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

Self-centering braces are an attractive new type of brace able to reduce structural residual deformations after earthquakes, with no requirement of major modifications to structural joints. One primary challenge in widespread implementations of self-centering braces is their high demands of prestressing forces, in order to counteract the anti-recentering resistance induced by their energy-dissipation system. This paper introduces a novel self-centering (SC) brace, denoted as a viscoelastic low-prestressing self-centering (VE-LPSC) brace, that needs only a low level of prestressing force to achieve self-centering. The proposed brace incorporates a novel frequency-independent viscoelastic damper (VED) as its energy-dissipation system. The new VED behaves similarly to displacement-based dampers that provide stable stiffness and damping across various frequencies. Meanwhile, as loading ends, the VED does not generate residual anti-recentering forces, unlike conventional velocity-based dampers. Performance tests on the VEDs were first conducted using three specimens to examine the material's deformation capacity, frequency-independent characteristic, fatigue-resistance capacity, and recovery capacity. Then, six full-scale brace prototype specimens were manufactured and tested, considering three levels of prestressing forces (15, 50, and 100 kN). Test results revealed that the brace achieved complete self-centering and consistent stiffness and strength under various frequencies, even with a prestressing force of 15 kN. With conventional steel strand and Belleville springs as its prestressed elements, the new brace was able to elongate 2.27% (corresponding to a story drift of 4.54%) while maintaining its recentering capacity. The VE-LPSC brace may experience some strength degradation after loading lower to 90%, but its capacity can recover to 98% of the original strength after 2 weeks. [ABSTRACT FROM AUTHOR]

Deformations in dam structures can have a critical impact on dam safety and life. Accurate methods for dam deformation prediction and safety evaluation are thus highly needed. Dam deformations can be predicted based on many factors. The analysis of these influences on the deformation of the dam reveals a problem that deserves further attention: dam deformation lags behind environmental factors of the water level and temperature as well as the time lag of the temporal dam deformation data. In this paper, a hybrid deep learning model is proposed to enhance the accuracy of dam deformation forecasting based on lag indices of these factors. In particular, dam deformations are predicted using deep networks based on gated recurrent units (GRUs), which can effectively capture the temporal characteristics of dam deformation. In addition, an improved particle swarm optimization (IPSO) algorithm is used for optimizing the GRU hyperparameters. Furthermore, the complete ensemble empirical mode decomposition with adaptive noise algorithm (CEEMDAN) and the partial autocorrelation function (PACF) are exploited to select the lag factor indices. The accuracy and effectiveness of the proposed CEEMDAN–PACF–IPSO–GRU hybrid model were evaluated and compared with those of other existing models in terms of four different evaluation indices (MAE, MSE, R2 , and RMSE) and using 9-year historical data for the case of a pulp-masonry arch dam in China. The experimental results show that our model outperforms other models in terms of the deformation prediction accuracy (R2 increased by 0.16%–9.74%, while the other indices increased by 14.55% to reach 96.69%), and hence represents a promising framework for general analysis of dam deformations and other types of structural behavior. [ABSTRACT FROM AUTHOR]

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

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

This paper, which is the second of two companion papers, presents the results of a large-scale testing program on a novel bridge column design, termed polyurethane (PU)-enhanced rocking column with energy dissipation (ED) links. The experimental program included cyclic testing of large-scale (approximately 1∶2.5) cantilever bridge columns, including (1) a rocking-only precast concrete column, which served as the reference column, (2) a PU-enhanced rocking column with a solid PU segment, and (3) a PU-enhanced rocking column with an axisymmetrically bilayered segment with an exterior PU layer to withstand seismic loads, an internal reinforced concrete core to sustain long-term gravity loads, and external ED links to provide energy dissipation and flexural stiffness and strength. The specimens were subjected to displacement-controlled lateral cyclic loading of increasing amplitude (exceeding a 10% drift ratio) at several drift ratio rates (up to 1 s−1). The tested PU column with ED links was further repaired via ED link release and retightening—the yielding of the ED links was small and did not justify replacement—to demonstrate its rapid reparability characteristics. The repaired column was subsequently retested to demonstrate that the original column properties had been practically recovered. This second companion paper experimentally quantifies the performance of all designs in terms of strength, ductility capacity, self-centering and energy dissipation capabilities, posttensioning losses, and ED link fracture capacity. It also quantifies the capability of ED link release and retightening (and, by extension, ED link replacement) in eliminating residual deformations and recovering the mechanical properties of the original/undamaged system. Compared to conventional RC rocking-only columns, the proposed PU-enhanced column design with ED links demonstrated higher energy dissipation and self-centering capabilities, while release and retightening of the ED links eliminated the residual deformations and resulted in the recovery of the mechanical properties of the original/undamaged column. While ED link release and retightening (i.e., ED link reuse) is adopted in this study, because the yielding of the ED links was small, as verified herein by the practically identical response of the original and repaired column, it can be deduced that ED link replacement (i.e., use of new/pristine ED links) would also restore the original column properties and eliminate residual deformations. [ABSTRACT FROM AUTHOR]

Conventionally, the pressure coefficients of tensile membrane structures are determined in wind tunnels on rigid models and the effect of the typically large deformations of the membranes on the pressure coefficients is not taken into account. The aim of the current research is to analyze the effect of the displacements of membrane structures on the pressure coefficients. A more precise wind analysis is introduced in this paper. Two rigid models were analyzed in a wind tunnel: the model of the unloaded construction shape, and the model of the deformed shape of the membrane under wind loads. The deformed shape was determined with the dynamic relaxation method on the basis of the pressure coefficients obtained from the construction shape subjected to wind loads. The two pressure coefficient fields, the corresponding membrane stresses and displacements are introduced and compared in this paper. Results show that the displacements of the membrane under wind load can result in significant differences of the pressure coefficients maximum values. Conversely, the introduced analysis and the determination of the pressure coefficients of the deformed shape improve the accuracy of the wind analysis of tensile membrane structures. [ABSTRACT FROM AUTHOR]

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

A slab-column joint in a flat plate structure may exhibit upward or downward punching shear (UPS and DPS) failure when subjected to different abnormal loading conditions. This can cause distinct residual deformations of the slabs, which in turn influences the behavior of the consequent progressive collapse of the entire structure. This paper presents two experimental tests on two 2×2-bay , 1/3-scaled flat plate substructure specimens. Both tests were conducted in two loading phases. In the first loading phase (LP-1), the interior column of specimens UPS-Sub and DPS-Sub was subjected to a gradually increased upward and downward concentrated load, respectively, until punching failure occurred at the interior slab–column joint. In the second loading phase (LP-2), an incremented downward uniformly distributed load was applied on the slab of both specimens up until the ultimate state just before a complete collapse of the slab. After LP-1, local and global damage patterns were observed respectively from UPS-Sub and DPS-Sub. The punching shear strength and the corresponding displacement of the interior joint in UPS-Sub were found to be 58.2% higher and 53.6% lower, respectively, than the corresponding ones in DPS-Sub. In LP-2, due to the upward residual deformation of the slab in UPS-Sub as a result of LP-1, its first peak load, vertical displacement, and horizontal displacement under compressive membrane action were, respectively, 8.4%, 91.1%, and 57.1% larger than those in DPS-Sub. On the other hand, the postpunching peak load of the two specimens under tensile membrane action were identical. To offer an in-depth understanding of the mechanical behavior that resulted from upward or download punching shear failure, the punching shear strengths of the interior slab–column joints and collapse resistance of the substructures were also analytically investigated. [ABSTRACT FROM AUTHOR]

A methodology is developed in this paper for the design and proportioning of interventions for seismic upgrading of substandard reinforced-concrete (RC) buildings. The retrofit approach is presented in the form of a simple design tool that aims toward both demand reduction and enhancement of force and deformation supply through controlled modification of stiffness along the height of the building. This objective is achieved by engineering the translational mode-shape of the structure, so as to optimize the distribution of interstory drift. Results from the proposed approach are summarized in a spectrum format in which demand, expressed in terms of interstory drift, is related to stiffness. Design charts, which relate the characteristics of commonly used global intervention procedures to influence drift demands, are developed to facilitate the retrofit design. The intervention procedures considered in this paper are reinforced-concrete jacketing, the addition of reinforced-concrete walls, and the addition of masonry infills. The proposed methodology is also amenable to adaptation to other strengthening methods, such as the addition of cross-bracing. [ABSTRACT FROM AUTHOR]

The initial rotational stiffness of connections is important for the design of semirigid frames. However, most current studies on steel beam to concrete-filled steel tube column connections with bidirectional bolts are based on experimental tests, and theoretical analysis and numerical analysis are rarely reported. As a result, there is no suitable analytical model for calculating the initial stiffness of the connection. Based on the component method, this paper proposes an analytical model to predict the initial stiffness of the connection. It is considered that the connection rotation is mainly induced by deformations of the endplate in bending, column flange in bending, bolts in tension, and panel zone in shear. Moreover, the effects of the endplate in bidirectional bending and bolt pretension are taken into consideration. Then, the prediction results based on the proposed analytical model are compared with experimental results to verify its accuracy, and comparison results indicate that the proposed analytical model can predict the initial rotational stiffness of steel beam to concrete-filled steel tube column connection well. In addition, bolt diameter and endplate thickness are the most influential parameters that affect the initial stiffness of the connection. It also provides a way for such connections to be designed as rigid connections. Finally, the proposed analytical model can be applied with good precision in elastic analysis and serviceability calculations in the design of semirigid steel-concrete composite frames. It can be applied to four types of connections: stiffened extended endplate connections, nonstiffened extended endplate connections, flush endplate connections, and T-stub connections. The proposed analytical model saves substantial resources and workload in experiments and simulations. DOI: 10.1061/(ASCE)ST.1943-541X.0002187. ' 2018 American Society of Civil Engineers. [ABSTRACT FROM AUTHOR]

A review of the most recently published literature suggests that the prediction of service life of corrosion affected concrete structures remains at the stage of parametric studies, in spite of intensive research on reinforcement corrosion in concrete structures for the past three decades or so. The intention of this paper is to present a performance-based methodology for service life prediction of corrosion affected concrete structures and apply it to flexural members in marine environments. Reliability methods are employed to determine the time period for each phase of service life. It is found that corrosion induced concrete cracking would occur in reinforced concrete flexural members at about 18% of its total service life, and that, once reinforced concrete flexural members become unserviceable due to corrosion induced excessive deflection, there is about 13% of the service life remaining before the structures finally become unsafe. It is concluded that the methodology presented in this paper can serve as a rational tool for decisionmakers with regard to repairs and strengthening of corrosion affected concrete structures. Accurate prediction of each phase of service life of corrosion affected structures can assist structural engineers and asset managers in achieving a cost-effective strategy in the management of reinforced concrete infrastructures. [ABSTRACT FROM AUTHOR]

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

This paper presents key findings of an experimental program performed to examine the rate-dependent behavior of weld material in transverse welded lap joints at elevated temperatures under steady-state thermal conditions. The data are intended to support the development of models of welded connections for structural-fire engineering applications. Two different loading rate scenarios (fast and slow) were incorporated in the experiments to evaluate the loading rate effect on the strength and deformation capacity of welded connection test specimens at ambient and elevated temperatures. Retention factors for the weld material under both slow and fast loading rates were computed and compared with those available in the literature. Results from this study indicate that the loading rate has a significant effect on the strength and deformation capacities of transverse welded lap joints for temperatures greater than 450°C. [ABSTRACT FROM AUTHOR]

The cast-steel yielding connector (YC) is a yielding fuse device designed to dissipate earthquake energy through inelastic deformations in specially designed distributed yielding regions, while ensuring primarily elastic behavior elsewhere in the structure. The YC exhibits a stable, symmetric hysteretic response with a characteristic postyield stiffness increase due to a combination of friction and second-order geometric effects. The ultimate limit state of the YC is governed by the ultralow-cycle fatigue (ULCF) fracture of the yielding sections, where fracture begins after a relatively low number of large inelastic cycles, followed by a slow strength degradation. This paper presents tests and finite-element analyses of small-scale coupons and full-scale tests of a variety of YCs. Detailed finite-element models of YCs are developed and a novel crack propagation simulation scheme is proposed to numerically simulate its ductile fracture initiation, propagation, and associated degradation and regaining of strength due to crack opening and closing. This simulation scheme is validated against 14 small-scale coupon tests and 11 full-scale YC tests. Full-scale test results and the validated model are then used to investigate the influence of in-plane rotation and out-of-plane demands on the overall performance of YC in a nonbuckling concentrically braced frame configuration. [ABSTRACT FROM AUTHOR]

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

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

This paper summarizes the results of experimental investigations on steel composite beams with simple connections at elevated temperatures. In the United States, three different types of simple connections are most commonly used in building construction with steel composite beams: (1) double-angle connections; (2) single-angle connections; and (3) shear-tab connections. A testing program was conducted to examine the structural behavior of all three of these connections at elevated temperatures. Each specimen consisted of a steel composite beam attached to a loading frame with simple connections. The specimens were subjected to controlled heating and cooling curves while the loading frames were fire protected and designed to remain in the elastic range. The shear-tab connections showed the largest connection rotation, but they fractured during the cooling phase of the tests. The prying of the angles in the double-angle and single-angle connection during the tests provided ductility to prevent fracture during the cooling phase of the experiments. The double-angle connections demonstrated the least connection rotation and excellent performance during the tests. [ABSTRACT FROM AUTHOR]

Gap between the outer steel tube and core concrete is a type of initial imperfection that may exist in concrete-filled steel tubular (CFST) columns. This paper is devoted to investigate the influence of the gap on the performance of eccentrically loaded CFST columns. Twelve CFST column specimens and two reference hollow steel tubes were tested under eccentric compression. The main test parameters included the gap type (circumferential and circular-segment) and gap ratio. A finite element model was established to simulate the behavior of the CFST columns with gaps, and the model was validated against the experimental results in terms of failure mode, load versus deformation response, and ultimate strength. Based on the experimental and numerical investigations, the performance of eccentrically loaded CFST columns with gaps was analyzed. Parametric studies were then conducted to reveal the influence of different parameters on the ultimate strength of the CFST columns with gaps. Finally, the maximum allowable gap ratio in practice was proposed for the eccentrically loaded CFST columns with circumferential gaps, and a simplified model was proposed to predict the ultimate strength of the composite columns. [ABSTRACT FROM AUTHOR]

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

The article presents a discussion of a paper which investigated the long-term behavior of composite beams at service loads on the basis of an experimental program and emphasizes the need to clarify some of its findings. It relates that the test reveals the nonlinear time-dependent phenomena for composite beams. It discusses the free shrinkage strain of concrete. The long-term deflection of prestressed and nonprestressed composite beams is explored.

A nonlinear finite-element analysis (FEA) model was developed in this paper based on the elastoplastic finite-element theory to analyze the load versus deformation relation of steel beam to concrete-filled steel tubular column connections. Six tests on steel beam to concrete-filled steel tubular (CFST) column connections using external ring after exposure to the ISO-834 standard fire were used to verify the theoretical model. The test parameters included the column cross-sectional type, the fire duration time, the level of axial load in the column, and the beam-column strength ratio. Each test specimen consisted of a CFST column and two steel beam segments in cruciform arrangement to represent an interior joint in a building. Three of the six composite connection specimens had circular cross sections and three had square cross sections. Five of the test specimens were simultaneously exposed to the standard ISO-834 fire condition. After they had cooled down to room temperature, each was tested under a constant axial load and a cyclically increasing flexural load. This paper presents an analysis of the experimental results to validate the FEA model and to evaluate the influences of different testing parameters on various characteristics of the beam-column connection performance. Comparisons between the predicted results and the experimental results indicate that the FEA model can predict the P–Δ relations of steel beam to CFST column connections and the column lateral load resistance after fire with reasonable accuracy. Finally, the FEA model was used to make a parametric study of the influence of the various factors on the postfire behaviors of steel beam to CFST column connections. [ABSTRACT FROM AUTHOR]

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

The viability of effective force testing (EFT), a real-time dynamic testing procedure for large-scale structures, has been validated by comparing results of tests on idealized structural models to analytical results. In this paper, the results of tests on a shake table are compared to those conducted using the EFT method. The test structure was a one-story steel structure consisting of typical structural components. The paper also presents an overview of critical issues required for conducting the EFT test, and highlights several problems and solutions that may affect the performance of EFT tests. The comparison of the test results indicates that with proper velocity feedback compensation, the EFT method can be used to apply real-time seismic simulation to structures undergoing nonlinear deformation. [ABSTRACT FROM AUTHOR]

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

This paper investigates the structural responses of generally restrained steel beams under fire conditions by the finite-element method. The axial restraint is represented by a linear elastic spring, whereas the rotational restraint is simulated as a semirigid rotational spring. The developments of beam internal forces, cross-sectional stresses and strains, together with displacements are examined. Moreover, the effects of some important factors such as load utilization factor, beam slenderness ratio, and axial and flexural restraint ratios, are also studied. Numerical analyses show that the critical temperature is reduced by axial restraint but increased by semirigid rotational restraint. Some stocky beams subjected to low utilization factors buckle at elevated temperature. The later part of the paper focuses on investigating the effect of cross-sectional thermal gradient; the associated thermal bowing is detrimental for a slender beam. This paper also tabulates the finite-element (FE) predictions of the lower and upper bounds of beam critical temperature for design purposes. Besides FE analyses, the simplified methods from EC3 Pt.1.2 and BS5950 Pt.8 for critical temperature are also examined. [ABSTRACT FROM AUTHOR]

This paper derives the maximum deformation demand placed on bolts in a single plate shear connection in response to rotation demands. The deformation demand is a function of connection neutral axis location. If the rotation demand is large enough to result in the beam bearing on the column, the neutral axis of the connection migrates to the point of bearing. Prior to bearing, the neutral axis will be located within the length of the connection plate. Forty-five data points obtained from three full-scale tests on T-type beam–column specimens connected with a single line of 19 mm (3/4 in.) diameter ASTM A325 bolts (threads included in the shear plane) and 108 mm (4.25 in.) wide 10 mm (3/8 in.) thick plates were used to determine the location of this neutral axis. Three-, four-, and six-bolt connections were tested through 0.06 radians of rotation. The mean location of the neutral axis was 0.63 times the length of the connection plate. The coefficient of variation was 5.9%. Only the six-bolt connection experienced a bolt shear limit state. The calculated ultimate displacement demands on the three A325 bolts that failed were 9.1, 8.9, and 7.9 mm (0.36, 0.35, and 0.31 in.). These values are consistent with the established maximum deformation value for fasteners, 8.6 mm (0.34 in.). Therefore, the equations presented in this paper provide an accurate estimate of the initial connection rotation capacity for single plate shear connections of common size. [ABSTRACT FROM AUTHOR]

This paper describes an analytical investigation of a new type of hybrid coupled wall system for seismic regions. Coupling of concrete walls is achieved by posttensioning steel beams to the walls using unbonded posttensioning tendons. Different from conventional hybrid coupled walls, the coupling beams of the new system are not embedded into the walls. The effect of structural design parameters such as the amount of posttensioning, beam properties, and wall properties on the behavior of multistory coupled walls under lateral loads, including the amount of coupling, energy dissipation, and displacement capacity is investigated. Systems with precast concrete walls as well as monolithic cast-in-place reinforced concrete walls are considered. The behavior of posttensioned coupled wall systems is compared with the behavior of systems with embedded steel coupling beams and systems without coupling. Design tools to estimate the nonlinear lateral load-displacement behavior of the walls are developed by quantifying selected limit states for the walls. The results indicate that posttensioned hybrid coupled walls with initial stiffness similar to walls with embedded steel coupling beams can be designed to provide stable levels of resistance under lateral loads over large nonlinear cyclic deformations. The degree of coupling between the walls can be controlled by changing the amount of posttensioning in the beams, as well as other beam and wall properties. [ABSTRACT FROM AUTHOR]

This paper discusses the nonlinear load-deformation behavior of coupling beam subassemblages in a new type of hybrid coupled wall system for seismic regions. Coupling of concrete walls is achieved by posttensioning steel beams to the walls using unbonded posttensioning tendons. Different from conventional hybrid coupled wall systems, the coupling beams of the new system are not embedded into the walls. One of the most important advantages of the new system is that it can be used to couple existing walls as a part of a strengthening and retrofit scheme. This paper describes an analytical investigation of the nonlinear behavior of coupled wall subassemblages that include a coupling beam and the adjacent wall regions at a floor level. The effect of structural design parameters such as the amount of posttensioning, beam properties, and wall properties on the behavior of the subassemblages, including the amount of coupling, energy dissipation, and deformation capacity is investigated. A simple design method to estimate the nonlinear load-deformation behavior of the subassemblages is developed. The investigation is based on an analytical model using fiber elements, which is verified by comparing with a finite element model. The results indicate that unbonded posttensioned steel coupling beams with initial stiffness similar to embedded steel beams can be designed to provide stable levels of coupling without experiencing significant damage over large nonlinear cyclic deformations. The amount of coupling between the walls can be controlled by changing the posttensioning force. [ABSTRACT FROM AUTHOR]

Establishing consistent criteria for assessing the performance of structural systems and infrastructure networks is a critical component of communities' efforts to optimize investment decisions for the upkeep and renewal of the built environment. Although member-level performance and reliability assessment procedures are currently well-established, it is widely recognized that a member-oriented approach does not necessarily lead to an efficient utilization of limited resources when making decisions related to the management of existing deteriorating structures or lifeline systems, especially those that may be exposed to extreme events. For this reason, researchers have renewed their interests in developing system-level assessment methods as a basis to modern structural and infrastructure performance evaluation and design processes. Specifically, system-level performance metrics and characteristics such as reliability, redundancy, robustness, resilience, and risk continue to be refined. The objective of this paper is to extend the content of the accompanying paper on reliability-based performance indicators for structural members by reviewing proposals for the development and implementation of performance-based criteria for structural systems and infrastructure networks. The paper reviews established concepts of reliability design along with emerging ideas of performance-based and resilience-based design that are especially relevant for assessing and managing system-level risk. The paper also studies structural redundancy and robustness concepts as well as network-level performance metrics along with ranking approaches. Insights from these analyses reveal the need for transitioning structural and infrastructure design processes from a traditional component-level reliability-based approach, to one that seeks uniform levels of risk across scales (from structural systems to interconnected infrastructure networks across communities). Implementation examples are drawn from experiences with buildings, bridges, offshore oil and gas platforms, and a variety of infrastructure systems. The paper also reflects on promising avenues for pursuing practical and calibrated system-level performance indicators that support life cycle performance, safety, reliability, and risk of structural and infrastructure systems as integral parts of resilient communities. [ABSTRACT FROM AUTHOR]

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

The bond of reinforcing steel bars is closely related to the stress state in the surrounding concrete. However, most of the current studies are limited to static monotonic loading and only few studies on the dynamic bond behavior of deformed bars under lateral pressures are reported in the literature. The purpose of this paper is to present an experimental investigation on the effect of the loading rate on the bond behavior of deformed bars subjected to biaxial lateral pressures. The test results indicate that the bond parameters are influenced by lateral pressures, loading rate, bar diameter, and concrete strength. Finally, an empirical bond stress-slip relationship for deformed steel bars is proposed and validated against experimental results. [ABSTRACT FROM AUTHOR]

This paper investigates the global in-plane failure and local web shear failure mechanism and strength of steel I-section circular arches with a sinusoidal corrugated web. In reference to a flat web that can resist both the shear and axial forces, the sinusoidal corrugated web can resist the shear force only. As a result, the sinusoidal corrugated web may fail in an elastic-plastic shear buckling mode. This study considers pin-ended circular steel arches with a sinusoidal corrugated web under a uniform radial load or a uniform vertical load to elucidate numerically their different failure modes. It is found that local web failure occurs suddenly without warning, and all aspects pertaining to the local web shear failure are investigated thoroughly with an equation for the ultimate shear-carrying capacity of nonuniformly sinusoidal corrugated webs being proposed. It is also found that the effects of the shear deformations of corrugated web on global in-plane buckling and the strength of steel arches are significant. A strength design equation for arches under nominal uniform axial compression and an interaction equation for arches under a uniform vertical load are developed. Strength design procedures for steel arches with a sinusoidal corrugated web against global failure and web shear failure are proposed. All of the equations proposed for global in-plane buckling, local web shear buckling, global in-plane strength, and web shear strength agree with finite-element results. [ABSTRACT FROM AUTHOR]

Prestressed-laminated timber (Pres-Lam) design has recently been adopted for multistory timber buildings based on ongoing research at the University of Canterbury, New Zealand. This system combines large timber members with unbonded posttensioning for recentering and ductile connections for energy dissipation. This paper describes the experimental, analytical, and numerical investigation of posttensioned laminated veneer lumber (LVL) walls coupled with plywood sheets subjected to both quasi-static cyclic and pseudodynamic seismic testing protocols. Different arrangements of nails, used to connect the plywood coupling panels with the posttensioned timber walls, have been tested to compare their energy dissipation characteristics. Simplified numerical macromodels with rotational spring elements have been developed to accurately represent the recentering contribution from the posttensioning and the pinched hysteric contribution of the nailed connections. The testing results provided good seismic performance, characterized by negligible damage of the structural members and very small residual deformations following drift levels of 2-2.5%. The only components significantly damaged, as designed, were the nailed connections between the plywood sheets and the LVL walls. These plywood sheets can be easily and cheaply removed and replaced with new sheets after an earthquake, creating a major reduction in postearthquake downtime. Combining these benefits together, the concept has potential for consideration as a cost-effective, high-performance solution for multistory timber buildings. [ABSTRACT FROM AUTHOR]

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

A fully prefabricated damage-tolerant beam-to-column connection is proposed as an approach toward an earthquake-resilient steel frame. By introducing a composite steel-ultrahigh-performance concrete (UHPC) joint and friction damper, the plastic deformation becomes concentrated on the designated plastic hinge region. Thus, the damage index and area of the connection can be limited to an acceptable level. In this paper, four full-scale specimens are tested to evaluate the cyclic performance of the novel connection. Some important design parameters are investigated, including the thickness of the UHPC layer, the length of the designated plastic hinge region, and the friction force. The experimental results confirm the expected damage-tolerance performance. Yielding does not occur in the main column and composite beams. The beam-to-column connection exhibits satisfactory energy dissipation and deformation capacity. Strength degradation is not observed, even when the beam-column relative rotation reaches 1=20. Based on the experiment, an analytical connection model is proposed. This model performs well in estimating the initial stiffness and yielding force of the connection. Several design suggestions are presented on the basis of this analytical model. [ABSTRACT FROM AUTHOR]

The prediction of creep deformations of concrete and reinforced concrete structures has been a field of extensive research. Several different creep models have been developed. Most of the models were developed for constant concrete stresses; thus, in the case of varying stresses, a specific time integration is necessary. Currently, when modeling concrete creep, the engineering focus is on the application of sophisticated time-integration methods rather than choosing more appropriate creep models or considering the scatter of input parameters. For this reason, this paper presents a method to quantify the uncertainties of creep prediction originating from the selection of creep models, from the time-integration methods, and from input parameter uncertainty. By adapting variance-based global sensitivity analysis, a methodology is developed to quantify the influence of different sources of uncertainty. By application of the developed method, it is determined that selecting more appropriate creep models is of higher importance than choosing sophisticated time-integration methods. [ABSTRACT FROM AUTHOR]

Several stages of performance need to be considered during the design of curved I-girders, including both the construction stage and the in-service conditions. Girder stability during the early stages of construction can be difficult to assess because the girders, at times, have little or no bracing present. One stage when there is no bracing present occurs when the girders are picked up from the ground or transport trucks by cranes and lifted into place. To better understand girder response during this critical stage, field studies were conducted on horizontally curved I-girders to measure rotations and stresses during the lifting process. This paper provides details of a semianalytical solution to predict the buckling and deformational responses of straight and curved girder segments during lifting. The deformations can be compared with rotational limits that were established to minimize problems with making connections to previously erected girder segments. The total rotational deformations of a horizontally curved girder result from two distinct components: (1) rigid-body rotation and (2) rotation caused by the girder cross-sectional twist owing to torsion from the girder's self-weight. A spreadsheet design tool, UT Lift, was developed to provide critical information for evaluating the rotational behavior of a horizontally curved I-girder during lifting and to estimate its lateral-torsional buckling capacity. An example of UT Lift's capabilities is presented along with background information on its development. Recommendations are given for safely lifting and erecting horizontally curved steel I-girders. [ABSTRACT FROM AUTHOR]

The tensile strength of varied-angle mortise and tenon connections in timber frames is discussed in this paper. Twelve full-size mortise and tenon connections (four 90°, four 67.5°, and four 45°) were tested under monotonic tensile loading. Initial yield modes observed during testing included peg bending, peg shear, tenon tear out, and mortise splitting. Decreased connection angle corresponded to equal or increased tensile strength but decreased ductility. A theoretical method to calculate the tensile strength of mortise and tenon connections is also developed. The method uses a modified set of yield-limit equations supplemented with local-stress-effect (mortise splitting and row tear out) equations to predict tensile strength. The governing theoretical yield modes agree well with yield modes observed during testing. The theoretical tensile strength is reasonably accurate, averaging 14% higher to 9% lower compared with test results. The findings indicate that mortise and tenon connections are significantly stronger when the tenon is oriented radially with respect to the mortise grain, especially in orthogonal connections. As a consequence, tangential loading of the mortise should be avoided. [ABSTRACT FROM AUTHOR]

The strength, ductility, and energy dissipation capacity of thin-walled, stiffened rectangular concrete-filled steel columns (thin-walled stiffened RCFT columns) subjected to cyclic loads are significantly upgraded by filling with concrete the internal hollow space of rectangular steel tube with longitudinal stiffeners and diaphragms. However, because of the accumulation of plastic strains and the high tensile stress concentration in thin-walled steel columns, metal fracture sometimes occurs before the columns develop their high strength and ductility. To elucidate the behavior of CFT columns and prevent the premature failure resulting from metal fracture, it is necessary to develop some geometrically and materially nonlinear finite element (FE) models that can accurately take into account important factors such as cyclic local buckling, stress and strain concentrations in the steel tube, confinement of the in-filled concrete, and interface action between steel tube and in-filled concrete. In this paper an accurate and yet, numerically stable FE model, which fully includes these important factors, is proposed. The accuracy of the proposed model is confirmed by comparison with the existing cyclic-loading tests on thin-walled stiffened RCFT columns. By utilizing the numerical results obtained by the proposed FE model, the upgrading mechanism and metal fracture of thin-walled stiffened RCFT columns are discussed in detail. [ABSTRACT FROM AUTHOR]

This paper is concerned with the ultimate shear capacity of steel-concrete composite plate girders in which one of the flanges of the steel girder is connected to reinforced concrete slab through shear connectors so that the steel girder and the slab act compositely as a single unit. The analysis of such girders becomes complex and it is necessary to have a simple method for design office use. Therefore, an attempt is made in this paper to propose an analytical method to determine the shear strength of a web panel in the girder. The method considers the tension field action in the plate girder web panel and shear failure of concrete slab. The method is approximate and can be applied to composite plate girders at the preliminary stages of design. The predicted results are compared with the corresponding experimental values for girders tested by other researchers and also with finite-element predictions. The predictions are found to be accurate enough for any design office use. [ABSTRACT FROM AUTHOR]

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

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

High-performance fiber-reinforced concrete (HPFRC) materials have a unique strain-hardening behavior in tension that translates into enhanced structural response, especially under reversed cyclic loading. Recent experimental research has shown that the use of HPFRC to replace regular concrete in components subjected to high cyclic deformation demands can lead to significant benefits, such as relaxation of detailing requirements and reduction in the amount of reinforcing steel. A structural system that is a good candidate to benefit from HPFRC is reinforced concrete coupled walls, where coupling beams and plastic hinge zones undergo large cyclic deformation demands during the design seismic event. This paper discusses the seismic performance of a prototype 18-story coupled-wall system in which the wall plastic hinge zones and the coupling beams are made of HPFRC materials instead of regular reinforced concrete. Computational simulation models are used to investigate system performance under various hazard levels, and system response is evaluated through various parameters including interstory drift, rotation, and distortion of critical structural parts. The simulation results show that the use of HPFRC in place of regular concrete leads to good overall seismic response with enhanced plastic hinging behavior in the wall piers and crack control in the coupling beams and piers. [ABSTRACT FROM AUTHOR]

A systematic approach to determining reliability-based acceptance criteria for deteriorating elements in structural systems is proposed as a basis for calibration of safety factors in codes and standards and for verifying acceptability of inspection and maintenance strategies for specific structures. The goal is to establish deterioration acceptance criteria for the elements of a structural system in compliance with criteria formulated for the system. Existing methods significantly overestimate the deterioration reliability of redundant structural systems because they neglect the joint effect of deterioration failures of different elements. To more realistically capture the load-sharing behavior of deteriorating redundant structural systems, it is proposed to establish deterioration acceptance criteria on the basis of easily computable, idealized structural systems, which are calibrated to the characteristics of the real structure. The approach is validated on an example structural system and is found to represent a significant improvement over current methods. The paper concludes with a study of the main factors influencing acceptance criteria of deterioration reliability. [ABSTRACT FROM AUTHOR]

This paper presents a finite-element formulation for the dynamic analysis of I-beams curved in-plan, in which geometric nonlinearities owing to large deflections and inelastic material behavior are taken into account. The developed finite element is based on the total Lagrangian formulation. Wagner and warping effects are considered in the analysis. The nonlinear dynamic equilibrium equations are solved by using Newmark's step by step numerical integration procedure. The von Mises associative isotropic hardening model is used to formulate the metal plasticity. The elastic predictor-radial corrector algorithm is used to consider gradual yielding on the cross section and along the beam. Simpler finite-element formulations are also developed by excluding the effects of geometric and material nonlinearities. Numerical examples are provided to illustrate the significance of the effects of geometric and material nonlinearities on the dynamic behavior of I-beams that are curved in-plan. [ABSTRACT FROM AUTHOR]

This paper presents a finite-element (FE) modeling approach to predict the deformation, softening, and failure of compression-loaded aluminum structures exposed to fire. A fully coupled thermal-mechanical FE model is outlined. The FE model can analyze the thermal profile and deformation as well as the initial and final plastic collapse of aluminum structures in fire. It calculates the temperature profile of an aluminum structure exposed to unsteady-state heating conditions representative of fire. Using the temperature profile, the elastic and plastic deformations together with the loss in the compression load capacity of an aluminum structure caused by elastic softening, time-independent plastic (yield) softening, and time-dependent plastic (creep) softening effects are analyzed by using a mechanics-based FE solution. The modeling approach is validated by structural tests on an aluminum alloy (5083 Al) plate supporting an applied compression load while locally heated at different radiant heat flux (temperature) levels. The modeling approach can estimate the deformations, initiation of plastic collapse, and final failure of the aluminum test article for heat flux levels representative of different fire types. The FE model described in this paper can be used as the basis for performing complex deformation and failure analysis of compression-loaded aluminum (and other metallic) structures in fire. [ABSTRACT FROM AUTHOR]

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

In this paper, new schemes are presented for the dynamic relaxation (DR) method so that the snap-through and the snap-back regions can be traced automatically. These procedures are based on the minimization of the residual force (MRF) and minimization of the residual energy (MRE), and they are capable of updating the load factor in each DR iteration. The suggested techniques are perfectly automatic. Therefore, they do not require any additional parameters such as arc length, incremental displacement, etc. For numerical verification, some frame and truss structures, all possessing geometrical nonlinear behaviors, are analyzed. Tracing the statical path shows that both the MRF and MRE methods can be used successfully in structures with snap-through and snap-back regions. The numerical results indicate that the MRE scheme traces the statical path with a greater number of increments than the MRF. While the jumping probability of the MRE is less than that of the MRF, the analysis time may increase in the MRE. Also, a comparison between the proposed DR methods and arc-length approach shows that the MRF and MRE procedures can present the limit points with higher accuracy. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study of six steel shear tab connections to hollow structural section columns. This study focuses on the plastic behavior of shear tabs and their supporting column walls. The column walls had width-to-thickness ratios ranging from 21 to 34. Large bending deformations were observed on both the column walls and the shear tabs. All six specimens failed owing to an excessive vertical deflection followed by a punching fracture of the tube wall around the perimeter of weld at the top of tab. The test results were found to agree well with two plastic mechanisms proposed for analysis. This study demonstrates that the shear strength of the tabs welded to a flexible wall support should be reduced when compared with that of the tabs welded to a rigid support. This paper also finds that the width-to-thickness ratio criterion for a rigid wall support is a function of the ratio of the length of tab to the width of the supporting wall and the relative bending strength between the tab and the wall. [ABSTRACT FROM AUTHOR]