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Discusses the technical paper of S. C. Lee, C. H. Yoo and D. Y. Yoon about shear lag anomaly in box girders. Detection of shear lag anomaly in the flange of cantilever with uniform load; Inaccuracy of the conclusions presented by the authors; Cause of shear lag.

To explore how steel-plate composite (SC) walls response to in-plane loading is essential for SC structural design, especially combined with thermal loading. This work focuses on the intermediate high temperature (≤400°C) that is often considered during design process. Individual mechanical behavior of steel plate and concrete in SC walls under intermediate high temperature are studied. Thermoplasticity is applied to describe steel plate as 2D element, by which plastic flow combined with mechanical property degradation can be considered. High-temperature mechanical behavior of concrete is very complicated. In this study, strain of concrete at high temperature is decomposed into transient thermal strain, free thermal strain, and mechanical strain. By elaborating the physical meaning of transient thermal strain and selecting mathematical models for every strain component, deformation of high-temperature concrete can be calculated. To study the in-plane behavior experimentally, an SC panel test with in-plane shear and thermal loading was conducted. Steady thermal state and transient thermal state were considered in two specimens, respectively. Comparison between test data and theoretical calculation results shows good agreement. Verifications from other researchers' tests show that the model can be applied to general situations of in-plane loading combined with intermediate high temperature. [ABSTRACT FROM AUTHOR]

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

This paper examines the accuracy of equations specified by the North American and Australasian steel structures codes for determining the net section tension capacity of a cold-formed steel angle brace bolted at one leg. The configurations tested in the laboratory include single equal angle, single unequal angle bolted at the wider leg, single unequal angle bolted at the narrow leg, double angles, and alternate angles. The steel materials used in the experiment are among those with the lowest ductility for which nominal tensile strength is permitted by cold-formed steel design codes to be fully utilized in structural design calculations. Based on a modification to the equation derived for channel braces bolted at the web, a design equation is proposed for determining the net section tension capacity of a cold-formed steel angle brace bolted at one leg. The proposed equation is demonstrated, through laboratory tests on 61 specimens composed of G450 sheet steel, to be more accurate than the code equations and those existing in the literature. [ABSTRACT FROM AUTHOR]

Previous research on steel plate shear walls (SPSWs) and current design codes have focused principally on achieving highly ductile behavior through stringent detailing requirements. As such, the system is generally considered to be economical only in high-seismic regions. However, lower demands in other regions may permit the use of more economical options. This paper describes a proposed concept for SPSWs that meets the intent of capacity design, while greatly improving competitiveness in seismic regions where maximum ductility is not required. A large-scale, 2-story SPSW specimen was tested to evaluate the associated performance. The wall had standard double-angle beam-to-column shear connections and was tested under vertical gravity load concurrent with reversing lateral loads at each floor level. The specimen survived 25 lateral load cycles, 18 of which were in the inelastic range. The test results indicated that excellent performance can be expected in low-seismic regions, despite significantly reduced costs, compared with traditional designs. The shear wall showed stable performance at large lateral deformation ratios with high levels of ductility and energy dissipation capacity. [ABSTRACT FROM AUTHOR]

This paper presents a numerical finite-element parametric study on the behavior of transverse or longitudinal X-type plate-to-circular hollow section connections loaded under branch plate tension or compression, to evaluate the suitability of present international (CIDECT) design recommendations, the effect of boundary conditions and chord length, and the influence of applied chord normal stress. A total of 449 connections with wide-ranging values of geometric properties and chord normal stress levels were modeled and analyzed using commercially available software. An analysis of the effect of chord length determined that, to exclude the influence of chord end boundary conditions, an effective chord length of at least 10 times the chord diameter should be used for experimental and numerical studies. Further, the present CIDECT chord stress functions () provide an acceptable lower bound for all connections examined. Evaluation of present CIDECT partial design strength functions () indicated general conservatism, lack of plate thickness incorporation, and underutilization of tension-only connections. Partial design strength functions, determined through regression analysis, are hence proposed with lower-bound reduction (resistance) factors. [ABSTRACT FROM AUTHOR]

Performance control (PC) is the ability to design a structure in such a way as to expect predetermined modes of response at certain stages of loading, extents of damage, and/or drift ratios. The primary purpose of this paper is to complement the existing literature on performance-based plastic design of moment frames. PC is, in fact, a new analytic performance-based elastic-plastic design method for ductile structures under seismic loading. It empowers the engineer to control the design rather than investigate design-related numerical output. Failure mechanisms and stability conditions are enforced rather than tested. Unlike traditional closed-form procedures, PC enables the designer to control the response of the structure at preselected performance stages such as before and at first yield, any fraction of the failure load, or specified drift ratios up to and including incipient collapse. It offers a simple design solution to a rather complex problem. [ABSTRACT FROM AUTHOR]

This paper focuses on an investigation of transverse joint details with tight bend diameter U-bars for accelerated bridge construction. It presents the testing results of potential alternate reinforcing materials and joint details in two phases. Headed bar and U-bar [stainless steel and deformed wire reinforcement (DWR)] specimens with the same joint detail configuration were tested and compared in Phase I, followed by testing of U-bars (DWR) with varied concrete strength, bar spacing, and overlap length in Phase II. Test results were evaluated based on tension capacity, cracking at service loading and failure, and steel strain. A strut-and-tie model is proposed to predict the tension capacity of a transverse joint, which is capable of identifying the most critical parameters and yields safe and consistent predictions. Based on the experimental results, a No. 5 U-bar joint detail with no less than 152 mm (6 in.) overlap length and No. 4 lacer bars was recommended. [ABSTRACT FROM AUTHOR]

Tensegrity structures are spatial systems composed of tension and compression components in a self-equilibrated prestress stable state. Although the concept is over 60 years old, few tensegrity-based structures have been used for engineering purposes. Tensegrity-ring modules are deployable modules composed of a single strut circuit that, when combined, create a hollow rope. The 'hollow-rope' concept was shown to be a viable system for a tensegrity footbridge. This paper focuses on the deployment of pentagonal ring modules for a deployable footbridge application. The deployment sequence of a module is controlled by adjusting cable lengths (cable actuation). The geometric study of the deployment for a single module identified the path space allowing deployment without strut contact. Additionally, a deployment path that reduces the number of actuated cables was found. The number of actuated cables is further reduced by employing continuous cables. A first-generation prototype was used to verify both findings experimentally. The structural response during both unfolding and folding is studied numerically using the dynamic relaxation method. The deployment-analysis algorithm applies cable-length changes first to create finite mechanisms allowing deployment and then to find new equilibrium configurations. Therefore, the actuation-step size is identified as the most critical parameter for a successful deployment analysis. Finally, it is shown that the deployability of the footbridge does not affect its element sizing because stresses during deployment are lower than in-service values. [ABSTRACT FROM AUTHOR]

The objective of this paper is to provide and verify a general design method for prediction of inelastic bending capacity in cold-formed steel members potentially subject to local, distortional, and/or lateral-torsional buckling modes. An extensive experimental database of tested cold-formed steel beams is collected and indicates that inelastic reserve in the bending capacity of thin-walled cold-formed steel members is more common than typically assumed. Elementary mechanics for inelastic reserve are reviewed and simplified expressions provided for connecting the strain demand to the inelastic bending capacity in the range between the yield moment and the fully plastic moment. The strain capacity that can be sustained in inelastic local and inelastic distortional buckling is investigated through existing experiments coupled with nonlinear finite-element (FE) analysis. The nonlinear FE models provide a comprehensive means to investigate the relationship between cross-section slenderness, normalized strain capacity, and the resulting bending strength. A design approach for inelastic lateral-torsional buckling is provided on the basis of the hot-rolled steel AISC Specification. The resulting relationships for inelastic local, distortional, and lateral-torsional buckling are provided in a Direct Strength Method format for potential adoption in the cold-formed steel American Iron and Steel Institute (AISI) Specification. The provided design method is assessed against available data and shown to be a reliable predictor of inelastic bending capacity in cold-formed steel members. [ABSTRACT FROM AUTHOR]

This paper presents a reliability-based evaluation of the American National Standards Institute/Steel Deck Institute (ANSI/SDI) C1.0 and Structural Engineering Institute/American Society of Civil Engineers (SEI/ASCE) 37 design provisions for composite steel decks in the construction stage. Reliability of the allowable stress design (ASD) and load and resistance factor design (LRFD) methods at the strength and deflection limit states was evaluated in terms of reliability indices employing the first-order reliability method. A large number of composite slab configurations, which cover the range of slab parameters typically used in the U.S. construction practice, were investigated. Obtained results demonstrate that the current design provisions for steel decks in the construction stage are overconservative. Modifications of the ANSI/SDI C1.0 construction load requirements are proposed. The modified load requirements result in longer maximum unshored construction spans and acceptable reliability. Safety of the deck designed according to the modified load requirements is more uniform across the typical design parameters when compared with the current design provisions. [ABSTRACT FROM AUTHOR]

The goal of this study is to design and evaluate simple and rapid seismic retrofit devices for relatively small rehabilitation projects for steel structures. These designs are consistent with the tenets of sustainable design and will result in a more resilient building stock as well as minimizing environmental and economical effects and social consequences during the rehabilitation project. To achieve these goals, a unique approach to designing supplemental systems by using tension-only elements is proposed, one that eliminates undesirable global and local buckling. The first generation of these devices, a bracing system consisting of cables and a central energy dissipating device [couples resisting (CORE) damper], is presented in this paper. Both analytical studies with advanced and simplified models and proof-of-concept testing demonstrated stable, highly efficient performance of the system under seismic loads. Preliminary applications of the CORE damper system to the retrofitting of a braced steel frame showed the ability of the system to minimize soft story failures and residual deformations. [ABSTRACT FROM AUTHOR]

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

This paper addressed the influence of stirrup configurations in wide beams on the effectiveness of stirrups in contributing to shear resistance as a ratio of the nominal shear stirrup strength. The evaluation was made by testing 16 continuous, wide, shallow, reinforced, concrete beams supported on interior narrow columns at their centers and simply supported at the ends. The 16 beams were composed of: three beams without stirrups, six beams having a constant amount of stirrups with either two-leg or four-leg configuration, and seven other beams with various configurations to verify the trend. The general trend is that reducing the transverse spacing of stirrups improves the stirrup efficiency to resist shear forces. For beams with a constant amount of stirrups, four-leg configuration showed a high increase in its efficiency to resist shear force over stirrups with two-leg configuration. Although code design equations assume that stirrups are fully effective, it was evident that wide shallow beams reinforced with two-leg stirrups were susceptible to becoming shear deficient if transverse spacing was not accounted for. On the basis of findings of this study, guidelines for computing the stirrup contribution in shear resistance were proposed and verified by comparisons with tested beams from the present study and a previous study by Serna-Ros et al. [ABSTRACT FROM AUTHOR]

This paper deals with the accurate evaluation of complete three-dimensional (3D) stress fields in beam structures with compact and bridge-like sections. A refined beam finite-element (FE) formulation is employed, which permits any-order expansions for the three displacement components over the section domain by means of the Carrera Unified Formulation (CUF). Classical (Euler-Bernoulli and Timoshenko) beam theories are considered as particular cases. Comparisons with 3D solid FE analyses are provided. End effects caused by the boundary conditions are investigated. Bending and torsional loadings are considered. The proposed formulation has shown its capability of leading to quasi-3D stress fields over the beam domain. Higher-order beam theories are necessary for the case of bridge-like sections. Various theories are also compared in terms of shear correction factors on the basis of definitions found in the open literature. It has been confirmed that different theories could lead to very different values of shear correction factors, the accuracy of which is subordinate to a great extent to the section geometries and loading conditions. However, an accurate evaluation of shear correction factors is obtained by means of the present higher-order theories. [ABSTRACT FROM AUTHOR]

This paper presents a finite element (FE) analysis to quantify the effects of weld-induced residual stresses on the flexural behavior of circumferentially butt-welded steel circular hollow section (CHS) members. FE modeling of the weld-induced residual stresses is first described. Nonlinear FE analysis in which the behavior of the CHS members subjected to bending is explored incorporating the residual stresses is discussed next. Two FE CHS tube models with different failure modes are developed in order to clarify the effects that the residual stresses have on the flexural behavior. Simulated results show that welding residual stresses can have significant effects on the initial stiffness and the ultimate strength of the CHS flexural members depending on the loading position; hence, they should be taken into account in assessing the behavior of steel CHS members with circumferential weld under bending. [ABSTRACT FROM AUTHOR]

This paper presents the results of experimental investigations conducted to determine the fundamental behavior of steel members under fire loading. A total of eleven full-scale steel members were tested under combined thermal and structural loading. First, five A992 steel beam-columns (W10×68) were tested to determine their fundamental moment-curvature responses at elevated temperatures and different axial load levels. The experimental approach involved the use of radiant heating and control equipment to apply the thermal loading, and close-range photogrammetry combined with digital image processing techniques to measure the deformations (curvature) in the heated zone. Next, six A992 steel wide-flange (W8×35 and W14×53) columns were tested to determine their inelastic buckling behavior and axial load-displacement responses at elevated temperatures. A self-reacting test frame was designed to subject the column specimens to axial loading and heating. The thermal loading was applied by using the same type of radiant heating and control equipment as the beam-column specimens. The measured behaviors (and strengths) of the tested beam-column and columns specimens are presented and then compared with those obtained from detailed 3D finite-element analyses. The experimental investigations showed that the fundamental behavior and strength of steel members is governed mostly by the steel surface temperature, and the strength and stiffness of steel columns decreases significantly with increasing temperatures, particularly in the range from 500-600°C. The elevated temperature behavior of steel members can be predicted reasonably by using detailed 3D finite-element models. These verified models are recommended for conducting analytical parametric studies. The experimental approaches are recommended for evaluating the fire behavior of other structural members and loading conditions. [ABSTRACT FROM AUTHOR]

In this paper, design expressions are derived that extend the American Iron and Steel Institute (AISI) direct strength method (DSM) to cold-formed steel columns with holes. For elastic buckling-controlled failures, column capacity is accurately predicted by using existing DSM design equations and the cross-section and global elastic buckling properties calculated including the influence of holes. For column failures in the inelastic regime, in which strength approaches the squash load, limits are imposed to restrict column capacity to that of the net cross section at a hole. The proposed design expressions are validated with a database of existing experiments on cold-formed steel columns with holes, and more than 200 nonlinear finite-element simulations that evaluate the strength prediction equations across a wide range of hole sizes, hole spacings, hole shapes, and column dimensions. The recommended DSM approach is demonstrated to provide a broad improvement in prediction accuracy and generality when compared to the AISI main specification, and, with the recent introduction of simplified methods for calculating elastic buckling properties including the influence of holes, it is ready for implementation in practice. [ABSTRACT FROM AUTHOR]

Stress-strain relationship for a steel bar embedded in concrete differs somewhat to that of a bare steel bar because the surrounding concrete is bonded to the bar. This behavior is known as tension stiffening. This paper presents the results of an analytical and experimental study on the performance of reinforced concrete beams subjected to pure torsion. In particular, the effect of the tension stiffening was discussed and included in the analytical study. Nine RC beams having different torsional reinforcements were tested. Although the torsional strength of RC beams according to the existing design codes (ACI 318-05, EC2, and JSCE-02) depends on neither the average yield stress of steel bars nor the tension stiffening effect, the test results indicated that the steel stress of the beams at peak load increased as the total percentage of reinforcement decreased due to the tension stiffening effect. A new equation including tension stiffening effect was proposed to predict the torsional moment capacities of RC beams. Comparisons between tested and calculated torsional moments of the seventy-one beams showed reasonable agreement. [ABSTRACT FROM AUTHOR]

An analysis method for predicting the shear strength and behavior of structural shear walls under both monotonic and cyclic loading is presented in this paper. The proposed analysis method is based on the softened truss model theory and utilizes a newly proposed cracking angle of the concrete strut. The cracking angle is developed using a regression analysis of the reported shear capacity values of 100 experimental shear walls. The analysis pays particular attention to parameters expected to influence the walls' shear capacity including the geometric properties, reinforcement ratios, internal stresses, and concrete strength. The proposed method has been used to predict the shear capacity of the tested walls, and their deformation behavior both pre- and postcracking, and the results compared well with the experimental data. The proposed strut cracking angle also matched well the cracking patterns obtained experimentally. [ABSTRACT FROM AUTHOR]

Distributed optical fiber strain sensors have attracted increasing attention in research and applications related to civil engineering because no other tools can satisfactorily detect the locations of unpredictable events. For instance, for crack detection, it is necessary to employ a fully distributed sensor because crack locations are a priori unknown. The Brillouin optical correlation domain analysis (BOCDA) system, a distributed sensor that offers high spatial resolution by using stimulated Brillouin scattering, has undergone significant development over the last decade, during which it has been used in a wide range of civil engineering applications. In this paper, we demonstrate how a BOCDA-based optical fiber strain sensor can be employed to monitor cracks in fiber-reinforced concrete. Crack monitoring is important for checking the structure of such high-performance concrete, which has enhanced strength and toughness since it incorporates fibers. In particular, early detection of tiny cracks is essential for preventing crack growth and dispersion. We carried out a concrete beam-bending test to detect crack-induced strain distribution during loading. For this purpose, we employed an improved BOCDA system that provides enhanced measurement length with high spatial resolution; hence, BOCDA can detect a tiny crack before visual recognition. Moreover, we demonstrate a field application of the BOCDA system to ensure a flawless pedestrian deck made of fiber-reinforced concrete. [ABSTRACT FROM AUTHOR]

A pontoon-type, very large floating structure (VLFS) undergoes uneven deformation when loaded unevenly. The resulting differential deflection may lead to a cessation of equipment operation, and even compromising the structural integrity of the VLFS. One cost effective solution for reducing the differential deflection is by introducing the innovative gill cells at appropriate locations in the VLFS. Gill cells are compartments in VLFS with holes or slits at their bottom surfaces to allow water to enter or leave freely. At these gill cell locations, the buoyancy forces are eliminated and this allows uneven buoyancy forces acting at the bottom hull of the VLFS to somewhat counterbalance the applied nonuniform loading. In this paper, we investigate the effectiveness of gill cells in pontoon-type VLFS in reducing the differential deflection and von Mises stresses as well as the optimal layout (i.e., the number and locations) of gill cells that minimizes the differential deflection subject to a draft constraint. As the decision variables, objective functions and the constraints are not continuous and differentiable, genetic algorithms are adopted as an optimization tool. The optimal layouts for gill cells are determined for various VLFS shapes such as square, rectangular and I-shape and loading configurations. [ABSTRACT FROM AUTHOR]

This paper continues a line of research aimed at the development of a dynamically based health condition monitoring of bridge structures in the area of Friuli Venezia Giulia, Italy. One subject of this research program has been a two-span highway bridge with a concrete slab supported by closely spaced precast beams, a constructive typology which is quite diffuse in the regional highway network. Forced-vibration tests and experimental modal analysis were used to determine the vibration properties of the structure. An identification procedure based on dynamic data allowed to define an accurate orthotropic plate model of the deck and to improve the description of some constructional details in the finite-element model of the bridge such as the boundary conditions on abutments and the connection between the deck and pier. The usefulness of the combined experimental and analytical process in the identification of structural properties has been proven and the procedure can be applied to other structures of the same typology. [ABSTRACT FROM AUTHOR]

Slender open-section cold-formed steel members that contain flanges with edge stiffeners may buckle in different modes and with mode interactions. The element design approach (effective width method) has been shown to produce unconservative capacity predictions for a particular class of such members. This paper presents a modification to the effective width method derived from an investigation of the fundamental behavior of edge stiffened flange elements and sections that contain them. The modified element design approach is validated against the results of 913 compression and bending members collected from the literature, where all section and member buckling modes and interactions were evident. A section design approach is also presented which is directly in line with the element approach. The unified element and section approach is shown to provide accurate and reliable design solutions for cold-formed steel compression and flexural members. Proposals for the North American specification for cold-formed steel structures are presented. [ABSTRACT FROM AUTHOR]

Buckling of reinforcement is one of the possible phenomena that limit the deformation capacity of reinforced concrete members under reversed cyclic loading. Previous experimental research suggests that occurrence of buckling is linked to displacement history, a parameter that is not explicitly accounted for in the available expressions for ultimate drift or curvature ductility capacities. This problem is explored in the present paper, by following through analytical expressions that relate the critical buckling strain as defined by the hysteretic stress-strain model of the reinforcement and the imposed cyclic history in terms of displacement. The analytical expressions thus derived are evaluated parametrically in order to establish behavioral trends. It is shown that when controlled by bar buckling, deformation capacity cannot be defined uniquely as it varies with the path of applied load. A primary conclusion of the research is that any quantifiable indices of deformation capacity referred to in the framework of displacement-based design using deterministic approaches need be adjusted to represent conservative lower bounds rather than approximations to the actual values of nominal failure. [ABSTRACT FROM AUTHOR]

Modeling the energy dissipation capacity of shear-yielding members is important in the evaluation of the seismic response of earthquake resistant structural systems. This paper presents the model of a frame element for the hysteretic behavior of these members. The model is based on a three-field variational formulation with independent displacement, stress, and strain fields. The displacement field is based on the Timoshenko beam theory. The nonlinear response of the element is derived from the section integration of the multiaxial material stress-strain relation at several control points along the element, thus accounting for the interaction between normal and shear stress and the spread of inelastic deformations in the member. With the derivation of the axial force-shear-flexure interaction of short members from the material response the proposed model is general, in contrast to existing concentrated plasticity models that require parameter calibration for different loading and support conditions. Furthermore, the model does not suffer from shear locking and does not require mesh refinement for the accurate representation of inelastic member deformations. Correlation studies of analytical results with available experimental data of the hysteretic behavior of shear-yielding members confirm the capabilities of the proposed model. Its computational efficiency makes it suitable for large scale simulations of the earthquake response of structures with shear-yielding members. [ABSTRACT FROM AUTHOR]

The experimental and analytical investigations carried out on lightly reinforced concrete beam-column joints subjected to seismic loading are presented in this paper. Five 3/4-scale reinforced concrete beam-column joints were tested to investigate the seismic behavior of the joints. The variables in the tested specimens include column orientations and the presence of slabs on the top of beams. The specimens were subjected to quasi-static load reversals to simulate earthquake loadings. Experimental results obtained include joint shear stresses, joint shear strains, observed cracking and initial stiffness. The test results provided some information about the seismic behavior of the specimens. However, due to the unique nature of the specimens, several key parameters could not be varied. Therefore, to elucidate further information, a numerical study consisting of three-dimensional nonlinear finite-element (FE) models was carried out. The FE models were then validated with the experimental results. This was followed by parametric studies, carried out to understand the effects of several critical factors, including column axial load, ratio of column depth to beam reinforcement bar diameter, and effective slab width, on the complex behavior of the joints. [ABSTRACT FROM AUTHOR]

This paper presents a series of tests on high strength aluminum square hollow sections subjected to concentrated bearing load. A total of 64 web-bearing tests was conducted. The test specimens were fabricated by extrusion using 6061-T6 heat-treated aluminum alloy. The tests were carried out under end and interior loading conditions, where the specimens were seated on a fixed solid steel base plate. These tests closely simulated the support condition of the floor joist members seated on solid foundation. The test results were compared with the design strengths obtained using the American Aluminum Design Manual and European code for aluminum structures. It was shown that the design strengths predicted by these codes are either quite conservative or unconservative. Furthermore, the Australian Standard AS4100 and British Standard BS5950 Part 1 were used for aluminum square hollow section with sharp corners. The design rules of steel codes were modified to predict the web-bearing strength based on this study. It was shown that the design strengths calculated using the modified web-bearing design rules are generally conservative and agree well with the experimental results. Furthermore, the critical values of web slenderness were proposed beyond which web buckling governs. [ABSTRACT FROM AUTHOR]

In this paper a numerical and an experimental study on reinforced concrete box culverts (BC) behavior is presented. A BC under a 9.5 m high embankment was instrumented and observed during the construction period. Numerical analyses were then performed using a finite-element code capable of considering the construction sequence, the nonlinear behavior of the reinforced concrete structure, and an elastic-plastic behavior for the soil and the interfaces. Once the computed results were in good agreement with the observed behavior, a parametric study was developed for the identification of the main parameters influencing the interaction mechanism and to evaluate the BC structural performance up to failure. The influence of the BC nonlinear behavior on the interaction mechanism, both in service and ultimate limit state conditions, was analyzed and discussed. It is concluded that the soil pressures and the BC nonlinear behavior are directly related and should be reflected in the design stage in order to achieve a more rational and economical design. [ABSTRACT FROM AUTHOR]

This paper describes a study in which finite-element (FE) analysis procedures were used to predict the behavior of a reinforced concrete (RC) frame shear strengthened with fiber-reinforced polymer (FRP) composites. Details are presented of the numerical techniques used to represent the RC frame, the FRP, and the bond properties between the FRP and the concrete. The FE analysis is performed using a two-dimensional nonlinear FE analysis program based on the disturbed stress field model. To augment verification studies undertaken with beam specimens previously tested, a large-scale RC frame with one-span and two-story height was constructed and tested under lateral load conditions. The frame was first heavily damaged in shear, repaired with FRP wrap, and then subjected to a regime of reversed cyclic loads. A detailed comparison is carried out between analytical and experimental results for the hysteretic response, damage mode, crack pattern, and deformation of the frame. It is concluded that reasonably accurate simulations of the behavior of FRP-repaired shear-critical structures can be achieved through finite-element modeling. [ABSTRACT FROM AUTHOR]

The properties of special concentrically braced frames (SCBFs) enable them to be designed to meet performance-based seismic design (PBSD) criteria. SCBFs have large stiffness and strength to meet serviceability performance states. Life-safety and collapse-prevention PBSD limit states are controlled by inelastic postbuckling and tensile yield deformation of the brace. In SCBF construction, the braces are connected to the frame using gusset plates. Inelastic deformation of the brace places severe inelastic demands on gusset-plate connections. To improve the understanding and design of the seismic performance of SCBF connections, a coordinated analytical and experimental research study was undertaken. This paper describes the analytical component and includes a brief description of the experimental results, which were used in the development and validation of the model. The validated model was used to evaluate the inelastic performance of structural elements and to determine the frame ductility and concentration of plastic strains at potential locations of member or weld tearing or fracture. Detailed comparisons between experimental observations and computed results show that the analyses provided good correlation to actual behavior. The results were used to develop a methodology to predict tearing or cracking of key elements in the frame. [ABSTRACT FROM AUTHOR]

I-shaped steel girders with tubular flanges have been studied for application in highway bridges because of their large lateral torsional buckling (LTB) strength relative to conventional I-shaped steel plate girders. This paper discusses the LTB strength of tubular flange girders, focusing on concrete-filled tubular flange girders (CFTFGs) where the concrete-filled tube is the compression flange. Using finite-element (FE) models of CFTFGs, a parametric study was conducted to investigate the influence of girder geometry and material strength on the LTB strength. Design flexural strength formulas, considering LTB, for construction conditions and for ultimate strength in the final constructed condition, were developed based on the results of the parametric study. These formulas estimate the LTB strength of CFTFGs that are perfectly braced laterally and torsionally at brace points. A similar FE study of conventional I-girders was conducted and the results are compared with those of CFTFGs. [ABSTRACT FROM AUTHOR]

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

This paper presents new equations for the design of confinement reinforcement for ductile earthquake-resistant rectangular and circular columns based on performance measured in terms of curvature demand. These equations are developed from a parametric study of a large number of columns to reach a certain level of sectional ductility and account for the influence of concrete strength, transverse reinforcement yield strength, axial load level, and transverse confinement reinforcement spatial distribution. Simplification of these equations, while retaining the main controlling parameters, leads to design equations appropriate for design codes. These equations are then validated against a large set of experimental results. Their implementation in the Canadian Standard for Design of Concrete Structures is explained. [ABSTRACT FROM AUTHOR]

This paper presents a set of parametric equations for predicting the stress concentration factor (SCF) at the crown toe, saddle, and crown heel of completely overlapped tubular circular hollow section joints under lap brace axial compression. In the study, a joint specimen is tested within the elastic limit of steel material for the verification of finite-element (FE) models. The comparison of results showed that the 8-node thick shell and the 20-node solid FE models simulate reasonably well the test specimen with average difference in strain concentration factor (SNCF) of 7.9 and 8.8%, respectively. The mean SCF-to-SNCF ratio of the joint is 1.15. The parametric equations are developed based on 5,184 8-node thick shell FE models and have been assessed against the Fatigue Guidance Review Panel criteria, the current and previous test data and the FE database. The results of the statistical analysis, which based on the frequency of occurrence of predicted-to-measured SCF, showed that the performances of the proposed parametric equations are acceptable. [ABSTRACT FROM AUTHOR]

The paper addresses the problem of describing the anisotropic damage process and the dissipative behavior of masonry structures under static incremental and dynamic loads. A homogenized continuum model, based on simplified micromechanical hypotheses, is presented. The plane stress is considered. The finite-element method is adopted as a framework for numerical implementation. Masonry is considered as a composite material made up of blocks, mortar bed joints, and mortar head joints. Mortar bed joints are schematized as interfaces characterized by cohesion, tensile strength and friction, whereas mortar head joints are considered as geometrical discontinuities. Internal symmetries of the material leads to distinguishing two couples of emisymmetric bed joints, characterized by equal state variables. The computation of the displacement jumps in these two couples of joints is sufficient to evaluate the displacement jumps of all the joints contained in the assumed unit cell. Constitutive equations consider the nonlinear stress–strain relation in terms of mean stresses and mean strains. The latter are produced by an elastic strain contribution and by different inelastic strain contributions depending on the damage in mortar joints and in blocks. The damage processes are described by means of an energetic approach. The hysteretic behavior is described by considering a Coulomb-type friction law on the mortar bed joints. The model is implemented in a general purpose finite-element code (ANSYS). A simple example of a cyclic load history is presented in order to demonstrate the effectiveness of the model. [ABSTRACT FROM AUTHOR]

This paper presents a new approach for the treatment of parameter uncertainty for linear static structural mechanics problems. Parameter uncertainties are introduced as interval numbers. Interval arithmetic is applied to finite-element method to analyze the structural responses due to uncertain loading, axial and bending stiffness. However, a naïve use of interval arithmetic in the formulation of finite-element method, i.e., replacing the deterministic parameters with corresponding interval ones, will result in meaningless wide results due to the so-called dependency problem. In the present approach, an element-by-element technique is used to reduce the overestimation and compatibility conditions are ensured by a penalty method. With the newly developed overestimation control, most sources of overestimation are eliminated and a very sharp enclosure for the system response is obtained. A number of numerical examples are introduced. [ABSTRACT FROM AUTHOR]

This paper presents relatively simple, analytically derived curves to model the axial and the lateral stress-strain relations of circular concrete columns. The analytical curves describe the full elastoplastic behavior of the confined concrete column. The solution to the partially confined reinforced concrete column in the elastoplastic range is derived by replacing the discrete lateral reinforcement with an equivalent tube and the Drucker–Prager (DP) yield criterion is applied to represent the concrete behavior in the plastic range. Application of the DP model does not require an iterative procedure in order to solve the problem and thus an explicit solution is obtained. It is shown that the proposed model properly simulates the behavior of reinforced concrete columns partially confined by steel ties and of columns that are fully confined by fiber-reinforced polymer sheets. [ABSTRACT FROM AUTHOR]

Empirical estimates of the fundamental frequency of tall buildings vary inversely with their height, a dependency not exhibited by the various familiar models of beam behavior. This paper examines and explains this apparent discrepancy by analyzing the consequences of using two models to estimate such natural frequencies: A two-beam model that couples the bending of a classical cantilever to that of a shear beam by imposing a displacement constraint; and a Timoshenko beam in which the Euler–Bernoulli beam model is extended by adding a shear-displacement term to the classical bending deflection. A comparison of the two beam models suggests that the Timoshenko model is appropriate for describing the behavior of shear-wall buildings, while the coupled two-beam model is appropriate for shear-wall–frame (e.g., tube-and-core) buildings, and that the coupled-beam model comes much closer to replicating the parametric dependence of building frequency on height. [ABSTRACT FROM AUTHOR]

The tensile capacity of concrete is usually neglected when calculating the strength of a reinforced concrete beam or slab, even though concrete continues to carry tensile stress between the cracks due to the transfer of forces from the tensile reinforcement to the concrete through bond. This contribution of the tensile concrete is known as tension stiffening and it affects the member’s stiffness after cracking and hence the deflection of the member and the width of the cracks under service loads. For lightly reinforced members, such as floor slabs, the flexural stiffness of a fully cracked section is many times smaller than that of an uncracked section, and tension stiffening contributes greatly to the postcracking stiffness. In this paper, the approaches to account for tension stiffening in the ACI, European, and British codes are evaluated critically and predictions are compared with experimental observations. Finally, recommendations are included for modeling tension stiffening in the design of reinforced concrete floor slabs for deflection control. [ABSTRACT FROM AUTHOR]

Reinforced concrete slabs typically have relatively small tensile reinforcement ratios and are generally regarded as very ductile structural elements. This is not the case for slabs reinforced with low-ductility welded wire fabric. Such slabs fail with little warning by fracture of the reinforcement in a brittle and catastrophic manner and, as a consequence, many of the assumptions implicit in structural design are not applicable. Slabs containing low-ductility reinforcement lack robustness and cannot absorb the energy required to resist significant impact or blast loading. This paper outlines the importance of ductility in concrete structures and describes the observed failure mode and ductility of reinforced concrete slabs containing both normal and low-ductility reinforcement. For slabs reinforced with low-ductility welded wire fabric, failure is characterized by relatively little plastic deformation prior to collapse, with small rotational capacities of the critical regions and, consequently, little moment redistribution. [ABSTRACT FROM AUTHOR]

Tests on steel beams with adhesively bonded elastic reinforcing strips are used to deduce the mechanics of stress build up in the steel-to-strip interface up to failure. The solely elastic nature of the strips is a key concept in this study, as this elasticity leads to high interface stresses due either to nonlinear stiffness disparities between the steel and the reinforcing material when the steel yields, or to nonlinear geometric effects which are parasitic on this elasticity, including buckling of the strips and sharp section changes along the reinforced beam. Four features have been used in the tests to study these nonlinear effects, namely, multi-layer multi-length strips, imperfections in the adhesive, strips in both compression and tension, and tapering of the strip. The test results suggest that interface stresses may be sensitive to through-thickness variations of axial strain in the strips and to local variations of interface quality. Data from a nonlinear finite-element analysis, based on a novel two-layer interface element, are given for further insight into interface stress profiles. Conclusions are drawn on interface performance in the tests. Improved measurement strategies are suggested for shedding further light on the stress-transfer mechanics of this interface. The term connection is used synonymously with interface in this paper. [ABSTRACT FROM AUTHOR]

This paper summarizes research done to evaluate the effect of axial compression on unreinforced brick masonry (URM) walls and various rehabilitation techniques for enhancing seismic performance of URM structures. Flexural behavior of slender piers subjected to repeated and reversed in-plane deflections, and varied axial compression, is summarized relative to FEMA 356. The effectiveness of four rehabilitation techniques for improving seismic resistance are examined: (1) adhered fiber-reinforced polymer strips; (2) reinforced shotcrete overlay; (3) ferrocement surface coating; and (4) grouted reinforcing bars within drilled cores. The effectiveness of each technique is judged relative to the lateral strength and ductility of control piers with no rehabilitation, which are governed by a nonlinear, elastic rocking mode of behavior. Experimental results suggest that rocking behavior may be equal to, or superior to that of retrofitted piers because of the large ductility capacity at the component level. Test results also indicate that the FEMA 356 document conservatively characterizes seismic capacity for both nonrehabilitated and rehabilitated unreinforced masonry piers. [ABSTRACT FROM AUTHOR]

This paper revisits a fundamental assumption used in most classical failure theories for postbuckled web plates under shear, namely that the compressive stresses that develop in the direction perpendicular to the tension diagonal do not increase any further once elastic buckling has taken place. This assumption naturally led to a well-known theory that tension field action in plate girders with transverse stiffeners must be anchored by flanges and stiffeners in order for the webs to develop their full postbuckling strength. However, a careful examination of the results of the nonlinear finite-element analyses carried out for this study reveals that the diagonal compression continuously increases in close proximity to the edges after buckling, thereby producing in the web panel a self-equilibrating force system that does not depend on the flanges and stiffeners. These findings provide a fuller understanding of the actual mechanics of tension field action. [ABSTRACT FROM AUTHOR]

This paper presents a plain strain analytical model, based on the elasticity theory, to determine the confining pressures of transverse reinforcements on the concrete core of a reinforced concrete member. The analytical evaluation of the confining pressures was first carried out on reinforced sections with square and circular stirrups, and subsequently on reinforcement configurations of greater complexity with square and rectangular stirrups and supplementary cross ties. Finally, the model has been used to evaluate the confining pressures applied by external wrapping in any material [fiber-reinforced polymer (FRP), S-glass, steel, etc.] and to design better combinations of techniques and confinement materials. In order to obtain the stress–strain curves due to passive confinement, an analogy between square and circular sections has been introduced. In this way, any active confinement model derived by triaxial tests on cylindrical specimens can be used. The model has been validated by comparing its predictions with results from existing models and experimental tests. [ABSTRACT FROM AUTHOR]

The flexural deformation of structural members is due to their curvature. For reinforced concrete (RC) members, this curvature depends on the tensile strain of the reinforcement and the compressive strain of the concrete. As concrete is a brittle material with little ductility, RC members achieve ductility and adequate deformation capacity mainly through the tensile straining or yielding of the reinforcement. When the tensile straining of the reinforcement is limited, such as in the case of over-reinforced RC beams and RC columns with large axial loads, whereby the tensile reinforcement does not yield and the member fails due to concrete crushing, the ductility of the member is limited. The application of high-strength steel or fiber reinforced polymer reinforcement significantly reduces the ductility of the tensile reinforcement, which results in a substantial reduction in the ductility of the structural member. Existing methods for improving the ductility of concrete structures with nonductile reinforcement are not satisfactory. A new scheme of providing ductility to RC members through compressive yielding instead of tensile yielding is developed and introduced in this paper. The effectiveness of the new scheme is illustrated by experimental testing of RC beams. The successful application of this novel technique may pave the way for a new field of research and application of concrete structures. [ABSTRACT FROM AUTHOR]

A new method for damage identification in large, massive civil structures is presented, which is based on the idea that dead load is redistributed when damage occurs in the structure. The method uses static strain measurements due to dead load only as input to the identification procedure. An analytical model of a fixed-fixed beam is developed in which the damage is represented by a section of reduced flexural rigidity. The damage state is determined by the location, length, and severity of the stiffness reduction. A forward analysis of the beam response is first presented to illustrate how the dead load is redistributed for different damage scenarios. The inverse problem is defined by a constrained optimization problem and is solved using a genetic algorithm. The proposed method correctly identified damage in the beam for a wide range of locations and damage severities. The identification procedure, in general, has a greater degree of success with increasing damage severity. Results show that damage is difficult to identify when it is close to the inflection point of the undamaged beam, where the dead load strain is zero. The effect of measurement noise on the ability to identify damage is investigated in the companion paper. [ABSTRACT FROM AUTHOR]

Overlap tubular K-joints are generally regarded as having higher axial strength than similar simple gap K-joints due to their more direct load transfer between braces. Due to congestion at the nodes in steel jackets, overlap K-joints are used as key structural elements in many existing offshore platforms. However, relatively little experimental research has been done to quantify their strength and this has prevented engineers from taking full advantage of overlapping in the design of new structures as well as in the life extension assessment of existing platforms. This paper presents the results of a numerical study on gap and overlap K-joints under in-plane bending. The parametric study reveals new insight into how the behavior and strength varies across the practical range of geometrical parameters. Based on the finite element strength database, a capacity equation has been derived and presented herein using nonlinear regression analysis techniques. [ABSTRACT FROM AUTHOR]

Application of structural optimization to transmission tower design is facilitated since major costs such as material, transportation, erection, and maintenance are directly proportional to structural mass. In this paper, structural topology and shape annealing (STSA), a structural topology optimization method that combines structural grammars with simulated annealing, is applied to reduce the structural mass of an existing tower. STSA has previously been validated only on smaller-scale benchmark tasks. The challenges of extending STSA for application to full-scale design tasks are presented. Key results include a 16.7% mass reduction of the existing primary members through combined optimization of the tower envelope, joint locations, and discrete section sizes. Also, the tower configuration was optimized to have 16 fewer joints and 80 fewer primary members. Promising results for a practical, full-scale application serve to validate the STSA method for combined structural optimization of topology, shape and discrete section size. [ABSTRACT FROM AUTHOR]

Ductile end cross frames have been proposed in the past as a seismic design and retrofit strategy for steel plate girder bridges. In this paper it is shown that with good connection details, single angles are able to undergo large cyclic deformations in excess of 6% average axial strain before failure occurs. Large-scale shake table experiments were performed on a straight steel I-girder bridge model to evaluate the performance of a superstructure with ductile end cross frames using single angle X braces. The cross frames exhibited no apparent overall strength degradation, but also a comparatively low postyield stiffness, allowing the cross frames to act as effective structural fuses. The measured base shear was 61% of the elastic base shear in response to 2.0 times the El Centro earthquake at an average drift of 3.4%. Large girder drifts were achieved without distress in the deck slab by removing selected studs between the slab and top flange of the girders at the end cross frame locations, with axial deformations in the angles well below their deformation capacity based on component experiments. [ABSTRACT FROM AUTHOR]