EFFECTS OF DAMAGE ON THE BEHAVIOR OF PRETENSIONED/PRESTRESSED CONCRETE BEAM (PPCB) BRIDGES

In June 1996, a series of field-tests were conducted on twin bridges carrying I-680 over country road L34 in Beebeetown, Iowa. The westbound bridge was damaged by an over-height load. The load fractured a portion of the bottom flange and web of the first two beam lines of the 11-beam structure. A majority of the strands were exposed in the process but no strands were severed. Several strands appear lax. The eastbound bridge is undamaged. The Iowa DOT decided to replace the two damaged beams due to uncertainties regarding their capacity and long term serviceability. Prior to removal of the beams, the westbound and eastbound bridges were load tested. Results from the tests are still being interpreted but the bridges do appear to behave differently. Results indicate that the differences may be only partially due to damage; the other causes being differences in end restraint of the center span and participation of the barrier rail in edge stiffening. Grillage models of an undamaged bridge have been developed and are shown to reasonably agree with the experimental results of both the damaged westbound and undamaged eastbound bridges. The analytical models are more flexible than the experimental results. This is likely due to neglect of the barrier rail stiffness and the treatment of the beams as simply supported. The influence of intermediate diaphragms has been analytically shown to have little effect on the distribution of loads in exterior lanes.