Revision of Material-Dependent Reduction Factors of HSS Hollow Section K-Joints Using Numerically Implemented Damage Mechanics

Welded hollow sections trusses are widely used in structural engineering, such as pedestrian bridges and crane constructions. High-strength steels (HSS) enable lightweight, high-capacity designs. Current design rules for hollow section joints, based on tests with mild-strength steels (MSS), assume that plastic load redistribution mitigates local stress peaks. However, HSS only allows limited plastic redistribution due to manufacturing-induced hardening. Due to the limited test data available for HSS hollow-section joints, existing design rules developed for mild-strength steel joints apply conservative reduction factors ( C f ) based on the material strength, which decrease the design resistance. To improve the competitiveness and resource efficiency of HSS hollow section joints, further experimental and numerical investigations are required. This paper presents comprehensive numerical investigations of HSS K-joints and the revision of existing material-dependent reduction factors, C f , for steel grades exceeding S355. Numerical models based on damage mechanics were validated against large-scale K-joint tests with circular and square hollow sections of varying geometries and chord preloading. The underlying material models were derived from extensive laboratory tests on the investigated steels to simulate the joint behavior up to failure accurately. The results include a detailed evaluation of the influence of the weld size on the load-bearing behavior and a presentation of the different observed failure modes of the HSS K-joints. Within the approximately 700 full-scale damage mechanical simulations, each individual parameter of the design rules could be evaluated. While the reduction factors currently applied provide a safe design, the design rules should be revised and adapted more specifically to the failure modes. This facilitates more appropriate structural designs and enables the full exploitation of the potential of higher steel grades.