DESTRUCTIVE TESTING OF DETERIORATED PRESTRESSED BOX BRIDGE BEAM

A deteriorated prestressed box bridge beam was tested to destruction to determine the effects of deterioration on prestressed beam performance. Three prestressing tendons in one corner of the beam had corroded causing spalling of that corner. One of the tendons had broken and the other two were badly corroded, so only 15 tendons were effective. The resulting tendon pattern was asymmetric. A destructive test was conducted by loading the beam with two point loads. For comparison purposes, an undamaged beam held an applied moment of 2720 kN-m (2005 kip-ft) and did not fail. The deteriorated beam failed suddenly at a total applied moment of 1805 kN-m (1310 kip-ft). This reduction in moment capacity is not totally attributable to loss of tendons or cross section. The deteriorated beam also showed less deflection capacity at the midspan [270 mm (10.7 in.) versus 432 mm (17 in.)], more lateral deflection [28 mm (1.1 in.) versus 0 mm] and more web cracking than the undamaged beam. The final failure of the deteriorated beam appeared to be a lateral instability, which resulted in the sudden collapse of the beam. This lateral instability was caused by the lateral bending and yielding of the steel. It was also found that the AASHTO Code was not conservative for the deteriorated beam. The applied failure moment was 8% lower than that predicted by the AASHTO Code.