Full-Scale AASHTO Type II Girders Prestressed with Stainless Steel Strands

Stainless steel strands are a new technology and option available for the bridge industry. They have high corrosion resistance, which will result in more durable and low-maintenance concrete bridges. However, stainless steel strands have lower ductility and different stress–strain behavior than carbon steel strands, affecting the design criteria for prestressed concrete girders. Stainless steel strands have already been deployed in substructure components (piles) in many projects around the United States. However, due to their low ductility and lack of full-scale research studies and structural design approaches, they have not yet been deployed in flexural members. This study investigates the flexural behavior of stainless steel strand prestressed concrete girders. Five full-scale 12.8-m (42-ft)-long AASHTO Type II girders prestressed with 15.2-mm (0.6-in.)-diameter duplex high-strength stainless steel (HSSS) strands were designed, fabricated, and tested in flexure. The prestressing reinforcement ratio was varied in this experimental program. The transfer length and prestress losses of 15.2-mm (0.6-in.)-diameter HSSS strands were measured. The flexural behavior of the girders was assessed by the evaluation of cracking load, ultimate load-carrying capacity, load-deflection response, and failure mode. As designed, all girders failed due to rupture of the HSSS strands. Experimental results showed that, although the HSSS strand has low ductility and it may control the capacity of the girders, adequate warning (noticeable deflection and many cracks before failure) can be achieved in HSSS strand prestressed concrete girders. The predicted analytical and numerical moment strengths of the five girders were in close agreement with those measured experimentally. Although the analytical model gave better predictions, the numerical approach is easier to use for design. A flexural design approach for HSSS strand prestressed concrete I-girders is proposed where rupture of strands is an acceptable failure mode. The findings from this experimental program will be useful for the development of new design specifications for concrete girders prestressed with stainless steel strands.