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A steel brace is effective to retrofit old reinforcement concrete (RC) buildings by increasing the horizontal load capacity of structures. However, concrete cracks that easily occur in the surrounding RC members under tension initiate early strength degradation, so this research aimed to develop a new self-centering brace (SCB) with the compression-only capacity such that no tension force is developed in the brace or to the adjoining RC members. Original SCBs have been developed to reduce the residual deformation of structures with a symmetrically flag-shaped hysteretic response. By altering the force transfer mechanism in the original SCB, a compression-only self-centering brace (C-SCB) can be developed under a symmetrically reversed cyclic loading, providing an alternative for the RC building retrofit. This paper first introduces the mechanics and deformation mechanism of the proposed C-SCB. A test program is then conducted on the cyclic tests of a buckling-restrained energy dissipating bar (EDB) to evaluate the energy dissipation. A 3,695-mm-long C-SCB is composed of posttensioning high-strength steel tendons, steel compression members, and buckling-restrained EDBs for the energy dissipation. The C-SCB in tests showed a good compression-only self-centering capability up to an axial displacement of 31 mm, with a maximum axial force of 1,530 kN. No damage of the steel tendons, compression members, or EDBs was found after three phase tests. Finite element analysis further validated the compression-only hysteretic response and mechanics of the C-SCB in a symmetrically reversed cyclic loading. [ABSTRACT FROM AUTHOR]

A full-scale, two-tiered steel buckling-restrained braced frame (BRBF) was tested to evaluate experimentally the seismic behavior of steel multitiered BRBFs, namely, column stability response, column seismic demands, and tier deformations under a loading protocol representing earthquake ground motions. The test specimen consisted of diagonal braces oriented in opposing directions in the two adjacent tiers to create the most critical multitier response. The test frame was designed in accordance with the 2010 AISC Seismic Provisions as a lateral load-resisting system of a single-story building. The frame was subjected to a three-phase loading protocol consisting of lateral displacement time histories corresponding to a far-field ground motion record and a near-field ground motion record applied sequentially achieving total frame drifts in excess of 3.5%, followed by a final monotonic lateral displacement corresponding to 4.5% story drift. The test frame exhibited a stable response despite a non-uniform distribution of frame inelastic deformation between the tiers, which induced significant in-plane bending moments in the columns. Flexural bending, combined with a large axial compression force, led to partial yielding in the columns. Large deformation demands were also observed in the BRB yielding in tension and attracting the majority of frame lateral deformation. On the basis of test results, a displacement-based analysis approach was proposed to relate column in-plane bending and flexural stiffness to relative inelastic tier deformations. [ABSTRACT FROM AUTHOR]

Little research has been reported that investigates the effects of plate local buckling and postbuckling on the in-plane behavior and strength of steel arches, and hitherto there has been no corresponding design guidance available. This paper presents a numerical investigation of the structural behavior of steel arches, and proposes a strength design method against their in-plane failure by considering plate local elastic-plastic buckling and postbuckling coupled with global elastic-plastic buckling. The failure modes of pin-ended steel circular arches having a box section under a uniformly distributed radial load are analyzed by using a large deformation elastic-plastic finite-element formulation. It is found that plate local buckling significantly influences the in-plane failure mode and strength of a steel arch. The arch may fail owing to local elastic-plastic buckling of its plates, global elastic-plastic buckling of the arch, or coupled local and global elastic-plastic buckling. The failure mode is found to depend on a number of factors such as the height-to-thickness ratio of the plate components, the aspect ratio of the cross section, the rise-to-span ratio, and the slenderness of the arch, as well as the yield stress of the steel. It is also found that the most important factors that influence the strength of the arch are the normalized global slenderness of the arch and the normalized height-to-thickness ratio of the plate components of the cross section. A strength reduction coefficient for estimating the in-plane strength of arches is developed based on these two most significant parameters, and a corresponding strength design method is proposed. [ABSTRACT FROM AUTHOR]

Experimental work was conducted on oriented strand board webbed wood I-joists to investigate the buckling behavior. Both lateral buckling and local web buckling were witnessed in the tests. The two types of buckling were reproduced in the finite element simulations using ABAQUS. The buckling modes and usually overestimated buckling loads of a joist were obtained from linear eigenvalue buckling analysis. The buckling modes were then introduced into a joist as initial geometric imperfections to conduct nonlinear buckling analysis, and more reliable buckling loads were obtained. Based on statistics of the analytical results, the local web buckling capacity at a support was empirically expressed by the postbuckling load. The empirical formula was extended to local web buckling under a concentrated load applied to the upper flange, where a reduction in buckling load was made to take the effect of moment into account. [ABSTRACT FROM AUTHOR]

An experimental and numerical study of the flexural buckling behavior of hot-finished high-strength steel (HSS) square and rectangular hollow section (SHS and RHS, respectively) columns is described in this paper. A total of 30 hot-finished S460 and S690 hollow section column specimens have been tested in compression with pin-ended boundary conditions. Finite element (FE) models have been developed to replicate the experiments and employed in a subsequent parametric study considering a range of member geometries. Based on the test and FE results, the applicability of the current column design curves in European, North American, Chinese and Australian structural steel design standards to hot-finished HSS SHS and RHS columns has been verified by means of reliability analyses [ABSTRACT FROM AUTHOR]

This paper presents a new design methodology for equal-width rectangular hollow section (RHS) X-joints failing by sidewall buckling. In the new approach, a slenderness parameter is defined based on the elastic local buckling stress of the sidewall, idealized as an infinitely long plate under patch loading. A Rayleigh-Ritz approximation is thereby used to obtain a closed-form solution. The proposed design equation is verified against experimental results over a wide range of wall slenderness values obtained from the literature and complemented by a brief experimental program carried out by the authors. It is demonstrated that the new design equation yields excellent results against the experimental data. Finally, a reliability analysis is performed within the framework of both the Eurocode and the AISI standards to ensure that the proposed design equation possesses the required level of safety. The newly proposed equation strongly outperforms the current Comité International pour le Développement et l'Etude de la Construction Tubulaire (CIDECT) design rule for sidewall buckling and also further extends the range of applicability to a wall slenderness ratio of up to 50. [ABSTRACT FROM AUTHOR]

This paper presents an experimental investigation on the evaluation of the seismic performance of a new hybrid buckling restrained brace (HyBRB) under cyclic load. Detailed design steps adopted for the HyBRB design are reported in this paper. The analytical method for estimation of critical loads corresponding to buckling mode formation of the steel core inside the restrainer has been presented. The design targets achieved for the HyBRB are ease of inspection of the detachable BRB core to facilitate replacement of the steel core after a seismic event, if necessary, and enhanced energy-dissipation capacity through restrained buckling about both weak and strong axes of the core. The proposed HyBRB has displayed stable hysteretic behavior with good energy-dissipation capacity in low to high levels of the core strain range. Permanent deformation about the strong axis of the core was observed on unfastening of the restrainers, although restrained buckling of the core was observed about the weak axis in lower displacement amplitudes. Analytical simulation was carried out using a phenomenological model to simulate the experimental behavior. The simulated axial force-deformation hysteresis loops were found to be in close agreement with those obtained from experimental investigation. [ABSTRACT FROM AUTHOR]

This paper describes an experimental program investigating the local-global interaction buckling of stainless steel I-section beams. Three alloys were included: austenitic S30401, ferritic S44330, and lean duplex S32101. Extensive coupon tests were conducted to determine the specific properties of stainless steel sheets, including nonlinearity, anisotropy, and strain hardening. The test program encompassed six laterally braced tests and 24 unbraced tests with spans ranging between 1.9 and 4.0 m. The unbraced specimens were tested in a specially designed setup featuring clearly defined loading and support conditions. Interaction buckling was successfully achieved in the tests. The geometric imperfections, bearing capacity, and sectional and global deformations of each specimen were carefully recorded before or during the tests. Key factors affecting the test conditions were identified. The research addressed the lack of experimental data for local-global interaction buckling of stainless steel beams with open cross section and establishes the foundation for further theoretical study, as described in a companion paper. [ABSTRACT FROM AUTHOR]

This paper deals with the effects of geometric imperfections on flexural inelastic buckling resistance of axially loaded columns with equally spaced lateral braces and presents a simplified way of forming the critical geometric imperfection for finite-element analyses, which leads to rational results for buckling resistances. First, laterally braced columns with geometric imperfections formed by the traditional single half sine wave or the eigenbuckling modes were analyzed by FEM to illustrate the effect of different imperfection shapes. Second, geometric imperfections of columns acquired from measurements in laboratory tests were adopted, and the statistical characteristic and probability distribution of initial deflections along the column length were obtained; then, extensive numerical results from finite-element analyses were obtained through random imperfection simulations. Last, the comparison was made between statistical results based on the random imperfections and those based on eigenbuckling modes to propose a critical geometric imperfection shape as a linear superposition of a limited number of scaled eigenbuckling modes, making it possible to obtain a rational buckling resistance result by one-time analysis, which is safe but not too conservative. The commonly used lowest eigenbuckling mode or equivalent sine shape for initial geometric imperfections do not provide a rational prediction for the inelastic buckling resistance of laterally braced columns. The critical geometric imperfection shape presented in this paper can be used in advanced analysis for inelastic buckling resistance of braced columns. [ABSTRACT FROM AUTHOR]

Part I of this work was concerned with the experimental and numerical analysis of the lateral force, or thrust, exerted by the inner core of a buckling-restrained brace (BRB) when, after buckling in compression, it arrives into contact with the external retaining case. As Part II of that study, this paper considers the case of a steel-bolted BRB, with an empty gap between core and containment struts, to attempt the derivation of engineering analytical expressions for such a thrust. It is found that the relationship between applied axial force and buckled wavelength does not obey Euler's formula. [ABSTRACT FROM AUTHOR]

This paper describes the buckling behavior of cold-formed steel equally lipped angle columns. The initial local imperfections, residual stresses, and corner material properties of the cold-formed steel angles have been measured experimentally and reported in this paper. An accurate finite element model was developed to carry out the buckling analysis. Both initial local and overall geometric imperfections have been incorporated in the model. The effect of residual stresses on the buckling behavior was investigated. The material nonlinearities of flat and corner portions of the angle sections were considered in the analysis. The finite element analysis was performed on equally lipped angles compressed between fixed ends for different column lengths, and column curves were obtained. The nonlinear finite element model was verified against recent experimental results. An extensive parametric study was carried out using the finite element model to study the effects of cross section geometries on the strength and behavior of lipped angle columns. The column strengths predicted by the finite element model were compared with the design strengths calculated using the North American Specification and Australian/New Zealand Standard for cold-formed steel structures. In addition, the results obtained from the finite element model were also compared with the design strengths obtained from proposed design rules. It is shown that the proposed design rules accurately predicted the column strengths for non-slender lipped angles and were quite conservative for slender lipped angles. [ABSTRACT FROM AUTHOR]

A practical model has been developed to predict, for a given level of lateral deformation, the likelihood that longitudinal bars in a reinforced concrete column will have begun to buckle. Three relationships linking plastic rotation, drift ratio, and displacement ductility with the onset of bar buckling were derived based on the results of plastic-hinge analysis, moment-curvature analysis, and the expected influence of the confinement reinforcement. These relationships, which account for the effective confinement ratio, axial-load ratio, aspect ratio, and longitudinal bar diameter, were calibrated using observations of bar buckling from cyclic tests of 62 rectangular-reinforced and 42 spiral-reinforced concrete columns. A version of the drift ratio relationship is proposed for earthquake engineering applications. The ratios of the measured displacements at bar buckling to the displacements calculated with the proposed model had a mean of 1.01 and a coefficient of variation of 25% for rectangular-reinforced concrete columns. The corresponding mean and coefficient of variation for spiral-reinforced columns were 0.97 and 24%, respectively. [ABSTRACT FROM AUTHOR]

Recently, passive vibration control design has gained popularity. The aim of this design is to absorb most of the seismic energy by using additional dampers while maintaining the elasticity of the main structure. Buckling restrained braces (BRBs) are used as one of the elastoplastic dampers in this design and, therefore, the cumulative deformation capacity of BRBs to the point of fatigue fracture is an important benchmark for their performance. The estimation of this value under a random amplitude is complicated however, as this value is affected by the loading history. In this study, past experiments on BRBs are revisited in order to investigate the relation between the cumulative deformation capacity and the applied loading history. Based on these analyses, a simple method is proposed for predicting the cumulative deformation and energy absorption capacities of BRBs under random amplitudes. In contrast to Miner’s method, the proposed method does not require analyses of the individual amplitudes, and the values of interest are directly determined from the response indexes. [ABSTRACT FROM AUTHOR]

A total of 23 tests were conducted to study the cyclic loading performance of links in steel eccentrically braced frames. The objectives of these tests were to reevaluate flange slenderness limits and overstrength factors for links. The effect of loading history on link performance was also investigated. Link specimens were constructed from five different wide-flange sections, all of ASTM A992 steel, with various lengths ranging from short shear yielding links to very long flexural yielding links. In addition to providing data on the effects of flange buckling and overstrength, these tests also showed some unexpected failure modes. The paper provides an overview of this experimental investigation, describing the overall research program, as well as details of the test specimens and test results. The paper concludes with a number of design recommendations for links in eccentrically braced frames. [ABSTRACT FROM AUTHOR]

The local buckling behavior of longitudinal reinforcing steel, which occurs between two transverse hoops, is examined using rational mechanics, taking into account the full plastic behavior of the steel and the effects of true stress and strain. A computational fiber element analysis is used to compute the coupled effect of axial compression and lateral buckling. The results of the computational analysis are then used to develop a simple model for the compressive behavior of longitudinal reinforcing steel in engineering stress-strain coordinates. Although several models exist that are capable of predicting compressive behavior with a moderate degree of precision, these models are generally computationally intensive and therefore of little practical use to structural designers. Other existing simple models either have a high degree of built-in empiricism or are based on overly simplified assumptions about the plastic behavior of the steel. The minimalist model developed in this study is compared with available experimental results. A statistical study shows favorable correlation between the proposed analytical model and experimental results. [ABSTRACT FROM AUTHOR]

Tubular-section members are commonly used as seismic-resistant braces because they have a higher moment of inertia than open cross sections of equivalent area. However, the cumulative cyclic deformation capacity of tubular sections after buckling is smaller than that of open sections, such as H-shaped sections, because fracture is initiated by local buckling of circular tubular sections. To evaluate the seismic performance of such diagonal braces, it is essential to predict the cumulative cyclic deformation capacity of these braces before any fracturing. In this study, the cumulative cyclic deformation capacity of circular tube braces under local buckling was assessed by performing cyclic loading tests for a range of slenderness and diameter-to-thickness ratios. The mechanism of strain concentration in the tubular braces was studied in various types of analysis, and a method is proposed for assessing the cumulative deformation capacity before fracture based on the entire axial deformation of the braces. [ABSTRACT FROM AUTHOR]

The paper presents a model for the inelastic buckling behavior of steel braces. The model consists of a force-based frame element with distributed inelasticity and fiber discretization of the cross section. With this approach, the response of the element can be derived by integration of the uniaxial stress-strain relation of the fibers and can account for kinematic and isotropic hardening as well as the Bauschinger effect of the material. The interaction between axial force and bending moment is thus accounted for. Even though the element only accounts for small deformations in the basic system, large displacement geometry is included in the nonlinear transformation of the force-deformation relation of the basic element following the concept of the corotational formulation. With this approach, two elements for each brace suffice to yield results that match an extensive set of experimental data of braces with different cross sections and slenderness ratios. Even though the model does not account for the effect of local buckling, this phenomenon does not seem to appreciably affect the global response of braces with compact sections. [ABSTRACT FROM AUTHOR]

This paper is concerned with an application of the Ritz method for elastic, axisymmetric, buckling analysis of moderately thick, rotational orthotropic shells under uniform external pressure. In order to capture the effect of transverse shear deformation, which is significant for thick shells, the Mindlin shell theory is used. In applying the Ritz method, the displacement components of the shell are approximated by the product of one-dimensional polynomial functions, and the boundary equations are raised to the appropriate powers so as to ensure the satisfaction of geometric boundary conditions a priori. The validity of the method, convergence and accuracy of solutions are demonstrated using spherical shells, which is a special case of rotational shells, where closed-form solutions exist for some cases. A parametric study is conducted on spherical and parabolic shells, considering the effects of height-to-base-radius ratios, thickness-to-radius ratios, and different support conditions on the buckling solutions. The new solutions should be useful to researchers and engineers who are developing analytical tools and designs of shells. [ABSTRACT FROM AUTHOR]

When subject to combinations of internal pressure and axial compression, experience shows that the often thin cylindrical shell walls of tanks and silos are prone to a local form of buckling failure that is essentially axisymmetric and is strongly influenced by the nature of the end or intermediate support conditions. This paper will outline the basis of an analytical solution to the inherently nonlinear elastic–plastic buckling into axisymmetric modes, in which end constraints and arbitrary radial pressure loading are modeled as essentially loading imperfections on an otherwise linear, classical, critical buckling formulation. Closed form analytical expressions for the imperfect behavior, including geometric imperfections, are then used to predict either first surface or full section plasticity, allowing buckling failure to be summarized in a form that is closely analogous to the Ayrton–Perry formula for the buckling of columns. It is suggested that a suitably simplified form of this general approach to axisymmetric buckling, when combined with similarly simple methods for the buckling into nonaxisymmetric modes, could provide an important alternative to the current procedures for the buckling design of thin-walled, cylindrical, tanks and silos. [ABSTRACT FROM AUTHOR]

An unconstrained gusset connection for buckling restrained braces in reinforced concrete frame structures is proposed and tested as an effort to mitigate the complicated and usually harmful interactions between the steel gusset plate and the adjoining reinforced concrete column. Local damage control incorporating the rearrangement of beam flexural strength is also proposed to enhance the reliability of the gusset connection by moving the potential plastic hinge of the beam away from the connection region. Two different connecting methods, one with posttensioned steel rods and the other embedded stud groups, were considered. The results of the cyclic loading tests on reinforced concrete (RC) beam-gusset connection subassemblies confirmed that both connecting methods are available as long as the local damage control is implemented, which is not only helpful in eliminating the unfavorable deformation loss at the connection, but more importantly, can prevent the buckling restrained braces (BRBs) from being dislocated as a result of the beam end failure in extreme earthquake events. [ABSTRACT FROM AUTHOR]

Although steel single angle sections are commonly used as beams to support distributed loads which cause biaxial bending and torsion, their behavior may be extremely complicated, and the accurate prediction of their strengths very difficult. Further, many design codes do not have any design rules for torsion, while some recommendations are unnecessarily conservative, or are of limited application, or fail to consider some effects which are thought to be important. This paper is one of a series on the behavior and design of single angle section steel beams. Two previous papers have studied the biaxial bending behavior of restrained beams, a third has studied the lateral buckling of unrestrained beams, and a fourth the biaxial bending of unrestrained beams. In each paper, simple design methods have been developed. In this present paper, an approximate method of predicting the second-order deflections and twist rotations of steel equal angle beams under major axis bending and torsion is developed. This method is then used to determine the approximate maximum biaxial bending moments in such beams, which are then used with the section moment capacity proposals of the first paper of the series and the lateral buckling proposals of the third paper to approximate the member capacities. This method is extended to steel unequal angle beams in a companion paper. [ABSTRACT FROM AUTHOR]

A structural engineer wishing to determine the buckling load of unequal-leg angle columns receives conflicting information from published literature because researchers offer two radically different models for their analyses of thin-walled open-profile bars. One model considers the bar to be a continuum whereas the American Institute of Steel Construction adopts a noncontinuum multifilament model. Furthermore, the continuum model defines the normal planes of the deflected bar with the line of centroids whereas the multifilament model uses the shear center line. A test program based on 5×3×1/4 in. (127×76×6 mm) steel angles is proposed to resolve the issue by determining which model produces computed buckling loads that better correlate with collapse loads obtained from tests. The possibility that neither method produces a buckling load that correlates with collapse loads is not ruled out. [ABSTRACT FROM AUTHOR]

This paper addresses, both theoretically and experimentally, the buckling of shallow concrete arches that may occur due to the effects of creep and shrinkage deformations of the concrete. Under sustained loading, these viscoelastic effects cause time-dependent changes of the deflections of a shallow arch and can lead to the establishment of a geometric configuration at which the arch is no longer stable, and which heralds the onset of creep buckling. By using a virtual work formulation, the equilibrium and buckling equations of an arch with horizontal spring supports are derived in closed form, and using the algebraically tractable age-adjusted effective modulus method to model the time-dependent behavior of the concrete allows the buckling load and the prebuckled life of the arch to be determined using prescriptive equations. Long-term tests on three 4.25 m span arches under sustained loading are described. Each arch failed because of creep buckling several months after first loading. These tests are used to validate the theory developed in the paper and to provide benchmark data for calibration. The study shows that creep and shrinkage of the concrete have a profound influence on the structural behavior of shallow concrete arches. [ABSTRACT FROM AUTHOR]

This paper describes a test program on full-scale fabricated simply supported I-beams with central concentrated load and an effective lateral brace at the midspan of the top compression flange that was performed mainly with the aim of experimental verification and investigation of distortion in doubly symmetric I-section beams. The experimental ultimate loads were compared with the buckling loads of the specimens determined by using the so-called Southwell, Modified, and Massey extrapolation techniques, and in most of the cases very little discrepancy was found between the maximum test and extrapolated loads. Moreover, the experimental beam strengths were compared with the design strengths predicted by the American AISC/LRFD and the Australian AS4100 specifications. Generally, the two specifications provide unconservative predictions in the inelastic range of structural response as the beam length decreases and inelastic behavior becomes more intense. However, the AS4100 specification provides conservative predictions in comparison with the AISC/LRFD specification. [ABSTRACT FROM AUTHOR]

Metal members are able to exhibit plastic deformations whose amplitude depends on the local slenderness of the plate elements constituting the member section, provided that global instabilities are prevented. This local slenderness depends on the width-to-thickness ratios of the plate elements and governs the occurrence of local buckling which can be developed either in elastic or in plastic range. Aiming at the development of a ductile behavior, the occurrence of local buckling in elastic range has to be prevented to assure the development of ultimate behavior in plastic range. To this scope, the width-to-thickness ratios of the plate elements constituting the member section have to be properly limited. Wide experimental research dealing with the influence of width-to-thickness ratios on the local buckling of heat-treated aluminum alloys has been recently completed with the aim of providing Eurocode 9 with the background data necessary for setting up classification criteria specific to aluminum members. The aim of the developed experimental activity is evaluation of the relationship between the strain corresponding to the complete development of local buckling and the slenderness parameters of the plate elements composing the section. This relationship has been derived by analyzing the results obtained from a great number of stub column tests carried out on specimens having width-to-thickness ratios covering the whole range of variability of commonly extruded profiles. The whole experimental program has dealt with square hollow section, rectangular hollow section members, channels, and angles made of 6,000 series alloy, provided by the major European aluminum industries. This paper presents and discusses the results of the part of the experimental program regarding aluminum alloy angles subjected to local buckling under uniform compression. Sixty-four stub column tests have been carried out at the Material and Structure Laboratory of the Department of Civil Engineering of Salerno University. These experimental results and their interpretation are presented in this paper. In addition, a classification criterion accounting for the interaction between the two slenderness parameters of the cross-section is proposed. [ABSTRACT FROM AUTHOR]

When the ratio of the minor axis flexural stiffness to the major axis flexural stiffness is not small, classical analysis may lead to an inaccurate prediction of the flexural-torsional buckling loads of an arch, because prebuckling in-plane deformations change the curvature of the arch. A systematic treatment of the effects of prebuckling in-plane deformations on the elastic buckling of monosymmetric arches is presented in this paper. Nonlinear relationships between the displacements and the strains are obtained using position vectors. Energy equations are formulated for the elastic flexural-torsional buckling of monosymmetric arches, which include the effects of prebuckling in-plane deformations, and closed-form solutions are obtained for arches in uniform bending. The effect of the arch slenderness on flexural-torsional buckling is investigated. Comparisons with the existing theoretical solutions are made. [ABSTRACT FROM AUTHOR]

A series of column tests on cold-formed steel built-up closed sections with intermediate stiffeners is presented in this paper. The test specimens were first brake pressed from structural steel sheets to form open sections with intermediate web stiffeners, then two of the open sections were connected at their flanges using self-tapping screws to form the built-up closed sections. The high strength structural steel sheets had the measured 0.2% proof stress up to 586 MPa. Initial and overall geometric imperfections as well as material properties and residual stresses of the test specimens were measured. Tests were performed over a range of lengths such that column curves could be obtained. The test strengths are compared with the design strengths calculated using the direct strength method in the North American Specification and Australian/New Zealand Standard for cold-formed steel structures. Three different methods were used to obtain the local and distortional buckling stresses for the calculation of the direct strength method. Reliability analysis was performed to assess the reliability of the direct strength method on cold-formed steel built-up closed section columns. It is shown that the direct strength method using single section to obtain the buckling stresses is generally conservative. [ABSTRACT FROM AUTHOR]

Ground movement along a buried pipeline often places the line in net compression. The local buckling resistance at cold bends is less than at straight sections, and hence, local buckling tends to occur at bends. Correspondingly, this full-scale testing program was conducted to investigate the local and global load-deformation relationships for seven cold bend pipes under applied loads. The specimens were loaded under bending, axial load, and internal pressure until local buckling occurred, and their curvatures were subsequently increased to establish their postbuckling behaviors. It was demonstrated though these tests that the buckling strain of the cold bend pipes was considerably lower than a straight pipe and that the presence of internal pressure exhibited a predominant role on the specimens load-deformation behaviors. It was also established that the behavior of the specimens was relatively unaffected by the bending methods that were employed during cold bending. [ABSTRACT FROM AUTHOR]

The paper presents the experimental and numerical study of a mild steel replaceable dissipation device. The dissipater is made of a milled-down mild steel bar that is confined by a steel tube filled with either grout or epoxy. The use of a reduced area concentrates yielding and plastic straining over a defined length while the tube prevents buckling. The device has been widely adopted in posttensioned rocking systems, and extensive experimental research was carried out on wall and beam-column subassemblies using this external dissipater. As part of those experimental programs, some component testing was carried out; nevertheless, a more comprehensive study was necessary to cover a wider range of geometric and mechanical parameters. The main objective of this research was to calibrate and suggest design parameters to support the design of the dissipation device. The paper shows a comprehensive experimental program under quasi-static cyclic loading carried out with varying geometrical parameters. This work forms the basis for the development of more refined analytical and numerical models to simulate the behavior of the device. In particular, the onset of the dissipater interaction with the confining tube and its buckling mechanism were targeted. Further numerical simulations made use of a fiber element–based model that was capable of capturing the full range of deformation mechanisms highlighted in the experimental program. Using this model, an extensive parametric analysis was carried out to determine significant design parameters, such as the maximum force in the dissipater and the buckling onset strain. Analytical models were also presented to predict the monotonic behavior of the dissipater and provide calibration of the hysteretic force-displacement rule proposed in the final part of the paper. [ABSTRACT FROM AUTHOR]

Braced frames are often used to resist lateral earthquake loads in steel buildings, but braces can interfere with architectural features. Eccentrically braced frames (EBFs) will accommodate windows, doors, and halls, but have performance limitations when link-to-column connections are required. An alternative to EBFs may be buckling-restrained braced frames with eccentric configurations (BRBF-Es). This paper introduces the concept of BRBF-Es and highlights design considerations. An analytical study was conducted that compares the performance and economy of BRBF-Es with EBFs. Results from non-linear time history analyses indicate that BRBF-Es will have greater residual drifts than comparable EBFs, but are less susceptible to failures at link-to-column connections. BRBF-Es require more steel than EBFs, but savings in design, fabrication, and erection may offset higher material costs. [ABSTRACT FROM AUTHOR]

The failure behavior of thin-walled shallow concrete domes under short-term and long-term loading is investigated theoretically and experimentally. The paper focuses on the long-term effects of creep and shrinkage, the material nonlinearity of the concrete under biaxial loading, and the geometric nonlinearity aspects of the structure through the development of nonlinear theoretical models for the short-term and long-term analyses. Special attention to the phenomenon of creep buckling is given in the development of the model, but without considering the nonaxisymmetric bifurcation response. The experimental phase involves the testing of two shallow domes. The first is loaded to failure under a gradually increasing pressure. The second dome is subjected to a constant sustained pressure for a period of 2.5 months. A series of tests for the characterization of the mechanical properties of the concrete, and its creep and shrinkage characteristics is also reported. The results and the theoretical-experimental comparison provide insight into the failure behavior of shallow concrete domes under both short-term and sustained loading, and contribute to the understanding of failure behavior of general concrete shells. [ABSTRACT FROM AUTHOR]

Lipped channel beams (LCBs) are commonly used as flexural members such as floor joists and bearers in the construction industry. These thin-walled LCBs are subjected to specific buckling and failure modes, one of them being web crippling. Despite considerable research in this area, some recent studies have shown that the current web crippling design rules are unable to predict the test capacities under end-two-flange (ETF) and interior-two-flange (ITF) load conditions. In many instances, web crippling predictions by the available design standards such as AISI S100, AS/NZS 4600 and Eurocode 3 Part 1-3 are inconsistent, i.e., unconservative in some cases, although they are conservative in other cases. Hence, experimental studies consisting of 36 tests were conducted in this research to assess the web crippling behavior and capacities of high-strength LCBs under two-flange load cases (ETF and ITF). Experimental results were then compared with the predictions from current design rules. Comparison of the ultimate web crippling capacities from tests showed that the design equations are very unconservative for LCB sections under the ETF load case and are conservative for the ITF load case. Hence, improved equations were proposed to determine the web crippling capacities of LCBs based on the experimental results from this study. Current design equations do not provide the direct strength method (DSM) provisions for web crippling. Hence, suitable design rules were also developed under the DSM format using the test results and buckling analyses using finite-element analyses. [ABSTRACT FROM AUTHOR]

This paper presents analytical approximate solutions for the geometrically nonlinear, large deformation postbuckling of a linear-elastic and hygrothermal beam with axially nonmovable pinned-pinned ends and subjected to a significant increase in swelling. The solution for the limiting case of a string is also obtained. Analytical approximations to large deformation of the beam are established by combining the Newton’s method with the method of harmonic balance. In contrast to the classical method of harmonic balance, the linearization is performed prior to proceeding with harmonic balancing, thus resulting in a set of linear algebraic equations instead of one of nonlinear algebraic equations. We are hence able to establish analytical approximate solutions. These approximate solutions show excellent agreement with the referenced solution obtained by the shooting method, and are valid for a small as well as a large angle of rotation at the end of the beam. [ABSTRACT FROM AUTHOR]

A test program was performed on aluminum alloy columns of square and rectangular hollow sections that were compressed between fixed ends. In total, five series of tests were conducted that included columns with both ends transversely welded to aluminum end plates using the tungsten inert gas welding method, and columns without welding of end plates. The tests were performed over a range of column lengths in order to obtain a column curve for each series of test. Heat-treated aluminum alloys of 6063-T5 and 6061-T6 material were used for the column specimens. Nonwelded and welded material properties were obtained from various coupon tests. The column specimens failed by local buckling, overall buckling, as well as interaction of local and overall buckling. In addition, some welded columns failed in the heat-affected zone. The test strengths were compared with the design strengths predicted by the American, Australian/New Zealand, and European specifications for aluminum structures. Reliability of the design rules for transversely welded aluminum columns in the three specifications was examined using reliability analysis. It is shown that the design strengths predicted by the three specifications are conservative for the nonwelded columns. For the welded columns, the design strengths predicted by the American and Australian/New Zealand specifications are generally conservative, whereas the design strengths predicted by the European Code are relatively quite conservative. It should be noted that the design strengths predicted by the American and Australian/New Zealand specifications are unconservative in some cases for the welded columns. [ABSTRACT FROM AUTHOR]

This paper presents a study to introduce and experimentally validate an innovative concrete filled steel tubular (CFT) column system, named as confined CFT or CCFT, for improved seismic design of steel and concrete composite structures. Based on fundamental mechanics, the concept is aimed at controlling the local buckling of the steel tube and confining the concrete in the potential plastic hinge regions of a CFT column. To achieve this, several efficient details of transverse confinement are proposed. In the first phase of the study, carbon-fiber-reinforced plastic as additional confinement of CCFT columns was examined through experimental testing. As demonstrated from the results of axial compression tests and seismic loading tests, the new type of CFT column system can provide excellent seismic performance. The complicated local buckling and confinement mechanisms were examined using a proposed simple analytical model. [ABSTRACT FROM AUTHOR]

This study investigates damage process to steel structural members after buckling by subjecting them to large repetitive deformations such as strong earthquake loading up to the ultimate cracking state. Experiments were conducted on steel angle members that were subjected to very low cycle loading that caused global and/or local buckling and plastic elongation. In this study, very low cycle loading means repetitive loading, five to 20 loading cycles, within the large plastic range. The objective of the experiments was to quantify the relationships of the important physical factors relating cracks and ruptures to large repetitive deformations. Also, a nonlinear finite-element-method analysis was performed to trace the experimental behavior of the steel structural members. Both the experimental and analytical results are comprehensively discussed with emphasis placed on the crack initiation process at the local buckling location. It is found that the FEM analysis effectively clarifies the detailed behavior of the steel members that has not been observed through the experiments, especially the behavior of local stress-strain histories at their cracking parts. [ABSTRACT FROM AUTHOR]

To study the effect of Grade 700 MPa longitudinal rebars and hoops on the deformation capacity of RC and composite columns, eight rectangular columns were tested under cyclic lateral loading and uniform axial compression. The test parameters were the hoop type (rectangular or spiral hoops), hoop spacing, the use of composite steel section, and the shape of cross section (square column or rectangular wall-column section). All columns exhibited ductile behavior after flexural yielding. Compared to rectangular hoops and crossties, spiral hoops significantly enhanced the deformation capacity of RC and composite columns by providing lateral confinement and by restraining local buckling and tensile fractures of longitudinal rebars. On the other hand, the use of embedded steel section had limited effect on the deformation capacity because of the relatively low yield strength of the steel section. In the case of wall-column section, as the section depth increased, the deformation capacity decreased due to the increased shear demand. Existing nonlinear analysis modeling methods were applied to the test specimens. The prediction results underestimated the tested deformation capacity, particularly for columns with spiral hoops. [ABSTRACT FROM AUTHOR]

Composite steel-concrete columns and beam-columns have been shown to provide superior performance when the intrinsic synergistic characteristics of concrete and steel are properly exploited. However, limited test data are available to justify the structural system response factors and comprehensive design equations in current design specifications. This research, through the testing of 18 full-scale, slender concrete-filled steel tube (CFT) beam-columns, addresses these needs by providing comprehensive data to calibrate advanced computational models and assess design equations. The CFT specimens were subjected to complex load protocols that included pure compression, uniaxial and biaxial bending combined with compression, pure torsion, and torsion combined with compression. The results for the pure compression tests reported in this paper indicate that current AISC design provisions provide an accurate estimation of column capacity for both strength and stiffness. The experimental loading response was also contrasted with column curves obtained from advanced, nonlinear fiber analysis models. The experimental and computational column curves are strongly correlated in the elastic critical load range, but showed some differences in the inelastic buckling load range. These differences are attributed to the higher concrete strength assumed in the computational analysis because of the confinement effect of the steel tube; this strength is underpredicted in current design specifications. [ABSTRACT FROM AUTHOR]

Presents procedures for hand prediction of the buckling stress in the local and distortional mode. What the finite strip analysis of a flexural member with an edge stiffened flange; Use of numerical investigations; Comparison of local mode with distortional mode; Distortional buckling prediction.

The strength of thin-walled stainless steel columns has been investigated extensively over the last few years. In European standards, the concept of section classification for determining the cross section capacity is used. In this system, for Class 4 cross sections, the effective width method (EWM) must be used to account for the effect of local buckling. Because of the complexity and limitations of this method, other methods have been developed, such as the direct strength method (DSM) for cold-formed thin-walled profiles and the continuous strength method (CSM), initially established for members made of nonlinear metallic materials. In the CSM, to take advantage of strain hardening, a deformation-based design approach using a continuous relationship between the cross-sectional slenderness and the cross-sectional deformation capacity is used. To a large extent, the CSM yields accurate predictions, especially in the low slenderness range where the current DSM design procedures for members submitted to pure compression tend to produce conservative predictions for materials with pronounced strain hardening such as stainless steel alloys. The present paper presents an extension of the traditional DSM, which provides accurate design strength predictions in the low slenderness range for stainless steel thin-walled section columns failing by distortional, local, and overall buckling. It contains practical information concerning the reference experimental data and draws conclusions about the justification of the proposed analytical formula. The paper is divided into three main parts: the description of the database, the establishment of the design model, and a reliability analysis of the method. [ABSTRACT FROM AUTHOR]

The stability of I-girders during erection can be difficult to assess because of the limited presence of bracing and uncertainty in the support conditions of the girders. The behavior of curved girders during the early stages of construction is complicated because the curved geometry can lead to significant torsion. This paper highlights results from a research study that included both field monitoring and parametric finite-element investigations. Curved I-shaped girders were instrumented and monitored during lifting to provide data to validate finite-element models. Both rotational displacements and stress were measured during the lifting process. In this paper, the writers compare data collected from field tests with results computed from detailed finite-element simulations. A prismatic and a nonprismatic girder (with two different cross sections) were considered in the investigation. The I-girders experienced both rigid body rotation and cross-sectional twist. Additionally, the torsional warping stresses were observed to be of the same order of magnitude as the strong-axis bending stresses. However, it should be noted that the total stresses were well below yielding. The fact that the stresses are low during lifting should not be confused with a noncritical stage in the safety of the girders. Although the applied stresses are low, the stresses necessary to buckle the girder or to cause large deformations are also relatively low because usually no bracing exists and limited restraint is provided to the girders during lifting. The finite-element models were able to capture the measured behavior accurately, providing insight into appropriate assumptions and critical features for modeling curved I-girders during lifting. [ABSTRACT FROM AUTHOR]

The out-of-plane elastic and inelastic flexural-torsional buckling behavior and strength of fixed steel arches are studied in this paper using an advanced finite element model for the three-dimensional nonlinear analysis. The initial out-of-plane geometric imperfections, residual stresses due to manufacturing and curving, yielding, and inelastic flexural-torsional buckling are considered in the investigation. It is found that both the elastic and the inelastic flexural-torsional behavior of fixed arches are quite different from those of pin-ended arches. The strength design equations for pin-ended steel arches cannot be extended directly to fixed steel arches using the effective length method. Design equations for fixed steel arches subjected to uniform compression or to uniform bending, and an interaction equation for the strength check against out-of-plane failure for fixed steel I-section arches subjected to combined bending and axial compressive actions, are proposed. [ABSTRACT FROM AUTHOR]

The buckling behavior of T-section columns is discussed in detail, followed by a numerical study using geometric and material nonlinear analyses (GMNIA) to produce column strengths for a wide range of geometries of T-sections and column lengths. The T-sections are assumed to be hot-rolled and include residual stresses and geometric imperfections typical of hot-rolled sections. On the basis of the numerical strengths thus produced and the available test strengths for T-section columns, the design provisions of the Australian, European, and American specifications for hot-rolled steel structures are evaluated. It is shown that the Australian standard provides fairly consistent and accurate predictions of strength. However, the design provisions for T-sections of current European and American specifications are conservative and associated with large variability, particularly for T-sections with slender elements. The paper recommends modifications to the European and American specifications that improve the design strength predictions of these specifications for T-section columns. [ABSTRACT FROM AUTHOR]

Most design codes for circular shell structures include a limit on out-of-round imperfections. However, commonly used measures of out-of-roundness fail to identify shapes that have constant diameter but are not circular. It is shown that out-of-roundness imperfections that take these forms can significantly affect the strength of nominally circular shell structures. An alternative measure of out-of-roundness is proposed that captures all out-of-round shapes, gives the same measure of out-of-roundness for elliptical structures as currently used measures, and is easy to apply. [ABSTRACT FROM AUTHOR]

Conventional reinforced concrete shear walls are widely used as primary lateral-force-resisting members owing to their high in-plane stiffness. However, some of these walls have been severely damaged in past earthquakes because of their limited energy dissipation capacity and ductility, thus requiring laborious repairs or even demolition. Self-centering rocking walls have recently been developed and proven effective for reducing the damage and residual displacement of structures after earthquakes. Because self-centering rocking walls are usually constructed by releasing constraints at the foundation, their contribution to structural stiffness may be limited, and they are very vulnerable to vibration. To overcome these limitations, a shear wall with variable phases of deformation was proposed; this wall consists of a rocking bearing, low-strength concrete zones, and buckling-restrained rebars. With increasing seismic intensity, the proposed wall first exhibits the shear–bending deformation mode of conventional reinforced concrete shear walls, which transitions into the rocking deformation mode of self-centering rocking walls. Cyclic loading tests were conducted to investigate the seismic performance of the proposed wall. The results demonstrated that the presented concept of the mechanism transformation is feasible in practice, and compared with conventional shear walls, the proposed wall displays improved seismic performance in terms of the damage mechanism, lateral resistance degradation, and deformation capacity. Moreover, a spring–truss model and a performance prediction model were also developed to predict the seismic performance of the proposed wall. Validating the predictions of the analytical models against the test results confirmed the accuracy of the developed models. [ABSTRACT FROM AUTHOR]

Concrete-filled steel tubular (CFST) arches are often used in engineering structures, particularly in bridge construction. In some instances, to expedite their construction and transport, curvilinear steel tube segments are fabricated and delivered to the construction site and then joined together at the crown to create a pin, so the arch becomes a crown-pinned arch.Wet concrete is then pumped into the steel tubes to form the concrete core after curing, which experiences time-dependent shrinkage and creep. This paper investigates the effects of geometric nonlinearity on the long-term in-plane behavior of crown-pinned circular CFST arches under a sustained central concentrated load, and derives analytical solutions for their nonlinear response and buckling loads. It is found that the geometric nonlinearity influences the long-term behavior of crown-pinned CFST arches significantly. The long-term deformations predicted by the nonlinear analysis are larger than those predicted by linear analysis, and they may be so large that the reserve of the serviceability limit state of crown-pinned CFSTarches may be reduced significantly. The nonlinear analysis also predicts significant long-term increases of the axial forces and bending moments in crown-pinned CFST arches, which is quite different from linear analysis that predicts no long-term changes of the axial force and bending moment for thee-pinned CFST arches and only small long-term changes for singly pinned CFST arches. It is also found that the nonlinear long-term in-plane buckling loads of crown-pinned CFST arches are smaller than their counterpart values determined from linear analysis. Hence, the geometric nonlinearity together with the shrinkage and creep of the concrete core may reduce the reserve of the stability limit state of crown-pinned CFST arches in the long term. To determine the long-term structural response and buckling of crown-pinned CFST arches correctly, nonlinear analysis is required. [ABSTRACT FROM AUTHOR]

Tension field theory assumes that after elastic shear buckling has occurred, compressive stresses in the web plate do not increase; therefore, postbuckling shear strength solely results from the development of tensile stresses within a defined diagonal tension field. Finite-element analyses have found this fundamental assumption to be invalid and a new theory (compression theory) was proposed that bases the development of postbuckling shear strength mostly on the compressive response of the plate (tension plays a secondary role). Previous work has validated compression theory against a wide variety of published experimental data at ambient temperature. This paper shows that compression theory can predict the ultimate postbuckling shear strength of steel web plates up to temperatures of 1,100°C. This finding is significant because steel plate girders subjected to fire loading are highly susceptible to web shear buckling. Experimentally validated finite-element models are used to develop temperature-dependent multiplicative parameters to permit the use of compression theory to calculate ultimate postbuckling shear strength at elevated temperatures. Comparisons with published experimental data show that predictions of ultimate postbuckling shear strength from compression theory closely agree with the literature. [ABSTRACT FROM AUTHOR]

Concentrically braced frames (CBFs) have been used for seismic-lateral-force resisting systems for many years, but prior to approximately 1988, they were not designed to promote ductile response using capacity-based design. These older, nonductile CBFs (NCBFs) have been investigated in prior research that identified severe deficiencies in these systems, but some deficiencies had more detrimental consequences than others. This paper describes a research study to evaluate retrofit strategies for NCBFs. Welded and bolted continuous and split shear-plate connections, end-plate connections, split double-angle connections, and integrated gusset-shear plate connections were investigated. Retrofit strategies included brace replacement, concrete in-fill of a locally slender brace, weld overlay, bolt reinforcement, development of in-plane brace buckling, and the use of buckling-restrained braces. In all cases, system deformation capacity was enhanced, and the extent of improvement depended on connection configuration, connection demand-to-capacity ratios, and bracing type. [ABSTRACT FROM AUTHOR]

A LiteSteel beam (LSB) is a new cold-formed steel hollow flange channel beam produced by using a patented manufacturing process involving simultaneous cold-forming and dual electric resistance welding. It has the beneficial characteristics of torsionally rigid closed rectangular flanges combined with the economical fabrication processes from a single strip of high-strength steel. Although the LSB sections are commonly used as flexural members, no research has been conducted on the shear behavior of LSBs. Therefore, experimental and numerical studies were conducted to investigate the shear behavior and strength of LSBs. In this research, finite-element models of LSBs were developed to investigate their nonlinear shear behavior, including their buckling characteristics and ultimate shear strength. They were validated by comparing their results with available experimental results. The models provided full details of the shear buckling and strength characteristics of LSBs and showed the presence of considerable improvements to web shear buckling in LSBs and associated postbuckling strength. This paper presents the details of the finite-element models of LSBs and the results. Both the finite-element analysis (FEA) and experimental results showed that the current design rules in cold-formed steel codes are very conservative for the shear design of LSBs. The ultimate shear capacities from FEAs confirmed the accuracy of proposed shear strength equations for LSBs on the basis of the North American specification and direct strength method (DSM) design equations. Developed finite-element models were used to investigate the reduction to shear capacity of LSBs when full-height web side plates were not used or when only one web side plate was used, and these results are also presented in this paper. [ABSTRACT FROM AUTHOR]

This paper presents an analytical study of the lateral-torsional instability and lateral bracing effects of wide-flange steel beams subjected to cyclic loading. Numerical analysis using the large deformation theory was conducted to collect the necessary data. Examined were wide-flange steel beams bent in double curvature and subjected to cyclic loading with increasing amplitudes up to the maximum beam end rotation of 0.045 rad. Cross-sectional properties, slenderness ratios, material strength, loading history, and unbraced length were chosen as analysis variables. The lateral instability effect was found to differ significantly between cyclic and monotonic loading. For slenderness ratios about the weak axis not smaller than 100, the strength that can be sustained under cyclic loading was much smaller than that obtained under monotonic loading due to the accumulation of out-of-plane deformations. Equations are proposed for the beam unbraced length with which no detrimental reduction in strength is present in cyclic loading up to the maximum beam end rotation of 0.045 rad. It was also found that the unbraced length requirements stipulated in the American Institute of Steel Construction Seismic Provisions are a reasonably conservative measure to ensure sufficient beam rotation capacity. Lateral instability of reduced beam section (RBS) beams was also analyzed. It is notable that the RBS beam is not necessarily more susceptible to lateral instability than the corresponding standard beam, primarily because of a smaller yielding region and smaller forces induced in the cross section of the RBS beam. This phenomenon was interpreted using a simple flange buckling analogy. The lateral bracing requirements stipulated for standard beams are applicable to ensure sufficient rotation capacity for RBS beams if local buckling effects would not occur. [ABSTRACT FROM AUTHOR]