Designing for deck stress over precast panels in negative moment regions
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One of the leading causes of structural deficiencies in the United States Bridge Inventory is related to deterioration and durability problems with concrete bridge decks (NCHRP 2004). The primary issue with bridge decks is related to cracking of the concrete that provides a direct conduit for moisture and other corrosion agents to permeate and attack the reinforcing steel. Adequate reinforcing steel is needed in the deck to minimize crack widths and therefore limit corrosion of reinforcing steel. A particular case of interest occurs when the bridge deck is constructed using partial-depth precast concrete deck panels (PCP) with cast-in-place (CIP) concrete topping. When this type of deck construction is used over the negative moment region of continuous steel or concrete girders, the amount of reinforcing steel that should be placed within the CIP concrete topping to provide adequate crack control is not currently well understood. This thesis is part of a larger study being conducted for the Texas Department of Transportation that is examining this issue. In the study reported in this thesis, two newly constructed bridges were instrumented to monitor the behavior of the bridge deck. These bridges did not use continuous girders, but rather had simply supported prestressed concrete girders, with a bridge deck constructed using a “poor-boy” construction joint detail over interior bents. Each bridge utilized three different reinforcement layouts centered over an interior bent within the poor-boy joint detail. Strain gages in each portion provided constant readings to display the distribution of strain across the bridge deck. Each bridge was monitored over a period from when the deck was cast until when the bridge was opened to traffic. Live load tests were also conducted to provide data on strains induced by heavy trucks. Based on the field data, no clear correlation was found between the amount of steel added and the strain measured. However, based on the measured data combined with field observations of cracking, the current standard reinforcement appears to be adequate in controlling the crack widths for the poor-boy deck detail. While the poor-boy deck joint detail is different from deck details used over negative moment regions of continuous girders, this data provides useful insights in to bridge deck behavior that will help guide future phases of the larger study.