Mechanical properties and stress-strain models of large diameter high-strength bolts.

This article focuses on the mechanical properties, stress-strain relationships, and constitutive modeling of grade 8.8 heavy hex high-strength (HS) bolts with large diameters (≥36 mm) used in a 276 m steel TV tower in Yinchuan, China. Through standard tensile tests on M36 and M48 bolts with and without hot-dip galvanizing, the study evaluates the effects of sampling positions and surface treatments on Young’s modulus, proof strength, tensile strength, ductility, pre-tension, and tightening torque. The results show that hot-dip galvanizing and sampling location slightly influence mechanical properties, with the standard sampling position recommended for conservative estimates. An improved two-stage constitutive model based on the Ramberg-Osgood framework is proposed, demonstrating higher accuracy in simulating the stress-strain curve—especially around the knee region—compared to existing models, and is suitable for design and numerical analysis of large diameter HS bolts.