**3. Mechanism of prestressing**

The structure of infrastructure can be a mix of different materials and elements [5]. This section focuses on one of the popular innovations which can be used in many different infrastructures. One of the most relevant concepts to structure is prestressing. Prestressing refers to the intentional creation of permanent stresses in an element of a structure, for the purpose of improving its strength and behaviour under various services and conditions [6]. Prestressed concrete is an engineering

**Figure 2.** *A simplified illustration of the mechanism of prestressing.*

innovation that improves many of the service and strength performance behaviours of reinforced concrete. This is a practical solution to the design of many engineering structures in a cost-effective manner. Prestressed concrete is a fastidious form of reinforced concrete. Prestressing engages the application of an initial compressive load to the structure to decrease internal tensile forces which may lead to controlling crack. The initial compressive load is imposed and sustained by highly tensioned steel reinforcement (tendons) reacting on the concrete. With eliminating cracking, a prestressed concrete section is significantly stiffer than the equal reinforced concrete section.

The tendons are cast within the concrete at first freely within ducts, which are grouted at a later stage to bond the tendons. Prior to grouting, the tendons are jacked to very high stresses. The jacking reactions are pressed against the ends of the concrete member and then transferred permanently to cast in end anchors. This is shown in a simplified form in **Figure 2**.

In practice the duct 'profile' will vary to suit the purpose of the member. The tendons are permanently 'prestressed' in tension; the concrete is permanently 'prestressed' in compression. High-tensile wire strands have fy ≈ 1870 MPa. Higher-strength concretes have *fc* ′ ≈ 30–50 MPa. Although strong in compression, concrete is weak in tension. **Table 3** presents the basic concepts in prestressed concrete structures.

The poor performance of the concrete in tension gave rise to the concept of 'prestressing' the concrete in order to overcome bending tensions and cracking produced under load, thereby retaining elastic behaviour. Early attempts at prestressing failed because of the shrinkage and creep strains in the concrete. For example, early reinforcing bars had yield stresses ≈ 200 MPa and could be pretensioned to a stress of order 120–150 MPa. The subsequent strains are of order

$$\mathbf{e} = \sigma/\mathbf{E} = \mathbf{120}/200, \mathbf{000} = 600 \times 10^{-6} \tag{1}$$

where ε is the strain, σ is the stress and E is the module of elasticity.

The development of prestressed concrete is credited to Eugene Freyssinet of France [7], who in 1928 started using high-strength steel wires for prestressing. Such wires, with an ultimate strength as high as 1725 MPa and a yield point over 1240 MPa, are prestressed to about 1000 MPa. At this level of stress, the losses are a much smaller percentage of the prestress. For example, assuming a total creep and shrinkage strain of order 800 × 10–6, this would result in a loss of prestress of order:

$$
\sigma = (800 \times 10 - 6) \times (2 \times 105) = 160 \text{ MPa} \tag{2}
$$

**5**

crete buildings (**Figure 3**).

Unbonded tendons

Immediate losses

losses

**Table 3.**

Time-dependant

*Introductory Chapter: Infrastructure Management, Construction, Structure and Industry 4.0*

Strand An element in which a number of high-tensile wires are woven together as a combined

Tendon Generally defined as the wire, strand or bar (or any discrete group of wires, strands or

Prestressed The prior stressing of both the concrete and the tendons prior to the service use of the

tendons are cut and bonded to the concrete after it attains strength. Used in precast

attains strength. This is the most commonly used system in buildings and other

tendons are stressed—this effectively bonds them to the concrete like reinforcing steel. Tendons can subsequently develop further stresses under bending actions due to strain compatibility, enabling the full strength of the bonded tendons to be realised at

Where the tendons are not grouted but are greased for corrosion protection and contained within a plastic sheath. This method is not permitted under as 3600 except for slabs on the ground. Unbonded tendons can be used in specialised applications such as cable-stayed bridge cables, for example, allowing the monitoring and replacement of

(a) Short-term elastic strain of the concrete (progressive stressing)

Pretensioned The tendons are tensioned (in a casting bed) prior to pouring of the concrete. The

Post-tensioned The tendons are laid in metal ducts in the concrete and tensioned after the concrete

Bonded tendons Where the ducts which contain the tendons are filled with cement grout after the

bars) that is intended to be prestressed Cable Groups of tendons, collected together in a duct or anchorage

methods of tensioning the strands and for the permanent end anchoring the strands to the concrete. Freyssinet [7] developed conical wedges for end anchorages and designed double acting jacks which tensioned the wires and then thrust the wedges into the anchor cones which held them. These early advances in prestressing were mainly European. Steel became the primary construction material in the USA, with the secondary use of structural concrete in buildings. However, the American engineer Lin [6] became a major contributor developing the load balancing theory during the 1950s. Australia, with a more developed concrete industry and low seismic activity, became a major advocate of prestressed con-

(a) Long-term creep and shrinkage strain of the concrete (b) Relaxation in the (seven wires twisted) strands

Loss of prestress in the tendon force up to 40% or more of the jacking force can be experienced, depending upon the cable length, drapes, concrete shrinkage and so forth. This becomes important in relation to AS3600 [12]. It is necessary that a minimum amount of prestress remains in the strands, so that they may develop their full-strength capacity in strain compatibility with the concrete as it bends.

In addition to the longitudinal force P (or C) exerted on a prestressed member

at the anchorages, transverse forces are also exerted on the concrete member wherever change of angle or curvature exists in the tendons. Other bending actions are also applied to the member where the member section changes due to

*DOI: http://dx.doi.org/10.5772/intechopen.86142*

unit

element

construction

structures in Australia

ultimate strength

individual strands

(b) Anchor wedge draw-in

(c) Friction loss along the length of the ducts

*The basic concepts in the prestressed concrete structures including main elements of the structure.*

**Element Description**

Hence, the residual prestress =1000–160 = 840 MPa or 84% of the original level. Practical development of prestressed concrete was made possible by further development of high-strength concrete and high-tensile wire strands through the twentieth century [8–11]. It was also necessary to develop reliable and economical *Introductory Chapter: Infrastructure Management, Construction, Structure and Industry 4.0 DOI: http://dx.doi.org/10.5772/intechopen.86142*


#### **Table 3.**

*Infrastructure Management and Construction*

*A simplified illustration of the mechanism of prestressing.*

reinforced concrete section.

**Figure 2.**

shown in a simplified form in **Figure 2**.

Higher-strength concretes have *fc*

concrete structures.

innovation that improves many of the service and strength performance behaviours of reinforced concrete. This is a practical solution to the design of many engineering structures in a cost-effective manner. Prestressed concrete is a fastidious form of reinforced concrete. Prestressing engages the application of an initial compressive load to the structure to decrease internal tensile forces which may lead to controlling crack. The initial compressive load is imposed and sustained by highly tensioned steel reinforcement (tendons) reacting on the concrete. With eliminating cracking, a prestressed concrete section is significantly stiffer than the equal

The tendons are cast within the concrete at first freely within ducts, which are grouted at a later stage to bond the tendons. Prior to grouting, the tendons are jacked to very high stresses. The jacking reactions are pressed against the ends of the concrete member and then transferred permanently to cast in end anchors. This is

In practice the duct 'profile' will vary to suit the purpose of the member. The tendons are permanently 'prestressed' in tension; the concrete is permanently 'prestressed' in compression. High-tensile wire strands have fy ≈ 1870 MPa.

concrete is weak in tension. **Table 3** presents the basic concepts in prestressed

The poor performance of the concrete in tension gave rise to the concept of 'prestressing' the concrete in order to overcome bending tensions and cracking produced under load, thereby retaining elastic behaviour. Early attempts at prestressing failed because of the shrinkage and creep strains in the concrete. For example, early reinforcing bars had yield stresses ≈ 200 MPa and could be pretensioned to a

≈ 30–50 MPa. Although strong in compression,

ε = σ/E = 120/200,000 = 600 × 10<sup>−</sup><sup>6</sup> (1)

σ = (800 × 10−6) × (2 × 105) = 160 MPa (2)

′

stress of order 120–150 MPa. The subsequent strains are of order

where ε is the strain, σ is the stress and E is the module of elasticity.

The development of prestressed concrete is credited to Eugene Freyssinet of France [7], who in 1928 started using high-strength steel wires for prestressing. Such wires, with an ultimate strength as high as 1725 MPa and a yield point over 1240 MPa, are prestressed to about 1000 MPa. At this level of stress, the losses are a much smaller percentage of the prestress. For example, assuming a total creep and shrinkage strain of order 800 × 10–6, this would result in a loss of prestress of order:

Hence, the residual prestress =1000–160 = 840 MPa or 84% of the original level. Practical development of prestressed concrete was made possible by further development of high-strength concrete and high-tensile wire strands through the twentieth century [8–11]. It was also necessary to develop reliable and economical

**4**

*The basic concepts in the prestressed concrete structures including main elements of the structure.*

methods of tensioning the strands and for the permanent end anchoring the strands to the concrete. Freyssinet [7] developed conical wedges for end anchorages and designed double acting jacks which tensioned the wires and then thrust the wedges into the anchor cones which held them. These early advances in prestressing were mainly European. Steel became the primary construction material in the USA, with the secondary use of structural concrete in buildings. However, the American engineer Lin [6] became a major contributor developing the load balancing theory during the 1950s. Australia, with a more developed concrete industry and low seismic activity, became a major advocate of prestressed concrete buildings (**Figure 3**).

Loss of prestress in the tendon force up to 40% or more of the jacking force can be experienced, depending upon the cable length, drapes, concrete shrinkage and so forth. This becomes important in relation to AS3600 [12]. It is necessary that a minimum amount of prestress remains in the strands, so that they may develop their full-strength capacity in strain compatibility with the concrete as it bends.

In addition to the longitudinal force P (or C) exerted on a prestressed member at the anchorages, transverse forces are also exerted on the concrete member wherever change of angle or curvature exists in the tendons. Other bending actions are also applied to the member where the member section changes due to

**Figure 3.**

*A prestressed section for analysis.*

**Figure 4.**

*Producing profile from an urban area to present building objects: (a) lidar data including road structure; (b) profile; (c) a selected lidar point cloud of Sydney areas produced by an UAV.*

steps and so forth or P is applied eccentrically. For this analysis it is very helpful to remember that the concrete is a free body distinct from the tendon until the ducts are grouted, at which point they start to act together. This is then considered how the tendon imposes forces on the concrete free body at the anchorages and through its changes of direction. Consider the concrete in half of the beam as a free body, which has forces imposed on it from the tendon and the other half of the beam (**Figure 3**).

**7**

*Introductory Chapter: Infrastructure Management, Construction, Structure and Industry 4.0*

Now determine *ec* the eccentricity between the two C forces. Note that the P force in the tendon reacts against the concrete as *C*a and there is no support reaction

P/A (pre − compression) ± M/Z (uplift moment due to the cable) (4)

= P/A ± P × e × y/I (5)

In order to designing prestressed concrete structures, a proper understanding of structural performance at all stages of loading is important. This can be essential where it is a comprehensive knowledge of the design criteria specified in the relevant design standard, such as the minimum requirements to fulfil both ultimate

This section presents different technologies and techniques which can be used for monitoring the structure of urban areas and infrastructures. The new trend of automation and data transferring process is called Industry 4.0. The core component of Industry 4.0 is digital data. Industry 4.0 refers to different technology applications using Internet of Things (IoT), cyber-physical systems, artificial intelligence, machine learning, cloud computing, machine-to-machine and humanto-machine communication and real-time technologies. The concept of Industry 4.0 is adopted by the construction industry. The concept of Construction Industry 4.0 can give better connectivity among construction supply chain stakeholders and real-time access to construction operation, enhancing safety, productivity and the quality of construction. Utilisation of digital technologies such as 3D printing [13], airborne lidar [3, 14, 15], hand-held laser scanners [16, 17], building information modelling (BIM) [18], wireless sensors [19] and automation is changing the infra-

For example, **Figure 4** shows the temporal airborne lidar which can be used for analysing 3D urban changes. Airborne lidar provides valuable digital data which is useful for analysis of the spatial pattern of building height and the proximity

Spatial data mining (SDM) methods have been used to investigate the unknown relationships between spatial and nonspatial attributes of data sets [20] that may not be apparent using more basic data analysis techniques. The need for knowledge discovery and spatial data mining 'to extract unknown and unexpected information from spatial data sets' was suggested by Mennis and Guo [21]. Two popular SDM methods being used in geographic information systems (GIS) and remote sensing

/8 (= P × e) (3)

For moment equilibrium about **A**, and ignoring friction losses

Cc (= Ca = P) × ec = wpL/2 × L/4 = wp L<sup>2</sup>

Now consider the elastic stresses in the concrete:

**4. Industry 4.0 technologies and digital data**

structure management including construction and maintenance.

*DOI: http://dx.doi.org/10.5772/intechopen.86142*

• *C*a and *C*c in horizontal equilibrium

since there are no externally applied loads.

and serviceability requirements.

analysis with the road's hierarchy.

• *w*p*L***/**2 and *V*anch in vertical equilibrium

The forces on the concrete are:

*Introductory Chapter: Infrastructure Management, Construction, Structure and Industry 4.0 DOI: http://dx.doi.org/10.5772/intechopen.86142*

The forces on the concrete are:

*Infrastructure Management and Construction*

**6**

**Figure 4.**

**Figure 3.**

*A prestressed section for analysis.*

the beam (**Figure 3**).

steps and so forth or P is applied eccentrically. For this analysis it is very helpful to remember that the concrete is a free body distinct from the tendon until the ducts are grouted, at which point they start to act together. This is then considered how the tendon imposes forces on the concrete free body at the anchorages and through its changes of direction. Consider the concrete in half of the beam as a free body, which has forces imposed on it from the tendon and the other half of

*Producing profile from an urban area to present building objects: (a) lidar data including road structure; (b)* 

*profile; (c) a selected lidar point cloud of Sydney areas produced by an UAV.*


Now determine *ec* the eccentricity between the two C forces. Note that the P force in the tendon reacts against the concrete as *C*a and there is no support reaction since there are no externally applied loads.

For moment equilibrium about **A**, and ignoring friction losses

$$\mathbf{C\_c \left(= C\_a = P\right) \times e\_c} = \mathbf{w\_p L/2 \times L/4 = w\_p L^2/8 \left(= P \times e\right)}\tag{3}$$

Now consider the elastic stresses in the concrete:

P/A (pre − compression) ± M/Z (uplift moment due to the cable) (4)

$$=\mathbf{P}/\mathbf{A} \pm \mathbf{P} \times \mathbf{e} \times \mathbf{y}/\mathbf{I} \tag{5}$$

In order to designing prestressed concrete structures, a proper understanding of structural performance at all stages of loading is important. This can be essential where it is a comprehensive knowledge of the design criteria specified in the relevant design standard, such as the minimum requirements to fulfil both ultimate and serviceability requirements.

## **4. Industry 4.0 technologies and digital data**

This section presents different technologies and techniques which can be used for monitoring the structure of urban areas and infrastructures. The new trend of automation and data transferring process is called Industry 4.0. The core component of Industry 4.0 is digital data. Industry 4.0 refers to different technology applications using Internet of Things (IoT), cyber-physical systems, artificial intelligence, machine learning, cloud computing, machine-to-machine and humanto-machine communication and real-time technologies. The concept of Industry 4.0 is adopted by the construction industry. The concept of Construction Industry 4.0 can give better connectivity among construction supply chain stakeholders and real-time access to construction operation, enhancing safety, productivity and the quality of construction. Utilisation of digital technologies such as 3D printing [13], airborne lidar [3, 14, 15], hand-held laser scanners [16, 17], building information modelling (BIM) [18], wireless sensors [19] and automation is changing the infrastructure management including construction and maintenance.

For example, **Figure 4** shows the temporal airborne lidar which can be used for analysing 3D urban changes. Airborne lidar provides valuable digital data which is useful for analysis of the spatial pattern of building height and the proximity analysis with the road's hierarchy.

Spatial data mining (SDM) methods have been used to investigate the unknown relationships between spatial and nonspatial attributes of data sets [20] that may not be apparent using more basic data analysis techniques. The need for knowledge discovery and spatial data mining 'to extract unknown and unexpected information from spatial data sets' was suggested by Mennis and Guo [21]. Two popular SDM methods being used in geographic information systems (GIS) and remote sensing

are spatial autocorrelation statistics [14, 21, 22] and nonparametric density estimation [23]. However, the potential of these SDM methods to explore urban height patterns using airborne lidar data has yet to be actively investigated. While a spatial autocorrelation statistic known as local Moran's I (LMI) is used to find the distribution pattern of building heights, the elevations of buildings were aggregated into large-sized cells using the mean elevation value of the included buildings [3, 22, 24].

Detection of the distribution pattern of clusters of relatively higher (CRH) buildings in a city with varying or heterogeneous heights is crucial for the spatial and temporal change analysis of vertical developments and for trend analysis of vertical urban compactness over time [15]. Detection of the CRH buildings in a city of heterogeneous heights is also essential for thermal urban modelling and urban heat island analyses because the level of heat produced by higher buildings is different from that by lower buildings [25].

Geostatistics is a useful technique for spatial analysis. It refers to statistics used to analyse spatial data and spatiotemporal data sets. Shirowzhan and Lim [22] utilised a spatial analysis procedure using temporal point clouds in advanced GIS. In this analysis a novel method examined ground elevation extraction in slant areas and building classifications. A relevant technique for measuring compactness in three-dimensional environment is Moran's *I* (MI) and *G* indices. Moran's I and *G* are global autocorrelation statistics, which computes the correlation between pairs of data points [14]. Autocorrelation can be calculated for a variable that changes over time, for linear spatial series and for two-dimensional spatial series. MI is an extended version of Pearson's product-moment correlation coefficient for a single variable [14]. Pearson's correlation between two variables x and y from n observations is defined as

Table [14]. Pearson's correlation between two variables x and y from n observations is defined as

$$\rho = \frac{\sum\_{l=1}^{n} (x\_{l} - \overline{x}) \left(y\_{l} - \overline{y}\right)}{\left[\sum\_{l=1}^{n} (x\_{l} - \overline{x})^{2} \sum\_{l=1}^{n} (y\_{l} - \overline{y})^{2}\right]^{1/2}}\tag{6}$$

**9**

**Author details**

Australia

Samad M.E. Sepasgozar1

provided the original work is properly cited.

South Wales, Sydney, NSW, Australia

© 2019 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,

1 Faculty of Built Environment, The University of New South Wales, Sydney, NSW,

2 School of Minerals and Energy Resources Engineering, The University of New

and Faham Tahmasebinia2

\*, Sara Shirowzhan1

\*Address all correspondence to: samad.sepasgozar@gmail.com

*Introductory Chapter: Infrastructure Management, Construction, Structure and Industry 4.0*

*DOI: http://dx.doi.org/10.5772/intechopen.86142*

where *x*´ and *y*´ are the mean values of x and y, respectively. For a univariate series, say x, MI will estimate the correlation between *xi* and *xj*.

For infrastructure monitoring, autocorrelation statistics can be applied to the variable describing the elevation of airborne lidar points in order to determine if *xi* and *xj* belong to the same class.

*Introductory Chapter: Infrastructure Management, Construction, Structure and Industry 4.0 DOI: http://dx.doi.org/10.5772/intechopen.86142*
