Seismic Behavior Evaluation of Concrete Elevated Water Tanks (original) (raw)
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Seismic Behavior Assessment of Concrete Elevated Water Tanks
Journal of Rehabilitation in Civil Engineering, 2013
Elevated tanks are very important structures and consist of various types. Water supply is vital to control fires during earthquakes. Also they are utilized to store different products, like petroleum supplies in cities and industrial zones. Damage to these structures during strong ground motions may lead to fire or other hazardous events. Elevated tanks should stay functional after and before earthquakes. However their dynamic behavior differs greatly in comparison with other structures. In this research, a sample of reinforced concrete elevated water tank, with 900 cubic meters capacity, exposed to three pair of earthquake records have been studied and analyzed in time history using mechanical and finite-element modeling technique. The liquid mass of tank is modeled as lumped masses known as sloshing mass, or impulsive mass. The corresponding stiffness constants associated with these lumped masses have been worked out depending upon the properties of the tank wall and liquid mass....
Seismic Evaluation of Elevated Water Tank Models under Different Earthquake Characteristics
—Seismic analysis of hydrodynamic structure such as elevated concrete water tank is somewhat complex when compared with other structures. Also, dynamic fluid-structure interaction (FSI) plays an important effect in this complexity. The main objective of this study is the analytical evaluation of seismic response of elevated water tanks under different earthquake time history records with SAP2000 structural software. Two models were simulated in empty, Half-full and full condition. For later conditions water mass has been considered in two parts as impulsive and convective suggested by GSDMA guidelines. In addition to that impulsive mass of water has been added to the container wall using Westergaard's added mass approach. Tank responses including base shear, overturning moment and roof displacement have been observed, and then the results have been compared and contrasted. The result shows that the structure responses are exceedingly influenced by the presence of water and the earthquake characteristics.
As we know from past records, many of reinforced concrete elevated water tanks were heavily damages or collapsed during the earthquakes all over the world. General observations are pointing out the reasons towards the failure of supporting system which reveals that the supporting system of the elevated tanks has more critical importance than the other structural parts of tanks. Most of the damages observed during the seismic events arise was might be due to the lack of knowledge regarding the proper behaviour of supporting system of the tank against dynamic effect and also due to improper geometrical selection of staging patterns. The main objective of this study is to understand the behaviour of supporting system which is more effective under different earthquake characteristics or earthquake zones with STAAD. Pro V8i software. A sample of a reinforced concrete elevated water tank (Intz type), with 900 cubic meters and with a height of 18m from ground level is considered. Here two different staging patterns such as radial bracing and cross bracing are compared with basic supporting system for various fluid filling conditions. The seismic zones of Zone-III & Zone-V and the corresponding earthquake characteristics have been taken from IS 1893 (PART 1)-2002 & draft code IS 1893 (Part 2). Consequently the water mass has been considered in two parts as impulsive and convective suggested by GSDMA guidelines. Tank responses including base shear, overturning moment and roof displacement have been observed, and then the results have been compared and contrasted. The result shows that the structure responses are exceedingly influenced by the presence of water and the earthquake characteristics. Finally study discloses the importance of suitable staging configuration to remain withstands against heavy damage or failure of elevated water tank during seismic events.
Seismic Assessment of Elevated Circular Water Tank
The present study reports the analysis and design (Response Spectrum Analysis, Frequency Analysis and Time History Analysis) of an elevated circular water tank using STAAD.Pro V8i. The design involves load calculations manually and analysing the whole structure by STAAD.Pro V8i. The design method used in STAAD.Pro analysis is Limit State Design and the water tank is subjected to live load, dead load, self – weight and seismic loads. Seismic load calculations are done as per IS 1893-2000. Response Spectrum Analysis gives displacement, bending moment, shear force, axial force, and torsion values. Eigen solution so obtained helps in determining the base shear and various peak story shear values of the structure. Frequency analysis gives the natural frequency of the structure and time history, which defines the behaviour of the structure in certain interval of time against various functions like velocity, displacement and acceleration and hence the graphical solutions has been drawn for each analysis. Notations: 1. CPS = Cycles per second 2. D.L. = Dead Load 3. E.L. = Earthquake Load 4. f ck = Compressive Strength of Concrete (Mpa) 5. f y = Yield Stress of Steel (Mpa) 6. L.L. = Live Load 7. STAAD.Pro = Structural Analysis and Design for Professionals 1. Introduction and Background Storage tanks are built for storing water, liquid petroleum, petroleum products and similar liquids. Analysis and design of such tanks is independent of chemical nature of product. They are designed as crack free structures to eliminate any leakage. Adequate cover to reinforcement is necessary to prevent corrosion. In order to avoid leakage and to provide higher strength, concrete of grade M30 and above is recommended for liquid retaining structures. A new procedure to determine hydrodynamic pressures for rectangular tanks was discussed by Chen J.Z & Kianoush M.R [1] in which the effect of wall flexibility on impulsive pressures is considered and the behaviour of three types of open type tanks namely " shallow " , " medium " and " tall " , under seismic ground motions has been studied. For dynamic time history analysis Chen J.Z & Kianoush M.R [1] uses three suites of time history representing low, medium and high earthquake zones and while calculating the hydraulic pressure they assumed that the liquid storage tank is fixed to the rigid foundation and a Cartesian coordinate system has been used with origin located at the centre of the tank base. The motion of water relative to tank and motion of tank relative to ground was accounted by Housner G.W[2] which indicates a simplified dynamic analysis for the response of elevated water tanks to earthquake ground motion and it has also been pointed out that if a closed tank is completely full of water or completely empty, it is essentially a one-mass structure and if the tank has a freewater surface, there will be slashing of the water during an earthquake and this makes the tank essentially a two-mass structure. The earthquake performance of storage tanks in terms of earthquake resistance in Turkish industrial facilities was evaluated by Korkmaz K.A Et.Al [4] who believed that modelling a typical storage tank of an industrial
Dynamic analysis and seismic performance evaluation of above-ground liquid-containing tanks
Engineering Structures, 2008
A large number of industrial facilities were damaged during the 1999 M w 7.4 Kocaeli, Turkey earthquake. One of those industrial facilities, Habas plant located within 10 km of the fault trace, provides liquefied gases to commercial plants and medical facilities. Two of the three tanks at the Habas facility collapsed during the earthquake. The main objectives of this paper were to evaluate the seismic performance of tanks and investigate the parameters influencing the dynamic behaviour. Simplified and finite element dynamic analyses of the tanks are carried out including the effect of liquefied gas-structure interaction using a ground motion recorded at a nearby site. The vulnerabilities of the structural system, the observed performance, and damage pattern are discussed by comparing the dynamic analysis results with the strength and deformation capacity of the support columns. The dynamic analysis results from a simplified three-mass model and a finite element model confirmed that the axial and lateral strength of the columns supporting the two nearly full tanks were not sufficient to resist the demand imposed during the earthquake. Consistent with the observed structural performance, an elastic response is predicted for the columns supporting the undamaged 25% full identical tank.
Dynamic response of ground supported rectangular water tanks to earthquake excitation
Momona Ethiopian Journal of Science, 2017
This study investigates an idealized ground supported reinforced concrete rectangular water tank under earthquake excitation. A linear three-dimensional finite element analysis and SAP2000 software have been used to predict tank response. The variable analysis parameters considered are the aspect ratio (tank height to length ratio) and tank water level, while the tank wall thickness is taken as a constant. The convective and impulsive masses are also represented by spring-mass model in the time history analysis for El-Centro earthquake ground motion record. Five tank models with a capacity of 216, 288, 360, 432 and 504 m 3 were developed and analyzed for hydrodynamic and hydrostatic effects. In general the results show that, there is a smooth increase in the moment and displacement of both hydrostatic and hydrodynamic analysis with a decrease in aspect ratio. The top displacement and moment for the hydrodynamic effects are greater than the hydrostatic results and it is observed that the maximum hydrodynamic moment is 91.3% higher than the corresponding maximum hydrostatic moment. Likewise the displacement obtained from hydrodynamic analysis is 63.58% more than the corresponding hydrostatic value.
RESPONSE OF ELEVATED WATER STORAGE TANKS UNDER SEISMIC EVENTS
IRJET, 2022
The current analysis and designs of elevated overhead tanks are extremely weak under adjacent forces due to an earthquake zone. In the past earthquakes, it has ensued found that the reinforced concrete elevated overhead tanks under lateral earthquake loads were suspectable where in some cases the structure has experienced collapse. Whereas the water works as an important role in the dayto-day life of a human being the elevated tanks should be designed as per the code provisions so that to avoid the failures of the structure and for the life of the structure. The study and creation of the elevated overhead tanks are done in ETABS software according to Indian Standards Codes. The reinforced concrete elevated water storage tank and the steel elevated water storage tanks have been designed for a full tank condition and the response spectrum plots and the time-history plots are also generated along with displacements & drifts. The columns and beams of the reinforced concrete storage tank are designed in accordance with IS456:2000 and the steel water tank is designed in accordance with IS800:2007. The designed structure is analyzed to check the reaction of the structure under the seismic events and the time history analysis is also being analyzed from the previous records.
A STUDY ON THE SEISMIC RESPONSE OF ELEVATED WATER TANK
IRJET, 2022
Water tanks have been the most vital lifeline structures. They serve as an essential component for most water supply schemes in urban and rural areas. Water storage is generally based on overhead water tanks since the required pressure in the water delivery process is achieved by gravity in elevated tanks rather than the need for large pumping systems. These elevated tanks consist of a large water mass at the top supported by a tall staging which is extremely weak against horizontal forces caused due to earthquakes. The selection of a suitable staging system plays a major role in the behaviour of elevated water tanks during earthquakes since these tanks are often utilized in seismically active regions. The ductility and energy absorbing capacity of such elevated tanks are less compared to conventional building and hence seismic safety of such structures are very important. Soil-structure interaction (SSI) is one of the most essential components of structural analysis. This interaction can change the Dynamic characteristics of a structure, which can be advantageous or detrimental to its performance. Conventional fixed base analysis disregards the effect of soil flexibility, resulting in an unsafe design. The present work is focused on the study of seismic response of elevated water tank considering the sloshing effect and to evaluate the behaviour considering Soil-Structure Interaction (SSI) effect in seismic Zone (II and III). Different soil conditions are also adopted as per IS1893(Part 2):2014. Modelling and analysis has been carried out using FEM based software SAP2000.
Seismic Performance of Circular Elevated Water Tank
International Journal of Science and Research (IJSR), 2015
Liquid storage tanks are used in industries for storing chemicals, petroleum products, and for storing water in public water distribution systems. Behaviour of Cylindrical liquid storage tanks under earthquake loads has been studied as per Draft code Part II of IS 1893:2002. A FEM based computer software (STAAD-PRO) used for seismic analysis of tanks which gives the earthquake induced forces on tank systems. Draft code Part II of IS 1893:2002 which will contain provisions for all types of liquid storage tanks. Under earthquake loads, a complicated pattern of stresses is generated in the tanks. Poorly designed tanks have leaked, buckled or even collapsed during earthquakes. Common modes of failure are wall buckling, sloshing damage to roof, inlet/outlet pipe breaks and implosion due to rapid loss of contents. Elevated water tanks should be competent of keeping the expected performance during and after earthquake. It has large mass concentrated at the top of slender supporting structure hence extremely vulnerable against horizontal forces due to earthquake. Staging is formed by a group of columns and horizontal braces provided at intermediate levels to reduce the effective length of the column. In this research, a circular cylindrical elevated water tank is analysed by using finite modelling techniques. This paper presents the study of seismic performance of the elevated water tanks for various heights and various seismic zones of India. The effect of height of water tank, earthquake zones on Nodal displacement have been presented in this paper with the help of analysis of 20 models for same parameters. Analysis is carried out by using finite element software STAAD-PRO.
Evaluation of Seismic Performance Factors for Elevated Reinforced Concrete Tanks
IABSE Conference, Sharm El-Sheikh 2012: Global Thinking in Structural Engineering: Recent Achievements, 2012
This paper presents a proposed methodology for reliable determination and evaluation of the seismic performance factors of elevated reinforcement concrete cylindrical tank with a frame supporting structure. The paper focuses on developing an analytical methodology using numerical modelling of representative archetype structural system. ACI 350.3-06 (Seismic Design of Liquid-Containing Concrete Structures and Commentary) [1] does not explicitly address the seismic design performance factors for this important structure. Furthermore, ASCE 7-05 (Minimum Design Loads for Buildings and Other Structures) [2] does not have an explicit provision relevance to seismic design of liquid-containing concrete structure. Therefore, the purpose of this study is to propose a reliable basis for defining/evaluating such seismic design parameters. The recommended methodology was based on the approach developed using the ATC-63 (2008); Quantification of Building Seismic Performance Factors, subsequently published as FEMA P695 (2009) [3]. The methodology referred to herein as "ATC-63" [3] represents a broad knowledge base of standard building code concepts, structural systems, relevant research and technologies utilizing state-of-theart nonlinear dynamic analysis and collapse simulation to reliably quantify system performance and response parameters for use in seismic design. In this study seismic performance factors including Qo overstrength factor, d ductility factor and R response modification factor of elevated reinforced concrete tanks were determined and evaluated by performing nonlinear static pushover analysis and nonlinear incremental dynamic time history analysis. The nonlinear dynamic time history analysis is realized by Far-Field Maximum Considered Earthquake (MCE) level ground motions consistent with ASCE 7-05 [2] provisions using three different earthquake data: El-Centro, Parkfield and Pacoima ground motion. Fluid-structure interaction is simulated using simplified analysis procedures: Housner's model. Based on the analysis results, Damage Index from the nonlinear time-history analysis is compared to that obtained by pushover analysis procedures.