Behaviour and design of high-strength Grade 12.9 bolts under combined tension and shear

摘要

As high-strength steel and concrete have been increasingly used in the construction industry, the major structural components are fabricated with reduced dimensions, which inevitably results in smaller joint regions and consequently requires higher strength bolts to be used. Over recent decades, structural bolts of Grade 8.8 and 10.9 have found widely applications. However, the utilisation of higher strength Grade 12.9 bolts are still limited due to the lack of proper design guidance. An experimental program that consists of 96 Grade 12.9 high-strength bolts have been conducted herein, through which the strength capacities of these bolts under tension, shear, as well as combined tension and shear have been determined. Hardness measurements on the cross-sectional surfaces of Grade 12.9 bolt shanks have been performed to facilitate the machining of bolt coupons. In addition, a simplified and accurate numerical model based on ABAQUS has been developed to predict the full-range behaviour of Grade 12.9 bolts until fracture. The accuracy and reliability of the proposed model has been demonstrated by a series of validation at both the component level (bolt) and structural level (beam-column joint). The obtained test results on Grade 12.9 bolts were compared with those of Grade 10.9 bolts. Similar normalised ultimate strength (P-U/P-0) and fracture deformation (delta(f)) indicates that the Grade 12.9 bolts can be safely utilised in the engineering practice. Furthermore, the test results on Grade 12.9 bolts were compared with international design standards, and proper modifications in terms of the design equations and reduction factors have been suggested. (C) 2020 Elsevier Ltd. All rights reserved.