Ultimate response of stainless steel bolted connections

Yapici, Orhan ORCID: 0000-0003-4320-3986 (2021). Ultimate response of stainless steel bolted connections. University of Birmingham. Ph.D.

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Abstract

The use of stainless steels in structural applications has been steadily growing for decades with most research focusing on the structural behaviour of stainless steel members. However, the material behaviour of stainless steels has essential differences from that of carbon steel, as it exhibits significant strain hardening and an absence of a well-defined yield plateau. Moreover, the design provisions of EN 1993-1-8 (2005) which was originally developed for carbon steel joints are currently applicable to design of stainless steel connections with only minor modifications, thereby leading to unduly conservative strength predictions and hence inefficient design. To provide more efficient design rules, assess and improve the current design guidance for stainless steel connections, extensive experimental and numerical studies have been performed and are reported in this thesis.

Firstly, an experimental programme on the determination of fracture properties and explicit fracture modelling of stainless steel bolts in tension has been performed. A predictive equation relating the equivalent plastic strain at fracture initiation and stress triaxiality for A4-80 stainless steel bolts was obtained experimentally and utilised within the phenomenological fracture model for ductile metals available in the FE code ABAQUS. Subsequently, an advanced FE model was developed in which the fracture of the bolts was incorporated utilising a ductile damage model with a damage initiation criterion and fracture propagation parameters. The developed FE model was validated against available experimental data published in the literature and was shown to accurately predict the available ductility and overall response of stainless steel joints failing by bolt fracture under predominantly tensile load.

Subsequently, an experimental study on the ultimate behaviour of ferritic stainless steel bolted T-stubs under monotonic tension was carried out and 17 T-stubs employing a wide range of geometric configurations, which were designed to fail in a ductile mode were tested to failure. The obtained ultimate and plastic resistances with corresponding displacements and material characteristics including material anisotropy have been reported in detail. It was observed that the ferritic stainless steel T-stubs exhibit significant anisotropy and overstrength which can be defined as the ultimate over the plastic resistances. The effect of membrane action on the ultimate resistance of the T-stubs has been experimentally observed and quantified and a recently proposed predictive equation was assessed based on the obtained results. This immense strength reserve may be relied upon to mitigate progressive collapse under a column loss.

Following the experimental investigations on ferritic stainless steel bolted T-stubs, an advanced FE model was developed and validated against the available test data. The FE models predicted the ultimate and plastic forces, and failure modes very accurately and the full force-displacement curves of each test specimen were obtained. Moreover, an extensive parametric study was conducted to reveal the effect of different parameters on the ultimate response of the stainless steel T-stubs and the results are reported comprehensively.

Based on the obtained experimental and numerical results, the EN 1993-1-8 (2005) was assessed. It was concluded that the plastic resistance predictions of EN 1993-1-8 (2005) are overly conservative for austenitic and duplex stainless steel T-stubs, but satisfactory for ferritic stainless steel bolted T-stubs. This was attributed to the similarity of the strain-hardening characteristics between ferritic stainless steels and carbon steel, which are markedly inferior to those of the austenitic and duplex stainless steel grades. A recently proposed design formula for estimating the ultimate resistances of carbon steel bolted T-stubs was applied to the stainless steel T-stubs. It was concluded that the proposed formula can predict the ultimate resistances of stainless steel bolted T-stubs with a significant accuracy. Finally, conclusions have been made and future research suggestions are given in the final chapter of the thesis.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):