Deformation and load transfer analysis of staggered composite-steel lap joints subjected to progressive damage

In bolted composite connections design, staggered arrangements might offer a good area usage especially for structural elements with a small width. In this research, experimental and numerical works were employed to study the composite-steel double lapped joints with staggered bolts arrangement under static loads. Staggered bolt arrangement was studied with different bolt diameters and numbers. The predictions of developed models were compared to the experimental results and a good correlation was evaluated. The experimental study shows that the side distance in the staggered bolted joint has a significant influence on the maximum load due to the out-of-plane rotation. Simulation of the experimental work shows that this out-of-plane rotation produces a horizontal force on the direction causing early failure for the joint. A parametric study was performed to investigate the effect of bolt numbers and diameters. It was found that the number of bolts has a more significant effect on increasing joint failure load than the bolt diameter. In all cases, the first bolt from the composite plate side has the maximum force, therefore, the first damage happened under this bolt. Considering the axial applied load direction as a reference direction, high perpendicular to parallel forces ratio was evaluated on the bolts of the staggered joint. It is recommended to consider this force during the design of the laminate. Furthermore, the staggered bolt arrangement was found to cause a significant out-of-plane bending which is recommended to be taken into consideration.