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In the current work, for the first time, bending and vibration information of the axisymmetric thick annular nanoplate made of laminated composite layers is studied. The structure is placed on Winkler-Pasternak substrate with elastic and tortional coefficients. Initial stress as an external load is also considered in the composite structure. For modeling the mechanical deformation in layer-wise composite materials, zigzag theory that its functions themselves are continues in the interface of layers is presented. By coupled quasi-3D new refined theory (Q3D-NRT) and nonlocal strain gradient theory are used for obtaining the nonclassical governing equations a general boundary condition of the current composite nanoplate. Also, for obtaining the static and dynamic equations of the current nanostructure, Hamilton's, and Minimum total potential energy principles are used, respectively. Via differential quadrature method with weighting factors and nth-order derivative, the nonclassical governing equations with the aid of size-dependent boundary conditions are solved. By comparing the current results with the outputs of previous reports, the accuracy of the results is shown. [ABSTRACT FROM AUTHOR]

The material properties of high-strength steels deteriorate under fire conditions and depends on the temperature and fire duration. As a time-dependent inelastic strain behavior, the thermal creep effect becomes significant at elevated temperatures and influences the fire resistance of connections. This paper presents numerical studies on the fire response of unprotected extended end-plate connections made of high-strength steels (Q460, Q690 and Q960), explicitly considering the creep effect. Transient state finite element models including or excluding creep were developed using ABAQUS and validated against the experimental results under the restrained sub-framework. The numerical analysis results exhibit a better agreement with the experimental results regarding the deformation ability and failure mode if the creep effect is considered. Thus, creep is a non-negligible effect in investigating the fire performance of end-plate joints. Parametric studies were carried out to quantitatively assess the influence of moment ratio of connection, axial pressure ratio of column, end-plate thickness and heating rates on rotation–time–temperature characteristics and stress distribution. The numerical results show that the magnitudes of bending moment applied on the connection and axial load on the column play crucial roles in evaluating the fire endurance and critical temperatures. However, the effect of end-plate thickness on the fire-structural behavior of extended end-plate connections is negligible. The heating rate has little effect on the critical temperatures of connections. The rotation capacity of high-strength steel extended end-plate connections depends on the failure mode to a large extent. Finally, fire resistance design suggestions for high-strength steel end-plate connections were put forward according to the observations on the parametric studies. [ABSTRACT FROM AUTHOR]

Using precast concrete floors can greatly improve the construction efficiency of steel structures, and the development of the connection between precast slabs affects the application of precast concrete floors in steel structures. In this paper, a new connection between the precast concrete floor and steel beam is proposed. The bending capacity of the connection was investigated through experiments, and compared with that of the cast-in-place floor. The test results showed that the reliability of the new connection was excellent, and the bending capacity of the floor with this connection is basically the same as that of the cast-in-place floor. The finite element software ABAQUS was employed to simulate the bending behavior of the new connection floor and cast-in-place floor, and the feasibility of the model was verified by comparing it with the experimental results. The model was used to analyze the structural response of the two types of composite beams composed of new connections and precast floor, cast-in-place floor, and steel beam, respectively. The load-bearing capacity and failure modes of the two composite beams were compared. The results showed that the bearing capacity of the composite beam fabricated with the new connection can reach that of the cast-in-place floor composite beam. This is only a preliminary investigation about the new connection and there are some limitations as well. [ABSTRACT FROM AUTHOR]

An innovative cold-formed steel center-sheathed shear walls (CFSCSSWs) was proposed in this paper to improve the horizontal load-carrying capacity of conventional cold-formed steel walls. However, the fire behavior of this wall configuration was particularly worthy of attention because it was designed to be used in multi-story buildings, and there is still a lack of in-depth exploration of the fire performance and high-temperature horizontal load-bearing capacity of CFSCSSWs under combined loads. In this study, a compression test was first carried out to obtain the vertical load-carrying capacity of a full-scale CFSCSSW, followed by a fire test on a similar CFSCSSW subjected to combined vertical and horizontal loads to investigate the fire behavior of walls. Then, a finite element model was established and validated by test results to investigate the influence of various critical factors, including vertical and horizontal load ratios, height-width ratio, and sheathing thickness, on the fire behavior of the CFSCSSW. The results showed that the vertical load ratio presented a larger influence on the fire behavior of CFSCSSWs compared to the horizontal load ratio. The increasing aspect ratio can slightly improve the fire resistance of the wall under the same load ratio. The wall with a 0.8 mm thick sheathing exhibits better fire behavior under the same load ratio. A high-temperature horizontal load-carrying capacity calculation method for CFSCSSWs was proposed, and its good accuracy was found. • Load capacity of cold-formed steel center-sheathed shear wall was investigated experimentally and numerically. • Parametric analysis was conducted to investigate the influence of key parameters on the fire behavior of the wall. • A method for predicting high-temperature horizontal load capacity of the wall was proposed. [ABSTRACT FROM AUTHOR]

Conventional cold-formed steel wall systems suffer from low lateral loading-carrying capacities and stiffnesses, which represent the main barrier to their use in multi-story buildings. To address it, a cold-formed steel center-sheathed shear wall (CFSCSSW) system with higher lateral load-carrying capacity and better lateral structural performance is proposed. This paper presents experimental, numerical, and analytical studies on the behavior of the proposed CFSCSSW subjected to combined vertical and horizontal loads. Firstly, a full-scale test was conducted, with the test setup, loading procedures and measuring instrument reported in detail. The obtained test results, including the load-carrying capacity, failure mode and strains, were fully analyzed. Then, finite element modeling was conducted to simulate the experimental observations, and parametric studies were carried out to investigate the influences of different geometric and loading parameters on the behavior of CFSCSSWs. Finally, a three-strip model with a variable position on end studs (TSM-VPC) was proposed for CFSCSSWs and shown to accurately simulate the direction of the tensile field within the sheathing and also resulted in high accuracy in calculating the load-carrying capacities, followed by a design example. ● An innovative cold-formed steel center-sheathed shear wall (CFSCSSW) system is proposed. ● A full-scale test on CFSCSSW under combined loading is conducted, with test results fully analysed. ● The influences of key geometric and loading parameters are investigated through parametric studies. ● A three-strip model is proposed for calculating the load-carrying capacity of CFSCSSW. [ABSTRACT FROM AUTHOR]

• Post fire tests of the high strength Q960 steel columns were carried out. • Numerical models were developed to predict post fire response of Q960 steel columns. • A post-fire design method was proposed to evaluate the load capacity of Q960 steel columns after fire exposure. High-strength steel exhibits extensive potential in large-span buildings and bridges. Therefore, it is of great significance to clarify its mechanical properties particularly in the realm of post-fire building repair and reconstruction, making it imperative to elucidate its bearing capacity after exposure to elevated temperatures. To comprehensively investigate the overall stability of high-strength Q960 steel columns under high-temperature conditions, a series of axial compression bearing capacity tests are conducted on eight Q960 steel columns—four of which featured H-shaped sections and the remaining four being box-shaped sections. The design of these members considered the effects of slenderness ratio and temperature. At the same time, the residual stress and geometric initial defects of the steel column were measured. Furthermore, the axial compression model for Q960 steel columns, encompassing both room and high-temperature scenarios, was established using the ABAQUS finite element software. This model duly accounted for the influence of residual stress and geometric initial defects. Subsequently, the test outcomes, encompassing horizontal and vertical displacements, ultimate bearing capacity, and failure mode, were compared with the results obtained from finite element analysis. This comparison serves to validate the accuracy of the model while facilitating parameter analysis. The results based on both the finite element analysis and experimental findings, indicate that when employing the Chinese code GB 50,017–2017, the stability coefficient calculation for Q960 steel columns following high-temperature exposure yields satisfactory safety margins. In light of these findings, a calculation method is proposed to accurately predict the stability coefficient of Q960 steel columns in the aftermath of high-temperature conditions, thus offering a reliable approach for assessing the stability bearing capacity of such columns in such scenarios. By comparing with EN 1993–1–12 and ANSI/AISC 360–22, it is found that EN 1993–1–12 has a better prediction effect, while ANSI/AISC 360–22 is conservative when the slenderness ratio is small. [ABSTRACT FROM AUTHOR]

The current cold-formed steel (CFS) wall is limited to the low-rise cold-formed thin-walled steel structure, which is inappropriate for multi-story constructions due to its low shear resistance and poor corrosion resistance of outer sheathing board. Therefore, a new composite wall of CFS frame sheathing with concrete and plasterboard was proposed, the cast-in situ concrete layer was used for the outer surface in response to the needs of corrosion resistance, and the plasterboard was utilized for the inner surface to reduce weight. This paper presented a quasi-static test on the seismic behavior of one CFS wall and three composite-walls' sheathings with concrete and plasterboard to obtain different failure modes and investigate the influence of different sheathing and opening sizes. Combined with the finite element model, a large parametric study of composite walls was conducted to analyze the impact of load ratio, reinforcement ratio, sheathing board, and concrete and steel strength. Test and finite element analysis (FEA) results demonstrate that the seismic performance of composite walls with concrete and plasterboard is satisfactory considering their shear strength, ductility, and energy dissipation. Load ratio, opening size, and reinforcement ratio significantly affect the seismic performance of the composite wall, while the concrete and steel strength and sheathing board have minimal effects. The seismic design suggestions of composite walls are given based on this study. [ABSTRACT FROM AUTHOR]

Due to its high load-bearing capacity, high-strength steel is progressively more used in present engineering applications. However, the current design codes methodology for the lateral-torsional buckling (LTB) ultimate capacity of laterally unrestrained steel beams is based on experiments limited to room temperature and mild steel. A numerical analysis of steel beams' ultimate bearing capacity in bending was carried out to evaluate the lateral-torsional bending of different high-strength steels, namely, Q460, Q690, and Q960 steel at high temperatures. As a comparison, the lateral-torsional bending of Q235 steel beam was also studied. Finite element models (FEMs) were generated using Abaqus with taking into account initial geometrical imperfection and residual stress. The validation of the FEMs has been established by comparing the ultimate flexural resistances obtained from previous tests with those from FEM. A number of parametric studies were taken to investigate the effects of different factors such as various span lengths, residual stress, steel grades, temperatures, and cross-section size on the flexural-torsional buckling (FTB) behavior of laterally unrestrained steel beams. Furthermore, the overall bending capacity of laterally unrestrained steel beams has been shown to be deteriorating at high temperatures. In addition, based on findings from the FEMs, design curves were proposed for evaluating the FTB of high-strength steel beams at elevated temperatures. The results were compared with the design curves given by design codes of GB 51249-2017 and EN 1993-1-2. [ABSTRACT FROM AUTHOR]

Exploring fire resistance of high strength steel end-plate connections is one of the key technical bases for fire resistance design and fire safety assessment of high strength steel structures. Numerical simulation and parameter analyses of high strength Q690 steel flush end-plates will contribute to a reasonable design of high strength flush end-plate connections. In this paper, a finite element model of high strength steel flush end-plate connection considering thermal creep effect was established and validated by experimental results. The thermal creep finite element model can simulate accurately heat performance, failure modes and deformations of high strength flush end-plate connections at elevated temperatures. The increase of axial compression ratio has little effect on rotation, deflection, failure time, critical temperature, and critical rotation with elevated temperatures. The increase of bending moment ratio has little effect on the development trend of rotation and deflection. Proper increase of thickness of the end-plate can improve failure time and critical rotation, and the increase range is within 7% and 36% respectively. Proper increase of diameter of bolt can improve failure time, critical temperature, and critical rotation to a certain extent, and the increase range is within 10%, 6% and 27% respectively. Proper increases of thickness of the end-plate and diameter of bolt will improve the fire resistance of flush end-plate connection. [ABSTRACT FROM AUTHOR]

The behavior of prestressed carbon fiber reinforced polymer (CFRP)-reinforced steel columns is intricately linked to CFRP stiffness and stress; when the system is exposed to fire, the performance is more complex because of the degradation of CFRP mechanical properties. Therefore, transient fire tests are first conducted on four prestressed CFRP-reinforced steel columns under axial preloading using the ISO 834 standard curve to investigate their high-temperature performance. The entire failure process is revealed, three significant time points (i.e., CFRP failure time, buckling time, and critical time) influencing system behavior are identified, and the effect of preload and prestress level on the time points is elucidated. It is observed that CFRP plates fail with a final hair-like rupture; steel columns undergo symmetric and asymmetric failure modes, related to the initial imperfection. Subsequently, the finite element models (FEMs) are established and validated by test results, followed by a parametric analysis. It indicates that the high-temperature behavior of the prestressed CFRP-reinforced steel columns is dependent on the preload, CFRP prestress level, and initial imperfection; the buckling and critical time of such columns decrease with increasing preload and initial imperfection, while an increase in prestress leads to an increase in the buckling and critical time. Moreover, even CFRP plates without protection, and prestressed CFRP plates can improve the high-temperature performance of steel columns when the preload is not very large or the initial imperfection is not very small. These findings serve as a valuable reference for applying such columns when considering fire issues. • Transient fire tests are conducted on prestressed CFRP-reinforced steel columns using ISO834 standard curve. • Three significant time points influencing the system behavior are identified. • Effects of initial imperfection and preload on high-temperature behavior and reinforcing efficiency are discussed. [ABSTRACT FROM AUTHOR]

A steel truss-concrete composite (STCC) shear wall is fabricated by replacing the reinforcement of the shear wall by steel truss, which has high bearing capacity, good fire resistance, good seismic performance, and an easy construction. In order to investigate the seismic performance of special shaped composite shear wall, a quasi-static test was carried out on four T-shaped and two L-shaped composite shear walls. The results showed that the change of diagonal bracing form from strip steel to channel steel can improve the ductility and energy dissipation capacity of the shear wall and delay the strength degradation. Increasing the thickness of steel vertical supports can effectively improve the initial stiffness, while decreasing the thickness of diagonal braces will reduce the bearing capacity of the wall. The strength and stiffness of shear walls loaded along the web in the positive direction (flange in tension) is high, but the ductility is relatively poor when compared with walls loaded in the negative direction (flange in compression). Numerical models were established by ABAQUS, in which the steel hysteretic constitutive model was adjusted to simulate the influence of bond-slip effect. The influence of shear span ratio, axial load ratio, steel ratio of vertical support, volumetric ratio of diagonal brace, tilt angle of diagonal brace and horizontal force direction on the seismic performance of T & L shaped composite shear walls were analyzed. Finally, a design method was proposed, and the calculated results by the design method were in good agreement with the test. ● Pseudo-static tests were carried out on four T-shaped and two L-shaped composite shear walls. ● Numerical models were developed to predict seismic response of special shaped steel-concrete composite shear wall. ● Key factors influencing seismic response of special shaped steel-concrete composite shear wall were investigated. ● A design method was proposed to evaluate the load capacity of special shaped steel-concrete composite shear wall. [ABSTRACT FROM AUTHOR]

This paper presented a series of tests to investigate the behaviour of the extended end-plate connection utilizing high strength Q960 steel. A total of 8 specimens were tested, including two under ambient temperature and three under high temperature. The results of the tests indicated that increasing the end-plate thickness from 8 mm to 12 mm significantly enhances the flexural capacity and initial rotational stiffness of the connections but reduces the critical temperature and ultimate rotation. In addition, a higher beam bending moment ratio was found to increase the ultimate rotation of the connections while having minimal impact on the critical temperature. Then, the finite element model of the connections was established to investigate the parametric effect, including column axial pressure ratio, beam bending moment ratio, and end-plate thickness on fire resistance. The numerical analysis indicated that increased column axial pressure ratio and end-plate thickness decreased fire endurance, critical temperature, and ultimate rotation of the connections. On the other hand, increasing the beam-bending moment ratio enhanced the ultimate rotation of the connections. Lastly, a rotation-temperature relationship model was proposed to accurately predict the temperature-rotation curve of high-strength steel Q960 end-plate connections, which was validated with experimental data. • Fire tests on response of high strength Q960 steel connections were carried out. • Numerical models were developed to simulate the behaviour of Q960 teel connections at elevated temperatures. • Parametric studies were performed to investigate the effect of key factors on fire resistance of the connections. • A rotation-temperature relationship model was proposed to predict the fire behaviour of Q960 steel connections. [ABSTRACT FROM AUTHOR]

The objective of this paper is to to ascertain the reliable mechanical properties of cold-formed Q345 steel at elevated temperatures while considerting the effects of tensile strain rate and specimen width. This paper presents an experimental study on the mechanical properties of cold-formed Q345 steel at temperatures ranging from 20°C to 800°C tested with two specimen widths and three tensile–strain rates, namely 0.06/min , 0.6/min , and 1.2/min. Tensile specimens were fabricated from a steel plate with a nominal thickness of 2.5 mm and tensile tests were carried out to determine the stress–strain relationship, yield strength, tensile strength, and elastic modulus. The test results showed that the tensile–strain rate has a maximum influence of 9% on yield and tensile strength at 600°C and the specimen width has a maximum influence of 14% on yield and tensile strength at 400°C. The maximum influence of the tensile–strain rate and specimen width on the elastic modulus is 18% and 12% respectively at 500°C. The necking phenomenon is less noticeable at temperatures below 300°C but is clearly observed at temperatures above 300°C. The comparison of the test results with predictions obtained from design standards (EC3, AISC, and AS4100) indicates a good agreement on the yield and tensile strength, but the magnitudes of elastic modulus obtained from the test are considerably higher than those obtained from the design standards. Based on averaged values of the test results associated with different tensile–strain rates and specimen widths, predictive equations were proposed to determine the mechanical properties of cold-formed Q345 steel at elevated temperatures. [ABSTRACT FROM AUTHOR]

In order to obtain the mechanical behavior of H-shaped high-strength Q960 steel column under axial compression in fire, the bearing capacity tests of two Q960 steel columns at ambient temperature and fire resistance tests of six Q960 steel columns at elevated temperature were carried out. By considering different slenderness ratios, load ratios, and heating rates of the test columns, the furnace temperature, column temperature, lateral displacement, and axial displacement were measured and recorded. Then, critical temperature, fire resistance, and failure mode of the columns were obtained. The thermal-mechanical coupling analysis model for the Q960 steel column was established by using ABAQUS finite element analysis software. After verifying the accuracy of the model, parameter analysis was carried out to investigate the effects of load ratio, slenderness ratio, geometric imperfection, thermal creep, residual stress, and steel strength on the fire resistance of steel columns. Based on the test data and analysis results, a fire resistance design method for high-strength Q960 steel columns under axial compression is proposed. • Fire-resistance tests of the high strength Q960 steel columns were conducted. • Numerical models were developed to predict fire response of Q960 steel columns. • A fire design method was proposed to evaluate the load capacity of Q960 steel columns. [ABSTRACT FROM AUTHOR]

A series of fire tests on eight circular tubed steel reinforced concrete (CTSRC) stub columns subjected to axial loading are presented in this paper. The influences of load level and steel tube thickness on the fire resistance of the CTSRC stub columns were investigated. Two similar specimens were tested with the same test scenario to obtain more reasonable data. The temperatures in steel and concrete, axial displacement, fire resistance, and failure mode were recorded and discussed. The test results show that the load level has a great influence on the fire resistance of CTSRC stub columns. The steel tube thickness has a significant influence on the fire resistance of CTSRC stub columns when subjected to a higher load level. Thermal and structural finite element (FE) models were developed to analyze the temperature distributions and fire responses of CTSRC stub columns by employing the program ABAQUS. These developed models were validated by the test data. Extensive parametric studies were carried out by using the FE method to investigate the influences of key factors on the temperature distributions and fire resistances of CTSRC stub columns. The factors considered for thermal analysis include cross-sectional dimension, steel tube thickness, and concrete type, while the factors considered for structural analysis include load ratio, cross-sectional dimension, steel tube thickness, concrete strength, and steel strength. The parametric studies indicate that the cross-sectional dimension has a more significant influence than the steel tube thickness on the temperature magnitudes of CTSRC stub columns. The load ratio, cross-sectional dimension, and steel tube thickness have more significant influence than concrete strength on the fire resistance of CTSRC stub columns. Based on the results of the parametric studies, a simplified method to predict the steel temperatures and the compressive load bearing capacities of CTSRC stub columns exposed to fire is proposed. • Full-scale fire tests on circular tubed steel reinforced concrete (CTSRC) stub columns were presented. • A finite element model was established to predict the fire response of CTSRC stub columns subjected to axial compression. • Parametric studies were carried out to investigate the factors effecting fire behavior of CTSRC stub columns. • Simplified methods to predict the temperatures and load capacities of CTSRC stub columns in fire is proposed. [ABSTRACT FROM AUTHOR]

This paper presents the experimental, numerical, and theoretical studies aimed at investigating the fire behaviors of high strength Q690 steel T-stub connections. The experiments determined failure modes, load–displacement curves, ultimate displacement, ductility factors, and load capacities of the specimens at elevated temperatures. The rupture of the flange disappeared at temperatures exceeding 600 °C. A finite element model was established using ABAQUS software, validated by the experimental results, to explore the effect of bolt preload and bolt grade on the fire behaviors of T-stubs. The first yield resistance derived from experimental and numerical findings was compared with EC3 predictions, highlighting a severe underestimation by EC3 for high-strength steel T-stubs with thin-walled flanges. A theoretical model was subsequently proposed and validated against numerical and experimental outcomes, serving as the basis for a novel design method. This model accurately anticipates the progression of the plastic hinge line and the first yield resistance, suggesting the use of 2.0% yield strength of high-strength steel to calculate the first yield resistance of steel T-stubs. • Tension test on high strength steel T-stub connections at elevated temperature were carried out. • Finite element model on T-stub connection were established and validated by test data. • Parametric studies were conducted to quantitatively assess the influence of key factors on capacity of T-stub connection. • The load capacity of T-stub connection predicted by EC3 were evaluated and design methods were proposed. [ABSTRACT FROM AUTHOR]

This paper presents experimental and numerical studies to investigate the fire behavior of high strength steel (Q690 and Q960) shear connections. The load-displacement curves, failure modes, and load capacities, including the slip load and ultimate load of the specimens at elevated temperatures were obtained from experiments. A finite element model was established by ABAQUS software and validated by the test results to investigate the effect of the friction coefficient and the assembly form of the bolt on the shear behavior. The numerical results of load capacity were compared with that predicted by EC3, AISC 360–16, and GB50017. Parametric studies were conducted to investigate the effect of the slip load on the ultimate load at ambient temperature, and design methods were proposed considering the friction coefficient and preload values. The research shows that the slip load decreases more rapidly than the ultimate load at elevated temperatures. The critical temperature from brittle failure to ductile failure is approximately 500 °C. The load capacity predicted by AISC 360–16 is accurate, while EC3 and GB50017-2017 predict conservative load capacity. The effect of the bolt load and friction coefficient cannot be ignored for high strength steel shear connections. In order to investigate the fire behavior of high strength steel (Q690 and Q960) shear connections, experimental and numerical studies were presented in this paper. The load-displacement curves, failure modes, and load capacity, such as the slip load and ultimate load of the specimens at elevated temperature were obtained from the experiment. Finite element model was established by ABAQUS software and validated by the test results to investigate the effect of the friction coefficient and the assemble form of the bolt on the shear behavior. The analytical results of load capacity were compared with that predicted by EC3, AISC 360–10, and GB50017. Parametric studies were conducted to investigate the effect of the slip load on ultimate load at ambient temperature, and design methods were proposed considering the friction coefficient and preload values. The research shows that the slip load decreased more rapidly than the ultimate load. The failure temperature from brittle failure to ductile failure is approximate 500 °C. The stiffness of the connection deceases significantly due to the eccentric assembly form of the bolt. The load capacity predicted by AISC 360–10 is accurate, while EC3 and GB50017-2017 predict conservative load capacity. [Display omitted] • Tests on shear capacity of high strength steel connections at elevated temperature were carried out. • Finite element models on shear connection were established and validated by test data. • Parametric studies were carried out to quantitatively assess the influence of key factors on shear capacity of connection. • The shear load capacity of connection predicted by AISC 360–10，EC3 and GB50017-2017 were evaluated. [ABSTRACT FROM AUTHOR]

When it is subjected to a fire, creep strain developed in a steel column can significantly influence the behaviour of the column. As the result, the column deformation will be increased and the strength will be decreased. However, the effect of creep in steel structures has not been fully considered in current fire resistance design codes. Presented in this paper is a study on creep buckling of Q460 steel columns subjected to elevated temperatures via experimental and numerical investigations. Six high-strength Q460 steel columns with welded H shape were tested for the determination of creep buckling strength at elevated temperatures. The effects of the slenderness ratio, load ratio, and elevated temperature on failure time corresponding to creep buckling (also called as creep buckling time) were taken into consideration in the investigations. The evolutions of furnace and column temperatures, column lateral and axial displacements associated with fire duration were measured. The creep buckling time of the columns were obtained based on the magnitudes of axial and lateral displacement of the columns subjected to constant elevated temperature and compressive load. The test results showed that the creep deformation of high strength Q460 steel columns became significant at temperature 800 °C even the applied load level was as low as 10%. The creep buckling time of Q460 steel columns are sensitive to load ratio, slenderness and temperature. Finite element analysis program ANSYS was employed to establish a structural model of Q460 steel column subjected to the constant elevated temperature and compressive load, with mechanical properties at elevated temperature, creep strains and residual stresses induced by welding being taken into account. The finite element model was validated by the test results. Parametric studies were carried out to quantitatively determine the effects of the slenderness ratio, load ratio, temperature and geometric imperfections on the creep buckling time of Q460 steel columns. • Creep buckling tests on high strength Q460 steel columns at elevated temperature were presented. • A finite element model was established to predict creep deformation and creep buckling time of Q460 steel columns. • The effect of key parameters on creep buckling were investigated by test and finite element simulation. [ABSTRACT FROM AUTHOR]

Highlights • Test on mechanical properties of Q690 steel after fire exposure were presented. • The thickness effect on mechanical properties of steels were investigated. • Equations to predict properties of Q690 steel after fire exposure were proposed. Abstract Presented in this paper are test results on mechanical properties of high strength Q690 steel after being exposed to high temperatures. Yield strength, tensile strength, elastic modulus and ratio of ultimate elongation were obtained based on tension stress-strain relationships of Q690 steel after exposure to temperature ranging from 300 to 1000 °C. Two cooling methods, namely air cooling and water cooling, were applied to cool down the heated specimens from high temperature to ambient condition. The mechanical properties comparison on different high strength steels with various thickness are carried out to investigate the effect of thickness on reduction factors of strength and elastic modulus of high strength steels after high temperature exposure. The study shows that the strength deterioration after being exposed to high temperatures is not significant for the temperature up to 600 °C, no matter which cooling method is applied. The strength reduction is approximately 25% after being exposed to temperature 700 °C. However, when the air cooling is applied, the strength decreases significantly and the ultimate elongation increases noticeably being exposed to temperature 800 °C−1000 °C but the opposite is found when water cooling is applied. The influence of elevated temperature and cooling method on the elastic modulus is negligible. The deteriorations of the material properties are different for different steels. The strength deterioration of thinner steel plate is more significant than that of thicker steel plate. Equations to predict residual factors of mechanical properties of high strength Q690 steel with 20 mm thickness were proposed to evaluate the post fire capacity of high strength Q690 steel members. [ABSTRACT FROM AUTHOR]

High strength steel has been widely used in various types of structures due to its merits of high strength and good ductility. However, high strength steel structures are vulnerable to fire hazards as the strength and stiffness of the steel deteriorate rapidly at elevated temperature. Presented in this paper are the investigations on the behaviour of restrained high strength steel columns at elevated temperature obtained from full-scale fire tests and finite element analyses. In the fire tests, applied load and restraint stiffness are two key factors to be examined. Column responses such as the axial displacement, deflection at column middle height and axial force induced by thermal expansion associated with temperature evolution were reported. Column buckling and failure temperatures were determined based on the criteria of the axial displacement and lateral deflection of the specimens at elevated temperatures. The test results show that both the applied load and restraint stiffness have considerable influences on fire resistances of high strength steel columns. It was observed that the columns with only axial restraints failed by flexure buckling about the weak axis whereas the columns with both axial and rotational restraints and subjected to large magnitude of the applied load failed by flexural torsional buckling. Finite element analyses were conducted to simulate the fire responses of the test specimens and the obtained numerical results are found to be reasonably agree with the test data. Parametric studies via finite element analysis were carried out to quantitatively determine the effect of applied load, restraint stiffness and slenderness ratio on fire resistance of high strength steel columns. [ABSTRACT FROM AUTHOR]

The mechanical characteristics of high-strength steel (HSS) at high temperatures vary significantly from those of mild steel, so fire design regulations derived from mild steel cannot be transferred to HSS structures. Therefore, this paper investigates the fire resistance of beams made of HSSs, which will facilitate the design and application of HSS structures. Due to the heat dissipation of the concrete floor, steel beams are generally heated from three sides, and the temperature distribution in the steel beam cross-section is nonuniform. For such cases, the fire resistance of HSS beams is assessed using finite element models (FEMs) with nonuniform temperature distribution. A Ramberg–Osgood model was used to predict stress–strain relationships of Q460, Q690, and Q960 HSSs at elevated temperatures, and the model was verified by material tests. In the FEM, the proposed stress–strain relationships of HSSs at elevated temperatures, initial geometric imperfections and residual stress are considered for better accuracy. After verifying the established model against experimental results, the influence of nonuniform temperature distribution, load pattern, steel grade, and slenderness ratio on the resistance of HSS beams is investigated by conducting parametric analyses using the verified FEM. It is found that the critical bending moment of steel beams at elevated temperatures associated with lateral-torsional buckling highly depends on the reduction of elastic modulus of steel. By comparing FEM results with EN 1993-1-2, it is evident that EN 1993-1-2 is unsuitable for assessing the fire resistance of HSS beams. Therefore, the expression specified in EN 1993-1-2 is modified by fitting the finite analysis results to more accurately evaluate the fire resistance of HSS beams considering the nonuniform temperature distribution. [ABSTRACT FROM AUTHOR]

It is a challenge for the conventional cold-formed steel (CFS) sheathed wall system to be adopted in multi-story buildings due to its limited lateral load capacity and stiffness. Therefore, an innovative cold-formed steel center-sheathed shear wall (CFSCSSW) system with better lateral load capacity and stiffness has been proposed and shown its potential application in multi-story buildings. However, the fire performance of CFSCSSW has become one of the major issues which have yet to be investigated and thus become the focus of the present paper, underpinned by tests and numerical simulations. In this study, a full-scale test at room temperature was firstly conducted on a CFSCSSW to obtain its vertical load capacity, while another four full-scale fire tests were then carried out with applied gravity loads to investigate the influence of the interior stud, load ratio, and aspect ratio on fire behavior of the walls. Following the tests, 11 finite element models were subsequently developed to investigate the influence of various critical parameters, such as the axial load ratio, aspect ratio, and end stud thickness, on the fire resistance of CFSCSSW. The fire test results showed that the heat loss of the wall surface could be more than 40% during the temperature transition from the fire exposed side to the cold side. It is found that the presence of interior stud, increasing the aspect ratio beyond 3.0 as well as the load ratio to be greater than 0.3 can result in a transition of the failure mode of the wall from global buckling to local buckling. The critical temperature declines approximately 12% if the load ratio increases by 0.1. The fire resistance of the wall was slightly improved with the increase of the aspect ratio. The end stud thickness of 2 mm is recommended preferentially based on the parametric results. In addition, it was found that the presence of the interior stud has little influence on the fire resistance of the walls. • An innovative cold-formed steel center-sheathed shear wall (CFSCSSW) system with better lateral load capacity and stiffness was proposed and analyzed experimentally and numerically. • Parametric analysis was conducted to investigate the influence of critical parameters on the fire behavior of the CFSCSSW. • The optimal end stud thickness was recommended in this paper. [ABSTRACT FROM AUTHOR]

In recent years, high-strength steel (HSS) is finding increasing applications in building construction due to its excellent strength and durability properties. However, structures, incorporating HSS, exhibit lower fire resistance due to rapid deterioration of their mechanical properties at elevated temperatures. For evaluating the fire resistance of steel structures, high-temperature properties of steel are to be specified as input data. The properties of steel not only vary with temperature but also the extent of variation is influenced by the type and grade of steel. This paper presents a state-of-the-art review on temperature-dependent properties of HSS. The available data and relations for thermal, mechanical, and deformation properties of HSS are compiled. Using these data, the variations in the elevated properties of HSS are established and the reasoning for such variation is explained. Finally, the critical properties to be considered for evaluating the fire resistance of structures, incorporating HSS, are discussed. [ABSTRACT FROM AUTHOR]

This paper presents the development of an analytical model of steel-concrete partially composite beams subjected to fire. The model includes consideration of temperature dependent material properties, temperature dependent interface slip between concrete and steel, non-uniform temperature distributions throughout the cross-section and the effect of different rates of thermal expansion at the concrete-steel interface. Model predictions showed good agreement with the results of fire tests on two composite beams reported in an earlier companion paper as well as with limited experimental data published in literature. An extensive parametric study was undertaken by using the proposed model. Parameters considered in this study included geometric dimensions of the composite beam, material grades of steel and concrete, shear connection ratio, reinforcing steel ratio in the concrete slab, and load level on the beam. The parametric study clearly shows that shear connection ratio and load level significantly influence the fire performance of partially composite beams. The critical temperatures with shear connection ratio of 50%, 75% and 100% are 645°C, 602°C and 548°C, respectively, under load level of 0.6. The critical temperatures under load ratio of 0.5, 0.6 and 0.7 are 468°C, 553°C and 633°C respectively, with a shear connection ratio of 50%. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study on high-strength Q460 steel extended end-plate connections at ambient and elevated temperatures. Ambient temperature tests were conducted on connections with 8 and 12 mm end-plates to investigate the ambient temperature structural response, including the initial rotational stiffness, plastic flexural resistance and ultimate rotation. The results show that high-strength steel connection with 12 mm end-plates significantly improves mechanical properties compared to that with 8 mm end-plate with an increase of 22% at least while not influencing the failure modes. Then, the experimental results were compared with the theoretical predictions of Eurocode 3. There are reasonable agreements between these two methods on plastic resistance, while the calculation by Eurocode 3 on initial rotational stiffness exhibits much higher results. In addition, the temperature distribution of the connection specimens and furnace air, rotation-temperature characteristics, and failure modes of the connections in transient tests were obtained to study the influence of different end-plate thicknesses. The 12 mm end-plate effectively improves the connection's rotation capacity at elevated temperatures with an increase of 29% compared to 8 mm end-plate while influencing the critical temperature and fire endurance lightly. Besides, the fire performance results were compared and discussed between mild steel and high-strength steel connections. Finally, a rotation-temperature relationship model was proposed to predict the fire behavior of high-strength steel end-plate connections under transient conditions and validated against the experimental data with considerable accuracy. • Fire tests on Q460 steel extended end-plate connections were carried out. • The effect of end-plate thickness on fire resistance of Q460 steel end-plate connections was evaluated. • A rotation-temperature relationship model was proposed to predict the fire behavior of Q460 steel end-plate connections. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive numerical analysis of high-strength Q690 steel beams in fire. A FE model is developed and validated against the full-scale experiments on restrained high-strength Q690 steel beams in fire presented in a previous study by the authors. The FE model adequately replicates the deflection, axial force, and actual failure modes identified experimentally. An extensive parametric investigation was performed to determine the variables affecting the behavior of restrained Q690 steel beams in fire. The analysis indicates that several factors, including load ratio, cross-section temperature distribution, rotational restraint stiffness, and span-to-depth ratio are critical for the fire resistance of restrained high-strength Q690 steel beams. Furthermore, additional numerical analysis for the ultimate bearing capacity of high-strength Q690 steel beams under bending was carried out to estimate the flexural-torsional buckling behavior of Q690 steel beams at elevated temperatures. Additionally, based on the results of the FE models, design curves for determining the flexural-torsional buckling strength of high-strength Q690 steel beams at high temperatures were proposed. The findings were compared to the design curves specified by several design standards. [Display omitted] • A FE model is developed and validated against the full-scale experiments on restrained Q690 steel beams in fire. • Parametric studies are performed to determine the factors influencing the fire behavior of restrained Q690 steel beams. • Design curves to predict the flexural-torsional buckling strength of Q690 steel beams at high temperatures were proposed. [ABSTRACT FROM AUTHOR]

In comparison to the isolated steel beam, the restrained steel beam is able to sustain fire loads using the effect of the surrounding restraints. However, Q690 steel has lower resistance to high temperatures than other types of carbon steel. To address this gap, a series of experimental tests on restrained high-strength Q690 steel beams subjected to fire are reported in this paper. Four full-scale restrained high-strength Q690 steel beams were investigated under several fire scenarios, and one was tested at room temperature. In this study, three transient tests and one steady-state test were chosen to fully comprehend the behavior of the restrained high-strength Q690 steel beams exposed to fire. Under the two test conditions, the impact of the steady-state and transient conditions on the fire response of the restrained Q690 steel beams are compared, and the variation of axial peak force, bearing capacity, and deflection were analyzed. The results showed that the critical temperature of the steady-state test is close to the critical temperature of the transient test, and the maximum axial force of the steady-state test is comparable to the one of the transient test. Due to the combined action of load and axial forces, the restrained Q690 steel beam generally develops flexural-torsional buckling failure after reaching the critical temperature in transient tests. In comparison, the steady-state test exhibits early flexural-torsional buckling behavior before reaching the critical temperature. In this study, three transient tests and one steady-state test were chosen to fully comprehend the behavior of the restrained high-strength Q690 steel beam in fire. Under the two test conditions, the impact of the steady-state and transient on the fire response of the restrained Q690 steel beams are compared, and the variation of axial force peak, bearing capacity, and deflection are analyzed. The results showed that the critical temperature of the steady-state test is close to the critical temperature of the transient test, and the maximum axial force of the steady-state test is comparable to the transient test. Due to the combined action of load and axial forces, the restrained Q690 steel beam generally develops flexural-torsional-buckling failure after reaching the critical temperature in transient tests. In comparison, the steady-state test exhibits early flexural-torsional-buckling behavior before reaching critical temperature. [Display omitted] • A series of experimental tests on restrained high-strength Q690 steel beams subjected to fire are carried out. • The impact of the steady-state and transient on the fire response of the restrained Q690 steel beams was compared. • The effect of load on fire resistance and critical temperature of restrained Q690 steel beams was investigated. [ABSTRACT FROM AUTHOR]

Residual stresses can have a significant effect on the stiffness of steel members. Residual stresses in welded H-shaped sections at room temperature have been widely studied. However, little information is available on residual stresses in steel members after fire exposure. Fire exposure affects the magnitude and distribution of residual stresses due to plastic deformation and creep in steel at elevated temperatures. This paper presents the results of an experimental investigation on post-fire residual stresses in thin-walled welded H-shaped sections, both for mild Q235 steel with a nominal yield stress of 235 MPa and high strength Q460 steel with a nominal yield stress of 460 MPa. Five Q235 steel H-sections and five Q460 steel H-sections were investigated. Residual stresses at ambient condition were also measured as a baseline. Specimens were heated to 200 °C, 400 °C, 600 °C and 800 °C and residual stresses were measured after the temperature of specimens reached the target temperature and cooled down to room temperature. It was found that the residual stresses after fire exposure decrease significantly with increase of specimen temperature. Based on these experiments, recommendations are provided for the distribution and reduction in magnitude of residual stresses after fire exposure. [ABSTRACT FROM AUTHOR]

In order to evaluate the residual strength of high strength Q460 steel structures after fire, an experimental study was undertaken to investigate the post-fire mechanical properties of high strength Q460 steel. Tensile coupons taken from high strength Q460 steel sheets were exposed to different temperatures up to 900 °C, and were then allowed to cool down to ambient temperature before they were tested to failure. Two cooling methods were considered, namely; natural air cooling and cooling by water. Tensile coupon tests were conducted to obtain their post-fire stress–strain curves and associated mechanical properties (yield strength, elastic modulus, ultimate strength and elongation). It was found that the post-fire mechanical properties of high strength Q460 steel are significantly reduced below the original ambient temperature mechanical properties if they had been exposed to temperatures exceeding 600 °C. Hence a new set of equations is proposed to predict the post-fire mechanical properties of high strength Q460 steel. Such post-fire mechanical property assessments allows structural and fire engineers to make an accurate prediction of the safety of fire exposed high strength Q460 steel buildings. [ABSTRACT FROM AUTHOR]

When subjected to a constant applied load and elevated temperature, structural steel columns may buckle after a certain duration due to increasing creep-induced deformation, and such mode of failure is referred to as creep buckling. This paper presents an analytical method to simulate the creep buckling behaviour of steel columns at elevated temperatures by incorporating the Fields-and-Fields creep model and a nonlinear constitutive model of steel at elevated temperatures. Fire and creep buckling tests on Q690 high-strength steel columns are selected to validate the proposed method, and a good agreement between the experimental and analytical results is achieved. This demonstrates that the proposed method can provide an accurate assessment of the lateral deflection of steel columns at elevated temperatures accounting for the creep effect. Time- and strain-hardening formulations are separately incorporated into the analysis. The obtained results indicate that the strain-hardening formulation is more suitable for cases with stress variations. The study also unveils the failure mechanism of creep buckling, which indicates that the creep-induced lateral deflection of an axially loaded steel column at elevated temperatures is initiated by the gradient of stress and strain distributions on the cross-section of the column triggered by the initial imperfection. The parametric study results show that the creep buckling time of the steel column decreases as the load ratio, elevated temperature, and initial imperfection increase; however, the creep buckling time increases as the slenderness ratio increases. [ABSTRACT FROM AUTHOR]

In order to investigate the local stability of Q235 steel and Q460 steel axially compressed stub columns at elevated temperatures, local stability experiments were carried out on six Q235 and six Q460 steel stub columns at room and elevated temperatures. The local stability failure modes of flange and web were obtained at room temperature, 450 °C and 650 °C. Based on ultimate strain method and curve inflexion point method, the critical loads were defined at room and elevated temperatures. The local buckling stress was calculated by the methods proposed in current design code of steel structures and published paper and the results of them were compared with experimental results. The study shows that the failure modes of specimen at room and elevated temperatures are similar, and compared with load bearing capacity of local buckling at room temperature, load bearing capacity at elevated temperatures of Q460 steel specimens is reduced more than that of Q235. There is a big difference between the calculated results of critical stress for flange and web of welded H-shaped steel stub column by codes and experimental results. [ABSTRACT FROM AUTHOR]

In recent years, cold-formed steel has been extensively used, and the mechanical properties of cold-formed steel at elevated temperatures have been received considerable attention. However, little research on mechanical properties of the corner parts at elevated temperatures has been published. Meanwhile, the tensile strain rates adapted in the previous research on cold-formed steel are different, and the effect of this factor on mechanical properties was rarely investigated. In order to get a deeper understanding of the mechanical properties of cold-formed Q345 steel at elevated temperatures, an experimental investigation on flat and corner parts in cold-formed Q345 sections with two nominal thickness of 1.5 mm and 2.5 mm under three different tensile rates, 0.06/min, 0.6/min and 1.2/min, was carried out at elevated temperatures ranging from 20 °C to 800 °C. The effects of tension strain rate, cold-forming and thickness on mechanical properties of Q345 steel were systematically studied. Then the test results were compared with the prediction results provided by the current design standards and the other researchers. Furthermore, prediction equations were proposed to determine the mechanical properties of cold-formed Q345 steel. In order to get a deeper understanding of the mechanical properties of cold-formed Q345 steel at elevated temperatures, an experimental investigation on flat and corner parts in cold-formed Q345 sections with two nominal thickness of 1.5 mm and 2.5 mm under three different tensile rates, namely 0.06/min, 0.6/min and 1.2/min was carried out at elevated temperatures ranging from 20 °C to 800 °C. The effects of tension strain rate, cold-forming and thickness on mechanical properties of Q345 steel were systematically studied. Then the test results were compared with the prediction results provided by the current design standards and the other researchers. Furthermore, prediction equations were proposed to determine the mechanical properties of cold-formed Q345 steel. [Display omitted] • Coupon tests on mechanical properties of cold-formed Q345 steel at elevated temperature were carried out. • Effect of cold-formed and tension strain rate on mechanical properties were investigated. • Comparison and discussion were conducted on test data and design codes. • Prediction equations were proposed to determine the mechanical properties of Q345 steel at elevated temperatures. [ABSTRACT FROM AUTHOR]

Even though creep behavior in steel at elevated temperatures has been widely observed, the effect of creep on steel members is not fully understood yet due to the extensive range of steel grades. In this paper, a tension creep test on high-strength Q960 steel at high temperatures was performed. Based on the test data in this paper and available creep data on Q345, Q460, and Q690 steels, a consistent creep model for each steel according to the Fields & Fields creep model was proposed and validated by the comparison with the test data. In order to quantitatively investigate the effect of creep on fire response of restrained steel beams, a finite element model (FEM) was established to analyze the critical temperature of restrained steel beams in fire conditions, with and without considering creep strain generated in steel beams. This was also carried out to better understand the impact of high-temperature on steel beams with various steel grades under the influence of the same load. The verification of the FEM was achieved by comparing the results with experimental data on a restrained Q235 steel beam and Q690 cantilever steel beam. The study reveals that creep has a noticeable effect on the fire resistance of the restrained steel beams and that the effect varies from one type of steel to another. A comparison has been made to observe the effect of high-temperature creep on the critical temperature for each steel type. In this paper, a tension creep test on high-strength Q960 steel at high temperatures was performed. Based on the test data in this paper and available creep data on Q345, Q460, and Q690 steels, a consistent creep model for each steel according to the Fields & Fields creep model was proposed and validated by the comparison with the test data. In order to quantitatively investigate the effect of creep on fire response of restrained steel beams, a finite element model (FEM) was established to analyze the critical temperature of restrained steel beams in fire conditions, with and without considering creep strain generated in steel beams. This was also carried out to better understand the impact of high-temperature on steel beams with various types of steel under the influence of the same load. The verification of the FEM was achieved by comparing the results with experimental data on restrained Q235 steel beams. The study reveals that creep has a noticeable effect on the fire resistance of the restrained steel beams and that the effect varies from one type of steel to another. A comparison has been made to observe the effect of high-temperature creep on the critical temperature for each steel type. [Display omitted] • High-temperature tensile creep tests on Q960 were carried out. • A consistent creep model for high strength steels was proposed. • A finite element model to predict fire respone of restrained steel beams was developed and calibrated by available test data. • Effect of creep strain and steel type on fire-resistance of restrained steel beams was investigated. [ABSTRACT FROM AUTHOR]

Abstract: Despite the great economic importance of bromeliads in flower production, little information is available regarding the inheritance of their horticultural traits thus far. The present study was to investigate the inheritance pattern and useful molecular markers for plant height, plant width, inflorescence length, inflorescence width, and offsets of Aechmea bromeliads. The result showed that plant height was governed by two pairs of major genes exhibiting equal additivity, plant width by one pair of major genes with additivity and partial dominance, inflorescence width by two pairs of major genes with additivity-dominance-epistasis, and offsets by two pairs of major genes with additivity-dominance, whereas no major gene was detected for inflorescence length. The heritability of the detected major genes was >73%, suggesting the possibility of selecting for these traits in an early generation. The marker-trait analysis identified 22 potential SRAP markers for the five traits. The findings of major genes and associated SRAP markers are a useful start to future QTL dissection for these traits. [Copyright &y& Elsevier]

Abstract: Bromeliads are among the most economically important potted ornamentals, however little is available about genetic variability among bromeliad cultivars or hybrids for breeding purposes. In this study, genetic relatedness among cultivars and selected hybrids of Aechmea bromeliad was investigated using amplified fragment length polymorphism (AFLP) markers and pedigree data. Eight AFLP primer combinations produced 1498 DNA fragments, of which 1465 (97.8%) were polymorphic. The AFLP-based genetic similarity ranged from 0.20 to 0.61 and averaged 0.33, while the corresponding pedigree-based coefficient of coancestry varied from 0 to 0.5, with an average of 0.07. This reveals large variability and genetic diversity among the investigated Aechmea bromeliads. The AFLP-based cluster analysis grouped the Aechmea bromeliads well according to their breeding years and ancestors, whereas pedigree-based cluster analysis divided the Aechmea bromeliads corresponding only to their ancestors. Additionally, the AFLP-based genetic similarity followed a normal distribution, while pedigree-based coefficient of coancestry displayed a skewed distribution. A significant though moderate correlation (r =0.35, P <0.001) and a significant linear relationship with low coefficient of determination (R 2 =0.12) were observed between the two measures. This indicates that AFLP is more effective in quantifying genetic relatedness among Aechmea bromeliads. The present study provides useful implications for the efficient conservation and utilization of bromeliad germplasm. [Copyright &y& Elsevier]

To investigate the local buckling behavior and obtain critical buckling stress of flange and web in Q690 steel stub columns at elevated temperatures, a total of 8 stub columns made of H-shape welded sections were tested under simultaneous axial compression and high temperatures. 2 stub columns were tested at ambient temperature and critical stress of flange and web were determined. 4 stub columns were tested in steady-state at 450°C and 600°C, respectively. 2 stub columns were tested in the transient state based on the critical stress of flange and web at 600°C. During the tests, temperature evolution, applied load, axial displacement, lateral deflection, failure modes of each specimen were recorded. The results showed that the critical buckling stress decreases significantly with the increase of temperature. At the same load level, the steady-state test's critical temperature was lower than that obtained in the transient state test. In parallel with the tests, a finite element model was established using ABAQUS software under high temperatures to evaluate the effects of the temperature on local buckling stress, and the model was validated by the test results. A parametric study was carried out to investigate the effect of numerous factors, including width-to-thickness ratio, residual stresses, initial imperfection, and temperature. The simulation and test results were compared with the current design provisions in Eurocode 3, and the comparison showed that the Eurocode 3 design method could not be applied to the Design of the local buckling bearing capacity and ultimate stress, and it might not be precise enough at elevated temperatures. [Display omitted] • Fire tests on local buckling of Q960 H-shaped welded columns were carried out. • Numerical models based on ABAQUS were developed and validated by the tests. • Parametric analyses on key effects on local buckling were conducted. • The applicability of design method on local buckling in EC3 was evaluated. [ABSTRACT FROM AUTHOR]

High-strength steel has been widely used in many engineering structures owing to its enormous economic benefits. A considerable amount of theoretical and experimental research on the fire resistance of high-strength steel structures has been reported. Most of the research has focused on the mechanical properties of steel and the overall buckling behavior of members, but less work has been done on the local buckling behavior, which is often observed in steel structures subjected to actual fires. Moreover, very few design provisions in codes and standards are available for calculating the local buckling capacity of steel columns under high temperatures. In this study, eight welded H-section columns (groups A and B) made of high-strength Q960 steel were tested under axial compression at ambient and elevated temperatures to investigate their local buckling behaviors. By considering different buckling zones, heating temperatures, and heating methods, the load–axial displacement, load–lateral deflection, and local buckling zone of steel columns were recorded. Compared with the ambient temperature test results, the ultimate load of group A specimens at 480 and 632 °C decreased by 26.1% and 57.2%, respectively, and the ultimate load of group B specimens at 472 and 683 °C decreased by 28.5% and 74.2%, respectively. The critical buckling temperature of the columns in transient-state testing was higher than that in steady-state testing under the same load conditions. A finite element model was established using the ABAQUS finite element software and was validated by the test results. The experimental values were compared with the design methods proposed in Eurocode 3 (EC3). The results reveal that EC3 is unsuitable for calculating the local buckling capacity of H-section Q960 steel columns at elevated temperatures. Eight welded H-section stub columns (groups A and B) made of high-strength Q960 steel were tested under axial compression at ambient and elevated temperatures to investigate their local buckling behaviors. By considering different buckling zones, heating temperatures, and heating methods, the load–axial displacement, load–lateral deflection, and local buckling zone of steel stub columns were recorded. Compared with the ambient temperature test results, the ultimate load of group A specimens at 480 and 632 °C decreased by 26.1% and 57.2%, respectively, and the ultimate load of group B specimens at 472 and 683 °C decreased by 28.5% and 74.2%, respectively. The critical buckling temperature of the columns in transient-state testing was higher than that in steady-state testing under the same load conditions. A finite element model was established using the ABAQUS finite element software and was validated by the test results. The experimental values were compared with the design methods proposed in Eurocode 3 (EC3). The results reveal that EC3 is unsuitable for calculating the local buckling capacity of H-section Q960 steel stub columns at elevated temperatures. [Display omitted] • Fire tests on local buckling of Q690 H-shaped welded stub columns were carried out. • Numerical models based on ABAQUS were developed and validated by the tests. • The applicability of design method in EC3 was evaluated by obtained local buckling stress. [ABSTRACT FROM AUTHOR]

Accurate assessment of the thermal properties of steel is a key issue in the fire simulation and design of steel structures. Thermal property tests were conducted for seven types of high-strength steels (HSSs), namely Q460, Q500, Q550, Q620, Q690, Q890, and Q960 steels, along with conventional mild steel Q345. The thermal expansion, specific heat, and thermal conductivity of various steels at a temperature range of 25–1000 °C were obtained and compared to the results proposed by Eurocode 3 and ASCE to validate the applicability of these codes to HSSs. The test results showed that the phase transition temperature of HSS was lower than that of mild steel, and HSS experienced substantial thermal expansion at elevated temperatures. Eurocode 3 and ASCE can be used to approximate the thermal expansion of the HSS only before the phase transition temperature. The endothermic capacity of HSS was weaker than that of mild steel at elevated temperatures. The specific heat of the various types of HSSs could only be effectively predicted by Eurocode 3 and ASCE up to 600 °C, whereas their thermal conductivity could not be reasonably predicted by these codes in temperature range of 25–1000 °C. New equations for thermal expansion, specific heat, and thermal conductivity were proposed to accurately assess the thermal properties of HSS. Accurate assessment of the thermal properties of steel is a key issue in the fire simulation and design of steel structures. Thermal property tests were conducted for seven types of high-strength steels (HSSs), namely Q460, Q500, Q550, Q620, Q690, Q890, and Q960 steels, along with conventional mild steel Q345. The thermal expansion, specific heat, and thermal conductivity of various steels at a temperature range of 25–1000 °C were obtained and compared to the results proposed by Eurocode 3 and ASCE to validate the applicability of these codes to HSSs. The test results showed that the phase transition temperature of HSS was lower than that of mild steel, and HSS experienced substantial thermal expansion at elevated temperatures. Eurocode 3 and ASCE can be used to approximate the thermal expansion of the HSS only before the phase transition temperature. The endothermic capacity of HSS was weaker than that of mild steel at elevated temperatures. The specific heat of the various types of HSSs could only be effectively predicted by Eurocode 3 and ASCE up to 600 °C, whereas their thermal conductivity could not be reasonably predicted by these codes in temperature range of 25–1000 °C. New equations for thermal expansion, specific heat, and thermal conductivity were proposed to accurately assess the thermal properties of HSS. [Display omitted] • Thermal properties, including thermal expansion, specific heat and thermal conductivity of high strength steels were tested. • The thermal properties prediction applicability of EC3 and ASCE to high strength steels were checked. • Thermal properties between high strength steel and mild steel were compared. • New equations to predict thermal properties of high strength steels were proposed. [ABSTRACT FROM AUTHOR]

Numerous experiments have been conducted to investigate the mechanical properties of high strength steel (HSS) at elevated temperatures. In this paper, test data in literatures on mechanical properties of HSS with strength grades from 355 MPa to 960 MPa at room and elevated temperatures were comprehensively summarized. Recent studies demonstrated that the downward trends of the reduction factors of Young's modulus and yield strength vary with the steel grade. In addition, an extensive review of experimental, numerical and theoretical studies performed on the fire resistance of high strength steel structures is presented. Various types of buckling under different loading conditions and the influence of different factors affecting the ultimate capacity and critical temperature of members are discussed. The research results show that existing fire design standards need to be updated to be applicable to HSS structures. The corresponding findings are summarized, and the research gaps as well as recommendations are discussed. Conclusively, the ultimate objective of this review is to promote the wide adoption of HSS structures in practice. • Review on studies performed on the fire performance of HSS members is presented. • Buckling modes, ultimate capacity and critical temperature of HSS members are discussed. • Knowledge gaps and research needs, as well as new directions for researchers, are highlighted. [ABSTRACT FROM AUTHOR]

This paper presents experimental studies to investigate the compressive and shear behaviors of cold-formed thin-walled steel-foam concrete composite walls. Three compressive walls and three shear walls were tested. The failure mode and load-displacement curve of the specimen were obtained from the compressive experiment. The compressive wall infilled with foam concrete mainly experienced distortion buckling of the end stud and local crushing failure of the concrete. The stud openings had a limited effect on the compressive bearing capacity of the composite wall. The failure mode and load-deformation curve were obtained in shear tests. The ductility index, shear stiffness, yield load, peak load, energy dissipation, and stiffness degradation were analyzed. The shear composite wall filled with foam concrete mainly occurred concrete crushing failure, local or distortional buckling failure of the end stud, and cracking failure of the calcium silicate board. The shear stiffness, shear capacity, ductility, and energy dissipation of the composite wall could be significantly improved after filling with foam concrete. [ABSTRACT FROM AUTHOR]

DDB1‐Cullin‐4‐associated factor‐2 (DCAF2, also known as DTL or CDT2), a conserved substrate recognition protein of Cullin‐RING E3 ligase 4 (CRL4), recognizes and degrades several substrate proteins during the S phase to maintain cell cycle progression and genome stability. Dcaf2 mainly expressed in germ cells of human and mouse. Our study found that Dcaf2 was expressed in mouse spermatogonia and spermatocyte. The depletion of Dcaf2 in germ cells by crossing Dcaf2fl/fl mice with stimulated by retinoic acid gene 8(Stra8)‐Cre mice caused a reduction in progenitor spermatogonia and differentiating spermatogonia, eventually leading to the failure of meiosis initiation and male infertility. Further studies showed that depletion of Dcaf2 in germ cells caused abnormal accumulation of the substrate proteins, cyclin‐dependent kinase inhibitor 1A (p21) and thymine DNA glycosylase (TDG), decreasing of cell proliferation, increasing of DNA damage and apoptosis. Overexpression of p21 or TDG attenuates proliferation and increases DNA damage and apoptosis in GC‐1 cells, which is exacerbated by co‐overexpression of p21 and TDG. The findings indicate that DCAF2 maintains the proliferation and differentiation of progenitor spermatogonia by targeting the substrate proteins p21 and TDG during the S phase. [ABSTRACT FROM AUTHOR]

Welding induced residual stresses in steel sections can be reduced by high temperatures in fire conditions and thus affect the load bearing capacity and stiffness of structural steel members. This paper presents effect of high temperature exposure on residual stresses relief in welded high-strength Q690 steel sections by experimental and numerical studies. The distribution and magnitude of the residual stresses in three Q690 steel H-sections and three Q690 steel box-sections after exposure to 600 °C and 800 °C were investigated by cutting method. In the numerical studies, finite element analysis software ANSYS was employed to simulate residual stress generation and relief in the entire welding and high temperature exposure stages, including the heating and cooling phases. The predicted results of the residual stresses after an exposure to high temperature obtained by the finite element analysis agree well with the test results. Parametric studies were conducted to investigate the influence of exposed temperature, high temperature duration, and creep strain in steel on residual stresses after being exposed to high temperature. For welded Q690 steel H- sections and box-sections, equations to evaluate the corresponding residual stress reduction factor at elevated temperatures and after high temperature exposure were proposed based on the results of finite element analysis. Welding induced residual stresses in steel sections can be reduced by high temperatures in fire conditions and thus affect the load bearing capacity and stiffness of structural steel members. This paper presents effect of high temperature exposure on residual stresses relief in welded high-strength Q690 steel sections by experimental and numerical studies. The distribution and magnitude of the residual stresses in three Q690 steel H-shape sections and three Q690 steel box-shape sections after exposure to 600 °C and 800 °C were investigated by sectioning method. In the numerical studies, finite element analysis software ANSYS was employed to simulate residual stress generation and relief in the entire welding and high temperature exposure stages, including the heating and cooling phases. The predicted results of the residual stresses after an exposure to high temperature obtained by the finite element analysis agree well with the test results. Parametric studies were conducted to investigate the influence of exposed temperature, high temperature duration, and creep strain in steel on residual stresses after being exposed to high temperature. For welded Q690 steel H- and box-shape sections, equations to evaluate the corresponding residual stress reduction factor at elevated temperatures and after high temperature exposure were proposed based on the results of finite element analysis. Unlabelled Image • Residual stresses in welded high strength Q960 steel sections after fire exposure were measured by sectioning method. • Residual stresses relief in welded sections in fire and after fire exposure were simulated by finite element modeling. • Parametric studies were conducted to investigate key factors on residual stresses relief after fire exposure. • Reduction factors of residual stresses at and after an exposure to high temperature were proposed. [ABSTRACT FROM AUTHOR]

Simple Summary: Taste receptor type 1 subunit 3 (T1R3), a sweet/umami taste receptor, is widely expressed from the tongue to the testis, and testis expression is associated with male sterility. In Congjiang Xiang pigs, T1R3 is expressed in elongating/elongated spermatids and Leydig cells in a stage-dependent manner during postnatal development and the spermatogenic cycle. T1R3 may contribute to regulation of spermatid differentiation and Leydig cell function, and may therefore help limit the incidence of various male reproductive pathologies. Testicular expression of taste receptor type 1 subunit 3 (T1R3), a sweet/umami taste receptor, has been implicated in spermatogenesis and steroidogenesis in mice. We explored the role of testicular T1R3 in porcine postnatal development using the Congjiang Xiang pig, a rare Chinese miniature pig breed. Based on testicular weights, morphology, and testosterone levels, four key developmental stages were identified in the pig at postnatal days 15–180 (prepuberty: 30 day; early puberty: 60 day; late puberty: 90 day; sexual maturity: 120 day). During development, testicular T1R3 exhibited stage-dependent and cell-specific expression patterns. In particular, T1R3 levels increased significantly from prepuberty to puberty (p < 0.05), and expression remained high until sexual maturity (p < 0.05), similar to results for phospholipase Cβ2 (PLCβ2). The strong expressions of T1R3/PLCβ2 were observed at the cytoplasm of elongating/elongated spermatids and Leydig cells. In the eight-stage cycle of the seminiferous epithelium in pigs, T1R3/PLCβ2 levels were higher in the spermatogenic epithelium at stages II–VI than at the other stages, and the strong expressions were detected in elongating/elongated spermatids and residual bodies. The message RNA (mRNA) levels of taste receptor type 1 subunit 1 (T1R1) in the testis showed a similar trend to levels of T1R3. These data indicate a possible role of T1R3 in the regulation of spermatid differentiation and Leydig cell function. [ABSTRACT FROM AUTHOR]

This study experimentally investigates the temperature-induced deterioration in the mechanical properties of high-strength Q960 steel. High-strength steel has numerous advantages compared with conventional mild-strength steel and has gained wide applications in engineering structures, particularly in high-rise and long-span buildings. The fundamental issue in the fire-resistance design of high-rise or long-span steel buildings is the evaluation of mechanical properties under elevated temperature. There is little information on the temperature-induced mechanical-property deterioration of Q960 steel because of the limited research on this subject. To bridge this knowledge gap, a series of tensile coupon tests on Q960 steel was carried out under various temperatures from 20 to 900 °C to obtain the corresponding stress–strain relationships, yield strength, ultimate strength, and elastic modulus at elevated temperatures. The test results were compared with the results of other high-strength steel types such as Q460, Q690, and S960 steels reported in previous studies as well as the mechanical properties recommended in applicable design codes or standards. The comparison showed that the effects of temperature on the mechanical properties among different types of high-strength steels are different. New predictive equations for evaluating the material properties of Q960 steel at elevated temperatures were presented. • Tensile tests on mechanical properties of high strength Q960 steel at elevated temperature exposure were presented. • Comparisons on mechanical properties among various high strength steels and design specifications were discussed. • Equations to predict the mechanical properties reduction of high strength Q960 steel at elevated temperatures were proposed. • Stress-strain relationships of high strength Q960 steel at elevated temperatures were established. [ABSTRACT FROM AUTHOR]

Cold-formed steel built-up box columns are commonly used in mid-rise cold-formed steel buildings to resist applied loads. Numerous studies have been conducted to evaluate the load-bearing capacity of the columns at ambient temperature but there is very limited research on the fire resistance of the built-up columns. In this paper, a full-scale experimental investigation on fire responses of sixteen axially loaded cold-formed steel built-up box columns was conducted. As a benchmark, the load-bearing capacity of the columns at ambient temperature was tested first. The effects of heating rate, load ratio, and temperature distribution pattern on the fire responses of the columns were investigated in the fire tests. The test results indicated that increasing the load ratio led to a significant decrease in the member critical temperatures, which consequently reduced the fire resistance of the columns considerably. For those columns with an applied load ratio lower than 0.6, they were expected to have member critical temperatures higher than 500 °C. Moreover, with thin-walled steel and no fire protection the column temperatures increased quickly, leading to failure in no more than 12 min in a fast fire even with a low load ratio. It was also found that creep deformation associated with the low heating rate was one of the important factors that could be detrimental to the fire resistance and member critical temperature. As for the effect of temperature distribution patterns in the columns on the member critical temperature, it was found that the member critical temperatures for specimens with non-uniform temperature distribution were slightly higher than those with uniform temperature distribution. • Full-scale tests on cold-formed steel built-up box columns were presented. • The tests contain two load-bearing capacity tests and sixteen fire-resistance tests. • Effects of Load ratio, heating rate and temperature distribution patterns were investigated in the tests. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive study on the flexural buckling behavior of Cold-formed steel (CFS) back-to-back built-up columns with Σ-section (CFS-BBC-Σ), where compression tests and numerical simulations were conducted to investigate the influence of slenderness ratio and fastener arrangements. The material characterization, shearing resistance behavior of the fastener, and imperfection measurements were also performed. The test and simulation results revealed that reducing the fastener spacing and increasing the shearing-resistance stiffness could enhance the load-bearing capacity. The elastic global buckling load (P cr) of CFS-BBC-Σ was determined using the energy method and verified against FEM simulations. The proposed energy method is an explicit expression that demonstrates high accuracy and ease of operation. Then, the P cr was introduced into AISI-S100 specifications as an alternative to the modified slenderness ratio method (MSR) for calculating the load-bearing capacity (P u) of CFS-BBC-Σ. Reliability analysis revealed that the proposed method provides more accurate and safe predictions for P u than the original MSR in AISI-S100 specifications. • Fifteen compression tests were conducted on cold-formed steel back-to-back built-up columns with different lengths and fastener arrangements. • Numerical models were developed and calibrated against the tests, followed by 84 parametric analyses to investigate the influence of fastener arrangements. • The theoretical global buckling load of the cold-formed steel back-to-back built-up columns was derived based on the energy method and verified against the numerical simulation. • A design method was proposed to evaluate the load-bearing capacity of the cold-formed steel back-to-back built-up columns, and it was assessed by reliability analyses. [ABSTRACT FROM AUTHOR]

This paper presents a study on the behavior of cold-formed steel built-up box-shape columns with longitudinal stiffeners (CFS-BCL) under axial compression. The specimens are fabricated using a pair of channel sections and lipped channel sections with longitudinal stiffeners, which are expected to enhance the local buckling resistance of the web. Sixteen specimens were prepared for compression tests, with varying lengths and screw arrangements. Prior to the tests, initial geometric imperfections of the specimens, material properties, and shearing-resistance behavior of the screw fasteners were measured. The results indicate that screw arrangements have a significant effect on simply supported specimens; reducing the screw spacing from 300 mm to 100 mm can increase load-bearing capacity by up to 11%. Finite element models were developed using ABAQUS and validated against test results. The parametric analysis revealed that screw arrangements had minimal impact on the local buckling capacity of specimens, with an increase in capacity of <8%. However, global buckling behavior was significantly affected by screw arrangements, resulting in an increase in capacity of up to 20% for slender columns. The test and analytical results were compared with the Direct Strength Method (DSM), and indicate that the DSM is conservative when the non-dimensional slenderness ratio λ g and λ l is higher than 1.2 and 1.4, respectively. The coefficients of the DSM were modified based on the test and simulation results, and its predictive accuracy was found to be highly increased. • Sixteen compression tests were conducted on cold-formed steel box-shaped built-up columns with longitudinal stiffeners. • Numerical models were developed and calibrated against the tests, and parametric analyses were conducted to investigate the influence of screw arrangements. • The Direct Strength Method was calibrated using both test and parametric analysis results. [ABSTRACT FROM AUTHOR]

Post-earthquake fires occur after earthquakes and have commonly been encountered throughout history. The fires are particularly deadly and threaten the stability of buildings as possible structural damages caused by seismic loading can be exacerbated by temperature loading. Moreover, damage to insulation during seismic events causes accelerated heating in portions of members experiencing large bending moments. A method is proposed for evaluating the stability and deflection of a semi-braced structural steel frame subjected to post-earthquake fire conditions. The proposed method adopts the interstorey drift concept and assumes that each member in the frame has three segments of differing temperatures, modelling the damage to insulation near moment connections and/or midspans of flexural members. The method is presented in the form of a deflection equation, which indicates the instability of the frame when the lateral stiffness in the denominator reaches zero. The proposed method is demonstrated via a numerical example, and the duration of fire until the given frame becomes unstable is computed, with the results validated via finite element analysis. The degrees of structural and insulation damage are also varied in parametric analyses, showing that the lateral stiffness and critical temperatures of a frame subjected to post-earthquake conditions can be severely reduced. [ABSTRACT FROM AUTHOR]

• An innovative CFS shear wall with improved lateral load capacity was proposed and studied. • Parametric analysis was conducted to further investigate the fire behavior of the wall. • An optimal sheathing thickness was recommended in this paper. Cold-formed steel center-sheathed shear wall (CFSCSSW) is an innovative shear wall applied to multi-story cold-formed steel buildings. In this study, six tests were carried out on CFSCSSWs, including one room temperature test to obtain load-bearing capacity and five fire tests to investigate the influence of the vertical load ratio, lateral load ratio, interior stud and aspect ratio on the fire behavior of the CFSCSSWs. Subsequently, finite element models were developed to investigate the influence of various combinations of vertical and lateral loads and the sheathing thickness on the fire behavior of the wall. The research results showed that the temperature distribution along the thickness of the wall section is quite non-uniform and the maximum difference reaches 65% from the hot flange to the cold flange. The effect of the vertical load ratio on the fire resistance of the wall is greater than that of the lateral load ratio. The interior stud plays a positive role in improving the fire resistance of the wall. The aspect ratio has little influence on the fire resistance of the wall. The failure model of the wall mainly depends on vertical or lateral loads as well as the aspect ratio. With the increase in the vertical load ratio, the failure location of the wall moves down. Based on the parametric studies, a sheathing thickness of 0.8 mm was recommended for CFSCSSWs. [ABSTRACT FROM AUTHOR]