International Journal of Civil Engineering and Technology (IJCIET), ISSN INTERNATIONAL JOURNAL OF CIVIL ENGINEERING

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1 INTERNATIONAL JOURNAL OF CIVIL ENGINEERING AND TECHNOLOGY (IJCIET) ISSN (Print) ISSN (Online) Volume 5, Issue 8, August (2014), pp IAEME: Journal Impact Factor (2014): (Calculated by GISI) IJCIET IAEME SEISMIC ANALYSIS OF SINGLE DEGREE OF FREEDOM STRUCTURE Khaza Mohiddin Shaik 1, Prof. Vasugi K 2 1 B.Tech Civil Engineering, Vellore Institute of Technologies, Chennai, Tamilnadu, India 2 Assosiate Professor, Civil Engineering Department, Vellore Institute of Technologies, chennai, Tamilnadu, India ABSTRACT In this study, Wind Force and Seismic forces acting on an Elevated water tank e.g. Intze Tank are studied. Seismic forces acting on the tank are also calculated changing the Seismic Response Reduction Factor(R). IS: /2002 for seismic design and IS: (Part III) for wind load has been referred. Then Analyzed the Elevated Tank by using the software STAAD PRO. Reinforcement detailing is done for the Tank. Base Shear and Base Moment are calculated and compared the results for Tank Full Condition and Empty Condition and found that the Base shear in the full tank condition is high and Base moment also high in the case of tank full condition. With the increase in R value Base Shear and Base Moment decreases. Considering the design aspect, the seismic forces remain constant in a particular Zone provided the soil properties remain same whereas the Wind force is predominant in coastal region, but in interior region earthquake forces are more predominant. Design of Elevated Tank is done by calculating the all Horizontal Thrust, Meridonal stress, Hoop Tension, Hoop Stress and Reinforcement is calculated for Top spherical Dome, Top Ring Beam, cylindrical wall, Bottom Ring Beam, Conical Portion, Circular Beam, Columns and Staging s and then Detail Drawing of Reinforcement is Done. Keywords: Seismic Analysis, Staad Pro, Base Shear, Base Moment. I. INTRODUCTION An Earthquake is a phenomenon that results from and is powered by the sudden release of stored energy in the crust that propagates Seismic waves. At the Earth's surface, earthquakes may manifest themselves by a shaking or displacement of the ground and sometimes tsunamis, which may lead to loss of life and destruction of property. Seismic safety of liquid tanks is of considerable importance. Water storage tanks should remain functional in the post-earthquake period to ensure potable water supply to earthquake-affected regions and to cater the need for firefighting demand. 44

2 (Print), ISSN (Online), Volume 5, Issue 8, August (2014), pp IAEME Industrial liquid containing tanks may contain highly toxic and inflammable liquids and these tanks should not lose their contents during the earthquake. The current design of supporting structures of elevated water tanks are extremely vulnerable under lateral forces due to an earthquake as it is designed only for the wind forces but not the seismic forces. The strength analysis of a few damaged shaft types of staging s clearly shows that all of them either met or exceeded the strength requirement of IS: however they were all found deficient when Compared with requirements of International Building Codes. Frame type stagings are generally regarded superior to shaft type of staging s for lateral resistance because of their large redundancy and greater capacity to absorb seismic energy through inelastic actions. This implies that design base shear for a low ductility tank is double that of a high ductility tank. Indian Standard IS: provides guidelines for earthquake resistant design of several types of structures including liquid storage tanks. This standard is under revision and in the revised form it has been divided into five parts. First part, IS 1893 (Part 1): 2002; which deals with general guidelines and provisions for buildings which is used as a Reference Code and for Ductile Detailing the IS 13920Code book is Preferred. II. LITERATURE REVIEW According to Guidelines of Seismic Design of Liquid Storage Tanks. In the spring mass model of tank, h i is the height at which the resultant of impulsive hydrodynamic pressure on wall is located from the bottom of tank wall. On the other hand, h i *is the height at which the resultant of impulsive pressure on wall and base is located from the bottom of tank wall. Thus, if effect of base pressure is not considered, impulsive mass of liquid, mi will act at a height of hi and if effect of base pressure is considered, mi will act at h i *. Heights h i and hi*, are schematically described in Figures. 45

3 (Print), ISSN (Online), Volume 5, Issue 8, August (2014), pp IAEME Provisions:- Description:- T i = Time period of impulsive mode T c = Time period of convective mode (A h ) i = Design horizontal seismic coefficient for Impulsive mode. (A h ) c = Design horizontal seismic coefficient for Convective mode. V i = Base shear at the bottom of staging, in impulsive mode. V c =Base shear at the bottom of staging, in convective mode. V =Total base shear at the bottom of staging M i * = Overturning moment at the base of staging in mode M c * = Overturning moment at the base of staging in convective mode M =Total overturning moment d max =Sloshing Wave Height 46

4 (Print), ISSN (Online), Volume 5, Issue 8, August (2014), pp IAEME Response acceleration coefficient (S a /g). Fig.1 & Table 1: Geometry and size of the Structure Sl.No. Code Books Preferred 1 IS 3370(part 1):2009 water structures general. 2 IS 3370(part 2):2009 water structures using RCC. 3 IS 3370(part 4):2009.General tables. 4 IS 875( (part 3):2009: wind load. 5 IS design for earthquake loads. 6 Is Ductile Detailing 7 IS 456:2000 design for RCC structures. 8 SP: 16 Design aids. SP: 34 Hand book for concreting & detailing of 9 Reinforcement. Sl.No Table 2: - Code Books Preferred for Analysis Component Size(mm) Top Dome 120 thick Top Ring Beam 250*300 Cylindrical wall 200 thick Bottom Ring Beam 500*300 Circular Ring Beam 500*600 Bottom Dome 200 thick Conical Dome 250 thick Braces 300*600 Columns 650 Dia 47

5 LOAD COMBINATION FOR FOUNDATION (IS1893) 1) 1(SW+D.L+L.L) 2) 0.75(SW+D.L±ELX) 3) 0.75(SW+D.L±ELZ) 4) 0.75(SW+D.L+R.LL±ELX) 5) 0.75(SW+D.L+R.LL±ELZ) Wind Load Combination in accordance with IS 875: 1964 Part3 1) DL+LL 2) 0.75 (DL + C, X WL,) 3) 0.75 (DL + c, X WL2) 4) 0.75 (DL + C, X WL,) Where C = 0.75 SEISMIC LOAD COMBINATION (As per IS1893): 1) ELX ± seismic load 2) ELZ ± seismic load 3) 1(SW+D.L+L.L) 4) 1.5(SW+D.L+L.L) 5) 1.2(SW+D.L+L.L±ELX) 6) 1.2(SW+D.L+L.L±ELZ) 7) 1.5(SW+D.L±ELX) 8) 1.5(SW+D.L±ELZ) 9) 0.9(SW+D.L) ±1.5ELX 10) 0.9(SW+D.L) ±1.5ELZ SPECIFICATIONS: 1) Grade of concrete - M25 2) Grade of steel - Fe 500D 3) Unit weight of concrete - 25 kn/m3 4) Height of Tank =16 m III. LOAD APPLICATION AND ANALYSIS OF ELEVATED TANK USING STAAD PRO Geometry (Size) &Property: 48

6 (Print), ISSN (Online), Volume 5, Issue 8, August (2014), pp IAEME STAAD MODEL Hydrostatic Load Application Post Processing (Mode Shape) Staad Analysis for the Model 49

7 IV. WEIGHT CALCULATIONS Top Dome (120thick): Radius of Curvature (R c ) =(r^2+h^2)/2h h= =1690=1.69m r= =8.8 (R c )= (((8.8)^2/1.69)+1.69)/2=6.57 Weight=2*π*6.57*1.69*0.12*25=209.3 KN. Top Ring Beam (250*300): r= ( ) =8.85 Weight=π*8.85*0.25*0.3*25= 52.1 KN Cylindrical Wall (200thick): r= =8.8 Weight=π*8.8*0.2*0.4*1000*25= 552.9KN Bottom Ring Beam (500*300): r= =9.1 Weight= (π*9.1*0.5*0.3*25) = KN Circular Ring Beam (500*600): r or l = =6.28 Weight=π*6.28*0.5*0.6*25=148KN. Bottom Dome (200 thick): r 2 =(r^2+h^2)/2h r=6.28/2=3.14 r 2 =1/2((3.14^2)/1.4) +1.4) =4.22m Weight=2*π*4.22*1.40*0.20*25=185.6KN Conical Dome (250 thick): Length of cone=l=square root of (h^2+r^2) h=1.65, r = 1.41, l=2.17 Weight=π*(( )/2)*2.17*0.25*25 =321.1KN Water: (((π*8.6^2*3.7)/4+π*1.5(8.6^2+5.63^2+ (8.6*5.63)/12))*9.81=2508 KN Total Weight of Water=2508 KN. Stagging Weight: Columns (650φ) Weight= (π*0.65^2*15.7*6*25)/4 =782 KN Braces (300*600): Weight=3.14*0.3*0.6*3*6*25=254KN From Above Results: Weight of Empty Container=Top Dome +Top Ring Beam + Cylindrical Wall + Bottom Ring Beam + Circular Ring Beam + Bottom Dome +Conical Dome = =1576KN. Weight of Stagging=Weight of Columns + Weight of Bracings = =1036KN. Hence, Weight of empty Container + 1/3(Weight of Stagging) =1576+ (1036/3) =1921KN Centre of Gravity of empty Container above top Circular Ring Beam= ((209.3*7.22) + (52.1*5.9) + (552.9*3.8) + (107.2*1.65) + (321.3*1) + (185.6*0.92)+ (148*0.3))/1576=2.88m Height of C.G. of empty container from top of footing =h cg Height up to Circular Ring Beam from the Footing = ( (0.6/2))=16.3 h cg = =19.18m 50

8 V. PARAMETERS OF SPRING MASS MODEL Total Weight of Water = N. Volume=2508 KN/9.81= m^3 Mass =255658kg D=8.6m Let h be height of equivalent circular Cylinder, (D/2) ^2*h=255.65h=4.4m Volume of water = 2,508 / 9.81 = m^3 h / D = 4.4 / 8.6 = 0.51 m i / m = 0.55; mi = 0.55 x 2,55,658 = 1,40,612 kg mc /m = 0.43; mc = 0.43 x 2,55,658 = 1,09,933 kg h i / h = 0.375; h i = x 4.4 = 1.65 m h * i /h =0.78, h i *= 0.78 x 4.4 = 3.43 m h c /h =0.61, hc = 0.61 x 4.4 = 2.68 m h * c /h =0.78, h c *= 0.78 x 4.4 = 3.43 m According to IS code,about 55% of Liquid mass is excited in impulsive mode while 43% liquid mass participates in convective mode.sum of impulsive and convective mass is 2,50,545kg which is about 2% less than the total mass of liquid. Mass of empty container+one third mass of staging, m s =( /3)*(1000/9.81)=195821kg. Table 3: Comparison of Base Shear and Moment for full tank and Empty Tank 51

9 VI. DESIGN OF ELEVATED TANK CONSIDERING SEISMIC FORCE I.Spherical Roof Dome (120mm) Total Load=4.5KN/m^2 Maximun Hoop Stress =0.083(N/mm^2) Meridonial Stress= 0.22 N/mm2 II.Design of Top Ring Beam Horizontal Thrust/cm length= 22.2 KN/m 2 (300x300mm) Hoop Tension= KN Tensile Stress= 10.9 Kg/cm 2 III.Design of Conical Dome Total Vertical Load= KN Meridonial Stress= N/mm 2 IV.Design of Bottom Dome: Tank will be at Chennai: Wind Speed: 50 m/s Thickness of Conical Dome= 350mm. Radius of Bottom Dome = m 200mm thickness is provided. Total Load= KN Meridonial Stress= N/mm 2 Hoop Stress= N/mm 2 V.Design of Cylindrical Wall VI.Design of Ring Beam at junction of cylindrical wall and conical wall VII.Design of Circular Beam Hoop Tension (Ft) = 172 KN/m Wall thickness is 250mm thick at base and 150mm at top Total Load= KN/m Meridonial Thrust in the Conical Dome= 48925N Total Hoop Tension= KN Tensile Stress= 1.05<1.2 N/mm Horizontal Thrust on circular beam= Kg/m Vertical load on beam /m= Kg/m Maximum Bending Moment (-ve) = 31330Kgm VIII.Design of Column(650Dia) IX.Design of Braces Total vertical load on column: 1944K N Provide 10mm Φ-2 legged c/c 52

10 VII. REINFORCEMENT DETAILING S.No. Component Reinforcement 1 Spherical Roof Dome 8mmφ@160 mm c/c both ways 2 Top Ring Beam 8,12mm Φ bars Main Reinforcement and 6mm Φ 20cm c/c are provided 3 Cylindrical Wall (0-2m) Main Hoop Steel 10mm-180mmc/c (2-4) vertical distribution 10mm-250mmc/c, (2-4m)Main Hoop Steel 10mm-180mmc/c (2-4) vertical distribution 10mm-250mmc/c. 4 Conical Dome Provide 25mm Φ both faces of the slab Distribution Steel c/c both faces along meridons 5 Bottom Dome 12mm Φ 120mm centers both circumferentially and meridonally. 6 Circular Beam Provide 6 bars of 20mm Φ at center and 5, 16mm Φ at support Shear Reinforcement: Provide 12 mm Φ, 6 legged 9cm c/c at support. Shear Reinforcement: Provide 12mm Φ, 4 legged 9cm c/c at center Longitudinal Steel: Provide 8 bars of 12mm Φ, 4 cm each face 7 Column Provide 8bars of 32 mm Φ and 10mm Φ ties at 300 mm c/c 8 Braces Provide 10mm Φ -2 legged c/c. VIII. REINFORCEMENT DRAWING OF ELEVATED WATER TANK 53

11 IX. RESULTS AND CONCLUSIONS 1. In India elevated tanks are widely used and these tanks have various types of supports. 2. Maintains hydraulic grade lines without automated controls. Provides pressure when power is lost. 3. Simple to operate Lower power cost because an elevated tank can be filled in evening when power costs are less. 4. The seismic design of the R/C elevated tanks, based on the rough Assumption that the subsoil is rigid or rock without any site investigation, may lead to a wrong assessment of the seismic base shear and overturning moment. 5. Suitable value of lower bound limits on spectral values for structure including tanks needs to be arrived at does not recommend consideration of Convective Mode of vibration. R Value taken in IS 1893:1984 is nowhere in the range corresponding to that value in different international Codes. 6. As per observed from Table 1, Base Shear and Base Moment have increased from Empty Tank Condition to Full Tank Condition. 7. we observe that due to change in place from Base Shear due to Wind Force decreases by 26% and Base Moment decreases by 18% 8. Analysis & design of elevated water tanks against earthquake effect is of Considerable importance. These structures must remain functional even after an earthquake. Elevated water tanks, which typically consist of a large mass supported on the top of a slender staging, are particularly susceptible to earthquake damage. Thus, analysis & design of such structures against the earthquake effect is of considerable importance. 9. Most elevated water tank are never completely filled with water. Hence, a two mass idealization of the tank is more appropriate as compared to one-mass idealization. 10. Basically, there are three cases that are generally considered while analyze the Elevated water tank (1) Empty condition. (2) Partially filled condition. (3) Fully Filled condition. For (1) & (3) case, the tank will behave as a one-mass structure and for (3) case the tank will behave as a two-mass structure. 11. If we compared the case (1) & (3) with case (2) for maximum earthquake force, the Maximum force to which the partially filled tank is subjected may be less than half the force to which the fully filled tank is subjected. Actual forces may be as little as 1/3 of the forces anticipated on the basis of a fully filled tank. 12. During the earthquake, water in the tank get vibrates. Due to this vibration water Exerts impulsive & convective hydrodynamic pressure on the tank wall and the tank base in addition to the hydrostatic pressure. 13. The effect of impulsive & convective hydrodynamic pressure should consider in the analysis of tanks. For small capacity tanks, the impulsive pressure is always greater than the convective pressure, but it is vice-versa for tanks with large capacity. Magnitudes of both the pressure are different. 14. The effect of water sloshing must be considered in the analysis. Free board to be provided in the tank may be based on maximum value of sloshing wave height. If sufficient free board is not provided, roof structure should be designed to resist the uplift pressure due to sloshing of water. 15. Earthquake forces increases with increase in Zone factor & decreases with increase in staging height. Earthquake force are also depends on the soil condition. 54

12 REFERENCES 1. Rai Durgesh C; Performance of Elevated Tanks in Bhurj Earthquake ; Proc. Indian Acad. Sci. (Earth Planet Sci.), 112, No. 3, September 2003, pp Jaiswal O. R., Rai Durgesh C and Jain Sudhir K; Review of Code Provisions on Design Seismic forces for Liquid Storage Tanks ; Document No.: IITK-GSDMA-EQ01-V1.0, Final Report: A - Earthquake Codes, IITK. 3. Indian Institute of Technology Kanpur, IITK GSDMA Guidelines for Seismic Design of Liquid Storage Tanks. 4. IS 1893:1984, Criteria for Earthquake Resistance Design of Structures. 5. IS 1893(Part I): 2002, Criteria for Earthquake Resistance Design of Structures. (PART 1: General Provisions and Buildings). 6. IS 875:1987, Code of Practice for Design Loads (Other than Earthquake) for Buildings and Structures Part 3: Wind Loads. 7. Vazirani & Ratwani, Concrete Structures, Khanna Publishers, Year of Publication Damodar Maity, C. Naveen Raj and Indrani Gogoi, Dynamic Response of Elevated Liquid Storage Elastic Tanks with Baffle, International Journal of Civil Engineering & Technology (IJCIET), Volume 1, Issue 1, 2010, pp , ISSN Print: , ISSN Online: Damodar Maity, C. Naveen Raj and Indrani Gogoi, Dynamic Response of Elevated Liquid Storage Elastic Tanks with Baffle, International Journal of Civil Engineering & Technology (IJCIET), Volume 1, Issue 1, 2010, pp , ISSN Print: , ISSN Online: Ming Narto Wijaya, Takuro Katayama, Ercan Serif Kaya and Toshitaka Yamao, Earthquake Response of Modified Folded Cantilever Shear Structure with Fixed-Movable-Fixed sub- Frames, International Journal of Civil Engineering & Technology (IJCIET), Volume 4, Issue 4, 2013, pp , ISSN Print: , ISSN Online: Vidula S. Sohoni and Dr.M.R.Shiyekar, Concrete Steel Composite Beams of a Framed Structure for Enhancement in Earthquake Resistance, International Journal of Civil Engineering & Technology (IJCIET), Volume 3, Issue 1, 2012, pp , ISSN Print: , ISSN Online: