Basis of AASHTO Specifications for High-Strength Shear Reinforcement

AbstractPrior to the 2013 Interim Revisions of the AASHTO LRFD Bridge Design Specifications [AASHTO (2013). Interim Revisions to AASHTO LRFD Bridge Design Specifications, 6th Ed., Washington, DC], the value of reinforcing steel yield strength used in design did not exceed 517 MPa (75 ksi). NCHRP Project 12-77 was initiated to evaluate the AASHTO specifications with respect to the use of high-strength reinforcing steel and other grades of reinforcing steel having no discernible yield plateau. Among the objectives of this project was the investigation of high-strength steel as transverse reinforcement in flexural members and as shear-friction reinforcement. This research led to a number of recommendations that were subsequently incorporated into the 2013 interim revisions of the specifications allowing reinforcing steel yield strengths up to 690 MPa (100 ksi) in many instances. This paper provides the background for the 2013 interim revisions related to the impacts of using high-strength reinforcement on shear strength and web cracking in girders, and on cold construction joint interfaces. The research shows that the use of standard sectional design methods is acceptable for shear reinforcement having yield strengths up to 690 MPa (100 ksi). However, a maximum design yield strength of 414 MPa (60 ksi) must be maintained when calculating shear-friction capacity regardless of the reinforcing steel used.