NONLINEAR DYNAMIC ANALYSIS AS SEISMIC ASSESSMENT TOOL FOR RC FRAME STRUCTURES Aleksandar ZHUROVSKI 1 , Golubka NECHEVSKA- CVETANOVSKA 2 , Mihail GAREVSKI 3 ABSTRACT Until recently the design philosophy of building structures followed sets of prescribed rules implemented in older design codes. On the other hand, modern design codes implement the latest knowledge in the form of performance- based earthquake engineering. Because of this, the level of seismic safety provided by existing RC structures is in some way suspicious. The need for exact prediction of the seismic behavior of structures causes the need of targeting nonlinear dynamic analysis as a tool for seismic assessment. For this purpose an eight story RC frame structure was chosen for analysis. The constructive elements were modeled with the concentrated hinges approach using trilinear hysteretic model without cyclic deterioration and trilinear hysteretic model with strength and stiffness deterioration. Afterwards, seven sets of bidirectional time- history records were selected and scaled to the EUROCODE-8 design spectrum to best match the most probable seismic action on the location for two main concerning limit states: collapse prevention and damage limitation. Presented in the paper will be selected results from the performed analytical investigations in the form of damage patterns of the structure, nonlinear behavior of the structural elements, displacement time histories and interstory drifts as well as energy balance graphs. The main conclusion points the necessity and usefulness of using time- history analysis for seismic assessment of existing structures. It is the only method which can exactly define the damage patterns of a structure, energy absorption in the constructive elements and intersotry drifts under seismic actions. Keywords: Nonlinear dynamic analysis; RC buildings; PERFORM 3D; Performance- based earthquake engineering 1. INTRODUCTION Seismic assessment of structures is required because of the occurrence of earthquakes. Ground shaking with its destructive potential commonly leads to significant damage and/or collapse of buildings and infrastructure systems (e.g. dams, roads, bridges, viaducts etc). As a result the assessment procedures established in order to quantify the damage to both structural elements and the entire structure and also to reduce loss of life are in constant progress. Strength- based design is the traditional code procedure, which is still used throughout the world for seismic design of new structures. This approach for design of new buildings prescribes the use of the 1 PhD student, Institute of Earthquake Engineering and Engineering Seismology- IZIIS, University “Ss. Cyril and Methodius”, Skopje, Republic of Macedonia, zurovski@pluto.iziis.ukim.edu.mk 2 Prof, PhD, Institute of Earthquake Engineering and Engineering Seismology- IZIIS, University “Ss. Cyril and Methodius”, Skopje, Republic of Macedonia, golubka@pluto.iziis.ukim.edu.mk 3 Prof, PhD, Institute of Earthquake Engineering and Engineering Seismology- IZIIS, University “Ss. Cyril and Methodius”, Skopje, Republic of Macedonia, garevski@pluto.iziis.ukim.edu.mk In line with the A/RES/47/225 resolution of the United Nations, the provisional State name is former Yugoslav Republic of Macedonia (F.Y.R.O.M.). Alternative names reflect the views of the Authors and are not adopted by the Hellenic Association of Earthquake Engineering.