Abstract    Water storage tanks not designed explicitly for seismic loading could require retrofit. One of the common ways of retrofit include some structural change in the lateral load resisting system that could be expensive and requires the tank to be out of service for relatively long time. This paper introduces a novel method to reduce seismic demand on tank’s wall without structural intervention. This is done by employing air cushions adjacent to the wall. The paper investigates the effect of air cushion system on the seismic response of the cylindrical water storage tanks. While in tank without air cushion, the boundary condition adjacent to tank wall is kinematic with no control on the wall pressure, in the proposed method this boundary condition becomes kinetic, enabling control of dynamic fluid pressure on the tank walls. The response parameters of the tank is developed in terms of wall pressure, wave height, base shear, and overturning moment in cylindrical tanks of different sizes with and without air cushions under the far field and near source ground motions. The results demonstrate that the proposed method is an effective way to reduce sloshing force demand.

Keywords    Keywords: Cylindrical water storage tanks, Air cushion, Seismic response, boundary condition, Wall pressure.

چکیده    مخازن ذخیره آب که برای بارهای لرزه ای طراحی نشده اند، اغلب نیازمند بهسازی هستند. روش‌ معمول بهسازی لرزه‌ای در برگیرنده تغییراتی در سیستم سازه‌ای مخازن می‌باشد که هزینه­بر بوده و توام با خروج از سرویس مخزن برای زمان طولانی است. مقاله حاضر روشی جدید مبتنی بر کاهش نیاز در دیواره‌های مخازن تحت بارگذاری لرزه‌ای معرفی مي­نمايد که نيازمند تغییر در سازه مخزن نیست. اين امر با تعبیه بالشتک هوا در حد فاصل ديوار مخزن و سيال انجام مي­شود. در مخازن عادی (بدون بالشتک) شرایط مرزی دیواره مخزن سینماتیکی است و هیچ‌گونه کنترلی روی فشار سیال وارد بر دیواره مخزن وجود ندارد. با تعبیه بالشتک، شرایط مرزی در دیواره سینتیکی شده، امکان کنترل فشار سیال بر روی دیواره مخزن ایجاد مي­گردد. در اين مقاله، پاسخ مخزن شامل فشار سیال بر دیواره، ارتفاع موج، برش و لنگر خمشی در مخازن استوانه‌ای به ابعاد مختلف با و بدون بالشتک هوا برای زلزله‌های حوزه دور و نزدیک ارائه شده و کارایی سيستم پيشنهادی بررسی شده است. نتایج نشانگر آن است که روش ارائه‌شده یک روش مؤثر برای کنترل نیروی ناشی از مواج شدگی است.

References    1.     Hashemi, S., Saadatpour, M. and Kianoush, M., "Dynamic behavior of flexible rectangular fluid containers", Thin-Walled Structures,  Vol. 66, (2013), 23-38. 2.     Kianoush, M. and Ghaemmaghami, A., "The effect of earthquake frequency content on the seismic behavior of concrete rectangular liquid tanks using the finite element method incorporating soil–structure interaction", Engineering Structures,  Vol. 33, No. 7, (2011), 2186-2200. 3.     Shekari, M., Khaji, N. and Ahmadi, M., "A coupled be–fe study for evaluation of seismically isolated cylindrical liquid storage tanks considering fluid–structure interaction", Journal of Fluids and Structures,  Vol. 25, No. 3, (2009), 567-585. 4.     Shekari, M., Khaji, N. and Ahmadi, M., "On the seismic behavior of cylindrical base-isolated liquid storage tanks excited by long-period ground motions", Soil Dynamics and Earthquake Engineering,  Vol. 30, No. 10, (2010), 968-980. 5.     Malhotra, P.K., "New method for seismic isolation of liquid-storage tanks", Earthquake Engineering & Structural Dynamics,  Vol. 26, No. 8, (1997), 839-847. 6.     De Angelis, M., Giannini, R. and Paolacci, F., "Experimental investigation on the seismic response of a steel liquid storage tank equipped with floating roof by shaking table tests", Earthquake engineering & Structural Dynamics,  Vol. 39, No. 4, (2010), 377-396. 7.     Anderson, J.G., "Liquid sloshing in containers: Its utilisation and control", Victoria University of Technology,  (2000). 8.     Guzel, B.U., Gradinscak, M., Semercigil, S.E. and Turan, O.F., "Control of liquid sloshing in flexible containers: Part 1. Added mass", in 15th Australasian Fluid Mechanics Conference, University of Sydney, Sydney, Australia. (2004(. 9.     Guzel, B., Gradinscak, M., Semercigil, S. and Turan, Ö., "Tuning flexible containers for sloshing control", IMAC XXIII, (2004(. 10.   Gradinscak, M., "Liquid sloshing in containers with flexibility", Victoria University,  (2009). 11.   Mousavi, J. and Tariverdilo, S., "Employing internal flexible wall as mass absorber in tanks subjected to harmonic excitations", International Journal of Engineering-Transactions A: Basics,  Vol. 27, No. 10, (2014), 1527-1536. 12.   Mahmoudi, R., Ashrafzadeh, F. and Tariverdilo, S., "Introducing padded wall to reduce sloshing induced wall pressure in water storage tanks", International Journal of Engineering-Transactions C: Aspects,  Vol. 27, No. 12, (2014), 1823-1832. 13.   Ibrahim, R.A., "Liquid sloshing dynamics: Theory and applications, Cambridge University Press,  (2005(. 14.   Hernandez-Barrios, H., Heredia-Zavoni, E. and Aldama-Rodriguez, A.A., "Nonlinear sloshing response of cylindrical tanks subjected to earthquake ground motion", Engineering Structures,  Vol. 29, No. 12, (2007), 3364-3376. 15.   Council, B.S.S., "Nehrp recommended provisions for seismic regulations for new buildings and other structures (fema 450): Provisions, Building Seismic Safety Council, National Institute of Building Sciences,  (2004(. 16.   American Concrete Institute, "Seismic design of liquid containing concrete structures",  (2006(. 17.   Housner, G., "Dynamic pressure on fluid containers", TID-7027, Nuclear Reactors and Earthquakes,  Vol., No., (1963), 183-209.