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Multi-objective optimal seismic design of buildings using advanced engineering materials

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Title: Multi-objective optimal seismic design of buildings using advanced engineering materials
Author(s): Gencturk, Bora E.
Director of Research: Elnashai, Amr S.
Doctoral Committee Chair(s): Elnashai, Amr S.
Doctoral Committee Member(s): Spencer, Billie F.; Popovics, John S.; Kuchma, Daniel A.; Song, Junho
Department / Program: Civil & Environmental Eng
Discipline: Civil Engineering
Degree Granting Institution: University of Illinois at Urbana-Champaign
Degree: Ph.D.
Genre: Dissertation
Subject(s): Engineered Cementitious Composites (ECC) Reinforced Concrete Sustainability Small-Scale Testing Life-Cycle Cost Analysis Optimization Taboo Search Dynamic Analysis Finite Element Analysis Constitutive Model Performance-Based Seismic Design Probabilistic Seismic Hazard Analysis Spectrum Matching Ground Motion Selection
Abstract: Although seismic safety remains a major concern of society--and unfortunately this observation has been underpinned by recent earthquakes--economy and sustainability in seismic design are growing issues that the engineering community must face due to increasing human population and excessive use of the earth’s nonrenewable resources. Previous studies have addressed the design and assessment of buildings under seismic loading considering a single objective, namely, safety. Seismic design codes and regulations also center on this objective. The goal of this study is to develop a framework that concurrently addresses the societal-level objectives of safety, economy and sustainability using consistent tools at every component of the analysis. To this end, a high-performance material; namely, engineered cementitious composites (ECC) is utilized. ECC is classified under the general class of fiber-reinforced concrete (FRC); however, ECC is superior to conventional FRC in many aspects, but most importantly in its properties of energy absorption, shear resistance and damage tolerance, all of which are utilized in the proposed procedure. The behavior of ECC is characterized through an experimental program at the small-scale (scale factor equal to 1/8). ECC mixtures with different cost and sustainability indices are considered. It is seen that all ECC mixtures outperform concrete to different extents of stiffness, strength, ductility and energy absorption under cyclic loading conditions. Under simulated earthquake motion, ECC shows significant damage tolerance resulting from increased shear and spalling resistance and reduced interstory drifts. Numerical modeling of ECC is also performed to carry out structural level simulations to complement the experimental data. A constitutive model is developed for ECC and validated at the material, component and system levels. The numerical tool is utilized in the experimental program for hybrid simulation and life-cycle cost (LCC) optimization as described briefly below. Additionally, a parametric study of ECC columns is performed to investigate the effect of material tensile properties on the structural level response metrics. It is observed that the material properties have a major effect on member strength, ductility and energy absorption capacity, while the member stiffness is relatively insensitive. Reducing the LCC of buildings (through reductions in material usage and seismic damage cost) is required to achieve the objectives of economy and sustainability. A rigorous LCC formulation that uses advanced analysis for structural assessment, and that takes into account all sources of uncertainty, is used along with an efficient search algorithm to compare the optimal design solutions. A novel aspect of this work is that three different structural frames are considered, RC, ECC and a multi-material frame in which ECC is deployed only at the critical locations (e.g. plastic hinges) to improve seismic performance. It is found that both the initial and LCC of frames that use ECC are lower due to savings in material and labor cost of transverse reinforcement for the former and due to increased capacity and reduced demand for the latter. By considering the inelastic behavior of structures and incorporating all the required components, the proposed framework is generic and applicable to other types of construction such as bridges, to other innovative materials such as high performance steels, and to other extreme loading scenarios such as wind and blast.
Issue Date: 2011-08-25
URI: http://hdl.handle.net/2142/26252
Rights Information: 2011 by Bora Esref Gencturk. All rights reserved.
Date Available in IDEALS: 2011-08-25
Date Deposited: 2011-08
 

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