Comparison of linear and nonlinear methods for seismic evaluation of existing reinforced concrete buildings in the Turkish earthquake code 2007

Abstract

Importance of more accurate estimation of the seismic behavior of buildings has been steadily increasing since the 1999 Marmara Earthquake. This increasing trend intensifies the need for a new Earthquake Code in Turkey. Turkish Earthquake Code 2007 has been put in force as of 06.03.2007. Relatively new analyses procedures in this code and developments in technology enable scientists and engineers to predict the seismic behavior of reinforced concrete buildings more realistically. Besides, 73 percent of buildings that collapsed in the 1999 Marmara Earthquake are 1 to 7 story buildings according to the Earthquake Master Plan for Istanbul [Ref. 1]. The purpose of this study is to determine the seismic performance of existing medium-rise (4 to 6 story buildings) reinforced concrete buildings with adequate transverse reinforcement in Turkey using linear and non-linear analysis methods in the Turkish Earthquake Code 2007. In this study, 4 structural system models which represent the existing medium-rise reinforced concrete buildings in Turkey are chosen and designed in accordance with TEC 75 and TEC 98 regulations. Two of the models are 4 story and the rest are 6 story. Also material properties and seismic zones of the models vary to represent the buildings in different seismic regions with different material characteristics. These models have a symmetric plan as commonly used. The seismic performances of these models are determined by using linear and nonlinear evaluation methods in TEC 2007. In the linear theory, it is assumed that the material is linear-elastic and displacements are very small. Second-order effects are neglected. Therefore, linear methods given in codes are used to obtain the seismic performance of the models. In the non-linear theory, pushover analysis is used. Pushover analysis is a static, nonlinear analysis procedure in which the magnitude of the lateral earthquake load is incrementally increased until the performance point. Also it is assumed that displacements are not very small in non-linear theory. Member damage levels calculated by using linear and nonlinear methods of the Turkish Earthquake Code 2007 are compared and evaluated. The basic conclusions obtained from numerical investigations are summarized below; The linear method of the Turkish Earthquake Code 2007 gives more conservative member damage levels as compared with those given by the non-linear method. Damage levels of structural members obtained from linear and nonlinear methods differ by at most one damage region. Members of structural system models designed in accordance with the Turkish Earthquake Code 1998 satisfy adequate seismic performance levels. On the other hand, members of structural system models designed to the Turkish Earthquake Code 1975 are generally in collapse prevention region or collapse region.