Showing papers in "Journal of Structural Engineering-asce in 2007"

Experimental Evaluation of a Large-Scale Buckling-Restrained Braced Frame

Abstract: As buckling-restrained braced frames (BRBFs) have been used increasingly in the United States, the need for knowledge about BRBF behavior has grown. In particular, large-scale experimental evaluations of BRBFs are necessary to demonstrate the seismic performance of the system. Although tests of buckling-restrained braces (BRBs) have demonstrated their ability to withstand significant ductility demands, large-scale BRBF tests have exhibited poor performance at story drifts between 0.02 and 0.025 rad. These tests indicate that the large stiffness of the typical beam-column-brace connection detail leads to large flexural demands that cause undesirable failure modes. As part of a research program composed of numerical and experimental simulations, a large-scale BRBF with improved connection details was tested at the ATLSS Center, Lehigh University. During multiple earthquake simulations, which were conducted using a hybrid pseudodynamic testing method, the test frame sustained story drifts of close to 0.05 rad and BRB maximum ductility demands of over 25 with minimal damage and no stiffness or strength degradation. The testing program demonstrated that a properly detailed BRBF can withstand severe seismic input and maintain its full load-carrying capacity.

Design of space trusses using big bang–big crunch optimization

Abstract: A procedure for designing low-weight space trusses based on the innovative Big Bang–Big Crunch (BB–BC) optimization method is developed for both discrete and continuous variable optimization. BB-BC optimization is a population-based heuristic search consisting of two parts: The Big Bang where candidate solutions are randomly distributed over the search space; and a Big Crunch where a contraction operation estimates a weighted average or center of mass for the population. Each sequential Big Bang is then randomly distributed about the center of mass. The objective of the optimization is to minimize the total weight (or cost) of the structure subjected to material and performance constraints in the form of stress and deflection limits. Designs are evaluated for fitness based on their penalized structural weight, which represents the actual truss weight and the degree to which the design constraints are violated. BB-BC optimization has several advantages over other evolutionary methods: Most significantly, a...

Seismic performance of self-centering structural walls incorporating energy dissipators

Abstract: This paper presents elements of seismic design for jointed precast cantilever wall units designed to rock about their foundation. Gravity loading and prestressed unbonded tendons provide the restoring force in these walls. Lateral displacements eventually result in a separation gap forming only at the wall-foundation beam connection. The gap reduces the wall stiffness and results in nonlinear response. Design of these walls is made with the explicit objective of ensuring a self-centering response. That is, the wall returns to its pre-earthquake position upon unloading from a large displacement excursion. The integrity of the walls is maintained because no plastic hinges form and there are no residual postearthquake displacements. Energy dissipators, in the way of longitudinal mild steel reinforcement crossing the joint between the walls and the foundation, are incorporated into these walls to add significant energy dissipation capacity while preserving the self-centering response. This paper also describe...

Behavior and Design of Posttensioned Steel Frame Systems

Abstract: A posttensioned (PT) steel moment resisting frame is a self-centering earthquake resistant steel frame that uses posttensioning steel to compress the beam flanges against the column flanges at the connections. The posttensioning contributes to the moment capacity of the connections and provides an elastic restoring force that returns the frame to its pre-earthquake position. This paper describes the behavior and design of PT frames and PT frame systems, where a PT frame system is a PT frame with the collector elements that connect it to the floor system. The interaction of the floor system with the PT frame produces axial forces in the beams that add to those from the posttensioning. This paper outlines a performance-based seismic design approach for PT steel frame systems. Seismic performance levels, seismic input levels, structural limit states and capacities, and structural demands for PT frame systems are defined. The design objectives are outlined, design criteria are given, and a step-by-step design procedure is given. The design approach is evaluated via comparisons with time-history analysis results.

Methods to Assess the Seismic Collapse Capacity of Building Structures: State of the Art

Abstract: The collapses of building structures during recent earthquakes have raised many questions regarding the adequacy of current seismic provisions to prevent a partial or total collapse. They have also brought up questions as to how to determine the collapse safety margin of structures, what is the inherent collapse safety margin in code-designed structures, and how to strengthen structures to effectively augment such margin. The purpose of this paper is to present a comprehensive review of the analytical methods that are currently available to assess the capacity of building structures to resist an earthquake collapse, point out the limitations of these methods, describe past experimental work in which specimens are tested to collapse, and identify what is required for an accurate evaluation of the seismic collapse capacity of a structure and the safety margin against such a collapse. It is contended that further research is needed before the collapse capacities of structures and their safety margin against collapse may be evaluated with confidence.

Design, Modeling, and Experimental Response of Seismic Resistant Bridge Piers with Posttensioned Dissipating Connections

Abstract: An increasing interest in the development of high-performance seismic resisting systems based on posttensioned, jointed ductile connections has been observed in the last decade. The extensive experimental and numerical studies carried out under the PRESSS program developed efficient alternative solutions for seismic resisting frame or wall systems in precast concrete building construction, typically referred to as jointed ductile connections. Low structural damage and self-centering behavior, leading to negligible residual displacements after an earthquake event, were recognized to be the main features of such systems. Recently, the extension and application of similar technology and seismic design methodologies to bridge piers and systems have been proposed in the literature as a viable and promising alternative to traditional cast-in situ or precast construction. However, a broad acceptance of these solutions in the bridge design and construction industry has yet to be observed. Valid justifications can be found in the lack of official guidelines for design and construction detailing as well as in the general apparent complexity of the design procedure and analytical models presented by the scientific community. In this contribution, confirmations of the unique design flexibility, the ease of construction, and the high seismic performance of jointed ductile hybrid systems, combining recentering and dissipation capabilities, are presented. After a presentation of simple design methodologies and modeling aspects herein adopted to fully control the seismic response of these systems, the experimental results of quasistatic cyclic tests on five 1:3 scaled, bridge pier specimens are reported and discussed. Four alternative hybrid configurations are implemented by varying the ratio between the posttensioning steel and the internal mild steel as well as the initial posttensioning load. Lower levels of damage and negligible residual/permanent deformations are observed in the hybrid solutions when compared to the experimental response of the benchmark specimen, representing a typical monolithic (cast-in situ) ductile solution. In addition, the efficiency of the simple analytical procedure adopted for design and modeling is further validated.

Sensitivity of Seismic Response and Fragility to Parameter Uncertainty

Abstract: As the use for regional seismic risk assessment increases, the need for reliable fragility curves for portfolios (or classes) of structures becomes more important. Fragility curves for portfolios of structures have the added complexity of having to deal with the uncertainty in geometric properties, along with the typical uncertainties such as material or component response parameters. Analysts are challenged with selecting a prudent level of uncertainty treatment while balancing the simulation and computational effort. In order to address this question, this study first evaluates the modeling parameters which significantly affect the seismic response of an example class of retrofitted bridges. Further, the relative importance of the uncertainty in these modeling parameters, gross geometries, and ground motions is assessed. The study reveals that savings in simulation and computational effort in fragility estimation may be achieved through a preliminary screening of modeling parameters. However, the propagation of these potentially variable parameters tends to be overshadowed by the uncertainty in the ground motion and base geometry of the structural class.

Seismic Response and Performance of Buckling-Restrained Braced Frames

Abstract: As the use of buckling-restrained braced frames (BRBFs) has increased in the United States, the need has grown for knowledge about member and system behavior under seismic loads and for implementing this knowledge into design provisions. In particular, methods for designing BRBFs and predicting seismic response require validation. To address this need, along with the need for experiments demonstrating system-level BRBF performance, a research program composed of numerical and large-scale experimental simulations was initiated at the ATLSS Center, Lehigh University. This paper describes the nonlinear dynamic analyses that were conducted as part of this research program. Numerical simulations of BRBF response were conducted using ground motion records scaled to two seismic hazard levels. The performance of the prototype BRBF was acceptable and performance objectives were met in terms of structural damage. It is shown that the currently accepted deflection amplification factor underestimates mean inelastic lateral displacements under design-level earthquakes and the system overstrength factor may be unconservative. The current method for predicting BRB maximum ductility demands is also shown to be unconservative and a more rigorous method for predicting BRB maximum ductility demands is provided.

Structures with Semiactive Variable Stiffness Single/Multiple Tuned Mass Dampers

Abstract: This paper proposes application of single and multiple semiactive variable stiffness tuned mass dampers (STMD/SMTMD) for response control of multistory structures under several types of excitation A new semiactive control algorithm is developed based on real-time frequency tracking of excitation signal by short time Fourier transform A parametric study is performed in the frequency domain to investigate the dynamic characteristics and effectiveness of STMDs Time history responses of single-degree-of-freedom and five-degree-of-freedom structures equipped with STMDs at the roof level, subjected to harmonic, stationary, and nonstationary excitations are presented STMD/SMTMD are most effective when they have low damping ratios and the excitation frequency can be tracked They are superior than their passive counterparts in reducing the response of the main structure both under force and base excitations In case the fundamental frequency changes due to damage or deterioration of the main structure then th

Seismic Performance of Segmental Precast Unbonded Posttensioned Concrete Bridge Columns

Abstract: The seismic performance of segmental precast unbonded posttensioned bridge columns with hollow cross sections is investigated in this paper. Bonded longitudinal mild steel reinforcement crossing the column segment joints is provided to enhance the hysteretic energy dissipation of the columns, also referred to as energy dissipation (ED) bars in this paper. The ED bars are detailed to provide energy dissipation without premature fracture at the critical column segment joint. For design purposes, a simplified analytical model to predict the lateral force-displacement response (pushover curve) is proposed. Moreover, a detailed three-dimensional (3D) finite-element (FE) model is developed and utilized to predict the behavior of segmental columns under cyclic loading. Parametric studies using the simplified analytical model and the 3D FE model are conducted to investigate the seismic behavior of this type of column construction. At the end of this paper, the comparisons of the results of the response-history analyses between the segmental columns with flag-shape hysteretic behavior and their comparable conventional counterparts are given.

Analytical and Experimental Lateral Load Behavior of Unbonded Posttensioned Precast Concrete Walls

Abstract: The use of unbonded posttensioned (UPT) precast concrete walls with horizontal joints as the primary lateral load resisting system in seismic zones has been considered in several previous studies This paper introduces a design-oriented analytical model that uses simple formulae to estimate the nonlinear lateral load behavior of UPT walls, and compares this simple model with available experimental results A previously developed UPT wall model based on fiber elements is also compared with experimental results Each model is formulated to consider several critical limit states in the lateral load behavior of UPT walls Comparisons showed generally good agreement between analytical and experimental results for three different test walls under monotonic and cyclic loading The simple model is found to be sufficiently accurate for seismic design of UPT walls, and the fiber model is found to be sufficiently accurate for estimating UPT wall response under earthquake loading

Evaluation, calibration, and verification of a reinforced concrete beam-column joint model

Abstract: A model for use in simulating the response of reinforced concrete interior beam-column joints is developed and evaluated using an extensive experimental data set. This model builds on previous work by Lowes and Altoontash in 2003, modifying the previously proposed model to improve prediction of response and extend the range of applicability. First, a new element formulation is proposed to improve simulation of joint response mechanisms. Second, a new method for simulating the shear stress-strain response of the joint core is developed. This method assumes joint shear is transferred through a confined concrete strut and simulates strength loss due to load history and joint damage following yielding of beam longitudinal steel. Third, modifications are made to enable better simulation of anchorage zone response. Comparison of simulated and observed response histories indicates that the new model represents well stiffness and strength response parameters for joints with a wide range of design parameters.

Collapse Behavior of Steel Special Moment Resisting Frame Connections

Abstract: There is a common perception that seismic detailing can improve the collapse resistance of steel frame buildings. However, the effect on connection performance of the potentially large catenary, i.e., tensile, forces that can develop during collapse has not yet been adequately studied. The objective of this paper is to use computational structural simulation to investigate a number of key design variables that influence formation of catenary action in steel special moment resisting frame subassemblages. The numerical model used in the study employs a calibrated micromechanical fracture model and is validated using existing test data. The simulation results demonstrate the ductility of seismically designed special moment frame connections and their ability to deform in catenary mode. It is shown that connection ductility and strength are adversely influenced by an increase in beam depth and an increase in the yield to ultimate strength ratio and that the beam web-to-column detail plays an influential role in connection response. A number of conclusions with practical implications are drawn from the numerical results.

Analytical Solution of Two-Layer Beam Taking into account Interlayer Slip and Shear Deformation

Abstract: A mathematical model is proposed and its analytical solution derived for the analysis of the geometrically and materially linear two-layer beams with different material and geometric characteristics of an individual layer. The model takes into account the effect of the transverse shear deformation on displacements in each layer. The analytical study is carried out to evaluate the influence of the transverse shear deformation on the static and kinematic quantities. We study a simply supported two-layer planar beam subjected to the uniformly distributed load. Parametric studies have been performed to investigate the influence of shear by varying material and geometric parameters, such as interlayer slip modulus (K), flexural-to-shear moduli ratios (E/G) and span-to-depth ratios (L/h). The comparison of the results for vertical deflections shows that shear deformations are more important for high slip modulus, for ``short'' beams with small L/h ratios, and beams with high E/G ratios. In these cases, the effect of the shear deformations becomes significant and has to be addressed in design. It also becomes apparent that models, which consider the partial interaction between the layers, should be employed if beams have very flexible connections.

Framed Steel Plate Wall Behavior under Cyclic Lateral Loading

Abstract: An experimental study was performed to investigate the cyclic behavior of framed steel walls with thin infill plates. Five specimens with a single bay and three stories were tested. Test parameters for the specimens were the plate thickness and the strength and compactness of the column. The test results showed that unlike conventional reinforced concrete walls and braced frames, well-designed steel plate walls exhibited large ductility and energy dissipation capacity as well as high strength. The steel plate walls with relatively thin plates showed shear-dominated behavior by the moment-frame action. On the other hand, steel plate walls with thick plates showed flexure-dominated behavior by the cantilever action. The shear-dominated walls showed better ductility. To achieve large ductility, the boundary columns must resist the combined axial force and transverse force developed by the tension-field action of the infill plates. Also, the columns must have compact sections to prevent their early local buckling.

Seismic Assessment of Concentrically Braced Steel Frames with Shape Memory Alloy Braces

Abstract: The use of special concentrically braced frames has increased since the 1994 Northridge and 1995 Hyogoken-Nanbu Earth- quakes. However, past performance suggests limited ductility and energy dissipation in braced frame systems due to buckling of conventional braces. In order to address this limitation, three- and six-story concentrically braced frames with superelastic shape memory alloy SMA braces are studied to evaluate their seismic performance in comparison to traditional systems. SMAs are unique metallic alloys that have the ability to undergo large deformations while reverting back to their original undeformed shape providing recentering capabilities to the braced frame. Detailed analytical models of the frames with SMA braces are developed and two suites of ground motions are used to evaluate the structures with respect to interstory drift and residual drift. The results suggest that the SMA braces are effective in limiting interstory drifts and residual drifts during an earthquake, in part, due to the recentering nature of superelastic SMAs.

Effect of Temperature on Modal Variability of a Curved Concrete Bridge under Ambient Loads

Abstract: This paper reports on the effect of temperature on the modal properties for a curved posttensioned bridge. The goal has been to explore how ambient vibrations based on routine traffic excitation can be used as part of a long-term bridge monitoring approach. This requires the establishment of a baseline that incorporates the sensitivity of the measured modal properties. The ambient vibration characteristics are based on both the health of the structure and the environmental and operational conditions which may mask normal changes due to structural changes. The primary environmental influence on the structural modal properties is temperature. A database developed over a 5 year period to explore bridge monitoring techniques has been used to evaluate how temperature variations influence the modal properties. The results show that the variability of measured modal parameters due to temperature should be well understood and quantified prior to the establishment of a baseline for use in damage assessment algorithms.

Behavior of Ultrahigh-Strength Prestressed Concrete Panels Subjected to Blast Loading

Abstract: This paper presents the results of an experimental investigation conducted in Woomera, South Australia in May 2004 on the blast-resistance of concrete panels made of ultrahigh-strength concrete (UHSC) material. A special concrete supporting frame was designed for testing concrete panel targets against blast loading. Four 2 m×1 m panels with various thicknesses and reinforcement details were tested under a 6 t TNT equivalent explosion at standoff distances of 30 and 40 m . Data collected from each specimen included blast pressures and deflections of panels. The test data were analyzed to assess the performance of UHSC and normal-strength concrete (NSC) panels. The test results and observations showed that the 100-mm-thick UHSC panels performed extremely well surviving the blast with minor cracks. The 75-mm-thick UHSC panel suffered moderate damage while the 100-mm-thick NSC panel was breached. Test results from this experimental program were used to validate a finite-element computer code that was develope...

Large-Scale Testing of a Replaceable “Fuse” Steel Coupling Beam

Abstract: When coupled core wall (CCW) systems are built in regions of high seismicity, the ductility demands on the coupling beams can be of critical concern. Steel coupling beams, whether encased in concrete or not, offer a very high degree of ductility relative to common concrete coupling beams. Hybrid core wall systems, that is CCW systems with steel or steel/concrete composite coupling beams, provide excellent lateral stiffness from the walls and coupling action, while providing excellent energy dissipation and ductility characteristics of steel coupling beams. Previous research pertaining to steel coupling beams has made great strides in furthering the understanding of the behavior of steel coupling beams, and recommendations regarding design methodologies have been established. However, as steel coupling beam ends are embedded in the wall piers, postdamage repair can be costly. This paper presents the results of large-scale cyclic tests of a steel coupling beam designed and detailed based on the writers’ pre...

Seismic Performance of Square High-Strength Concrete Columns in FRP Stay-in-Place Formwork

Abstract: The use of high-strength concrete (HSC) in seismically active regions poses a major concern because of the brittle nature of the material. The confinement requirements for HSC columns may be prohibitively stringent since they require proportionately greater confinement than columns of normal-strength concrete. An alternative to conventional confinement reinforcement is the use of fiber reinforced polymer (FRP) casings, in the form of a stay-in-place formwork. This paper investigates the use of stay-in-place FRP formwork as concrete confinement reinforcement for HSC columns with square cross sections. Large scale HSC building columns, encased in FRP casings, were tested under simulated seismic loading. The columns had 270 mm square sections and concrete strengths up to 90 MPa. The casings were manufactured from carbon FRP and epoxy resin. The unique aspects of the test program were the introduction of the corner radius as a test parameter, and the presence of internally placed FRP crossties, integrally built with column casings, to improve the effectiveness of concrete confinement. Results indicate that the deformation capacity of HSC columns can be improved significantly by using FRP casings. The results further indicate that the confinement effectiveness of columns is significantly affected by the corner radius of casings. Additionally, the confinement efficiency can be improved with the use of FRP crossties. The columns developed inelastic drift capacities of up to 11%, demonstrating the usefulness of FRP stay-in-place formwork in improving deformability of HSC columns.

Deterioration of strength of RC beams due to corrosion and its influence on beam reliability

Abstract: This paper examines the effect of corrosion of reinforcing steel on flexural and shear strength, and subsequently on reliability, of reinforced concrete beams. Two types of corrosion—general and pitting—are considered, with particular emphasis on the influence of pitting corrosion of stirrups on the performance of beams in shear. Variability of pitting corrosion along a beam is considered and the possibility of failure at a number of the beam cross sections is taken into account. Probabilities of failure are evaluated using Monte Carlo simulation. Uncertainties in material properties, geometry, loads, and corrosion modeling are taken into account. Results show that corrosion of stirrups, especially pitting corrosion, has a significant influence on the reliability of reinforced concrete beams.

Classification and Seismic Safety Evaluation of Existing Reinforced Concrete Columns

Abstract: This study contributes to the critical need for safety assessment tools for existing reinforced concrete structures. Of particular concern is the possibility of collapse due to shear failure followed by axial failure of columns supporting gravity loads. This is a potential threat to a number of existing buildings in seismically active regions. Due to unavoidable uncertainties, drift capacity predictions can only be made in a probabilistic manner. This is addressed by the development of probabilistic drift capacity models at two performance levels: lateral strength degradation and axial load failure. First, a classification method is proposed to approximately distinguish between shear-dominated columns and flexure-dominated columns. Second, for each type of column, a probabilistic shear capacity model is developed by applying an existing Bayesian methodology to an experimental database. The focus of the presentation is on the physical insight gained from the model development. Third, a probabilistic model ...

Vertical Stiffness of Elastomeric and Lead–Rubber Seismic Isolation Bearings

Abstract: An experimental study investigating the influence of lateral displacement on the vertical stiffness of elastomeric and lead–rubber seismic isolation bearings is summarized. Two identically constructed low-damping rubber and lead–rubber seismic isolation bearings were subjected to a series of tests with varying levels of combined lateral displacement and axial (compressive) loading to study this relationship. The results of these tests showed the vertical stiffness decreases with increasing lateral displacement for each bearing tested. Additionally, the vertical stiffness data are used to evaluate four formulations for the estimation of the vertical stiffness as a function of the lateral displacement. From this comparison, two formulations, one based on the Koh–Kelly two-spring model and the other on a piecewise linear relationship, showed good agreement with the experimental data over the wide range of lateral displacements considered in this study.

Limitations in Structural Identification of Large Constructed Structures

Abstract: The objective of this paper is to discuss the limitations in structural identification of large constructed structures. These limitations arise due to the geometric complexity, uncertain boundary and continuity conditions, loading environment, and the imperfect knowledge and errors in modeling such large constructed facilities. In this paper, the writers present their studies on developing a mixed microscopic-structural element level three-dimensional finite-element (FE) modeling of a long-span bridge structure and its structural system identification by integrating various experimental techniques. It is shown that a reasonable level of confidence (50–90%) can be achieved with a model that is calibrated using global and local structural monitoring data with a sufficiently high spatial resolution. The reliability of the global attributes, such as boundary and continuity conditions that may be identified and simulated by means of field-calibrated models using only dynamic test results (globally calibrated m...

Near-Fault Ground Motion Effects on Reinforced Concrete Bridge Columns

Abstract: Characteristics of near-fault ground motions warrant special consideration due to their severe and impulsive effects on structures. These characteristics are unique compared to far-field ground motions, upon which nearly all seismic design criteria are based. The objectives of this study were to explore the shake table response of reinforced concrete, to investigate near-fault ground motion effects on reinforced concrete bridge columns subjected to near-fault ground motions, and to provide a framework for the evaluation of bridge columns near active faults. Two large-scale columns were designed and tested under a near-fault ground motion on a shake table at the University of Nevada, Reno. One column represented the current California Department of Transportation far-field design, and the other was based on the American Association of Highway and Transportation Officials provisions. The most unique measured response characteristic in both columns was the large residual displacements even under moderate motions. A new hysteresis model was developed to capture this effect and was incorporated in an analytical model. Based on this finding, a framework for the evaluation of reinforced concrete bridge columns with respect to the control of residual displacement was proposed.

Fourth-Moment Standardization for Structural Reliability Assessment

Abstract: In structural reliability analysis, the uncertainties related to resistance and load are generally expressed as random variables that have known cumulative distribution functions. However, in practical applications, the cumulative distribution functions of some random variables may be unknown, and the probabilistic characteristics of these variables may be expressed using only statistical moments. In the present paper, in order to conduct structural reliability analysis without the exclusion of random variables having unknown distributions, the third-order polynomial normal transformation technique using the first four central moments is investigated, and an explicit fourth-moment standardization function is proposed. Using the proposed method, the normal transformation for indepen- dent random variables with unknown cumulative distribution functions can be realized without using the Rosenblatt transformation or Nataf transformation. Through the numerical examples presented, the proposed method is found to be sufficiently accurate in its inclusion of the independent random variables which have unknown cumulative distribution functions, in structural reliability analyses with minimal additional computational effort.

Realistic Models for Local Bond Stress-Slip of Reinforced Concrete under Repeated Loading

Abstract: The crack widths of reinforced concrete flexural members are influenced by repetitive fatigue loadings. The bond stress-slip relation is necessary to estimate these crack widths realistically. The purpose of the present study is, therefore, to propose a realistic model for bond stress-slip relation under repeated loading. To this end, several series of tests were conducted to explore the bond-slip behavior under repeated loadings. Three different bond stress levels with various number of load cycles were considered in the tests. The present tests indicate that the bond strength and the slip at peak bond stress are not influenced much by repeated loading if bond failure does not occur. However, the values of loaded slip and residual slip increase with the increase of load cycles. The bond stress after repeated loading approaches the ultimate bond stress under monotonic loading and the increase of bond stress after repeated loading becomes sharper as the number of repeated loads increases. The bond stress-slip relation after repeated loading was derived as a function of residual slip, bond stress level, and the number of load cycles. The models for slip and residual slip were also derived from the present test data. The number of cycles to bond slip failure was derived on the basis of safe fatigue criterion, i.e., maximum slip criterion at ultimate bond stress.

Simulation of cyclically loaded concrete structures based on the finite-element method

Abstract: The finite-element method for simulating the nonlinear behavior of reinforced concrete structures has progressed to the point where it is close to being a practical everyday tool for design engineers. Further advancements have made the analysis of arbitrary loading conditions, including reverse cyclic loading or earthquake-type loading, feasible. Recent criticism has questioned the practicality, reli- ability, and robustness of the finite-element method due to perceived complexities involved in developing the model and interpreting the results. A series of analyses are presented on reinforced concrete structural walls of varying height-to-width ratio, varying wall cross section, and varying levels of reverse cyclic loading to demonstrate that the finite-element procedure is capable of providing quick and reliable simulations, while employing simple modeling techniques. The modeling herein utilizes low-powered rectangular membrane elements, and material properties are smeared within the elements. Behavioral aspects such as ultimate strength, displacements, postpeak ductility, energy dissipation, and failure mechanisms are well simulated.

Analysis of Flange Transverse Bending of Corrugated Web I-Girders under In-Plane Loads

Abstract: This paper presents theoretical, experimental, and finite-element analysis results for the linear elastic behavior of corrugated web steel I-girders under in-plane loads. A typical corrugated web steel I-girder consists of two steel flanges welded to a corrugated steel web. Previous research has shown that a corrugated web I-girder under primary moment and shear cannot be analyzed using conventional beam theory alone, and a flange transverse bending analysis is required. A theoretical method, the fictitious load method, is presented herein as an analytical tool for quantifying flange transverse bending in corrugated web I-girders. To validate this method, four-point bending experimental results for a large-scale corrugated web I-girder are presented. The measured flange transverse displacements and flange stresses were in good agreement with the theoretical results especially in regions of constant shear. To gain additional insight, finite- element analysis results for the test girder are presented, and compared to both the experimental and theoretical results.

Multiobjective optimization for performance-based design of reinforced concrete frames

Abstract: In order to meet the emerging trend of performance-based design of structural systems, attempts have been made to develop a multiobjective optimization technique that incorporates the performance-based seismic design methodology of concrete building structures. Specifically, the life-cycle cost of a reinforced concrete building frame is minimized subject to multiple levels of seismic performance design criteria. In formulating the total life-cycle cost, the initial material cost can be expressed in terms of the design variables, and the expected damage loss can be stated as a function of seismic performance levels and their associated failure probability by the means of a statistical model. Explicit formulation of design constraints involving inelastic drift response performance caused by pushover loading is expressed with the consideration of the occurrence of reinforced concrete plasticity and the formation of plastic hinges. Due to the fact that the initial material cost and the expected damage loss are conflicting by nature, the life-cycle cost of a building structure can be posed as a multiobjective optimization problem and solved by the e-constraint method to produce a Pareto optimal set, from which the best compromise solution can be selected. The methodology for each Pareto optimal solution is fundamentally based on the Optimality Criteria approach. A ten-story planar framework example is presented to illustrate the effectiveness of the proposed optimal design method.