PACE 2021- Ataturk University, Engineering Faculty, Department of Civil Engineering, Erzurum, 25030, TURKEY 20-23 June 2021 1 Research Article 20-23 June 2021 Investigation of Seismic Behavior of Soft Storey Structure in Frequency Time Domain Oğuzhan ÇELEBİ *1 ,Barış BAYRAK 1 ,Haluk Görkem ALCAN 2 ,Abdulkadir Cüneyt AYDIN 1 1 Departmant of Civil Engineering, Atatürk University, 25240, Erzurum, Turkey 2 Departmant of Civil Engineering, Kafkas University, 36100, Kars, Turkey Corresponding Author E-mail: celebioguzhan@atauni.edu.tr Corresponding Author ORCID: 0000-0002-6696-4297 Keywords Abstract Frequency Domain, Passive Isolator, Soft Story, Center and External Center Members Today, ground or basement floors of buildings are designed as soft floors for use as parking lots and workplaces. Therefore, the soft story of the structure under the effect of earthquake may show non-ductile behavior. In this study, a number of approaches have been proposed to improve the behavior of the soft story and ensure its usability. In order to eliminate the negative effects of the soft story, passive isolation systems were preferred as well as the use of central and external central braces. A computer-based Matlab program was used to understand the behavior of the structure in the frequency domain, and a finite element program was used to perform the related analysis. According to the analysis results, it has been determined that the use of the central and external center improves the behavior of the structure in appropriate frequency ranges, but the use of passive isolator systems is not suitable for the relevant structure. It has been confirmed that the passive isolators should be designed according to each structure and any possible earthquake feature. 1. Introduction The soft story effect is defined as the ratio of the relative story drift ratios occurring at the relevant floor in one direction to the relative story drift ratios occurring at the next or higher floors [1]. Earthquakes such as the Erzincan Earthquake-1992 and the Izmit Earthquake-1999 that took place in Turkey caused heavy damage to the soft storeys of the structures [2]. Considering the damages that have occurred in the past, a number of strengthening methods have been proposed to protect structures from soft storey effect. Javadi and Yamakawa (2013) [3] placed the steel braces on the soft storeys by establishing a hybrid connection, thus ensuring the ductile behavior of the soft plies. Hirde Suchita and Tepugade Ganga (2014) [4] investigated the behavior of soft storey effect by applying nonlinear static pushover analysis in a structure. They observed that the displacement decreased when the soft story was provided at a higher level. They concluded that as a result of soft floor shear wall applications, there is no plastic hinge formation in the columns and lateral displacement is reduced. Tahamouli Roudsari et al. (2017) [5] carried out a series of tests by connecting the steel braces to the reinforced concrete soft storey as eccentrically. As a result of the test, it was observed that the soft story behavior was improved. Fabio Mazza et al. (2018) [6] used base isolation systems for seismic reinforcement of a soft-story reinforced concrete frame under the effect of near-field earthquakes. As a result of the study, it was observed that the use of both elastomer and friction ısolators strengthened the ductile behavior of the reinforced concrete frame. Aydin et al. (2018) [7] showed that the steel plate model creates uniform tension along the surface and keeps the reinforced concrete cross-section deformation under control by using a lead-based rubber ısolator system in the structure under earthquake risk. In this study, the structure with soft storey effect is examined in the frequency domain and different strengthening procedures are discussed. Analysis of the structures in the frequency domain has been used especially for the earthquake performance of historical structures [8]. Except for the effect of the soft story, central braced system structure, external central braced system structure, lead based rubber isolator structure, friction based isolator structure, central braced friction isolator structure, central braced lead based rubber isolator structure, external braced friction isolator structure, including the braced lead-based rubber insulator structure, eccentric 8 different structures, were evaluated with the frequency domain method under the effect of earthquakes with 11 different characteristics. 2. Testing process 2.1. Descrıption of the structure In the study, it is a structure with 3 spans in the X direction, each span distance of 4 m, and each span distance of 5 m, with 3 spans in the Y direction. The normal floors are 3 m high and the ground floor is 5 m high, and the building is at 39.90 Latitude and 41,368 longitude. The strengthening methods used to improve the earthquake behavior of the building with a soft ground floor are shown in Figure 1. In Figure 1, forming the frame system for the columns is made of HEA300 and the beams are made of IPE240 steel profile. In Figure 1a, by using the L150*12 bracket, the central and eccentric braced systems shown in Figure 1d and Figure 1g, respectively, were obtained. Static and geometric information of the profiles that make up the frames are given in Table 1.