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In this study, three reinforced concrete (RC) columns with and without corrosion and different reinforcement details are tested under lateral cyclic loading. One of these columns is well-confined to represent modern RC bridge piers that are designed according to the current seismic design codes, and the second column has the same detail with corrosion damage. The third column is a lightly confined corroded column to represent aging RC bridge piers that are not designed to the current seismic design codes. The experimental results showed that corrosion significantly impacts the ductility loss more than the strength loss of the tested corroded columns. In addition, although the uncorroded column was designed according to the current seismic design code, severe inelastic buckling in the vertical bars was observed during the cyclic tests. [ABSTRACT FROM AUTHOR]

Recent massive earthquakes have raised concerns that megathrust earthquakes with magnitude 9 can occur in the near future. This article discusses the critical behavior of structures involving torsion caused by extreme ground motions. Unlike factors such as mass and stiffness eccentricity and accidental torsion in a structure that induce torsion, torsional buckling can occur in a moment-resisting frame (MRF) when all beam ends in the longitudinal and transverse directionsyield in the lower stories, even if the frame is well designed and its eccentricity is negligibly small. In this study, the theoretically predicted buckling load was presented and validated via numerical analyses. This article shows that excluding the P-Delta effect resulted not only in underestimated deformation but also in overlooked torsional buckling. This study suggests that a high-rise MRF designed in accordance with modern seismic design codes can suffer torsional collapse when the beam ends of the lower stories yield owing to extreme ground motion. Based on these findings, we recommend considering the P-Delta effect when examining the critical behavior of high-rise buildings so as not to overlook the brittle failure mode. [ABSTRACT FROM AUTHOR]

Currently, finite-element (FE) simulation is ubiquitous in engineering research and practice as a tool for solving a wide variety of problems. In steel structures, high-fidelity continuum FE (CFE) analysis is often used to characterize the mechanical behavior of structural members and geometrically complex components such as connections. Accurate description of the material constitutive behavior lies at the heart of these CFE simulations, and over the years, many phenomenologically-based rate-independent constitutive models have been proposed, and a select few have been incorporated in commercially available FE software. In this study, we examine the effect of constitutive model selection on the accuracy of FE analysis predictions of structural steel component responses. Models were selected to have a gradual progression in complexity; some are well-established, widely available in commercial FE software, and extensively used by researchers and practitioners, whereas others, despite being more advanced, have so far been limited in application. Given the difficulties in accurately accounting for extraneous variables common to full-scale experimental testing of realistic structural steel components such as, residual stresses, geometric imperfections, complex boundary conditions, and material inhomogeneities, a set of small-scale configured component experiments were designed to economically minimize these sources of uncertainty and establish a benchmark for critically examining the accuracy of model predictions. Data from these experiments, which included the accurate measurement of local strains that were as high as 75%, facilitated detailed comparisons between model predictions and experiment results, revealing both strengths and limitations of various models. [ABSTRACT FROM AUTHOR]

Recent massive earthquakes have raised concerns that megathrust earthquakes with magnitude 9 can occur in the near future. This article discusses the critical behavior of structures involving torsion caused by extreme ground motions. Unlike factors such as mass and stiffness eccentricity and accidental torsion in a structure that induce torsion, torsional buckling can occur in a moment-resisting frame (MRF) when all beam ends in the longitudinal and transverse directions yield in the lower stories, even if the frame is well designed and its eccentricity is negligibly small. In this study, the theoretically predicted buckling load was presented and validated via numerical analyses. This article shows that excluding the P-Delta effect resulted not only in underestimated deformation but also in overlooked torsional buckling. This study suggests that a high-rise MRF designed in accordance with modern seismic design codes can suffer torsional collapse when the beam ends of the lower stories yield owing to extreme ground motion. Based on these findings, we recommend considering the P-Delta effect when examining the critical behavior of high-rise buildings so as not to overlook the brittle failure mode.

While carbon steel cross‐sections are traditionally categorized as Class 1, 2, 3 or 4, depending on when local instability occurs relative to the key stages of yielding, for stainless steel the lack of a well‐defined yield point and the presence of continual strain‐hardening render this approach artificial and superfluous. A new design methodology is therefore needed, which accounts for the effects of both strain‐hardening and local buckling. The proposed method is based on a modified finite strip method, which accounts for the effects of gradual loss of stiffness due to yielding on the stability of thin‐walled members. Extensive verification of the new method against experimental data showed that cross‐sectional capacities are generally well predicted, with average ratios of the measured to the predicted capacity of 1.18 and 1.19 in compression and bending, respectively, and a standard deviation of 0.10 in both cases. This is a significant improvement over the EN 1993‐1‐4 design rules, where the averages over the same dataset were 1.27 and 1.40, respectively, with standard deviations of 0.14 and 0.17. The rotational capacity of stainless steel cross‐sections in bending was also reasonably well predicted, with an average ratio of measured to predicted curvature of 1.79. [ABSTRACT FROM AUTHOR]

Torsional stiffnesses of chords contribute considerably to the sectional torsional stiffness of steel tubular Vierendeel truss arches and hence determine their out-of-plane buckling. To obtain a more accurate stability design for the Vierendeel truss arches, torsional effects of chords on their out-of-plane stability and failure mechanisms were investigated theoretically and numerically. This paper firstly derives the theoretical formulas of the sectional torsional stiffness and the out-of-plane elastic buckling loads for the pin-ended circular steel tubular Vierendeel truss arches. It is found that incorporating the torsional stiffness of chords can remarkably enhance the sectional torsional stiffness of the Vierendeel truss arches and their out-of-plane elastic buckling loads by ~41%. Then, the out-of-plane elastic buckling loads are calculated for the pin-ended arches by the equilibrium theorem and for the fix-ended arches by the numerical fitting. In both cases, the sectional torsional stiffness and elastic buckling loads are closely dependent on the transverse-to-chord member stiffness ratio (it/ic). Furthermore, the out-of-plane inelastic buckling behaviors are investigated numerically in the end-fixed Vierendeel truss arches with large it/ic, where the ultimate bearing load in full-span radially uniform manner can be significantly enhanced by ~43% by incorporating the torsional stiffness of chords. The calculated reduction factors confirm the design curve b from GB50017-2017 or Eurocode 3 and can provide a conservative design for the out-of-plane stability of the circular steel tubular Vierendeel truss arches. [ABSTRACT FROM AUTHOR]

This article presents experimental and numerical studies on the axial compressive behavior of square concrete‐encased concrete‐filled steel tubular (CECFST) short columns composed of a circular inner steel tube. Tests on six full‐scale short CECFST columns with the inner circular tube diameter varying from 320 to 500 mm were carried out to study the influences of sectional diameter and the tube thickness of circular CFST columns on their axial performance. A theoretical model is developed using fiber analysis method and validated against a large test database. The accuracy of various codified design models is evaluated and a simple model is proposed to calculate their ultimate strengths. Test results show that CECFST columns have improved load carrying capacity and can sustain large axial loads without significant strength degradation. In addition, increasing the thickness of the steel tube significantly improves the composite action of the steel and concrete of the inner CFST column, which increases the compressive strength of CECFST columns by 27.3%. However, the rate of increase in the compressive strength of the core concrete of the CFST column has been found to be higher for the column with a smaller local slenderness ratio. The ductility of CECFST columns is influenced by the concrete strength and the spacing of the stirrups. Furthermore, the design model suggested in this study can provide a better estimation than the codified design models. [ABSTRACT FROM AUTHOR]

The corrugated steel plate shear wall (CSPSW) with inelastic buckling of a corrugated steel plate (CSP) could restrict the elastic out-of-plane buckling of in-filled steel plates with appropriate CSPs, and lateral displacement could be restricted in the structures. So, the CSPSWs with inelastic buckling of CSPs could be applicable in high buildings or the structures with strict requirements of lateral displacement. This paper presents the research works on the seismic behaviour of the CSPSW with inelastic buckling of a corrugated steel plate. A numerical model was developed to simulate the seismic performance of the CSPSW with the inelastic buckling of the CSP, and the FE model was validated through experiment. Subsequently, parametric analyses were performed to investigate for the effects of those key parameters on the seismic behaviour of CSPSWs, such as the height—thickness ratio, aspect ratio, horizontal panel width, corrugation angle, initial imperfections, and surrounding frame stiffness. The buckling and post buckling behaviour, failure modes, ductility and energy absorption capacity of the shear walls were discussed. The results reveal that the CSPSW show high strength, better ductility, and stable hysteretic characteristics. The failure modes of the CSPSWs with CSPs inelastic buckling are the failure of the tension field strips along the along the diagonals in the whole CSPs. And the corners of CSPs in CSPs are weak parts, which should be strengthened in future designs. Besides these, the surrounding frame stiffness should be greater than I c min to ensure energy-dissipating capacity and buckling capacity stability of CSPSWs. [ABSTRACT FROM AUTHOR]

Torsional stiffnesses of chords contribute considerably to the sectional torsional stiffness of steel tubular Vierendeel truss arches and hence determine their out-of-plane buckling. To obtain a more accurate stability design for the Vierendeel truss arches, torsional effects of chords on their out-of-plane stability and failure mechanisms were investigated theoretically and numerically. This paper firstly derives the theoretical formulas of the sectional torsional stiffness and the out-of-plane elastic buckling loads for the pin-ended circular steel tubular Vierendeel truss arches. It is found that incorporating the torsional stiffness of chords can remarkably enhance the sectional torsional stiffness of the Vierendeel truss arches and their out-of-plane elastic buckling loads by ~41%. Then, the out-of-plane elastic buckling loads are calculated for the pin-ended arches by the equilibrium theorem and for the fix-ended arches by the numerical fitting. In both cases, the sectional torsional stiffness and elastic buckling loads are closely dependent on the transverse-to-chord member stiffness ratio (it/ic). Furthermore, the out-of-plane inelastic buckling behaviors are investigated numerically in the end-fixed Vierendeel truss arches with large it/ic, where the ultimate bearing load in full-span radially uniform manner can be significantly enhanced by ~43% by incorporating the torsional stiffness of chords. The calculated reduction factors confirm the design curve b from GB50017-2017 or Eurocode 3 and can provide a conservative design for the out-of-plane stability of the circular steel tubular Vierendeel truss arches.

The direct analysis method (DAM), featuring second-order elastic analysis with two stiffness reduction factors (τb and τg), is the primary means of stability design for steel structures in AISC 360 and AISI S100. The equivalent provisions for stainless steel structures, which are due to be incorporated into the upcoming AISC 370 and ASCE-8 specifications, are developed in this paper. Stainless steel exhibits a rounded stress–strain response, typically described by the Ramberg–Osgood formulation. The slope of this function (i.e., the tangent modulus), adjusted to consider the influence of residual stresses, is used to define the stiffness reduction factor τb at a given axial load level to be applied to members in compression to allow for the adverse influence of the spread of plasticity and residual stresses. The dependency of the degree of stiffness reduction on the roundedness of the stress–strain curve, which varies between the different grades of stainless steel is also directly captured through the strain hardening exponent n that features in the Ramberg–Osgood formulation. Values of 0.7 for AISC 370 and 0.9 for ASCE-8 are proposed for the general stiffness reduction factor τg to be applied to all member stiffnesses to account for the development and spread of plasticity, and to ensure a suitable reduction in stiffness for slender members with low axial load levels. The different τg values between the two specifications are required to reflect the different buckling curves and axial-bending interaction expressions employed. The accuracy of the proposed method for the design of stainless steel members and frames is assessed through comparisons with benchmark shell finite-element results. Comparisons are also made against the new provisions in AISC 370 for design by second-order inelastic analysis. The reliability of the design proposals is demonstrated through statistical analyses, where it is shown that a resistance factor ϕ of 0.9 can be adopted. [ABSTRACT FROM AUTHOR]

The tensile fracture and buckling of longitudinal steel bars, as two important limit states, are often considered critical performance indicators in seismic design and post-earthquake safety assessment of structures. Corrosion significantly deteriorated the mechanical properties of materials. To discuss the degradation patterns of the tensile and buckling performance of corroded steel bars under critical design parameters, monotonic tensile tests and monotonic compression tests considering the lateral constraint of stirrups based on a self-developed stirrup lateral constraint device were conducted. The experimental results showed that the nominal yield strength and nominal peak strength of the tensile curve of corroded steel bars decrease continuously with the increase in corrosion level, and the strength degradation rate is numerically comparable to the corrosion ratio. Corrosion leads to a significant reduction in the buckling capacity and deformation capability of steel bars. The slenderness ratio is a key parameter determining the buckling performance of corroded steel bars. The reduction in cross-sectional area caused by corrosion amplifies the influence of the slenderness ratio. The lateral constraint provided by stirrups enhances the buckling capacity and deformation capability of corroded steel bars. Additionally, the corrosion level, slenderness ratio, and stirrup spacing cause a transition in the compressive stress-strain curve type of corroded steel bars. Finally, a bearing capacity prediction model of corroded steel bars with good accuracy based on a BP neural network was proposed. • The morphology of non-uniformly corroded steel bars was reconstructed. • Corroded buckling test considering constraints effect of stirrup was completed. • The corrosion, slenderness ratio and stirrup spacing changed buckling curve type. • The prediction model of bearing capacity of corroded steel bars was proposed. [ABSTRACT FROM AUTHOR]

Many structural parts are exposed to high temperatures and loading. It is then important to have data about material inelastic behaviour under such exploiting conditions. Influence of temperature on mechanical characteristics of a material may be inserted via the creep coefficient in the range of visco-elasto-plastic (VEP) strains. This damage parameter is implemented in this paper in conjunction with mathematical material modelling approach named rheological-dynamical analogy (RDA) in order to address structural stiffness reduction due to inelastic material behaviour. The aim of this paper is to define structural-material internal damping based on both the RDA dynamic modulus and modal damping ratio, by modelling critically damped dynamic systems in the steady-state response. These systems are credible base for explanation of the phenomenon of thermo-visco-plasticity and creep in structural-material response due to high temperatures and loading. Though elastic buckling information for folded-plate structures is not a direct predictor of capacity or collapse behaviour on its own, both the mode and the load (moment) are important proxies for the actual behaviour. In current design codes, such as AISI S100, New Zealand/Australia, and European Union, the design formulae are calibrated through the calculation of elastic critical buckling loads (or moments) to predict the ultimate strength, thus the ability to calculate the associated elastic buckling loads (or moments) has great importance. Moreover, the buckling mode shapes are commonly employed into non-linear collapse modelling as initial geometric imperfections and thermal performance of folded-plate structures in fire. To examine the buckling behaviour of folded-plate structures, the main numerical solution methods are used such as the finite element method (FEM) and finite strip method (FSM). This paper aims at providing a unified frame for quasi-static inelastic buckling and thermal loading of uniformly compressed folded-plate structures using the FSM.

This paper reports the results of a set of benchmark medium-scale shaking table tests to investigate the significance of the non-stationary characteristics of ground-motion on nonlinear dynamic responses and the structural damage of reinforced concrete (RC) columns. To examine the influence of ground-motion characteristics, four RC columns are tested under (1) near-field without pulse, (2) near-field pulse-like, and (3) far-field ground-motions. These ground-motion records were spectrally matched by the reweighted Volterra series algorithm without changing non-ergodic characteristics. To explore the confinement effects, two sets of column specimens are designed to represent the modern well-confined and older lightly-confined RC columns. Each column is tested in slight, extensive and complete damage limit states. Then aftershock excitations are conducted to investigate the performance of severely damaged RC columns. Low amplitude white-noise tests are conducted on pristine columns and after each damage limit state experiment to detect natural frequency variant of damaged columns using transfer function estimate. Furthermore, using time–frequency analysis, the real-time variant frequency of test specimens is estimated. The significant duration of ground-motions accounting for the effect of non-stationary characteristics of ground-motion is also estimated by time-cumulative damage analysis of the test results. Finally, the time-variant stiffness degradation of RC columns is estimated. [ABSTRACT FROM AUTHOR]

• Stiffness reduction method developed for LTB assessment of tapered beams. • Proposed method eliminates the need to use member design equations. • Comprehensive verification of the stiffness reduction method against shell FE results. • The proposed approach compared against Eurocode 3. • Illustration of the accuracy of proposed method for laterally braced tapered beams. A stiffness reduction method for the lateral-torsional buckling (LTB) assessment of welded web-tapered steel beams is presented in this study. The method is implemented by (i) modelling a tapered steel beam using elastic beam finite elements specifically developed to represent the elastic instability response of tapered steel members, (ii) reducing the Young's modulus E and shear modulus G of each element through a stiffness reduction function considering the bending moments and cross-section properties at the middle of each element and (iii) performing an elastic Linear Buckling Analysis of the beam with reduced stiffness, referred to as LBA-SR herein. Since the adverse influence of the development of plasticity and imperfections on the ultimate member strengths are fully accounted for through stiffness reduction, the presented method does not require any further global instability assessment using member design equations; thus, the proposed method is both direct and practical. Verification of the method is shown for a wide range of web-tapered steel beams using results from nonlinear shell finite element modelling. [ABSTRACT FROM AUTHOR]

Highlights • An analytical hysteretic model for reinforcing bars including buckling is proposed. • Model control parameters are identified using the genetic algorithm. • Prediction equations of control parameters are established by regression analysis. • The proposed model is implemented in OpenSees. • Nonlinear analyses of both isolated reinforcing bars and RC columns are performed. Abstract This paper proposes an analytical hysteretic model for reinforcing bars considering the effects of inelastic buckling and low-cycle fatigue. A strain-dependent post-yield stiffness ratio formula is introduced into the traditional Bouc-Wen model to make it possess the asymmetrical characteristic, so that the compressive stress softening effect generally exhibited by buckling bars can be reasonably described. Meanwhile, the low-cycle fatigue degradation is also contained in the model. Based on the collected experimental hysteresis loops of reinforcing bars, the model control parameters are identified using the genetic algorithm. The corresponding prediction equations of control parameters in terms of physical parameters of the reinforcing bar, such as the slenderness ratio, yield strength and ultimate strength-to-yield strength ratio, are then established by regression analysis. Furthermore, the proposed model is implemented in OpenSees, an open-source computational platform. The effectiveness of the proposed model is verified by performing the comparison with the experimental results of both isolated reinforcing bars and reinforced concrete columns. [ABSTRACT FROM AUTHOR]

Continuous multispan beams in bridges experiences high negative moment at interior supports and the top flanges of these beams are laterally braced due to the concrete slab or steel deck above it. The negative moment can be resisted by increasing the cross sections of the beams at the supports. An earlier study on the elastic lateral torsional buckling of stepped beam with continuous lateral bracing was conducted to propose new design equations. The main focus of this study is to continue the previous research considering the inelastic buckling of stepped beams. ABAQUS, a finite element method program was used to conduct the buckling analysis of the beams. A total of five different load cases were used in the analysis. The effects of the residual stress and geometric imperfection were also considered for the inelastic buckling strength. Results showed that the inelastic buckling strength exceeds the plastic moment of the section and it is not needed to focus on the inelastic range when computing the lateral torsional buckling strength. [ABSTRACT FROM AUTHOR]

A refined constitutive model (called "RDM model") is proposed for simulating the complete stress-strain response of longitudinal reinforcing bars, including the onset of inelastic buckling and subsequent degradation in the post-buckling regime. This model accounts for interactions between lateral ties and longitudinal bars, and is verified using 45 experimental and 58 analytical specimens previously tested by nine research groups. The RDM model is incorporated into a global modeling procedure and validated with six axially loaded columns, 16 axially and laterally loaded columns, and four beams previously tested by nine research groups. The validated procedure is used to study the influences of global second-order mechanisms such as geometrical nonlinearities, shear effects, and confinement effectiveness on the local buckling behavior. The proposed RDM model is shown to provide accurate response simulations for the buckling of reinforcing bars with a wide range of mechanical and geometrical properties. This model employs simple equations and defines full-range compressive response from well-known tensile material properties. [ABSTRACT FROM AUTHOR]

Abstract Large earthquakes are rare natural hazards, having catastrophic impact on society due to loss of lives, damage to constructed facilities, and business interruption. Because of damage accumulation due to the main strong shaking, aftershocks potentially endanger the safety of residents and subsequently increase financial loss due to downtime and repair costs. Therefore, accurate prediction of the seismic performance of structures in the post-earthquake stage is critical for disaster risk mitigation. This paper employs an advanced structural modeling technique, which can simulate various features of cyclic degradation in material and structural components using nonlinear fiber beam-column elements. The model accounts for inelastic buckling and low-cycle fatigue degradation of longitudinal reinforcement and can simulate multiple failure modes of reinforced concrete structures under dynamic loading. Furthermore, a comprehensive ground motion selection accounting for multiple types of ground motions, such as shallow crustal, deep inslab, and subduction earthquakes, is implemented. Finally, a new set of fragility curves has been developed for each ground motion type, which accounts for the aftershock effects and influence of ground motion types on cyclic degradation and failure modes of low-rise reinforced concrete structures. It was found that slight and moderate damage is not significantly affected by major aftershocks for different ground motions types. However, considering aftershocks increases the probability of exceedance of damage for extensive and complete damage up to 5% and 10% for inslab and crustal event, respectively. The proposed methodology significantly improves the accuracy of seismic risk and vulnerability assessment by reducing the uncertainties associated with structural modeling and variability of earthquake ground motions. Highlights • Low-cycle fatigue and inelastic buckling of reinforcing bars on dynamic response of RC structures are considered. • Impact of real mainshock-aftershock sequences and different ground motion types are investigated. • Fragility curves for low-rise RC structures considering cyclic degradation and different ground motion are developed. • Incremental damage due to aftershocks was found to be negligible for slight and moderate damage. • Considering rebar buckling and low-cycle fatigue increased the probability of collapse, up to 10%. [ABSTRACT FROM AUTHOR]

The Wagner coefficient is a key parameter used to describe the inelastic lateral-torsional buckling (LTB) behaviour of the I-beam, since even for a doubly-symmetric I-section with residual stress, it becomes a monosymmetric I-section due to the characteristics of the non-symmetrical distribution of plastic regions. However, so far no theoretical derivation on the energy equation and Wagner’s coefficient have been presented due to the limitation of Vlasov’s buckling theory. In order to simplify the nonlinear analysis and calculation, this paper presents a simplified mechanical model and an analytical solution for doubly-symmetric I-beams under pure bending, in which residual stresses and yielding are taken into account. According to the plate-beam theory proposed by the lead author, the energy equation for the inelastic LTB of an I-beam is derived in detail, using only the Euler-Bernoulli beam model and the Kirchhoff-plate model. In this derivation, the concept of the instantaneous shear centre is used and its position can be determined naturally by the condition that the coefficient of the cross-term in the strain energy should be zero; formulae for both the critical moment and the corresponding critical beam length are proposed based upon the analytical buckling equation. An analytical formula of the Wagner coefficient is obtained and the validity of Wagner hypothesis is reconfirmed. Finally, the accuracy of the analytical solution is verified by a FEM solution based upon a bi-modulus model of I-beams. It is found that the critical moments given by the analytical solution almost is identical to those given by Trahair’s formulae, and hence the analytical solution can be used as a benchmark to verify the results obtained by other numerical algorithms for inelastic LTB behaviour. [ABSTRACT FROM AUTHOR]

• The behavior of the most potential temperature distributions is presented and applied in calculating column axial load capacity. • A direct formula to predict the inelastic buckling load at compartment fire is presented and validated. • The column behavior is sensitive to the values of the yield stress. • Thermal gradients are likely to occur, and have a great impact on the buckling capacity, due to the second-order effects which are induced by thermal bowing. This paper presents a comprehensive numerical study of the inelastic buckling behavior of I and H shaped steel columns subjected to different fire scenarios. A numerical computer code was developed and validated against numerical and experimental studies considering the impact of different temperature distributions on columns during fire. The study suggests practical temperature distributions, for design purposes, along the column height and the cross section and outlines the isolated behavior of columns in localized fire situations. Moreover, the study provides design guidelines for the inspected scenarios. The study indicates that the assumed temperature profile has a significant impact on the column buckling capacity. A direct formula to predict the inelastic buckling capacity of columns under uniform temperatures as well as design charts for S355 and S235 steel columns under various non-uniform temperature distributions are presented. [ABSTRACT FROM AUTHOR]

This paper presents the results of numerical simulations on three main factors and their influence on the buckling resistance of reinforcing bars and on their behaviour in the range of postcritical deformations. These three factors are the shape of initial deformation, the amplitude of geometric imperfection and the slenderness of bars. The analysis was made of bars fixed on both sides for three initial shapes of deformation between adjacent stirrups, four amplitudes of geometric imperfections and eight bar slendernesses. The results of the numerical analyses carried out showed that the factors analysed have a very high influence on the inelastic buckling of the bars. The initial deformation shape, the radius of curvature and the slenderness of the bars have a significant influence on the buckling resistance of these bars and their longitudinal and transverse deformations. The research demonstrates that bars which are bent or compressed initially have a smaller resistance to buckling compared to straight bars, as the amplitude of geometric imperfections increases and the slenderness of the members increases. However, for the deformation shape of the bars, which is accompanied by shear forces, the drop in the buckling resistance of the members is small, and resistance to buckling for items with a small slenderness was higher than that of straight bars.

In this research the behavior of cylindrical shells under axial load have been studied. The experimental program is included two groups: the first consists of nine cylinders; each has a diameter of 150 mm, while the height varies from 100 to 500 mm and thickness of 1.5 mm, test results show that the optimum height to achieve the maximum strength is 300 mm with L/D equal to 2. The second group consists of two cylinders with diameter of 150 mm and height of 300 and 500 mm strengthened with stiffeners plate welding from inside at four quarters with thickness of 1.5 mm and width 20 mm fabricated from the same metal of the cylinders. After testing these two cylinders were gain an increase in the strength reached to 42% for 300 mm cylinder and 26.4% for 500 mm cylinder. The failure modes for these two groups are: the buckling at bottom like “elephant’s foot” for cylinders height from 100 to 300 mm and “inelastic buckling” for cylinders height from 350 to 500 mm for the first group, and the ” inelastic buckling” for the second group.

This paper describes experimental and numerical investigations of the hysteretic behaviour of the corrugated steel plate shear wall (CSPSW). Two single-bay, two-storey CSPSWs without elastic buckling were cyclically tested. A numerical model was developed to simulate the experimental results. The inelastic buckling capacity and failure mode of the corrugated steel plate shear wall were examined. The results revealed that through the proper design of the corrugation parameters, the corrugated steel plate shear wall could avoid elastic buckling, and this shear wall had high initial stiffness buckling, strength, energy dissipation and ductility. In addition, the feasibility of the simultaneous construction of corrugated steel plates and frames was discussed. Finally, the serviceability of the existing design methods for corrugated steel plate shear walls was examined, which proved that the plate-frame interaction model could predict the shear strength and initial stiffness of the corrugated steel plate shear walls with good accuracy. [ABSTRACT FROM AUTHOR]

A non-linear finite element (FE) framework for time-dependent capacity assessment of corroded rectangular reinforced concrete (RC) columns is developed. The proposed non-linear FE model includes the impact of corrosion on inelastic buckling and low-cycle fatigue degradation of longitudinal reinforcement. The proposed non-linear FE model is validated against a set of experimental data and then extended to evaluate the impact of corrosion on damage limit states to be used in seismic performance and evaluation of corroded structures. This is done through a parametric study on hypothetical RC columns, varied in axial force ratios, mass loss ratios, cover crack widths and confinement levels. Moreover, the application of the proposed model in seismic collapse capacity assessment of corroded structures is shown through non-linear dynamic analyses of prototype columns. Results show that, depending on the axial force ratio, corrosion changes the failure mechanism of the columns. The results of this study suggest that in seismic fragility analysis of corroded structures, the damage limit states should be considered as time-variant parameters. [ABSTRACT FROM AUTHOR]

Trabecular bone is a cellular composite material comprising primarily of mineral and organic phases with their content ratio known to change with age. Therefore, the contribution of bone constituents on bone’s mechanical behaviour, in tension and compression, at varying load levels and with changing porosity (which increases with age) is of great interest, but remains unknown. We investigated the mechanical response of demineralised bone by subjecting a set of bone samples to fully reversed cyclic tension-compression loads with varying magnitudes. We show that the tension to compression response of the organic phase of trabecular bone is asymmetric; it stiffens in tension and undergoes stiffness reduction in compression. Our results indicate that demineralised trabecular bone struts experience inelastic buckling under compression which causes irreversible damage, while irreversible strains due to microcracking are less visible in tension. We also identified that the values of this asymmetric mechanical response is associated to the original bone volume ratio (BV/TV). [ABSTRACT FROM AUTHOR]

A study on how a mathematical material modeling approach named rheological-dynamical analogy (RDA) can be used to predict the quasi static and dynamic inelastic buckling and failure of structures is presented in this paper. An analysis of the uniformly compressed folded-plate structures, made of isotropic materials, is carried out. Two sources of non-linearity, one involving geometrical non-linearity due to large deflection, and the other involving material non-linearity due to inelastic behavior, are analyzed by implementing a full-energy finite strip method (FSM). The material non-linearity is analyzed using the RDA. A very basic continuum damage model with one damage parameter is implemented in conjunction with a mathematical material modeling approach in order to address stiffness reduction due to inelastic behavior. According to the analogy, a very complicated material non-linear problem in the inelastic range of strains is solved as a simple linear dynamic one. The orthotropic constitutive relations are derived and modulus iterative method for the solution of nonlinear equations is presented. [ABSTRACT FROM AUTHOR]

A stiffness reduction method for the design of laterally restrained web-tapered steel structures fabricated through the welding of individual steel plates is presented in this paper. Stiffness reduction functions for welded members, accounting fully for the deleterious influence of the spread of plasticity and imperfections on the structural resistance, are developed. The method is implemented through (i) dividing tapered members into prismatic segments along their lengths, (ii) reducing the flexural stiffness of each segment by means of the developed stiffness reduction functions considering the first-order forces and cross-section properties of each segment, (iii) performing Geometrically Nonlinear Analysis and (iv) making cross-section strength checks. Essentially, it is proposed to replace the current typical approach to structural design of conducting a simple elastic (with nominal stiffness) structural analysis followed by elaborate member checks with an integrated process utilising more sophisticated second-order analysis (with stiffness reduction) but very simple design checks. The distribution of internal forces within the structure is captured more accurately due to the allowance for imperfections, residual stresses and plasticity through stiffness reduction and the allowance for frame and member instability effects through the use of second-order analysis. The need for determining effective lengths and for conducting member buckling checks is also eliminated. Verification of the proposed approach against the results obtained from nonlinear shell finite element modelling is presented for various tapering geometries, slenderness values and loading conditions. Assessment of the proposed method against the European and North American steel design codes for tapered steel structures is also provided. [ABSTRACT FROM AUTHOR]

The current AASHTO and AISC Specification equations characterizing the lateral-torsional buckling (LTB) resistance of steel I-section members are the same, with minor exceptions, and are based in large part on unified provisions calibrated to experimental data. This paper takes a fresh look at the correlation of the flexural strength predictions from these equations with a large experimental data set compiled from research worldwide. To account fully for the moment gradient and end restraint effects present in the physical tests, the study employs practical buckling calculations using inelastic stiffness reduction factors (SRFs) based on the design resistance equations. The study focuses on uniform bending tests as well as moment gradient tests in which the transverse loads are applied at braced locations. Reliability indices are estimated in the context of building design. It is shown that a proposed modified form of the current resistance equations provides a more uniform level of reliability, as a function of the LTB slenderness, consistent with the target intended in the AISC Specification. The paper also calls attention to the limited experimental data pertaining to the inelastic LTB resistances in certain cases. The paper concludes by providing additional recommendations for LTB strength calculations in routine design, including illustrative plots conveying the impact of the proposed changes. [ABSTRACT FROM AUTHOR]

Steel-Equal Angle (SEA) has recently been utilized as longitudinal reinforcement in high-strength concrete columns to improve their strength and ductility. However, investigations have been very limited on the responses of eccentrically loaded SEA Reinforced Concrete (SEARC) columns. This paper presents the development of a computer simulation model based on fiber element discretization for determining the structural behavior of eccentrically loaded SEARC short columns. The inelastic buckling of SEA sections and the concrete confinement induced by SEA sections are explicitly taken into account. The modeling procedures are given for axial load moment-interaction curves and moment-curvature curves of SEARC columns. The accuracy of the developed fiber model is verified against the available test data. The performance of eccentrically loaded SEARC columns incorporating various design parameters is extensively investigated. It is shown that the developed computer simulation model captures well the experimentally measured responses of short SEARC columns and can be utilized in the analysis and design of such columns in practice. It has been found that the behavior of SERAC columns under eccentric loads is significantly influenced by the longitudinal steel ratio, the compressive strength of concrete, and the axial load level. The width of SEA sections and tie spacing considerably influence the ductility of the columns. • A fiber model is developed for the analysis of eccentrically-loaded SEARC columns. • Validation of the developed fiber model of SEARC columns is presented. • Effects of various column parameters on load-moment interaction curves are studied. • Effects of various column parameters on moment-curvature responses are studied. [ABSTRACT FROM AUTHOR]

This paper quantifies the impact of the non-stationary content (time-varying parameters that are not captured by power spectral content alone) of different ground-motion types (near/far field, with/without pulses time-series) on the nonlinear dynamic response of reinforced concrete bridge piers, taking into account the material cyclic degradation. Three groups of ground motions are selected to represent far-field, near-field without pulse and near-field pulse-like ground motions. Three analysis cases are considered corresponding to acceleration series matched to the mean response spectrum of: (1) far field, (2) near-field without pulse and (3) near-field pulse-like ground-motions, respectively. Using the selected ground motions, several nonlinear incremental dynamic analyses of prototype reinforced concrete bridge piers with a range of fundamental periods are conducted. Finally, a comparison between the response of the structures using the material model accounting for both buckling and low-cycle fatigue of reinforcing steel and the more conventional material model that does not account for these effects is made. The results show that the inelastic buckling and low-cycle fatigue have a significant influence on the nonlinear response of the RC bridge piers considered and that pulse effects can increase the mean acceleration response by about 50%. [ABSTRACT FROM AUTHOR]

This research proposes the inelastic buckling and modal analysis to design optimal shape and size through UL700 steel arch-grid unit module which is for localized reinforcement of soft ground. The optimal arch-grid design is achieved among its most efficient design possibilities such as different plate type, extended grid, multi-story grid, combined grid. The steel arch-grid unit module is composed of a vertical member and a board member combined with the top and bottom sides of the said vertical member, including the horizontal member equipped with multiple arm parts combined with the center part into one body in the shape of a cross. The construction method for reinforcement of soft ground is proposed in detail in this research. Numerical experiments are provided to survey optimal shape and size of arch-grid structures with differential models applied to buckling analysis, modal and static load, in consideration of both linear and nonlinear behaviors, by using SAP2000 version 15.0.1 software. With sufficient features of steel arch-grid for supporting structural foundations, this research suggests the possibility of requiring more studies and of providing more applications in the field of constructional structures. [ABSTRACT FROM AUTHOR]

A total of 110 inelastic buckling tests on corroded and uncorroded reinforcing bars with various bar diameters are conducted. Through regression analyses of experimental data, the combined effect of nonuniform pitting corrosion and bar diameter (size effect) on buckling and postyield buckling response of corroded and uncorroded bars are investigated. The experimental result shows that bar diameter has a minor influence on postyield buckling response of uncorroded bars. However, it is found that bar diameter has a more significant impact on buckling capacity of corroded bars. Finally, the experimental data of tested corroded bars in this research are used to calibrate and update a new uniaxial material model of corroded bars to account for size effect. The proposed updated model simulates the inelastic buckling and postbuckling behavior of corroded bars accounting for size effect. This model is implemented in an open source finite element code and is readily available to the community for nonlinear analysis of corroded reinforced concrete structures. [ABSTRACT FROM AUTHOR]

Finite-element (FE) analysis was used to compare the high-temperature responses of steel columns with two different stress-strain models: the Eurocode 3 model and the model proposed by National Institute of Standards and Technology (NIST). The comparisons were made in three different phases. The first phase compared the critical buckling temperatures predicted using forty-seven column data from five different laboratories. The slenderness ratios varied from 34 to 137, and the applied axial load was 20% to 60% of the room-temperature capacity. The results showed that the NIST model predicted the buckling temperature as or more accurately than the Eurocode 3 model for four of the five data sets. In the second phase, thirty unique FE models were developed to analyze the W8 × 35 and W14 × 53 column specimens with the slenderness ratio about 70. The column specimens were tested under steady-heating conditions with a target temperature in the range of 300°C to 600°C. The models were developed by combining the material model, temperature distributions in the specimens, and numerical scheme for non-linear analyses. Overall, the models with the NIST material properties and the measured temperature variations showed the results comparable to the test data. The deviations in the results from two different numerical approaches (modified Newton-Raphson vs. arc-length) were negligible. The Eurocode 3 model made conservative predictions on the behavior of the column specimens since its retained elastic moduli are smaller than those of the NIST model at elevated temperatures. In the third phase, the column curves calibrated using the NIST model was compared with those prescribed in the ANSI/AISC-360 Appendix 4. The calibrated curve significantly deviated from the current design equation with increasing temperature, especially for the slenderness ratio from 50 to 100. [ABSTRACT FROM AUTHOR]

Concrete-encased concrete-filled steel tube (CECFST), an innovative type of concrete-steel composite structure, has been increasingly employed in mega construction projects due to its outstanding structural performance. However, although intermediate and sometimes slender columns have become commonplace in high-rise buildings and large-scale bridges, the research on member behaviour of CECFST slender columns barely exists in the current literature. In this paper, a comprehensive experimental and numerical modelling programme was conducted to study buckling resistance and structural behaviour of CECFST slender columns. Pin-ended concentric load column tests were carried out on four slender columns, together with a fixed-ended stub column as a reference specimen. Key test results of all specimens, such as failure modes and effects of slenderness on strength, ductility and stiffness, showed that buckling failure and P - δ effect degraded the performance indices of CECFST slender columns. Afterwards, a finite element (FE) modelling programme was performed, where a range of member imperfections was incorporated and validated against test results. Parametric studies were then conducted to supplement the test data bank, from which over sixty FE results were generated. The test and FE failure loads obtained were utilised to examine the applicability of current design methods in the European code, American specification and Australian standard. The buckling curve 'b' set out in the European code was found to result in the most accurate and consistent buckling resistance predictions, while the American specification and Australian standard generally yielded over-conservative and unsafe results, respectively. • Four slender and one stub CECFST columns were tested under concentric compression. • The compression strength, ductility and stiffness of CECFST columns are inversely correlated with slenderness ratio. • The confinement effect of CECFST slender columns is less significant than that of stub columns. • The applicability of the design methods specified in current standards to CECFST slender columns was examined. [ABSTRACT FROM AUTHOR]

This study aims to investigate the effects of load height, stepped beam configuration and section compactness on the inelastic lateral buckling strength of doubly and singly stepped I-beams. To study the effects of load height, the loads are situated at three points: at the center of the top flange, at the shear center and at the center of the bottom flange. To check for the effect of stepped beam configuration, beams were stepped either at both top and bottom flanges or at top flange only. Meanwhile, to investigate the effects of section compactness, two sections are analyzed: one section with compact flanges and web and another section with non-compact flanges and a compact web. The loadings are limited to those having an inflection point of zero. To also check the effect of steps, stepped parameters α, β and γ are varied. The buckling strengths of the beams investigated are obtained by conducting nonlinear analysis using the finite element program, ABAQUS. In conducting the nonlinear analysis, the residual stresses and geometric imperfections are taken into consideration to clearly simulate the inelastic behavior of the beams. The results of the analysis would then determine if the location of the loads, configuration of stepped flanges and compactness of flanges have significant effect on the inelastic buckling strength of the stepped beams. [ABSTRACT FROM AUTHOR]

In this paper, the development and assessment of a stiffness reduction method for the in-plane design of steel frames is presented. The adopted stiffness reduction approach is implemented by reducing the flexural stiffnesses ( EI ) of the members of a steel frame by considering the first-order forces they are subjected to through the stiffness reduction functions and performing Geometrically Nonlinear Analysis (i.e. second-order elastic analysis). Since the presented approach uses stiffness reduction functions that fully take into account the deleterious influence of imperfections and the spread of plasticity on the structural response and member strengths, it obviates the need of using member design equations, and only requires cross-section strength checks. The accuracy of the presented approach is illustrated for individual steel members and non-redundant and redundant benchmark steel frames from the literature. In all the considered cases, the presented method is verified against the results obtained from nonlinear finite element modelling. A comparison of the presented approach against the notional load method of the European structural steel design code EN 1993-1-1 and the direct analysis method of the US structural steel design code AISC 360-10 is also provided. [ABSTRACT FROM AUTHOR]

The paper presents the results of numerical analyses of elasto-plastic buckling of steel reinforcing bars. Bars with different geometrical parameters made of steel with various mechanical characteristics were analyzed. The commercial program COSMOS/M based on the finite element method was used. It follows from the results that slenderness is not the only parameter that affects the elasto-plastic buckling of reinforcing bars. Such parameters as the length of the plastic plateau, ultimate stress and the plastic hardening module play an important role as well. [ABSTRACT FROM AUTHOR]

The paper presents a theory of inelastic column buckling which is consistent with the principles of plastic flow theory. The theory accounts for flexural, torsional and flexural-torsional modes. While the use of the tangent modulus to describe inelastic flexural buckling has been common place for a long time, efforts to comprehensively unite the torsional and flexural-torsional modes with the principles of plastic flow theory have so far been hampered by the ‘plastic buckling paradox’. New theoretical developments presented in this paper provide a way to achieve this goal. The solution hinges on the derivation of the inelastic shear stiffness while considering an infinitesimal solid element embedded within the column at a stage immediately past the point of buckling. The proposed inelastic column theory is verified against selected experimental data pertaining to aluminium and stainless steel columns of various cross-sections. Particular attention is paid to the torsional buckling problem of the inelastic cruciform section column. [ABSTRACT FROM AUTHOR]

This paper presents the findings of an experimental and analytical research study that was conducted to evaluate the buckling behavior of steel bridge piles with localized severe section loss. Seven full-scale H-piles with different degrees of simulated corrosion were tested under axial compression. A nonlinear, three-dimensional (3D), finite-element model was developed to predict the inelastic buckling behavior of corroded piles under axial compression loading. The model was validated by comparison with the experimental results. The validated model was used to conduct a parametric study. Six parameters were investigated: (1) pile slenderness, (2) reduction of the flange thickness, (3) reduction of the web thickness, (4) location of the corroded region, (5) extent of the corroded region, and (6) magnitude of the residual stresses. The results indicate that the reduction of the flange thickness is the most significant factor affecting the inelastic buckling behavior. The pile slenderness and the magnitude of the residual stresses affected only the capacity of piles for which global buckling was the dominant failure mode. The experimental and numerical results were compared to three existing design methods to evaluate the suitability of the current design specifications for predicting the axial capacity of steel compression members with localized corrosion. [ABSTRACT FROM AUTHOR]

This paper presents the finite element analyses made which determine the inelastic buckling capacity of monosymmetric stepped I-beams under uniform bending. The stepped beams analyzed have non-compact flanges and varying degree of symmetry about the x-axis. Beams with degree of symmetry, ρ, of 0.1 to 0.9 with an interval of 0.2 are investigated for this study. Both doubly stepped and singly stepped beam configurations are analyzed. To determine the inelastic buckling strength of the beams, nonlinear analysis is performed using the finite element program ABAQUS. Different design standards such as AISC, AS4100 and EN1993 are then used to compare the strengths of prismatic and stepped beams. The results from the comparisons are also used to check the accuracy of the values obtained from finite element analysis. The results showed that finite element analysis can be a very useful tool in determining the inelastic buckling capacity of stepped beams. Also, the comparisons for the stepped beams analyzed with stepped length parameter α of 0.25, 0.333 and 0.5, with increase in flange thickness of about 20–80% and no increase in flange width, showed that there is about a 10% increase in the buckling strength when the beams are stepped. The new stepped beam correction factor, C nfist m , is then introduced to take into account the increase in strength when the beams are stepped. [ABSTRACT FROM AUTHOR]

• Failure performance of BSB specimens with different slenderness ratios and strain amplitudes were discussed. • Effects of inelastic buckling on fatigue properties of BSB specimens were studied. • A fatigue model including the effects of inelastic buckling was proposed. Reinforcement corrosion is the main factor that affects the durability of reinforced concrete (RC) structures in corrosive environments. In this study, a bimetallic steel bar (BSB) composed of a stainless-steel cladding and a carbon steel substrate has been proposed to solve the issue of corrosion. When a RC structure is subjected to a seismic load, a reciprocating load is usually applied to the resistant member. Longitudinal steel reinforcements tend to cause fatigue failure. Inelastic buckling significantly affects the fatigue properties of the steel reinforcement. In this study, we investigated the low-cycle fatigue properties of a BSB, including inelastic buckling. Based on the experimental results, the cyclic curves of the BSB specimens exhibited a shuttle shape. The effects of the slenderness ratio (L / D) on the peak stress of the stable hysteretic curve of the BSB specimens were discussed. Predictive equations were suggested to quantify the effects of L / D and fatigue strain (ε a) on the low-cycle fatigue properties of BSB specimens. The effects of L / D and ε a on the variation trends of the peak stresses of BSB specimens were investigated. The failure performances of BSB specimens with different L / D and ε a values were discussed. Based on the experimental results, a fatigue model was proposed to quantify the effects of inelastic buckling on BSB specimens. [ABSTRACT FROM AUTHOR]

In this paper, a stiffness reduction method for the flexural–torsional buckling assessment of steel beam–columns subjected to major axis bending and axial compression is presented. The proposed method is applied by reducing the Young’s E and shear G moduli through the developed stiffness reduction functions and performing Linear Buckling Analysis. To account for second-order forces induced prior to buckling, the in-plane (in the plane of bending) and out-of-plane analyses of a member are separated and stiffness reduction for the out-of-plane instability assessment is applied on the basis of member forces determined from the in-plane analysis. Since the developed stiffness reduction functions fully take into account the detrimental influence of imperfections and spread of plasticity, the proposed method does not require the use of member design equations, thus leading to practical design. For the purpose of verifying this approach, the strength predictions determined through the proposed stiffness reduction method are compared against those obtained from nonlinear finite element modelling for a large number of regular, irregular, single and multi-span beam–columns. [ABSTRACT FROM AUTHOR]