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Abstract:
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The Texas U -Beam standard designs were released in the 1990’s and have been used increasingly in bridges across the state since . While prototypes of the 54 -in . deep prestressed concrete beam were built during the design phase , no full -scale load tests were performed .
This study of the U -Beam had five goals : (i ) determine the magnitude and location of stresses induced in reinforcing bars in the end region of the beam at prestress transfer , (ii ) measure concrete curing temperatures in square and skewed end blocks , (iii ) establish the vertical shear capacity of the standard section , (iv ) evaluate interaction between behavior at prestress transfer and performance under shear -critical loads , and (v ) identify design and detailing improvements and make recommendations . Eight full -scale Texas U54 prestressed concrete beams were fabricated to achieve these goals .
Load testing of the first four of these beams revealed a critical weakness along the bottom flange -to -web interface of the beam . The weakness caused failures that occurred at loads well below the calculated shear capacity . Given the horizontal sliding observed , the failure mode was called horizontal shear . The next two beams were fabricated to test three modifications to the end -region design , two of which were deemed successful . The final two beam sections tested contained the recommended new standard reinforcement and concrete geometry .
A method to evaluate the horizontal shear demand on and capacity of the bottom flange -to -web interface of prestressed concrete beams was developed . The calculations were formulated using the theories of beam bending and shear friction . This method was calibrated and verified using the U -Beam test data , a series of small -scale specimens , and results of shear tests in the literature .
Stresses induced in reinforcing bars at prestress transfer met expectations set by existing codified equations . No modifications to the current U -Beam standard design are needed to manage these stresses . The induced stresses did not influence vertical shear behavior , and no interaction between the two is believed to exist for U -Beams .
This dissertation contains the specifics of the beams tested and the data collected , and provides the details of recommended changes to the Texas U -Beam standard drawings . |