High-strength steel S700 K-joints: Experimental investigation on ultimate resistance and deformation capacity

K-joints are a common type of welded hollow section joints used in structures, specifically trusses. Current design guides impose reduction factors on K-joints made of high-strength steel (HSS). Three K-joint failure modes are affected by these reduction factors: chord face, brace and punching shear failures. Additionally, there is a deformation-based criteria that determines the load-bearing capacity of joints regardless of joint type and behavior. This research investigates these limitations using an experimental study on 21 K-joints. The joints were made of cold-formed rectangular hollow section S700 steel members. The testing campaign targeted all the impacted failure modes by having a group of test specimens for each failure mode. Two parameters (gap size and chord preloading) were varied to study their effects as limited research is available on them. Full strength butt welds and fillet welds were employed in the fabrication of the tested joints. The load-displacement behavior of all joints is captured along with local deformation data. The resistance and observed failure mode of all specimens are compared to the prediction of the second-generation Eurocode and the level of agreement is reported. The need for the reduction factors and the applicability of the deformation criterion for K-joints are both thoroughly investigated. The results show that reduction factors are too conservative for one of the failure modes, but necessary for the rest. In addition, the widely used deformation criteria is not needed for K-joints due to its unsuitability. Other observations about the studied parameters and design factors are made. • The research studies high strength steel S700 K-joints using 21 experiments. • The research focuses on investigating reduction factors and the widely accepted 3 % deformation criteria. • The tested failure modes are chord face failure, brace failure and punching shear failure. • The research compares the ultimate resistance of joints to their predicted values by the Eurocode. • Conclusions are made on the material factor ( C f ), the reduction criterion ( f y ≤ 0.8 f u ) and the 3 % deformation rule.