Vol. 19, No. 1 EARTHQUAKE ENGINEERING AND ENGINEERING VIBRATION January, 2020 Earthq Eng & Eng Vib (2020) 19: 161-177 DOI: https://doi.org/10.1007/s11803-020-0554-1 Estimation of drift limits for different seismic damage states of RC frame staging in elevated water tanks using Park and Ang damage index Suraj O. Lakhade † , Ratnesh Kumar ‡ and O. R. Jaiswal § Department of Applied Mechanics, Visvesvaraya National Institute of Technology, Nagpur, India Abstract: Damage to elevated water tanks in past earthquakes can be attributed to the poor performance of their supporting frame staging. In order to ascertain the performance of these elevated water tanks, it is crucial to categorize the damage in quantifiable damage states. Among various parameters to quantify the damage states, the top drift of frame staging can be conveniently correlated to the different damage levels. In literature, drift limits corresponding to different damage states of the frame staging of the elevated water tank are not available. In the present study, drift limits for RC frame staging in elevated water tanks corresponding to different seismic damage states have been proposed. Various damage states of the elevated water tank have been determined using the Park and Ang damage index. The Park and Ang damage index utilizes results of both pushover analysis and incremental dynamic analysis. Twelve models of elevated water tanks have been developed considering variation in staging height and tank capacity. Incremental dynamic analysis has been performed using the suite of twelve actual earthquake ground motions. Based on the regression analysis between damage indexes and drift, limiting drift values for each damage state are proposed. Keywords: elevated water tank; frame staging; damage states; drift limit; 3D modelling; incremental dynamic analysis; pushover analysis Correspondence to: Ratnesh Kumar, Department of Applied Mechanics, Visvesvaraya National Institute of Technology, South Ambazari Road, Nagpur, Maharashtra 440010, India Tel: +91-937 254 8232 E-mail: ratnesh.eq@gmail.com † PhD Candidate; ‡ Associate Professor; § Professor Received May 4, 2018; Accepted December 12, 2018 1 Introduction Elevated water tanks are an essential part of public water distribution systems and are very common, particularly in developing countries (Fig. 1). These structures are considered as lifeline structures since they not only provide potable water but also water required for fire-fighting operations in post-earthquake scenarios. Reinforced concrete (RC) elevated water tanks primarily comprise three parts: tank container, supporting structure and foundation. Among the various types of staging, frame type staging (Fig. 1) is very common and is composed of columns and braces. In past earthquakes, a number of elevated tanks suffered damage; however, this damage was primarily located in supporting structures (Steinbrugge and Flores, 1963; Mehrain, 1990; Astaneh and Ashtiany, 1990; Jain et al., 1994; Saffarini, 2000; Rai, 2002; Rai, 2003). The damage can be attributed to various reasons, but was mainly related to shortcomings in design and ductile detailing of the frame staging. Figure 2 shows damaged elevated water tanks during the Bhuj and Killari earthquakes (Rai, 2003; Jain et al., 1994). For seismic performance evaluation and fragility analysis, discrete damage states are required. Quantitatively, the damage states can be defined in terms of limiting drift for various damage levels: slight, moderate, extensive and collapse damage states (Barbat et al., 2006; Giovinazzi, 2005). Unlike other structures, such as buildings and bridges, quantitative identification of damage states for RC elevated water tanks with frame staging is not available in the literature. Moreover, the frame staging of elevated water tanks behave very differently than the building frame (Rai, 2003) and hence, its damage states cannot be assigned to frame staging of the elevated water tank. Generally, the seismic performance criteria (performance objective) are decided on the basis of an acceptable damage level for a particular class of structure under the design earthquake. Most seismic design building codes emphasize that a normal building should satisfy “life safety performance” under the anticipated design level earthquake. To satisfy this criterion, relatively large inelastic drift in buildings is allowed (i.e., 2% as per ASCE 41-06, 2007 and ATC 40, 1996). Moreover, to accommodate large inelastic drift, the building will suffer considerable structural damage, which will require post-earthquake repair and retrofitting before it can be reoccupied. On the other hand, elevated