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The performance-based seismic design suggests multiple performance objectives for building structures. A preselected yield displacement may be chosen as a design target to control the inelastic deformation threshold of structural elements. The yield displacements of knee-braced steel frames are related to the yield displacements of the main lateral-force-resisting elements, i.e., knee braces. However, the yield displacements of the commonly used straight steel knee braces (SSKBs) are difficult to adjust because they are inherently proportional to the steel yield strain and brace length. A special type of steel knee braces, called curved steel knee braces (CSKBs), is proposed in this paper. An eccentricity is introduced into the CSKBs by a circular arc-shaped axis to adjust the yield displacement. A simplified physical model is proposed to approximate the backbone curve of the CSKBs. An experimental study is conducted on three CSKB specimens, and the adjustability of the yield displacement of the CSKBs is verified. The test results also show that all specimens exhibit an asymmetric hysteretic behavior. High equivalent viscous damping ratios (0.29–0.44) and high tensile fully plastic stiffness ratios (0.059–0.298) are obtained with a maximum strain of approximately 0.02. The ultimate compressive loading tests of two specimens indicate that the strength degradation is more moderate than that in the SSKBs that are not buckling-restrained.

Shape memory alloys (SMAs) are high-performance metallic materials that can experience large strain and still recover their initial shape through either temperature-induced effect (shape memory) or stress-induced effect (superelasticity). The superelasticity of SMAs is very attractive to the earthquake resilient design because of the inherent material feature with excellent self-centering (SC) and energy dissipation capabilities. This paper presents a comprehensive numerical simulation of the steel columns with SMA bolts. A finite element model was validated by tests of two SC steel columns in terms of global hysteresis loops and local strain states. Subsequently, special attention to the effects of prestrain in the SMA bolts, bidirectional loading, and multi-earthquake loading was paid to offer insights into the cyclic responses of the SC steel column. Results showed that the steel columns equipped with SMA bolts could exhibit satisfactory and stable flag-shaped hysteresis loops with excellent SC and energy dissipation capabilities under different loading conditions. In addition, SC column exhibited nearly equivalent seismic performance under multi-earthquake loading. Therefore, the SC steel columns can achieve earthquake resilient design that requires no (or minimal) repair even after strong earthquakes and remains highly functional for immediate aftershocks or future earthquakes.

A comprehensive experimental and numerical study on flexural buckling behaviour of welded stainless steel box-section beam-columns is presented in this paper. A total of ten test specimens were prepared and tested subjected to eccentric compression. The cross-section and length of the test specimens were carefully designed by referring to existing design specifications to be insusceptible to local buckling. The full experimental load versus deformation and load versus strain curves were obtained. Prior to member testing, both material tests and geometric imperfection measurements were conducted and reported in detail. Finite element (FE) models were developed and validated against the obtained beam-column test results afterwards, which were utilised to perform parametric studies on the flexural buckling behaviour, generating sufficient numerical data points. Based on the obtained test and FE results, the design methods provided in EN 1993-1-4+A1 and AISC DG 27 were assessed. It was shown that both EN 1993-1-4+A1 and AISC DG 27 provided generally conservative and scattered predictions for the buckling resistance of welded stainless steel box-section beam-columns. Moreover, a newly revised proposed interaction factor was proposed in the framework of EN 1993-1-4+A1, and strength predictions with reduced scatter were therefore achieved.

This paper is the first part of a comprehensive experimental and numerical study on the vibration behaviour of innovative steel-timber composite (STC) floors under service loading conditions. Due to the lighter weight and lower inherent damping of STC floors compared to conventional steel-concrete composite floors, vibration performance is a major serviceability concern that should be addressed to ensure that the dynamic characteristics of the system are within the range of human comfort. Extensive modal testing and numerical analysis were carried out on six STC beams and the acceleration response, natural frequencies, damping ratios and mode shapes were extracted. A 3D finite element (FE) model of the STC beams was generated and calibrated/updated by the Genetic Algorithm to minimise the difference between the experimentally measured and the numerically predicted natural frequencies, mode shapes and dynamic flexibility matrix. It is shown that the updated FE models can predict the vibration response of the idealised STC floors with reasonable accuracy. In Part 2 of the paper, the validated FE model in conjunction with the available guidelines in BS EN 1995-1-1 (EC5), AISC Design Guide 11 and the ECCS reports are utilised to assess the performance of STC floors subject to human-induced vibrations.

This paper describes a restraint tube local bulging study of newly developed small-type buckling-restrained braces (SBRBs). An analytical calculation model for the restraint tube stress distribution is established by the shell theory and the Fourier series. It is demonstrated that the stress concentration lies mainly in a region with a length of 2R0, which is approximately equal to the tube middle surface diameter. A simplified design method including a safety factor and recommended thickness-radius ratio is then proposed based on the analytical study. To verify the accuracy of this calculation method, four SBRB specimens with different tube thicknesses were tested under quasi-static cyclic loading. The calculation results are in reasonable agreement with the test results and can predict the local bulging occurring instant with acceptable accuracy.

Five simple beam-column joints with composite slabs were tested under a middle column removal scenario. Fin plate connection was used in all the joints. The influences of joint type, slab thickness, number of shear studs and bolt holes were investigated. Load-resisting mechanism of the composite joints against the applied ‘push-down’ load was investigated and the respective contribution of flexural action, compressive arch action and catenary action was quantified. Structural behaviour of the joints in terms of axial force, bending moment, failure mode and energy absorption was presented. To evaluate design values provided by current design guidelines and building codes, test results of the joints were compared with design values. It was found that the composite slab was beneficial to flexural resistance of the joints. Although tying capacity was reduced due to bending moment, tie force requirement could be met for conventional composite joints with 75 mm thick slab. A proposed novel fin plate connection with slotted bolt holes had better performance than conventional connection in terms of energy absorption and tying resistance. The test results provided a better quantitive understanding of FP connections under progressive collapse scenario and were able to serve as benchmark for further simplified numerical models.

The blind bolting technique, recognized as a novel solution to connect a beam to a closed section column for unavailable installation from one side, has been gradually employed in concrete filled steel tube (CFST) column to steel beam connections recently. However, unexpected failure modes including bulge of the thin-walled steel tube and anchorage failure of the blind bolt in the core concrete still existed for this type of connection, which resulted in a limited ductility and inferior strength of the connection. Therefore, a novel blind bolted joint was proposed by replacing the CFST column with the concrete-filled double skin steel tubular (CFDST) column to overcome the above problems. A series of interior joint specimens to square CFDST columns were carried out to investigate their seismic behavior. Compared with the CFST column joints, typical failure modes of the CFDST column joints were characterized. Seismic response was also analyzed in terms of the hysteretic performance, strength and stiffness degradation and energy dissipation capacity to explore the effects of the column hollow ratio and end plate type. The experimental results denoted the CFDST column to steel beam joint with blind bolts performed excellent seismic performance. Based on the equivalent method, two simplified analytical models were discussed to evaluate the initial stiffness of this type of joint. The experimental and analytical results were beneficial for the application of semi-rigid connections to CFDST columns in engineering practice.

A new moment connection for a steel beam to hollow structural section (HSS) and concrete-filled tube (CFT) columns using the through-plate technique is proposed. In the through-plate connection, all the demands of the beam are initially transferred to a vertical plate by in-plane action and are subsequently transferred to a column. Three full-scale interior planar connections are loaded cyclically under displacement control as per the AISI/AISC341-16 loading protocol. An axial compression force corresponding to 10% of the column axial capacity is applied to the column. The goals of the experimental study are as follows: (1) to evaluate the connection performance under cyclic loading and (2) to evaluate the connection components for extracting key design parameters. Square-shaped HSS sections with electric resistance welding are utilized for the column. To investigate the effect of concrete infill on the connection performance, the HSS column and one of the CFT columns are constructed using the same steel tube. The width-to-thickness ratio (b/t) for the corresponding specimens is 27, and another CFT specimen with a higher ratio of 34.5 is considered. In all the specimens, the plasticity is concentrated in the beam hinges, without any damage to the column or connection components. The proposed connection exhibits extremely high strength, stiffness, and ductility and is categorized as a rigid connection. Additionally, it exhibits stable cyclic behavior and high energy dissipation up to a story drift of at least 6% and satisfies the AISC seismic provisions as a special moment connection.

Spiral-welded tubes (SWTs) are fabricated by helically bending a steel plate-coil and welding the resulting abutting edges. The cost-effectiveness of concrete-filled stainless-steel tube (CFSST) columns can be improved by using SWTs rather than longitudinally welded tubes as their fabrication is more economical and efficient. However, due to the high level of residual stresses and unique imperfection patterns present in SWTs, such concrete-filled spiral-welded stainless-steel tube (CF-SWSST) columns require separate consideration. Even though most practical columns are ‘long columns’, where the capacity is length dependant, only the behaviour of CF-SWSST short columns has previously been investigated. To address this research gap, twelve CF-SWSST long columns with effective length to diameter (Le/D) ratios in the range 10.5–12.0 were tested under axial compression considering end load eccentricity ratios of 0, 0.15D and 0.4D and diameter to thickness ratios (D/t) ranging from 62 to 116. A global flexural buckling type failure mode was obtained for all the tested columns similar to that reported for CFSST long columns of other tube types. It was found that the guidelines of several existing design standards relating to mild-steel concrete-filled steel tube (CFST) columns are directly applicable to CF-SWSST long columns under eccentric loading. However, for concentric loading the predictions were non-conservative indicating that separate guidelines are needed for purely axially loaded CF-SWSSTs, including procedures to consider column slenderness effects of CFSSTs distinct from those specified for mild-steel CFSTs. In addition, fibre-element analyses considering unconfined concrete models gave conservative, yet close, predictions of the experimental eccentric axial capacities which was consistent with the experimentally determined negligible level of concrete confinement.

Bridge weathering steel produced in China has been used in bridges worldwide. Bridge weathering steel Q345qNH is the most common steel grade used in China and for export, the fatigue crack growth thresholds and fatigue crack growth rate (FCGR) parameters of Q345qDNH are investigated in this paper. The FCGR tests are conducted on 9 compact tension (CT) specimens of base metal and butt welds respectively, the fatigue crack growth threshold tests are conducted on 3 CT specimens of base metal. The fatigue crack growth threshold decreases as stress ratio increases, Q345qDNH has considerably higher fatigue crack growth thresholds than Q345qD and universal thresholds given in BS7910. Two data processing methods are employed to calculate characteristic FCGR parameters. The FCGR parameters determined by small sample method are more conservative than those obtained by group sample method. The FCGR of butt weld increases faster than that of base metal as stress intensity range increases, therefore butt weld is more brittle than base metal. Q345qDNH has slower FCGR than Q345qD and the universal parameters given in BS7910, hence Q345qDNH has better fatigue resistance. The fatigue crack growth was numerically simulated, the largest difference between predicted fatigue life and tested fatigue life is 11.3%, therefore fatigue life can be predicted reasonably accurately by numerical simulation on the basis of measured FCGR parameters, which illustrates the potential and effectiveness of numerical simulation for fatigue assessment of complex bridge structural details based on fracture mechanics and the significance to obtain accurate FCGR parameters.

Much research has been conducted on circular hollow steel tubes subjected to indentation loads, but the response of a circular hollow steel tube when subjected to a combination of an indentation load (the load applied by an indenter) acting together with other loading conditions has received markedly less appraisal. An experimental study was conducted on two groups of circular hollow steel tubes that were either free-spanning or were base-supported. These tubes were first subjected to a uniform axial pre-compression, which is the most common service load across many tube applications, followed by the application of indentation loads while the magnitude of axial pre-compression was maintained. Strength, top surface and mid-height cross-sectional deformation, longitudinal and circumferential strains, and the failure mechanism of the tubes were compared, with a significant difference found between the response of the two groups of tests, and with this difference increasing as the magnitude of axial pre-compression and indenter displacement were increased. Additionally, it was identified that for the same level of absorbed energy, a deeper dent was produced for base-supported tubes than for free-spanning specimens. Moreover, analytical equations available in the literature were compared to the experimental results and good correlation was found between the experiments and the predictions.

Many older bridges are constructed with structural systems consisting of a non-composite concrete deck over steel girders. A potentially economical method for strengthening these bridges is to develop composite action by attaching the existing concrete deck to the steel beams using post-installed shear connectors comprised of adhesive anchors. Because fatigue is one of the main concerns in designing bridges, investigating the fatigue properties of these post-installed shear connectors is crucial. Although the fatigue life of post-installed shear connectors has been explored through direct-shear tests, the actual fatigue performance of post-installed shear connectors in large-scale beam tests has not been extensively studied and may differ from component tests. The current paper describes the results of large-scale beam experiments on the fatigue performance of post-installed shear connectors. The results of this research indicate that adhesive anchor post-installed shear connectors have much better fatigue performance in beam tests compared to the previously reported fatigue test results based on direct-shear tests.

The steel-concrete (SC) or steel-concrete-steel (SCS) composite structures are widely used in large-scale structures like immersed tunnels, protection structures, etc., due to their superior performances in capacity, ductility, waterproofness, construction efficiency, etc. The steel plates in these structures are usually stiffened with ribs to increase the out-of-plane rigidity and to improve the local buckling performance. While there have been several applications, the buckling design of the composite stiffened plates, based on the methods for steel structures, is still immature and conservative. To deal with this problem, a selected series method (SSM) based the energy theory is proposed, which could both be utilized in composite stiffened plates and steel stiffened plates. The special series shape functions, which could efficiently and accurately represent the 3-dimentional spatial buckling deformation of the stiffened plates with multiple stiffeners, are selected. The explicit high-order solutions for the buckling stress of stiffened plates are derived. Furthermore, a finite element model (FEM) is established. Based on the FEM, a numerical database including most common design parameters is derived, and extensive numerical analyses are conducted to modify and verify the proposed SSM. It is found that, for steel structures, the SSM has a 10%–20% improvement in accuracy compared with the existing methods, and for composite structures, the SSM fills the blank in this area and has acceptable accuracy for design. Finally, from the above studies, the design suggestions are given and discussed.

With an increasing use of ultra-high performance concrete (UHPC) in civil engineering, steel-concrete composite structures continue to progress. However, studies focusing on headed studs embedded in UHPC are limited, which hinders the design of steel-UHPC composite structures. This paper investigates the shear-resisting behavior of headed studs embedded in thin UHPC by using the finite-element (FE) analysis technique. A FE model was established for a push-out test, aiming to reflect the plastic behavior of the specimens and to evaluate the damage process in the headed studs and UHPC. The analysis results were compared to test results. It was revealed that the load-slip curve, shear strength, and failure mode all agreed well with the experimental observations. A parametric analysis was performed based on the validated FE model. The influence of stud diameter, stud height, and compressive strength of UHPC on the shear behavior of the headed studs was revealed. Further, the shear strengths obtained in the FE analysis were compared to the results predicted through theoretical equations. The comparison indicates that for headed studs embedded in UHPC, the contribution of the weld collar should be considered to evaluate the shear strength.

This paper deals with the shear behaviour of steel stud connectors in composite beams with profiled steel sheeting under static and impact loads. An experimental program including five static and ten impact push-out tests is firstly carried out, and the failure modes, the time history of impact load and slippage displacement, as well as the shear capacity of stud connectors are presented and discussed. Based on the dynamic responses, the influence of the arrangement form of profiled steel sheeting on the shear mechanism of steel stud connectors under impact loading is examined. Moreover, a design proposal developed previously by the authors is verified to reasonably predict the shear capacity of stud connectors with profiled steel sheeting parallel to the steel beam under impact loading. However, it is unsafe to predict the dynamic shear capacity of stud connectors with profiled steel sheeting transverse to the steel beam when the strain rate effect is considered. Additionally, the failure mode of shear connectors with solid slab in this paper is different from that of the previous work, which lead to the lower dynamic shear capacity of the connectors with the solid slab, and some further discussion is also carried out. The testing results can provide an essential data for future analytical and design-oriented study of composite beam with shear stud connectors with profiled steel sheeting under extreme loading conditions.

Residual stress is always present in steel structures and can cause a premature plasticity of the steel and considerably affect the stiffness, ultimate bearing capacity, and fatigue resistance of members or joints. This paper presents experimental and numerical investigations on residual stresses in a hot-bent circular steel tube. Longitudinal residual stresses are measured through a cutting method. The residual stress distribution is symmetrical for both extrados and intrados of a hot-bent circular tube. The maximal tensile or compressive residual stress occurs at the extrados or intrados near the neutral axis of steel tubes. A parametric study with 54 numerical models is then conducted to investigate the influencing factors of the residual stress (e.g. bending ratio, diameter-to-thickness ratio, and steel yield strength). According to the results, the bending ratio (as the most important factor) has a significant influence on the residual stress distribution and magnitude. The results imply that the residual stress and diameter-to-thickness ratio exhibit no distinct correlation. The hot-bent circular tubes with higher steel yield stresses exhibit greater residual stresses. The effects of the yield strength fy can be simplified in the form of the residual stress multiplied by fy/345. Finally, the residual stress model of the hot-bent circular tube is proposed as a polyline formation. It fits the actual residual stress distribution well when the self-equilibrium characteristics are considered.

The real capacity of steel-concrete composite slabs currently used in buildings tends to be governed by the longitudinal shear failure mode. However, in many cases, the design of these structural members according to Eurocode 4, Part 1.1 (EN 1994-1-1) is governed by the vertical shear capacity. The design methodology for the determination of the vertical shear resistance predicted in the referred standard underestimates the shear resistance of steel-concrete composite slabs because it is based on the design model for reinforced concrete slabs stated in Eurocode 2, Part 1.1 (EN 1992-1-1), does not take the contribution of the profiled steel sheeting into account adequately. The results of an experimental programme, comprising 4 experimental tests on short-span steel-concrete composite slabs and carried out at the Department of Civil Engineering of the University of Coimbra, Portugal, are then shown and discussed. In order to induce a failure by vertical shear, the composite slabs tested were provided with a longitudinal shear reinforcement system composed by transversal bars crossing longitudinal stiffeners placed along the upper flange of the steel sheets. The results of the experimental tests were also used to calibrate numerical models, which made it possible to carry out a parametric analysis. The experimental and numerical results showed that the design methodology prescribed by Eurocode 4, Part 1.1 is quite conservative as it underestimates the relevant contribution of the resistance of the profiled steel sheeting to the slab's vertical shear capacity.

Conventional steel-plates-strengthened-composite ring (SPSC) joints are extensively used in composite structures to connect concrete-filled tubular (CFT) columns and reinforced concrete (RC) beams. However, the refinancing-bars of the adjacent beams require on-site welding to the steel strengthened plates of the SPSC joint, which, regarding workmanship, is difficult and time-consuming. Recently, a new type of joint, the steel-concrete-composite-ring (SCCR) joint, has been proposed as a substitute for the SPSC joint since it has been successfully used in several construction projects in Hong Kong. An SCCR joint consists of a steel tube, a concrete ring beam with reinforcements in both the radial and hoop directions, and shear studs. This research develops a sophisticated Finite-Element (FE) modelling method for SCCR joints, where the dominant factors affecting the joint's behaviors are considered, such as the explicit simulation of the complex reinforced bar details and shear studs, the cracking and crushing of concrete, the yielding of reinforced bars, and the contact behaviors between the steel tube and the concrete. From the FE analysis results, four possible failure modes are identified. Parametric studies are sequentially conducted in regard to these modes, yielding corresponding design eqs. A design procedure developed through the proposed equations is illustrated with a flowchart. Finally, a real-world example project is presented and further validated by sophisticated FE analysis.

Fire disaster-induced collapse rarely occurs for space grid structures because of their high redundancy and their fire protection design. Consequently, with reasonable evaluation and repair, most space grid structures after fire can still be used. The post-fire axial compression properties of welded hollow spherical joints, which have been commonly used in space grid structures, were studied through experimental and numerical analyses. Then, the influence of factors such as material mechanical properties, loading condition and plastic residual deformation on the post-fire mechanical properties were analyzed. A calculation formula was presented to evaluate the post-fire bearing capacity of welded hollow spherical joints.

This paper evaluates the influence of supporting frames on the seismic performance of an ultra-high voltage (UHV) gas insulated switchgear (GIS) bushing. Shaking table tests were carried out on a full-size UHV-GIS bushing mounted on two identical supporting frames except for their braces and joints. Finite element analyses were carried out on the joints' stiffness of the two frames, and seismic analyses on the bushing-supporting frame systems were conducted. Afterwards, parametric analyses on the joints' rotational and axial stiffness in the frames were carried out. The results indicated that the dynamic properties of the supporting frames affect the seismic performance of the bushing. After retrofitting, the amplification effects of the frame were reduced, and the seismic performance of the system improved. Moreover, the frame mainly amplified the acceleration response spectra near the fundamental frequency of the frame itself. The supplemented braces made greater contributions to reduce the seismic responses of the GIS bushiung, and increasing the joints' stiffness could reduce the severity of seismic responses on a bushing.

Built-up box sections are becoming increasingly popular for column members in cold-formed steel (CFS) construction; uses of such sections include CFS trusses, space frames, and portal frames. In this article, the built-up box sections are formed through two identical lipped channels connected at their flanges with self-drilling screws. In such an arrangement, independent buckling of the individual channels is prevented by the screws. This paper presents an experimental investigation on axial capacity of built-up CFS box sections. Tests were conducted for different values of slenderness from short to slender columns. In total, the results from 16 experimental tests are reported. Of these, 8 tests were conducted on built-up CFS box sections and the remaining 8 tests were conducted on single channel sections. Load-axial shortening relationship, and failure modes are discussed for built-up columns. Nonlinear finite element (FE) models were developed for built-up CFS box sections and single channels. FE models considered material nonlinearities, initial imperfections and modeling of intermediate fasteners. FE results showed good agreement against the test results. A parametric study was conducted which comprises 148 models to investigate the effect of fastener spacing on axial capacity of built-up CFS box sections. Both FE and test results were compared against the design strengths calculated in accordance with the American Iron and Steel Institute (AISI) and Australian and New Zealand Standards (AS/NZS). From the comparison, it was observed that the AISI & AS/NZS are conservative by around 17% while determining the axial capacity of such built-up CFS box columns.

Structural connections in bridges supporting directly the railway track have cumulated large amount of load cycles from passing trains. The connections were not originally designed for fatigue and some of them have found to be in poor condition by inspection. To study their structural behaviour under large number of repeated load cycles, five 85 year old stringer-to-floorbeam connections from a decommissioned railway bridge were loaded in laboratory. Each connection had four angle plates connecting stringer webs to floorbeams and two connection plates connecting stringer top flanges together. During the load tests, the connection plate maximum stress ranged from 60 MPa to 150 MPa. It was estimated that the peak stresses under traffic were in the range of 40–60 MPa. Despite large stresses in load tests and long active use under traffic, only three connections failed after 0.5–1.6 million load cycles. Two connection tests were run out after 2.4 and 2.6 million cycles. By measuring strains and displacements continuously during testing it was seen that failures occurred gradually as components fractured slowly during tens of thousands of cycles. Any of the connection failures was not complete and the connections showed substantial residual bending stiffness and capacity after failure. Load tests showed that even if connection is seen to be in poor condition and close to its theoretical fatigue life, it still might function safely for hundreds of thousands of stress cycles if stress redistribution between connection components is possible and connection is monitored for major fractures.

Based on two quasi-static experiments of steel tube confined reinforced concrete columns (STRC) under pure torsion load, detailed finite element (FE) simulation and theoretical derivation of the corresponding calculation methods were conducted in this paper. FE models of STRC specimens under pure torsion were established using the finite element software ABAQUS, the feasibility of which was then validated against the testing results in terms of both ultimate torsional capacity and failure modes. Comprehensive parametric analysis was presented, including the yield strength of steel tube, the thickness of steel tube, the dimension of cross-section, the strength of concrete, the yield strength of longitudinal reinforcement, the ratio of longitudinal reinforcement, the yield strength and the ratio of stirrup, to investigate the influence on the torsional capacity of STRC columns with important structural factors. It can be found from the parametric analysis results that, the thickness of steel tube, the dimension of cross-section and the ratio of longitudinal reinforcement are the most important parameters for the torsional capacity of STRC. Based on the results parametric analysis, an accurate and simplified calculation method for the ultimate torsional capacity of STRC columns under pure torsion was proposed.

It is commonly known that compression resistance of longitudinally stiffened orthotropic plates depends on both the column and plate-like behavior. Large number of previous investigations studied the structural behavior of stiffened plates subjected to compression. However, a comprehensive investigation and a parametric study is not available in the international literature about applicable interpolation function for plates having closed section stiffeners. It is known from previous research results that the interpolation function can be different depending on the calculation method of the critical stresses (analytical or numerical). It is also known, that the application of the numerically computed critical stresses in the Eurocode based design method can lead to overestimation of the compression resistance through the increased critical stress resulting in smaller slenderness ratio. However, there is no recommendation for applicable interpolation formula when computed critical stresses are used by the designers. Therefore, the current research program focuses on the investigation of longitudinally stiffened orthotropic plates, studying the interpolation curve between plate and column-like buckling behavior. The applicability of the EN 1993-1-5 based interpolation curve is discussed and evaluated. The reason of the differences by using analytical and numerical critical stresses are explained and applicable interpolation function is proposed for both cases.

Double skin steel-concrete composite walls offer structural merits over conventional reinforced concrete walls in terms of high strength, good ductility and convenience for construction. The stability of the external steel faceplates is significantly influenced by the types of internal mechanical connectors and the ratio of connector spacing to plate thickness. In this paper, a new type of steel truss was proposed as the fastener to connect the two faceplates. Compressive tests were conducted on three full-scaled composite walls with different truss spacing. The structural response of the walls was comprehensively discussed in terms of failure modes, load-axial displacement response, buckling stress, stiffness, ductility, strength index, load versus out-of-plane displacement response, and load-strain curves. The influences of truss spacing on key parameters were explored in details. The test results showed that the truss spacing could considerably affect the buckling shapes, load-carrying capacity, stiffness and ductility of the specimens.

The seismic performance assessment of bridges by nonlinear time history analysis using unidirectional spectrum-matched accelerograms is generally adopted in Japan's specifications. However, the simultaneous action of two horizontal components is known to induce a potentially higher inelastic response in steel piers relative to that under unidirectional excitation. In this background, a rising concern within research communities is the bidirectional effect on the risk of bridge failure or damage under a given seismic intensity during the service life of a bridge. In this study, the difference in the risk of steel pier damage/failure between unidirectional ground motion and bidirectional ground motion is assessed using seismic fragility. Fragility curves are constructed by subjecting a single steel pier with various geometric designs to a large number of earthquake ground motions using the incremental dynamic analysis methodology. The study indicates that the damage state of collapse is not changed by bidirectional excitations, whereas the use of bidirectional excitations in less damaging states reduces the bridge seismic performance and induces higher fragility. The response difference is quantified by introducing an equifragility factor. This factor is calculated as the ratio of intensity of the unidirectional input to the bidirectional input, which causes the same fragility caused by the unidirectional counterpart. The constant characteristic value of the equifragility factor provides useful information for considering the bidirectional effect in seismic design.

In recent years, the prequalified rigid connections of radius-cut reduced beam section (RBS) have been widely used in the design and construction of steel moment frames. Despite extensive investigations performed on the seismic performance of RBS connections, there is little research into the impact of these connections upon the elastic story drift in steel moment frames. In the current study, a precise formulation (partially based on a previous research) has been developed so as to evaluate the amount of stiffness variation or amplified elastic drift introduced by radius-cut RBS connections in a story of steel moment frames. Herein, by defining a novel and accurate method along with the method of virtual work, the amplified elastic drift of a 2-dimensional one-story single-span moment frame due to utilizing radius-cut RBS connections is calculated. The reliability and accuracy of the presented approach are validated using finite element modeling of the moment frame. Sensitivity analyses are also conducted upon the RBS connection parameters to derive the most effective parameters on the amount of elastic drift in steel moment frames. Then, by employing a statistical approach called response surface method (RSM) and combining findings of this study with some premises considered in a previous research, rigorous amplification factor of elastic drift formulas based on utilizing each of IPE and HEA beams in a story (from the first to the last one) with RBS connections are developed. Ultimately, two simple, linear, and functional amplification factor of elastic story drift formulas for each set of IPE and HEA story beams with RBS connections are proposed for designers. The scope of these formulas will be expanded to plate girders as well.

Non-structural components contribute significantly to the lateral stiffness of a cold-formed steel (CFS) building structure, but are cumbersome to model explicitly in the structural analysis. They are therefore commonly ignored in a 3D structural analysis, and their benefits are lost to the design. This paper proposes an efficient modelling method that enables practical and accurate 3D elastic analysis of a multi-storey CFS building structure to study its lateral behaviour within the serviceability limit state. Each shear or gravity wall is represented by an equivalent shear modulus four-node orthotropic shell element, which incorporates the lateral stiffness (or flexibility) contributions of all components including sheathing, braces and fasteners as present in the wall. The equivalent shear modulus is determined from the experimental test of a representative wall panel, or from the analysis of a finely detailed finite element model of the panel. The resulting two-storey building model, which has much fewer degrees of freedom compared to conventional models, is verified against full-scale shake table test results with respect to the natural period, the peak storey drift and the peak floor acceleration at two different construction phases. This paper demonstrates that the proposed modelling method not only saves analysis time considerably through the drastic reduction of degrees of freedom, but also compares favourably against a published modelling method in terms of accuracy and modelling efforts.

A reciprocating constitutive model of cold-formed thick-walled rectangular steel tube was constructed by a reciprocating loading test and then used to determine the influences of strain hardening on the seismic behavior of the tube. A cold-formed thick-walled rectangular steel tube with a side range of 600–800 mm and thickness range of 16–22 mm was used as the research object. The mechanical properties and constitutive models at different positions, such as the weld, adjacent weld, corner, and flat regions, were investigated through a reciprocating loading experiment under seven loading patterns. The recommended values of Ramberg–Osgood model's cyclic hardening parameters were provided on the basis of a skeleton curve. Based on the experimental data, a refined constitutive model that involves monotonic loading, loading along the skeleton curve, unloading, and reloading was proposed and was compiled by applying the user-defined material subroutine of ABAQUS-UMAT. The simulation results of UMAT conformed well with the experimental results. Therefore, the proposed constitutive model is applicable to studies on the seismic behaviors of ultra-thick cold-formed rectangular steel tubes.

To meet the requirements of good seismic behavior, rapid assembly, and economic feasibility for a high-rise steel residential apartment, the authors developed two innovative double-skin composite walls (DSCWs) with L-shaped and C-shaped connectors. DSCWs are composed of concrete-filled double steel faceplates, which are divided into several compartments by connectors and two boundary columns filled with concrete at the ends of the composite wall. In this paper, eight DSCWs were tested under cyclic loads to investigate the seismic behavior of these new composite walls considering the effect of low axial compression ratio and spacing-to-thickness ratio. Results show that no significant buckling of steel faceplates was observed before the peak load was reached. No obvious pinching effect was observed on the hysteresis curves for all specimens. Ultimate drift ratio ranged from 1/59 to 1/45, and the ductility coefficients varied from 2.45 to 3.80. The equivalent viscous damping coefficient versus drift ratio curves were close to an exponential distribution, and all specimens exhibited great energy dissipation capacity. The strain on connectors was below the yield strain throughout the experimental process, indicating the connectors have a good working performance. Finally, formulas were established for calculating the load-carrying capacity.

Metal dampers have been widely used to improve the seismic performance of the building structure. However, conventional metal dampers only possess one yield point and cannot protect the structure efficiently under earthquakes of different intensities. A new type of metal damper composed of two annular metal dampers with different sizes is proposed in this paper. It is a graded yield metal damper having two yield points, which can be used to reduce the responses of the structure efficiently under earthquakes of different intensities. Firstly, the mechanical properties of single annular metal damper, such as the failure mechanism, hysteretic behavior and anti-fatigue performance, are investigated by cyclic loading tests. The test results show that the annular metal dampers possess large deformation capacity and energy-dissipation capacity as well as excellent anti-fatigue performance. The calculation formulae are derived to determine major mechanical parameters of the damper. The theoretical results obtained by using the proposed calculation formulae are in good agreement with experimental results. Cyclic loading tests are carried out on the graded yield metal damper. The yielding process of the graded yield metal damper is simulated using the ABAQUS program. The trilinear kinematic hardening model is adopted to simulate the hysteretic behavior of the damper. Nonlinear time history analyses are carried out to compare the responses of a conventional reinforced concrete (RC) moment-resisting frame structure with that of the structure installed with the graded yield metal dampers under three levels of earthquakes using SAP2000. The results indicate that the seismic performance of the structure installed with the graded yield metal dampers under all levels of earthquakes is improved significantly. The graded yield metal dampers are more effective in displacement control of reinforced concrete moment-resisting frame structure in comparison with single yield point metal dampers.

In order to examine and compare welding-induced residual stresses in welded H-sections of different steel grades and heat input energy, extensive parametric studies were carried out using fully calibrated and highly efficient finite element models to perform coupled thermomechanical analyses. Numerical results including temperature history and distributions, residual stress distributions and magnitudes, and force equilibrium were discussed, and comparisons were made between calibrated finite element models with different steel grades, and different heat input energy during welding. It was established that the residual stresses in S690 welded H-sections were proportionally less pronounced when compared with those in S355 welded H-sections of similar dimensions. Residual stresses in multi-pass S355 and S690 welded H-sections were shown to be significantly reduced, when compared with those in single-pass welded H-sections of similar dimensions. A simplified pattern was proposed to describe both the distributions and the magnitudes of residual stresses, and a set of formulae was also provided. It was confirmed that the residual stress pattern given in a definitive ECCS document for S355 sections was very conservative, and applicability of that pattern to S690 welded H-sections would significantly over-estimate residual stresses in these S690 sections. Hence, the proposed residual stress pattern together with the set of formulae for both S355 and S690 welded H-sections with single-pass and multi-pass welding should be adopted for accurate prediction of their structural behaviour.

Experimental researches on the behaviors of large-diameter concrete-filled steel tube (CFT) columns are quite limited because of expenses and capacity of testing equipment. Finite element (FE) technique is an alternative and efficient method if suitable models of materials are available. Many FE models have been proposed to simulate the behaviors of CFT columns. Results predicted by the existing models are generally found to agree well with the experimental results of CFT columns, the diameters of which, however, are generally

The basic features of residual stress generated by patch-plate welding for the repair of steel structural members were examined through a series of experiments and numerical simulations. The welding residual stresses in the patch and base plates covered by the patch plate comprised of tension and compression, respectively. The reason for this tendency might be the difference in the temperature rise during welding owing to the size difference between the patch plate and the base plate. A high tensile residual stress close to the yield stress of the material was generated at the weld toe along the direction across the weld line. The fatigue life of the patch-plate joints was improved by residual-stress release with post-weld heat treatment (PWHT) using an induction-heating device available for the repair of existing steel structural members. Furthermore, a simulation method for this PWHT process, which was expected to be useful for investigating the PWHT conditions of actual structural members, was proposed.

The cooling tower is a very important building for the thermal power plant. The large steel cooling tower is proposed to overcome the serious challenges that arise from modern cooling towers being higher, larger, and more complex. In this study, for the large-scale hyperbolic steel cooling tower, seven different latticed shell systems with different grid forms, including five double-layer systems and two single-layer systems, were designed and studied in detail. For different heights, grid sizes, and shell thicknesses, numerous parametric analyses (792 models) of the structures were performed. The static behaviors—including the steel quantity, peak displacement, and peak stress—of the seven structural systems were obtained and compared. The variation laws of the steel quantity and peak displacement with respect to the parameters were presented, and the reasonable range of the parameters for the steel cooling tower with different heights were obtained. The results show that the optimal structural system is different for the steel cooling towers with different heights. Additionally, based on the nonlinear stability analysis, a reasonable strengthening scheme was proposed for the single-layer system with poor stability. The results will be of great help for further research on large steel cooling towers and provide guidance for actual engineering design of the structures.

A new type of tubular joint made of rectangular hollow section (RHS) braces welded onto concrete-filled RHS (CFRHS) chords stiffened by longitudinally welding perfobond ribs to the inner faces has been studied earlier and demonstrated a better fatigue behaviour than a conventional empty RHS joint. In this paper, stress concentration factor (SCF) parametric design equations were developed for CFRHS K-joints with perfobond ribs through finite element (FE) analysis to fill a gap in current design guides for this type of K-joints. Three-dimensional FE models were developed using the ABAQUS software to simulate the hot spot stress distribution at the brace-chord intersection. FE results were successfully verified using experimental results of nine Y-joints from literature and one truss K-joint in this research. A comprehensive parametric study including 570 models was then carried out on CFRHS K-joints with perfobond ribs to examine the SCFs with five key dimensionless geometric parameters and three basic loading conditions involving axial loading in the chord and brace and bending in the chord. Consequently, a total of 36 SCF parametric equations were established using regression analysis. Subsequently, the number of formulae was reduced to six equations to predict the maximum SCFs for practical application.

The behavior of eight-bolt extended endplate connection with circular bolts configuration under monotonic and cyclic loadings was experimentally investigated. The results of a series of component experimental tests and finite element (FE) simulations were used to develop a strength model to predict the connection capacity and prying forces. The effect of the column flange thickness, the endplate thickness, and the bolt diameter on the connection performance and the prying forces were investigated. Three failure modes were identified. Based on the experimental and FE results, a design procedure and an example were proposed. The results showed that a minimum of 7.4 bolts out of the 8 bolts present in the investigated connections were effective in carrying the applied load and reached their full capacity at the point of ultimate. This leads to a higher design capacity of the connection. Compared to the rectangular bolt configuration, the circular configuration requires less fabrication when omitting stiffeners but requires thicker endplate.

The main objective of the research program is to develop solid knowledge on the structural behavior of curved steel panels for optimized applications in steel and composite bridges. Moreover, the new findings in this field should spur and contribute to the extension of the EN 1993-1-5 design methodology, which is still limited only to the design of flat plates. Therefore, two identical prototype box-girder bridge segments, in scale 1:3 with respect to a real study case, with two different steel grades (S460 and S690) were experimentally tested. Segments are tested as three-point bending tests, with the aim to assess the complex behavior of a box girder bridge deck near the intermediate support, where the moment-shear (M - V) interaction occurs. This paper gives a detailed description of the experimental program executed and most relevant results, which will be used for the calibration of a numerical model, where the influence of several key parameters will be further investigated.

Although the stochastic nature of several parameters, the application of the methodology given in EN1993-1-5:2006 for the determination of the resistance of class 4 cross-sections under direct stresses leads to the use of the effective area where each plate is individually assessed by a semi-empirical approach proposed by Winter in 1947. Once the level of reliability of this approach is not adequate in light of the rules given in EN1990, this paper aims at finding the actual safety level of the methodology given in EN1993-1-5. In order to achieved this, Monte Carlo simulations with a Latin Hypercube sampling strategy is performed in selected cross-sections under pure compression and pure bending with varying slenderness and aspect ratio of the web plate. All parameters are stochastically modelled, and each generated element (I- and H-section stubs) is numerically computed using a general-purpose finite element software. The final results are actual partial factors values and width reduction factors for each cross-section.

Based on field investigation of a damaged transmission line following Typhoon Mujigae in 2015, a failure analysis is performed to estimate the load-bearing capacity of a transmission tower. Static nonlinear buckling analysis and dynamic analysis are employed to assess the ultimate load capacity and the most vulnerable parts of the tower. In the dynamic analysis, a tower-line (TL) coupled model is established which accounts for members buckling capacity. The two methodologies predicted close wind load capacity (34.8 m/s in static analysis and 34 m/s in dynamic analysis), while the failure modes and buckled members are different. While static analysis shows that the leg members buckled, dynamic analysis reveals that it is the diagonal members that buckle. Reasons are explained in this paper and suggestions are given that the dynamic analysis should be adopted in integrally evaluating a transmission tower, especially when locating the buckled member. More, emphasis should be given to the design of diagonal members.

Press-braking is one of the typical cold-forming techniques in manufacturing stainless steel members. In general, cold-forming process brings material strength enhancement, which can be utilized in advanced design methods to reduce the initial cost of stainless steel structures. This paper is targeted at the accurate predictions of material properties in the press-braked austenitic stainless steel sections. A series of material tensile tests were carried out on press-braked austenitic stainless steel corner sections with varied ratios of the inner corner radius over the thickness. Material properties of corner sections were obtained and compared with those of virgin sheets, which shows considerable increases in nominal yield stress and ultimate tensile stress, and reduction in elongation. Based on test data and “equivalent plastic strain” concept, material strength enhancement model was developed for each material parameter. Predictions using material strength enhancement models were compared with test data in this study and literature, which indicates that the proposed models could give not only accurate predictions for the normal yield stress in press-braked austenitic and ferritic stainless steel corner sections, but also provide reasonable predictions for full-range stress-strain curves.

In recent years, advanced manufacturing techniques, such as high-definition plasma, water jet, and laser cutting, have opened up an opportunity to create a new class of steel connections that rely on intermeshed (i.e. interlocked) components. The main advantage of this type of connection is that they do not require either welding or bolting, which allows faster construction. Although the interest in intermeshed connections has increased in recent years, the mechanical behavior of these connections has not been fully understood. This paper presents a numerical study on the ultimate load capacity failure modes of intermeshed connections under mixed-mode loading. The experimental behavior of the connection components is also investigated through a series of tests. The study considers a recently developed intermeshed connection for beams and columns. The numerical simulations were performed by using a commercially available 3D finite element software package. By considering different types of mixed mode loading, interaction diagrams of axial, shear, and moment capacities of the intermeshed connection were obtained. The results indicated that there exists an intricate interaction among axial, shear, and moment capacities, which arises from the intermeshed configuration of the flanges and web. For each interaction diagram, the corresponding failure mechanism was analyzed. The simulated interaction between axial, shear, and moment capacities were further compared with the provision of the current design codes. While the intermeshed connection studied here showed promise for gravity loading, further study is needed to ensure alignment of the flanges so as to avoid axial and/or flexural failures.

Application of high-strength steel can serve improving structural efficiency as well as solve structural problems when traditional materials are inapplicable due to strength limitations. Innovative structural solutions, however, are facing problems related to the absence of corresponding design procedures and reliable constitutive models. Cold-formed profiles are frequently used as structural elements in buildings. The enhancement of a material strength in the profiles with nominal geometry increases slenderness of the cross-section that can cause a local increase of deformations due to high stress concentrations. The increase is a consequence of web crippling often followed by failure of the flange. The investigation of the combined web crippling and flange failure effects is rather complicated due to localized deformed behaviour that is not a trivial subject for experimental identification. The premature deformation increase in a critical cross-section is not necessarily caused failure of the profile that continues to carry further loads. This paper investigates local deformation effects in cold-formed square tubular profiles subjected to bending load. A four-point bending test was used to estimate the effect of local nonlinear deformation on the overall deformation behaviour. The profiles made of high strength steel S700 and S900 grades were considered. Similar profiles made of the steel S355 were tested for the reference. A digital image correlation system was used to monitor deformations of the web surface. A nonlinear finite element model was developed to investigate the local deformation effects on the overall deformation behaviour and load-bearing capacity of the profiles. The model was customized with the reference to the experimental results. After the verification, it was used to illustrate deformation analysis procedure of a continuous tubular beam.

This paper investigates the effects of bolt threads on the initial and final stiffnesses of double-shear bolted connections through laboratory tests and finite element (FE) analyses. Nineteen specimens composed of 4.7 mm and 8.0 mm thick structural steel plates with bolt diameters of 20 mm and 30 mm having varying end distances are studied. The investigation, which involves shank and thread bolted connections, has found that the threads reduce the initial stiffness but increase the final stiffness. The FE analysis shows that the reduction in the initial stiffness is due to the bolt threads cutting into the connected plate, increasing the initial displacement. However, the same factor moderates the softening behaviour of a thread bolted connection as it approaches its ultimate capacity. The FE simulation shows that in certain cases this newly discovered phenomenon is caused by the threads restraining the crimpling of the plate material downstream of it. The present modelling technique significantly improves the simulation results of bolted connections tested by independent researchers, compared to their own modelling techniques including that which attempts to simulate the thread effects by reducing the diameter of the bolt model. The “elastic” stiffness values obtained from the present laboratory tests are compared against the Eurocode's provision based on the ASTM definition, and ad hoc stiffness formulae are proposed for shank and thread bolted connections.

Cold-formed steel composite floor systems have been widely used in cold-formed steel framing for mid-rise building construction, primarily owing to its structural and economic efficiency. The composite floors consist of cold-formed steel C-shape joists and subfloor with cold-formed steel form-deck and gypsum-based self-leveling underlayment. This paper presents a theoretical method, an experimental investigation, and a simplified model analysis on the in-plane displacement of cold-formed steel composite floors under horizontal loads. Based on the design method of timber floors, the calculation methodology of the mid-span in-plane displacement of cold-formed steel floor with steel form-deck and gypsum-based self-leveling underlayment is proposed. Subsequently, cyclic shear tests of two full-scale floors with and without gypsum-based self-leveling underlayment were executed to investigate the failure mode, load bearing capacity, and in-plane displacement. The test results indicated that the primary failure mode of the specimens was the shear failure of self-drilling screws that connected the steel form-deck and end joists. Furthermore, the in-plane displacement of the test results agreed well with that of the proposed method. Finally, referring to the deformation results of floors under different loading stages, the composite floor analysis model was simplified to a nonlinear diagonal spring model according to the method of equivalent in-plane stiffness, and it was verified through ABAQUS finite element analysis. This study provides a useful design basis for the design and application of cold-formed steel composite floors.

Reusing structural elements is an effective way to prompt sustainable development with reduced energy consumption and gas emission. In current practice, steel members can be easily deconstructed and reused whilst the recycling of structural materials in steel-concrete composite construction has been found challenging. With the increasing material consumption in composite construction due to their well-recognized structural benefits, it is essential to explore the demountability of such structures. Limited previous research indicates that there is a lack of understanding or mature design specification for demountable composite connections. This paper thus presents an innovative design of demountable K-joints with concrete-filled steel tubular (CFST) chords and circular hollow section (CHS) braces connected using blind bolts. A detailed finite element analysis (FEA) modelling was established and validated against reported test data on both bolted and welded CFST connections. The model was then used to evaluate the possible failure modes, full-range load-deformation relationships, stress distributions and material interactions for the innovative connections. Behaviour of the demountable CFST K-joints was compared with that of traditional welded ones. Finally, simplified methods for the strength prediction of demountable CFST K-joints were proposed based on theoretical derivation and parametric analysis on the effects of various factors.

To examine the seismic performance of steel plate shear walls (SPSWs) and the corresponding steel plate reinforced concrete composite shear walls (SPCSWs), six 1:2 scale shear wall specimens (flat, vertical and horizontal corrugated SPSWs and the corresponding SPCSWs) are tested. The deformation capacity and failure modes of the specimens under cyclic loading are studied. The force–displacement hysteretic curves, envelope curves, bearing capacity and displacement values at various stages are obtained. The failure characteristics, deformation and energy dissipation capacity and the stiffness and the characteristics of degradation of the bearing capacity are analysed, and the design formulas of the shearing capacity of corrugated SPSWs and the corrugated SPCSWs are also proposed. The test results indicate that the lateral stiffness, ductility and energy dissipation capacity of composite shear walls are all better than those of the SPSWs. The lateral force bearing capacity of flat steel plate, vertical corrugated and horizontal corrugated SPCSW are 176%, 92%, 41% higher than that of the corresponding SPSWs, respectively. The displacement ductility coefficient of flat steel plate, vertical corrugated steel plate and horizontal corrugated steel plate composite wall is 1.86, 1.6 and 1.83 times higher than that of corresponding SPSWs, respectively. Due to the mechanical constraints that concrete applies to steel, the initial stiffness of composite shear walls is considerably higher than that of SPSWs.

In this study, a discontinuous cover plate connection (DCPC) was proposed for a prefabricated steel plate shear wall with a beam-only-connected infill plate. This design is suitable for prefabricated high-rise steel structures and assumes that bolt slippage does not precede the yielding of the steel plate tension field. Three 1/3-scale specimens were designed, and the hysteretic behaviour, skeleton curves, energy dissipation capacity, ductility, and failure modes were investigated using quasi-static tests and finite element analyses. Then, the hysteretic behaviour, ductility, and energy dissipation capacity of the prefabricated steel plate shear wall were compared to those of a traditional welded steel plate shear wall through finite element analyses. The results showed that the prefabricated steel plate shear wall with a DCPC had good hysteretic behaviour, energy dissipation capacity, and ductility. Further, the bolt pre-tightening force in the connection was directly proportional to the thickness of the infill plate. The ultimate lateral bearing capacity of the prefabricated steel plate shear wall was slightly less than that of the welded steel plate shear wall. In addition, the prefabricated steel plate shear wall can be assembled rapidly and simply on-site, and it provides a good post-earthquake repairable function.

A mechanical model is developed to predict the time-independent (fast) and time-dependent (due to thermal creep) force-rotation characteristics of shear tab connections subjected to fire. The time-independent behavior of the connection is modeled using a group of springs that can predict the rotational stiffness and the strength of the connection when subjected to fire temperatures. A modified Burgers model is incorporated in the mechanical model to include the thermal creep effect. The modified Burgers model is composed of linear springs and viscous dashpots that can predict the time-dependent behavior of the shear tab connection before and after beam-column contact, and bolt bearing. The proposed model shows excellent agreement when compared with experimental results and finite element (FE) simulations. Furthermore, isochronous curves are developed to study explicitly the effect of different parameters, on the strength and rotational capacity of shear tab connections. The proposed model can be considered an important step toward the inclusion of thermal creep in fire design of shear tab connections.

To study the fatigue and fracture behavior of I-shaped steel bracing members, numerical simulations based on OpenSees for 18 Q235 and 21 ST12 welded steel braces under constant-amplitude cyclic axial displacement were conducted. As the numerical results are consistent with experimental data, a representative strain, which is modified by correlative parameters (including slenderness ratio, width-to-thickness ratio, height-to-thickness ratio and yield stress) of the brace and calculated by corresponding equations, has been proposed as a new control parameter to predict the fracture life of bracing members under low-cycle fatigue loads. According to the good logarithmic—linear relationship between the representative strain and the fracture life, the predicted fracture lives of all specimens were almost always located within a safe scatter band of 1.5. Moreover, the miner method was used for calculating the cumulative damage of 39 bracing members. An allowable damage factor was discussed to assess the fatigue damage and to predict the fracture life under a variable-amplitude cyclic load. Then, a simulation of 5 single diagonal and 8 inverted-V braced frame tests was conducted. It was found that the predicted fracture lives of all these braced frames are very close to their true lives shown in tests and are mostly located within a safe scatter band of 1.5, indicating that the simulation can provide a relatively accurate evaluation on the fatigue performance. In addition, the damage distribution and damage development of the brace section in simulations are in good agreement with the failure mode in the physical tests, which can generally correspond to the cracking process and the complete fracture behavior of the bracing members.