Advanced numerical simulation on high strength steel with welding-induced reductions in their mechanical properties

Abstract

High strength S690 steel is considered to be highly effective to act as heavily loaded structural members in construction, and many structural engineers are very interested in adopting these high strength steel members in buildings and bridges. However, reductions in mechanical properties of welded sections are usually found, especially when the welding processes are not controlled properly. It is highly desirable to develop rational numerical modelling methods to simulate structural responses of these welded sections with welding-induced reductions in their mechanical properties. In this paper, an advanced numerical modelling approach proposed by the authors, namely, the critical transformed regions (CTR) approach, is adopted to assess structural responses of the welded sections of the high strength Q690 TMCP steel, and both 28 and 44 mm thick welded sections have been examined. Tensile tests on standard coupons of these welded sections were conducted to provide data for detailed verification of the proposed approach. It should be noted that in this approach, the critically transformed regions (CTR) within HAZ of the welded sections with the most reduced mechanical properties are modelled. Both the locations and the boundaries of CTR are determined after highly non-linear analysis for heat transfer. Tensile tests on heat-treated coupons of the Q690 TMCP steel are carried out to provide reduced mechanical properties of these CTR in welded sections according to various maximum temperature T<inf>max</inf>and cooling rates t<inf>8/5</inf>. Structural models are then established and a comprehensive comparison between the simulated and the measured structural responses of these welded sections is presented. A good comparison is achieved to confirm validity of the proposed CTR approach.