Behaviour of top-seat double web angle connection produced from austenitic stainless steel

Highlights

• Full-scale experimental test of top-seat double web angle connection produced from austenitic stainless steel were presented

• Elasto-plastic deformations of various connecting elements were recorded

• Developed 3D FE study showed good agreement with the experimental results

• Material nonlinearity exhibited in the moment-rotation curves, whilst comparison was made

• Pronounced strain hardening as well as ductility was observed for stainless steel connection

Abstract

Beam-to-column connections are regarded as one of the critical elements in structures, especially in the case of bare metallic frame construction, as the overall structural performance is highly influenced by the connection behaviour. Significant research on stainless steel members has been reported in the recent past, but research on beam-to-column connections is still scarce. This paper presents an experimental and numerical investigation on the moment-rotation (M-φ) behaviour of a top-seat with double web angle (DWA) connection produced from austenitic stainless steel. A comprehensive investigation on the elasto-plastic deformation patterns observed in individual connection elements has been reported to gain in-depth knowledge in assessing overall stiffness, strength and rotational capacity of the considered connection type. Beam and column sections, as well as the connecting angles and fasteners used in the experiment, were produced from austenitic stainless steel AISI 316 L (equivalent to EN 1.4301). Significant strain hardening, as characterised by stainless steel, was observed throughout with the top angle experiencing most significant deformations. 3D finite element (FE) model was developed to replicate the observed experimental behaviour, and good agreement was observed between numerically obtained results and experimental observations. Based on the experimental and numerical results, semi-rigid connection behaviour was recognized for stainless steel alloy to lay a foundation for the development of the top-seat DWA connection. The observed behaviour for the considered stainless steel connections was compared with those obtained analytically for equivalent carbon steel connections; this comparison demonstrated enhanced ductility and significantly higher plastic moment for stainless steel connections.

Introduction

Over the past few decades, stainless steel has received increasing attention in the construction industry due to its pleasing appearance, corrosion resistance, low maintenance cost, higher ductility and better performance in fire [[1], [2], [3], [4], [5]]. Stainless steel is 100% recyclable and can be indefinitely recycled into new high quality stainless steel [6,7]. Reported mechanical test results on various grades of austenitic stainless steel showed significantly higher strain hardening than carbon steel. Significant progress has recently been reported in devising rational design rules for structural stainless steel members. A strain-based design technique, the continuous strength method (CSM) has been proposed and is gradually being developed as a practical design tool to account for the beneficial properties of stainless steel [[8], [9], [10], [11], [12], [13], [14]]. A number of design codes for stainless steel are currently available including the American code [15], the Australia/ New Zealand code [16] and the European code [17]. However, all available codes do not provide sufficient details on connection design primarily due to the unavailability of experimental evidence.

Analysis and design of a bare steel building frame will require a clear understanding of the moment-rotation (M-φ) behaviour of beam-to-column connections. Considerable numbers of studies are available on carbon steel to predict the M-φ behaviour of bolted connections; experimental investigations reported by Azizinamini et al. [[18], [19], [20]], under monotonic and cyclic loadings, have been extensively used in devising analytical models for carbon steel connections. Numerical modelling techniques, especially the finite element method (FEM), were widely used to investigate the behaviour of top-seat DWA connections [[21], [22], [23]]. Three-parameter power model proposed by Kishi and Chen [24] is a simple and useful analytical model and has been widely used in the relevant field. Chen and Kishi [25,26] also developed a very useful data bank for semi-rigid connections based on experimental evidence and developed a computer program to predict the M-φ behaviour of connections.

Appropriate understanding of the connection response characteristics is mandatory to exploit all special features of stainless steel in practical applications. A number of researchers have recently investigated the behaviour of stainless steel bolted connections. Bouchair et al. [27,28] conducted an experimental and numerical investigation for cover plate connections for the austenitic grade of stainless steel. Bearing strength behaviour and design of austenitic and duplex stainless steels under in-plane tension was investigated by Kiymaz [29]. Parametric studies on the various geometric features were investigated to observe the effect of curling (out-of-plane deformation) on bolted connections by Kim et al. [[30], [31], [32]]. Salih et al. [[33], [34], [35]] reported the influence of various connection parameters, where net section and bearing failure mode of connections were studied both experimentally and numerically. Salih et al. [36] also performed some parametric studies on stainless steel angle, and gusset plate bolted connections. All the aforementioned research investigated the in-plane behaviour of stainless steel connections.

First numerical investigation on the top-seat stainless steel connection which consists of the parametric study of various geometric features was conducted by Hasan et al. [37,38]. However, due to the absence of proper experimental evidence on stainless steel, the reported study was based on the carbon steel test data. Most recent experimental study on stainless steel beam-to-column connections was reported by Elflah et al. [39]. In their experimental study, they considered four different type of semi-rigid connections; such as – end plate connection, extended end plate connection, top-seat connection and top-seat with DWA connection. Their experimental research focussed on the M-φ behaviour of these connections and comparison with the EC3 [40] prediction.

Since there is an obvious behavioural change in material properties between stainless steel and carbon steel due to the enhanced strain hardening properties, significant gain could be achieved if stainless steel alloys are appropriately utilised in the semi-rigid/partially- restrained connections. However, very limited experimental evidences are currently available to justify this perceived knowledge. The current study was aimed to characterise the in-depth structural behaviour of three types of stainless steel connections, and results obtained from a full-scale top-seat DWA connection are presented herein. This paper thoroughly presents the observed moment-rotation behaviour for top-seat DWA connections so that the stress conditions are appropriately recognized in FE modelling approach. A comprehensive understanding of the stress patterns observed in stainless steel beam-column connections is required prior to modifying design rules to incorporate any perceived advantage due to extensive strain hardening. Present study discussed all necessary details regarding deformation patterns of various connecting elements and their contributions in the end restraint of the connection. Moreover, an efficient FE model has been generated which diligently match with the all observed deformation characteristics and replicate the M-φ behaviour of the connection. This modelling technique can be used for reliable parametric studies, which can help devising rational design rules for stainless steel structures.