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Bi J.,University of North Carolina at Charlotte | Fang H.,University of North Carolina at Charlotte | Wang Q.,Kal Krishnan Consulting Services Inc. | Ren X.,University of North Carolina at Charlotte
Finite Elements in Analysis and Design | Year: 2010

Thin-walled columns play an important role on passenger safety in vehicular collisions for their progressive deformation patterns and large energy absorptions. A thin-walled column with a large specific energy, i.e., the ratio of energy absorption to its mass, is often desirable to the automotive industry, because such designs could enhance safety and reduce manufacturing cost. Due to the complexity of crash mechanism, obtaining such designs has been a challenge to the trial-and-error approach using physical prototype testing. To this end, combining finite element simulations with optimization methodologies has become the viable means to meet the challenge. In this paper, singleand triple-cell hexagonal columns filled with aluminum foams were optimized for maximum specific energy with simultaneous consideration of section geometry, tube thickness, and foam density. The effects of crushing forces on column designs were analyzed by comparing optimum solutions with and without constraints on the mean crushing forces. The interaction effects between the tube and foam of composite columns and the relative advantages of single- and triple-cell structures were investigated and discussed. © 2010 Elsevier B.V. All rights reserved. Source

Wang Q.,Kal Krishnan Consulting Services Inc. | Fang H.,University of North Carolina at Charlotte | Zou X.-K.,Arup
Structural and Multidisciplinary Optimization | Year: 2010

Seismic isolation and energy dissipation systems are innovative strategies for seismic design and upgrade or retrofit of bridges. In a retrofit design, base isolation devices can be easily incorporated into existing bridges to replace conventional bearings and to improve the overall structural performance. In this paper, an optimal cost base isolation design or retrofit design method for bridges subject to transient earthquake loads is studied. The goal of this study is to push forward the concept of retrofit design optimization of structures using this isolation design as an example. This is achieved by combining nonlinear time history analyses with an optimization procedure to select base isolators that minimize the cost of the isolation system while satisfying certain design requirements. An improved genetic algorithm (GA), Micro-GA, is employed to search for the optimal solutions for such discrete optimization problems. An example of the optimal design of a highway bridge is presented and the minimum cost expense of the isolation system is achieved with improved structural response under multiple transient earthquake loads. © 2009 Springer-Verlag. Source

Shi H.,Kal Krishnan Consulting Services Inc. | Salim H.,University of Missouri | Shi Y.,A. Morton Thomas and Associates Inc. | Wei F.,Hohai University
Mechanics Based Design of Structures and Machines | Year: 2015

A formulation of the nonlinear FEM truss element that takes into account both the geometric nonlinearity and material nonlinearity of the structure is derived. The associated iterative algorithm for the application is described. Based on two inelastic material models (isotropic hardening and dynamic hardening), three space truss structures are subjected to static and to dynamic loads in order to illustrate the application of nonlinear FEM. The nonlinear FEM described can accurately trace the complex structural behavior of space truss structures, including snap-through, and buckling. The FEM results match well with the theoretical results. © 2015 Taylor & Francis Group, LLC. Source

Zou X.-K.,Arup | Wang Q.,Kal Krishnan Consulting Services Inc. | Li G.,Dalian University of Technology | Chan C.-M.,Hong Kong University of Science and Technology
Journal of Structural Engineering | Year: 2010

This paper presents an effective numerical reliability-based optimization technique for the design of base-isolated concrete building structures under spectrum loading. Attempts have been made to automate the integrated spectrum analysis, reliability analysis, and design optimization procedure and to minimize the total cost of the base-isolated building subjected to multiple design performance criteria in terms of the story drift of the superstructure and lateral displacement of the isolation system or corresponding reliability constraints. In the optimal design formulation, the cost of the superstructure can be expressed in terms of concrete member sizes while assuming all these members to be linear elastic under a specified design earthquake. However, the base isolation is assumed to behave nonlinearly and its cost can be related to the effective horizontal stiffness of each isolator. Based on the principle of virtual work, the drift responses and corresponding reliability indexes can be explicitly formulated and the integrated optimization problem can be solved by an optimality criteria method. The technique is capable of achieving the optimal balance between the costs of the superstructure and isolation systems while the seismic drift performance or corresponding reliability of a building can be simultaneously considered. An illustrative example shows that conventional deterministic design optimization cannot ensure designs with satisfactory reliability levels, whereas the reliability-based design optimization can achieve the objective when uncertainties are considered. It is believed that such an optimization technique provides an effective tool for seismic design of building structures. © 2010 ASCE. Source

Shi H.,Kal Krishnan Consulting Services Inc. | Wang Q.,Manhattan College | Wei F.,Hohai University | Shen L.,University of Hawaii at Manoa
Structural Engineer | Year: 2013

The combination of FEM and LPA provides a powerful and accurate tool for analysing the load fl ow inside the complex fl oating concrete structure, i.e., the concrete gate. Both the reaction forces at the supports and the internal forces inside the shear walls and decks are fi rst obtained using the FEM software SAP2000. Through the static load equilibrium, the attributed external loads on the front side of the gate can be derived. The loads are then dissipated through the combined interaction of the internal structural members in the form of direct shear forces or bending moments. All the loads eventually go into the support in the rear side of the gate structure, i.e. The abutment wall and the base sill. Interesting observations can also be made in regard to the load transfer pattern inside the fl oating concrete gate structure: • Less than 7% of the unbalanced external load is transferred by the top deck, whereas 38% is transferred through the middle deck and 31% through keel slab • Approx 9% of the total external load is transferred through the two internal walls at the abutment wall locations (at gridlines 2 and 12), and 14% through the two internal walls at gridlines 5 and 9 in the middle of the gate • A total of 34% of the reaction force is along the abutment wall, and the remaining 66% transfers from the base sill to the foundation Through the application of LPA in the concrete gate, the complex load fl ow inside the structure is identifi ed. The methodology introduced in this paper is universal as long as FEM can be conducted for the target structures. Source

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