Finite Element Analysis of Isolated Composite Joints: Validation against Experimental Data

The study investigates the mechanical performance of isolated steel–concrete composite joints subjected to both positive and negative bending moments through an advanced finite element modeling approach. The research addresses a critical gap in existing design codes, which often overlook the nonlinear interaction between steel and concrete components in semi-rigid connections. The primary aim is to evaluate the joint behavior under realistic service and extreme loading conditions, offering a validated numerical framework that can support future enhancements in structural design standards. A three-dimensional nonlinear finite element model was developed using ABAQUS, integrating the Concrete Damaged Plasticity (CDP) model to capture concrete cracking, steel yielding, and interfacial slip. Experimental data from composite specimens tested in Warsaw University of Technology and replicated at the Libyan Concrete Materials Laboratory were used for calibration and validation. Parametric analyses considered variations in end-plate geometry, bolt arrangements, and column dimensions to assess their influence on joint stiffness, ductility, and load transfer mechanisms. The results demonstrated excellent agreement between experimental and numerical findings, with a correlation coefficient exceeding 0.95 for moment–rotation relationships. Among the tested configurations, the CSB7 joint (eight-bolt symmetric extended end plate) exhibited the highest performance, achieving sagging and hogging moments of 144 kNm and 269 kNm, respectively. These results highlight the joint's superior ductility and robustness under nonlinear loading, indicating its suitability for structures exposed to exceptional conditions such as seismic or fire events. The research contributes to the ongoing development of Eurocode-based composite joint design, emphasizing the need for nonlinear performance criteria and predictive modeling tools. While the study was limited by the absence of cyclic and high-temperature testing, its implications extend to safer, more resilient, and sustainable structural systems, promoting optimized connection design and improved global design standards.