**4.2 Regulations**

All the rules, restrictions and limitations imposed on the process of creating and design fall into this category. Details such as the budget, the client's guidelines, construction regulation and allowed materials are some of the established rules.

### **4.3 Output**

All the information processed to be able to build any bridge is placed in this category and can be divided into the description and justification of the results. The description refers to all drawings, including architecture, structural, facilities and roads. The justification refers to all technical information that supports the drawings, from structural engineering to budgets.

## **4.4 Design procedure**

In the central part of the flowchart is located the bridge design process, where the input data, regulations and results are interacting together. The design of a bridge implies the imagination of engineers and architects to solve the problem statement, use of the previous knowledge to select the best geometry option and justify the solution with the required calculations.

The flowchart process applies to any type of bridge and can be simple or complicated as required. If we want a successful development of any bridge, there must be a balance between the variables described in **Figure 12**.

Another point regarding the design process of bridge is the selection of the appropriate material and geometry. According to **Table 1**, a recommended bridge's type is shown using geometry, material and span range selection variables [3].

*Bridges: Structures and Materials, Ancient and Modern DOI: http://dx.doi.org/10.5772/intechopen.90718*


**Table 1.**

**4.1 Inputs**

*Model of the bridge design process [13].*

*Infrastructure Management and Construction*

**Figure 12.**

**4.2 Regulations**

**4.3 Output**

**106**

**4.4 Design procedure**

ings, from structural engineering to budgets.

justify the solution with the required calculations.

be a balance between the variables described in **Figure 12**.

All the information required to start the design process of any bridges is placed in this category and can be classified as public and personal. Public information refers to all existing bibliography like books, magazines, publications and software available in the industry. These references should include all topics related to bridges such as material properties, construction process, architectural design and structural design. Personal information refers to the experience acquired by engi-

All the rules, restrictions and limitations imposed on the process of creating and

design fall into this category. Details such as the budget, the client's guidelines, construction regulation and allowed materials are some of the established rules.

All the information processed to be able to build any bridge is placed in this category and can be divided into the description and justification of the results. The description refers to all drawings, including architecture, structural, facilities and roads. The justification refers to all technical information that supports the draw-

In the central part of the flowchart is located the bridge design process, where the input data, regulations and results are interacting together. The design of a bridge implies the imagination of engineers and architects to solve the problem statement, use of the previous knowledge to select the best geometry option and

The flowchart process applies to any type of bridge and can be simple or complicated as required. If we want a successful development of any bridge, there must

Another point regarding the design process of bridge is the selection of the appropriate material and geometry. According to **Table 1**, a recommended bridge's type is shown using geometry, material and span range selection variables [3].

neers, architects and companies dedicated to the construction industry.

*Span lengths for various bridge types [3].*

The recommended span range is related directly with budget challenges of each project. As an example, consider the construction of 100 m span length structure which can be developed using a concrete slab and concrete girder, according the recommendations of **Table 1**.

Performing a structural and design of the proposed bridge, we can find the minimum size for the concrete slab and the concrete girders; considering concrete slab, the thickness to support 100 m of span will require a great depth in slab and therefore, a large amount of concrete material will be required; therefore, if we use girders, the amount of material will be less in comparison.

Depending the span range and geometry of the project, the best economical option of bridge selection will be the efficient use of each material mechanical properties, stress-strain relationship and the characteristics of the site.

### **4.5 Steel bridges**

Bridges with steel material can enter into any of each three categories described on Section 3.2.2. Depending on the type of steel to be used, yielding allowable stress of the structural steel can vary between 36 ksi (249 MPa) and 70 ksi (483 MPa). According to the American Institute of Steel Construction [14], common steel alloys are A36, A992 and A572 Grade 50.

Within the steel bridges, the most common geometries are:


A steel truss bridge is shown in **Figure 13**, with straight truss at the center of the span and variable height near the column supports. The incremental height on the truss near the columns occurs due an increment axial stress in each truss member. The foundation, anchorage and check slab are made of reinforcement concrete; piers can be made of steel or reinforced concrete, depending the site characteristics.

Steel cable-stayed bridge and suspension bridge with general geometry are shown in **Figures 14** and **15**. Both structures have a main tower supporting the main

**Figure 13.** *Steel truss bridges for long span lengths.*

**Figure 14.** *Steel cable-stayed bridges for long span lengths.*

**4.6 Concrete bridges**

*Steel bridges for short and medium span lengths.*

*Bridges: Structures and Materials, Ancient and Modern DOI: http://dx.doi.org/10.5772/intechopen.90718*

composite structural material.

find the following geometries:

c. Bridges supported by girders.

purposes is 300–1380 ft. (90–420 m).

tensors.

**109**

a. Arc-shaped concrete below the main deck.

used [15].

**Figure 16.**

Concrete bridges can be categorized as below or directly on the main structure,

There are many advantages of concrete material compared with structural steel, including its capacity to support compression stresses and the availability on construction industry. Tension stresses are carried out by the reinforcement, making a

Within the reinforced, pre-stressed and post-stressed concrete bridges, we can

b. Cable-stayed bridges, where the entire structure used concrete except for

Arc-shaped concrete bridge is shown in **Figure 17**, which consists of an arc shaped element below all the structure, supporting the piers and the main deck. The concrete arch-shaped element is working mainly by compression stress due its curvature, taking advantage of the material capacity. Piers are working as flexurecompression stress and the main deck is working as shear and bending stress. According to **Table 1**, the recommended span length for structural and economical

The principal feature of pre-stressed concrete girders against simply reinforced concrete girders is the increase of the span length without the need of increases the

as described on Section 3.2.2. According to the American Concrete Institute (A.C.I.), the compression strength of concrete can vary from f'c of 3 ksi (20 MPa) to 7 ksi (48 MPa), depending on cement, water, natural gravel and sand ratios

**Figure 15.** *Suspension bridges for long span lengths.*

cables; the difference between these two bridges is the arrangement of the cables. Cable-stayed bridges use a series of cables to support the deck connected directly with the main tower; when the suspension bridges use a main cable supported between the towers and a series of secondary cables supporting the main deck.

For both cable-stayed and suspension bridges, the main deck has a high slender ratio due the long span covered and need additional structural elements to increase the stiffness. Trusses are commonly used to stiff the main deck and allow the wind to flow through these structural elements.

Tension stress is developed by the cables, which are the optimal geometry giving a capacity to increase the span length. Looking into **Table 1**, for span lengths higher than 3500 ft. (1100 m), the suspension bridge is the only economical option to choose.

Bridges supported by steel girders are shown in **Figure 16**. The main deck is the combination of the concrete slab, a wide variety of structural steel beam, piers and anchorage geometries. The steel girders can be simply or continuous beams using hot rolled sections or developed by steel plates.

Steel girders are working with bending stresses, which usually requires more material if it is compared with truss elements. However, according to **Table 1**, these types of bridges can be economical competitive for short and medium span lengths due its easy construction procedures and less time-consuming during installation of the girders. Also, these girders have a great stiffness compared with truss bridges, reducing vibration responses produced by traffic and wind flow.

*Bridges: Structures and Materials, Ancient and Modern DOI: http://dx.doi.org/10.5772/intechopen.90718*

**Figure 16.**

cables; the difference between these two bridges is the arrangement of the cables. Cable-stayed bridges use a series of cables to support the deck connected directly with the main tower; when the suspension bridges use a main cable supported between the towers and a series of secondary cables supporting the main deck. For both cable-stayed and suspension bridges, the main deck has a high slender ratio due the long span covered and need additional structural elements to increase the stiffness. Trusses are commonly used to stiff the main deck and allow the wind

Tension stress is developed by the cables, which are the optimal geometry giving a capacity to increase the span length. Looking into **Table 1**, for span lengths higher than 3500 ft. (1100 m), the suspension bridge is the only economical option to

Bridges supported by steel girders are shown in **Figure 16**. The main deck is the combination of the concrete slab, a wide variety of structural steel beam, piers and anchorage geometries. The steel girders can be simply or continuous beams using

Steel girders are working with bending stresses, which usually requires more material if it is compared with truss elements. However, according to **Table 1**, these types of bridges can be economical competitive for short and medium span lengths due its easy construction procedures and less time-consuming during installation of the girders. Also, these girders have a great stiffness compared with truss bridges,

to flow through these structural elements.

hot rolled sections or developed by steel plates.

reducing vibration responses produced by traffic and wind flow.

choose.

**108**

**Figure 13.**

**Figure 14.**

**Figure 15.**

*Steel truss bridges for long span lengths.*

*Infrastructure Management and Construction*

*Steel cable-stayed bridges for long span lengths.*

*Suspension bridges for long span lengths.*

*Steel bridges for short and medium span lengths.*
