Computational Structural Engineering : An International Journal
Computational Structural Engineering Institute of Korea (COSEIK)
- Semi Annual
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- 1598-2378(pISSN)
Domain
- Construction/Transportation > Design/Analysis for Facilities
Volume 1 Issue 1
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Collapse behavior of Mission-Gothic Undercrossing under Northridge earthquake is studied by performing nonlinear time-history analysis and three-dimensional nonlinear finite element method for flared columns. Bridge structural model is characterized as three-dimensional with consideration of columns, superstructures, and abutment conditions. Three components of ground motion, corresponding to bridge's longitudinal, transverse, and vertical direction and their combinations are used to investigate bridge collapse. Studies indicate that bridge collapse is dominantly caused by transverse ground motion and the consideration of three-dimensional ground motion leads to a more accurate assessment. Failure mechanism of flared columns is analyzed applying nonlinear finite element method. Reduction of column capacity is observed due to orientation of flare. Further investigation demonstrates that the effects of flare play an important role in predicting of bridge failure mechanism. Suggestions are offered to improve the performance of bridges during severe earthquake.
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The paper describes the conceptual design, structural modelling and wind load analysis of tall buildings. The lateral stiffness of the building can be obtained economically through the interaction of core walls with peripheral frame tube and/or bundle of frame tubes and integrated design of the basement. The main structural components should be properly distributed such that the building will deflect mainly in the direction of the applied force without inducing significant response in other directions and twist. The cost effectiveness can be further enhanced through close consultation between architects and engineers at an early stage of conceptual design. Simplified structural modelling of the building and its response in three principal directions due to wind load are included. Effects of the two main structural components on the performances of a 70-story reinforced concrete building in terms of peak drift and maximum acceleration under wind load are discussed.
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The general topology optimization can be considered as optimal material distribution. Such an approach can be unstable, unless composite materials are introduced. In this research, a nodal volume fraction method is used to obtain the optimum topology of continuum structures. This method is conducted from a composite material model composed of isotropic matter and spherical void. Because the appearance of the chessboard patterns makes the interpretation of the optimal material layout very difficult, this method contains a chessboard prevention strategy. In this research, several topology optimization problems are presented to demonstrate the validity of the present method and the recursive quadratic programming algorithm is used to solve the topology optimization problems.
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In the case of the non-proportionally damped system such as the soil-structure interaction system, the structural control system and composite structures, the eigenproblem with the damping matrix should be necessarily performed to obtain the exact dynamic response. However, most of the eigenvalue analysis methods such as the subspace iteration method and the Lanczos method may miss some eigenvalues in the required ones. Therefore, the eigenvalue analysis method must include a technique to check the missed eigenvalues to become the practical tools. In the case of the undamped or proportionally damped system the missed eigenvalues can easily be checked by using the well-known Sturm sequence property, while in the case of the non-proportionally damped system a checking technique has not been developed yet. In this paper, a technique of checking the missed eigenvalues for the eigenproblem with the damping matrix is proposed by applying the argument principle. To verify the effectiveness of the proposed method, two numerical examples are considered.
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An analytical compressive stress-strain relationship model for circular and rectangular concrete specimens confined with laminated carbon fiber sheets (CFS) is studied. Tsai-Hill and Tsai-Wu failure criteria were used to implement orthotropic behavior of laminated composite materials. By using these criteria, an algorithm which analyzes the confinement effect of CFS on concrete was developed. The proposed analytical model was verified through the comparison with experimental data. Various parameters such as concrete strength, ply angle, laminate thickness, section shape, and ply stacking sequences were investigated. Numerical results by the proposed model effectively simulate the experimental compressive stress-strain behavior of CFS confined concrete specimens. Also, the pro-posed model estimates the compressive strength of the specimen to a high degree of accuracy.
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This paper presents exact solutions for the modal stress-resultant distributions for vibrating rectangular Mindlin plates involving two opposite sides simply supported while the other two sides free. These exact stress-resultants of vibrating plates with free edges, hitherto unavailable, are very important because they serve as benchmark solutions for checking numerical solutions and methods. Using the exact solutions of a square plate, this paper highlights the problem of determining accurate stress-resultants, especially the transverse shear forces and twisting moments in thin plates, when employing the widely used numerical methods such as the Ritz method and the finite element method. Thus, this study shows that there is a need for researchers to develop refinements to the Ritz method and the finite element method for determining very accurate stress-resultants in vibrating plates with free edges.
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This study is intended to propose a systematic approach for reliability-based assessment of life cycle cost (LCC) effectiveness and economic efficiency for cost-effective seismic upgrading of existing bridges. The LCC function is expressed as the sum of the upgrading cost and all the discounted life cycle damage costs, which is formulated as a function of the Park-Ang damage index and structural damage probability. The damage costs are expressed in terms of direct damage costs such as repair/replacement costs, human losses and property damage costs, and indirect damage costs such as road user costs and indirect regional economic losses. For dealing with a variety of uncertainties associated with earthquake loads and capacities, a simulation-based reliability approach is used. The SMART-DRAIN-2DX, which is a modified version of the well-known DRAIN-2DX, is extended by incor-porating LCC analysis based on the LCC function developed in the study. Economic efficiencies for optimal seismic upgradings of the continuous PC segmental bridges are assessed using the proposed LCC functions and benefit-cost ratio.
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A reliability approach to evaluate structural performance has gained increased acceptability and usage over the past two decades. Most reliability analyses are based on the reliability of an individual component without examining the entire structural system. These analyses often result in either unnecessary repairs or unsafe structures. This study uses examples of series, parallel, and series-parallel models of structural systems to illustrate how the component reliabilities affect the reliability of the entire system. The component-system reliability interaction can be used to develop optimum lifetime inspection and repair strategies for structural systems. These examples demonstrate that such strategies must be based on the reliability of the entire structural system. They also demonstrate that the location of an individual component in the system has a profound effect on the acceptable reliability of that component. Furthermore, when a structure is deteriorating over time, the reliability importance of various components is a1so changing with time. For this reason, the most critical component in the early life of the structure may not tie the most critical later.