SEISMIC ANALYSIS OF RC ELEVATED WATER TANK IN DIFFERENT SEISMIC ZONES

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1 International Journal of Civil Engineering and Technology (IJCIET) Volume 10, Issue 02, February 2019, pp , Article ID: IJCIET_10_02_234 Available online at ISSN Print: and ISSN Online: IAEME Publication Scopus Indexed SEISMIC ANALYSIS OF RC ELEVATED WATER TANK IN DIFFERENT SEISMIC ZONES L.Raghava Naidu M.TECH student, JNTU college of engineering,anantapuram,india, Dr.H.Sudarsana Rao Professor in CIVIL department, JNTU college of engineering, Anantapuram,India Dr.Vaishali G Ghorpade Professor in CIVIL department, JNTU college of engineering, Anantapuram,India ABSTRACT Elevated water tanks are becomes most vital life line structures in earthquake prone areas. These structure are generally used to store the liquids in containers which are placed at the top end of assisting systems (staging s) and are most effected by seismic forces during earthquakes. They are very important in water supply, fire-frightening systems and also in many industrial use to store water. At the time of earthquake, damage to these tanks creates so many problems like interruption in drinking water supply, creates uncontrollable flames when damage to tank with flammable fluids in industries. So therefore these elevated water tanks must remain in working condition even after the earthquake. Due to this reason, a very large studies carried on seismic behavior of tanks at different conditions. In this, we are going to analyze the tank under seismic forces with the variations of different seismic zones and shape of containers e.g. rectangular tank and circular tank with constant staging height. In this paper, analysis is carried according with IS (i.e. single lumped mass method) and IS (i.e. two mass model method), by changing seismic zone and soil type i.e. hard rock and soft soil. Analysis is carried out for two different tank fill conditions i.e. full and empty tank conditions. Seismic forces acting on the tank are evaluated by the response spectrum method by changing response spectrum value (R), by using the software STADD PRO. Seismic response such as nodal displacement, base shear, base moment, shear force& bending moment are evaluated and compared. Key words: Elevated water tank, Lumped mass model, Two mass model, Base shear and base moment editor@iaeme.com

2 L.Raghava Naidu, Dr.H.Sudarsana Rao and Dr.Vaishali G Ghorpade Cite this Article: L.Raghava Naidu, Dr.H.Sudarsana Rao and Dr.Vaishali G Ghorpade, Seismic Analysis of Rc Elevated Water Tank in Different Seismic s, International Journal of Civil Engineering and Technology, 10(02), 2019, pp INTRODUCTION Generally, India is subjected to so many natural disasters like cyclones, earthquakes, floods etc. but 65% of India is frequently subjected to earthquakes are takes place first position in India. During earthquakes, it will not kill any human beings directly, but it badly damaging to build structures. After earthquake some existence losses are recovered but human beings loss are not. So, we need to concentrate for the proper design of tank to withstand during earthquakes. Water tanks are used to store water and supply to people in rural and urban areas. In industries tanks are used to store flammable liquids. Damaging to those structures creating so many problems like interruption to drinking water supply and creates uncontrollable fire when damage of flammable fluid tank. Elevated tanks generally stores water in container, which is placed at top of supporting systems. That is the most critical consideration for the dynamic analysis of water tank. So that for any tank, supporting system must be had greater resistance to take larger seismic forces during earthquakes. So in this study we are aiming to design suitable supporting systems and properties of tank in different seismic zones by considering both impulsive and convective masses by using STADD Pro. 2. SESIMIC ANALYSIS OF R.C TANKS: Generally the analysis of tanks for seismic forces are carried in to two ways 1. Static approach 2. Dynamic approach Static approach is traditional method for analysis of tank in which seismic forces are converted in to static loads. Seismic analysis of tank is carried with IS recommendations. For the converting of seismic load in to static load, So many factors comes in to action, those are zones, properties of soil at where we are analyzing and frequency of seismic loads. In static approach the structure and water are taken at same time for analysis. So that, the moment of water is not included in the analysis (sloshing action). Therefore, static approach is restricted and commonly used for to analyze the small capacities of tanks. For large capacity of tanks, dynamic approach is used Single lumped mass model: Generally in 1950 s, the analysis of tanks are carried by single mass model method. If a tank is completely packed with water, there is no movement of water tanks places in container during seismic forces. So that it is acting as a single lumped mass model. Therefore, in this method real character of fluid not comes in to picture editor@iaeme.com

3 Seismic Analysis of Rc Elevated Water Tank in Different Seismic s Figure 1. Structure behavior with the effect of both soil and water The analysis of tank is also mainly depending on the supporting system to carry mass of water which is locating at top of assisting system. In case of during seismic forces the total load acting on supporting structure. So, indirectly the life time of tank are depends on strength of supporting system. These are so many types of supporting structures are using for tanks those are in the form of steel and concrete. But supporting structure used for tank must had uniform rigidity at anywhere from top to bottom. These structures must have the resistance capacity to carry all the design forces. Figure 2. Single mass model But, generally concrete assisting systems used more to compare with steel structures. If it having same flexural rigidity tank behaving cantilever carrying water at top of supporting structure. So therefore the lateral stiffness of supporting structure can be calculated by assuming that the tank is cantilever carrying water at top. Generally this method is applied when water load (75%) more than gravity load (25%) Double lumped-mass model Figure 3. Two mass model editor@iaeme.com

4 L.Raghava Naidu, Dr.H.Sudarsana Rao and Dr.Vaishali G Ghorpade but, if tank is not completely filled with water it having some free space for the ease movement of water in case of seismic forces. So in this method sloshing effect of water comes in to play. Due to these seismic forces the dynamic action of water takes places. The water at the bottom of container behaves like rigid with structure and moves along with structure that mass is called as impulsive mass. The top portion of water undergoes sloshing effect and moves opposite direction to structure, called as convective mass. In this method both masses are taken in consideration for analysis, so that in this method real behavior of fluid present in container is known. That s why two mass models preferred over single mass model method. 3. DESIGN AND ANALYSIS OF WATER TANK 3.1. Problem statement: Capacity Dia. Of container Rectangular tank size Depth of water in container Free board Roof slab Bottom slab Bottom beam Wall Bracing column Depth of footing c/c distance between column 1,00,000 liter 5.89 m 7m x 4m 4.0 m 0.3 m 140 mm 270 mm 300 x 700 mm 200 mm 250 x 350 mm 4 nos mm dia 2.0 m 4.31 m 4. RESULTS Circular water tank Full tank condition Nodal displacement Horizontal Vertical Horizontal X(+ve) X(-ve) Y(+ve) Y(-ve) Z(+ve) Z(-ve) II III IV V editor@iaeme.com

5 Seismic Analysis of Rc Elevated Water Tank in Different Seismic s Base shear F x(kn) F y(kn) F z(kn) II III IV V Base moment Along X Along Y Along Z II III IV V Shear force bending moment Along X Along Y Along Z F x (KN) F y (KN) F z (KN) II II III III IV IV V V Empty tank condition Nodal displacement Horizontal Vertical Horizontal X(+ve) X(-ve) Y(+ve) Y(-ve) Z(+ve) Z(-ve) II III IV V Base shear F x (KN) F y (KN) F z (KN) II III IV V editor@iaeme.com

6 L.Raghava Naidu, Dr.H.Sudarsana Rao and Dr.Vaishali G Ghorpade Base moment Along X Along Y Along Z II III IV V Shear force Fx (KN) Fy (KN) Fz (KN) II III IV V Bending moment Along X Along Y Along Z II III IV V Rectangular water tank Full tank condition Nodal displacement Horizontal Vertical Horizontal X(+ve) X(-ve) Y(+ve) Y(-ve) Z(+ve) Z(-ve) II III IV V Base shear F x (KN) F y (KN) F z (KN) II III IV V editor@iaeme.com

7 Seismic Analysis of Rc Elevated Water Tank in Different Seismic s Shear force Base moment Along X Along Y Along Z II III IV V bending moment F x (KN) F y (KN) F z (KN) Along X Along Y Along Z II III II IV III V IV V Empty tank condition Nodal displacement Horizontal Vertical Horizontal X(+ve) X(-ve) Y(+ve) Y(-ve) Z(+ve) Z(-ve) II III IV V Base shear F x (KN) F y (KN) F z (KN) II III IV V Base moment Along X Along Y Along Z II III IV V editor@iaeme.com

8 L.Raghava Naidu, Dr.H.Sudarsana Rao and Dr.Vaishali G Ghorpade Shear force F x (KN) F y (KN) F z (KN) II III IV V Bending moment Along X Along Y Along Z II III IV V SEISMIC RESPONSES AS PER LUMPED MASS AND TWO MASS IDEALIZATIONS: Base shear ( tank full) Soil type Lumped mass model Two mass model -III -V -III -V Soft soil Hard rock Base shear ( tank empty) Soil type Lumped mass model Two mass model -III -V -III -V Soft soil Hard rock Base moment ( tank full) Soil type Lumped mass model Two mass model -III -V -III -V Soft soil Hard rock editor@iaeme.com

9 Seismic Analysis of Rc Elevated Water Tank in Different Seismic s Base moment ( tank empty) Soil type Lumped mass model Two mass model -III -V -III -V Soft soil Hard rock GRAPHS: Figure 4. Variation of Base shear against seismic zone in case of tank full condition Figure 5.Variation of Base shear against seismic zone in case of tank empty condition Figure 6. Variation of Base moment against seismic zone in case of tank full condition editor@iaeme.com

10 L.Raghava Naidu, Dr.H.Sudarsana Rao and Dr.Vaishali G Ghorpade Figure 7. Variation of Base shear against seismic zone in case of tank empty condition 6. CONCLUSION Following are the conclusions based on the dynamic analysis of water tank are as follows: 1. Base shear, nodal displacements, shear force& bending moment are increased in full water tank and empty water tank with the changing of seismic zone from II-V because of change in zone factor& response reduction factors. 2. Base shear in empty water tank is slightly less than full water tank due to the absence of hydro-static pressure. 3. Maximum and minimum nodal displacements are formed at the wall of water tank when the tank is full condition. 4. Shear force& bending moment in empty tank slightly less than full tank condition due to the absence of hydro static pressure. 5. The analysis of tank as lumped mass model is applicable to closed tanks with the full of water. Hence tanks with free board are analyzed by using two mass model of tank. 6. Base shear and base moments obtained from lumped mass method are far less than two mass model methods. Hence lumped mass model method should not used for dynamic analysis of water tanks. REFERENCES [1] Gaikwad, M.V. (2013). Comparison between static and dynamic analysis of improved water tank. International Journal of Civil Engineering and Technology, four (3), [2] Gaikwad, M.V.(2013). Seismic performance of Circular Elevated Water Tank with Framed Staging. International Journal of advanced studies in Engineering and Technology, 4(four), [3] Hirde, S., Bajare, A. And Hedaoo, M. (2011). Seismic overall performance of elevated water tanks. International Journal of Advanced Engineering Research and Studies, 1(1), seventy eight-87. [4] IITK-GSDMA (2007). Guidelines for seismic design of liquid storage tanks, National Information Centre for Earthquake Engineering, IIT Kanpur. [5] IS: Criteria for Earthquake Resistant Design of Structures, Bureau of Indian Standards, New Delhi. [6] IS:1893(Part-1) Criteria for Earthquake Resistant Design of Structures, Bureau of Indian Standards, New Delhi editor@iaeme.com

11 Seismic Analysis of Rc Elevated Water Tank in Different Seismic s [7] IS:1893(Part-2) Criteria for Earthquake Resistant Design of Structures Part 2 Liquid Retaining Tanks, Bureau of Indian Standards, New Delhi. [8] IS: Criteria for Design OfRcc Staging For Overhead Water Tanks, Bureau of Indian Standards, New Delhi. [9] Jaiswal, O.R., Jain, S.K. (2005). Modified proposed provisions for a seismic layout of liquid storage tanks: Part I codal provisions. Journal of Structural Engineering, 32(3), [10] Jaiswal, O.R, and Jain, S.K. (2005). Modified proposed provisions for a seismic design of liquid storage tanks: Part II remark and examples. Journal of Structural Engineering, 32(4), [11] Jain, S.K., and Sajjad, S.U. (1993). A Review of necessities in Indian codes for a seismic design of Elevated water tanks. The Bridge and structural Engineering, [12] (1), [12]Ekbote, S.P. (2013). Seismic behaviour of RC expanded water tank below exclusive styles of staging sample. Journal of Engineering, Computers & Applied Sciences, 2(eight), [13] Vamsidhar, S. (2007). Analysis of water Tanks according with IS: (Part-II) Draft code. Indian Concrete Institute Journal, 7(four), editor@iaeme.com