spanned. Furthermore, due to the infinite potential for form-finding of shells, maximum functionality of the structure and aesthetic satisfaction are ensured.

#### **3. Research methodology and study of universality**

Humankind has constantly developed cognitive skills to adapt to the world through the tools of comparisons, metaphors and analogies. Through these tools of juxtaposition between objects, phenomena and images, the existence of 'similarity', 'resemblance' and 'uniformity' is established, and the cognitive process of transmitting information from one particular subject to another is realized. As a result, comparisons, analogies and metaphors play an important role for the perception and creativity, problem-solving, knowledge gaining, insight, discovery and decision-making. Many researchers postulate the heuristic and productive value of analogies and metaphors for both science and arts. The transfer of meanings from the known to the unknown and the discovery of similarities are a natural mental activity for assimilation of new information. An interesting fact is that psychoanalysts postulate a subconscious basis of the metaphorical thinking. From the point of view of the functional asymmetry of the brain, it has been found that the right hemisphere plays a major role in the understanding of metaphors. The brain works with gestalts. Most probably, it is the right hemisphere which carries the metaphorical (archaic, mythological, complex) consciousness and participates in the decoding of metaphors through the use of the complex, gestalt perception, while the left hemisphere is oriented towards the rationally presented information. The heterogeneity of thinking is determined by the functional specialization of the two hemispheres of the human brain [12].

The specifics of every creative process can be described as metaphorical thinking, which is based on a compound of mental images where image and concept are inseparable. By metaphorical thinking psychologists understand the ability to approximate the semantic differentiation between the individual images of the objects, symbols and concepts, as well as the unexpected connection in an inseparable whole of several normally unconnected parts; the ability to converge concepts and to reach new conclusions. The metaphoric transfer from the known to the unknown with the convergence of different images and the establishment of similarities is actually the way to create new and original ideas. It is quite probable that creative thinking operates with global inseparable visually spatial images [13].

We set the task to trace the cognitive process of adoption of shells in human activity, through analogous models of the structural type found in the living and non-living nature, along with examples from the historical and current human experience. In this way we will verify their objective universality.

#### **4. Distribution of shells as a structural type in the living and non-living nature. Analogies for universality. Interpretations**

The meaning of the word 'discovery' is that man discovers for himself, for his existence, for his adaptation or for aiding his daily life, something that already exists in the world. This is valid for all non-technical 'discoveries' including the subject of

**Figure 1.** *Shells as a structural type in non-living nature. Analogies.*

**Figure 2.** *Shells as a structural type in fauna. Analogies.*

our study—the shell as a structural type. Shells can be found everywhere around us, in the living and non-living nature. They have been adopted in their huge variety to serve humans from ancient times to the present day.

Shells in non-living nature for example, are represented by earth's crust, earth's mantle, various earth and rock bridges, caves, tunnels, air bubbles, foam, etc. (**Figure 1**).

In living nature shells are very common both in the flora and the fauna. The examples are numerous. In the animal world these are skulls, turtle shells, the plates

#### **Figure 3.**

*Shells as a structural type in animal constructions. Analogies.*

**Figure 4.** *Shells as a structural type in flora. Analogies.*

of armadillos, beetles' elytra, eggshells, molluscs, snails, tusks, skin, biological membranes, etc. (**Figure 2**).

Shells can also be observed in various animal constructions—nests, termite mounds, formicaries, animal shelters (**Figure 3**).

In the world of plants shells are found in coconuts and other types of nuts, the skin-shell of seeds and fruits, soft shells of leaves and flowers, etc. (**Figure 4**).

#### **5. Mastering and dissemination of shells as a structural type in human activity. Analogies for universality**

#### **5.1 Historical retrospective of human experience**

In his historical development, man has adapted to the environment as a result of his instincts for self-preservation, home and construction, through cultivating observation skills of the surroundings and imitation of wildlife. Thus personal experience has been accumulated and skills have been developed. A historical fact is that with the progress of civilization humans have gained understanding and mastered both the intuitive and the deliberate use of shells for the benefit of the individual and social existence.

#### **5.2 Areas of application**

#### *5.2.1 Pottery*

Pottery is one of the most ancient crafts in the world. It is believed that it appeared with the transition to sedentary life, at the end of the Stone Age more than 20,000 BCE. Pottery was used to meet daily necessities in the form of various utensils, tableware, storage containers such as amphorae, silos, depositories for water, olive oil, wine, grain, olives, etc., ritual vessels for weddings and funerals, etc. This is one of the first human activities where shells have been mastered as a structural type. As a result of its strength, resistance to climatic changes, moisture, temperature and other properties, among them their structure and shape, archaeologists have discovered preserved earthenware from prehistory and the late Palaeolithic. In general, early earthenware was deliberately made with rounded bottoms to avoid sharp corners that are prone to cracking. The potter's wheel predetermined the achievement of a favourable curvilinear, spherical or oval shape which ensured both the functional and constructive pertinence of the vessels (**Figure 5**).

#### *5.2.2 Basketry*

Another traditional craft common for all people around the world is basketry. The process of weaving twigs, reeds, grasses or leaves has been practiced since ancient times to the present. This is one of the most universal arts, which also ranks amongst the earliest industries. In addition, weaving probably indicates the origins of all textile arts. Baskets are containers made of willow, wicker, reed, palm leaves or other vegetal material, intertwined in a variety of shapes and sizes depending on the function. They were used mainly for storage, protection and transportation of different goods. It is worth noting that weaving preceded pottery, if judged by the decoration found on ancient pottery which was derived by the traces left by the shape of the baskets used to make earthenware before the invention of the potter's wheel. The influence of

**Figure 5.** *Pottery—Shell structures in human daily life.*

the art of basketry is clearly traceable in the development of the art of porcelain, as well as the capitals-baskets in Byzantine architecture. In antiquity the shields of the soldiers were also made using the weaving technique. Boats-baskets used on Tigris and Euphrates rivers were mentioned by Herodotus. They were round and covered with bitumen. Boats with such shape can still be found on these rivers and similar types with analogous construction are used on the rivers of India. The methods of construction have not changed significantly [14]. If we study and analyse the shape of the different types of baskets, the complex curvilinear surface typical for the shell structural type can be observed, including the complex shape of the parabolic hyperboloid (**Figure 6**).

#### *5.2.3 Building construction*

In building construction shells have been utilized since ancient times in a wide variety of buildings. At first, these were residential and farm structures, granaries, barns, furnaces, tombs. Subsequently, the functional typology is extended and covered markets, religious buildings, wide-span public buildings, sports facilities, engineering structures such as water tanks, dams, containment shells of nuclear

**Figure 6.** *Basketry—Shell structures in human daily life.*

*Shells as a Universal Structural Type in Nature and Design DOI: http://dx.doi.org/10.5772/intechopen.106851*

power plants, piping systems and others are included. Today shells as a structural type are ubiquitous.

The initial stage of the distribution of shells is especially interesting. Similar to animals, man possesses building instincts. In the primitive phase of his development, to adapt to the environment, man built shelters using the locally available materials. The efficiency of the natural shells was observed, borrowed from the flora and fauna and imitated in the constructive process. Depending on the availability of materials and the nature of the local climate, shells were constructed either by weaving, gluing, combining both methods or by masonry, intuitively following the imperative role of the physical laws of gravity, the properties and formal qualities of the materials. Among the construction materials used were the traditional stone, wood (cane, reed, rods, etc.), animal bones and skins, straw, mud and clay, ice, etc. Gradually, the construction skills of weaving, knitting, masonry, coating, pressing, moulding, etc. were cultivated. Through intertwining branches, sticks, leaves, bones and other materials at hand, a lattice was created—a kind of reinforcement which was then plastered with mud or clay. Walls were constructed either with stone, compacted snow cut into rectangular blocks or pressed sun-dried mud reinforced with straw. It can be asserted that shells in the form of domes developed as one of the major and most common constructive type in the building tradition worldwide. Indeed, one of the earliest

**Figure 7.** *Shell dwellings.*

shelters was the small woven dome. 'The framework was made of pliable branches or saplings, woven together, utilizing the strength inherent in a double-curved surface to span a useful space. It was then covered with leaves, thatch, or animal skins, whatever was locally available' [15]. This construction type is still implemented today in some ethnic groups in Africa. An impressive example of a vernacular building practice is the tolek of the Mousgoum—an ethnic group living in Northern Cameroon. This thin domed hut (5–7 m in diameter and 7–8 m high) is constructed of mud mixed with straw which sets hard in the sun. The almost perfect parabolic curve eliminates all hoop tensions and ensures the stability of the structure in spite of being extremely thin [16]. The external ornamental ribs are not introduced to strengthen the structure but to protect from local injuries, to serve as water drainage and to allow people to climb atop the house to aid construction or maintain the coating without the use of scaffolding (**Figure 7**) [17].

#### *5.2.4 Transportation industry*

Alongside these traditional types, shells as a structural type are closely related to the modern world. The industrial era saw a rise in their utilization in various domains of human activity. A huge field of application is the transportation industry. Among the examples are car chassis, boat hulls and airplane fuselages. The so-called monocoque construction consisting of a single shell outer skin which performed the loadbearing function was indispensable for reducing the vehicle weight while providing greater strength and better streamlining. In addition to these properties, monocoque shells increased the safety of the people using the vehicle as it efficiently absorbs the impact and spreads the energy on its surface [18]. The materials utilized initially were plywood and aluminium and later fiberglass and carbon fibres. Moreover, all machines connected to some kind of movement, including such of the military industry such as submarines, missiles or rockets are taking advantage of the shell structure to ensure appropriate weight to strength ratio and aerodynamics (**Figure 8**).

**Figure 8.** *Shell vehicles.*

#### **5.3 Pioneers: discoverers of shells as structural type. Legacy and analogies for universality**

The beginning of the scientific research, engineering implementation, formalization and technological application of shells began in the late nineteenth century. This beginning was set by the Russian engineer and inventor Vladimir Grigoryevich Shukhov (1853–1939), who was the first to introduce grid shell structures in 1896. He patented a number of inventions and laid the foundations of the theory of shells [19]. In 1895, Shukhov submitted a patent application for mesh coverings in the form of a shell. These were meshes made of steel strips and profiles with characteristic rhomboid cells. They were used for lightweight suspended roofs and grid vaults with a large span. The development of these mesh coverings marks the invention of a completely new loadbearing constructive type. For the first time, Shukhov converted a suspended covering into a completed spatial structure which was used again not until several decades later. Compared with the highly developed at that time constructions with metal arches, his lattice shell vaults formed by rods of the same size made a significant progress and replaced the traditional spatial trusses [20]. After two experimental buildings (two lattice arches built in 1890 and a suspended roof built in 1894), Shukhov presented his innovative roofs at the All-Russia Exhibition in Nizhny Novgorod in 1896. The Bari Company built eight pavilions with quite impressive dimensions. Four of them were with suspended roofs and the other four had cylindrical lattice arches. One of the exhibition halls had a load-bearing structure which was not a mesh but a thin membrane—a construction which has never been used before. In addition to the pavilions, a water tower was built in which Shukhov transferred the gridshell to a vertical lattice structure with hyperboloid shape.

Legends are told about the sources of inspiration for his heuristic ideas. Shukhov himself shared: 'One day I arrived in my office earlier than usual and I saw: my wicker waste bin is turned upside down, and on it stands a rather heavy pot with a ficus. And the future design of the tower was standing clearly in front of me' [21]. Thus, the waste bin with interwoven wicker twigs became the analogy for the famous Shukhov tower which together with his gridshells became universal and served as models for different types of design (technical, constructive, architectural, furniture, product, etc.) for more than a century. Based on Shukhov's projects, approximately 200 towers were built in Russia and abroad, including the celebrated Shabolovka Radio Tower in Moscow (1919–1921)—a modification of Shukhov's huperboloid structures.

According to Shukhov, 'what looks beautiful, it is also strong, sturdy. Human eye is accustomed to the proportions in nature, and in nature what is strong and appropriate survives'. He designed numerous water towers based on the same constructive principles but though mass-produced all of them featured a striking variety of shapes. Shukhov delightedly used the property of the hyperboloid to take various forms and experimented by changing the position of the connections between the rods or the diameters of the upper and lower ends. Thus, each tower obtained its own appearance, differing from the others and demonstrating its own load-bearing capacity (**Figure 9**). The complexity of the design task, including in terms of the construction, has always been resolved with a remarkable understanding and sense of the form. The work of Shukhov gained great popularity in the twentieth century, and his lightweight spatial structures have influenced many contemporary architects, among them Sir Norman Foster (**Figure 10**).

Another upsurge in the utilization of shells in architecture took place as a result of the development of reinforced concrete, the advances in the production possibilities and the development of calculation methods and theoretical analysis of shells. Among the most notable early examples exploring the structural strength and formal qualities

#### *Prefabricated Construction for Sustainability and Mass Customization*

**Figure 9.** *Shukhov's gridshell structures.*

**Figure 10.** *Modern interpretations of Shukhof's gridshells.*

of concrete, which influenced the building of thin shells were the Centennial Hall in Breslau, Germany (1911–1913) by Max Berg featuring a diameter of 65 m and the Dirigible hangar at Orly Airport, France (1916), by Eugene Freyssinet spanning 75 m. A few years later appeared the first single shell building made of reinforced concrete—the Zeiss Planetarium, constructed in 1923–1924 in Jena, Germany. This was a 16 m concrete dome with an unprecedented thickness of only 3 cm which allowed the reduction of the

*Shells as a Universal Structural Type in Nature and Design DOI: http://dx.doi.org/10.5772/intechopen.106851*

**Figure 11.** *Precursors of concrete thin shells.*

weight to 1/30 of the weight of a conventional dome structure. This radically new structural type developed by Dr. Walter Bauersfeld—chief engineer at Carl Zeiss AG, together with the structural engineer Franz Dischinger from Dyckerhoff & Widmann AG featured a framework made of steel rods, sprayed with ferroconcrete using the shotcrete technique, later patented as the Zeiss-Dywidag-System [22]. This forerunner of concrete thin shells gave impetus to the design of many remarkable lightweight structures spanning hitherto unthinkable distances with shells' characteristic slenderness (**Figure 11**).

One of the major discoverers of shells as a structural type in architecture was Pier Luigi Nervi (1891–1979). The trajectory to reach the application of this structural type in his engineering and later architectural career is very interesting. In the 1940s, Nervi invented and patented a new material called ferrocement. His patent was based on ferciment, a product devised by the Frenchman Joseph-Louis Lambot in the midnineteenth century to construct boats. Nervi refined this material to use less steel. His ferrocement was composed of dense concrete reinforced with a fine steel mesh which ensured both lightness and strength of the structure. The difference between ferrocement and reinforced concrete is mainly in the reinforcement—the first consists of a series of layers of wire mesh with a small diameter (0.5–1.5 mm), reinforced with rods which is then immersed in a cement mortar. This allowed the creation of very thin sheets that were very elastic, flexible, malleable, lightweight, resistant to cracking and extremely economical. It was possible to bend the metal mesh in any shape and this liberated the experimentation with the form.

Using this new material Nervi built his first shell boats. He had ambitious plans to build a 400-ton concrete ship which was impeded by WWII. After the end of the war he succeeded in building a 165-ton sailboat with a thickness of the hull 3.6 cm and a 11.6 m ketch with hull thickness just 1.27 cm. The first application of ferrocement in building construction was a warehouse in Rome featuring an undulating roof with a thickness of 3 cm. The structural properties of the material were vital for the creation of his most renowned shells like the Torino Esposizioni, Turin (1949), Palazzo dello Sport, Rome (1956), Palazzetto dello Sport, Rome (1958), Paul VI Audience Hall, Vatican City, Vatican (1971), Norfolk Scope, USA (1971). Analysis of these diverse buildings, differing in scale, construction, function and appearance shows certain sameness. It is exhibited in the ribbing as though the shell (the skin of ferrocement) was stretched and cast over the ribs. The ribs, as those applied in Gothic cathedrals, perform both constructive and decorative function. By applying ribs and curvilinear surfaces, Nervi improved the strength of the structure while making them lighter, spanned greater distances and covered bigger areas without the need of intermediate columns. Impression of continuity with the historical architectural tradition is created. He combined simple geometry with assembly of prefabricated elements to propose innovative designs. This constructive method transfers analogies to both wildlife and some traditional crafts. Undoubtedly, Nervi's innovative engineering solutions possess a great aesthetical appeal, completely

natural and organically interweaved with the visible narrative of the constructive logic. Though he claims that he never thought directly about the beauty of his works, which he believes appears always when the construction is appropriate. Moreover, Nervi gives prominence to intuition which should be used as much as mathematics in design, especially when thin shells are considered (**Figure 12**) [23].

There are many engineers and architects, shell apologists who have contributed with their outstanding work to the theoretical and practical adoption of shells, for their mathematical formalization and universal application. Among them are:

Buckminster Fuller (1895–1983), who invented the lightweight and durable 'geodesic dome'—a three-dimensional steel shell made of straight rods, the first self-contained building that can withstand its own weight without any limits in its dimensions (**Figure 13**).

**Figure 12.** *Nervi's shells.*

**Figure 13.** *Shells by Buckminster Fuller.*

*Shells as a Universal Structural Type in Nature and Design DOI: http://dx.doi.org/10.5772/intechopen.106851*

Idelfonso Sánchez del Río Pisón (1898–1980)—Spanish engineer who introduced an innovative roof system based on manufactured on site modular corrugated thin shells and lightweight fired clay elements, famous for his innovative prototype for rationalized construction of water tanks (**Figure 14**).

Eduardo Torroja y Miret (1899–1961), who advanced the concept of the shell as a structural element bringing its formal expression to new heights in the building of market halls, stadiums, hangars, churches (**Figure 15**).

Anton Tedesko (1903–1994)—German-born architect who introduced concrete thin shells in the United States as a representative of Dyckerhoff & Widmann AG and was responsible for the design of more than 60 shells adapted to the American context (**Figure 16**).

Oscar Niemeyer (1907–2012), who created the modern ensemble Pampulha, which is considered the forerunner of concrete shells in Brazil (**Figure 17**).

Félix Candela (1910–1997) known for his shells with double curvature, namely hyperbolic paraboloid, where the shape was reduced to its pure essence through elimination of the supporting edge ribs allowing its main characteristic—extreme thinness, to be exposed to the attention of the viewer (**Figure 18**).

Eero Saarinen (1910–1961)—Finnish-born American architect who gained recognition not only for his innovative buildings using catenary curves, but also for his furniture designs where shells were utilized (**Figure 19**).

**Figure 14.** *Shells by Idelfonso Sánchez del Río Pisón.*

**Figure 15.** *Shells by Eduardo Torroja.*

**Figure 16.** *Shells by Anton Tedesko.*

**Figure 17.** *Shells by Oscar Niemeyer.*

**Figure 18.** *Shells by Félix Candela.*

*Shells as a Universal Structural Type in Nature and Design DOI: http://dx.doi.org/10.5772/intechopen.106851*

**Figure 19.** *Shells by Eero Saarinen.*

Kenzo Tange (1913–2005)—the Japanese protagonist of shell architecture whose stadiums for the 1964 Olympic Games in Tokyo are referred to as the most beautiful structures of the twentieth century (**Figure 20**).

Eladio Diestre (1917–2000)—Uruguayan engineer who preferred traditional brick over concrete to design double-curvature masonry shells with spectacular cantilevers showcasing the possibilities of the material (**Figure 21**).

**Figure 20.** *Shells by Kenzo Tange.*

**Figure 21.** *Shells by Eladio Diestre.*

Frei Otto (1925–2015) famous for his pioneering lightweight tensile and fabric membrane structures advancing the ideas of sustainability even before the term itself was coined (**Figure 22**).

Heinz Isler (1926–2009), who rarely used mathematical theories to calculate his shells but relied on experiments with reversed hanging cloth and membrane under pressure physical models in the form-finding process to validate the design of his remarkable thin shells (**Figure 23**).

Among our contemporaries, this group of shell masters includes Frank Gehry (1929), Norman Foster (1935), Nicholas Grimshaw (1939) and Santiago Calatrava (1951).

#### **5.4 Zaha Hadid's homage to Félix Candela**

The influence of the shell masters and their visionary work on contemporary architecture is indisputable. Their revolutionary shells changed profoundly the way structure is understood. They altered once and for all the nature of the architectural form and opened new possibilities for the generations to come. Furthermore, they inspire and encourage experimentation from the perspective of the current day through the use of new media and technologies.

In 2018, during her first exhibition in Latin America 'Design as a second nature', Zaha Hadid Architects created an impressive shell installation in honour of the Spanish-Mexican architect and engineer Félix Candela. *KnitCandela* is an experimental sculpture rethinking his inventive concrete shells by introducing new computational design

**Figure 22.** *Shells by Frei Otto.*

**Figure 23.** *Shells by Heinz Isler.*

#### *Shells as a Universal Structural Type in Nature and Design DOI: http://dx.doi.org/10.5772/intechopen.106851*

methods and innovative KnitCrete formwork technology. The dynamic geometry is inspired by the smooth shapes of the colourful traditional Mexican dress *sarape* and at the same time refers to Candela's famous restaurant Los Manantiales at Xochimilco. While Candela explored various combinations of hyperbolic paraboloids in his projects to obtain variety of designs, KnitCrete allows the realization of much wider range of anticlastic geometries. The cable network and fabric formwork system enables the efficient building of expressive free-form concrete surfaces without the need for complex formworks. Its thin, double-curved concrete shell with an area of almost 50 sq. m. and weight of 50 tons is made with a formwork of only 55 kg which was transported to Mexico from Switzerland in a suitcase. The experimental structure explored the possibilities for integration of digital production with traditional craft and construction methods. 'KnitCrete is an innovative material-saving, labour-reducing and cost-effective formwork system for the casting of doubly curved geometries in concrete…KnitCrete formworks use a custom, 3D-knitted, technical textile a lightweight, stay-in-place shuttering, coated with a special cement paste to create a rigid mould, and supported by additional falsework elements such as tensioned cable-net or bending-active splines' [24]. With this installation Zaha Hadid Architects display not only their admiration for one of the pioneers in the development of shell structures, but also unambiguously declare their creative credo to follow his oeuvre. In fact, Zaha Hadid is devoted to developing curvilinear structures, elevating them to an architectural and design style—the style of Parametricism (**Figure 24**).

#### **5.5 Mathematical, engineering and technological development of shells. Future perspectives**

Mathematical, engineering and technological development of shells continues for more than a century. In the beginning of the twentieth century, they were rarely used due to the complexity of their calculation, the increased requirements towards the quality of the materials and compliance with building technologies. An indicative example is the building of Sydney Opera House, whose complex geometrically undefined shape of the roof shells impeded the engineering team to calculate and detail the design. The initially envisioned thin shells were technically impossible to be realized which required rationalization of the form and construction. The challenge was resolved after 15 years of rigorous problem-solving process extensively using the then emerging computer analysis. Subsequently, the structural scheme was fundamentally converted with the introduction of fanlike ribs to support the distinctive roof that we recognize today [25]. In the 1960s came the 'golden' period of shells—the heyday of Pier Luigi Nervi, Eduardo Torroja, Félix Candela and the other shell masters. This was the period when structural engineering emerged as a separate discipline, when computation entered design, architecture and engineering to aid structural optimization. Though at the end

**Figure 24.** *KnitCandela by Zaha Hadid architects.*

of the twentieth century, a decline in the construction of concrete thin shells is observed, in the last two decades shells are already mastered and widely used in architecture and design. The invasion of computers in the practice of structural analysis, the emergence of new materials and new technologies has a positive impact on the spreading of shells in all fields of design. The ubiquitous application of shells is also supported by the advent of relatively new branches of scientific knowledge such as bionics, biomimetics, synergetics, etc. The introduction of new knowledge is always ensured by the constant progress of computer technology. The aim of bionics is to search for analogies and know-how in nature and their transfer into human activity. Biologically inspired engineering consists of the application of biological methods and systems for the study and design of engineering systems and technologies. More specifically, biomimetics borrows creative techniques through the use of biological prototypes to derive engineering ideas and solutions. This approach is motivated by the fact that biological organisms and their organs are fully optimized by evolution. Technology transfer between living forms and artificial artefacts is desirable because the evolutionary pressure forces living organisms to be efficient. Synergetics is another interdisciplinary research field with the objective to study natural phenomena and processes based on the principles of self-organization of systems. This refers to synergetics, as defined by B. Fuller, according to his views on nature's geometry and the consistent self-organization of natural forces (his thesis is that 'energy has a form'), and the universality of the ideas about the world. The achievements of these sciences, in the context of our study, support the thesis and add evidences for the universality of structures and constructions, including shells as a structural type.

#### **6. Conclusion**

Traditionally, the opinion that shells are structures developed and applied mainly in engineering and architecture is popular. In the present study, however, we set the objective to prove that shells are a universal structural type, i.e. that they are ubiquitous in living and non-living nature, that they have been utilized in various spheres of human activity since antiquity, that they are subject of development and application in all fields of design.

Evidences for this universality were traced in the distribution of different shell types, by comparing and extracting similar patterns found in living and non-living nature and in human activity—pottery, basketry, weaving, building construction, mechanical engineering, etc. from antiquity to the present day. An overview was made of the achievements of some of the most prominent pioneers—'discoverers' of shells who contributed to their adoption in science and engineering and their practical application, again in various fields of human activity.

We found that the acquisition of shells in antiquity was ubiquitous and was based on instincts, intuition, observation and borrowing from nature during the process of development of practical skills. The adoption of shell structures took place independently in various human activities, organically and naturally, applying one and the same materials and methods adapted to the living environment. Despite the geographical remoteness and the lack of interaction, the structural solutions around the world are surprisingly universal. With the cultivation of various crafts shell structures were gradually spread through internal and local interactions, thus expanding the universality of their application.

*Shells as a Universal Structural Type in Nature and Design DOI: http://dx.doi.org/10.5772/intechopen.106851*

Regarding the pioneers in the professional, scientific, theoretical and practical acquisition of shell structures, a general conclusion related to the form is made: 'work by form'—stability and structural strength according to or by the form, says Nervi; the most efficient structure is the one whose reliability is ensured by its shape, writes Torroja; geometry is the most important because energy has a form is Fuller's maxim. In general, the strength of the shell is hidden in its form. It is the form, that is key to the universality of shells, not the size, nor the materials but the spatial curvature determines its efficiency. This is where is implemented the principle of mini-max which is pursued in contemporary design—maximum effect with minimal consumption of materials, energy, labour, etc. a priori embedded in the evolved natural objects and the traditional crafts around the world.

The contribution of the research is in revealing the possibilities for activation of the interactive ideas exchange in the form-generation process between scientists, practicing engineers and designers, as a result of the conscious understanding of the universality of the structural type. If hitherto shell structures have been used intuitively and independently in the various human activities, this research highlights the perspectives for unifying the efforts based on their universality. We can stipulate that the interactive study of shells and their formalization will lead to even greater application in the different fields of design.

#### **Acknowledgements**

The publication of this chapter is funded by the Research Department at the University of Monterrey, Mexico.

#### **Author details**

Miroslava Nadkova Petrova1 \* and Dobrina Zheleva-Martins Viana<sup>2</sup>

1 University of Monterrey, San Pedro Garza García, Mexico

2 Centre for Architectural Studies, Bulgarian Academy of Sciences, Sofia, Bulgaria

\*Address all correspondence to: miroslava.petrova@udem.edu

© 2022 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

### **References**

[1] Zheleva-Martins D, Petrova M. Formoobrazuvane. Sofia: Bismar; 2015. pp. 185-195. Available from: https://www. academia.edu/33154142/ (In Bulgarian)

[2] Adriaenssens S et al. Shell Structures for Architecture Form Finding and Optimization. New York: Taylor and Francis; 2014

[3] Building Code Requirements for Concrete Thin Shells (ACI 318.2014), 2014

[4] Nervi PL. Stroit pravilno. Moskva: Gosstroiizdat; 1956. p. 71. (In Russian)

[5] Candela F. The shell as a space encloser. Arts and Architecture. January 1955:12

[6] Collonneti G. Tonkostennie konstruktzii. Moskva: Stroiizdat; 1963. p. 3. (In Russian)

[7] Silver P et al. Structural Engineering for Architects: A Handbook. London: Laurence King Publishing; 2014

[8] Farshad M. Design and Analysis of Shell Structures. Dordrecht: Kluwer Academic Publishers; 2010

[9] Candela F. Hacia Una Nueva Filosofia de las Estructuras. Buenos Aires: Artes Graficas Bodoni; 1962. pp. 55-56

[10] Ventsel E, Krauthammer T. Thin Shells and Plates. Theory, Analysis and Applications. Basel: Taylor and Francis; 2001

[11] Isler H. Structural beauty of shells. In: Presented at: 11th IABSE Congress, Vienna, Austria, 31 August - 5 September 1980. IABSE Congress Report. Vol. 11. 1980

[12] Chernigovskaya TV, Deglin VL. Metaforicheskoe I sillogisticheskoe

muishlenie kak proyavlenie funktzionalnoy asimmetrii mozga. Tartu. 1986;**19**:68-84. (In Russian)

[13] Nikolaenko NN. Metafora kak puti poznania. Independent Psychological Journal. 2005;**1**. Available from: http:// www.npar.ru/journal/2005/1/metaphor. htm [Accessed: June 15, 2022] (In Russian)

[14] Balfet HJ. "Basketry". Encyclopedia Britannica, 2019. Available from: https:// www.britannica.com/art/basketry [Accessed: June 19, 2022]

[15] Kahn L, Easton B, editors. Shelter. Bolinas, CA: Shelter Publications; 1973

[16] Waldram P. The Principles of Structural Mechanics. London: Batsford; 1912

[17] Nelson S. From Cameroon to Paris: Mousgoum Architecture In and Out of Africa. Chicago: University of Chicago Press; 2007

[18] Rosario M. What is Monocoque? 2022. Available from: https://www. aboutmechanics.com/what-is-monocoque. htm/ [Accessed: June 15, 2022]

[19] Shukhov VG, Trudui I, editors. Ishlinskogo, Akademia nauk USSR. Vol. 1. Moskva: Stroitelna Mehanika; 1977. p. 192. (In Russian)

[20] Schadlich C. Das Eisen in der Architektur des 19.Jhdt. Weimar: Habilitationsschrift; 1967. p. 104

[21] Volodin M. Ot solomui do setchatai obolochek I giperboloidnuih bashen. Ruskie korni arhitekturnaga hajteka. In Chastnui correspondent. 2011. (In Russian)

*Shells as a Universal Structural Type in Nature and Design DOI: http://dx.doi.org/10.5772/intechopen.106851*

[22] Finsterwalder, R. Form Follows Nature : Eine Geschichte der Natur Als Modell Für Formfindung in Ingenieurbau, Architektur und Kunst—A History of Nature as Model for Design in Engineering, Architecture and Art, edited. Walter de Gruyter GmbH, 2011

[23] Iori T, Poretti S. Conserving Pier Luigi Nervi's ferroconcrete. Proceedings of the Institution of Civil Engineers— Engineering History and Heritage. 2016;**169**(1):22-35

[24] KnitCandela. Available at: https:// www.zaha-hadid.com/design/ knitcandela/ [Accessed: June 23, 2022]

[25] Arup O, Zunz J. Sydney opera house. The Arup Journal. 1973;**8**(3):4-21

#### **Chapter 6**

## Perspective Chapter: Prefabricated Low-Carbon Panels for Exterior Walls

*Alberto Reaes Pinto and Marlene Canudo Urbano*

#### **Abstract**

The construction industry plays a relevant role in the economy but also has some major negative environmental impacts. Such impacts need to be reduced, hence the importance of guiding the industry towards the principles of sustainable construction, which allow for greater productivity, as well as for significant reductions in terms of costs and labour. In spite of the lingering popularity of on-site execution techniques, the construction site is progressively becoming a place for the assembly of prefabricated components, which are lighter and more flexible, have dry metallic connections, can be easily assembled and disassembled and are, therefore, reusable. This paper means to present an alternative method for the prefabrication of panels for exterior walls, also for use in the construction of small-scale buildings, using renewable, often local, non-polluting building materials, such as wood, cork, or straw. These have thermal insulation functions that are essential for the outer envelope of the building to achieve high energy efficiency and may be applied with the use of simple but effective mechanised technologies.

**Keywords:** construction industry, sustainable construction, prefabrication, low-carbon materials, housing shortages

#### **1. Introduction**

In step with the principles of sustainable construction, this paper explores an alternative method for the prefabrication of components, made from low-carbon materials, for use in the external walls of buildings. We believe this alternative method may prove useful in circumventing some of the downsides to the heavy, conventional prefabrication used in industrial construction.

Our proposal focuses on renewable building materials with low environmental impact: wood, straw, cork, and other materials, such as hemp or coconut fibres. The exploitation, manufacture, and shipping of such materials involve little fossil energy, while on the other hand, they still demonstrate high energy efficiency, good hygrothermal performance and acoustic comfort. Furthermore, they are easily reusable and recyclable, thus allowing for a circular system of production and consumption.

#### **2. Prefabrication: general concepts**

Prefabrication, a technological solution used in industrialised construction, implies production and manufacture prior to construction. The concept of industrialised construction was born during the Industrial Revolution. The general tendency towards industrialisation that began to take place in the early 18th century was accompanied by the introduction of an organised and mechanical workforce, thus allowing for a new, industrialised type of construction to be born and developed. "Industrialisation is the use of technologies, which substitute the craftsman's skill with the machine [1]."

There are a number of varying definitions of "prefabrication":


For our purposes, prefabrication should be considered as an industrialised form of construction in which some or all of the building components are produced in a factory, where many of the processes usually carried out on-site are undertaken. These components are later assembled on-site with the aid of mechanical lifting equipment [5].

#### **3. On the economic viability and development of industrialised construction, particularly of prefabrication**

The great transformations and technological advances that have been made in the area of building, in an industrialised sense, have, generally speaking, been obtained through scientific, theoretical, and experimental methods.

In certain cases, however, in spite of apparent technical viability, processes have proved economically impracticable. And sometimes, it is only later, due to changing market conditions, that these same processes assume practical viability. Prefabrication is one such example.

Prefabrication (one of the processes involved in industrialised construction) was born more from the consideration of economic factors than from scientific speculation or specific technological advances. As Blâchère reminds us, "at every moment, the option of technological solutions is undertaken through strict cost competition [4]."

After World War II, the lack of buildings resulting from the massive destruction of cities by bombing, combined with a demographic explosion and the rising concentration of industrial units in urban areas, made industrialised construction and prefabrication economically viable and were the main driving forces behind their development [1].

Facing the urgent need to solve housing shortages, European countries came to the conclusion that only industrialised construction processes were quick enough and cost-effective enough. Countries like France allocated 5% of their GDP. They used Marshall Plan funding, for building residential units and other infrastructures, adopting industrialised technologies based on reinforced concrete, and setting up large construction sites, each with a large number of buildings.

In 1947, 2 years after World War II, things had reached distressing proportions. In France, for instance, 420,000 houses had been completely destroyed, and 1,500,000 were seriously damaged, which meant that one-fifth of 1939s built heritage needed rebuilding. In England, in London alone, 5.4 million square metres of commercial and industrial floor area were destroyed or damaged. In England and Wales, about 475,000 houses were destroyed by "Luftwaffe" bombing [6].

After the war, all throughout Europe, there was a great population explosion (particularly between 1960 and 1975). French population increased by more than 7 million people, growing almost twice as much as it would grow between 1975 and 1990 (4 million people). Fast industrial development also drew migrants towards the urban centres, thus deepening the housing crisis.

The construction industry at the time was fragmented and disorganised, and its techniques were traditional. France had a production capacity of about 80,000 housing units per year (similar to what they had in 1928, more than a decade before the war), which did not come close to fulfilling housing needs, originally estimated at about 470,000 houses per year [1].

Throughout Europe, there was a shortage of workers (especially qualified ones), and raw materials and energy were also in short supply. Countries such as France, England, Germany, Italy, and the Soviet Union, among others, agreed to solve the housing problem, which meant building enough houses in a fast and cost-effective way. Industrialisation was the only way to solve the crisis.

#### **4. In Portugal**

The use of total heavy prefabrication in Portugal began in the mid-1960s to increase the country's construction capacity, which was deficient in about 500,000 dwellings per year, considering the country's housing needs. The first experience with this method of prefabrication took place in 1964 and was made by ICESA, a construction company that applied the French FIORIO process of heavy prefabrication. The system was first applied in building the Santo António dos Cavaleiros (SAC) residential complex in Lisbon's metropolitan area.

#### **4.1 Santo António dos Cavaleiros residential complex**

This residential complex is located in Lisbon's metropolitan area, on a calm and wind-protected rural site with an area of 42 hectares, near Frielas Bridge, in the municipality of Loures. The SAC residential complex comprises approximately 3000 housing units and was built by a real estate developer [7].

#### **4.2 ICESA and the FIORIO process**

The FIORIO process is a French system of total heavy prefabrication using large panels of concrete and brick. This system is one of the oldest prefabrication systems, along with the French processes CAMUS (1948) and COIGNET (1951), the British processes REEMA (1946) and BMB (1952), and the Dutch process RBM (1946), all

of them post-World War II. The two engineer brothers, George and Henri Fiorio, patented their invention in 1951.

The FIORIO prefabricated construction system is based on the use of large-dimension construction elements, one-storey-high wall panels and room-sized floor panels, which are prefabricated at the factory. These are then assembled on-site, interlinked with ring beams at floor level and with reinforced concrete uprights moulded in situ, forming a three-dimensional, reticular solid structure. The foundations and support structures of this type of prefabricated construction are generally built

#### **Figure 1.**

*Lubricating the bottom of the mould in order to facilitate demoulding. Source: Reaes Pinto/ICESA.*

#### **Figure 2.**

*Pouring gypsum plaster into the mould. Source: Reaes Pinto/ICESA.*

**Figure 3.** *Resistant interior panels. Source: Reaes Pinto/ICESA 1968.*

#### *Perspective Chapter: Prefabricated Low-Carbon Panels for Exterior Walls DOI: http://dx.doi.org/10.5772/intechopen.114131*

using traditional methods. There should also be a top ring beam to lock the vertical framework of the panels in place. This can also be achieved by installing prefabricated lintels on slab-on-grade foundations or deep foundations.

The following are examples of resistant prefabricated walls built with the FIORIO/ ICESA system and used in the SAC housing complex in Greater Lisbon (**Figures 1**–**16**).

#### **Figure 4.**

*Reinforced resistant exterior wall. Source: Reaes Pinto/ICESA 1966.*

#### **Figure 5.**

*Pouring concrete. Source: Reaes Pinto/ICESA 1966.*

**Figure 6.** *Resistant exterior walls. Source: Reaes Pinto/ICESA 1966.*

#### **Figure 7.**

*Resistant interior panels. Ceramic tile finish for kitchens. Source: Reaes Pinto/ICESA 1968.*

**Figure 8.** *Panel storage areas. Source: Reaes Pinto/ICESA 1968.*

#### **Figure 9.** *Storage areas. Source: Reaes Pinto/ICESA 1968.*

**Figure 10.** *Exterior panels storage area. Source: Reaes Pinto/ICESA 1968.*

*Perspective Chapter: Prefabricated Low-Carbon Panels for Exterior Walls DOI: http://dx.doi.org/10.5772/intechopen.114131*

#### **Figure 11.**

*Structure for transporting panels on a truckbed. Source: Reaes Pinto/FIORIO – Limoux/France 1965.*

#### **Figure 12.** *Transporting vertical panels. Source: Reaes Pinto/ICESA 1968.*

**Figure 13.** *SAC: Assembling panels on site. Source: Reaes Pinto/ICESA 1966.*

#### **Figure 14.** *SAC: Assembling panels on site. Source: Reaes Pinto/ICESA 1966.*

#### **Figure 15.**

*SAC: Towers, category 3 with 12 floors, typologies T2 and T3. Source: Reaes Pinto/ICESA 1968.*

**Figure 16.** *Santo António dos Cavaleiros. Source: Reaes Pinto/ICESA 1970.*

#### **5. Prefabricated, low-carbon panels for exterior walls**

The use of fossil and other highly polluting energies, which have supported growth policies for many years, is generally associated with the emission of greenhouse gases, global warming, and climate change. Many fundamental changes taking place in our society today are reactions to these concerns, and the move towards sustainable development and sustainable construction has become the focus of global combined efforts, exemplified, for instance, in the goals established at the Paris COP 21 International Conference regarding the reduction of greenhouse gas emissions [8].

The construction industry is harmful to the environment, and it is important that we are aware of its negative environmental impact (along with that of related, upstream and downstream industries) in order to reduce it substantially. According to Charles Kibert, a diagnosis of the environmental impacts of the construction industry reveals that there is an urgent need for change, in order to achieve the goals of sustainability. Our first priority should be to analyse the characteristics of traditional construction and compare them with the new sustainable criteria for construction materials, products and processes [9].

#### *Perspective Chapter: Prefabricated Low-Carbon Panels for Exterior Walls DOI: http://dx.doi.org/10.5772/intechopen.114131*

The construction industry plays an important role in terms of national and international economy due to the investments it usually involves, its share in countries' GDPs and its contribution to gross fixed capital formation (GFCF). We should also mention the amount of jobs it creates and the importance it has in its interrelationships with a number of other industries. However, it is also harmful to the environment, and its negative impact must be reduced; hence, the importance of promoting the principles of sustainable construction naturally requires a change of mindset and an integrated view of all the actors involved in the construction process [10].

Over time, industrialised construction has been the focus of considerable research, which has led, namely through the use of prefabrication, to an evolution in the direction of sustainability, meaning the reduction of the industry's negative environmental impacts. Prefabrication comprises different construction systems and uses new building materials as well as traditional ones. Compared to traditional construction, it also reduces execution times on site, the need for specialised labour, the production of waste on work fronts, and costs improving overall performance. We should also mention that prefabricated components assembled through dry connection can be reused or recycled at the end of the life cycle of buildings [11].

This paper is the result of a research project and is meant as a contribution to the realm of sustainable construction. It focuses on an alternative method for the construction of small buildings, using renewable, often local, non-polluting building materials and simple but effective mechanised technologies geared towards productivity and the reduction of execution times and construction costs.

Our method, which consists of prefabricated panels/modules, uses renewable and low-carbon building materials, both in the structure or framework, which consists of reinforced, solid wooden hoops (*aros de madeira*), and in the filling of this structure, made with straw bales or granulated cork. Such building materials have thermal insulation functions that are essential for the outer envelope of the building to achieve high energy efficiency. They were carefully chosen, just like the technologies for their application, because they involve little fossil energy and can be reused and recycled, which means a reduction in the production of waste and one more step in the direction of a circular economy.

#### **5.1 The construction system**

This paper and the research it is based on were born out of the necessity of developing a construction system that made sense in the Portuguese context, focused on the use of easily available, cheap, sustainable, low-carbon building materials. The construction system can generally be said to adhere to the following principles:


### **5.2 Steps in panel construction**

We built four-panel prototypes. The bales of hay were inserted into the wooden structures and attached laterally (**Figures 17**–**19**).

The type of plaster for the bales' surfaces, which are a part of the panel's outer face, was experimented with and decided upon at a still early stage of the research process. It was chosen according to two major criteria: it had to adhere to the bales' surfaces, and it should not retain moistness, as that would probably cause the bales to start deteriorating.

The plaster revealed good adherence to the bales from the outset. It was applied in four layers: a first, pre-plaster or foundation layer, made of clay and quicklime; a second layer of water-repellent quicklime, which includes olive husk in its composition, so as to have a layer that is water-repellent but permeable to water vapour; a third layer, which is applied on-site with the panels in an upright position, and which includes a synthetic fibre mesh for structure; and a fourth layer of clay-and-lime-rich plaster (**Figures 20**–**22**).

**Figure 17.** *Panel structure.*

*Perspective Chapter: Prefabricated Low-Carbon Panels for Exterior Walls DOI: http://dx.doi.org/10.5772/intechopen.114131*

**Figure 18.** *Bale of hay.*

**Figure 19.** *Panel structure filled with hay.*

**Figure 20.** *Four plastering stages: First layer of clay; water-repellent quicklime.*

#### *Prefabricated Construction for Sustainability and Mass Customization*

**Figure 21.** *Reinforced quicklime plaster.*

Observations made during panel construction:


#### **5.3 Trials at the SerQ laboratory**

SerQ (the Forestry Innovation and Skills Centre) is a civil engineering laboratory that specialises in testing wooden structures. It is a product of the cooperation

#### *Perspective Chapter: Prefabricated Low-Carbon Panels for Exterior Walls DOI: http://dx.doi.org/10.5772/intechopen.114131*

between the University of Coimbra, LNEC (National Laboratory for Civil Engineering), and the Sertã City Council. Also, it functions as a business incubator and fab lab. We proceeded to try the modules for their mechanical resistance to vertical and horizontal pressure.

#### *5.3.1 Trial preparation*

We began by assembling and levelling a metal trial platform, which was attached to the concrete floor with 50 mm threaded rods (**Figure 23**). This serves to hold the basic wooden elements that support the panels in place, as well as to mount the measuring equipment that will accurately register any movement.

**Figure 23.** *Installing the support framework.*

**Figure 24.** *Actuator.*

In **Figure 24**, we see the installation of the actuator, a computer-controlled, hydraulic component used for applying a given pressure during a given period of time. Besides applying pressure, it also measures the movement or the deformation produced in the element that is being tried.

**Figure 25.** *Support module.*

**Figure 26.** *Attaching the module to the platform.*

**Figure 27.** *Attaching the support elements for a corner wall to the platform.*

*Perspective Chapter: Prefabricated Low-Carbon Panels for Exterior Walls DOI: http://dx.doi.org/10.5772/intechopen.114131*

After assembling the platform, the support framework, and the actuator, we proceeded to instal the first solid wood element, which will be used for supporting and connecting panels (**Figures 25**–**27**).

In **Figures 28**–**30**, we see the first panel being raised, fitted, and attached to the support framework.

**Figure 28.** *Raising the panel.*

**Figure 29.** *Raising the panel. Outer side.*

**Figure 30.** *Fitting the panel to the support framework. Inner side.*

The plaster used for covering the surface of the bales of hay did not crack during transport, nor when the panels were set upright, which we thought would be likely to happen.

At this stage, besides fitting and fastening the panel to the framework, we mounted other fixed metallic elements, meant to hold the measuring devices that will measure, in mms, the movement that the applied pressure will produce in the module's base and top.

*Perspective Chapter: Prefabricated Low-Carbon Panels for Exterior Walls DOI: http://dx.doi.org/10.5772/intechopen.114131*

We attached a strong, solid wood element to the top of the panel in order to receive the pressure applied by the actuator (**Figures 31**–**33**).

**Figure 32.** *Assembling the horizontal displacement measuring devices.*

**Figure 33.** *Assembling the horizontal displacement measuring devices.*

#### *5.3.2 Testing*

The purpose of these trials was to determine the panels' structural resistance to horizontal pressure and whether such resistance increases according to the placement and total number of interlinked panels. The trials were meant to simulate, to a degree, the conditions that the panels will be facing when integrated into a finished building.

Tests were conducted on a single panel, on three panels in line, and on a set of three panels plus a corner panel.

The first three panels had been previously plastered with quicklime and clay. Each panel had a wall area of 2.75 m2 (2.50 m height, 1.10 m width, and 0.410 m thickness) and weighed an average of 190 kgs.

#### *5.3.3 Phase 1*

In the context of testing, δ represents the measuring devices (in millimetres), and F represents the actuator, which applies the preset force after the preset time. In this context, we shall also be referring to the panels as samples.

The trial followed the EN594:2011 standard, and the applied force (F) and displacement δ1, δ2, and δ3 (**Figure 34**) were measured for 300 seconds until reaching 40% of the expected breaking load in order to determine the panel's stiffness (SerQ report).

**Figure 34.** *EN594 standard trial diagram.*

**Figure 35.** *Phase 1 results.*

*Perspective Chapter: Prefabricated Low-Carbon Panels for Exterior Walls DOI: http://dx.doi.org/10.5772/intechopen.114131*

#### **Figure 36.**

The results of the first phase of testing determined the structure's stiffness. As shown in **Figure 35**, the set of three modules plus the corner one has ten times more stiffness than the independent module (**Figure 36**). This leads us to conclude that the framework created by the floor, ceiling, and the four walls would make for a much greater stiffness. Still, the stiffness that the independent module revealed under trial was already considered satisfactory, considering the type of housing unit in which it is meant to be used.

#### *5.3.4 Considerations following phase 1*

Following the first phase of testing, we paused to look at the results and consider the positive and negative aspects.

#### *5.3.5 Positive aspects*


#### *5.3.6 Negative aspects*


#### *5.3.7 Improving the panels*

Having analysed the results of the first set of trials, we came to the conclusion that our method could be improved:


#### *These improvements allow for:*


#### *5.3.8 Finding the heat transfer coefficient for alternative types of insulation*

The thermal resistance for the 41-cm-thick panel (with 36 cm of hay for thermal insulation) was 0.14 W/m2 k, which is three times more efficient than the current regulation's minimum requirements for external walls: 0.50 W/m<sup>2</sup> k.

As an alternative, we found that the heat transfer coefficient of a panel filled with granulated cork was about 0.12 W/m2 k, which is four times more efficient than the minimum standards. We thus reduced the panel's weight to 180 kg while keeping the same length and width.

This solution creates a hollow space within the panel, which can then be filled with different types of thermal insulation, allowing for the reduction or enlargement of wall thickness.

**Table 1** shows the panel's heat transfer coefficient using different types of insulation.


**Table 1.**

*Different types of thermal insulation.*

*Perspective Chapter: Prefabricated Low-Carbon Panels for Exterior Walls DOI: http://dx.doi.org/10.5772/intechopen.114131*

#### *5.3.9 Phase 2*

In the second phase of trials, we focused on testing out new solutions for increasing the resistance of independent panels to horizontal forces.

We made changes to one of the panels in terms of insulation, substituting granulated cork for the bales of hay, and also applied a structural sheet of wood on the outside to reinforce the whole structure.

HP panel – filled with hay for insulation with no outer plaster, reinforced with wooden framework (**Figure 37**).

CP panel – filled with cork for insulation, to be reinforced with a structural sheet of wood on the outside at a later stage (**Figure 38**).

The performance of the cork-filled panel was inferior to that of the plastered hay panel, showing worse deformation. This can, however, be solved with stronger wind bracing (**Figure 39**).

The panels showed an already satisfactory level of stiffness, but there are still other structural reinforcement methods that can be tested.

#### *5.3.10 Rupture testing for horizontal forces*

In order to determine the panel's most vulnerable areas, the last phase of trials consisted of rupture testing the plastered hay panel for horizontal forces. This kind of testing implies applying progressively greater pressure with no time or, force, limit.

The test ended when the module showed visible deformation. The rupture took place in the mechanical fastener and in the module's connection to the floor at 6kN, about 600 kg (**Figure 40**).

**Figure 37.** *Hay-filled (HP) panel.*

*Prefabricated Construction for Sustainability and Mass Customization*

**Figure 38.** *Cork-filled (CP) panel.*

**Figure 39.** *HP (hay) panel and CP (cork) panel test results.*

#### *5.3.11 Rupture testing for vertical forces*

In the vertical force rupture test, we applied an evenly distributed pressure with no preset limit. The test ended when the actuator reached its maximum pressure of 96 kN (about 10 tonnes), with no visible deformation of the panel (**Figures 41**–**43**).

*Perspective Chapter: Prefabricated Low-Carbon Panels for Exterior Walls DOI: http://dx.doi.org/10.5772/intechopen.114131*

**Figure 40.** *Rupture testing for horizontal forces.*

#### **Figure 41.** *Rupture testing for vertical forces.*

#### *5.3.12 Post-test considerations*

Even though the trials did not fully simulate the reality for which these panels are being built, as they were not tested as part of a whole building, they nevertheless proved this system's potential for the construction of single-storey and multi-storey buildings, as the panels were able to support the weight of floors and ceilings with no additional structures.

#### *5.3.12.1 Interior and exterior finishes*

Our prefabricated panel system allows for several different interior and exterior finishes. We focused particularly on finishing materials that can be installed on-site and attached mechanically. These may be reused and recycled, which would prove impossible in the case of plastered walls, whether interior or exterior.

*Prefabricated Construction for Sustainability and Mass Customization*

**Figure 42.** *Rupture testing for vertical forces.*

**Figure 43.** *Rupture testing for vertical forces.*

In the first trial assembly for exterior, mechanically attached finishing materials, we used panels of flat, ceramic roof tiles (plasma model, from the Coelho da Silva company), which are easy to disassemble and reusable (**Figure 44**).

We also considered different types of cladding that can be attached mechanically, such as a solid wood bardage (weatherboards), slatted wood panels, cane or bamboo panels (**Figure 45**), cork panels, stacked stone panels, and photovoltaic panels (**Figure 46**).

*Perspective Chapter: Prefabricated Low-Carbon Panels for Exterior Walls DOI: http://dx.doi.org/10.5772/intechopen.114131*

**Figure 44.** *Trial assembly of exterior finish using flat, ceramic roof tiles.*

#### **Figure 45.**

*Different types of cladding: Solid wood bardage; slatted wood panel, cane, or bamboo panel.*

**Figure 46.**

*Different types of cladding: Cork panel, stacked stone panel, and photovoltaic panel.*

#### **6. Final considerations**

Earlier in our paper, we described the heavy prefabrication system based on the use of bricks and concrete, which proved viable in a certain social and economic context.

In the second part of our paper, we explored an alternative and sustainable system for low-carbon prefabricated exterior walls and described the trials that proved its technical viability. The building materials used for the walls' structure and filling (with thermal insulation functions), as well as for cladding and interior finishes, are renewable, clean, may be reused and recycled, and produce little waste on-site.

In terms of energy efficiency, the energy expenditure of our construction system and building materials proves negligible when compared to that of the finished building's everyday use and maintenance. This is partly because we chose not to use fossil-based materials for thermal insulation.

When compared to traditional/conventional, on-site construction, our system of light and partial prefabrication, which, furthermore, involves little use of machinery, shows considerable advantages. It cuts down on construction time, the need for skilled labour, construction site waste, and costs, making for a more ecological solution. It is also important to remember that prefabricated components assembled through dry connection can be reused or recycled at the end of the life cycle of buildings, thus becoming part of a circular process that excludes raw material extraction.

#### **Acknowledgements**

The author gratefully acknowledges the funding received from FCT - Fundação para a Ciência e Tecnologia, I.P. by project reference <UIDB/04026/2020> and DOI identifier <10.54499/UIDB/04026/2020 (https://doi.org/10.54499/ UIDB/04026/2020)>.

#### **Author details**

Alberto Reaes Pinto\* and Marlene Canudo Urbano CITAD – Territory Architecture and Design Research Centre, Lusíada University, Lisbon, Portugal

\*Address all correspondence to: reaespinto@lis.ulusiada.pt

© 2024 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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[2] Koncz T. Manuale Della Prefabbricazione. Milano: Edizioni Tecniche Bauverlag; 1962

[3] Lewicki B. Batiments d'Habitation Prefabriqués en Elements de Grands Dimensions. Paris: Editions Eyrolles; 1965

[4] Alonso M et al. Prefabricacion Teoría e Práctica - Tomo 2. Barcelona: Editores Técnicos Associados SA; 1974

[5] Reaes PA. A pré-fabricação na indústria de construção. In: Proceedings of the 1° Congresso da Indústria de Préfabricação em Betão. Porto: Associação Nacional dos Industriais de Produtos de Cimento; 2000

[6] Powell C. The British Building Industry since 1880. London: Publications E & in Spon; 1980

[7] Reaes Pinto A. Total heavy prefabrication: Santo António dos Cavaleiros (SAC) and Quinta do Morgado (QM). Overview of the building process, exterior panel pathologies and a study for their rehabilitation. In: Proceedings of the International Conference Sessions Selected Works. Cidades, Comunidades e Territórios; April 2022. Lisboa: ISCTE. Lisboa: ISCTE – Instituto Universitário de Lisboa; 2022. pp. 102-136

[8] Reaes Pinto A. Changing society and architecture. In: Proceedings of the 2ª International Conference on Environmental Design; 2017; Milano. Torino: Lettera Publisher; 2017. pp. 163-168. ISBN: 978-88-90516-05-4

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### *Edited by Masa Noguchi*

Building is a system of energy and environment, which needs to accommodate diverse needs and demands at individual and societal levels. Nearly 40% of global energy use derives from construction. In fact, a house consumes a significant amount of energy before and after occupancy, and the associated CO2 emissions are contributing to climate change. Prefabrication is a means to mass-produce buildings or parts and components. Thus, in theory, production costs can be reduced through economies of scale. In the 1920s, the significance of mass-produced houses was widely propagated by Le Corbusier who saw standardization as fundamental to mass production. Nonetheless, today, in response to growing global warming issues and the constant increase in energy prices, the construction industry is becoming more responsive to the delivery of sustainable architecture than ever. Within this context, sustainability may embrace not only building economy but also the adequacy beyond the legitimacy in which the quality barely coincides with individuals' various dynamic needs, desires, and expectations today. In this respect, mass-produced prefabs alone fail to realize total sustainability. In 1987, a paradoxical concept of mass customization was introduced by Stanley Davis. Nonetheless, the idea applied to housing dates back to the 1950s. The essence of mass customizable architecture was speculated by Walter Gropius, as he emphasized the need for standardizing and mass-producing not only entire buildings but also their components. The combination of standard building components, which can be prefabricated, results in mass producing various types of constructions through economies of scope, where the quality can be defined by user choices of the components given in consideration of economic constraints and needs and demands. This book is an initial attempt to integrate the two notions of sustainability and mass customization by reviewing the potential capacities of prefabricated construction.

### *Assed Haddad, Civil Engineering Series Editor*

Published in London, UK © 2024 IntechOpen © Jarwis / iStock

Prefabricated Construction for Sustainability and Mass Customization

IntechOpen Series

Civil Engineering, Volume 6

Prefabricated Construction

for Sustainability and Mass

Customization

*Edited by Masa Noguchi*