Capacity and Acceptance Criteria of Welded Splices on Cold-Bent Reinforcing Steel

The American Association of State Highway and Transportation Officials (AASHTO) Load and Resistance Factor Design (LRFD) Bridge Design Specifications require welding of bridge reinforcing steel (rebar) splices to conform to the American Welding Society (AWS) D1.4 Structural Welding Code – Steel Reinforcing Bars. Alaska Department of Transportation and Public Facilities (DOT&PF) uses cold-bent reinforcing steel hoops and spiral bars as confinement in its concrete-filled steel pipe pile bent system. Structural adequacy of this system is essential for seismic performance. In Alaska, and other seismic states, ASTM A706 Grade 60 reinforcing steel (rebar) is routinely specified for members expected to form plastic hinges. A706 rebar has a restricted chemical composition and carbon equivalent to enhance its weldability. AWS D1.4 describes filler metal selection, preheat/interpass temperatures and performance and procedure qualification requirements for welding of steel reinforcing bars. However, welded splices on hoops and spiral bars are technically not in compliance with AWS D1.4, which does not allow welding within two bar diameters of the bent portion of the steel. Despite this AWS D1.4 code provision and decades of research on the pipe pile system, no known defects have arisen from these welded splices. However, the reliability of the splices to behave as anticipated is extremely important in plastic hinge regions. Specific testing of cold-bent reinforcing steel welds has not been completed to ensure that current materials and methods would not adversely affect the strength and ductility of the reinforcing bars. The goal of this research program is to investigate the effect of welding on cold-bent ASTM A706 Grade 60 reinforcing steel. Specific objectives are (1) to determine changes in microstructure and microhardness in the heat-affected zone (HAZ) of welded cold-bent reinforcing steel, (2) to compare the tensile strength and ductility for welds made on cold-bent versus unbent reinforcing steel, (3) to determine the monotonic stress-strain behavior locally in the HAZ of welded cold-bent reinforcing steel, and (4) to identify specific requirements and/or acceptance criteria for welding on cold-bend reinforcing steel beyond those in AWS D1.4.