Progressive fracture of reinforced deck slab in girder-slab type bridge deck.

Abstract

An experimental investigation was conducted on two types of reinforced concrete deck slabs, restrained and unrestrained, to determine their static and fatigue life under a simulated wheel load. For the restrained panels, large size simulated girder-slab type bridge decks were cast and for the unrestrained panels, small size concrete slabs were used. One of the significant aspects of this study was to observe the influence of initial non-structural cracks in deck slabs which are caused by different phenomena such as plastic shrinkage, plastic settlement and thermal effects on the static capacity and fatigue of deck slabs. Two construction practices were followed, good and bad. The only difference between the two was in the curing method. Badly constructed panels were left to self cure in air immediately after casting in order to induce initial non-structural cracks, whereas well constructed panels were covered with polythene sheeting immediately after casting and water was sprayed twice a day for seven days. Static and fatigue tests were conducted on these panels using a 50T MTS actuator to apply a patch load that increased slowly until the failure was reached. The loaded area was kept small to induce punching type failure and to reflect the behavior under high abnormal loads exceeding the design limits. In fatigue tests a fraction of the ultimate static capacity was taken as the maximum load for the fatigue cycle, and the load ratio was kept close to 0. 1. Based on the test data, fatigue life has been prescribed in a nondimensionalized form which appears to be independent of the type of concrete. Test results show that the static capacity of reinforced concrete deck slabs is impaired by the pressure of initial precracks and that it is enhanced to ascertain degree by edge restrained and increase in tension steel. Both static and fatigue failure under a highly concentrated patch load portray a localized punching type failure of a conical concrete whose top corresponds to the loaded area and bottom encompasses a relatively large area.