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The development of transportation infrastructures stimulates increasingly more welded steel bridges in cold and severe cold regions in China. The low temperature there imposes additional challenges for the welded fatigue details. This study firstly examines experimentally the fatigue properties of the butt-welded joints made of Q345qD bridge steel under high-cycle constant-amplitude tensile action at the room and low temperature of −60 °C. The experimental results reveal the occurrence of multiple fatigue crack initiation and illustrate that the low temperature increases slightly the fatigue strength of the butt-welded details. The numerical simulation examines the fatigue crack propagation behavior of butt-welded joints with initial pre-existing single and multiple cracks under the room and low temperature, which achieves a good agreement with the experimental results. Based on the experimental and numerical validation, this study finally discusses the effect of the low temperature on the fatigue life of butt-welded joints and demonstrates that the lower fracture toughness under the low ambient temperatures influences marginally on the fatigue crack propagation life of the butt-welded details. The enhanced resistance to the fatigue crack propagation of structural steels at low temperatures contributes to the improved fatigue strengths of the butt-welded joints.

The fire-resistant steel as a type of high performance steel has significant application potential in building structures. The overall buckling behavior of fire-resistant steel columns at elevated temperatures is remarkably different from those of mild steel and high strength steel. However, structural behavior at ambient temperature had to be understood first before the investigation at elevated temperatures. This paper presents compressive tests on WGJ high performance fire-resistant steel welded I-section columns. The experimental results are compared with suggested values of Chinese, European and American specifications. Finite element models are established and the parameter analysis are carried out, showing current Chinese specification, Eurocode and American specification cannot be directly applied to determine the buckling resistance of high performance fire-resistant steel welded I-section columns. In addition, the modification on the design methods specified in current Chinese specification is also proposed.

With the progress in metallurgical technique and steel production process, the strength of structural steels can be improved, along with other material properties, including higher toughness and better weldability. Meanwhile, there are numerous potential civil structural applications for high strength steel (HSS), such as large-span space frames, transfer truss in high-rise buildings, as well as truss bridges. The mechanical behavior of structural members made up from HSS must be closely investigated and quantified before HSS can be widely used in engineering structures. In this paper experiments on six Q550 HSS I-section beams under moment gradient (MG) and four Q550 HSS I-section beams under patch loading (PL) were carried out, to investigate the local buckling behavior of I-section beams subjected to different loading conditions. The failure modes, critical local buckling strengths, ultimate strengths, load–deformation curves, load–strain curves and moment–rotation curves of the specimens were obtained. The test results of ultimate strengths were further compared with the design results in accordance with the available design methods in current specifications, ANSI/AISC 360-16, Eurocode 3, AS 4100-1998, AIJ LSD 2010 and GB 50017-2003. Accounting for material nonlinearity, geometric imperfection and residual stress, finite element models were established and verified with the existing test results, which were used for the parametric analysis of two series of 240 beams. The parametric investigation focused on the effects of the material properties and component plate slenderness on the ultimate strengths of I-section beams under MG and the ones under PL. The comparisons between the parametric analysis results, test results and the design results from ANSI/AISC 360-16 and Eurocode 3 were also conducted.

Embedded cable support (ECS) glass facades are increasingly used in architectures, due to their good-looking appearance. In order to study the static and the dynamic behaviors of ECS glass facades, static and dynamic loading tests are carried out. The structural deflections, the axial forces of cables, and the natural frequencies under various test conditions are measured. Two finite element (FE) models are established in ABAQUS and calibrated by the test data. A parametric study is conducted to discuss the effects of preload, glass panel thickness, and cable diameter on the static and the dynamic behaviors of ECS glass facades. The results show that the sealing of adjacent insulated glasses has little effect on the structure. The structural deflection is the controlling factor for ECS glass facades, while the Mises stresses on the glasses are fairly low. The discrepancy of the results obtained from the two FE models is small. Preloads on cables have a significant effect on the static and the dynamic behaviors of ECS glass facades, whereas the effects of glass panel thickness and cable diameter on the structure are relatively small.

Performance-based engineering methodologies allow for the design of more reliable seismic resistant structures. Nonetheless, to implement this technique, an accurate constitutive model to predict the elasto-plastic behavior of structural steel components or systems under various loadings is needed to properly evaluate their strength, deformation and energy absorption capacities in case of severe earthquakes. Such a model should also be relatively simple to use for practical purposes in engineering. With these objectives in mind, a new constitutive model is formulated to describe the elasto-plastic behavior of structural steels with yield plateau. This model uses nonlinear kinematic hardening to trace well the significant Bauschinger effect in full-range cyclic loadings, and couples nonlinear isotropic hardening with a memory surface in the plastic strain space to account for the stabilization phenomena of cyclic softening and hardening. An impermanent bounding surface in the stress space is employed to correctly describe the yield plateau response. The consistency condition is investigated in detail, which results in implications that will greatly facilitate the calibration of material dependent parameters. The implementation technique is also presented for three-dimensional and two-dimensional problems respectively. Using the resulting integration algorithms, the proposed constitutive model is successfully incorporated into ABAQUS/Standard by the UMAT subroutine feature.

Welded I-section steel beams with longitudinally profiled (LP) flanges, in which LP steel plates are utilized as the flanges may be applied to achieve structural optimization. Their special geometry raises challenges in deformation design, which leads to requirement of calculation equations. In this paper, theoretical solutions for mid-span deflections considering the influence of variable flange thickness have been deduced with the unit-load method and mathematical integration, and three different static loading conditions are incorporated. Then the reliability is verified by comparing with finite element (FE) models and test results. Straightforward design formulae are proposed by introducing a coefficient on the basis of formulae of conventional beams, which depends on all independent geometrical parameters and is determined through a nonlinear fitting of abundant theoretical results. It also indicated that remarkable amount of steel could be saved with a certain amount increase of additional deformation. The formulae developed herein for SLS deformation design of LP beams may be applied in practical construction design of building and bridge structures, which may also promote application of such advanced steel products.

Superior high-performance (SHP) steel is a kind of advanced steel with high strength and ductility, fire-resistant, and corrosion-resistant performance. It is especially suitable for structural engineering resistant to natural disasters such as fire, earthquake, environmental corrosion, etc. This paper aims to investigate the hysteresis behaviour of SHP steel welded I-section beam-columns. Four full-scale specimens under the combined action of constant axial load and horizontal reciprocating load were tested, and finite element models were developed accordingly. Based on comparisons of the test phenomena, failure modes, hysteretic curves, strain curves, energy dissipation capacity and ductility, effects of flange and web width-to-thickness ratio on the performance of the specimens were clarified. In addition, a 3-D finite element model was developed and further validated against the test results. Variation ranges of flange width-to-thickness ratio, web width-to-thickness ratio and axial load ratio were increased to further analyze the influence of critical parameters on the seismic performance of SHP steel beam-column in the parametric analyses. Finally, according to the test and finite element modelling results, whether the seismic performance of the SHP steel welded I-section beam-columns complies with the relevant provisions of the national standards Eurocode 3 and GB 50011–2010 was evaluated, and design suggestions were proposed accordingly. Research outcomes showed that the SHP steel beam-columns with good energy dissipation capacity and ductility could be applied to seismic steel frames in practical engineering; the failure modes of the specimens are local buckling rather than member instability; a smaller width-to-thickness ratio of the specimen could lead to a plumper hysteresis curve, more sufficient development of plasticity, a greater total energy consumption, and better ductility performance; the web and flanges have certain restrained effects, which should be comprehensively considered in seismic design of the SHP steel beam-columns. The research findings herein may provide an important basis for understanding the hysteresis behaviour of the SHP steel beam-columns as well as for their application in practice.

Concrete-filled steel tubes (CFST) incorporating high-strength steel (HSS) could produce more efficient structural system with lighter weight and higher capacity. However, the design methods for applying concrete-filled high-strength steel tubes (CFHST) are not available yet and limited investigations had been reported. In this research, 8 full scale mid-slenderness circular CFHST specimens, made of innovative high-performance Q460qENH structural steel with actual yielding stress fy as high as 530 MPa, were tested subject to axial and eccentric compression. The main parameters considered in the experimental program included: (a) infilled concrete strength fc' = 39.8–75.3 MPa and (b) loading eccentricity ratio e/D = 0–0.3. The numerical model for CFHST was established and validated with load–displacement curves, failure modes and neutral axis locations obtained from the 8 experiments. The numerical models were further validated in capacity predictions with 232 axial compressions and compression-bending CFHST experimental data collected from the literature, proved to be generally applicable with fy = 435–835 MPa, ξ = 0.5–8.5 and λn = 0.07–1.90 in both circular and square sections. Based on the validated numerical models, total 526 simulations were performed to investigate the influence of: (a) higher yielding strength fy and thinner-walled steel tubes; (b) confinement factor ξ and (c) normalized slenderness ratio λn, on the composite strength fsc and compression-bending (N-M) interaction behavior. Experimental and numerical investigations showed that high strength steel could further improve the CFST capacity with basically no reduction in safety margin and ductility performance, but was in need of design method modifications due to changes in composite mechanism. On this basis, an analytical refined plastic-section equilibrium model (RPE model) was proposed to derive practical N-M interaction design curve with consideration of strength enhancement due to the composition and actual stress distribution at ultimate state. The further proposed general design method for compression-bending CFHST included: (a) formulas of fsc-ξ relationship; (b) validated formulas of pure-bending capacity and overall stability inherited from GB 50936; (c) practical design curves of N-M interaction considering the effect of ξ and λn. By comparing with GB 50936, AISC 360, EC 4 and CECS 28 provisions, the proposed method provided more accurate solutions in capacity predictions of CFHST members.

Brittle cracks were observed in the welded beam-to-column connections of steel frames during an earthquake. The crack propagation and accumulated damage to the connections can lead to fractures at much lower ductility ratios. Understanding the connections’ damage behavior during an earthquake is crucial for the design of steel moment frames in seismic areas. Nine full scale beam-to-column connections were tested under constant amplitude and variable amplitude cyclic loading. The effects of loading amplitude, loading history, and peak load on the connection damage were analyzed. The damage characters were studied and three damage evolution models were calibrated and validated based on test results. The damage mechanism was investigated and an effective plastic strain index was developed to evaluate connection damage based on a ductile fracture mechanism. A fatigue fracture mechanics-based model, for evaluating the damage process of beam-to-column connections under cyclic loading, was proposed.

Flexural tests on full-scale I-section beams built up from Q460 and Q890 high strength steel subjected to uniform moment about their major axis were carried out in this article to investigate the effects of geometric and material properties on the local buckling behavior. Failure modes, load–displacement responses, load–strain curves, critical local buckling loads, ultimate resistances, and rotation capacities of the specimens were studied. Then the test results were compared with the design results from current specifications to examine the appropriateness of extrapolating current design method to high strength steel flexural member. Three-dimensional finite element models were established and validated against the experimental results accounting for material nonlinearity, initial geometric imperfections, and welding-induced residual stresses. A parametric study was performed using the validated finite element model, which revealed the variation of normalized ultimate moment with interactive plate slende...

In full-scale cyclic loading tests conducted by the authors on six one-bay two-story high strength steel moment frames, strains on surfaces of beams, columns and their joints were extensively monitored, and the shear distortions in east-side panel zones at both stories were recorded. The global responses of all specimens at the frame level were prepared and analyzed in the first companion paper. This paper deals with those local responses of members and joints under real boundary conditions in frame structures, which were expected to assist more accurate and reasonable assessment of their seismic behavior than individual tests on extracted specimens. Beams remained essentially elastic throughout all tests, while columns developed significant yielding and maximum moments at column bases that were 30% to 75% higher than the fully plastic moment depending on section slenderness. Compact columns of 460 MPa high strength steels exhibited superior cyclic behavior with stable energy dissipation, so did those panel zones that underwent inelastic deformation. Cover-plate connections finished all loading cycles in all specimens and were effective to reduce the risk of fracture at beam-to-column welds. Continuity plates might not be able to resist the seismic demand specified by current codes, since they fractured in one specimen with a demand-to-capacity ratio of 0.72, which was also the highest among all specimens. Plastic resistances of panel zones predicted by various codes except for the Chinese code, underestimated the experimental results due to the effect of strain hardening, while seismic demands on panel zones specified in various codes differed a lot. It was the Chinese code that both provided the lowest demand and overestimated the resistance, and thus resulted in the weakest panel zone design.

The steel shear walls are one of the most resilient lateral force resisting systems. In a typical steel shear wall, a steel panel is welded or bolted to columns and beams. The steel plate can be unstiffened or stiffened. The steel panel resists the bulk of the story shear force, and the entire shear wall system resists the overturning moment. In stiffened shear walls, the stiffeners are usually designed to prevent diagonal buckling of relatively thin steel plate until the plate yields in shear. In unstiffened shear walls, diagonal buckling occurs under relatively small story shear, and after buckling, the additional story shear is resisted by the diagonal tension field action in the steel panel similar to plate girders. The chapter introduces the reader to the mechanics, behavior, and design of various types and configurations of steel shear walls, and how actual steel plate shear wall buildings have performed during the earthquakes. Design considerations, modeling technics, and analytical approaches for analysis and design of steel shear walls are discussed. Two issues that somewhat reduces the cost-efficiency of the unstiffened steel shear walls are (1) the application of relatively large lateral forces to the boundary columns due to tension field action, and (2) the use of relatively expensive field welded moment connections in the boundary beams. A new steel shear wall system called High-Performance Steel Plate Shear Wall System resolves both of these issues by separating the steel plate from the column and by using an innovative gusset plate moment connection. Another innovative system resolves the problem of column subjected to large lateral loads by introducing vertical slits in the steel panel.

The steel, whose nominal yielding strength fy is greater than or equal to 460 MPa, is generally referred to as high strength steel (HSS). Through the comparison with conventional strength steel (CSS) members, HSS members are more vulnerable to local buckling since the component plates are usually designed to be more slender in order to exploit higher material strength. The different mechanical properties between HSS and CSS, including yielding strength, ductility and so on, may lead to different local buckling behavior of steel members. However, little guidance is applicable in existing standards for the stability design of HSS members. In this paper, elaborate finite element (FE) models of HSS welded I-section beams under the loading conditions of uniform moment (four-point loading) and moment gradient (three-point loading) were developed by means of the general-purpose FE software package and validated against the available test results. Continuous lateral supports were ideally applied to restrict the occurrence of coupling with overall lateral‐torsional buckling. Comprehensive parametric analyses on key parameters containing the plate width-to-thickness ratio and the steel material properties were further conducted, reflecting the influence of these parameters on the mechanical performance of local stability. Through this work, the variation rules on rotation capacity and postbuckling resistance of HSS welded I-section beams with plate width-to-thickness ratio and steel nominal yielding strength were clarified. Taking into account the interaction of local buckling modes between flanges and webs, new cross-section classification of HSS welded I-section beams was proposed based on the FE analysis results. After the introduction of the concept of interactive local slenderness, the design methods of postbuckling ultimate moment resistance for HSS welded I-section beams subjected to uniform moment and moment gradient were also proposed, which were assessed by comparing the design results with the ones obtained from the corresponding design approaches in Eurocode 3, ANSI/AISC 360–16 and GB 50017–2017. And the reliability of the new proposals was also confirmed by further statistical analysis.

Based on the experimental investigations on compressive buckling behavior of fire-resistant steel columns subjected to elevated temperatures, the numerical analysis models were established and validated by the experimental results of 12 fire-resistant steel columns and 15 conventional steel columns. The parametric analysis was performed to examine the influence of cross-section types, axial load ratios, normalized slenderness ratios, initial imperfections, residual stress and temperature elevation procedure on critical temperatures of fire-resistant steel columns. The parametric analysis indicated that: (1) The critical temperatures increased with decreasing axial load ratios and slenderness ratios; (2) The fire resistance of column with higher axial load ratios and middle slenderness ratios were more sensitive to the residual stress and initial imperfections; (3) Cross-section size and temperature elevation curve variations had less influence on critical temperatures. Furthermore, a total of 1674 numerical simulations were compared with the results determined from the current standards. It was found that provisions in Chinese GB 51249 and European EC 3 tended to overestimate the compressive buckling coefficient while underestimate the critical temperature, when applied to fire-resistant steel columns. Based on Perry-Robertson formula and EC 3 critical temperature formula, the fire resistance determination methods were proposed to facilitate the engineering application of the fire-resistant steel. The proposed methods were proved to meet both safety and economic requirements of structural design.

Steel structures have been increasingly applied in contemporary infrastructures, which always require high loading capacities and strong resistance to disasters such as earthquake actions, fire and environmental corrosion, etc. Recently a superior high-performance (SHP) steel is developed accordingly, possessing combined beneficial features of high-strength, high-ductility, corrosion-resistance and fire-resistance, which may well satisfy the structural requirements. The present study aims to investigate mechanical properties of the SHP steel at elevated temperatures and to propose its constitutive models for further usage in fire design and analyses of structural members. A comprehensive experimental programme including a series of standard tensile coupon tests at both ambient and elevated temperatures is described herein, and key mechanical properties including modulus of elasticity, yield strength, ultimate tensile stress as well as stress-strain curves of the SHP steels are obtained based on the test results. Reduction effects of elevated temperatures on their mechanical properties are quantitatively clarified, and further comparisons with prediction results in accordance with national standards as well as with independent test results reported in literature are made. It is indicated that the mechanical properties of the SHP steels differ significantly from that of conventional mild steel and fire-resistant steel. Specific prediction equations are proposed for evaluating the temperature-dependent mechanical properties of the SHP steel; furthermore, an adapted Ramberg-Osgood model is developed for describing its full range stress-strain relation. The research outcomes of the present research may serve as an essential basis for better understanding mechanical performance of the SHP steel at elevated temperatures as well as for further investigations on its structural members' behaviour; and it is helpful to promote its application in practice.

Seismic provisions to guide the design of steel moment frames in Europe, the United States, Japan and China are comprehensively examined. Seismic hazard levels and performance requirements, ground type classification, magnitude and shape of elastic response spectra, seismic design force and distribution of required story shear strength, local ductility requirements, and reduction factors are compared. The results show that the no-collapse requirements in Eurocode and Japanese code correspond to a lower level of ground motion than the other two codes. The unreduced elastic response spectra given in four codes are quite different in recognition of different ground types and seismicity, in particular, Japanese code generally specifies much larger elastic spectrum than other codes. Although local ductility requirements are quite similar, U.S. code specifies higher reduction factors than Eurocode and Japanese code, while Chinese code stipulates a constant reduction factor with a relatively small value regardless of the ductility level of structures. As a result of such over-conservatism, Chinese code designed steel moment frames exhibit 20% to 150% larger lateral stiffness and resistance than Eurocode and U.S. code in most cases, while the significant even larger lateral stiffness and resistance predicted by Japanese code than that by Chinese code is mainly due to the larger seismic force from elastic response spectrum.

The pinned connection method was used to connect the large-span floor truss to the steel column in Zoucheng International Conference Center project, which played a quite important role to achieve the in-plane rotation and transfer heavy loads directly. Four specimens were tested experimentally to investigate the monotonic and cyclic behavior of this connection method, including two independent pinned connections and two assembled truss connections. The load–displacement curves, deformation development, failure mode, ductility, and energy dissipation capacity were discussed in detail. Besides, the nonlinear multi-scale finite element models of the pinned and truss connections were established. The numerical simulations not only captured the global behavior and local limit states observed in tests but also revealed valuable new information that could not be directly obtained from the tests. The experimental and numerical results showed that both the pinned and truss connections had good ductility, load transfer ability, and ideal rotation capacity with large safety margin, indicating these constructions could be used as references for similar projects.

The flexural strength of steel I-beams is influenced by the local and lateral-torsional instabilities, where the presence of shear also reduces the moment carrying capacity. The objective of this research is to investigate the interactive buckling modes for hybrid steel I-shaped flexural members subjected to uniform moment loading. A three-dimensional finite element (FE) model subjected to monotonic loading is developed using nonlinear buckling analysis. The analytical model was experimentally verified based on the results of six full-scale 3 m beams that were tested previously. An extensive parametric study is conducted for 526 FE models and different instability modes including local buckling, lateral-torsional buckling, and shear buckling modes are identified. Subsequently a classification is proposed based on slenderness to predict buckling mode shapes of flexural member. Attention is given to the interaction between shear and flexural buckling modes, and their effect on inelastic flexural capacity. The flexural strength is evaluated based on local and overall slenderness and interactive buckling behavior. Based on the obtained buckling modes as well as local and overall slenderness ratios, some mathematical expressions are developed and presented to determine the ultimate shear-moment capacity when lateral torsional buckling is also associated with interactive buckling modes in hybrid and non-hybrid I-shaped flexural members.

Tempered glass panels in the point supported glass facade (PSGF) are usually subjected to large in-plane load. In order to investigate the bearing capacity of tempered glass panels against in-plane load, three tests are firstly carried out. Afterwards, finite element method (FEM) is adopted to study stresses around holes under different loading conditions and explore the influence of the in-plane load on the stress distribution of the glass panel. It is concluded that stresses around holes in tempered glass panels are principally affected by the in-plane load, while stresses at centers of the surface and edges are mainly controlled by the out-of-plane load. When the in-plane load is relatively high, the out-of-plane load is probably able to reduce stresses at some points around holes, contributing to the improvement of the load-bearing capacity of tempered glass panels. If the in-plane load is large enough, specimens are bound to experience state transitions which are caused by large plastic deformation of stainless steel bolt fittings and result in the rapid increase of stresses on glass panels. Therefore, by enhancing the shear strength of bolt fittings one can improve the bearing capacity of tempered glass panels in the PSGF against the in-plane load.

With the formulation and implementation of a new constitutive model for full-range elasto-plastic behavior of structural steels with yield plateau being presented in a companion paper, this paper is concerned with the detailed calibration methods of material dependent parameters incorporated in that model. The restriction equations extracted from the consistency condition in the formulation together with some empirical assumptions give rise to a very concise technique to evaluate the model parameters using only tensile coupon test results. After calibration, the constitutive model is used to predict the cyclic behavior of materials, members, connections and frames made of structural steels with yield plateau. The close fit between the experimental results and simulated ones validates the accuracy of the constitutive model. The work in this paper demonstrates further the advantages and efficiency of the proposed constitutive model, especially in the absence of cyclic coupon test results.

Stresses around holes of tempered glass panels are tend to be ignored in the practical design of point supported glass facades. With the intent of investigating the stress distribution around holes in tempered glasses, the experimental and theoretical studies were firstly carried out and the finite element model was subsequently developed using ANSYS software. Afterwards, the theoretical formula was combined with test results to predict the failure stresses in the vicinity of holes and the stress limitations were proposed. It is concluded that the theoretical and numerical results are at least consistent with the chosen test data although they have some uncertainties and limitations in the analyses. The stresses around holes are significantly higher than those on the large area and lateral surface and ought to be the controlling parameter in the design. The maximum principal stress of some random point on the tempered glass panel is proportional to the external load and inversely proportional to the square of the panel thickness if the spacing between this point and the centroid of glass panel is determined. Furthermore, the clamping effect of the button head bolt fitting is more pronounced than that of countersunk bolt fitting and capable of reducing stresses near holes, especially for the thin plate.

The Q370qE steel has a wide application in the medium and long span railway steel bridges in China, due to its excellent material characteristics including high strength, high toughness and good weldability at room temperature. Nevertheless, the limited research work on the fatigue properties of the Q370qE steel challenges the safety of steel bridges in cold and severe cold regions under the cyclic actions. This study first conducts a series of strain-controlled fatigue tests of coupon specimens at room temperature and −60 °C to characterize the cyclic stress-strain curve, hysteresis loops, Masing behavior and fatigue crack initiation resistance by Coffin-Manson relationship. Thereafter, the fatigue crack propagation tests of the compact tension specimens under different stress ratios and different temperatures reveal the effect due to stress ratios and temperatures on the fatigue crack propagation resistance of the Q370qE steel through the Paris formula. Results demonstrate that the low temperatures enhance the resistance to the fatigue crack initiation and propagation of the Q370qE steel. Finally, to better quantify the performance of the Q370qE steel, this paper collects different bridge steels and compares the fatigue crack initiation resistance and fatigue crack propagation between the Q370qE steel and other bridge steels. The results quantify the excellent higher fatigue resistance of Q370qE steel in comparison with other bridge steels.

In order to quantitatively describe the effect of strength and stiffness degradation on seismic behaviors of steel frame, numerical models (the equivalent constitutive model considering damage and steel hysteretic constitutive model without considering damage) for predicting seismic behaviors of steel frame structures were described. Three frame models of five-floor, ten-floor and fifteen-floor frames were analyzed. Eight earthquake records were selected for time history analysis. The differences of inter-story drift ratio distribution calculated by two constitutive models were compared. The influencing laws and degrees of damage and degradation on seismic behaviors were also obtained. Finally, a prediction curve of degradation index was proposed, which could be used for damage control. Preliminary evaluation methods for seismic performance of steel frames considering damage and degradation were discussed. The analysis of the results showed that: the inter-story drift ratios of the three frames calculated by damage model were obviously larger than the results of non-damage model, showing that damage and degradation amplified the structural deformations. With the increasing of floors, the differences of inter-story drift ratio between damage model and non-damage model were gradually reduced. The weak stories of three models were located at 0.4 to 0.5 times of structural height, which should be paid more attention in design process.

In order to investigate the accuracy and applicability of steel equivalent constitutive model, the calculated results were compared with typical tests of steel frames under static and dynamic loading patterns firstly. Secondly, four widely used models for time history analysis of steel frames were compared to discuss the applicability and efficiency of different methods, including shell element model, multi-scale model, equivalent constitutive model (ECM) and traditional beam element model (especially bilinear model). Four-story steel frame models of above-mentioned finite element methods were established. The structural deformation, failure modes and the computational efficiency of different models were compared. Finally, the equivalent constitutive model was applied in seismic incremental dynamic analysis of a ten-floor steel frame and compared with the cyclic hardening model without considering damage and degradation. Meanwhile, the effects of damage and degradation on the seismic performance of steel frame were discussed in depth. The analysis results showed that: damages would lead to larger deformations. Therefore, when the calculated results of steel structures subjected to rare earthquake without considering damage were close to the collapse limit, the actual story drift of structure might already exceed the limit, leading to a certain security risk. ECM could simulate the damage and degradation behaviors of steel structures more accurately, and improve the calculation accuracy of traditional beam element model with acceptable computational efficiency.

Concrete-filled steel tubular (CFST) columns are widely used in infrastructure applications and thus usually are subject to long-term service loading. However, understanding the influence of sustained loading on the ultimate performance of these structural members is still lacking. The objective of this work is to develop a constitutive model to account for strength and ductility change of CFST columns under sustained loading, validated by experimental data reported in the literature. In this framework, a simplified analytical method equipped with a monolithic iterative scheme is developed to efficiently estimate the creep deformation of these composite columns at any designated target time. Based on the calculated creep status, an analytical stress–strain curve is proposed to characterize the post-creep mechanical behavior of steel-confined concrete. This stress–strain behavior incorporates the combined effects of enhanced compressive strength of plain concrete and reduced confining strength provided by steel tube, both of which are caused by sustained load. Finite element based numerical study together with the available test database are used to validate the mechanical analysis and to assess the performance of the proposed constitutive model. The predicted post-creep response is found to be in good agreement with the experimental results for CFST columns with circular and square cross-sections. Finally, an extensive parametric study based on a pushover analysis is conducted to examine the influence of individual critical design parameters on structural ultimate strength and ductility due to long-term service loading.

The pseudo excitation method (PEM) has been improved into a more practical form, on which the analytic formulae of seismic response power spectral density (PSD) of simplified large-span structural models have been derived. The analytic formulae and numerical computing results of seismic response PSD have been derived to study the mechanism of multi-support excitation effects, such as the wave-passage effect and incoherence effect, for the seismic response of multiand large-span structures. By using a multi-span truss as an example, the influence of multi-support excitation effects on the seismic response of such structures is studied.

In order to investigate the seismic behaviors of unstiffened thin steel plate shear wall structure, tests of four three-story unstiffened steel plate shear wall specimens under cyclic loads were carried out. Parameters of the specimens included height-to-thickness ratio, span-to-height ratio and middle brace. The carrying capacity, hysteretic behavior, degraded characteristics, ductility, failure modes, energy dissipation capacity were analyzed and compared deeply. Besides, the nonlinear finite element method of shear wall structure was also established, which was verified by test results. Finally, the effect of column stiffness on load-carrying capacity was studied. The practical requirements of in-plane and out-of-plane stiffness of edge column were suggested. The experimental and numerical results showed that: this kind structure exhibits high strength, good energy dissipation capacity, and good ductility (the ductility coefficients are more than 3.0). When the inter-story drift angle reaches 1/50, the strength degradation is no more than 5%, indicating that the structure has good seismic behaviors. The span-to-height ratio has little effect on load-carrying capacity, while slightly affects the initial stiffness and ductility. The effect of height-to-thickness ratio (thickness) on load-carrying capacity is relatively larger than other factors. The middle braces do not improve the behaviors of structures. The stiffness of edge column has great effect on lateral load-carrying capacity of shear wall structures. The value of column stiffness index could be within 2.0–2.5 to achieve the sufficient constraints and economical benefit.

Experimental study was carried out on the in-plane bending behavior of glass plates without lateral supports, and the effects of the factors, such as height-to-span ratio, on the stability of glass panels were studied. Results show that the in-plane bending glass plates with both ends simply supported and their upper edge free lose overall stability under loads, which belongs to the limit-point type of instability. It is found that the buckling load increases linearly with the increase of height-to-span ratio of the glass plates. The lateral stress of in-plane bending glass plates without lateral supports increases linearly under loads; while the large-area stress increases nonlinearly and the lateral stress is not the controlling factor of instability. In finite element analysis, the first buckling mode is regarded as the initial imperfection and imposed on the model as 1/1000 of the span of the components. The numerical buckling load according to the theory of large deflection is less than the experiment result, which is more conservative and can provide some reference for design. For the design method, when the in-plane load is imposed on the glass plate, its lateral strength and the deflection should be verified. Considering the stability of the in-plane bending glass plate without reliable lateral support, buckling is another possible failure mode and calls for verification.

The present investigation studies the load bearing performance of stainless steel bolted connections. The austenitic stainless steel developed in China containing approximately 17% of Cr, which could be graded as EN 1.4401, has been selected for this research. In order to study the bearing strength of stainless steel bolted connections, experimental tests on 5 specimens have been conducted. In addition, complementary finite element (FE) models, which have been validated by the test results, have been adopted to analyse the effect of the key factors for bearing strength of the stainless steel bolted connections. The key factors include end distance, thickness of connecting plate, diameter of stainless steel bolt and edge distance. According to the FEA results, the loading capacity increases with the increase of the thickness of the plate and the diameter of the bolt approximate linearly. However, the end distance and edge distance have a comparatively complicated influence on the loading capacity of the connection. Based on mathematical analysis of the experimental and FEA results, a calculation method as well as its simplified form for the bearing strength of stainless steel bolted connections has been proposed.

This paper presents a new method to determine moment resistance of I-beams with hybrid and homogeneous sections based on a design procedure independent from the section classification, considering local and overall interaction instabilities of beams. Flexural tests on six full-scale I-shaped beams, three with hybrid sections and three with homogeneous sections, built up from high-strength steels (Q345 and Q460), subjected to constant moment about their major axis were carried out to verify numerical models. Three-dimensional nonlinear finite element models were established and verified with the experimental results accounting for material nonlinearity and manufacturing distortions. Stress–strain relationships obtained from tensile coupon tests were incorporated in the finite-element model. Close agreement was achieved between the test and finite element analysis results in terms of moment-rotation response and ultimate strength. A comprehensive parametric study was conducted for a wide range of local and overall slenderness ratios to investigate interactive effects of flange local buckling, web local buckling and lateral torsional buckling modes on flexural strength of steel beams. The main goal of this research is to simplify the current design procedure of steel members subjected to bending. Presented equation to determine flexural strength may also applicable for hybrid sections made of high strength steel grades. A comparative study was performed between the proposed method with EC3 and AISC. Results show a close agreement of current work with EC3.

Three-point bending tests were conducted at various low temperatures to obtain the crack-tip opening displacement (CTOD) values of three varieties of structural steels with several plate thicknesses. Parameters of the crack growth resistance curve (Rcurve) of each specimen were calibrated by regression of the test data points (CTOD versus crack extension). The temperature and the plate thickness had great effects on the R-curve shape (flat or rising) and the fracture mode (brittle or ductile). In a design process of a steel component, an initial crack is assumed according to its fatigue category. Through the analyses of the crack driving force and the resistance, a practical method is proposed for fracture resistant design and evaluation of flawless or flawed steel components at low temperature.

In order to have a systematic and comprehensive comparison of seismic behaviors of steel plate shear wall structures with different construction details, a numerical method was proposed, which was proved accurately to predict the performance of structures with published quasi-static tests. Then, eight typical steel shear wall models with different structural construction details were established. Also an advanced stiffened low yield point steel plate shear wall was proposed to avoid excessive out-of-plane deformation. The seismic behaviors of above nine shear wall models were fully compared and analyzed, and key issues, such as energy-dissipating capacity, ductility, out-of-plane deformation and the effect of tension field on the columns were discussed in depth. The results showed that: in high-intensity seismic area, load-carrying capacity, hysteretic behaviors, failure modes, seismic ductility and economic performance should be taken into account comprehensively to choose the appropriate form of steel plate shear wall structure; the proposed low yield point steel plate shear wall with T type stiffened ribs could most effectively improve the energy dissipation capacity and ductility, and lessen the impact of tension field on the columns, besides, it had better load-carrying capacity and smallest out-of-plane deformation. This method provided a good way for improving the seismic behaviors of steel shear wall structures.

An experimental study was conducted to investigate the mechanical behavior of four I-section steel beams, which were reinforced by welding a plate to the bottom and top flange, respectively. For all welding reinforced specimens, the ultimate capacity was obviously enhanced relative to that of the original beams. Preload while the beam is reinforced is proved to be an adverse factor for the capacity if the failure of the beam is controlled by lateral–torsional buckling. During the welding process, larger vertical deflection and web curvature were generated. The torsional section angle decreased if the appropriate welding procedure was adopted. In addition to the experimental study, a type of thermo-mechanical coupling analysis by ANSYS, considering the welding process, was conducted. A generally good agreement between FE analysis and the experiments could be observed from the comparison of the load versus deflection curves obtained from FE and the experiments. It was proved that the FE analysis is reasonable and can allow for the prediction of residual deflection after welding reinforcement. The FE analysis presented in this paper is a reasonable method for simulating the behavior of the steel beams reinforced while under load. With more accurate material parameters and heat source models, the simulation can be further enhanced.

In order to discuss the influencing factors of damage and degradation and the effect on steel frame subject to strong earthquakes, firstly, a constitutive model was proposed for 3D finite element models to calculate the seismic behaviors of steel frame more accurately. The model was proved correct and applicable due to typical quasi-static tests. Then, based on the verified model, the damage and degradation factors were discussed by parametric analyses, including the panel zone, loading history, loading amplitude, the width to thickness ratio and yield strength. The cumulative damage phenomena of steel frame connections were further studied and the degradation distribution curve was obtained. Finally, the traditional beam element model and proposed shell element model of structure were established by ABAQUS for time history analysis. The effect of damage and degradation on seismic behaviors of steel frames were compared and discussed. The tests and analysis results revealed that: panel zone strength, loading amplitude and width-thickness ratios of plates had significant impact on damage and degradation behaviors and failure modes of connections. Premature weld cracking would lead to earlier damage and degradation under “strong to weak” earthquake, which would seriously affect the overall mechanical properties of the structure. Once local buckling caused damage, the results of the beam element model and accurate shell element model were remarkably different. Beam element model without considering damage and degradation underestimated the structural deformations, which should be paid more attention for design safety.

Lamellar tearing and crack-induced brittle failures along steel plates in the through-thickness direction seriously threaten the safety and reliability of steel thick plate structures in construction and service, especially at low ambient temperatures. Three kinds of tests, including uniaxial tensile tests, Charpy V-Notch impact tests, and three-point bending (TPB) tests were performed at normal and low temperatures to investigate the through-thickness mechanical properties, impact and fracture toughness of Q345B structural steel plates with thicknesses from 60 to 165 mm. The test specimens were mainly sampled along the through-thickness direction of the plate, but transverse specimens along the rolling direction were also involved. The ductility index (percentage reduction of area), impact toughness index (Charpy impact energy), and fracture toughness index (critical crack tip opening displacement (CTOD) values) all decrease as the temperature declines. All the mechanical properties and the impact and fracture toughness along the through-thickness direction are worse than those along the rolling direction. The results also offer experimental support for the determination of an evaluation indicator for structural steel thick plates with through-thickness characteristics.

This paper presents an experimental study on a full-scale two-storey, two-bay by one-bay steel-concrete composite slim floor that was subjected to horizontal pseudo-dynamic and cyclic pseudo-static loadings. The primary objective of this test is to investigate the bearing behavior and load bearing capacity of the composite slim floor under horizontal loads. The time-history load-displacement curves, hysteretic curves, skeleton curves, structural deformation and the failure mode were obtained from the tests. The test results indicated good load bearing capacity and good ductility of the test structure and also required improvement of the construction of the beam-column connection. At the end of this paper, some suggestion on the improvement of composite beam-column connection has been proposed.