**4.6 Concrete bridges**

Concrete bridges can be categorized as below or directly on the main structure, 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 used [15].

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 composite structural material.

Within the reinforced, pre-stressed and post-stressed concrete bridges, we can find the following geometries:


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 purposes is 300–1380 ft. (90–420 m).

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

**Figure 17.** *Concrete bridges for medium span lengths.*

beam height, taking advantage of the effective inertia and providing greater stiffness to the bridge. This geometry type is widely used to build bridges across the cities, highways or interstate roads.

According to **Table 2**, there are a wide variety of recommended girders, considering precast pre-stressed or cast-in-place post-stressed concrete with different cross-sectional geometries, taking account the clear span to cover and the material mechanical properties [16].

Each construction procedure have its own benefits; for example, precast prestressed girders have the advantage of less time installation consuming and minimum frameworks to use compared with cast-in-place post-stressed girders or castin-place slabs, but only can be performed a simple cross-sectional area; by the other hand, cast-in place girders can have any desired cross-sectional geometry, which is adaptable and commonly required on any project.

A concrete girder bridge is shown in **Figure 18**, considering few types of construction procedures and geometries, using the same piers and anchorage.

Cast-in-place reinforced concrete slab or T-beams can be used for small span lengths, as recommended in **Table 1**, and precast pre-stressed I-beams are used for spans lower than 150 ft. (45 m) according **Table 2**. All these types of girders works for bending stress, which limits the span range; however, due its easy construction procedures, are widely used for most common bridges.

a. Wooden bridges, used for small crosswalks or where span lengths are short

b. Stainless steel, where it replaces carbon steel parts of the bridge, increasing

The general process for the development of any bridge are described in the flow chart showed in **Figure 12** and includes planning, design, operation and maintenance procedures. To ensure the useful life of the bridge, a maintenance plan must

According to AASHTO, there are a high variety of loads that the bridge must support and should be considered in the structural design process [17]. These loads

Refers to the own weight of the structure, including installations, finishes, bear-

c. Carbon fibers, used as rehabilitation process and perform capacity

be established, depending on the physical and environmental factors.

are considered as physical factors and can described as follows:

ing surface and all loads that will not have variability over time.

resistance to humidity and environmental factors.

improvement of existing structural elements.

**5. Maintenance avoids bridge deterioration**

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

and loads are low.

*Concrete bridges for short span lengths.*

**Figure 18.**

a. Dead loads

**111**

#### **4.7 Other materials**

Most bridges use structural steel and concrete as main materials. However, there are other materials that can help to complement the structure, depending on some features:


#### **Table 2.**

*Span lengths for various concrete bridge types [16].*

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

#### **Figure 18.**

beam height, taking advantage of the effective inertia and providing greater stiffness to the bridge. This geometry type is widely used to build bridges across the

ering precast pre-stressed or cast-in-place post-stressed concrete with different cross-sectional geometries, taking account the clear span to cover and the material

According to **Table 2**, there are a wide variety of recommended girders, consid-

Each construction procedure have its own benefits; for example, precast prestressed girders have the advantage of less time installation consuming and minimum frameworks to use compared with cast-in-place post-stressed girders or castin-place slabs, but only can be performed a simple cross-sectional area; by the other hand, cast-in place girders can have any desired cross-sectional geometry, which is

A concrete girder bridge is shown in **Figure 18**, considering few types of con-

Cast-in-place reinforced concrete slab or T-beams can be used for small span lengths, as recommended in **Table 1**, and precast pre-stressed I-beams are used for spans lower than 150 ft. (45 m) according **Table 2**. All these types of girders works for bending stress, which limits the span range; however, due its easy construction

Most bridges use structural steel and concrete as main materials. However, there are other materials that can help to complement the structure, depending on some

**Bridge type Span range** Precast pre-stressed I-beam 0–150 ft. (0–45 m) Cast-in-place post-stressed box girder 100–300 ft. (30–90 m) Precast balanced cantilever, constant depth 100–300 ft. (30–90 m) Precast balanced cantilever, variable depth 200–600 ft. (60–180 m) Cast-in-place cantilever segmental 200–1000 ft. (60–300 m) Cable-stayed with balanced cantilever segmental 800–1500 ft. (240–450 m)

struction procedures and geometries, using the same piers and anchorage.

cities, highways or interstate roads.

*Concrete bridges for medium span lengths.*

*Infrastructure Management and Construction*

adaptable and commonly required on any project.

procedures, are widely used for most common bridges.

mechanical properties [16].

**Figure 17.**

**4.7 Other materials**

features:

**Table 2.**

**110**

*Span lengths for various concrete bridge types [16].*

*Concrete bridges for short span lengths.*


## **5. Maintenance avoids bridge deterioration**

The general process for the development of any bridge are described in the flow chart showed in **Figure 12** and includes planning, design, operation and maintenance procedures. To ensure the useful life of the bridge, a maintenance plan must be established, depending on the physical and environmental factors.

According to AASHTO, there are a high variety of loads that the bridge must support and should be considered in the structural design process [17]. These loads are considered as physical factors and can described as follows:

a. Dead loads

Refers to the own weight of the structure, including installations, finishes, bearing surface and all loads that will not have variability over time.
