International Journal of Steel Structures最新文献

Recently, the fully integral bridge system that integrates the entire superstructures and substructures together to form a monolithic rigid frame has been presented, since it is anticipated that this approach will lead to improvements in aesthetics, economic efficiency, and seismic performance of a bridge system. This study is related to a fully integral steel bridge with struts installed in-between the piers at the middle of the bridge span, which is called a strut-braced pier. Thus, it is expected that the strut-braced pier mainly prevents horizontal loads like earthquake load or vehicle braking load. In this study, the seismic performance of the fully integral steel bridge was evaluated in accordance with Caltrans Seismic Design Criteria which involves displacement criteria, displacement ductility capacity requirement, and member force criteria. The capacities of the member forces and the displacement were determined through nonlinear static pushover analysis using OpenSees. As a result, the fully integral steel bridge met the seismic performance criteria specified in Caltrans with a great margin. A parametric study was conducted to investigate the effect of strut stiffness on the seismic capacities and effects from the horizontal load of the fully integral steel bridge. The results show that the displacement capacity and displacement ductility capacity of the fully integral steel bridge have a slight change when the strut stiffness increases. The member force capacity is primarily affected by the strut-braced pier and increases significantly along with the strut stiffness. The lateral displacement and the sectional member forces are well controlled to a converging value by a proper application of the strut stiffness. Therefore, it was found that the minimum stiffness required for the struts can be defined to sufficiently resist design seismic loads, and thus, the sectional properties of all intermediate piers can be reasonably adjusted by varying only the stiffness of the struts connected to the braced piers. It has a great significance in that such results lead to the feasibility of various economical designs of bridge substructure including piers suitable for each situation.

Transfer columns are the essential elements in a building frame structure wherein some stories are constructed with steel-reinforced concrete (RC) columns and others with RC columns. The stories with transfer columns may suffer severe damage due to sudden changes in strength and stiffness along their heights. This study investigates the structural behavior of transfer columns subjected to axial compressive loading and bending about major/minor axes. Forty transfer columns are modeled in the finite element software ABAQUS to study their failure mechanism, lateral bearing capacity, and ductility ratios. The parameters investigated are the levels of embedment length of the structural steel, and the detailing of lateral ties and the base plate at the truncation zone in the column. It is concluded that hybrid columns have higher lateral strengths than the RC columns but exhibit limited ductility due to the sudden shear failure. The specimen with structural steel extended by 50–60% of clear column height exhibited improved ductility. The precipitous failure of the transfer column is alleviated with the provision of a base plate and anchor bolts at the end of the structural steel section.

Abstract

To investigate the impact resistance of steel beams with different web openings, falling-hammer impact trials and numerical models analyses were performed, focusing on the impact energy, inter-opening space, and opening diameter. The impact resistance of steel beams with different web openings was analyzed, and damage-assessment curves for web-opening steel beams (WOSBs) under impact loads were established. The results showed that web-hexagonal-opening steel beams (WHOSBs) yielded greater damage-related deformation than web-circular-opening steel beams (WCOSBs) for the same impact energy. The average maximum mid-span displacement of the WCOSBs under the falling-hammer was 86.49% that of the WHOSBs, whereas the average energy absorption rate was 6.07% higher. The WCOSBs were more resistant to impacts than the WHOSBs. The impact velocity and mass were the key damage-assessment parameters, and velocity–mass damage-assessment curves and determination equations were established according to on the WOSBs’ maximum mid-span displacement under hinge-supported restraints at both ends. Thus, this study will serve as a reference for assessing the damages of WOSBs subjected to impacts.

This paper presents a numerical study to investigate the effects of axial misalignment for the fillet welded cruciform joints using the traction stress method. A parametric study, involving 100 finite element (FE) models, was conducted with plate thickness and misalignments treated as independent parameters. In the parametric study, different fillet weld leg sizes were chosen based on the minimum criteria specified in the New Zealand standard (NZS 3404.1). Normalized shear traction stresses were calculated for each plate thickness and misalignments at different cut planes through the fillet weld. In each model, the maximum normalized shear stress occurred at an angle of 15° to the loading plate, which represents the critical angle for weld failure. Finally, based on the results of the parametric study, an equation for the multiplication factor was proposed for the cruciform joint to obtain the maximum normalized shear traction stress for different misalignments and weld size. The multiplication factor obtained from the FEA matched well with the multiplication factor predicted by the proposed equation, and reliability analysis was conducted to confirm the accuracy of the proposed equation.

At present, the seismic structure of recoverable functional bridges based on seismic resilience is one of the hotspots in bridge seismic engineering research. Therefore, a new type of hybrid piers is designed in this paper, which mainly relies on replaceable components to achieve repairable structural performance after earthquakes. At the same time, four-level seismic fortification objectives based on seismic resilience is proposed, and the follow-up stiffness phenomenon is found on this basis. The finite element software OPENSEES was used to perform IDA analysis on a hybrid pier and an ordinary reinforced concrete (RC) pier. The fragility curves and seismic resilience curves of two piers were compared, and the seismic resilience performance and the follow-up stiffness phenomenon of the hybrid pier were studied. The results show that under the action of different seismic waves, the top displacement angle of the pier of the hybrid pier is slightly larger than that of the ordinary RC pier, but the overall difference is not large. The fragility curve of the hybrid pier is slightly larger than that of the ordinary RC pier. However, with the damage to the hybrid pier, the follow-up stiffness phenomenon impacts the seismic performance, which reduces the seismic force acting on the structure and improves the seismic resilience of the structure. The post-earthquake recovery time of two piers under different damage states was determined. Combined with the fragility curves, the seismic resilience curves of two piers were presented. The resilient index of the hybrid pier was always maintained at 0.9–1, and the seismic resilience performance was excellent.

Due to its superior strength and ductility, the utilisation of concrete-filled steel tube (CFST) columns has grown over the last few years. However, due to unequal lateral inflation properties, infill concrete and steel tube slip against one another during early loading phases. This paper presented a novel type of CFST section, a diagonally stiffened CFST column as a solution to this problem. It consists of a circular steel tube with stiffening bars installed inside the outer steel tube from one top end to the diagonally opposite bottom end. The suggested section is presented using various stiffening strategies, including binary, tertiary, and quaternary arrangements. The effectiveness of the suggested column section under an axial load is examined using finite element (FE) modelling, and the validation of the FE model was established using experimental testing carried out by previous researchers on unstiffened and stiffened CFST columns. Analysis was done on specimens of diagonally stiffened CFST columns to evaluate the load-carrying capacity, load vs deformation behaviour, stress distribution, and failure pattern. According to the findings of this study, CFST sections with diagonal stiffeners have higher ultimate load capacity than unstiffened CFST columns. Stiffening bars increase the ductility of brittle infill concrete and eliminate localised steel tube buckling. It was recommended that the number of stiffeners be altered to even numbers since odd numbers of stiffeners can cause asymmetry in the section, which can increase the concentration of stress.

To investigate the bond behavior of the concrete filled steel tubular (CFST) using the molybdenum tailing as the fine aggregate, 24 test specimens of the CFST are designed in consideration of molybdenum tailing replacement ratio, concrete strength, ratio of the filling height to the outer diameter and ratio of the outer diameter to the wall thickness. A series of push-out tests are conducted to analyze the working mechanism, failure mode, and bond stress-slip relation of the test specimens. The results show that the usage of the molybdenum tailing as the fine aggregate has no obvious effect on the working mechanism and failure mode of the CFST regardless of the test parameters, even though a slight difference is observed in the failure processes. The increase in the molybdenum tailing replacement ratio remarkably decreases the ultimate bond strength, but increase the ultimate failure slip of the test specimens whilst the ultimate failure slip shows no distinct change under the same ratio of the filling height to the outer diameter and ratio of the outer diameter to the wall thickness. The CFST test specimens with the molybdenum tailing shows slightly worse bond behavior than those without the molybdenum tailing. The proposed formula for the ultimate bond strength of the CFST with the molybdenum tailing fits well with the test results. Since, the limitations regarding the ultimate bond strengths of the CFST in the existing relevant specifications show the enough safety reserve, the proposed formula can be directly used for the design of the CFST with the molybdenum tailing.

Numerous studies have been conducted regarding the fatigue strength of longitudinal welded gusset joints. Most studies employed relatively small specimens. Thus, this study aims to evaluate the variation of fatigue life of longitudinal welded gusset joints by using the probabilistic fracture mechanics approach, particularly for larger specimens. Although some studies claimed that lower fatigue strength is found in the thicker main plate specimens, however only a limited number of fatigue test was conducted. A probabilistic approach was employed to conquer the shortfall. In this study, fatigue crack propagation analysis was performed on the main plate thicknesses of 12, 40, and 60 mm to evaluate the effect of main plate thickness on the fatigue life of the joints. Then, a probabilistic approach is given to investigate the variation of fatigue life of the joint. In addition, fatigue tests were carried out to investigate the crack propagation behavior on larger specimens. A significant decrease in fatigue life was observed by the increase of the main plate thickness from 12 to 40 mm, however, no further decrease thereafter. The fatigue strength of longitudinal welded gusset joints with the main plate thickness of 12 mm was appertained to category F in the JSSC design curve. Meanwhile, the fatigue strength of longitudinal welded gusset joints with the main plate thickness of 40 and 60 mm falls into category G in JSSC. This condition was also confirmed by the fatigue test results, where both specimens were classified as category G in JSSC.

Steel structures are commonly used in engineering projects and infrastructure. Steel structures should have high bearing capacity and be able to resist fire, earthquake, and corrosion. A new type of Q235 refractory steel has recently been developed in China, and the residual mechanical properties of steel structures are key indicators for estimating structural damage and reusability. Therefore, in-depth research is urgently needed. The yield stress, residual elastic modulus, ultimate tensile strength, and ultimate strain at room temperature to 900 °C and under air and water cooling conditions were detected. The residual mechanical properties of Q235FR steel were compared with other structural steels, and it was confirmed through experiments that they are closely related to temperature and cooling methods. In the case of the above cooling methods, the loss of mechanical properties can be negligible when exposed to temperatures up to 600 °C. When the temperature exceeds 600 °C, the high temperature and cooling method significantly impact the residual mechanical properties of Q235FR steel. The advantages of Q235FR steel are high strength, good ductility, strong corrosion resistance, and fire resistance. The suggested predictive equations could be used to accurately evaluate the residual mechanical properties of Q235FR steel at high temperatures.

Premature failure of transmission towers due to extreme weather conditions and inadequate design methods have severe socio-economic implications. This study presents a state-of-the-art review of the research work related to failure of self-supported lattice steel transmission towers. Selected articles from literature were divided into broad categories namely—failure analysis techniques, joint slippage effects, retrofitting and investigations of failure due to earthquakes and high intensity winds. The former three aspects mentioned above are chosen for review in this paper since the latter two are very broad aspects by themselves. A systematic literature review has been conducted based 76 research articles after filtering from reputed journals. Advanced analysis involving computational models based on nonlinear formulations and modern finite element software and their potential to reduce the need for full-scale prototype testing have been highlighted. A description of the studies available on retrofitting techniques for transmission towers for intervention against impending tower failures—diaphragm and leg member retrofitting techniques and studies on retrofitting connections are also discussed. Key conclusions from the study that highlight the most useful findings from the various studies, limitations of the current study and directions for future research have been established.