Shear lag of bolted and welded single angles with high strength steels

Abstract

High strength steels (HSS) have been attracting increasing attention in the design and construction industry because of their high ultimate strength and reduced cost of production. With the increased ultimate strength, smaller HSS structural sections can be designed and used in structural systems. This scenario translates to weight reduction and cost saving. However, HSS possess lower ductility than normal steels (NS), thereby possibly affecting the structural behaviour of members and connections. In particular, the reduced ductility of steel materials may have a significant influence on the tensile strength and behaviour of angle sections, which are usually governed by the shear lag effect. The current design equations used to evaluate the tensile capacity of angle sections considering the shear lag effect are based on studies using NS materials, and the existing literature on HSS tension member strength and behaviour is scarce. Therefore, a study including both experimental and numerical works was conducted to examine the tensile strength and the behaviour of HSS angle sections. A total of 18 full-scale bolted and welded single angles were tested, including 14 HSS angle specimens and 4 NS angle specimens. The test parameters included steel grade, connection length and out-of-plane eccentricity. Finite element models were established and validated using test results, and a numerical parametric study was subsequently conducted for further investigation. According to the experimental and numerical results, the low ductility of HSS has a negligible effect on the tensile capacity of angles with long leg connections, whereas the tensile capacity of angles with short leg connections is reduced because of the low ductility of HSS. The test tensile capacities of the HSS welded single angles and HSS bolted single angles with long leg connections can be accurately predicted using the 1 x/L rule to consider the shear lag effect. On the contrary, the predictions for HSS bolted single angles with equal and short leg connections are un-conservative. A reduction factor is proposed on the basis of the results of the tests and numerical study to consider the effect of steel grade by modifying the 1 x/L rule. The modified equation provides a more accurate prediction of the test results.