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A total of 50 bolted connections of carbon steel and stainless steel subjected to monotonic loading and cyclic loading conditions were investigated. The connection specimens were fabricated from carbon steel grades 1.20 mm G500 and 1.90 mm G450, as well as cold-formed stainless steel types EN 1.4301 and EN 1.4162 with nominal thickness 1.50 mm. In the monotonic tests, the specimens were tested under a constant loading rate by the displacement control test method, while in the cyclic tests, the specimens having the same dimensions as those in the monotonic tests were subjected to loading, unloading and re-loading processes, where displacement control and load control test methods were used. The results obtained from the cyclic tests were compared with those obtained from the monotonic tests. It was found that the ultimate loads obtained from the cyclic tests were, on average, larger than those obtained from the monotonic tests for carbon steel bolted connections; this was in contrast with the compared results for stainless steel bolted connections. The elongations corresponding to the ultimate loads obtained from the cyclic tests were, on average, larger than those obtained from the monotonic tests for both carbon steel and stainless steel, which may indicate that the loading processes in the cyclic tests generally delayed the bolted connection specimens from reaching the ultimate loads. Generally, the failure modes in the cyclic tests were consistent with those in the monotonic tests for the same specimen series, where the specimens mainly failed in the connection plate bearing. • Fifty carbon steel and stainless steel bolted connection specimens were tested. • The specimens were subjected to monotonic loading and cyclic loading (loading, unloading and re-loading) processes. • The results obtained from the cyclic tests were compared with those obtained from the monotonic tests. • The ultimate loads and the corresponding elongations were generally larger for carbon steel bolted connections. • Failure modes of the connection specimens were generally consistent for both monotonic loading and cyclic loading tests. [ABSTRACT FROM AUTHOR]

Abstract Significant progress has been made on structural behavior of hot-finished (HF) steel members with elliptical hollow sections (EHS) in the past few years. However, there is very limited research on cold-formed (CF) steel members with EHS. In this study, both CF and HF steel elliptical tubular stub columns are investigated. The investigation includes laboratory testing, numerical analysis and design evaluations. The geometric imperfection measurements, full load-end shortening relationships and load-strain curves of the stub columns are detailed in this paper. A non-linear finite element model was developed and validated against test results obtained from the present study as well as from the literature. The validated numerical model was employed to perform an extensive parametric study, where the CF and HF stub columns with EHS were carefully designed to include a broad range of the cross-section slenderness and aspect ratio. The cold-forming effect on the CF sections was taken into account in a conservative manner. The ultimate strengths obtained from the tests and numerical analysis were compared with the predictions in the design strengths predicted by the design methods proposed in the existing literature and the Direct Strength Method (DSM). The comparisons showed that the strengths predicted by the equivalent diameter method, the DSM and the modified DSM are generally conservative and reliable. The modified DSM provides the most accurate and the least scattered predictions among these design methods. Therefore, the modified DSM is recommended for the design of CF and HF steel elliptical tubular stub columns. Highlights • Cold-formed and hot-finished steel elliptical tubular stub columns were tested. • Non-linear FEM was developed and validated against the test results. • Parametric study was performed on cold-formed and hot-finished steel elliptical tubular stub columns. • The equivalent diameter method, the Direct Strength Method (DSM) and the modified DSM were assessed. • The modified DSM is recommended for the design of cold-formed and hot-finished steel elliptical tubular stub columns. [ABSTRACT FROM AUTHOR]

Abstract This paper presents an experimental investigation on cold-formed stainless steel single shear and double shear bolted connections at post-fire condition. The connection specimens were fabricated by three different grades of stainless steel. The three different grades of stainless steel are austenitic stainless steels EN 1.4301 (AISI 304) and EN 1.4571 (AISI 316Ti) as well as lean duplex stainless steel EN 1.4162 (AISI S32101). The post-fire connection specimens were heated to different nominal temperatures of 350, 650 and 950 °C, respectively, and then cooled down to room (ambient) temperature condition. A total of 82 new connection tests was conducted. The test results of post-fire specimens were compared with those tested without post-fire condition for the same specimen series. Generally, it is found that the single shear and double shear bolted connection specimens cooled down from the nominal temperatures of 350 and 650 °C had higher ultimate strengths than those specimens without expose to high temperatures for all three different grades of stainless steel. The specimens cooled down from 950 °C generally had lower ultimate strengths than the aforementioned specimens. It is also found that the failure modes of cold-formed stainless steel bolted connection specimens at post-fire condition are similar to those tested without post-fire condition. Finally, design rules are proposed for cold-formed stainless steel bolted connections at post-fire condition for temperature up to 950 °C. Highlights • Cold-formed stainless steel bolted connections were experimentally investigated at post-fire condition. • Connection specimens were assembled by austenitic and lean duplex stainless steel. • Connections cooled down from different nominal high temperatures were investigated. • Bearing failure and nest section tension failure modes were observed in the tests. • Equation is proposed for the residual strength prediction of connections at post-fire condition. [ABSTRACT FROM AUTHOR]

Abstract A series of tests was conducted to investigate the web crippling behaviour of cold-formed lean duplex stainless steel (LDSS) tubular sections. The LDSS had two grades, including EN 1.4062 and EN 1.4162. The tests were performed under three different conditions of concentrated end bearing loads, namely, the loading conditions of End-One-Flange (EOF), the End-Two-Flange (ETF) and end loading (EL). The loading conditions of EOF and ETF are specified in the American and Australian/New Zealand cold-formed stainless steel design specifications, while the loading condition of EL simulated the floor joist members positioned on a solid foundation under concentrated end bearing load. The test specimens were mainly failed by web crippling. The test strengths were compared with the predicted strengths that calculated by the stainless steel design specifications, including the American Society of Civil Engineers (ASCE) Specification, Australian/New Zealand Standard (AS/NZS) and European Code (EC). In addition, the web crippling strengths predicted by the North American Specification (NAS) for cold-formed carbon steel structures and using the design equations proposed in the literature for cold-formed duplex stainless steel tubular sections were also compared with the test strengths. It was found that the predicted strengths calculated by the ASCE, AS/NZS and EC specifications are conservative and reliable for LDSS sections under the three different concentrated end bearing loads. The predictions by NAS and proposed equations in the literature are generally less conservative compared with those by ASCE, AS/NZS and EC. However, the predictions by NAS are found to be unconservative and not reliable for the loading condition of ETF. Highlights • A total of 50 lean duplex stainless steel tubular sections were tested. • The tests were conducted under three different concentrated end bearing loads. • Bearing capacity of cold-formed lean duplex stainless steel tubular sections was obtained. • Existing stainless steel design provisions for web crippling were assessed. • The stainless steel design predictions are generally conservative. [ABSTRACT FROM AUTHOR]

A total of 87 cold-formed stainless steel single shear bolted connections was conducted. The specimens were tested using transient state test method. The single shear bolted connection specimens were fabricated by three different grades of stainless steel. The three different grades of stainless steel are austenitic stainless steel EN 1.4301 (AISI 304) and EN 1.4571 (AISI 316Ti having small amount of titanium) as well as lean duplex stainless steel EN 1.4162 (AISI S32101). Three different load levels of 0.25, 0.50 and 0.75 of the failure load at room temperature were investigated. The tendency of the test strength reduction of the stainless steel single shear bolted connections conducted using the transient state test method is similar to those results obtained by the steady state test method. However, the critical temperatures determined by the transient state test results are usually slightly higher compared with those deduced from the steady state test results at the load levels of 0.25 and 0.50 of the failure load at room temperature. The austenitic stainless steel grade EN 1.4571 (AISI 316Ti) generally has better resistance than the other two stainless steel grades in transient state tests as higher values of critical temperatures were obtained. Two main failure modes, namely the bearing and net section tension failures, were observed in the transient state tests. The failure modes of the specimens in transient state tests at the load level of 0.25 are generally consistent with those specimens in the steady state tests. [ABSTRACT FROM AUTHOR]

Abstract: The current design rules on bolted connections of cold-formed stainless steel structures are allowed for room (ambient) temperature condition only. Research on structural behavior of single shear bolted connections at elevated temperatures is limited. In this study, 100 single shear bolted connection specimens and 22 coupon specimens involving three different grades of stainless steel were conducted by using steady state test method in the temperature ranged from 200 to 950°C. The three different grades of stainless steel are austenitic stainless steel EN 1.4301 (AISI 304) and EN 1.4571 (AISI 316Ti having small amount of titanium) as well as lean duplex stainless steel EN 1.4162 (AISI S32101). Furthermore, different bolts arrangement was also considered in the investigation. Two main failure modes were observed in the single shear bolted connection tests, namely the net section tension and bearing failures. The test results were compared with the predicted strengths calculated from the American Specification, Australian/New Zealand Standard and European Codes for cold-formed stainless steel structures. In calculating the nominal strengths of the connections, the reduced material properties of stainless steel obtained at elevated temperatures were used. It is shown that the strengths of the single shear bolted connections predicted by the specifications are generally conservative at elevated temperatures. A similar tendency of reduction was found when compared the reduction factor of material properties with that of the deterioration of the bolted connection test strengths with the corresponding type of cold-formed stainless steel at elevated temperatures. The austenitic stainless steel type EN 1.4571 (AISI 316Ti) generally performed better than the other two stainless steel types at elevated temperatures. [Copyright &y& Elsevier]

This paper presents the experimental and numerical investigations of concrete-filled cold-formed high strength steel (CFHSS) circular stub columns. Firstly, a series of tests was conducted on CFHSS circular tubular sections infilled with three different concrete grades, i.e., C40, C80 and C120. The CFHSS circular tubular sections had the nominal 0.2% proof stress (yield stress) up to 1100 MPa. The test specimens were subjected to uniform axial compression The ultimate loads and failure modes of the specimens were obtained and reported in this paper. Secondly, an extensive numerical study accounting for the confinement effect, as well as the non-linearities of materials, geometry and contacts was performed. Upon validation against the test results, a parametric investigation was conducted. A wide range of the cross-section dimensions and section slenderness of CFHSS circular tubular sections infilled with different grades of concrete were considered. The structural behaviour of concrete-filled CFHSS stub columns was investigated, including the ultimate load, end shortening, strength enhancement index and ductility index. Finally, the experimental and numerical results were used to assess the suitability of the design equations specified in the existing American Specifications (AISC and ACI), European Code (EC4) and Japanese Code (AIJ) for the compressive strength of the concrete-filled CFHSS circular stub columns. It was found that the predictions from the existing international design specifications were generally conservative, except for EC4. The predictions by the AIJ are the least conservative and least scattered. However, by using the effective section area of steel tubes for slender cross sections, EC4 provided the most accurate and consistent predictions than the other design specifications. • Concrete-filled cold-formed high strength steel (CFHSS) circular stub columns were tested. • A validated nonlinear FEM was developed, followed by an extensive parametric study. • Structural behaviour of the concrete-filled CFHSS circular stub columns was investigated. • Effects of parameters on the stub column behaviour were examined and discussed. • Current design rules specified in the international specifications were assessed. [ABSTRACT FROM AUTHOR]

Thin sheet steel (TSS) single shear bolted connections at elevated temperatures were investigated experimentally in this study. The TSS 0.42 mm G550 and 1.90 mm G450 were used to fabricate the connection specimens. The connection specimens were designed with the variation of end distance. The specimens were tested at 5 different nominal temperature levels up to 900 °C using the steady state test method. The effects of end distance and temperature on the behaviour of bolted connections were investigated. It was found that the ultimate loads increased with the increment of the end distance up to three times the bolt diameter. Generally, the deteriorations of the connection strengths are in a similar manner to the corresponding material properties at elevated temperatures. The experimental results were compared with the predictions by using the Australian/New Zealand Standard (AS/NZS), European Code (EC3-1.3) and North American Specification (NAS) for cold-formed steel structures. In calculating the nominal strengths of the connections, the reduced material properties of TSS obtained at elevated temperatures were used. Overall, it is shown that the predictions from the AS/NZS, NAS and EC3-1.3 are conservative, with the AS/NZS providing the least conservative and least scattered predictions. However, the reliability analysis showed that the design provisions of the three design specifications are not reliable for the TSS single shear bolted connections in this study, with considerable scope for the development of improved design formulae. Generally, the AS/NZS and NAS could provide accurate predictions of failure modes for TSS connection specimens failed in tearout failure and bearing failure at different temperature levels. [ABSTRACT FROM AUTHOR]

The structural behavior of concrete-filled hot-finished (HF) and cold-formed (CF) steel elliptical tubular stub columns was investigated and is presented in this paper. A series of tests was conducted on HF and CF steel elliptical tubular sections infilled with three different concrete grades, namely C40, C80 and C100. The tested HF and CF steel elliptical hollow sections (EHS) had an aspect ratio of 2 with the same nominal section dimension of 200 × 100 × 6.5 mm. The test specimens were subjected to uniform axial compression. The initial local geometric imperfection measurements, ultimate loads and failure modes of the concrete-filled HF and CF EHS stub columns are presented. An extensive numerical study accounting for the confinement effect, as well as the non-linearities of materials, geometry and contacts was also performed. After a successful model validation against test results, a parametric investigation was conducted by considering a wide range of the cross-section dimensions and section slenderness of HF and CF EHS with different grades of the infilled concrete. A total of 111 concrete-filled HF and CF EHS specimens were carefully designed and analyzed by using the validated numerical model. The behavior of concrete-filled HF and CF EHS stub columns was investigated, including the maximum load, end shortening, strength enhancement index and ductility index. Effects of section strength factor and column sectional characteristics on the stub-column behavior were also investigated. Furthermore, the experimental and numerical results were used to assess the suitability of the design equations specified in the current American Specifications (AISC and ACI) and European Code (EC4) for the compressive resistance of the concrete-filled HF and CF EHS stub columns. It was found that the predictions from the current international design specifications were overall conservative for both concrete-filled HF and CF EHS stub columns. Generally, the predictions by EC4 were less conservative but more scattered than those predicted by AISC and ACI specifications for the concrete-filled HF and CF EHS stub columns. • Concrete-filled CF and HF steel elliptical tubular stub columns were tested. • A validated nonlinear FEM was developed, followed by an extensive parametric study. • The structural behavior of stub columns was investigated. • Effects of parameters on the stub column behavior were examined and discussed. • Current design rules specified in the international specifications were assessed. [ABSTRACT FROM AUTHOR]