**4.1 Inputs**

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 engineers, architects and companies dedicated to the construction industry.

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

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

**Bridge type Material Span range** Slab Concrete 0–40 ft. (0–12 m) Girder Concrete 40–1000 ft. (12–300 m) Girder Steel 100–1000 ft. (30–300 m) Cable-Stayed Steel 300–3500 ft. (90–1100 m) Truss Steel 300–1800 ft. (90–550 m) Arch Concrete 300–1380 ft. (90–420 m) Arch Steel 800–1800 ft. (240–550 m) Suspension Steel 1000–6600 ft. (300–2000 m)

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

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

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

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

properties, stress-strain relationship and the characteristics of the site.

Within the steel bridges, the most common geometries are:

a. Straight truss, variable geometry truss or arc-shaped trusses.

girders, the amount of material will be less in comparison.

recommendations of **Table 1**.

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

are A36, A992 and A572 Grade 50.

b. Cable-stayed bridges.

c. Suspended bridges.

**107**

d. Bridges supported by girders.

**4.5 Steel bridges**

**Table 1.**
