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Graphene platelets (GPLs) exhibit outstanding mechanical and physical properties and therefore are employed as a reinforcement in advanced polymer composite structures. The purpose of this paper is to analyze the biaxial buckling of functionally graded graphene-reinforced sandwich plates with a soft orthotropic core. A new high-order three-layer theory is developed for the accurate modeling and analysis of the sandwich structure. The sandwich plate is divided into three layers including two face sheets and a core and a different third-order kinematic assumption is dedicated to each layer. The transverse flexibility of each layer as well as the displacements continuity at the interfaces are considered. Additionally, the continuity conditions and the conditions of zero transverse stresses in the whole structure are satisfied. The plate is subjected to a biaxial compressive loading and the governing equations are derived using the principle of minimum potential energy. Analytical solutions are presented for simply supported boundary conditions to obtain the critical buckling load. The influences of plate geometry and GPL properties on buckling load are investigated. The results obtained in specific cases are compared with the published results and the validity of the present results is confirmed. It can be drawn that the use of GPL increases the buckling load of graphene-reinforced sandwich plates. [ABSTRACT FROM AUTHOR]

This paper aims to evaluate the seismic response of multitiered buckling-restrained braced frames (MT-BRBFs), assess the design provisions specified by the 2022 AISC Seismic Provisions for multitiered BRBFs, and propose improvements to these provisions. A set of 17 frames is first selected by varying bracing configuration, frame height, number of tiers, and tier height ratio. The frames are then designed in accordance with the 2010 and 2022 AISC Seismic Provisions. A numerical parametric study is performed under scaled ground motion accelerations. The results of the parametric study show that when the frames are designed to the 2010 provisions, the frame inelastic deformation tends to concentrate in the tier(s) undergoing tensile yielding due to their lower postyield stiffness, compared to BRBs yielding in compression, which creates unequal story shear, contributed by braces, in adjacent tiers with BRBs in tension and compression and engages column flexure to compensate for unbalanced brace story shears between tiers. Columns experience yielding and even buckling in several cases due to combined flexural and axial load demands. MT-BRBFs designed to the 2022 AISC Seismic Provisions exhibit a more uniform deformation response between tiers and relatively lower flexural demands in their columns. However, these provisions may overestimate column in-plane flexural demands (on the order of 3), resulting in potentially uneconomical design solutions. On the basis of the numerical simulations, modifications are proposed to compression BRBs' adjusted strength to better estimate column in-plane flexure and tier deformation while achieving an economical column design. The proposed improvements are validated using dynamic analyses. [ABSTRACT FROM AUTHOR]

Angle profiles belong to the most common steel profiles used in several types of civil engineering structures, such as in lattice towers. Although, in such towers, they are usually considered as axially loaded (truss) members, an additional bending moment develops due to the eccentricity between the point of load application and the gravity center of the profile. Therefore, this paper focuses on the buckling resistance of single-angle members subjected to combined compression and bending. The investigations have been performed through numerical parametrical studies and have been compared to different normative documents where interaction equations are provided. [ABSTRACT FROM AUTHOR]

The durability of profiled metal-faced insulating sandwich panels (MFISPs) in terms of exposure to high temperatures and thermal cycles is critical for their use in civil engineering applications. In this paper, a total of 20 full-scale panels made with two different thicknesses were tested under instantaneous lateral pressure loading at ambient conditions as well as under various combinations of high temperatures, thermal cycles, and lateral pressure. The pressure was applied through a vacuum chamber whereas thermal blankets were used for sustained and cyclic thermal exposure of the panels. Each thermal cycle entailed 24 h of time duration with a temperature range of 20–80°C. The results show a consistent reduction in the initial stiffness, local buckling pressure, and strength of the panels when they were loaded at high temperatures. These reductions were more substantial (up to 24%) under the combined effects of high temperature (80°C), thermal cycles, and pressure loading. The study also shows that the thickness of the foam core can play an important role in controlling the local buckling capacity and strength of the MFISPs. A nonlinear finite-element analysis was also conducted with a relatively good correlation with the test results. The numerical results provide further insights into the structural response and explain certain aspects that could not be obtained from the tests. Given that MFISPs are typically used for roof panels, where the combination of high temperatures and wind load is inevitable at certain regions, the results presented in this work are recommended for consideration in their design. [ABSTRACT FROM AUTHOR]

This paper presents a numerical study to model the thermal-induced pipeline buckling–soil interaction as a demonstration of the feasibility of modeling global buckling using an effective stress remeshing and interpolation technique with a small strain (RITSS) approach in 3D. The numerical results are compared with a previously published large-scale laboratory test, centrifuge, and numerical models. The influence of embedment depth, pipe weight, and pipe–soil interface roughness on the global pipe–soil response is investigated. The current study unveiled some of the key behaviors of partially embedded and buried pipes during thermal expansion. First, the expansion-induced displacements comprise vertical and lateral displacements. Heavy pipes dive deeper into the soil, whereas lightweight pipes rise above their initial position as they move laterally for partially embedded and buried pipes. Furthermore, expansion-induced displacements become insignificant as the burial depth increases. The soil in front of the buried pipe flows up and above to its rear end as the expansion-induced displacements increase. Moreover, lateral buckling occurs in buried pipes even though the lateral out-of-straightness of the pipe is within the recommended limit set by the Det Norske Veritas (DNV) guideline. Finally, the pipe–soil interface roughness significantly influences the undrained lateral resistance for partially embedded pipes. [ABSTRACT FROM AUTHOR]

A new beam element only having the translational displacement degrees of freedom is developed to analyze fracture and buckling behaviors of bilayer beams or columns with delamination using the multilayer modeling method. By comparing their degrees of freedom, it is found that the present beam element is equivalent to the conventional Timoshenko beam element. The upper and lower layers are both divided into one or several sublayers, which are modeled by the developed beam elements. The element stiffness matrix, load vector, and geometric stiffness matrix using the linear interpolation polynomial are derived by the principle of minimum potential energy. To illustrate the effectiveness, accuracy, and efficiency, both the fracture and buckling analyses are conducted. Four typical fracture specimens (i.e., homogeneous and asymmetric double cantilever beams, single leg bending, and asymmetric end-notched flexure specimens) are analyzed using the developed beam element, and the obtained energy release rate and its components using the virtual crack closure technique are compared with those of analytical and conventional two-dimensional (2D) finite element solutions. Further, buckling analysis of bilayer beam-columns with delamination is conducted, focusing on the effect of the number of sublayers. The results show that the developed beam element is capable of effectively and efficiently calculating the convergent stress intensity factor ratio, total energy release rate and its components, and critical buckling load of delaminated bilayer beams or columns with relatively few elements, but without introducing the interface continuity condition in comparison to the conventional modeling method. [ABSTRACT FROM AUTHOR]

Fiber-reinforced elastomeric isolators (FREIs) have been proposed as a cost-effective solution for expanding the use of seismic isolation to normal-importance structures. By using lightweight fiber reinforcement and eliminating the attachment plates, FREIs reduce cost while improving the isolation efficiency and reducing tensile stresses in the rubber. However, the flexural flexibility of the fiber allows cross-sectional distortions (i.e., warping) to occur, which significantly impacts the stability of these devices. This paper evaluates the buckling of rectangular, circular, and annular FREIs, taking into account shear warping effects. A planar buckling theory previously proposed by the authors is adapted for the three-dimensional problem, and effective warping rigidities and warping-related areas are derived for the above bearing geometries, accounting for rubber compressibility. To assess the adequacy of the proposed buckling theory and derived warping properties in predicting the buckling of FREIs, a parametric finite element study is conducted. The critical load predictions of the proposed analytical formulation are found to be in excellent agreement with those of the numerical simulations. It is shown that traditional estimations of the buckling load that neglect warping are significantly unconservative. Finally, design recommendations and resources are provided for practice-oriented applications. [ABSTRACT FROM AUTHOR]

Buckling of slender members due to gravity loading or thermal effects is influenced by the member's geometric imperfections, boundary conditions, and intermediate lateral supports. When assessing the capacity of such members, these parameters are often unknown (e.g., the rotational stiffness of end connections in a truss or the lateral support provided by the ties to a rail track), and conservative assumptions must be made resulting in conservative assessments. Distributed fiber optic sensors (DFOS) can potentially be used to determine these parameters with greater accuracy using strain measurements along the length of a member. A series of buckling experiments was conducted on a slender member instrumented with DFOS subjected to axial load with varying levels of lateral restraint or to increasing temperature. The distributed strain data were then used to evaluate the geometric imperfections, boundary conditions, and lateral support stiffness. These inputs were used to create a finite-element model to estimate the ultimate load response of the member using data acquired at service loads. [ABSTRACT FROM AUTHOR]

Large infrastructure projects can efficiently use large diameter bars as longitudinal reinforcement in reinforced concrete elements. In earthquake-prone zones, critical regions of these elements must be detailed for ductility and hysteretic energy dissipation. Longitudinal bars in these regions are expected to sustain large-amplitude strain cyclic reversals before bar fracture occurs, in a mode of failure defining the collapse prevention limit state. To date, no successful large strain-amplitude cyclic loading testing has been reported on large-diameter reinforcing bars to observe the large-strain amplitude fatigue life of such bars, which often involves plastic bar buckling. This paper describes a test program designed to determine the plastic buckling/straightening fatigue life of ASTM A706 Grade 60 No. 18 bars (Ø57 mm) reinforcing bars subjected to cycles of reversed plastic strains. The design and implementation of the loading apparatus, critical for the gripping of the bars, the metallurgical characterization of the bars, and several key test results are discussed in the paper. Finally, the paper discusses a general unidimensional fatigue damage index precursor to bar fracture following a few plastic buckling and straightening cycles. [ABSTRACT FROM AUTHOR]

The North American Standard (NAS) and the European Standard (EC3) for cold-formed steel design provide limited guidelines for the strength predictions of built-up columns. The existing design equations are limited to flexural buckling and local-flexural interactive buckling. The present study evaluates the local-flexural interactive design equations for cold-formed steel built-up back-to-back I-section columns against the results of experimental and numerical studies. The results show that the existing design guidelines for local-flexural interactive buckling are unconservative by about 17%, 5%, and 15% for DSM-NAS, EWM-NAS, and EWM-EC3, respectively. Furthermore, a maximum reduction in the built-up column strength by local-flexural interaction is observed when its nominal local and flexural buckling loads are close. Based on the results and observations, new design equations are proposed by including the product of nominal local and flexural buckling loads for the North American and European standards, which capture the local-flexural interactive buckling in built-up I-section columns. The effect of fastener spacing on the ultimate load for local-flexural interactive buckling is also evaluated, and its effect is found to be small, unlike for global buckling. The minimum fastener spacing criteria of NAS are assessed, and suitable recommendations are provided for fixed-end columns. Overall, the present study provides insights into the local-flexural interactive buckling behavior of built-up I-section columns and proposes reliable design equations to predict the ultimate load. [ABSTRACT FROM AUTHOR]

Double-beam systems have found many applications in civil and mechanical engineering. Extensive works of research have been conducted on the investigation of double-beam systems in which some have studied the vibration characteristics of general double-beam systems without considering the effect of axial load, whereas others investigated the vibration and buckling of axially loaded double-beam systems with classical boundary conditions. A few previous studies have considered a general axially loaded double-beam system, but none of them have provided a general solution to calculate the critical buckling load of the system with arbitrary boundary conditions. In the present study, free vibration and buckling of an axially loaded double-beam system, which was composed of two nonidentical beams with generalized boundary conditions, were analytically studied by using the Euler–Bernoulli beam theory. A semianalytical method was proposed to calculate the natural frequencies and mode shapes of the system, and an explicit formula was derived to determine the critical buckling load of the system. Parametric investigations were performed to study the influences of the connecting stiffness of the interlayer and axial loads on the dynamic characteristics and critical buckling load of the system. Results show that the proposed method can be used for free vibration and buckling analyses of generalized double-beam systems subjected to axial loads. [ABSTRACT FROM AUTHOR]

Although it is often asserted that, in view of their reduced length, axially compressible beams have a higher buckling load than their inextensible counterparts, a detailed analysis demonstrates that this is not necessarily the case. The argument to arrive at this conclusion is made in terms of relatively straightforward concepts of elasticity and structural mechanics. It is shown that for certain classes of materials, the reduced prebuckling length is more than compensated for by a softening of the elastic response, leading to a reduction of the Euler critical load. [ABSTRACT FROM AUTHOR]

The paper develops a stiffness reduction factor to be used in geometric nonlinear beam-element type elastic analysis of cold-formed steel structures. The factor accounts for the reduction in flexural and warping torsion rigidities resulting from local and distortional buckling as well as residual stresses, particular to cold-formed steel structures. The purpose of applying the factor is to accurately account for the geometric second order effects when predicting the internal distributions of moments of cold-formed steel structural frames. The stiffness reduction factor arising from local and distortional buckling is first determined followed by the stiffness reduction factor caused by residual stresses. Subsequently, the two effects are combined in a single expression, which is a format suitable for incorporation in the North American specification for cold-formed steel structures, AISI-S100. [ABSTRACT FROM AUTHOR]

Concrete encasements are usually utilized to protect bridge above-ground piles from corrosion. These concrete encasements are usually square or round shapes reinforced by longitudinal rebars. However, the contributions of concrete encasements are not considered in traditional pile design procedures. On the other hand, rating engineers need to have realistic evaluations of the piles to estimate the capacity of the foundation for scour-critical bridges. Underestimation and overestimation of pile capacity can result in either potential bridge failure or uneconomical assessment. The objective of this paper is to investigate the effect of concrete encasement on pile buckling behavior subject to concentric load. To achieve this objective, four full-scale concrete encased pile specimens with various pile and concrete encasement lengths were fabricated and tested with concentric axial loading to measure the specimen ultimate capacity. In addition, the finite-element (FE) approach was utilized to simulate the buckling behavior and predict the ultimate capacities of the lab-tested specimens. The developed FE models were validated against the laboratory test data. Finally, the validated FE models were utilized in the parametric study to investigate the effect of the length and shape of the concrete encasement on the ultimate capacities of the steel H-piles. The results indicated that the concrete encasement could increase the buckling load of the pile, and ignoring the effect of the concrete encasement, as with the use of the equations suggested by the AISC, could result in a significantly underestimated prediction. It was also found that the concrete encasement increases the initial axial stiffness of the pile before the buckling load is achieved. [ABSTRACT FROM AUTHOR]

For the first time, a two-node beam element with nine degrees of freedom (DOFs) was developed in this paper using a combination of modified couple stress and k th-order shear deformation beam theory to analyze the free vibration and static buckling responses of rotating bidirectional functionally graded porous (BDFGP) microbeams resting on variable elastic foundations, in which the whole structure was exposed to a magnetic field in the hygrothermal condition. The mechanical properties and the length-scale parameters varied in both the thickness and length directions, which in the novel porosity model and power-law indexes of the material were considered to be a function of the x - and z -coordinates. The present method's accuracy was determined by comparing it with published findings. Additionally, extensive research was conducted to evaluate the effect of various parameters on the mechanical responses of the rotating BDFGP microbeam. The numerical results showed that porosity coefficient, elastic foundation parameters, and hygrothermal environment all significantly affect the rotating BDFGP microbeam's free vibration and static buckling behavior. [ABSTRACT FROM AUTHOR]

Current standard evaluation procedures for compression gusset plates, the two-fold Whitmore section (Whitmore) buckling and the partial plane shear yielding (PPSY), as specified in The Manual for Bridge Evaluation (MBE), are conservative and may result in unnecessary strengthening and retrofitting. To provide accurate and rational load rating factors for decision-making, the two-strut buckling model, which is based on the lower bound theorem of limit analysis, is developed to evaluate compression diagonal gusset plates in steel truss bridges. The proposed model includes two struts, horizontal and vertical strut plates that are subjected to moments, axial compression, and shear forces, and satisfies equilibrium and the M–P–V interaction equation, where the moment on the vertical or the horizontal strut sections is M, the axial force on the vertical or horizontal strut sections is P, and the shear force on the vertical or horizontal strut sections is V. The predicted results were compared with 116 large-scale experimental and finite-element (FE) analytical tests that were reported in the National Cooperative Highway Research Program (NCHRP) 12-84 project, the MBE refined methods including the basic corner check (BCC) and the truncated Whitmore section (TWS) buckling. Of the three methods, the proposed two-strut buckling (TSB) model had the best professional factor [PF (Ptest/Ppredication)] and the relatively low coefficient of variation (COV). The procedures and concepts in the proposed model combine established engineering principles with simplicity and good engineering intuition to achieve uniformity when evaluating compression diagonal gusset plates in steel truss bridges. To provide accurate and rational load rating factors for decision-making for the bridge owners, the two-strut buckling model that is based on the lower bound theorem of limit analysis is developed to evaluate compression diagonal gusset plates in steel truss bridges. The predicted results were compared with 116 large-scale experimental and finite-element (FE) analytical tests that were reported in the National Cooperative Highway Research Program (NCHRP) 12-84 project, the Manual for Bridge Evaluation (MBE) refined methods, the basic corner check (BCC), and the truncated Whitmore section (TWS) buckling. Of the three methods, the proposed two-strut buckling model had the best professional factor [PF (Ptest/Ppredication)] and a low coefficient of variation (COV). The procedures and concepts in the proposed model combine established engineering principles with simplicity and good engineering intuition to achieve uniformity when evaluating compression diagonal gusset plates in steel truss bridges. [ABSTRACT FROM AUTHOR]

The possible failure modes of cold-formed steel (CFS) lipped angle (LA) compression members are yielding, local, flexural torsional, or flexural buckling, and any possible interaction among these buckling modes. In general, the strength estimated by current design guidelines are conservative for these members when flexural-torsional buckling (FTB) is the first global buckling mode because the postbuckling strength of this mode is not accounted for in the global buckling strength equations. The initial part of this paper reports the results of an experimental and numerical study of CFS-LA members undergoing independent FTB. Modifications are suggested to global buckling strength equations based on these results. Subsequently, the reduction in the ultimate strength from strength corresponding to independent buckling modes for LA members undergoing interaction between buckling modes such as local-flexural torsional, flexural-flexural torsional, local-flexural, and local-flexural torsional-flexural are studied systematically using finite-element analysis results. A simple and more accurate interaction equation that accounts for these interactions among buckling modes in CFS-LA compression members is proposed. [ABSTRACT FROM AUTHOR]

Steel eccentrically braced frames (EBFs) combine the advantages of both moment-resisting frames and concentrically braced frames and provide an attractive seismic design solution. Shear-critical replaceable links were developed about a decade ago to improve the performance, design process, construction, and postearthquake repair process in EBFs. However, replaceable shear links are still susceptible to the commonly observed limit states in EBF links such as web fracture close to web stiffeners, local buckling, and lateral torsional buckling. This paper presents the experimental validation of a new generation of optimized cast steel replaceable yielding links for use in EBFs, which address the shortcomings of conventional and fabricated replaceable links. The performance of the proposed cast steel links is investigated through nine large-scale component-level and system-level experiments, covering a range of link sizes and loading conditions, while also studying the impact of other phenomena influencing the response such as the presence of axial load, the level of axial restraint in the links and the presence of a concrete slab. The tested series of cast links demonstrated enhanced ductility levels and low-cycle fatigue life when compared to fabricated links, achieving up to 0.21 radians of link rotation under the AISC protocol used for the qualification of EBF links. [ABSTRACT FROM AUTHOR]

This paper studied the thermomechanical nonlinear stability analysis of simply supported geometrically imperfect porous functionally graded nanoplates (FG-nPs) resting on an elastic medium. The inverse trigonometric shear deformation theory was used in conjunction with the nonlocal strain gradient theory, which accounts for small-scale effects. The non-linear stability equations using the von Karman sense of the strain–displacement relation and generic imperfection function were derived for FG-nPs under thermomechanical loading conditions. The FG-nP was subjected to mechanical and thermal loading. An expression for the critical buckling load and temperature of a geometrically imperfect porous FG-nP was obtained. The impact of geometric imperfection, porosity inclusion, and geometric and boundary conditions on the nonlinear stability characteristics of FG-nPs was addressed thoroughly after validation of the superior accuracy of the derived expression. [ABSTRACT FROM AUTHOR]

This paper introduces a new design procedure for the strength prediction of pultruded glass fiber–reinforced polymer (pGFRP) angles subjected to compression through a parametric analysis. Experimental results were used for the calibration of a finite-element numerical model according to linear and nonlinear analyses. Sensitivity to the initial geometric imperfections, material damage, and leg-junction rotational stiffness was then investigated for an evaluation of the influence of material and geometric nonlinearities on the column behavior. A parametric study including 100 pGFRP angles within slenderness ranges not covered by previous tests was developed for increasing the available data, and the results were evaluated by two normative and four nonnormative design procedures. Finally, a new design procedure based on the direct strength method (DSM) is proposed. It adopts modified global and local strength curves of the original American Specification for the Design of Cold-Formed Steel Structural Members (AISI) from the adjustment of the original expressions based on a large database, including experimental data collected from the literature and numerical data obtained from the parametric study. The proposed DSM approach led to accurate ultimate strength estimates for columns covering a wide slenderness range. [ABSTRACT FROM AUTHOR]

A number of incidents of pile tip damage and extrusion buckling have been reported within the offshore industry, generally arising during driving of relatively thin-walled tubular pile foundations through hard layers or potentially heterogeneous sediments. The issue has become of particular concern with modern trends toward larger diameter piles, with higher ratios of diameter to wall thickness, for monopile or jacket foundations of offshore wind turbines. The paucity of good-quality data available in the public domain about this kind of failure has impaired the development of simple design guidelines for industry to address the issue. The paper presents results from a series of centrifuge model tests where pile tip damage and extrusion buckling were observed during driving of either (1) undamaged cylindrical piles into a sand bed containing a layer of different sizes of boulders, or (2) predented piles into medium dense homogeneous sand. Following a previously reported pilot study, a new and higher energy model pile-driving hammer was designed to permit driving through the hard layers and allow pile embedment by up to five diameters. Two test beds were prepared, one of which contained boulder layers of different sizes either near the surface or at a depth of about one pile diameter, into which piles of two different diameter to wall thickness ratios were driven. The test series led to observations of pile tip damage that ranged from abrupt tip crumpling to gradual extrusion buckling. For 2 of the 22 piles installed, dent growth during installation was detected by optical fiber sensors attached to the piles. For the uninstrumented piles, damage was deduced from the trends in blow counts during installation, with later confirmation from detailed visual inspections and laser scanning, and also from careful layer by layer excavation of each sample. The high-quality database generated from the model tests forms a valuable resource for further study and validation of advanced numerical models to simulate pile tip damage and for calibration of simple guidelines for practical design. [ABSTRACT FROM AUTHOR]

The seismic performance of structures could be enhanced by the inclusion of supplemental components that dissipate the earthquake-induced energy. This is especially crucial for rocking structures that possess low energy dissipation properties due to their damage avoidance mechanism. Amongst variously developed yielding-type energy dissipaters (EDs), buckling-restrained energy dissipating carbon steel bars have received considerable attention as they make the most use of the inherent energy dissipation of steel and are easy to fabricate. However, maintenance, repair costs, and performance disruptions owing to corrosive environments have been mostly disregarded in past investigations. Employing stainless steel can be a viable solution to overcome such issues. The work described in this two-part study sheds light on various aspects of the buckling-restrained stainless steel EDs through experimental and finite element (FE) investigations. The mechanical properties of type 304L stainless steel including uniaxial monotonic response, strain sensitivity, and cyclic hardening are characterized. It is shown that the material possesses high ductility along with substantial hardening characteristics. In the first phase of testing, energy dissipating bars with different fuse diameters and lengths are designed. Load and strain capacities and bar-tube interactions of the buckling-restrained energy dissipation device are studied through quasi-static tests. In the second phase of testing, various EDs are designed, fabricated with stainless and mild steel, and tested under quasi-static loading to validate the findings of the FE investigations. The test results demonstrate a stable hysteresis response of the buckling-restrained stainless steel EDs with a cyclic average strain capacity of 10%. The FE modelling procedure, calibration, and parametric studies are presented in the companion paper as Part II. [ABSTRACT FROM AUTHOR]

The first phase of experiments presented in Part I of this study is used to calibrate the 3D finite element (FE) modelling procedure of the tested fuse-type filler-injected buckling-restrained stainless steel energy dissipaters (EDs). The models are generated using a combined continuum-macro FE approach. A discussion is provided on the selection and calibration of material models. Sensitivity analyses are performed to investigate the effects of mesh sizes, imperfection shape and size, contact stiffness and friction coefficient on the cyclic response. After validating the FE analysis results against those obtained from the experiments, a parametric study is conducted with the objective of quantifying the required stiffness of the restraining system to avoid global-level buckling. At the end, an idealized elastic-perfectly plastic model with equivalent energy dissipation property is proposed for use in macro models. [ABSTRACT FROM AUTHOR]

Initial geometric imperfections have been identified as the main cause for the large discrepancies between experimental and theoretical buckling loads of thin-walled circular cylindrical shells under axial compression. The extreme sensitivity to imperfections has been previously addressed and mitigated through the introduction of stiffeners; however, sensitivity still remains. Optimized corrugated cylindrical shells are largely insensitive to imperfections and hence exhibit excellent load-bearing capacities, but their complex geometries make their construction difficult and costly using conventional manufacturing techniques. This was overcome in the present study through additive manufacturing (AM). Nine optimized corrugated shells with different diameter-to-thickness ratios, together with one reference circular cylindrical shell, were additively manufactured by means of powder bed fusion (PBF) from austenitic and martensitic precipitation hardening stainless steel. The structural behavior of the AM shells was then investigated experimentally with the testing program comprising tensile coupon tests, measurements of basic geometric properties, and axial compression tests. Numerical analyses were also conducted following completion of the physical experiments. The experimental and numerical results verified the effectiveness of optimized corrugated cylindrical shells in achieving improved local buckling capacity and reduced imperfection sensitivity. Initial recommendations for the structural design of the studied cross-sections are made. [ABSTRACT FROM AUTHOR]

Single-layer reticulated shells (SLRSs) are highly sensitive to initial geometric imperfections (IGIs) with respect to their nonlinear buckling behavior. However, the traditional random imperfection modal method assumes the joint deviations to be independent, which leads to the member length deviations always exceeding the manufacturing error limit given by design codes, i.e., the IGIs are unrealistic, and the nonlinear buckling load must be inaccurate. This paper proposes a simple and efficient method to generate stochastic IGIs for SLRSs considering topology constraints. By applying nonlinear heuristically perturbed virtual interaction forces to the joints, the joint coordinates can be updated using the iterative forward Euler method, aiming to generate realistic stochastic IGIs. Numerical experiments show that all the members in the IGIs generated by the proposed method satisfy the topology constraint, resulting in more significant out-of-plane joint deviations. Moreover, compared with the traditional method, the proposed method has better potential to search for the lower boundary of the nonlinear buckling load of SLRSs. [ABSTRACT FROM AUTHOR]

Current design specifications for cold-formed steel incorporate the Direct Strength Method (DSM) to design cold-formed steel members under compression. Although the DSM has been used for quite some time, its buckling strength curves have not been experimentally assessed thoroughly. This study attempts to fulfill this objective. First, a thorough literature review was conducted to inspect the buckling strength curves in the DSM, and the issues are summarized in this paper. Second, experimental data associated with compression tests of 453 solid and 228 perforated cold-formed steel columns were collected from the literature. Design parameters (e.g., elastic critical buckling loads) of the columns were then determined and assembled with the experimental results in a database to be used as a source to assess the buckling strength curves in the DSM. Finally, the LRFD resistance factors (ϕc) of the DSM buckling strength curves were determined in accordance with the AISI S100. This paper highlights the level of accuracy of the buckling strength curves in the DSM. [ABSTRACT FROM AUTHOR]

An accurate nonlinear hygrothermal-electro-elastic (HTEE) buckling analysis of piezoelectric fiber-reinforced composite cylindrical shells subjected to the coupled loading effects of axial compression and hydrostatic pressure was established by considering the nonuniform prebuckling effect. Nonlinear governing equations were derived based on higher-order shear deformation theory and Novozhilov's nonlinear shell theory. Accurate critical buckling stresses and pressures and explicit buckling modes for both axisymmetric and nonaxisymmetric buckling were obtained by the Galerkin method. A comparison between the new prediction and existing results is presented and excellent agreement is reported. A comprehensive parametric study of geometric parameters, end conditions, distribution patterns, and hygrothermal-electric multiphysical fields on the buckling behavior of HTEE composite cylindrical shell is also analyzed and discussed. [ABSTRACT FROM AUTHOR]

A new design of functionally graded graphene-reinforced composite laminated (FG-GRCL) toroidal shell segments in the thermal environment with a piezoelectric layer attached to the surface of the shells is presented in this paper. The piezoelectric FG-GRCL toroidal shell segments are reinforced by a FG-GRCL stringer and/or ring stiffener system. The nonlinear electro-thermo-torsional buckling and postbuckling of the shells are analyzed considering the geometrical nonlinearities described by von Kármán in the framework of the classical Donnell thin shell theory. Airy's stress function and Galerkin's process are applied, in which the deflection solution of the shell is approximately presented. The effects of thermal load, volume fraction and distribution type of graphene, piezoelectric layer, geometric parameters of the toroidal shell segments, and stiffeners on the torsional buckling load and postbuckling curves are analyzed and investigated in the numerical investigations. [ABSTRACT FROM AUTHOR]

Offshore pipelines that deliver raw fluids usually work under high temperature/high pressure (HPHT) conditions to ease the flow and prevent the solidification of wax fractions. Under HPHT conditions, lateral buckling and axial pipeline walking can occur. Existing studies have shown that axial walking is prone to occur in short pipelines and lateral buckling tends to occur in long pipelines. However, there is no clear definition for distinguishing between short and long pipelines, nor are there criteria to determine the occurrence of these two behaviors under certain conditions. In this study, the relationship between the length of a pipeline and lateral buckling critical temperature was derived based on an analytical solution, considering the influence of tension forces and seabed slope angle. A theoretical analytical solution of axial walking was reviewed and summarized. The two solutions for axial walking and lateral buckling were combined, and a criterion based on critical pipeline length was proposed to estimate the possibility and priority of these two behaviors for a given pipeline under certain conditions. The influence of seabed slope and axial and lateral friction factors on the two behaviors was explored by carrying out parameter analysis, and the influence regularity of these factors on critical pipeline length and critical temperature was obtained. [ABSTRACT FROM AUTHOR]

A cellular beam is a widened I-profile section with circular web openings. This type of perforated-web beam has been used immensely throughout the world during the last two decades. Lateral torsional buckling is one of the steel beam's limit state designs. This study aims to investigate the behavior of cellular beams against lateral torsional buckling. A validated numerical model was employed in a sort of parametric study. The examined parameters are applied load configurations and the geometrical ratios of flange width-to-thickness, web height-to-thickness, openings' spacing-to-diameter, beam's span-to-depth, and opening's diameter to beam-depth. Based on the results of the parametric study, a lower-bound design formula for predicting the lateral torsional buckling moment resistance of simply supported cellular beams was proposed. The suggested design formula can predict, with an acceptable degree of accuracy, the lateral torsional bending strength of simply supported cellular beams being subjected to various types of destabilizing loads. [ABSTRACT FROM AUTHOR]

This study investigates the distortional buckling strength of a partially closed cold-formed steel (CFS) channel section with intermediate web stiffeners and outward lips under axial compression. Generally, a closed CFS cross section has higher torsional resistance when compared to an open cross section. However, an open cross section is more popular in the construction industry. Despite the popularity of CFS open sections, distortional buckling can reduce the load-carrying capacity of such open cross sections. To improve the distortional buckling strength of the proposed selected section, a simple spacer plate is added externally to the channel section in the transverse direction. Initially, a numerical model is developed using the finite element software ANSYS, which is then validated against the experimental results available in the literature. A detailed parametric study was also conducted to investigate the influence of thickness, depth, and spacing of spacer plates on the distortional buckling strength of stiffened CFS channel sections. From the results of the parametric study, it was found that the presence of spacer plates can increase the axial capacity of stiffened CFS channel sections by as much as 32%. Finite element results were compared with the design strengths calculated in accordance with the direct strength method (DSM). [ABSTRACT FROM AUTHOR]

The present study investigates the elastic lateral torsional buckling resistance for steel I-beams that are strengthened with steel cover plates while being subjected to loading. A variational principle was developed for the problem by accounting for the full sequence of prestrengthening load application, strengthening process, poststrengthening load application, up to the buckling response. The variational principle was then used to develop a finite-element formulation for the problem leading to a quadratic eigenvalue problem. The formulation successfully captures the effects of prestrengthening loads, the beneficial effects due to prebuckling deformation, and the interactions between both effects. The study documents the benefit of providing transverse stiffeners to maximize the critical moment capacity attained when cover plates are used for strengthening. The study determines the locations of cover plates that would maximize the gain in critical moments in strengthening scenarios where only part of the beam span is to be strengthened. A systematic parametric study was developed to characterize the gain in elastic critical moment strength attained by cover plate strengthening and associated prebuckling deformation effects, in terms of dimensionless parameters that characterize the effects of prestrengthening load magnitude, beam span, cross-sectional geometry, length of cover plates, and cover plate cross section. Other parameters investigated include the distributions of prestrengthening and poststrengthening loading. [ABSTRACT FROM AUTHOR]

This paper summarizes recent findings concerning the elastic bifurcation and postbuckling behaviors of thin-walled regular convex polygonal tubes subjected to uniform compression. Such cross sections exhibit rotational symmetry, a feature that is at the root of several behavioral peculiarities, which are demonstrated using a specialization of Generalized Beam Theory (GBT). In particular, it is shown that (1) duplicate bifurcation loads can occur both in linear stability analyses and postbuckling analyses; (2) local or distortional buckling can be critical, depending on the cross-section geometry; (3) the pure local postbuckling behavior is very similar to that of simply supported plates under uniaxial compression; (4) the pure distortional postbuckling behavior has no postcritical strength and is imperfection-sensitive; and (5) the unstable nature of distortional buckling generates an unstable local-distortional interaction even if the distortional critical load is well above the local one. For comparison and validation purposes, results obtained with finite strips and shell finite-element models are reported. [ABSTRACT FROM AUTHOR]

This paper presents the evaluation of two methods for manually estimating the elastic lateral-torsional buckling (LTB) resistance of general doubly and singly symmetric I-section members having a linear variation in the web depth. The study focuses on unbraced lengths having idealized torsionally simply supported (fork) end conditions. The first method uses cross-sectional properties at the midspan of the unbraced segment along with a moment gradient modifier equation, written in terms of the flange stresses, to develop its strength approximation. This approach is employed in the first edition of the AISC-MBMA Design Guide 25 (DG 25). The second method is an extension of an approach that has been shown to be accurate and efficient for prismatic doubly and singly symmetric I-section members and is recommended in the second edition of DG 25. This approach uses cross-sectional properties at a critical section within the unbraced length, defined as the cross section where the ratio of the moment demand to the base LTB resistance in uniform bending is maximum, along with a moment gradient modifier equation written in terms of the above maximum ratio and the corresponding ratios at the quarter points of the unbraced length. Furthermore, Method 2 employs an additional calibration factor that accounts for an apparent destabilizing effect of the inclination of the shear center with respect to the axis of torsional restraint. The predictions from these methods are evaluated by an extensive parametric study encompassing the full design space for I-section members with linearly-varying web depth, as defined by DG 25. The second method is shown to provide improved accuracy, avoiding undesirable nonconservative errors in certain situations. The calibration factor developed as part of the second method is shown to eliminate undesirable errors in the first method as well, providing streamlined and accurate buckling estimates for linearly tapered member unbraced lengths. [ABSTRACT FROM AUTHOR]

Corrugated web plate girders (CWPGs) have grown in popularity in Canada in recent years because of their economic efficiency. Although research on the flexural performance of such members has increased in recent years, there are still additional advancements that can be made in their design, particularly in the calculation of lateral torsional buckling resistance. However, no research has been presented in Canada on this subject, and very minimal research has been published on CWPGs with sinusoidal corrugated webs. The purpose of this study was to examine the lateral torsional buckling strength of CWPGs with sinusoidal corrugated web profiles through experimental analysis of CWPGs that are currently being used in Canada. Nine simply supported specimens were loaded and failed in lateral torsional buckling (LTB). The nine specimens were chosen according to size in order to observe variations in LTB strength based on web thickness, web depth, and variations in identical beams. All beams tested recorded strengths far greater than conventional design strength, confirming the conservative nature of the current design procedure. As web thickness increased, a trend of ultimate capacity increasing was observed. The depth of the webs had no significant effect on LTB strength apart from what was gained by increasing the depth of the flanges. Based on the results, an equivalent web thickness equation is proposed for the purpose of calculating a more precise LTB resistance. A numerical analysis was run on a wide range of beam sizes and compared with the physical testing results. It was determined that the proposed equation effectively captured the physical testing results among more than just the tested beams. However, future work should further examine the reliability of the proposed equation by testing more specimens and/or using the finite-element method. [ABSTRACT FROM AUTHOR]

Recent studies investigating lateral torsional buckling suggest that North American steel design provisions may overestimate the bending resistance of welded girders that buckle laterally in the inelastic range. Furthermore, these provisions do not distinguish between rolled and welded members, but welded girders are widely suspected of possessing unfavorable residual stress distributions that may cause them to be more susceptible to lateral torsional buckling than their rolled counterparts. However, lack of sufficient supporting experimental test data may render existing analytically based assessments of the design equations inadequate. To address the paucity of physical testing, an experimental program was developed to determine the lateral torsional buckling resistance of full-scale I-shaped welded three-plate steel girders fabricated with current shop processes. This paper describes the development of the test program and a unique girder-stability test bed. Test results for seven girders, including measured initial geometric imperfections, load–displacement responses, and moment capacities, are then presented. A finite-element model of the test specimens, validated against the test data, is finally used to investigate the adequacy of the beam design provisions specified in the Canadian and US steel design standards. The results confirm that the current design equations can accurately predict the moment resistance of compact welded steel girders that fail in either the elastic or inelastic lateral torsional buckling mode. [ABSTRACT FROM AUTHOR]

Wire arc additive manufacturing (WAAM) is a metal three-dimensional (3D) printing method that enables large-scale structural elements with complex geometry to be built in a relatively efficient and cost-effective manner, offering revolutionary potential to the construction industry. However, fundamental experimental data on the structural performance of WAAM elements, especially at the member level, are lacking. Hence, an experimental study into the flexural buckling response of WAAM tubular columns has been conducted and is presented in this paper. A total of 18 stainless steel square and circular hollow section (SHS and CHS) columns were tested under axial compression with pin-ended boundary conditions. Regular SHS and CHS profiles were chosen to enable direct comparisons against equivalent, conventionally manufactured sections and, hence, to isolate the influence of the additive manufacturing process, whereas the cross-section sizes and column lengths were varied to achieve a broad spectrum of member slendernesses. Given the geometric undulations inherent to the WAAM process, 3D laser scanning was used to determine the as-built geometry and global geometric imperfections of the specimens; digital image correlation (DIC) was employed to monitor the surface deformations of the specimens during testing. Full details of the column testing program, together with a detailed discussion of the experimental results, are presented. The applicability of the current column design provisions in EN 1993-1-4 and AISC 370 to WAAM stainless steel members was assessed by comparing the test results with the codified strength predictions. The comparisons emphasized the need to allow for the weakening effect of the inherent geometric variability of WAAM elements to achieve safe-sided strength predictions. [ABSTRACT FROM AUTHOR]

Casting nodes are used to connect branch members at joints of freeform grid shell structures. In this study, the structural performance of a rectangular hollow section (RHS) branch-to-casting node connection was investigated. A RHS branch member with an access hole (i.e., opening) for temporary bolting was weld-connected to the T-shaped node fabricated by a conventional casting method. Six RHS branch-to-node connection specimens were tested under tensile and compressive loading. The eccentricity of axial loads was considered as the main test variable. Tests showed that, despite the opening near the weld joint, the RHS branch-to-casting node connections exhibited good performances. For tensile specimens, the ultimate strengths were greater than the yield strengths of the casting nodes, and weld rupture eventually occurred at the stiffener-to-casting node wall joints. On the other hand, for compressive specimens, the ultimate strengths were limited by flexural and torsional buckling modes accompanying local buckling and crippling of the casting node walls. The ultimate strengths degraded by the eccentric loading and openings were evaluated in accordance with current design codes. The failure modes and consequent strengths of compressive specimens were further investigated through finite-element analysis. Based on the investigations, design recommendations of RHS branch-to-casting node connections with openings were given. [ABSTRACT FROM AUTHOR]

The objective of this paper is to propose the prediction method of the cross-sectional moment capacity for continuous steel box girder bridges based on the continuous strength method (CSM). First, the critical buckling strain of the compressed members in box girders is determined using the base curve in the CSM, with which the elastoplastic cross-sectional analysis is conducted to derive the ultimate bending moment of steel box girders under sagging and hogging bending states. Then, a large number of applicable cross sections of steel box girders are designed, and their cross-sectional moment capacities based on the CSM and the elastic and plastic analyzing methods are calculated. Based on an analysis of the mutual relationship of these three moment capacities, the linear and quadratic prediction equations are proposed for both the positive and the negative moment capacities of steel box cross sections. The proposed equations are adopted to predict the cross-sectional bending capacities of some steel box girders in experiments, and the predicting results agree well with the experimental ones. Lastly, the proposed equations are applied to predict the cross-sectional moment capacities of the main girder in Xiamen Second East Passage as a case study. Compared with their elastic moment capacities, the analysis results show that using the proposed linear prediction equations, the cross-sectional moment capacities presented a 5.2% increase for cross sections with a nominal width-to-thickness ratio of 39.2 at support and a 22.2% increase for cross sections with a nominal width-to-thickness ratio of 37.6 at midspan. The linear and quadratic interpolation equations can well predict the cross-sectional moment capacity of the steel box girder. [ABSTRACT FROM AUTHOR]

The aim of this study is to investigate the effect of corrosion on the hysteretic behavior of Q235 steel. To this end, the surface features of Q235 steel specimens subjected to different corrosion durations are determined using a reverse reconstruction method based on the experimental data of corrosion pit configuration. The buckling and hysteretic behaviors of these specimens are analyzed using a numerical simulation method that considers corrosion surface characteristics. The results show that the buckling of corroded specimens occurs at the weak parts of plates with large corrosion pits under cyclic loading. The surface characteristics have a significant influence on the buckling stress of corroded steel, which results in stress mutation at corrosion pits and a change in load gradient. In addition, an increase in the surface roughness and width-to-thickness ratio due to corrosion are the main reasons for the degradation of the buckling and hysteretic behavior of the corroded specimens. The ultimate load-carrying capacity and elastic stiffness decrease with increases in corrosion degree. The hysteretic energy of specimens decreases by nearly 33% as the average mass loss ratio increases by 19%. Finally, a nominal cyclic constitutive model of corroded steel is proposed, and the results essentially agree with the numerical simulation results. [ABSTRACT FROM AUTHOR]

This paper theoretically analyzes the symmetrical global buckling behavior of imperfect prestressed carbon fiber-reinforced polymer (CFRP) laminate-reinforced steel columns (PCRSCs) with two hinged supports under axial and eccentric compression loadings. First, the causes of the buckling of the component are revealed; either the steel yields or the CFRP becomes slack. Therefore, four buckling cases are found, and a theoretical calculation method for the buckling capacity is established. On this basis, a theoretical calculation method for the optimal CFRP initial prestressing force and maximum buckling capacity is built from physical explanations. The results of the theoretical method fit well with the test and finite-element results. Finally, a design method of PCRSCs is proposed for engineering applications, followed by a design example, by which the optimal reinforcing efficiency is realized. [ABSTRACT FROM AUTHOR]

Day by day, technology has been changing progressively because of the remarkable hastening of research and development activities. Perforated beams are one such example of advancement in construction technology. Steel beams with web openings are those that have regularly spaced web openings along the length of the beam. The web openings are created in various ways such as wire cutting and welding. Castellated and cellular beams differ in the creation of web openings. Studies addressing the effect of web post width of steel beams with web openings on the strength capacity of beams are rare. Therefore, the objective of the present work was to examine the influence of web post width on the strength capacity of beams with web openings. First, experimental tests were carried out on three full-scale specimens of a steel beam with oval-shaped web openings, cellular beam, and solid web beam. The same beam was modeled using finite-element software ANSYS and the behavior was compared in terms of load–displacement curve and failure modes. Later, a detailed parametric study was carried out to study the behavior of beams with web openings having variation in web post width using nonlinear finite-element analysis. The simply supported steel beams with web openings subjected to midspan concentrated load with varying web post width and shape of openings were modeled and analyzed. From the analysis results, it was found that the shape of web openings and the web post width play an important role in the strength capacity of the perforated beams. The maximum strength reduction capacity was found to be 51.78% for hexagonal openings of depth 150 mm and having a web post width of 50 mm. The minimum strength reduction capacity was found to be 8.93% for hexagonal openings of depth 100 mm having a web post width of 500 mm. Web post width plays a significant role in the ultimate strength capacity of beams. Web post buckling is a predominant failure mode in steel beams with web openings and it can be prevented by maintaining sufficient web post width. [ABSTRACT FROM AUTHOR]

Some of Louisiana's bridges built in the 1950s and 1960s used two-girder or truss systems, in which transverse floor beams are carried by main longitudinal members and continuous (spliced) beams supporting the deck are supported by the floor beams. The main longitudinal members are either two edge (fascia) girders or trusses. Continuous-beam bottom flanges are in compression in the negative moment region, which could result in lateral torsional buckling. When the continuous beams are load rated, Cb is calculated in accordance with a standard specification that does not account for potentially beneficial bracing effects from a noncomposite concrete deck and could therefore underestimate actual flexural strength. As a result, the rating may require a restrictive bridge posting or closure. This issue affects bridges that are key parts of Louisiana's highway system, i.e., longer, multispan crossings with high average daily traffic (ADT) counts. The calculated load rating could require expensive, and possibly unnecessary, bridge rehabilitation or replacement with significant traffic disruption. This research reassessed the methodology behind load rating these continuous beams, with efforts focusing on deriving more realistic values for Cb. Its main objective was to evaluate the capacity of bridges built with continuous beams and noncomposite decks and to develop a new approach for rating those beams by more accurately representing the moment gradients using Cb. An experimental study was conducted to evaluate lateral torsional–buckling resistance of a reduced-scale, two-span grillage system that included three lines of continuous beams supporting a noncomposite concrete deck. A significantly higher moment gradient factor as compared to the existing codes and standards was recommended by accounting for the bracing effect provided by a noncomposite deck. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the buckling behavior of cold-formed steel built-up closed section members subjected to combined minor axis bending and compression. The channels were fabricated from zinc-coated steel sheets of grades G500 and G550 to compose built-up closed sections. A total of 30 beam-column specimens with nominal member lengths of 300, 900, and 1,500 mm as well as nominal plate thicknesses of 0.75 and 1.2 mm were eccentrically loaded under pin-ended boundary condition. The initial loading eccentricity was varied for the specimens in each test series to obtain the data evenly distributed in the axial load-moment interaction diagram. Experimental results including failure modes, loading capacities, and full-history responses of the test specimens were obtained. In addition, the experimental loading capacities were compared with nominal strengths to evaluate the suitability of the provisions as stipulated in the North American specification, Australian/New Zealand standard, European code, and American specification for the built-up section beam-columns. It is shown that the aforementioned design codes are overall unreliable and unconservative for strength predictions of the cold-formed steel built-up closed section members under combined minor axis bending and compression. [ABSTRACT FROM AUTHOR]

The theoretical lateral-torsional buckling solutions for I-beams utilized in many design specifications may the overestimate lateral torsional buckling (LTB) resistance when significant shear is present due to web distortion. This paper investigates the effects of shear on the elastic LTB of doubly symmetric steel I-beams through computational models. A parametric study was conducted considering a range of geometric parameters and loading conditions commonly found in design applications in buildings and bridges. The results show that shear can have a substantial impact on the LTB resistance under many practical design circumstances. The impact of shear on LTB is more significant for sections with larger web slenderness ratios and smaller depth-to-flange width ratios. Postbuckling shear resistance does not significantly impact the reductions in LTB resistance due to shear. A practical design method that accounts for shear effects on the LTB behavior in stiffened and unstiffened beams was proposed and verified by comparison with computational solutions. Design examples demonstrating the proposed method are provided. [ABSTRACT FROM AUTHOR]

Heavy glulam timber framed structures are facing a growing inadequacy in resisting lateral actions from earthquakes and winds due to the increasing building heights. This paper presents the experimental and numerical analysis results on the hysteretic behavior of newly developed carbon fiber reinforced polymer (CFRP) confined timber-steel buckling-restrained bracings and the lateral performance of bolted glulam timber frames with such bracings. Ten timber-steel bracings and four frames with different bracing provisions were tested via reversed cyclic lateral loading. A finite-element method based model was developed, verified, and used for parametric studies. The bracing test results indicated that the design requirements for ordinary buckling restrained bracings on the confinement ratio and the transverse bulging force are adequate for the proposed timber-steel bracings. A confinement ratio no less than 4.6 is suggested. Compared to an otherwise similar bare frame, two frames with the proposed bracings were found to be 132% and 176% higher in the peak loads, more than 10 times higher in the elastic stiffness, 40% and 43% higher in ductility ratio, and on average 106% higher in the equivalent viscous damping ratio. The two frames also exhibited higher stiffness and energy dissipation than a frame braced by timber bracings, which are prone to buckling failure. Parametric studies indicated that the secant stiffness and the damping ratio of the frames at small drift can be substantially affected by the bolt slippage of the bracing-frame connections. The increased lateral stiffness ratio will lead to increase in the peak load and stiffness, but the equivalent viscous damping ratio remains nearly constant for lateral stiffness ratios larger than 2.5. The frame stiffness and peak load increase with increased rotational stiffness of the beam-column connections while the equivalent viscous damping ratio decreases. [ABSTRACT FROM AUTHOR]

The conventional buckling type of brace members offers lateral stiffness to the structural system; however, such members are likely to yield under tension and buckle under compression when loaded. Their unequal strength tends to produce higher demand on the framing system. Buckling-restrained braces (BRBs) offer excellent lateral force resistance, energy dissipation, and higher ductility thanks to their symmetrical hysteretic responses. The higher amount of friction, the gap between the core and restraining segment depending on the length, and the stoppers within the core segment are critical factors. This study investigates the effect of varying the yielding core length, the gap size between the steel core and the outer restraining segment, the position, and the frequency of stoppers on the hysteretic response of all-steel BRBs, considering the interaction between different parameters. Numerical analysis is performed with Abaqus finite-element software. A calibrated analytical model is used for the parametric study. The considered parameters are the cyclic behavior, axial resistance, energy dissipation capacity, compression strength adjustment factor, and strain hardening factor of the BRBs. Appropriate interface details are suggested based on the parametric finite-element analysis, considering the interactions among parameters. The study results reveal that the performance of BRBs with appropriate yielding core length, provided with sufficient gap size, is superior. Further, the selection of an appropriate gap size is of utmost importance. Finally, the provision of an increased number of stoppers enhances the performance of BRBs. [ABSTRACT FROM AUTHOR]

Sheathed cold-formed steel (CFS) wall panels comprise studs, tracks, and sheathings on one side or both sides. It has been observed in the literature that sheathing contributes significantly to the axial load carrying capacity of CFS wall panels. Limited studies are available on comparing the efficacies of available design methodologies to evaluate the axial strength of CFS wall panels with sheathing. The present study investigates the efficacy of analytical/semianalytical methods, namely, the Rayleigh–Ritz (R–R) method and direct strength method (DSM), for evaluating the axial load carrying capacity of sheathed CFS panels. In DSM, three elastic buckling loads are evaluated, namely, local, distortional, and global, using an open-source finite strip method based software CUFSM version 4.05. The bracing provided by sheathing to the section is presumed as springs. For the first time, a problem is undertaken to verify the efficacy of both the mathematical models together to evaluate the axial load carrying capacity of sheathed CFS wall panels. The evaluated results by both the models are compared with experimental strengths of sheathed CFS wall studs from the experimental database including the tests conducted by the authors. Results demonstrate that DSM may be used effectively for predicting axial strength of sheathed CFS wall panels, as a substantially lower coefficient of variation (CoV) is obtained for DSM, which is 0.1274, than the R–R method (CoV=0.1897). DSM is suggested over the R–R method for evaluating the axial load carrying capacity of sheathed CFS wall studs as it better takes into account the local buckling and inelastic effects. [ABSTRACT FROM AUTHOR]

To better understand the mechanical behavior of cold-formed steel (CFS) quadruple-limb built-up box-section (QBB) columns associated with flexural buckling, 12 axial compression tests with different slenderness ratios and screw spacing were conducted. The test results showed that, for a slender specimen (L=2,700 and 3,300 mm), when the screw spacing was reduced from 600 to 300 mm, the load-bearing capacity increased by about 6%–10%. When the screw spacing was reduced from 600 to 150 mm, the load-bearing capacity increased by about 14.6%–17.5%. Arranging end fastener groups can enhance the strength of the column, but it may be cumbersome and uneconomical. A finite-element model (FEM) was developed and calibrated against the test results. A series of parametric analyses was carried out to investigate the effects of the screw spacing and shear stiffness on the elastic buckling load and ultimate load-bearing capacity. Finally, a practical design method was proposed to evaluate the column's elastic buckling load and load-bearing capacity associated with flexural buckling. Compared with the simulation and test results, the proposed design method was accurate at predicting the load-bearing capacity of the specimens, with a relative difference of less than 6%. [ABSTRACT FROM AUTHOR]

A finite-element formulation is presented for the elastic distortional buckling analysis of doubly symmetric wide flange beams. The formulation characterizes the distribution of the lateral displacement along the web height through Fourier modes and is equipped with features to capture the load height effect and to enforce user-defined kinematic constraints. The formulation is used to investigate the load height and bracing height effects and develop a database of over 20,000 runs on practical beam cross-sections to characterize (1) the reduction in critical moment capacity due to web distortion; and (2) the effect of a load height on the elastic critical moments. A novel indicator characterizing web distortion along the beam span is proposed and integrated within the finite-element formulation in a procedure devised to optimize the location of transverse stiffener(s) along beam spans so as to reduce cross-sectional distortion and maximize the elastic critical moment attainable. The procedure is then applied to optimize the design of beams in two case studies. [ABSTRACT FROM AUTHOR]