**6.2 Degradation due physical factors: wear and fatigue**

Wear degradation during the life of a bridge occurs due its continuous use, where the friction is present by physical forces, including the pass of the vehicles over the main deck. These vehicles generate frictional forces when perform braking and accelerating, causing wear on the structure. For bridges where the piers are in contact with water flow, the friction causes degradation.

Usually traffic flow perform low wear degradation over the deck, however, if the road have any defect, will create bumps and wear will be increased rapidly, creating damages. Bridges using simply supported girders will require construction joints between supports; these joints are examples of places were bumps are easily created

**Figure 19.** *Concrete piers of reinforced steel with corrosion problems [18].*

**Figure 20.** *Bridge of structural steel with corrosion problems [19].*

due poor construction procedures. **Figure 21** shows a typical bump problem, which can be avoided using any joint procedure and materials offered in the industry.

Another physical factor that affects the structure is fatigue, caused by the loading and unloading forces due the traffic flow, affecting the stressed elements of the bridge. Fatigue causes degradation on material mechanical properties with each load cycle; this means each vehicle passing over the deck. If each cyclic load produces a stress equal or higher to yielding stress of the material, therefore a large amount of cycles will cause a decrease on the material allowable, allowing brittle failure of the element. **Figure 22** shows a crack developed due fatigue stress loads; notice there are no yielded zones on the beam, only a sudden crack.

corrosion, wear and fatigue. Prevention and protection procedures are required,

Corrosion prevention is the best economic way to preserve the structural elements of any bridge and the result is a positive benefit in the useful life of the materials [22]. Acidic corrosive emissions and hydrocarbons, in combination with high humidity accelerate the process of corrosion and degradation. The designer should analyze the type of electrochemical attack that would occur during the life of

For structural steel, epoxy paints are used to insulate direct contact of water or moisture. For the reinforcement of concrete, should take care of the coating to avoid exposure to moisture. As shown in **Figure 23**, the possibility of install a cathodic

Wear degradation process is unavoidable for any surface subjected to friction; therefore, the damage depends of the applied load and affected zone. If a flexible roadway is used, wear degradation is higher and requires additional maintenance compared with reinforced concrete roadway. By the other hand, reinforced concrete piers may have contact with the water flow of the river; frictional forces would be present and wear factor became an issue, requiring additional coating to

For fatigue degradation process, the designer must consider the weight of all vehicle types, cyclic loads, loading scenarios and fatigue material properties as a way to prevent brittle failure. All elements should have enough stiffness to avoid high stresses under typical cyclic load cases, therefore the fatigue allowable stress should be greater than the applied loads. Fatigue procedures as Modified Goodman

To ensure the success of all methods implemented to avoid bridge degradation, a testing and monitoring plan must be established as part of the maintenance procedure. The cost of maintenance plan should be incorporated on the bridge's budget [25]. As a first step, visual review of the bridge structural elements should be performed in a scheduled given time. The girders, piers, connections, cables, deck and materials used must show no damage, such as cracks, corrosion, visible deformations or any variable that indicates a problem. Monitoring techniques are used as a way to measures the loading cycles, cracks or corrosion and prevent any damage on the bridge. For corrosion mitigation and prevention, the maintenance process must have a

including maintenance process to avoid possible damage.

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

protection system should be considered.

*Steel beam with fatigue crack failure [23].*

Diagram or Miner's Rule are used [24].

plan taking into account the next features:

a. Expected useful life of the bridge.

b. Environmental exposure.

**115**

protect the reinforcing bars.

**7. Testing and monitoring**

the structure.

**Figure 23.**
