Structural Engineering and Mechanics, Vol. 68, No. 3 (2018) 289-297 DOI: https://doi.org/10.12989/sem.2018.68.3.289 289 Copyright © 2018 Techno-Press, Ltd. http://www.techno-press.com/journals/sem&subpage=7 ISSN: 1225-4568 (Print), 1598-6217 (Online) 1. Introduction Allocation of the materials’ strengths and the mechanical properties of materials is the first step in the designing process of structures. In the designing process, the strength level of structures should be in the elastic behavior range or overtake the elastic phase by considering a response modification factor (which considers the seismic behavior of the structure), based on the purpose of the design. One of the main preconditions to satisfy the design’s expectations and achieve the targeted purposes is the coincidence of the designing assumptions and the constructed mechanical properties of the used materials. This control may be carried out by non-destructive tests (Moshtagh and Massumi 2011). In the last decade, some nonlinear numerical simulation methods to model the behavior and the damage to the structures counter to the earthquake lateral loading are proposed. Massumi et al. (2013) offered a damage index for the seismic damage assessment of RC buildings based on Corresponding author, Professor E-mail: massumi@khu.ac.ir a Professor E-mail: Kabir.sadeghi@neu.edu.tr b Ph.D. E-mail: ehs.moshtagh@ut.ac.ir the variation of the nonlinear fundamental period obtained by field tests. They assessed precisely and expeditiously the seismic situation of a couple of existing RC buildings that have experienced an earthquake by employing their proposed damage index. Heo and Kunnath (2013) proposed a damage-based approach for the performance-based seismic assessment of RC frame-structures. A new methodology for structural damage assessment was developed by them that utilizes response information at the material level in each section fiber. The material level damage parameter is combined at the member, story and structural level using weighting factors. The damage model was used to compare the performance of two typical 12- story frames that have been designed for different seismic requirements. A probabilistic approach was finally used to quantify the expected seismic performance of the building. Habibi and Asadi (2017) have proposed a drift-based index to estimate the damage to RC MRFs with the setback. The inelastic dynamic time-history analysis was performed on several frames with different types of setbacks subjected to various earthquake records and the damage to them computed by the Park-Ang DI. They showed that the proposed damage index is capable to estimate the damage of setback frames. Merter (2017) presented an energy-based method to determine the earthquake safety of RC frame structures. This method is based on the comparison of plastic energy capacities of the structures with plastic energy demands obtained for selected earthquake records to perform the nonlinear time history analyses. Earthquake Effects of deviation in materials’ strengths on the lateral strength and damage of RC frames Ali Massumi 1 , Kabir Sadeghi 2a and Ehsan Moshtagh 3b 1 Department of Civil Engineering, Faculty of Engineering, Kharazmi University, Tehran, 15719-14911, Iran 2 Civil Engineering and Environmental Faculty, Near East University, North Cyprus, Via Mersin 10, Turkey 3 School of Civil Engineering, College of Engineering, University of Tehran, Tehran, Iran (Received June 5, 2018, Revised August 17, 2018, Accepted August 20, 2018) Abstract. The real behavior of the RC structures constructed based on the assumed specifications of the used materials is matched with the designed ones when the assumed and the applied specifications in construction are the same. Despite in the construction phase of the reinforced concrete (RC) structures always it is tried to implement the same specifications of materials as given in the executive drawings, but considering the unpredicted/uncontrolled parameters that affect the specification of materials, always there is a deviation between the constructed and the designed materials’ specifications. The objective of this paper is to submit a guideline for the evaluation of the strength and damage to the existing RC structures encountered deviation in materials’ strengths. To achieve this goal, the lateral strength (plastic behaviors) and damage to twenty-five RC moment- resisting frames (MRFs) are studied by applying the inelastic analysis. In this study, a couple of concrete and reinforcement strengths’ deviations are investigated. The obtained results indicate that in general, there is a semi-linear relationship between the deviation in the strength of reinforcement and the changes in the lateral strength values of the MRFs. The relative effect of the deviation in the strength of reinforcements is more than the relative effect of the deviation in the concrete strength on the damage rate. The obtained results could be a guideline for the engineers in the survey of the existing buildings encountered deviation in materials’ strengths during their construction phase. Keywords: deviation; strength; material; inelastic; vulnerability; damage