Shear tests on high-strength prestressed bulb-tee girders: Strengths and key observations

The 2006 and prior AASHTO LRFD Bridge Design Specifications limit the cylinder compressive strength of concrete to 10 ksi (69 MPa) due to a lack of experimental evidence to justify the use of higher strength concretes. To examine the 10 ksi (69 MPa) limit for shear design, ten 52 ft (16 m) long and 73 in. (1.8 m) deep prestressed concrete bridge girders were load tested to failure in shear. The primary test variables were concrete strength, 10 to 18 ksi (69 to 124 MPa); maximum design shear stress, 0.7 to 2.5 ksi (5 to 17 MPa); strand anchorage details (straight, unbonded, and draped); and end reinforcement detailing (bar size, spacing, and level of confinement). A total of 20 tests were conducted to evaluate various combinations of the most critical mechanisms of shear resistance. From the results of this and previous research, the use of the LRFD Sectional Design Model for concrete strengths up to 18 ksi (124 MPa) is recommended.