Enhancing the Collapse Resistance of a Composite Subassembly with Fully Welded Joints Using Sliding Inner Cores

This study presents a novel approach to enhancing the progressive collapse resistance of a fully welded joint (FWJ) by introducing sliding inner cores within the joint, which is referred to as the FWJ with sliding inner cores (FWJS). Two specimens were prepared and designed with additional consideration of composite action of the slab. Quasi-static tests and refined numerical simulations were conducted to analyze the damage mode, deformation behavior, strain distribution patterns, internal forces, and resistance development in both specimens. The test results revealed that the first fracture occurred in the tensile beam flanges for both FWJ and FWJS specimens, whereas the FWJS specimen exhibited delayed crack of the tensile beam flange compared to the FWJ specimen. The FWJS specimen demonstrated better utilization of the catenary mechanism during the flexural-catenary combined stage. Additionally, in the elastic, elastic-plastic, plastic, and flexural-catenary combined stages, the addition of the sliding inner cores in the FWJS specimen significantly enhanced its resistance by 15.6%, 22.3%, 23.4%, and 70.2%, respectively. It is also revealed that the response of the sliding inner core consisted of bending, transition, and full tension stages, which was shown to effectively replace the fractured beam flange in redistributing the internal forces. Based on the analysis of the working mechanism and numerical parametric analysis, optimal values for the 10 design parameters of the FWJS are suggested, and a comprehensive design procedure for the FWJS is proposed.