Structural behaviour of high strength steel bolted connections

Abstract

The use of high strength steel has been increasingly prevalent in construction of large-scale structures, such as long-span bridges and high-rise buildings, mainly due to its high material strength, allowing structural members and connections to be designed with smaller sizes and simpler configurations. However, despite of high material strength, high strength steel has low ductility, which is potentially unfavourable to the behaviour of connections. Owing to the limited research into high strength steel connections and the lack of accurate design rules, this PhD thesis aims to systematically investigate the structural behaviour and design of high strength steel bolted connections.

A comprehensive experimental study was firstly conducted, including material tests, in order to derive the material stress–strain responses and key material properties of high strength steel, and connection tests, in order to study the structural behaviour and load-carrying capacities of high strength steel plate-to-plate connections and gusset plate connections. For S690 high strength steel plate-to-plate connections, tests were carried out on a total of 69 connection specimens with different bolt configurations and geometric dimensions, where 32 of them failing by net section fracture, 21 of them failing by bearing and 16 of them failing by block tearing. For S690 high strength steel gusset plate connections, a total of 23 angle-to-plate connection tests and 27 channel-to-plate connection tests were carried out and all the gusset plate connection specimens failed by net section fracture. The experimental programme was supplemented by a numerical modelling programme, where finite element models were firstly developed to replicate the experimental responses and then used to conduct parametric studies to generate further data over a wide range of geometric dimensions. On the basis of the experimental and numerical results, the underlying failure mechanisms and the effects of various parameters on structural behaviour and resistances were analysed and discussed.

The obtained test and numerical data were used to assess the accuracy of the existing design rules for high strength steel plate-to-plate connections and gusset plate connections. For high strength steel plate-to-plate connections, the assessment results generally indicated that the existing codified design framework cannot capture the complex nature of connection behaviour and thus resulted in a low level of accuracy. Since many influencing geometric parameters cannot be fully separated and considered, it is difficult to develop pure mechanical-based design methods for high strength steel plate-to-plate connection. Therefore, a machine-learning-based design approach has been proposed and shown to yield substantially improved failure load and mode predictions than the codified design rules. For high strength steel gusset plate connections, the assessment results generally revealed that the existing codified design rules led to inaccurate failure load predictions, owing to the lack of consideration of the effects of material grade and influential geometric parameters. Therefore, a set of new mechanical-based design approaches were proposed and shown to offer more accurate and reliable failure load predictions over the design codes for high strength steel gusset plate connections.