Effects of pretensioning on the Z Block modular column-to-column connection

This study investigates the effects of bolt pretensioning on the column-to-column connection made of the Z Block connector under tensile axial load. Five full-scale specimens, comprising of various pretension levels (30, 50, 61.5, 70, and 85 kips) were tested under Axial Tension Single Column (ATSC) connection. The failure mode in all specimens was the rupture of the Socket-Head-Cap-Screws (SHCSs) that connect the lower and upper block components of the Z Block. Experimental tests showed that there was a decrease in block separation and tensile capacity as bolt pretension was increased. Notably, specimen with 61.5 kips pretension was adopted as the optimal design pretension level for the Z Block connector. The specimen showed an 82 % reduction in block separation and only a 6.7 % reduction in tensile capacity in comparison to specimen with no pretension applied. Test validation and parametric study was subsequently carried out using finite element analysis to investigate other level of pretension as well as identifying the alternate design pretension level for the Z Block connector. The results of the numerical analysis showed that a pretension preload of 245 kN (55 kips) resulted in a further decrease of 0.23 mm in block separation, while maintaining a 24 % increase in tensile capacity compared to the optimal preload obtained from the experimental test. • This paper presents a comprehensive experimental and numerical investigation of the structural performance of the Z Block connection under various levels of bolt pretension. • This paper examines the effect of different pretension magnitudes on the tensile capacity and block separation behaviour of the Z Block connection through full-scale laboratory testing. • This paper develops and validates a finite element (FE) model using ABAQUS to replicate the behaviour of the Z Block connection, enabling extended parametric studies beyond the tested scenarios. • This paper presents parametric analyses that establish the relationship between pretension magnitude, block separation, and load capacity, offering practical guidance for selecting pretension levels in design. • This paper highlights an optimal pretension range that balances reduced block separation and tensile capacity, contributing to the development of more reliable connection design for modular steel buildings