A new bending connection between a steel beam and concrete-encased composite column (CECS) with a bolted flange plate is proposed which maintains the integrity of the column and allows for the interchangeability of the beam for improvement of the connection. The confinement of the steel plates and the central steel core (H-section column) is provided by reinforced concrete and cover plates, thus lateral torsional and local buckling of the through plate (TP) and the central core is prevented. Three full-scale samples of the proposed exterior connection with variable TP thickness and different bending capacities under lateral cyclic and constant axial loads in the column were tested. The moment contribution in the components and seismic behavior of the connection were studied. The load transfer to the panel zone occurred through four components in the bending plane; TP, concrete performance, tensile studs, and side plates. The average share of the resistant elements which is immediately behind the front plate were determined as 56%, 26%, 12.50%, and 5.5%, respectively. The internal panel zone remained undamaged and the stresses were below the yield limit, so that the plastic hinge could occur outside the connecting members in the beam. In general, the specimens with sufficient pre-tensioning in the connection bolts had stable hysteresis curves and less pinching. In addition, these specimens showed acceptable energy dissipation that provided a high ductility index.

This study aims to investigate the behaviour of concrete filled composite walls (CF-CWs) without any boundary elements under lateral loading and combined axial and lateral loading. Under this objective, an experimental programme was set covering both compact and slender CF-CWs utilising different connector types and arrangements. Specimens were designed with the aspect ratio (height to width ratio) of 1.9 so that the in-plane flexural behaviour dominated the failure modes. Meanwhile, for the combined loading, different axial load ratios (n) were applied to the specimens in order to investigate the effects of axial load and the relative lateral load-displacement responses. An extensive numerical study was conducted following the experiments with over one hundred three-dimensional finite element models. The simulations involved S690 high-strength steel together with high-strength concrete C100. The accuracy of the models was validated with the experimental results. The experimental and numerical outcomes were presented, analysed and discussed in detail. In addition, design provisions were proposed to calculate the in-plane flexural capacity of CF-CWs without boundary elements with different aspect ratios. The design recommendations can be applied to the CF-CWs with mild steel as well as high-strength steel up to S690. The validity of the recommendations was examined by this study and the available data from the previous literature.

The mechanical performance of the steel reinforced reactive powder concrete (SRRPC) structural components significantly depends on the steel-concrete interfacial bond behavior. This paper presents an experimental and analytical investigation on the bond-slip behavior between the reactive power concrete and the H-shaped steel. A total of 11 specimens, considering the cover thickness, embedded length, stirrup ratio and bonding part (whole section, flange and web), were tested through the push-out configurations. Results showed that the cover thickness has the most significant impact on the interfacial properties. Moreover, the SRRPC exhibited the highest residual bond strength compared with the other steel reinforced concretes. The five-stage model and the modified tri-linear model were proposed to describe the average bond stress-slip relationship. It was found that the five-stage model had an excellent accuracy while the modified tri-linear model can reasonably predict the average bond stress-slip relationship. Finally, a comprehensive analytical model was developed to investigate the local longitudinal strain of the shape, bond stress and relative slip.

Fiber-reinforced polymer (FRP)-confined steel-reinforced concrete column (FCSRC), which consists of an external FRP tube and a steel-reinforced concrete (SRC) core, have been proposed to avoid the brittleness of SRCs. Capitalizing on the benefits of FRP-confine concrete, it is expected that full strength capacities of high-strength materials (i.e., high-strength concrete and high-strength steel) in FCSRCs can be exploited. Axial compression tests on FCSRCs with different strengths of concrete and steel were conducted in this study. A cruciform steel was adopted in FCSRCs. The parameters investigated in this study included the concrete strength, the steel strength and the FRP tube thickness. The test results demonstrated that the excellent performance of FCSRCs. Compared with normal-strength cross-shaped steel, the high-strength cruciform steel delays the development of hoop strains in the FRP tube for FCSRCs with normal-strength concrete. Additionally, the ultimate axial load of FCSRCs is generally larger than the direct summation of those of the steel section and FRP-confined concrete section (i.e., CFFT), demonstrating that the interaction between the three components (concrete, steel profile and FRP tube) in FCSRCs are in a benificial manner.

To improve the deformation capacity of low-rise shear walls, an alternative approach of self-slitting squat composite shear wall with concrete-filled steel tubular columns (SSLSST) was proposed by the authors. This paper presents the experimental results of five SSLSST specimens subjected to cyclic loading, experimental parameters included steel tube thickness (ts), spacing of transverse reinforcement (S), axial compression ratio (n), and shear stud arrangement of inner steel tube. The results showed that owing to weakened effects of both horizontal anchorage to concrete and vertical shear resistance, the self-slit occurred in the SSLSST specimen with half-section shear studs of inner steel tube; SSLSST specimens maintained integrality to resist lateral force like the normal shear wall before the yielding status; with the lateral deformation increasing, the SSLSST specimens were divided into three independent column-type segments to jointly resist both lateral and compressive forces, and the seismic damage mainly concentrated within the slits, resulting in the seismic damage of the whole shear wall body was reduced. Increasing both S and ts can not only greatly improved the seismic resistance and ductility but also reduced the seismic damage and post-earthquake residual deformation (PERD). As expected, high n was not beneficial for the ductility ratio, energy dissipation, and PERD. Generally, the proposed SSLSST showed slight seismic damage, good seismic resistance capacity, ductility, and self-centering ability. Therefore, it is worthy to promote this new type of low-rise shear wall system to actual engineering.

To study the dynamic performance of stainless-clad (SC) bimetallic steel under coupling actions of high temperature and strain rate, a total of 72 compression experiments were designed and conducted at four strain rates (0.001, 1000, 2000 and 3000 s−1) and four temperatures varying from 20 °C to 600 °C. The deformation patterns, stress versus strain responses, as well as strain rate and temperature effects were obtained and analyzed. Experimental results indicated that the dynamic compression performances of SC bimetallic steel were sensitive to both temperature and strain rate. The dynamic yield strength at 3000 s−1 was approximately 1.7 times than that under quasi-static conditions, while reduced by 24–35%, 37–50% and 52–62% when temperatures rose from 20 °C to 200 °C, 400 °C and 600 °C, respectively. Moreover, the strain rate sensitivity increased with the growing strain rate and temperature. The observation of microstructures showed that the grain dimensions declined with increase in strain rate or a decreased temperature. According to test data, a modified Johnson-Cook model was developed for predicting the stress versus strain response of the SC bimetallic steel subjected to combined actions of high strain rate and elevated temperature (20–600 °C), in which the influences of temperature softening, strain-rate strengthening and strain hardening were considered.

Weld beading is one of the typical welding defects commonly found in steel connections. Severe defects of weld beadings may significantly decrease the welding quality between the steel components; therefore, improving the safety risk in steel connection joints. To obtain a prediction model for shear resistance of frontal fillet weld (FFW) with weld beading defects, the influence laws of the weld beading on the shear properties of (FFW) was investigated in terms of the uniaxial shear loading test on 90 FFW specimens. The test results show that FFW specimens with a higher number of weld beads as well as greater toe height tend to suffer shear failure on one side of the weld. The contribution of the extended weld length to the strengthening of the ultimate shear load capacity of FFW specimens with weld defects is limited, while the amplification of the ductility ratio and initial shear stiffness is more pronounced. When the weld length exceeds 200 mm, the difference in weld toe height should be fully considered for the influence on the shear properties of the frontal fillet weld. Moreover, if the ratio of weld diameter to weld toe height is greater than 2, the impact of weld defects on FFW shear properties rises sharply as the weld diameter increases. A prediction model for the shear load capacity of FFWs with weld beading defects is proposed, which matches well with the test results and can serve as guidance for assessing the shear performance of FFWs with weld beading defects.

This paper proposes a new residual stress model for hot-rolled wide flange steel cross sections. For this purpose, a dataset of 85 residual stress measurements is first assembled. The dataset is comprised of prior measurements available in the literature that are complemented by additional ones as part of the present study. A constrained optimization problem is then formulated by assuming parabolic residual stress distributions for both the flanges and the web of hot-rolled wide flange cross sections. The parameters of the developed residual stress model are inferred from the results of the optimization method and from rigorous statistical analyses. The results demonstrate that the cross-sectional area and the depth-to-width ratio strongly influence the residual stress distributions in the flanges and the web of a hot-rolled wide flange profile. The results suggest that there is no evidence that the yield strength of the material influences the developed residual stresses within a cross section. Contrary to available residual stress models in the literature that may be applicable for a limited range of cross-sectional geometries, the proposed model reduces the mean error between all available measurements and predictions by 60%–70%. The variance of the error is also reduced by a factor of two to four across all known cross-sectional properties.

Disproportionate collapse of steel frame is often an indicator of the overall behaviour of multi-storey building. The corner column failure is followed by deformation of all beams and columns above removed columns and redistribution of the load carried by the corner columns. Although several experimental studies of disproportionate collapse have been carried out after corner column loss, most of them only focused on the single-storey substructure, while inevitably ignoring the interaction between the storeys in the multi-storey frames (Vierendeel action). In this study, the performance of a two-storey substructure after corner column loss was experimentally studied and a corresponding numerical model was established utilizing LS-DYNA. FE model was validated and used to further study the effects of the proposed boundary assumptions, load redistribution of multi-bay steel frames, and number of bays and storeys on load resisting mechanisms. The results indicated that Vierendeel action is essential in resisting disproportionate collapse, with a contribution of 43% to the peak load. For a multi-storey frame with more than two storeys, the normalized load resistance of each storey is approximate. However, due to Vierendeel action, further internal force analysis indicates that the load resisting mechanisms are different in each storey. The two-storey substructures for understanding the disproportionate collapse behaviour of multi-storey steel frames under corner column loss are highly recommended by the parametric analysis.

This paper conducted lateral impact tests on 10 concrete-filled weathering steel tubular (CFWST) columns and studied the effect of prestressing on their resistance to lateral impact. The results indicate that by using prestressed cantilever members, the impact resistance of the column can be significantly improved. This is mainly due to the reduction of tensile stress level in the steel tube at the fixed end of the cantilever column and of the overall plastic deformation of the member, which is achieved through the application of prestress. Furthermore, the test process was also simulated numerically. Based on verifying the correctness of the numerical simulation, the parameters of the full-scale model are analyzed. The impact resistance of the model was evaluated by considering various factors such as impact angle, impact point height ratio, prestress ratio, width-thickness ratio, slenderness ratio, and mass ratio. Based on these analyses, empirical formulas for the lateral ultimate displacement and bending moment of the cantilever members were derived. Particularly, considering the difference in yield strength between tension and compression sides, the theoretical calculation of plastic limit bending moment of concrete-filled square steel tubular members is modified. Additionally, the damage level of the component is defined, and the damage limit value of the concrete-filled steel tubular cantilever column is given based on the different damage grades. On this basis, considering the bending bearing capacity and displacement response of the component, an impact resistance design approach based on the performance of the component is proposed.

This paper presents the results of an experimental program to evaluate the low-cycle fatigue-related characteristics of the tensile region of Hollo-bolted angle connections. A summary of a total of 40 tension tests of equivalent T-stub connections is reported. The geometric parameters vary with the bolt gauge width, the column wall's thickness, the bolt type, and the angle's thickness. Based on the experimental test results, the typical failure mechanisms, the hysteretic load-deformation relationship, and the response characteristics such as degradations of strength and energy dissipation capacity of the connections are examined. It is shown that the bolt gauge width and the angle's thickness have significant influences on the failure mode. Energy-based model is proposed to overcome certain geometric limitations and five commonly used damage models are used to predict the damage behavior of connections. Moreover, the low-cycle fatigue life test results are compared with the codified S–N curves through a transformation of the displacement range into the effective stress range. Furthermore, the cumulative damage mechanism is analyzed and the fatigue life formula is obtained. Finally, the results are evaluated and verified by regression analysis. The 90% confidence level was used to test the availability of the regression equation, and the equivalent level of fatigue strength of the tensile region of angle connections is not less than Category 40 (ΔσC = 40 N/mm2). The EC3, BS7608, and AISC-LRFD-1999 specifications are used to evaluate the low-cycle equivalent fatigue strength, and it is found that there is a certain safety reserve when using Category 36.

Extensive experimental and analytical investigations have evaluated the hysteresis behavior of welded flange-bolted web beam-to-column joints made of high-strength steels subjected to simulated earthquakes. However, the seismic behavior of newly developed high-performance seismic structural steels, which exhibit a combination of high strength and high ductility at the joint level, has been less attentively scrutinized. In this study, four welded beam-to-column joints were designed with standard or reinforced configurations. The reinforced joints included tapered haunch and transition plate connections. Hysteresis tests were conducted on these joints under low-cycle reversal loading to evaluate their seismic performance. The results indicated that the failure modes of these joints were primarily influenced by the welded heat-affected zones. Last, numerical models were developed and validated. The analysis focused on assessing their ductility coefficient, load-bearing capacity, stiffness degradation, and energy dissipation. The reinforced connections proved to be more effective in improving the initial stiffness, load-carrying capacity, and energy dissipation of the joints compared to the standard joints with the same beam and column sections. The initial stiffness of tapered haunch and transition plate reinforced joints were found to be 29.9% and 12.7% higher than that of the standard joint without reinforced configuration. And the equivalent viscous damping coefficient of the standard joint was 23% lower than the transition plate reinforced joint. However, the reinforced joints exhibited a slight reduction in ductility coefficient compared to the standard joints, with decreases of 11% and 2% for the tapered haunch and transition plate reinforced joints, respectively.

To investigate the influence of circumferential gap on the impact-resistance capacity of CFST columns, 12 CFST specimens were tested under constant axial load and lateral impact loading at mid-span. The test parameters included gap ratio, impact velocity, and slenderness ratio. The failure mode, impact force versus time curves, and deflection versus time curves of CFST specimens with circumferential gap were experimentally investigated and compared with those of the reference samples without any gap. Based on the test results, the failure mode, impact force history, deflection response, and energy dissipation of the specimens were experimentally investigated, and the influence of the above parameters on the impact-resistance of CFST specimens was analyzed. To further explore the force transfer mechanism of CFST with gap under lateral impact, a finite element analysis (FEA) model was established, and the influence of the gap on the contact stress, internal force transfer mechanism, and dynamic flexural capacity of CFST specimens was analyzed. Lastly, a simplified formula for predicting the dynamic flexural capacity of CFST considering the influence of circumferential gap was proposed, which could provide a reference for practical engineering applications.

The cold-formed steel (CFS) frame has the advantages of high strength, light weight, high construction efficiency, so it has been widely applied in building structures. However, the research on the seismic performance of multistory frames, especially those with braces, is rarely reported, the design method is also incomplete. In view of this, a pseudo static experiment of a three story double leg C-section CFS frame with brace is carried out. The bearing capacity, ductility, stiffness degradation and energy dissipation performance of the specimens are studied. The finite element analysis (FEA) method is used to simulate the failure process of the CFS frame and the design suggestions are proposed. The experiment result show that the failure process of the cold-formed thin-walled frame without braces has satisfactory ductility and energy dissipation performance; For framed CFS frame, the lateral stiffness and bearing capacity of the CFS frame increases, but the ductility decreases. Replacing double angle steel brace by steel plate strip brace can improving the seismic performance of structures, but there is an optimal width thickness ratio of steel plate strip. In this paper, the optimal width thickness ratio of brace is 5.0. When the design suggestions proposed in this paper are met, the CFS frame can achieve “strong structure, weak brace”, so as to improve the seismic performance of the frame.

This study proposes a new interior diaphragm joint between wall-type reinforced concrete column with high-strength spiral stirrups and steel beams, and the quasi-static test was conducted to investigate the seismic performance of the new joint under cyclic lateral force. Finite element model (FEM) simulation was carried out using the software ABAQUS, and the correctness of the FEM was verified by the results of the test. Additionally, the effect of parameters including the strength of concrete, thickness of the beam flange, interior diaphragm, joint flange, and joint web on the seismic performances of the joint was analyzed. Based on the parametric analysis and existing codes, a shear capacity formula was determined with the consideration of the shear capacity of the joint web and flange, and concrete. The comparison between the calculated and FEM results indicates that this formula could be regarded as an accurate calculation method for the shear-bearing capacity of different joint types in engineering design.

The present paper reports experimental and numerical investigations into the post-fire cross-sectional behaviour and residual resistances of hot-rolled austenitic stainless steel channel section stub columns under combined compression and minor-axis bending. An experimental programme included heating, soaking and cooling of specimens as well as post-fire initial local geometric imperfection measurements and minor-axis eccentric compression tests on fourteen specimens. The minor-axis eccentric compression test results were used in a parallel numerical modelling programme for validation of finite element models, which were then adopted to perform a series of parametric studies to generate further numerical data. Since there are no existing design rules for stainless steel structures after exposure to elevated temperatures, the relevant codified ambient temperature design interaction curves in combination with post-fire material properties were evaluated for their applicability to eccentrically loaded hot-rolled austenitic stainless steel channel section stub columns after exposure to elevated temperatures. The evaluation results revealed that the design interaction curves given in the European code and American specification led to rather conservative and scattered resistance predictions, which were attributed to the conservative end points and inefficient shapes. To address the shortcomings, new design interaction curves anchored to more accurate end points and having more efficient shapes were developed and resulted in more accurate and consistent resistance predictions than their codified counterparts. The reliability of the new design interaction curves was also confirmed by means of statistical analyses.

The fire performance of special-shaped concrete-filled steel tubular (SCFST) columns under axial load was investigated in this paper. The ABAQUS based finite element models were conducted for heat transfer and structural analysis. Twelve fire tests on SCFST columns under the ISO-834 standard fire curve by the authors' research were used to verify the model. In addition, heat transfer and fire-resistant mechanism of full-scale SCFST columns were studied; and extensive parametric studies were investigated to examine the influence of fire protection layer thickness, column limb thickness, slenderness ratio and other factors on temperature distribution and fire behavior of SCFST columns. Through the calculation and analysis of temperature field and fire resistance, a simplified temperature calculation method for steel tube, tension reinforcement, and inner steel plate are proposed along with the modularization temperature calculation method for special-shaped concrete sections. Moreover, the ultimate bearing capacity calculation method for SCFST columns under the standard temperature rise curve is proposed allowing for the influence of high temperatures on material properties, which can also be applied to determine fire resistance of SCFST column. Finally, the calculation method for the thickness of fire protection layer and the corresponding fire design is proposed based on the delaying temperature mechanism.

Conventional buckling-restrained braces (BRBs) exhibit stable compressive and tensile strengths and excellent energy dissipation characteristics. Nevertheless, the low post-yield stiffness limits the capacity of BRBs to control the peak displacement of the structure. This leads to large residual displacements in structures, which increases the probability of collapse under strong earthquakes. Consequently, introducing a reliable system that dissipates seismic energy, and provides an adequate self-centering capability, is necessary. This study has been carried out to investigate the hybrid BRBs response with different yield strengths (DY-HBRB) using numerical analysis. The cyclic responses, residual displacement, energy dissipation, and equivalent damping coefficient of the DY-HBRB models have been assessed. A simplified core-spring finite element model was utilized to model DY-HBRB elements. Moreover, an innovative trilinear kinematic hysteresis (TKH) model is proposed to simulate the cyclic behavior and facilitate the application of DY-HBRBs to seismic designs. The proposed model has been validated with the experimental investigation and numerical analysis results. The results indicate that selecting appropriate combinations of steel cores with different yield strengths in DY-HBRB provides a stable cyclic response with adequate energy dissipation and eliminates a significant part of the residual displacement. In addition, it was confirmed that the proposed TKH model could logically represent the double yield point of the DY-HBRBs with remarkable precision.

Hybrid steel plate girders are used worldwide as primary structural members in steel and composite bridges, when there is a need for deeper sections with greater stiffness and bending resistance than rolled sections to carry heavy loads. With the increasing importance of sustainability and lifecycle (cost) analysis, design for maintenance has become an important consideration for infrastructure projects like bridges which have a design working life exceeding 100 years over which they need to be regularly inspected and maintained. Stainless steels are known for their excellent corrosion resistance and low maintenance costs and thus the application of hybrid plate girders in bridge designs could be explored. This paper reports a numerical study on stainless steel hybrid plate girders subjected to compression and to bending and assesses relevant recommendations for their design. Previously developed FE models validated against stub column and four-point bending tests are employed and a parametric study is conducted on hybrid I-sections over a wide range of cross-section slenderness and aspect ratios. Based on the obtained results, the EN 1993-1-4 design predictions for stainless steel cross-sections in compression and in bending are assessed and the accuracy of the codified slenderness limits for both homogeneous and hybrid stainless steel girders is discussed. Furthermore, the numerically obtained deformation capacity at ultimate load is plotted against the CSM base curve originally derived for homogeneous sections and the accuracy of the CSM predictions of the cross-section resistance is also assessed, demonstrating that the CSM can be employed to predict the cross-section resistance of hybrid girders.

One of the advantages of stainless steel is its better behaviour under elevated temperatures when compared to the conventional carbon steel, which can be important for structural applications where the fire action should be considered. The second generation of Part 1–2 of Eurocode 3 (prEN 1993-1-2:2021) proposes new calculation formulae resulting from studies on profiles with I-sections. However, it is still important to evaluate the accuracy and safety of the same formulae for columns with circular and elliptical hollow sections (CHS and EHS respectively), whose application in stainless steel structures is common. Hence, this work presents a numerical parametric study on the fire resistance of columns subjected to axial compression, with CHS and EHS, considering different stainless steel grades, cross-sections and member slendernesses, and elevated temperatures. The ultimate load capacities of the columns are obtained by geometrically and materially nonlinear analyses including imperfections, using the SAFIR finite element program and considering the constitutive law based on the two-phase Ramberg-Osgood formulation proposed in prEN 1993-1-2:2021. Based on the comparisons between the numerical results and the methodology of prEN 1993-1-2:2021, small suggestions are proposed to improve the fire design formulae for the cases of CHS and EHS profiles subjected to axial compression.