Experimental and numerical study on shear performance of grouped bolt-UHPC pocket connections under static loading

Prefabricated steel-ultra-high-performance concrete (UHPC) composite beams using grouped single embedded nut bolts (SENBs) in full-depth precast slabs are a competitive alternative for accelerated bridge construction (ABC), with advantages such as shortening on-site construction time, improving structural quality, and conveniently dismantling deteriorated components. In this study, a systematic experimental and numerical study was conducted to investigate the shear performance of grouped bolt-UHPC pocket connections. The experimental results indicated that a dense arrangement of SENBs led to a slight reduction in shear capacity (less than 5%) and ductility. Increasing the number of bolts in the pockets can effectively improve the shear performance of the connections. Significant reductions in the per-bolt ultimate shear capacity and initial shear stiffness were observed for specimens with multi-row bolts compared to their singlerow counterparts. In addition, specimens with grouped bolt-UHPC pocket connections achieved a considerable shear capacity, low shear stiffness, and better slip capacity than those with monolithic casting slabs. Based on the validated finite element models, extensive parametric studies were carried out. Accordingly, a conservative recommendation of 4d (d is the bolt diameter) was suggested as the minimum bolt spacing in both the longitudinal and transverse directions. Furthermore, more accurate formulae were developed to predict the ultimate shear resistance and load-slip relationship of the grouped bolt-UHPC pocket connections in prefabricated steel-UHPC composite beams.