Precast, prestressed concrete panels (PCPs) are used in 85% of bridges in Texas. The goal of this thesis is to reduce collinear cracking (cracks propagating parallel to strands) in PCPs. One way to reduce collinear cracking would be to reduce the initial prestress force. In design, TxDOT conservatively assumes total prestress losses of 45 ksi. Based on eight panel specimens, instrumented and fabricated at two different precast plants in Texas, actual prestress losses were measured as at most 25 ksi. This difference (about 20 ksi) is consistent with a reduction in initial prestress force from 16.1 kips per strand to 14.4 kips per strand. Another way to reduce collinear cracking would be to provide additional transverse reinforcement in the end regions of the panels. By comparing crack spacings and crack widths in current and modified panel specimens, it was found that additional reinforcement consisting of one or two #3 bars placed transverse to strands at panel ends would effectively control collinear cracking in PCPs. / text

Precast, prestressed concrete panels (PCPs) have been widely used in Texas as stay-in-place formwork in bridge deck construction. Although PCPs are widely popular and extensively used, Texas is experiencing problems with collinear cracks (cracks along the strands) in panels. One reason for the formation of collinear cracks is thought to be the required level of initial prestress. Currently, PCPs are designed assuming a 45-ksi, lump-sum prestress loss. If the prestress losses are demonstrated to be lower than this value, this could justify the use of a lower initial prestress, probably resulting in fewer collinear cracks. For this purpose, 20 precast, prestressed panels were cast at two different plants. Half of those 20 panels were fabricated with the current TxDOT-required prestress of 16.1 kips per strand, and the other half were fabricated with a lower prestress of 14.4 kips per strand based on initially observed prestress losses of 25 ksi or less. Thirteen of those panels were instrumented with strain gages and monitored over their life time. Observed losses stabilized after five months, and are found to be about 24.4 ksi. Even with the reduced initial prestress, the remaining prestress in all panels exceeds the value now assumed by TxDOT for design. / text