Engineering Structures 31 (2009) 2617–2629 Contents lists available at ScienceDirect Engineering Structures journal homepage: www.elsevier.com/locate/engstruct Dynamic behavior of R/C elevated tanks with soil–structure interaction Sekhar Chandra Dutta a,∗ , Somnath Dutta a , Rana Roy b a Department of Civil Engineering, Bengal Engineering and Science University, Shibpur Howrah 711 103, West Bengal, India b Department of Applied Mechanics, Bengal Engineering and Science University, Shibpur Howrah 711 103, West Bengal, India article info Article history: Received 3 June 2008 Received in revised form 12 June 2009 Accepted 15 June 2009 Available online 1 July 2009 Keywords: Elevated tanks Frame staging Shaft staging Dynamic characteristics Seismic behavior Soil–structure interaction abstract A critical review of past earthquakes reveals damage/failure of important lifeline facilities like elevated water tanks in recurrence, leading to serious hazards even after the event. In the context of such hazards indicating deficiencies in the existing seismic design strategy of such structures, dynamic characteristics of elevated tanks supported by cylindrical shaft (shaft staging) are comprehensively studied in the first part of present investigation. The same is made through analytical formulations developed and validated by rigorous finite element analysis and small-scale experimentation. Subsequent examination on seismic response of representative tanks indicates that the columns of the frame-supported tanks (tanks with frame staging) and the wall of the shaft-staging of such reinforced concrete (R/C ) tanks are susceptible to tension, particularly at tank empty condition. Such possibility seems to be further aggravated if the effect of soil–structure interaction (SSI) is ignored in design. Identifying the deficiencies in current design, simple design procedure of such elevated tanks utilizing the formulations developed is proposed. Torsional vulnerability of shaft-supported elevated water tanks is also identified to be marginal as opposed to the same for frame supported ones. © 2009 Elsevier Ltd. All rights reserved. 1. Introduction Investigating the effects of earthquakes has long been recog- nized as a necessary step to understand the natural hazards and its risk to the society in the long run. A rapid assessment of general damage survey and documentation of initial important observations, besides facilitating in emergency management and rehabilitation activities, identifies the need of follow-up areas of research. However, long-term preparedness requires in-depth re- search on the identified issues with suggestions for preparedness. At this backdrop, the damage survey conducted following few severe Indian earthquakes such as 2001 Bhuj earthquake, 2005 Kashmir earthquake etc. are critically examined. The scrutiny of such damage histories revealed damage/failure of reinforced con- crete (R/C ) elevated water tanks of low to high capacity—a very important lifeline facility and damage of the same often results in significant hardships even in the post-earthquake scenario, claim- ing human casualties and economic loss to built environment. A pictorial rundown of such damages as observed in the past may be of help to recognize the problem with further gravity. The 2001 Bhuj earthquake; India illustrated such vulnerability when large number of tank stagings suffered damage as far as 100 km ∗ Corresponding author. Tel.: +91 3365175505. E-mail addresses: scdind2000@yahoo.com (S.C. Dutta), rroybec@yahoo.com (R. Roy). (328 × 10 3 ft or 62 miles) from the epicentral tract, as shown in Fig. 1 [1]. It is observed from the reconnaissance study after the recent North Kashmir earthquake, India on 8th October, 2005 that an overhead water tank (Fig. 2) supported by shaft staging suffered circumferential flexural tension and shear cracking [2]. It is worth mentioning that the tank was empty at the time of earthquake. Similar observation was also made in the past, as described in Fig. 3 in the sample form [1]. Such cracks may seriously affect the lateral load-carrying capacity, increasing their susceptibility to a greater damage or collapse in the recurrence of such an event. Impact of soil–structure interaction is ignored in many ear- lier studies on the seismic behavior of elevated water tanks [3–6]. In fact, a number of elevated water tanks, failed in last Bhuj earth- quake of Gujrat, India, 2001 [1,7], are found to have propensity to experience increased spectral ordinate with an increase in the lateral natural period of vibration. Hence, a slight underestima- tion of the lateral natural period, under such circumstances, may lead to an underestimation of the design forces of the structure. In this context, the investigation, through practical examples, demon- strates the vulnerability of such elevated water tanks because of the tension likely to be developed in the shaft walls at tank-empty condition, particularly if the effect of soil–structure interaction is ignored in design. Investigation on the possibility of the genera- tion of such tension in the columns of the frame-supported ele- vated water tanks may also be of interest and hence included in the sample form. A simple approximate method is also proposed to estimate the base shear of the elevated tanks incorporating the effect of soil–structure interaction. 0141-0296/$ – see front matter © 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.engstruct.2009.06.010