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The I-25/Dona Ana Interchange in Las Cruces NM is a simple span, high performance concrete (HPC)prestressed girder bridge. The girders are six prestressed, BT-63 HPC girders with a span length of 112.5 ft (34.2 m). The bridge was monitored from fabrication through service with an embedded optical fiber sensor system. Thirty two Fiber Bragg Grating (FBG) optical fiber deformation sensors were installed in the beams during fabrication. The strands were 6/10 inch ( 1.5 cm ) low relaxation strands and the concrete had a design compressive strength of 8 ksi (55.2 MPa) at release and 9.5 ksi (66.5 MPa) at 28 days. The bridge was monitored for two years, from transfer of the prestressing force through service. Several topics that are studied in this project: prestress losses, camber, shear and moment girder distribution factors, impact factor, insitu material properties and serviceability under traffic loads. The results from sensor measurements were compared to the values predicted by the AASTHO codes and other design codes or empirical equations, to check the accuracy of these codes when applied to HPC girder bridges.
This report details the design and construction of an AASHTO Type IV prestressed girder and a PCI BT-56 prestressed girder. It also details the shear testing and shear performance of the BT-56 girder. The results are compared with results from previous research dating back to 1986. Finally, all research was compared with the AASHTO Standard (2002), AASHTO LRFD (1998) and AASHTO LRFD (2004) Specifications to examine thier overall accuracy in predicting shear strengths.
This research embodied a three-prong approach for directly determining the residual prestress force of prestressed concrete bridge girders. For bridges that have yet to be constructed, outfitting girders with instrumentation is a highly effective means of determining residual prestress force in prestressed concrete bridge girders. This constitutes the first prong. Still, many bridges are constructed without such instrumentation. For these bridges, a destructive technique can be used to directly determine the residual prestress in a prestressed concrete bridge girder. This implies that the girder(s) being tested have already been taken out of service. This constitutes the second prong. For bridges that are anticipated to remain in service that are lacking embedded instrumentation, the development of a non-destructive technique used to estimate the remaining force in the tendons of prestressed bridge girders is extremely important. This constitutes the third prong used to directly determine residual prestress force. The flexural capacity was also determined from field tests and compared to analytical estimates. By design, the code estimates are meant to be conservative. Alternatively, the residual prestress force for in-service members can be determined directly through the non-destructive technique presented in this research. As such, bridge service capacities can be determined directly and do not need to be conservatively estimated.