Behaviour and design of duplex stainless steel bolted connections failing in block shear

Duplex stainless steel (DSS) is an emerging construction material for structural engineering, which is featured with high mechanical strength and superior corrosion resistance. Compared with considerable research on DSS structural members, available research is relatively limited for structural joints/connections between these members. In line with this concern, this paper presents a comprehensive experimental and numerical study of duplex stainless steel bolted connections (DSSBCs), focusing on the behaviour and design related to block shear failure. Eleven specimens are tested to investigate the effect of different bolt arrangements on the block shear behaviour. Furthermore, a detailed numerical study was performed as a supplement to the experimental tests, where the anisotropic mechanical properties of DSS are considered in the finite element modelling. Based on the test and analysis results, it is found that the block shear failure mode of DSSBCs resembles that of carbon steel bolted connections, which can be characterised as necking of the tensile section and yielding of the shear sections. Using the experimental and numerical data obtained in this and previous studies, the applicability of various block shear design methods to stainless steel bolted connections is assessed. An updated design method is proposed for predicting the block shear capacity of duplex and austenitic stainless steel bolted connections. A proper partial safety factor/resistance factor is suggested for the proposed method based on the results of reliability analyses

Cyclic behaviour of an innovative extended end-plate connection with shape memory alloys

Shape memory alloys (SMAs), with superelastic and shape memory effects, have attracted research interests in civil engineering in recent decades. Many research endeavours have been made to investigate the feasibility of SMAs applications in column-to-beam connections, aiming to minimise or even eliminate permanent post-earthquake deformations in main structural members. In this paper, an innovative extended end-plate (EEP) connection incorporating SMA bolts, high strength (HS) bolts and SMA Belleville washers is introduced which has been numerically investigated by the co-authors previously. This paper presents experimental data for the first time to prove the feasibility of the connection. One full-scale test is conducted under cyclic loading. Besides, the hysteretic performance including ductility, strength, self-centring performance, and energy dissipation is studied. The test results show that the innovative connection possesses excellent deformation capacity, self-centring ability, with moderate energy dissipation ability under seismic loading. More experimental and numerical works are currently in progress in order to further understand the structural performance of this type of hybrid connection

Cyclic behaviour of an innovative extended end-plate connection with shape memory alloys

Shape memory alloys (SMAs), with superelastic and shape memory effects, have attracted research interests in civil engineering in recent decades. Many research endeavours have been made to investigate the feasibility of SMAs applications in column-to-beam connections, aiming to minimise or even eliminate permanent post-earthquake deformations in main structural members. In this paper, an innovative extended end-plate (EEP) connection incorporating SMA bolts, high strength (HS) bolts and SMA Belleville washers is introduced which has been numerically investigated by the co-authors previously. This paper presents experimental data for the first time to prove the feasibility of the connection. One full-scale test is conducted under cyclic loading. Besides, the hysteretic performance including ductility, strength, self-centring performance, and energy dissipation is studied. The test results show that the innovative connection possesses excellent deformation capacity, self-centring ability, with moderate energy dissipation ability under seismic loading. More experimental and numerical works are currently in progress in order to further understand the structural performance of this type of hybrid connection

Block shear failure of austenitic stainless steel bolted connections

Austenitic stainless steel possesses very high ductility and ultimate-to-yield strength ratio, which could possibly affect the block shear failure mechanism and the corresponding ultimate capacity of bolted connections made of this material. In response to this concern, a comprehensive experimental and numerical study on the block shear behaviour of austenitic stainless steel bolted connections (ASSBCs) is conducted and reported in this paper. Based on the results of 15 experimental tests, it is found that the governing block shear mechanism of ASSBCs (for 14 out of the 15 tests) at the ultimate load corresponds to cracking of the shear sections prior to fracture of the tensile sections. This differs significantly from the conventionally accepted block shear mechanism of mild steel bolted connections, which is net section fracture of the tension area and yielding of the shear area. This observation was further confirmed by a numerical study based on validated finite element models, where three block shear mechanisms were identified for ASSBCs. A thorough parametric study was then carried out to clarify the effects of key design parameters on the block shear behaviour of ASSBCs. Finally, the experimental and numerical results are used to evaluate the applicability of existing design equations to predicting the block shear capacity of ASSBCs. An improved block shear equation is subsequently proposed based on the available data.</p

Numerical investigation into net-section resistances of high strength steel bolted connections

This article presents a numerical investigation of the net section resistance of 30 bolted connections made of high strength steel (HSS) and mild steel (MS) using finite element method. Three types of steel were investigated, namely, S275, Q690 and Q960. All the connections were equipped with four bolts with double lap plates. The failure mode of the specimens was net section fracture. The connection efficiency, the ratio of the test ultimate load to the ultimate net section resistance (Anetfu), was also analysed. The connection efficiency of the specimens with S275, Q690 and Q960 steels varied between 1.03 and 1.09, 1.04 and 1.12, and 1.05 and 1.12, respectively. It can be concluded from the analysis results that the examined HSS bolted connections are able to reach the ultimate net section resistance (Anetfu) at failure even though the ratio of tensile strength to yield strength and the ductility of HSS material are relatively much lower than those of normal structural steel

Block shear strength of high strength steel staggered bolted connections

This paper presents an experimental and numerical study of block shear strength of staggered bolted connections made of high strength steel (HSS). The study aims to examine the effect of low ductility and low tensile‐to‐yield strength ratio of HSS material on the behaviour and block shear strength of staggered bolted connections. Two Q690 HSS staggered bolted connections were tested and failed in block shear failure, which was characterised by tension fracture of the staggered net tension plane and significant shear deformation along the shear plane. The test observations were further interpreted by finite element (FE) analysis. The test results and FE analysis indicate that the block shear failure mechanism of staggered bolted connections is the fracture of the staggered net tension plane combined with the yielding of the effective shear plane. Finally, the design methods in various design codes for evaluating the block shear strength of bolted connections were assessed and the results showed that the existing design methods provided inconsistent predictions of the block shear strength of HSS staggered bolted connections. More experimental and numerical works are currently in progress to further understand the block shear strength of HSS staggered bolted connections

Net section capacity of high strength steel bolted connections with or without staggered bolts

This paper mainly presents an experimental and numerical investigation of the net section resistance (fuAnet) of bolted connections made using high strength steel (HSS). The main objective of the study is to examine the effect of low tensile strength to yield strength ratio and low ductility of HSS material on the tensile capacity of HSS bolted connections. Two types of HSS material were studied, namely, Q690 and Q960. Each connection was equipped with two lap plates and eight bolts in staggered or unstaggered arrangement and was designed to fail by net section fracture through the staggered or transverse section, respectively. The connection efficiency of each connection, which is the ratio of the ultimate load obtained from tests or FE analysis to net section resistance (fuAnet), was found to be close to 1.0. This indicates that the net section resistance (fuAnet) of the examined HSS bolted connections can be achieved at the ultimate state, where the net section area (Anet) of HSS staggered bolted connections can still be determined by the s2/4g rule

Numerical investigation into net-section resistances of high strength steel bolted connections

This article presents a numerical investigation of the net section resistance of 30 bolted connections made of high strength steel (HSS) and mild steel (MS) using finite element method. Three types of steel were investigated, namely, S275, Q690 and Q960. All the connections were equipped with four bolts with double lap plates. The failure mode of the specimens was net section fracture. The connection efficiency, the ratio of the test ultimate load to the ultimate net section resistance (Anetfu), was also analysed. The connection efficiency of the specimens with S275, Q690 and Q960 steels varied between 1.03 and 1.09, 1.04 and 1.12, and 1.05 and 1.12, respectively. It can be concluded from the analysis results that the examined HSS bolted connections are able to reach the ultimate net section resistance (Anetfu) at failure even though the ratio of tensile strength to yield strength and the ductility of HSS material are relatively much lower than those of normal structural steel