Study Of Corrosion Effects On Steel Truss Bridges

Abstract

Bridges span over the water bodies, deep gorges and the roads. Truss bridges are used for the medium to long-span bridges. Under railway loading, steel bridges are subjected to reversal of loads called fatigue. Fatigue is a serviceability limit state so excessive deflection may cause discomfort, rendering the bridge unserviceable. Fatigue life is a term introduced in design for defining the number of cycles a structure can withstand for a working stress range. Fatigue life is affected by corrosion, as corrosion reduces the net section available for resistance and also affects the regions of connections and bearing locations. Pitting corrosion in small areas leads to formation of the small pits which on application of fatigue load develop as cracks. These pits act as stress raisers, which leads to stress concentration. Along with this residual stress acts as a base about which stress reversals take place. Residual stresses and material reshaping leads to crack initiation, these cracks elongate when subjected to stress reversals. The coupled study of corrosion along with fatigue in a time-based manner needs to be conducted to evaluate the service life of structure. In practice fatigue is considered exclusively without consideration of corrosion. The uncoupled analysis may lead to serious complacency in calculation of fatigue life. Other supporting elements like stiffeners, connection angles are crucial in design for corrosion fatigue. These are the regions which have heavy moisture-holding capacity. The regions cannot be regularly serviced to know the damage levels of location. Combination of corrosion with fatigue gives a conservative design which leads to elongated service life of the structure.