Failure of concrete T-beam and box-girder highway bridges subjected to cyclic loading from traffic

Concrete cast-in-place T-beam highway bridges are often constructed by casting the girders and the deck separately, creating a cold joint between the girders and the deck. Under certain circumstances, cracking and visible slippage can occur in this joint, resulting in fracture of the reinforcing steel crossing the joint, greatly reducing the composite action between the flange and the web. After observing the movement of this joint at some bridges, a detailed evaluation was performed on 12 five-girder T-beam bridges on Interstate 40 (I-40) in the southwestern US, and a potential failure mechanism was identified in all of them. In addition, alkali silica reaction (ASR) had been known to affect bridges in the area; therefore the study evaluated whether ASR had contributed to the failures. Several factors were identified as contributors to the failure mechanism, including a limited recognition in the original design standard of cyclic loading, high volume of heavy truck traffic, and transverse moments caused by unbalanced wheel loading. After the investigation, recommendations were made for instituting special inspections of construction joints in similar existing bridges.