*3.1.1.2 Wooden and steel truss bridges*

ii. If the bridge is not operating, alternate routes will be affected.

need to use an alternative route, which probably is not designed for a sudden increase of vehicular flow, causing wasted time, greater distances and additional

fuel required.

designs [3].

centuries.

**Figure 2.**

**96**

*View of Mexico City road system [4].*

*3.1.1 Ancient bridges*

*3.1.1.1 Stone arch bridges*

bridges and several road accesses.

*Infrastructure Management and Construction*

**3.1 Types of bridges: ancient and modern**

When a bridge does not work, people who used the affected road will have the

For a successful transportation system, a balance should exist between vehicle volume, supported loads and proper budget. **Figure 2** shows a section of Mexico City's transportation system, showing balance between the number of lanes, signs,

We can think that all existing bridges with the variety of materials, geometries,

loads and designs have always existed. However, the evolution of bridges has occurred within the changing needs of the society since the 19th century, with the improvement of materials, optimization techniques, architectural and structural

In the beginning, bridges were built with a simple geometry and had very limited uses, because they only covered very short span, such as small rivers. These

The first bridges that were built based on mathematics methods were the stone arch. The exact construction date is not known, but there are structures built by civilizations such as the Greeks or the Romans, where they used this type of bridges

The stone arch bridges, as shown in **Figure 3**, take advantage of the compressive capacity of the rock due its geometry, supporting its own weight and live loads. These structures are usually robust and each of the arches supports the upper deck. Some examples of this bridge's type are the Segovia Aqueduct, located in Spain and the Pont Du Gard Aqueduct, located in France, both built between the 1st and 2nd

bridges used basic materials such as wood, ropes and stone.

as aqueducts, roads for people walking and carriages.

By the beginning of the 19th century, the structures used wood as common material and truss bridges began to emerge (**Figure 4**). These wooden trusses took advantage of the axial stress capacity of the bar elements, creating bridges with longer spans, low weight and enough stiffness to withstand higher loads. Due the large number of geometries that can be created with trusses, there are possible arrangements which the bar elements can have taking advantage of the tension and compression stress capacities. Some examples can be mentioned:

	- i. Geometries as Pratt, Warren and Baltimore types.
	- ii. Geometries using cables for tension elements.
	- i. Geometries as Wernwag and Burr types.
