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A noteworthy feature of the hybrid steel moment resisting frames (MRFs) with energy dissipation bays (EDBs) is the damage-control behaviour characterised by concentration of plastic damages in the energy dissipation bay (EDB) under earthquakes. This paper presents a design methodology for conducting the damage-control design of hybrid steel MRFs with EDBs. First, the structural damage-control behaviour quantified by the classical bilinear kinematic hysteretic model with significant post-yielding stiffness ratio is clarified utilising the test results extracted from a large-scale quasi-static test programme. Then, based on the seismic energy balance of single-degree-of-freedom systems incorporating significant post-yielding stiffness ratios, the design philosophy and governing energy balance equations featuring the damage-control behaviour of low-to-medium rise hybrid steel MRFs with EDBs under earthquake ground motions are presented. Subsequently, a stepwise design procedure that can be used to search for a design strategy of a hybrid steel MRF with EDBs under expected ground motions is developed. Three low-to-medium rise prototype structures are designed by the proposed methodology, and the seismic responses of the systems are evaluated by pushover analyses and nonlinear response history analyses based on numerical models validated by the test results. The results indicate that all the prototype hybrid steel MRFs with EDBs can achieve the damage-control behaviour with the prescribed drift threshold, and hence the post-earthquake residual deformations are also mitigated. Since the proposed method is a direct-iterative design procedure, it also retains practical attractiveness and will facilitate the seismic design of hybrid steel MRFs with EDBs.

Tapered Concrete-Filled Double Skin Steel Tubular (CFDST) columns have been commonly used in structures. To report further information, it is necessary to perform more studies on the structural behaviour of tapered CFDST columns, especially for those with high hollow ratios. This paper thus conducted an investigation on the tapered CFDST stub columns under axial compression. Specimens with varied tapered angle, hollow ratio and tubes' thickness were tested, and then typical failure modes, load versus displacement relations as well as strain development were revealed. Validated finite element models were given to further analyse the columns' structural mechanisms including the stress distributions, the interaction between the steel tubes and the sandwiched concrete, and the influence of main parameters. The ultimate strength of specimens was calculated tentatively using the methods in the existing design guidelines, and their accuracy and applicability for the tapered CFDST stub columns with high hollow ratios were preliminarily evaluated. A simplified method was suggested to predict the ultimate strength based on one of the guidelines, and the predictions show reasonable agreement with the test results.

This study explored the load-carrying mechanisms of a seismic resistant steel-concrete composite connection with angle fuse elements at the bottom flange. The research was commenced by examining the test results of three full-scale test connections, in particular, the moment/force evolution responses of the connections were studied. Subsequently, detailed finite element (FE) models of the three full-scale test specimens were developed. The predictions by the FE analysis were in good agreement with the test results in terms of the hysteretic responses and the forces of the angles. Following the verification study, the results of the FE analysis were utilised to offer an in-depth insight into the behaviour of the connections, and the force transfer mechanism of the connection was examined. In particular, it was confirmed that the fuse angles could resist the applied moment via axial forces, and the shear resistance was mainly provided by the connection plates at the top flange in the inelastic stage. In addition, an analytical model for quantifying the connection resistance was developed. Design considerations were also proposed to offer design guides for practicing engineers

A composite wall is the primary lateral force-resisting system in a cold-formed thin-walled steel structural system. The shear force between the upper and lower walls is transmitted through an inter-story connection in the cold-formed thin-walled steel platform framing system. In this study, the 16 platform framing inter-story connection specimens were subjected to cyclic loading to study the shear resistance, the failure modes, deformation, and the influence of stiffeners, lateral rigid blocking, X-shaped straps, and vertical. Hysteretic curves, skeleton curves, shear bearing capacity, and lateral stiffness values were obtained from the testing. The results showed that the specimens with only stiffeners had a lower shear capacity and lateral stiffness, which were significantly affected by the vertical force. Further, short stiffeners were not fully effective. The highest shear capacity and lateral stiffness values were characterized for the specimens with rigid blocking. Increasing the rigid blocking improved the shear resistance of the specimens, and rigid blocking with the same height as the floor joists contributed to excellent shear capacity and lateral stiffness of the specimens under vertical loading. The lateral stiffness of the inter-story connection was also significantly increased by using X-shaped straps, and the vertical force resulted in substantial decrease of the lateral stiffness. Based on the test results and a comparison of the nominal shear strength values required by current specifications, this study proposed improvements to the design of cold-formed thin-walled steel platform framing inter-story connections.

Ductile crack initiation and propagation simulation is of great importance in metal structures, which is one of main failure modes. Research objects of common fracture mechanics are solids with existing cracks. However, ductile fracture of uncracked solids is also one of the main concerns in structural engineering, especially for strong seismic loading. There is a great difficulty in simulating both crack initiation and propagation of uncracked solids using conventional fracture mechanics. A simple unified method to simulate the two stages with acceptable accuracy is thus required. For ductile crack initiation, a number of models based on the void growth concept have been proposed. However, research on ductile crack propagation is still limited, and there is still a lack of simple approaches to simulate both ductile crack initiation and propagation of uncracked solids. This paper aims to investigate ductile crack initiation and propagation of high strength steel under high stress triaxiality by combination of the void growth model for ductile crack initiation and an energy balance approach for ductile crack propagation. In this paper, a straightforward approach to obtain the ductile fracture energy only using smooth tension coupon tests is proposed. Two series of single edge notched specimens with different notch depths and notch configurations are manufactured. Both experimental and numerical studies under monotonic tension are conducted. The ductile crack initiation and propagation processes of notched high strength steel specimens are simulated with acceptable accuracy using the proposed approach.

Block shear is a common failure mode for bolted-steel shear connections. However, limited research has been conducted on the block shear failure of bolted high-strength steel (HSS) angle members. In this study, a test programme was conducted using eight single-line bolted angle specimens made of grade S690 steel and five S275 counterparts, to examine their block shear behaviour. The test parameters included steel grades, bolt arrangements (bolt number, pitch, and edge distance), and connection legs. Eleven of the specimens failed by block shear, and the remaining two by shear-out. Finite element models were developed to study the behaviour of the test specimens and to investigate the effects of connection legs on the block shear resistance. Laboratory tests and numerical analyses indicated that the block shear resistance increased only slightly with increasing lengths of the angle legs, and the relatively lower ductility of HSS did not significantly influence the block shear resistance of the HSS angles. It was also found that the predictions made by AISC 360–16 and Eurocode 3 were conservative, whereas CSA S16–14 provided unconservative predictions. The predictions obtained from design equations proposed in previous studies were also evaluated for their accuracy.