I-shape steel columns in many old bridges can be rehabilitated by welding steel plates to the flanges of the existing columns. However, the effect of welding residual stresses, initial imperfections, and column load at the time the reinforcing plates are welded to the column can significantly affect the column strength. Currently there are no guidelines available for the design of columns reinforced under load with welded cover plates. This paper presents a numerical study to determine the appropriate column curve, whether SSRC column curve 1 or 2, i.e. n = 2.24 or 1.34 in the Canadian steel design standard, to use for design of columns reinforced with steel cover plates welded to the flange tips, either parallel to the web or parallel to the flanges. A validated finite element model is used to conduct a parametric study to investigate several parameters that affect the strength of the reinforced column. Considering the variation in the resistance, a detailed statistical analysis, which provides a uniform level of safety, is conducted based on the results obtained from the parametric study to determine appropriate resistance factor to use for limit state design of columns reinforced with welded steel plates. A reliability analysis indicated that steel columns reinforced with plates welded under load should be designed using SSRC column curve 2 (n = 1.34) with a resistance factor of 0.90. (C) 2016 Elsevier Ltd. All rights reserved.
