Seismic performance assessment and strengthening of asymmetric in plan reinforced concrete structures

TitleSeismic performance assessment and strengthening of asymmetric in plan reinforced concrete structures
Publication TypeThesis
Year of Publication2005
Kosmopoulos AJ
Thesis TypePhD
Abstract

This thesis deals with the problem of seismic performance assessment and strengthening of existing, asymmetric in-plan reinforced concrete buildings. In a highly seismic region such as Greece, the fact that the majority (over 70%) of existing buildings are not designed against earthquake loads constitutes a serious problem. Furthermore, the structural configuration of these buildings often is such that promotes torsional response during the earthquake, thus worsening their already poor performance. In addition to the technical and financial difficulties inherent in the seismic strengthening procedures, until now (i.e. before Eurocode 8 – Part 3 and the Greek Code for Structural Interventions - KANEPE) there was a lack of a framework of codes addressing the issues of the assessment of seismic performance and strengthening of existing buildings. This dissertation suggests computational tools and procedures for a detailed assessment of the seismic performance of this problematic category of structures, aiming to the understanding of their response and the identification of their “weak points” so that the strengthening procedure can focus exactly there. Four real buildings are used as specimens for this study, two of which were designed and constructed to be tested pseudo-dynamically. The four buildings are: the four-story apartment building that collapsed during the 1999 Athens earthquake; the municipal theater of Argostoli “O KEFALOS”; the three-story building that was constructed and pseudo-dynamically tested at the reaction wall facilities of the ELSA laboratory of the European Joint Research Centre in Ispra, Italy, and the two-story building that was constructed and pseudo-dynamically tested at the reaction wall facilities of the Laboratory of Structures of the Department of Civil Engineering of the University of Patras in Greece. The first Chapter of the thesis deals with the definition of the problem that is posed by the existence of a big majority of structures without adequate (or any) resistance to lateral, earthquake loads. Also present are brief references to the historical evolution of the Greek Seismic Codes, and to the practical difficulties of the assessment of seismic performance and strengthening. The second Chapter defines the targets of seismic performance assessment and strengthening according to modern Codes, looks into the Limit States that they induce, and the comparison of deformational capacity and demand, with a reference to the relevant safety factors. The third Chapter presents briefly the computational tool that was developed during the course of this PhD work, namely the computer program ANSRuop that was used to carry out all the analyses, including linear static, modal, multimodal response spectrum, nonlinear static (pushover) and nonlinear time-history analyses. Next are presented the analytical equations that are used for the modeling of reinforced concrete buildings, and the quantification of the terms of forces and deformations that are involved in the assessment and strengthening procedures. The fourth Chapter contains the application of the seismic performance assessment procedures to the four buildings of the thesis, including the identification of their static eccentricities in-plan (which give an indication or whether or not torsional response is to be expected during the earthquake, which leads to a magnification of the deformations), their dynamic characteristics (natural periods and modes of vibration), as well as the carrying out of sets of nonlinear time-history analyses aiming to the understanding of their seismic response and the detailed identification of their “weak points”. In the fifth Chapter, strengthening schemes are proposed for three of the buildings of the thesis, the efficiency and adequacy of which are investigated using the computational methods also used in the fourth Chapter. Special attention is made to whether the strengthening scheme succeeded in reducing the static eccentricities in-plan, which in turn leads to a reduction of the torsional response. The sixth Chapter investigates the relation between inelastic and elastic deformations, which are the results of nonlinear time-history analyses and elastic analyses (equivalent static or multimodal response spectrum), respectively. The seventh Chapter introduces a simple computational model with one vertical element per floor, which aims to the replication of the three-dimensional dynamic response of complex, asymmetric in-plan structures, but also to the further investigation of the effect of static eccentricity to the response. The eighth Chapter utilizes the results of the sets of the nonlinear time-history analyses for one of the buildings of the thesis, as well as the results of seismic risk analyses, which were also conducted within the framework of this PhD work, with an aim to the expression of the assessment of seismic performance in probabilistic terms (specifically with the application of a methodology proposed by Cornell, which leads to the mean annual rate of exceedance of a specific limit state at a structural member). Finally, the ninth Chapter presents the general conclusions that can be extracted from the application of the methods and procedures of seismic performance assessment and strengthening of existing, asymmetric in-plan reinforced concrete buildings.

URLhttp://nemertes.lis.upatras.gr/dspace/handle/123456789/259
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