Journal of Structural Engineering

A seismic loss curve of a real-world building is obtained by means of state-of-the-art models for the impending ground motion, the structure, the damage of structural and nonstructural components, and the ensuing losses. In particular, the seismic hazard at the building’s location (Vancouver, Canada) is described by a comprehensive probabilistic model. It is argued that this ground motion model is particularly appropriate in reliability analysis compared with the more common utilization of a limited set of scaled ground motions. In this paper the probabilistic integrals are carried out by means of a reliability formulation, in which a series of probabilistic models enter. This is referred to as unified reliability analysis to contrast the unified format of the probabilistic models with alternatives, such as suites of ground motions and fragility curves that themselves are created by reliability analysis. A key contribution in this paper is the comprehensive numerical example, which entails an inelastic dynamic analysis of a finite-element model of a building located in Vancouver.

A full-scale, two-story, light-frame wood townhouse building, designed according to modern U.S. engineered seismic design requirements, was tested on two triaxial shake tables operating in unison. The main objective of this experimental study was to determine the dynamic characteristics and the seismic performance of the test building under various base input intensities, representative of both ordinary and near-field ground motions in southern California. The building was tested with and without interior (gypsum wallboard) and exterior (stucco) wall finishes. The test results revealed that the installation of gypsum wallboard to the interior surfaces of structural wood sheathed walls substantially improved the seismic response of the test building. The application of exterior stucco further improved the seismic response of the test building, particularly in its longitudinal direction, where the shear response of low aspect ratio wall piers dominated. These shake table test results provide the evidence of the significant influence that wall finish materials have on the behavior of lateral load-resisting systems in light-frame wood construction.

The seismic behavior of the proposed precast segmental unbonded posttensioned concrete bridge columns for use in regions of high seismicity was investigated experimentally. Posttensioning tendons were placed in the hollow core of the columns and left unbonded with the surrounding concrete to decrease prestress loss during earthquakes. Bonded mild steel bars continuous across the segment joints, also referred to as energy dissipation (ED) bars, were used to enhance the seismic resistance of the columns. The bars were unbonded at the critical joint to avoid premature low cycle fatigue failure. The objectives of this study were to (1) verify the proposed construction method and seismic detailing for the ED bars and (2) investigate the seismic behavior of the columns with different ED bar ratios and posttensioning forces. Four large-scale specimens were designed and tested with lateral cyclic loading. Test results showed that the proposed construction method and seismic detailing for the ED bars were effective in ensuring the ductility and ED capability of the bars. The specimens exhibited excellent drift capacities that are adequate for use in regions of high seismicity. The hysteretic ED capacity and residual drift of the column increased as the ED bar contribution to the expected column strength ${\lambda }_{\text{ED}}$ increased. To maintain self-centering capability, ${\lambda }_{\text{ED}}$ of more than 35% is not recommended.

The long-term behavior in the service stage of continuous composite steel-concrete beams with deformable connectors subjected to uniaxial bending and axial load is presented. The problem is dealt with by recurring to the displacement method, assuming the bending curvature and the longitudinal deformation as unknowns, and obtaining a system of differential and integro-differential equations. The results are compared with literature experimental tests. A case study is then discussed, referring to a continuous beam subjected to permanent and variable loads, to concrete shrinkage, and to a vertical displacement imposed to the central support or to the prestressing of the central part of the beam.

A three-dimensional (3D) eight-noded brick element, which is capable of representing the performance of composite structures subjected to 3D stress conditions at ambient and high temperatures, has been developed and incorporated into a finite-element analysis program Vulcan. In the formulation of this element, geometric nonlinearity, material nonlinearity, material degradation, and thermal expansion at elevated temperatures have been taken into account. The von Mises and Drucker-Prager theories were chosen as the 3D failure criteria for steel and concrete, respectively. In particular, a series of postfailure criteria and corresponding 3D constitutive relations for concrete at high temperatures were defined in this study. The accuracy and efficiency of this newly developed structural element was verified against the results from a number of tests on composite structures subjected to 3D stress conditions at both ambient and elevated temperatures. The proposed 3D structural element can be used to model a large range of composite structures in fire, and perform more detailed studies on them.

The evaluation of the seismic performance of masonry-infilled reinforced concrete (RC) frames has been a major challenge for structural engineers. This paper addresses pertinent issues on the development and calibration of nonlinear finite-element models for assessing the seismic performance of these structures. The modeling scheme considered here combines the smeared and discrete crack approaches to capture the different failure modes of infilled frames, including the mixed-mode fracture of mortar joints and the shear failure of RC members. A systematic approach is presented here to calibrate the material parameters, and the accuracy of the nonlinear finite-element models has been evaluated with experimental data. The comparison of the numerical and experimental results indicates that the models can successfully capture the highly nonlinear behavior of the physical specimens and accurately predict their strength and failure mechanisms. The validated models have been used to assess the sensitivity of the numerical results to the modeling parameters and to identify the critical material parameters through a parametric study.

This paper describes the development of a finite-element model capable of representing a blast-resistant flexible window (flex window) system developed by the Air Force Research Laboratory/Airbase Technologies Division. Computational fluid-structure interaction finite-element simulations are used to develop an improved understanding of the manner in which fluid phenomena, such as air compression and flow, affect the behavior of the flex-window system under blast loading. Compressible airflow interacting with a flexible thin-shell structure of the flex window (transient air-window panel interaction phenomena) is found to significantly influence system performance. The influences of shock wave propagation and fluid venting inside the damping chamber of the flex-window system are quantified and the influences of such phenomena on panel deflections, deformations, and internal forces are presented.

This paper presents a sensitivity-based damage identification of a three-dimensional truss tower tested in the laboratory. A finite-element model is updated by modal parameters obtained from ambient vibration measurements. The paper focuses on details of modeling and model updating. To get a realistic model, it was necessary to include eccentric connections, bending stiffness in truss members, and foundation flexibility. For model updating, a number of mathematical techniques are combined in a consistent way, including regularization of the nonlinear updating problem and its linearization. Considering all these details correctly, damage in the truss has been successfully identified. However, it is also demonstrated how neglecting some of these algorithmic details can lead to incorrect results. It is also shown how static condensation can lead to a model that is valid for the undamaged case but cannot adequately represent the damaged case.

A cold-formed steel framed shear wall may fail in shear buckling of the sheathing, local buckling or distortional buckling of the framing member under compression forces or connection failures. An unusual distortional buckling mode on boundary studs under uplift forces was recently observed in a shear wall test program conducted at the University of North Texas. It was found in monotonic pushover shear wall tests that the flanges of the boundary studs undertaking uplift forces were distorted at the bottom area of the studs near the hold-down. This paper presents the test program and analysis of the unique distortional buckling mode. The paper also provides procedures for predicting the distortional buckling strength of the boundary studs, as well as the construction details to mitigate the damage by this unexpected distortional buckling mode.

This study investigates the effect of base connection geometry on base plate flexibility and the fatigue performance of multisided high-mast lighting towers. Three parametric studies investigating the effect of base plate thickness, tube wall thickness, and anchor rod configuration are discussed in this paper. The results of this study show that of the geometric parameters considered, base plate thickness has the largest influence on the stresses in the tube wall adjacent to the weld toe. By increasing the base plate thickness of the tower, significant improvement to the fatigue life is observed because the maximum stress, and hence stress range, at the base plate-to-tube wall thickness is reduced due to a reduction in local bending in the tube wall.

In accordance with the ASCE Standard 7-05, in regions subjected to wind and earthquakes, structures are designed for loads induced by wind and, separately, by earthquakes, and the final design is based on the more demanding of these two loading conditions. Implicit in this approach is the belief that the standard assures risks of exceedance of the specified limit states that are essentially identical to the risks inherent in the provisions for regions where only wind or earthquakes occur. We draw the attention of designers, code writers, and insurers to the fact that this belief is, in general, unwarranted, and that ASCE 7 provisions are not risk consistent, i.e., in regions with significant wind and seismic hazards, risks of exceedance of limit states can be up to twice as high as those for regions where one hazard dominates. This conclusion is valid even if the limit states due to wind and earthquake are defined differently, as is the case in ASCE 7. We propose an approach to modifying ASCE 7 provisions which guarantees that risks implicit in minimum ASCE 7 requirements for regions where one hazard dominates are not exceeded for structures in regions with strong wind and seismic hazards.

The current investigation extends the previous work in calculating components and cladding loads for standing seam metal roof clips. It was found that the ASCE 7-05 wind loads for these clips are conservative, while several other studies have shown that the ASCE 7-05 is unconservative when compared to integrated wind tunnel pressure data. The current note resolves this contradiction, showing that the observed conservatism is primarily due to the fact that the critical clips are not located in the worst aerodynamic region of the roof.