Influence of Connection Configuration on Stress Redistribution and Joint Core Damage in Grout-Filled Steel Tubular X Assemblies Under Compression

The compressive resistance of tubular X supports in building structures depends on the stress state in the joint core. This study combines laboratory compression tests and three-dimensional finite element analysis to investigate grout-filled steel tubular X assemblies with a directly intersecting joint (IJ) and a rib-plate joint (RPJ). Load–displacement responses, peak resistance and visible joint damage were compared. The results have indicated that the RPJ configuration improves compressive resistance by modifying local restraint and force transfer, with RPJ having achieved a 26.9% higher mean peak load at an 8.0% smaller mean recorded peak displacement than IJ under the investigated conditions. Under the investigated displacement-controlled conditions, stress redistribution reduces the maximum steel equivalent stress in the joint core and shifts the region of maximum stress toward the lower limbs. The local failure mode changes from transverse cracking at the intersecting weld region to longitudinal or oblique separation along the plate connections, highlighting the need to coordinate reinforcement of the joint core with the resistance of adjoining connections and members.