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To investigate the mechanical deformation characteristics of the 'Segment-SCC-Steel Tube' combined bearing lining structure under internal and external pressure, the loading device and monitoring system for the stability analysis of the full-scale lining were proposed. The effect of cracked encased concrete and local external pressure on the instability mode of thin-walled steel pipes was explored by full-scale model experiment and three-dimensional FEM numerical simulation. The influence of SCC (Self-Compacting Concrete) and stiffening rings on the stability of steel pipes subjected to external pressure was discussed. The results show that SCC cracks occur and intensify with increasing internal pressure. The external water acts directly on the steel tube through cracking, resulting in wavy deformation, and the gap between the SCC and steel tube further increases. When calculating the critical external pressure for the steel pipe, the constraint of encased concrete can be ignored, and only the constraint effect of the stiffening ring can be considered. Therefore, the Von Mises formula was used to predict the critical external pressure between the stiffening rings with high accuracy. In addition, the stiffening ring can mitigate the crack propagation of nearby SCC. The steel tube remained in the elastic stage under internal pressure. In the full-scale experiment, the external pressure could not continue to rise after reaching 0.65 MPa. Nevertheless, the amplitude of the buckling wave continued to increase. It is considered that the steel pipe is in an unstable state, and the failure mode is dominated by single-lobe buckling. • According to the performance of the 'Segment-SCC-Steel Tube' lining structure, the influence of cracked encased concrete and local external pressure on the buckling mode of steel pipes is investigated. • The loading device of the full-scale model test is proposed for the external pressure stability analysis of the 'Segment-SCC-Steel Tube' lining structure, and the monitoring system combining distributed optical fiber and traditional vibrating wire sensors is established. • The mechanical deformation characteristics of the SCC and Steel Tube lining under internal and external pressure are revealed, and the influence of SCC and stiffening rings on the stability of steel pipes under external pressure is discussed. [ABSTRACT FROM AUTHOR]

To date, many studies have been conducted on the experimental behaviors of circular and square hollow section braces. In those studies, the effect of material properties, cross-sectional shape and loading history on the performance of braces were investigated independently of each other. In this study, the effects of the combined actions of these variables on the performance of steel braces were examined. For this purpose, approximately 1/3 scaled 12 specimens (6 circular and 6 square), which were cold formed from carbon/stainless steel sheets, were experimentally and numerically investigated under 3 different cyclic load effects representing far field and near fault loadings. The buckling strength, energy dissipation capacity and displacement ductility of the specimens were evaluated. In addition, parametric studies, using 198 FE analyses verified with current study, were conducted. Experimental results indicate that the buckling strength limits provided in AISC 360–22 and EN 1993-1-1 for carbon steel braces are significantly influenced by the cross-section, loading protocol and material properties. On the other hand, it has been determined that the buckling strength limits given in AISC 370–21 and EN 1993-1-4 for stainless steel braces are safe for far field loadings, but insufficient for near fault loadings along the full slenderness range. It has been seen that the most disadvantageous results for the buckling strength, energy dissipation capacity and displacement ductility of the braces can only be obtained by applying different loading protocols. Moreover, It has been determined that the effect of material properties on the performance of braces varies considerably depending on the cross-section geometry. • Stainless steel braces tested under near-fault loadings for the first time. • Combined effect of material properties, cross section and loading history on the performance of braces has been investigated. • The experimental and numerical results are discussed. • Important differences with the previous studies were pointed out and discussed. • Parametric studies were carried out across a range of global and local slenderness ratios. [ABSTRACT FROM AUTHOR]

This paper delivers a comprehensive analysis of the thermomechanical behavior of steel–concrete (SC) composite elements under elevated temperatures, up to 200 °C, as these can be encountered in accidental scenarios within nuclear power plant operations. The focus lies on the thermal buckling of external thin steel plates. We undertake an integrated approach, combining an experimental campaign and numerical simulations, to investigate thermal buckling phenomena. Using these findings, along with principles from thermoelasticity and thin plate theory, we establish an analytical model to guide preliminary SC element design. The efficacy of this model is ascertained through rigorous comparisons with experimental and numerical results. The paper concludes by demonstrating the model's practical utility for thermal buckling verification through a relevant case study. • Local thermal buckling in SC elements was studied via experiments and simulations. • Database expansion and key buckling factor identification conducted numerically. • Analytical formulas for SC design were derived from thermoelasticity and plate theory. • Formulas were validated against numerical and experimental data for reliability. • Significance of diagonal connector spacing in SC walls was demonstrated. [ABSTRACT FROM AUTHOR]

Steel bracing systems are usually introduced to assure the structural stability and seismic resistance of steel storage pallet racks, whose height over the last years has increased more and more to improve warehouse efficiency. In the present paper, the axial response, under monotonic and cyclic load, of perforated cold-formed steel diagonals of concentric bracing systems is investigated through experimental tests. To satisfy the design and detailing rules required by the capacity design approach, such as the ratio between overstrength coefficients and the value of the non-dimensional slenderness, tested diagonals are equipped with additional holes at one end. Results of monotonic tests, under compression and tensile load, provide useful information about the influence of the number and shape of holes on the ultimate strength, ductility and buckling load of bracings. Cyclic tests highlight how the member slenderness and the class of its cross-section affect hysteresis loops and energy dissipation. Finally, some novel considerations are presented concerning the influence of the shape, dimensions and distance of additional holes, in addition to member geometrical features like the cross-section class, on the cyclic response of tested members. In the framework of the "Design Assisted by Testing", results could be adopted for the capacity design of perforated concentric cold formed diagonal bracings as those adopted in steel storage pallet racks. • The axial response of CFS members with holes is experimentally investigated. • The effect on the ductility of holes, member compactness and slenderness is shown. • Segment with additional holes represents a ductile fuse for investigated members. • Ductility of very slender class 3 specimens is comparable to class 2 specimens. • Energy dissipation of class 3 specimens is lower than class 2 specimens. [ABSTRACT FROM AUTHOR]

Gusset plates are key connection components in steel truss and braced frame structures. To provide a comprehensive insight into the behaviour and design of these components, this paper thoroughly reviews the research studies and design methods of steel gusset plates subjected to various loading conditions. A particular focus is placed on the design of steel gusset plates under tension and compression, including the well-known Whitmore method, block shear and buckling design approaches. Representative design methods are reviewed and evaluated based on available test data. It is concluded that a proper block shear method in conjunction with a proper net section tension check can accurately predict the tension capacity of steel gusset plates. In comparison, the design for compression capacity is subjected to a much greater uncertainty due to the complexity of the compressive behaviour that is largely affected by the boundary condition, plate action and post-buckling effect. Further discussions are made on the frame action, as well as the stiffening and seismic detailing strategies of steel gusset plates. Finally, future research needs are identified in the field of gusset plate research. • Research on steel gusset plates is reviewed. • Early age research and design practice of gusset plates are overviewed. • Whitmore and block shear methods for gusset plates in tension are reviewed and evaluated. • The buckling behaviour and design of gusset plates in compression are overviewed. • Strengthening strategies and seismic detailing of steel gusset plates are briefy discussed. [ABSTRACT FROM AUTHOR]

This paper presents a cross-sectional optimization procedure to increase the load carrying capacity of a perforated rack column under a compression load. The optimization method is based on a Genetic Algorithm (GA) combined with the Generalized Beam Theory (GBT), which allows to take perforations as well as sectional deformations into account. The results indicate that the optimal cross-section geometry depends on the dominant buckling mode. Therefore, a combined optimization criterion to consider distortional and global buckling is defined. Finally, nonlinear shell finite elements analyses are done in order to assess the structural behaviour of optimized cross-sections. • Cross-sectional optimization of rack columns under compression load. • Influence of perforations and sectional deformations. • Combination of Genetic algorithm and Generalized Beam Theory. • Influence of dominant buckling mode. [ABSTRACT FROM AUTHOR]

A poor seismic design of liquid storage tanks may result in large economic losses or environmental impacts due to the spillage of their contents; therefore, an effective seismic design of these tanks is of vital importance. Moreover, many liquid storage tanks have suffered severe damage during recent earthquakes worldwide due to the buckling of their wall, which is one of the most common failures. In continuously supported tanks, anchors are an essential part of the seismic design; however, the effectiveness of incorporating them and the predictive ability of design codes on the behavior of these structures has not been extensively studied. This research evaluates the design recommendations (API-650 and NZSEE) through a comparison with nonlinear 3D finite element models. In particular, the compressive stress and the buckling capacity of the tank wall are evaluated. Three anchorage conditions are analyzed: (i) tank with a fully anchored base, (ii) tank with flexible anchors at the periphery of the base (bolted anchorage), and (iii) unanchored. Four tank geometries, two materialities (stainless steel and carbon steel), and different amounts of anchors for each geometry were analyzed. In total, 24 nonlinear 3D finite element models were developed and analyzed. The presented results provide a better understanding of the effectiveness of including anchors depending on the tank slenderness and the predictability capacity of design codes for these structures. Finally, some code guidelines for flat tanks are validated, and the need for additional detailed guidelines for slender tanks is highlighted. • The buckling capacity of liquid storage tanks is investigated using finite element models. • Anchoring system effectiveness and predictability of design codes on behavior of anchored tanks are investigated. • The design codes underestimate the compressive axial stress demand in slender anchored tanks. • The design codes effectively measure the buckling failure on broad anchored tanks. [ABSTRACT FROM AUTHOR]

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

Abstract The present study investigates the flexural-torsional struts buckling and beam lateral buckling analyses. In the highlight of braced structures, analytical solutions are derived for higher 3D buckling modes of simply supported struts with arbitrary cross-sections. Closed-form solutions are also investigated for lateral buckling strength of beams with doubly symmetric cross-sections. For more general cases, the finite element approach is adopted. In presence of torsion, warping is of primary importance. For this aim, 3D beams with 7 degrees of freedom (DOFs) per node are adopted in the analysis. The model is able to carry out higher buckling modes of bars under compression or lateral buckling modes of beams initially in bending. The analytical and the numerical results of the present model are compared to some available benchmark solutions of the literature and to finite element simulations of some commercial codes (Abaqus, Adina). The efficiency of the closed form solutions and the numerical approach is successfully verified. Applications of higher buckling modes in design of braced structures are considered according to Eurocode 3 code. A particular attention is pointed out to torsion and flexural-torsional buckling modes not considered in bar strength. At the end, some solutions are proposed in order to cover the full strength of columns and beams in presence of instabilities. This proposal makes steel structures more performant and attractive when effects of instabilities are limited at a minimum. Highlights • Closed form solutions are derived for higher buckling of thin-walled beams with arbitrary cross sections. • Analytical solutions of higher buckling moments of I beams are derived. Load height position is included. • The finite element approach of the model implemented. • Higher buckling mode applications in design of braced beams according to Eurocode 3 are studied with details. [ABSTRACT FROM AUTHOR]

Abstract This research work presents a parametric numerical study on the resistance at elevated temperatures of stainless steel members, subjected to combined bending and axial compression. Previous studies have shown the need for the development of further research works aiming at better predicting the fire behaviour of stainless steel beam-columns. However they have only considered beam-columns composed of stocky I sections. Hence, this paper focuses on austenitic stainless steel (European grade 1.4301 also known as 304) beam-columns composed of square hollow sections (SHS) and circular hollow sections (CHS), considering different cross-sections classes (1 to 4), according to Eurocode 3 (EC3) classification. The numerical analyses were performed using the finite element program SAFIR, with material and geometric non-linear analysis considering imperfections. The influence of the following parameters was evaluated: bending moment diagram shape, cross-section slenderness considering the local buckling occurrence on the thin-walled sections, and member slenderness for the global instability due to flexural buckling. Comparisons between the obtained numerical results and the interaction curves of Eurocode 3 are presented. The results show that specific design approach should be developed for these stainless steel members under fire situation, taking into account the above mentioned parameters. Highlights • The behaviour of stainless steel beam-columns with square and circular hollow sections in case of fire is studied • Numerical analysis with material and geometric imperfections of stainless steel structural elements are performed • The accuracy and safety of EC3 design for beam-columns are not suitable for these stainless steel members in fire. [ABSTRACT FROM AUTHOR]

Abstract Steel beams and girders with corrugated webs have found many applications, especially in industrial structures and bridges. This choice is backed by the many features, this class of structural members can offer, such as the high load carrying capacity before failure due to the web geometry. The failure of a corrugated web may occur due to material yielding or due to geometrical buckling. Three modes of shear buckling are typical for corrugated webs: local, global, and interactive shear buckling. In this paper, the shear failure mechanisms of trapezoidal corrugated webs are investigated. Nine, shear-critical, corrugated web panels were tested until failure. The new test results confirmed a previous observation that all panels achieved a residual strength of about half of the buckling shear strength, regardless of their geometry and most of them reached yielding before buckling takes place. Since the shear strength of corrugated webs is a function of several material and geometric parameters, a comprehensive global, density-based, sensitivity analysis was performed to estimate the relative contribution of each parameter to the behavior of shear strength through a previously developed mathematical model. The analysis revealed that the length of the flat folds is the most influential parameter on the shear strength of corrugated webs, while the modulus of elasticity is the least influential. The study was extended to determine ranges on which each parameter is non-influential. Highlights • Nine corrugated web steel panels were tested until failure; • The residual strength is not influenced by the mode of shear buckling; • The flat fold length and web thickness are the most influential parameters on the shear strength followed by the web height; • The steel modulus of elasticity is a non-influential parameter; • Ranges of non-influence for each parameter were determined at 0.05 and 0.001 confidence levels. [ABSTRACT FROM AUTHOR]

When structural steel members are in contact with horizontal members, such as concrete slabs, dust and moisture easily accumulate at their junction. This can induce local corrosion at their ends, and consequently, reduce their compressive strengths. In this study, compressive tests were conducted on circular tubular short columns to examine the change in compressive strength with local corrosion at the ends of the columns. The columns were fabricated to have corrosion levels of various depths, heights, and circumferences. As a result, local buckling occurred near the column ends. Moreover, residual compressive strengths linearly decreased as the corroded depth, height, and circumference increased. An evaluation method using the effective volume was proposed to assess the residual critical compressive strengths of circular tubular short columns with locally corroded ends. [ABSTRACT FROM AUTHOR]

In cold-formed steel structures, such as trusses and portal frames, the use of back-to-back gapped built-up cold-formed steel channel-sections for column members are becoming increasingly popular. In such an arrangement, the lowest flexural buckling mode may not necessarily be overall buckling of the whole column. In the literature, only three test results have been previously reported for such cold-formed steel columns, and limited to values of non-dimensional slenderness ranging from 1.08 to 1.16. This issue is considered herein. The results of 40 experimental tests are reported, conducted on back-to-back gapped built-up cold-formed steel channel-sections covering the range of non-dimensional slenderness from stub to slender columns. A nonlinear finite element model is then described that shows good agreement with the experimental results. The finite element model is then used for the purposes of a study comprising 84 models. Using the experimental and finite element results, it is shown that design in accordance with the American Iron and Steel Institute (AISI) and Australian and New Zealand Standards (AS/NZS) can be conservative by as much as 53%. However, use of a modification to the non-dimensional slenderness, that considers the gap, results in the design standards being within 5% conservative with respect to the experimental and finite element results. [ABSTRACT FROM AUTHOR]

This paper reports on experiments addressing the buckling and collapse behavior of back-to-back lipped channel built-up cold-formed steel (CFS) columns assembled using 16 different CFS lipped channel sizes. The lipped channel sections are connected at the web using a pair of self-drilling screw fasteners at a specified spacing along the column length of 1.83 m (6 ft). These experiments aim to quantify the effect of two web fastener layouts on composite action for each section size, study member end fixity, observe buckling and collapse behavior, and provide benchmarks for design that includes specific considerations for thin-walled member buckling. A total of 32 monotonic, displacement-controlled, concentric compression tests are completed with up to 17 position transducers monitoring displacements at key locations. All tests are conducted with the built-up member seated in CFS tracks, as would be found in practice. Local–global interaction is shown to be a prevalent failure mode, and the stud-to-track end condition is determined to be semi-rigid, but generally closer to a fixed condition. End rigidities are estimated using a Southwell approach. Rational design approaches extending the application of the Direct Strength Method (DSM) and employing current state-of-the-art numerical modeling techniques are proposed and validated with test data. In addition, the development of definitive design recommendations that help reduce the complexity of fastener designs and incorporates the DSM framework when predicting built-up member strength is underway. [ABSTRACT FROM AUTHOR]

The problem addressed in this paper is the thermal buckling behaviour of thin-walled steel cylindrical fixed-roof tanks under non-uniform loading, induced by an adjacent tank. This specific type of thermal loading can be triggered by a neighboring tank fire where heat is transferred mainly through radiation. Since the calculation of the temperature field of the heated tank lies in other scientific fields (e.g. Computational Fluid Dynamics), a thermal pattern, proposed in literature, is used for the simulation of the fire-induced load and the investigation of the structural response of the tank due to heating. The study is conducted numerically through the Finite Element method, using coupled thermo-mechanical analysis. The general purpose Finite Element code MSC Marc, is used for the simulation. Three-dimensional models are developed using shell elements. Firstly, a detailed study of the failure mechanisms that take place in case of non-uniform loading is carried out. Furthermore, tanks with different geometries are studied. The main objective is the calculation of the critical temperature i.e. the temperature where the failure appears and the determination of the failure modes. Finally, a parametric study is conducted for the evaluation of the effectiveness of stiffening methods that are commonly used at ambient temperature design (stiffeners and stepwise wall thickness), in the case of the non-uniform heating load. In this study, the heated tanks are considered to be empty, which is the most severe scenario, for their structural integrity. [ABSTRACT FROM AUTHOR]

Global and local imperfections are required to capture accurate buckling loads and overall structural behaviour of axially loaded structural steel hollow sections in finite element (FE) models. In this paper, three methods of geometrical imperfections are considered for square and rectangular structural steel hollow sections: (i) creating the profile of the brace using a half sine wave, (ii) applying an equivalent notional lateral load at mid-length, and (iii) combining sinusoidal local imperfections with an equivalent notional lateral load for global imperfections. When modelling the initial shape of brace members with global imperfection at mid-length of the magnitude used to establish the European buckling curves (L/1000, where L is the length of the brace member), it was found that the equivalent notional lateral load methodology could best predict the buckling capacity of brace members when compared to physical test data and European buckling curves. However, both methodologies neglect the effect of local imperfection on the initial buckling loads. When it was included by generating a continuous sinusoidal wave along the member length, it did not affect the initial buckling loads, but gave a more overall representative behaviour of the brace members. The FE model is then validated using sixteen cyclic tests for brace members. The FE results are found to match the physical tests values relatively well. In other words, when comparing the ratio of yield force, buckling resistance, and total energy dissipated estimated from the FE model to the measured values in physical tests, the mean values are found to be 1.04, 0.99 and 1.24, respectively, with a coefficient of variation of 0.07, 0.07 and 0.17, respectively. [ABSTRACT FROM AUTHOR]

Carbon fiber is considered as a newly alternative technique used in enhancing the strength and behavior of different members in many steel structures applications. In this research, an experimental study for strengthening of cold-formed lipped channel columns using carbon fiber reinforced polymers (CFRP) is conducted. Twelve cold-formed columns specimens with different parametric variables are chosen. Different variables such flange width-thickness, web depth-thickness ratios for un-strengthened, partially, and fully strengthened short columns, as well as overall slenderness ratios for partially strengthened short and medium columns are selected. The cold-formed column specimens were tested under axial compression load. A finite element model is developed using ANSYS program to simulate and verify the laboratory tested specimen's results. The developed FE model includes both geometric and material nonlinearities. The strengthened columns behavior along with local, distortion and rupture failure modes are investigated. A comparison between experimental and finite elements as well as the direct strength method (DSM) axial capacities, is carried out. Finite element and direct strength method results are comparable with the experimental results. [ABSTRACT FROM AUTHOR]

This paper studied buckling of parallel Z - and C-purlin systems inter-braced by sag-rods at mid-span under pure hogging moment. The purlins are connected to metal sheeting by self-drilled screws and the lateral movement of the top flange is prevented. The paper studied first in detail the buckling of a single purlin, and then buckling of parallel purlin systems. The alternate offset of the sag-rods in adjacent bays and the local deformation of the purlin web have been taken into consideration in parallel purlin systems. For one-purlin system, the buckling moments are given, valid for different combinations of sag-rod and distributed rotational stiffness. The threshold stiffness of the sag-rod, at which the buckling mode changes from symmetrical buckling to anti-symmetrical buckling, is also given. For parallel purlin systems, the buckling moments are calculated by the formulas of one-purlin system, but with a reduced equivalent sag-rod stiffness used in the calculation. Numerical examples for the reduced sag-rod stiffness reveal that an astonishingly large reduction of the sag-rod effective stiffness occurs when the purlin number and the sag-rod offset increase, and the sag-rod stiffness is maximum if the sag-rod is set as close to the bottom flange as possible. And finally some strengthening practices and details are recommended. [ABSTRACT FROM AUTHOR]

Infrastructure resilience is the ability of an infrastructure asset to limit the effect and duration of damaging extreme events. The four main components of the concept of resilience are robustness, resourcefulness, recovery and redundancy most of which are very difficult to be quantified. In addition to this difficulty, a careful study of extreme event cases can demonstrate that it is very common for an extreme event scenario to include cascading multi-hazard events such as blast, floods, earthquake, and fire. This paper studies the resilience of a multi-story steel frame with multi-hazard considerations which include a post-event fire scenario. The initiating extreme event is simulated through the threat-independent alternate load path method of analysis and a post-event fire is considered following the extreme event. The work in the paper combines previous work by the authors on stability-induced collapse of damaged steel structures and closed-form solutions for temperature predictions of wide-flange components during a fire scenario. For the purposes of the fire scenarios, new fire time-temperature curves are developed based on experimental data from the well-known Cardington fire tests. The results show that even when a structure can withstand an extreme event scenario, a post-event fire consideration is highly critical to evaluate the remaining time of survival of the structure before collapse. It is shown that the sequential method of multi-hazard analysis can lead to very short available time periods before the post-event fire leads to the complete collapse. [ABSTRACT FROM AUTHOR]

Cylindrical shell structures such as silos and wind turbine towers often feature openings for internal access, and these may have a significant detrimental effect on the buckling load. This paper numerically investigates the buckling of cylindrical shells with cutouts near the cylinder end using nonlinear finite element analysis. The finite element (FE) model was validated against published experiments on the axial compression of moderately thin-walled cylinders with cutouts of various sizes and shapes. The results indicate excellent qualitative and quantitative agreements for loads, deflections, and buckled mode shapes. Using the validated FE model, it was found that the opening width is the most critical geometric parameter in terms of loss of carrying capacity. The model was then extended to explore a variety of stiffener configurations aimed at recovering the capacity lost due to the opening. These configurations included a frame ring, as well as the simpler option of straight ribs on either side of and above the hole. Thickness and protrusion were also considered in the analysis. It was found that the frame ring achieved full recovery of the lost capacity, while the straight stiffeners were effective where only up to 67% recovery was required. The results also indicated that the optimum placement of stiffeners was immediately adjacent to the cutout. This study demonstrates that the optimum stiffener is a fully enclosed ring immediately adjacent to the cutout edge, and that full load recovery can be achieved with an appropriate design. [ABSTRACT FROM AUTHOR]

This study investigates the stability of the structural systems assembled by system scaffolds. Loading tests were conducted on the indoor single-bay system scaffolds and the outdoor full-scale structural system assembled by system scaffolds. Test results were compared with the second-order inelastic analysis with semi-rigid joints to determine the reliability of various analytical parameters. The study reveals that, while the failure model of the single-bay two-storey system scaffold without diagonal braces is overall buckling failure of the structure, the failure model of the same structure with diagonal braces is buckling failure of the vertical standards between the upper and lower storeys. The critical load of the configuration with diagonal braces is about double that of the same structure without diagonal braces. At the moment of buckling failure of the outdoor full-scale two-row, two-bay, six-storey structural system assembled by system scaffolds, the vertical standards at the four corners appeared to have large horizontal displacements owing to without diagonal braces. However, the vertical standard in the center did not exhibit obvious horizontal deformation because it was reinforced with diagonal braces on four sides. In addition, the use of diagonal braces can significantly increase the load capacity of vertical standards. This study recommends that all vertical standards be reinforced with diagonal braces to ensure the load capacity of the structural systems assembled by system scaffolds. A second-order inelastic analysis with semi-rigid joints and various notional lateral forces is recommended to determine the critical loads of full-scale structural systems assembled by system scaffolds. [ABSTRACT FROM AUTHOR]

Many tank structures may not be stable during the construction phase, and this may lead to their becoming vulnerable to buckling under environmental loading conditions such as wind. Installing intermediate ring stiffeners of the proper size at the mid-height of the cylindrical shell may be the most effective way to stabilize these structures, especially under the effects of wind action. In the study, analytical and numerical studies were conducted to identify the required strength and stiffness for the intermediate ring stiffener. First, a new cylindrical shell-to- intermediate ring stiffness ratio was derived by considering curved beam and shell membrane theories. For strength criteria, the tributary height and the effect of shell- ring interaction on the internal forces and moments were examined by making use of Linear Analysis (LA) and Geometrically Nonlinear Analysis (GNA). The stress resultants developed in the intermediate ring stiffener were identified so that they could be used as strength criteria. For stiffness criteria, by considering the changes in the buckling resistance based on the developed stiffness ratio, an expression to compute the minumum intermediate ring stiffness was determined. In addition, Geometrically Nonlinear Analysis including Imperfections (GNIA) was also performed to examine the effect of the geometric imperfections on buckling strength of the steel tank with an intermediate ring stiffener, taking different imperfection amplitudes into account. The developed design equations in simple algebraic form can be utilized for the structural stability of cylindrical steel tanks during erection. • The tanks may collapse under environmental effects such as wind before the roof is installed. • The weakness of the shell part of the structures during construction phase was addressed. • Effect of reinforcing steel tanks with ring stiffeners on wind buckling was studied. • A new stiffness ratio of cylindrical shell to intermediate ring stiffener was developed. • A novel stiffness criterion is proposed by taking into account the buckling strength of CS [ABSTRACT FROM AUTHOR]

Steel corrugated webs are vertical and lightweight plates responsible for carrying large in-plane loads before buckling. Three modes of shear failure are typical for these elements: local, global, and interactive shear buckling. In this paper, previously published analytical models for the estimation of the shear strength of trapezoidal corrugated webs are summarized, and a new model is developed. The proposed model takes into account the interaction between the modes of shear buckling. Twelve shear-critical corrugated web steel beams (CWSBs) were manufactured and tested to failure. The results were added to update the existing database, resulting in 125 test results, which were then used to compare the performance of developed and existing models. The new model is shown to be more accurate than previously published models for estimating the shear strength of corrugated steel webs, allowing for more economic designs. [ABSTRACT FROM AUTHOR]

The article presents the seismic evaluation and retrofit of a 10-storey steel building located in Vancouver, British Columbia, designed following the provisions of the 1980 NBCC and the CSA-S16.1-M78 steel design standard. Lateral resistance is achieved by tension-only X-bracing with back-to-back double angle members. Seismic evaluation is first performed in accordance with the recommendations of the User's Guide to NBCC 2010 using response spectrum analysis. A Tier 3 systematic evaluation according to ASCE 41-13 is then carried out using both linear and nonlinear dynamic analysis procedures. The performance objectives are set same as those implied in NBCC 2010. The ASCE 41 approach results in much less corrections to the structure. Using the mean results from 10 ground motions is also less stringent than using the maximum of three records. For this structure, nonlinear dynamic analysis permitted to identify the concentration of inelastic deformations demands on the braces along the frame height. This behaviour induced considerable bending moment demands on the columns not captured by linear dynamic analysis. Finite element analysis of the structure columns showed that columns of braced steel frames can exhibit higher ductility compared to acceptance criteria specified in ASCE 41. [ABSTRACT FROM AUTHOR]

Large steel silos are widely used to store huge quantities of granular solids in industry and agriculture. In the present analysis, a novel type of silo structure, designated the cellular silo, is proposed and discussed. The performance advantage of the cellular silo is the clustered construction of individual hexagon silos, which can be formed by different numbers and arrangements of cell silos. The structural system is firstly determined for the cell silo by comparison between the plate model and 3D-stiffened plate models, and it is shown that the 3D-stiffened plate assembly composed of shell elements and beam elements is feasible for the cell silo, which is quite distinct from the shell structure fit for circular silos. The horizontal solid pressure, which is beneficial to circular silos, is unfavourable to the buckling of cell silos, and the buckling design is governed mainly by the horizontal pressure rather than the vertical frictional pressure. The buckling behaviour of group silos is investigated by considering load cases defined by the number of working cell silos and their relative position in the group. The common features of group silos during buckling are summarized, and it is referential for structural design of a cellular silo. An illustrative example of a cellular silo is presented at the end to demonstrate the design procedure, and it is concluded that the buckling design of the cellular silo is governed by the full loading condition and can be completed by optimization of the cell silos and their combinations. [ABSTRACT FROM AUTHOR]

Bracing that is used to reduce the effective length of compressive members, and thereby increase their load carrying capacity, must be designed to provide adequate stiffness and strength. In practice, a targeted minimum or ideal brace stiffness is typically defined, and then this value is increased by a factor of two or three in order to ensure brace strength demands can be satisfied efficiently. While straightforward expressions are available to determine the ideal brace stiffness for single members, the brace stiffness for systems of multiple parallel compression members is more complex. This paper presents the derivation and validation of a simple mathematical expression that is useful for obtaining the ideal brace stiffness of structural systems composed of multiple parallel compression members or sub-assemblages. Use and validation of the proposed expression is explored through a variety of examples. Agreement with results obtained using finite element analyses suggests that the developed expression sufficiently determines the minimum bracing stiffness for systems of multiple parallel members with single and multiple brace points. [ABSTRACT FROM AUTHOR]

Shaking table tests of two one-third scale steel portal frames with tapered members were conducted to study their seismic performance. Test models were designed as ordinary moment frames, and their members consisted of non-compact sections. The dynamic characteristics, acceleration, displacement, strain and failure modes were analyzed. The test results showed that the governing failure modes were the loosening of bolts at column bases and local buckling accompanied by lateral-torsional buckling of rafters. The damping ratio was approximately 0.03. The deformations of the test models were large, with a maximum drift of up to 1/35 of the eave height. The test models did not collapse under rare earthquakes, suggesting that the seismic behavior of this structure is adequate to survive large seismic excitations. However, the significant stiffness degradation in the elastic-plastic stage demonstrated that the ductility of light steel portal frames was limited. In addition, the responses of torsional vibrations were weak and could be neglected for this structure. [ABSTRACT FROM AUTHOR]

The structural resistance of high-strength steel seamless tubular beam-columns of circular cross-section subjected to axial compression and bending loading is investigated, using experimental testing and numerical finite element simulations. Experiments on short and slender seamless tubular specimens are conducted, and simulated with rigorous finite element models. Prior to experimental testing, initial imperfections and residual stresses are measured, and the measurements are taken into account in the numerical models as initial conditions. Α good comparison is achieved between numerical simulations and experimental results in terms of ultimate strength capacity. Using the finite element tools, parametric numerical analyses are conducted under combined axial-bending loading conditions. First, the influence of initial imperfections (wrinkling) on the structural behavior of high-strength steel tubular members is examined, in terms of their cross-sectional strength. Subsequently, stability curves for axial compression, and thrust-bending interaction diagrams for the high-strength steel tubular members are obtained. The cross-sectional strength, the stability curves and the interaction diagrams obtained numerically are compared with existing relevant provisions of European and American specifications (ΕΝ 1993, ΑΡΙ RP 2Α and AISC) for the design of beam-column tubular members. The comparison shows that the provisions of those specifications, originally developed for mild steel CHS members, result in reasonable, yet conservative, predictions for the structural resistance of high-strength steel seamless CHS members. It is also suggested that significant improvement of EN 1993 predictions can be achieved revising the classification of high-strength steel CHS sections. [ABSTRACT FROM AUTHOR]

The stability of steel columns strengthened using bolted components under a preload (the existing load during the strengthening process) is studied. An analytical model that considers the effects of the preload and bolting is proposed. The preload effect is expressed as the combined effect of equivalent initial deformation and stresses, based on which a preload-effect factor is derived. The adverse effect of bolt holes on the column stability is considered, and a bolting factor is derived based on interpolation and stress integral. A prediction formula, containing the preload-effect factor and bolting factor, for the ultimate load capacity of strengthened steel columns, is obtained. The proposed formula and the formulas in the current standards are evaluated against existing numerical and experimental results. The proposed formula is validated to be capable of providing accurate predictions, with a mean absolute percentage error of approximately 10%. [Display omitted] • The preload effect on the stability of strengthened steel columns is explicitly expressed. • A factor accounting for the adverse effect of bolt holes is derived. • The prediction formula for the ultimate load capacity is validated using existing numerical and experimental results. [ABSTRACT FROM AUTHOR]

The process of implementing principles of sustainable development in building for existing structures is much more challenging than for new designs. This issue is particularly acute when it comes to improving the stability of an axially compressed bar elements made of rectangular hollow section (RHS). This paper presents the results of experimental and analytical studies that address the question whether blind bolts BOM may be an effective alternative to bolted fasteners in one-sided lap connections between strengthened bar and strengthening branches. The results of shear tests of single lap connections with blind BOM-R16-4 bolts prove that the structural properties of the tested joints are similar to the structural properties of connections with M16-8.8 grade bolts. Results of the parametric analysis carried out for a perfectly straight axially compressed RHS columns, symmetrically strengthened by two U-shaped branches indicate the special potential of BOM fasteners in applications for joining the walls of strengthened tubular bar and strengthening branches of open cross-section. The analytical results demonstrate that the lack of the main slip in the lap bearing connections of branches with BOM fasteners gains efficiency in strengthening of the axially compressed column in comparison with solutions using bolts. The results obtained provide the basis for the development of an efficient method of strengthening bar elements with closed cross-sections that is characterized by low energy expenditure, in accordance with the principles of sustainable building. [ABSTRACT FROM AUTHOR]

Buckling capacity of axially loaded steel columns with hot-rolled I-sections, circular and rectangular hollow sections in fire is studied. The current Eurocode method for checking the stability at elevated temperatures has been derived on the same basis as in ambient conditions. Due to significant nonlinearities in the behaviour in fire the standard method appears to be not fully appropriate in certain ranges of parameters. In the present work the behaviour of columns is studied by comprehensive numerical simulation at a wide range of temperatures and slenderness values. Based on the results two alternative analytical procedures have been proposed and validated for evaluation of buckling strength. One of them needs numerical determination of a number of parameters beforehand. The other is based on the modification of the nonlinear material model and despite some limitations, it is convenient to use with common design procedures and applicable for an appreciable range of typical sections. [ABSTRACT FROM AUTHOR]

This study develops and validates an effective material model for cold-formed rectangular hollow sections. Advanced design methods utilize non-linear finite element analysis in design. An accurate calculation model, which is usually beam element-based, is crucial such that the design outcome is safe but economical. Unfortunately, cold-formed sections have non-linear residual stress distribution over the material thickness, that cannot be explicitly modelled in general-purpose beam elements. Additionally, corner regions of cold-formed sections have higher material strength compared to flat regions. This beneficial feature is usually disregarded by assuming the flat region properties for the entire cross-section. This study develops an effective material model that replicates a stress-strain curve that would be obtained if the tensile test was made for the entire cross-section instead of a separate tensile coupon. Consequently, the effects of residual stresses and corner strength enhancements are included in the effective material model such that their consideration in beam element-based advanced design method is effortless. The effective material model is validated for the steel grade S700 against numerical shell element buckling tests and excellent modelling accuracy is achieved. • Nonlinear material model with effects of residual stresses and cold-forming • Proposed model is applicable to nonlinear finite element analysis with beam elements • Material model facilitates implementing material imperfections in advanced analysis • Accurate prediction of global member buckling capacity • The model is validated for cold-formed tubular sections made of high-strength steel [ABSTRACT FROM AUTHOR]

This experimental study investigates the effect of changing the debonding gap between the core and the mortar filler on the global stability of BRBs using different cross-section restrained members. A total of eight mortar-filled BRBs were produced using a rectangular cross-section steel core and two different restraining members, a circular hollow cross-section (BRB-C series) and a square hollow cross-section (BRB-S series). In choosing the gap sizes, the gap limit formulas in the literature were considered. Not exceeding the limits of the gap, 2.8 mm, 5.6 mm, 8.4 mm, and 11.2 mm gaps were left as the multiples for the radius of inertia of the rectangular cross-section core in the BRBs. All specimens were subjected to displacement-controlled axial cyclic loading. As a result, failure modes, hysteretic performance, energy dissipation, and ductility were summarized and analysed for each specimen. The results showed that the specimens had a better structural performance with a 2.8-mm gap size, which is the radius of inertia of the core. Furthermore, the local buckling modes throughout the core increased in number as the size of the gap decreased, thus raising the members' axial load capacity and energy dissipation. It was concluded that the best structural behaviour of the tested series was provided with the smallest gap of 2.8 mm, better behaviour in energy dissipation may be obtained with smaller gap sizes. However, in this case, it is more likely to increase buckling at the gusset plates and cause local deformations with the end of the restraining members. • Four different gap sizes were taken as a basis and BRBs were produced. • Test of BRBs with two different cross-section restraining members was presented. • The changes of the gap variation in terms of axial force strength, energy dissipation and ductility were revealed. • After the test, the specimens were opened and the damage mechanisms and buckling modes were examined. [ABSTRACT FROM AUTHOR]

Steel structures are often strengthened under a preload, which is defined as the existing load on the structure during the strengthening process. This study aims to understand the preload effect on the stability of strengthened steel columns. A numerical study on steel columns strengthened by bolted steel profiles under a preload is presented. Finite element (FE) models are developed and verified using experimental results. Furthermore, a parametric study is conducted with 242 FE models on parameters, including the preload, strengthened section properties, column length, and bolt configuration. The numerical results indicate that the preload effect on the ultimate load capacity can be beneficial, negligible, or adverse, ranging from −17% to 8%. The preload effect is found to be dependent on the preload level, section geometry, steel properties, and column length. Subsequently, a prediction model is proposed, wherein the preload effect is expressed as a function of the preload level and normalized slenderness. The prediction model is validated by existing experimental results and found capable of providing practically accurate predictions. [Display omitted] • Finite element models of steel columns with bolted strengthening were developed and verified by experimental results. • The preload effect on the ultimate load capacity of strengthened steel columns can be either beneficial or adverse. • The preload effect depended on the preload level, section geometry, steel property, and column length. • A prediction model for the preload effect was proposed and validated using existing experimental results. [ABSTRACT FROM AUTHOR]

In this study, the slenderness limits for flanges and webs were examined to rationally evaluate the flange local buckling (FLB) strength of longitudinally stiffened I-girders. It is known that the bending resistance of a plate girder greatly increases when the web is longitudinally stiffened. This additional strength can be attributed to the fact that the stiffened web provides improved restraint to the rotation of the compression flanges as well as web bend-buckling strength. This study conducted a series of numerical analyses and it was found that the American Association of State Highway and Transportation Officials' (AASHTO's) load and resistance factor design (LRFD) requirements provide highly conservative estimates of the FLB strength of longitudinally stiffened plate girders, especially in noncompact sections. The reason is that the buckling coefficient and corresponding slenderness limit for a noncompact flange is determined based on the bending resistance of an unstiffened girder. Therefore, this study conducted a series of eigenvalue analyses in which the slenderness ratios of flanges and webs were considered. As a result, a buckling coefficient equation that reasonably reflects the interaction of the stiffened web and flange was derived. Based on the results of the analyses, this study proposed modified slenderness limits for the noncompact web and noncompact flange of a stiffened girder. It was verified that the bending resistance of longitudinally stiffened girders could be rationally estimated on the basis of the AASHTO LRFD specifications only by replacing the slenderness limits with the proposed formulas. [ABSTRACT FROM AUTHOR]

Double-skin composite (DSC) panels can offer high strength and robustness while improving the convenience of construction, with great potential for application in high rise buildings and nuclear power plants. In DSC panels, the stability of the outer surface steel plates are governed by the constraints of the in-fill concrete and the discrete shear connectors, i.e., the ratio of connector spacing ( B ) and surface steel plate thickness ( t ). In this paper, tests were performed on 10 specimens to assess the buckling behavior of DSC panels. The arrangement of the shear studs and the B / t ratio were varied in the tests. The results show that the arrangement and spacing of the shear studs can considerably influence the buckling shapes and loading capacity of the steel plates. Three-dimensional finite element (FE) models were developed to simulate the behavior of DSC panels subject to compression, and the FE results were found to be in good agreement with the observed buckling behavior during tests. A theoretical model based on Euler's equation was also proposed to predict the buckling stress of steel plates, and it showed reasonable agreement with the experimental measurements and FE results. The formula proposed in this paper can be used for determining the number or spacing of shear studs in DSC walls. [ABSTRACT FROM AUTHOR]

Submarine pipelines are important and influential structures in marine engineering because they transport important, useful, and common fuels around the world. The pipeline structure is affected by different environmental forces from the surrounding conditions such as the external uniform hydrostatic pressure, hydrodynamic pressure, seismic forces, installation forces, free span forces, and forces scouring the pipeline. These conditions cause the pipeline to express complicated behavior. Local buckling and buckling propagation along the pipeline are common examples of collapses under these conditions and loadings, which can destroy thousands of meters of pipeline. These post-buckling phenomena cause great damage and losses to the oil and gas industries and to the environment; the imposed costs for the repair and protection of pipelines and mitigation of environmental problems are high. The use of ring-stiffeners is one way of increasing the buckling capacity of a pipeline in order to prevent and control the buckling propagation in pipelines. In this study, the buckling and post-buckling behaviors of ring-stiffened pipelines were investigated at a small scale through experiments and the finite element method (FEM). Two different ring-stiffeners were attached to the specimens. Only the uniform hydrostatic pressure was considered as the main loading; the axial stress was neglected in this study. The buckling modes, lateral displacement of the pipeline, ring tilt, formation of yielding lines, and torsion of yielding lines were examined. The results indicated that increasing the number of ring-stiffeners greatly increases the buckling capacity and lateral displacement of the pipeline. The buckling modes were changed, the post-buckling region was shortened, and torsion in the yielding lines and tilting in the ring-stiffeners clearly appeared in the tests. The results of this study were compared with those of recent research and reliable guidelines and standards. [ABSTRACT FROM AUTHOR]

The main aim of this paper is to present results of a full-scale pushover test of a 40 meter telecommunication tower under breaking load. A detailed description of the studied tower has been presented with emphasis on the geometrical imperfections of the selected members of the structure. The results of the experiment consisting of the axial forces in the tower's members, as well as the displacements of the observed nodes as a function of external load have been presented. A comparison of a wind load based on the current standards with the load based on the experimental breaking force has been discussed for a typical set of telecommunication equipment. The main conclusion was that the structure's overall carrying capacity depended on the buckling resistance of the legs. Additionally, theoretical buckling resistances (based on standards) of the tower's legs made with round solid bars were smaller than the experimental axial forces in compression. [ABSTRACT FROM AUTHOR]

Cylindrical steel silos are often supported by discrete supports or columns to be able to provide a hopper and to facilitate emptying operations beneath the cylindrical barrel. The simplest mean of support for a light silo is by the use of engaged columns, without the use of unnecessarily expensive ring stiffeners. Such engaged columns gradually introduce the support load into the silo wall by shear, spreading the stresses in circumferential direction. In general, the highest axial compressive stress concentrations can be found in the shell wall in the vicinity of the top of the engaged column, resulting in failure due to excessive yielding and/or local instability. The study aims to identify the optimal combination of dimensions of an engaged column (i.e. the height, the widths in circumferential and radial direction and the thickness) to obtain a failure load as high as possible with as little material in the column as possible. An important condition is the requirement that the columns must withstand a higher load than the silo wall itself. In other words, failure should occur in the vicinity of the terminations of the columns (and not in the column itself). All results and conclusions are based on numerical finite element analyses. [ABSTRACT FROM AUTHOR]

The paper describes a series of pin-ended compression tests and numerical analysis of channels with complex edge stiffeners and two different types of web stiffeners. In the tests, axial compression and eccentric compression loading were imposed respectively on 18 and 12 specimens. The stability capacity, buckling mode and deformation behavior of these specimens were studied. It was found that the longitudinal intermediate stiffeners could reduce the web width-to-thickness ratio effectively and enhance the stability capacity of members subjected to axial loading or eccentric loading with the eccentricity close to the web side. Compared with channels with complex edge stiffeners under the same condition, the ultimate load-carrying capacity of Σ shape section members and members with V type web stiffeners was increased by 65% and 50%, respectively. But distortional buckling of the complex section member was the governing failure modes of the specimens. Tests were then simulated by finite element analysis. The numerical analysis results show good agreement with experimental results. Furthermore, parametric study on a total of 144 samples was conducted to obtain the optimal web sub-element proportion for Σ cross-section columns. [ABSTRACT FROM AUTHOR]

This paper presents an efficient mathematical model for studying the global buckling behavior of concrete-filled steel tubular (CFST) columns with compliant interfaces. The present mathematical model is used to evaluate exact critical buckling loads and modes of CFST columns for the first time. The results prove that the presence of finite interface compliance may significantly reduce the critical buckling load of CFST columns. A good agreement between analytical and experimental buckling loads of circular CFST columns is obtained if at least one among longitudinal and radial interfacial stiffnesses is high. The design methods compared in the paper give conservative results in comparison with the experimental results and analytical results for almost perfectly bonded layers. The parametric study reveals that critical buckling loads of CFST columns are very much affected by the diameter-to-depth ratio and concrete elastic modulus. Moreover, a material nonlinearity has a pronounced effect for short CFST columns, and a negligible effect for slender ones. [ABSTRACT FROM AUTHOR]

Special concentrically braced frames (SCBFs) are commonly used to resist lateral forces in the structures located in high-seismic regions. Steel braces of SCBFs are expected to undergo large inelastic axial deformations in order to provide an adequate level of structural ductility and hysteretic energy dissipation under cyclic loading. The energy dissipation capacity and ductility of SCBFs largely depend on the slenderness ratio and width-to-thickness ratio of braces. The main objective of this study is to find an optimum range of these parameters for braces of hollow circular steel (HCS) sections in order to achieve the enhanced seismic performance of SCBFs. A finite element (FE) study has been conducted on a wide range of values of these parameters using a software package ABAQUS. The FE models account for the inelastic hysteretic characteristics and the fracture behaviour of braces. The results of simulation models matched very well with the past experimental results with respect to the performance points, namely, global buckling, local buckling, fracture initiation, and complete fracture. Finally, a relationship has been established between the slenderness ratio and the width-to-thickness of HCS braces based on the simulation results. [ABSTRACT FROM AUTHOR]