Shear behavior of lap connection using T-head square-neck one-side bolts

To advance the understanding of the shear behavior of T-head Square-neck One-side bolt (TSOB) bolted lap connections, this paper presents a systematic experimental and finite element investigation. Ten groups of specimens with different parameters were designed and tested under static loading. The failure modes and ultimate resistance were predicted using Eurocode 3–1-8 and subsequently compared with test outcomes. The experimental results, including failure modes, load-displacement relationships, and strain development patterns, were analyzed in detail. A Finite Element Model (FEM) was developed and validated against the test data. Utilizing the validated FEM, key parameters influencing the shear resistance of the connections were further examined. The results show that TSOB lap connections exhibit two primary failure modes: bolt shear failure and hole-wall bearing failure. The governing failure mode depends on the plate thickness and the orientation of the bolt hole. Bolt pretension is found to influence only the resistance during the slip phase, with negligible effect on the ultimate resistance. While Eurocode 3–1-8 provides accurate predictions for connections with vertical bolt holes, it shows significant deviation in estimating the bearing resistance of horizontal bolt holes. Consequently, a modified theoretical model for predicting the bolt-hole bearing resistance of horizontal bolt-hole connections is proposed, which demonstrates good agreement with test and numerical results. • TSOB lap connections show bolt shear or hole-wall bearing failure modes, governed by plate thickness and hole orientation. • Bolt pretension affects only slip-phase resistance, with negligible impact on ultimate load capacity. • EC3-1-8 underestimates bearing resistance for horizontal holes; a modified model is proposed and validated. • Square neck length and T-head aspect ratio significantly influence shear resistance and failure behavior.