PERFORMANCE BASED EVALUATION OF RESPONSE REDUCTION FACTOR FOR ELEVATED CIRCULAR WATER TANK

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1 International Journal of Recent Innovation in Engineering and Research Scientific Journal Impact Factor -. by SJIF e- ISSN: 8 PERFORMANCE BASED EVALUATION OF RESPONSE REDUCTION FOR ELEVATED CIRCULAR WATER TANK Dr.H.J.Puttabasavegowda, Shivaraj nayak and Ramya H S Professor, Civil Engineering Department, P. E. S College of Engineering /VTU Belgaum,India Assistant Professor, Civil Engineering Department, P. E. S College of Engineering /VTU Belgaum,India Post Graduate student, Department of civil engineering. P.E. S College of Engineering /VTU Belgaum,India Absract- Earthquakes are one of the most dangerous natural hazards causing damage and collapse to livelihood and they are the result of ground shaking caused by sudden release of energy in earth s lithosphere. Due to Earthquake ground motions, there is heavy economic and life loss. Most of the losses are due to collapse of structures such as buildings, bridges, water retaining structures. Response reduction factor is defined as the factor by which the actual base shear force should be reduced to obtain the design lateral force. It represents the ratio of the maximum lateral force VB (Design seismic base shear) which would develop in a structure to the Design base shear calculated using the approximate fundamental period Ta. To compare response reduction factor of elevated water tank having different capacities (m, m) for different seismic zones and also be evaluation of strength factor ductility factor and redundancy factor for all various seismic zones. Then evaluate the response reduction factor of elevated water tank for various capacities using non linear static (Pushover analysis) analysis in CSI SAP Software. Keywords Elevated storage reserviour,capacity of tank,different staging height different zone factor,base shear,over strength factor,ductility factor,redundancy factor,non linear-static analysis CSI SAP. I. INTRODUCTION. GENERAL: Water is considered as the source of every creation and is thus a very crucial element for humans to live a healthy life. High demand of clean and safe drinking water is rising day by day as one cannot live without water. It becomes necessary to store water. Water is stored generally in concrete water tanks and later on it is pumped to different areas to serve the community. One of the oldest known water tanks in kenya was built by the railway at makindu river in 97. It appears the tank was connected to a hydra pump that used the power of the flowing water in the river to push water into the tank from where it was used by steam locomotives. Water tanks can be classified as overhead, resting on ground or underground depending on their location. The tanks can be made of steel or concrete. Tanks resting on ground are normally circular or rectangular in shape and are used where large quantities of water need to be stored. Overhead water tanks are used to distribute water directly through gravity flow and are normally of smaller capacity. As the overhead water tanks are opening to public view, their shape is influenced by the aesthetic view in the surroundings.. NEED OF STUDY: It is very important to consider earthquake load in design of elevated tank. Response reduction factor (r) is very important to find out earthquake load. the response reduction factor reflects the capacity of structure to dissipate energy by inelastic behaviour. The purpose of this paper is to explore a methodology for evaluation of the response modification factor, r, of reinforced concrete frame staging (supporting system) elevated tanks, which behave in a ductile manner under seismic loads and expectedly fail in flexural mode instead of shear mode. The values of rights Reserved -8 Page

2 Volume: Issue: June 8 (IJRIER) reduction factor(r) of rc elevated water tank are given in is89 draft code, which is calculated at empirically based on engineering judgment.. OBJECTIVES: The main objective of this study is to verify the r factor of most common designed elevated intze tank through comparing the assumed r factor during design to actual r factor obtained from non-linear analysis. the specific objectives of the study are to: Conduct static non-linear (pushover) analysis and calculate r factor of elevated intze tank. Compare the calculated r factor with the assumed r factor. Evaluate ductility, redundancy and over strength factor of elevated circular water tank. Study the effect of staging height and staging type on response reduction factor (r). To study effect of zone factor on response reduction factor (r). II. DESIGN METHODOLOGY. SPRING MASS MODELING TECHNIQUE: Two mass model for elevated tank has been used for modeling fluid, was proposed by Houser, which is more appropriate and is being commonly used in most of the international codes including Draft code for IS 89 (Part-II). The pressure generated within the fluid due to the dynamic motion of the tank can be separated into impulsive and convective parts. When a tank containing liquid with a free surface is subjected to horizontal earthquake ground motion, tank wall and liquid are subjected to horizontal acceleration. The liquid in the lower region of tank behaves like a mass that is rigidly connected to tank wall. This mass is termed as impulsive liquid mass which accelerates along with the wall and induces impulsive hydrodynamic pressure on tank wall and similarly on base Liquid mass in the upper region of tank undergoes sloshing motion. This mass is termed as convective liquid mass and it exerts convective hydrodynamic pressure on tank wall and base. For representing these two masses and in order to include the effect of their hydrodynamic pressure in analysis, spring mass model is adopted for ground-supported tanks and two- mass model for elevated tanks as shown in Figure. Figure.: Two mass idealization for elevated tank Available Online at: Page

3 Volume: Issue: June 8 (IJRIER) In spring mass model convective mass (mc) is attached to the tank wall by the spring having stiffness Kc, whereas impulsive mass (mi) is rigidly attached to tank wall. For elevated tanks twomass model is considered, which consists of two degrees of freedom system. Spring mass model can also be applied on elevated tanks, but two - mass model idealization is closer to reality. The two - mass model is shown in Fig.. where, mi, mc, Kc, hi, hc, hs, etc. are the parameters of spring mass model and charts as well as empirical formulae are given for finding their values. The parameters of this model depend on geometry of the tank and its flexibility.. Review of basic component about response reduction factor: In the mid-98s, data from experimental research at the University of California at Berkeley were used to develop base shear-roof displacement relationships for steel braced frames and a draft formulation for the response modification factor. The base shear-roof displacement relationships were established using data acquired from the testing of two code-compliant braced steel frames; one concentrically braced (Uang and Bertero, 98) and one eccentrically braced (Whittaker et ai., 987). The force-displacement curves were developed by plotting the roof displacement at the time corresponding to the maximum base shear force for each earthquake simulation and each model. Response reduction factor is the factor by which the actual base shear force should be reduced, to obtain the design lateral force. The response reduction factor reflects the capacity of structure to dissipate energy by inelastic behaviour. This process is combined effect of over strength, redundancy and ductility. Response reduction factor is also known as ratio of maximum elastic force to designed force. Response reduction factor is depended on three factors. ) Over strength factor ) Ductility factor ) Redundancy factor R = Rs * RR * Rμ The concept of r factor is based on the observations that well detailed seismic framing systems can sustain large inelastic deformations without collapse and have excess of lateral strength over design strength. Response reduction (r) factors are essential seismic design tools, which are typically used to describe the level of inelasticity expected in lateral structural systems during an earthquake. The response reduction factor (r) is depends on over strength (rs), ductility (rμ), redundancy. a) Estimation of strength factor: The steps in the procedure are as follows:. using nonlinear static analysis, construct the base shear-roof displacement relationship for the building.. At the roof displacement corresponding to Available Online at: Page

4 Volume: Issue: June 8 (IJRIER) the limiting state of response, calculate the base shear force Vo in the building. The reserve strength of the building is equal to the difference between the design base shear (Vd) and (Vo'). Calculate the strength factor using the following expression: ) Strength factor is the ratio of Maximum Base Shear (from pushover curve) VO to Design Base shear (as per EQ calculation) Vd. Rs = Vo / Vd b) Estimation of ductility factor: Equations for estimation of ductility factor is as below: R μ = {(μ - / Ф) + } Ф for rock sites: = + { / (T -μt)} {( / T)*e^ (-(ln (T).) ^)} Ф for alluvium sites: = + { / (T -μt)} {( / T)*e^ (-(ln (T).) ^)} μ = Δm / Δy Δm = Maximum drift capacity (. H) Δy = Yield drift (from pushover curve) c) Estimation of redundancy factor: The value of redundancy factor as suggested in ATC-9 is summaries in Table. LINES OF VERTICAL SEISMIC DRIFT FRAMING.7.8. Hinge formation: The RC beams and columns are modeled as -D frame elements with centerline dimension. Wall and domes are modeled as shell elements. Column foundations are assumed to be fixed. Default hinges are considered for analysis Flexure moment (M), axial biaxial moment (P-M-M) and axial compressive shear force (V) hinges are assigned at the face of beam, column, and bracing respectively using the static pushover analysis.. Static nonlinear analysis of tank: SAP software is used to perform the nonlinear static pushover analysis. The RC beams and columns are modeled as -D frame elements with centerline dimension. Wall and domes are modeled as shell elements. Column foundations are assumed to be fixed. Default hinges are considered for analysis Flexure moment (M), axial biaxial moment (P-M-M) and axial compressive shear force (V) hinges are assigned at the face of beam, column, and bracing respectively using the static pushover analysis. Figure shows the procedure of pushover analysis. Damping ratio is.% considered.. PUSHOVER ANALYSIS PROCEDURE: Following are the steps followed in the present study to carry out analysis, design and performance study of RC frame. D model of RC frame was created.. Corresponding section and loads for the beam and column were assigned.. Analysis was carried out for both gravity and earthquake loads.. Design was carried out using CSI SAP, itself, as per IS: - provision.. Default hinge properties at assumed potential points (near beginning and ending of the Available Online at: Page

5 Volume: Issue: June 8 (IJRIER) element) were assigned.. For column PMM hinge property was assigned and for beam M hinge property was assigned. These points have pre-defined properties as per ATC-. 7. For non-linear/pushover cases, in which first case is force control and second case is displacement control were defined. 8. For displacement control case, earthquake force is used to push the frame laterally upto maximum displacement (% of building height). 9. Run the non-linear static analysis to get pushover curve. III. PROBLEM FORMULATION & ANALYSIS.. General The non-linear static procedure is a simple option for estimating the strength capacity in the post-elastic range. The procedure consists of applying a predefined lateral load pattern to structure model which is distributed along the structure height. The lateral forces are then monotonically increase in constant proportion with a displacement control node of the building until a certain level of deformation is reached. The applied base shear & the associated lateral displacement at each load increment plotted. Based on the capacity curve, a target displacement which is an estimate of displacement which is produced by design earthquake on the building is determined. At this target displacement extent of damage experienced by the building is considered representative of the damage experienced by the building when subjected to design level ground shaking. Modeling Table :Description for water tank for m Tank vessel property (m) Tanks staging property (m) Vessel Capacity m No. of column Nos Cylinder diameter 8. m Columns Diameter. m Wall Height.7m Columns height m, m, m Top Dome rise.7m diameter.78m Conical dome rise.m Bracing Interval. m Bottom dome rise.m Beams bracing Size Top Ring Beam.m.m No of bracing per level.m.m Nos Middle Ring Beam.m.m Bottom Ring Beam.m.m Seismic Data Top Dome thickness. m Zone II, III, IV, V Vessel thickness. m Response Reduction Factor. Available Online at: Page

6 Volume: Issue: June 8 (IJRIER) Conical dome thickness. m Soil Type Medium Bottom Dome thickness. m D Modeling of water tank for m with m height in zone II, III, IV, V D Modeling of water tank for m with m height in zone II, III, IV, V D Modeling of water tank for m with m height in zone II, III, IV, V Table :Description for water tank for m:- Tank vessel property (m) Tanks staging property (m) Vessel Capacity m No. of column Nos Cylinder diameter m Columns Diameter. m Available Online at: Page

7 Volume: Issue: June 8 (IJRIER) Wall Height.7m Columns height m, m, m Top Dome rise.7m diameter 7m Conical dome rise.m Bracing Interval. m Bottom dome rise.m Beams bracing Size.m.m Top Ring Beam.m.m No of bracing per level Nos Middle Ring Beam.m.m Bottom Ring Beam.m.m Seismic Data Top Dome thickness. m Zone II, III, IV, V Vessel thickness. m Response Reduction Factor. Conical dome thickness. m Soil Type Medium Bottom Dome thickness. m D Modeling of water tank for m with m height in zone II, III, IV, V D Modeling of water tank for m with m height in zone II, III, IV, V Available Online at: Page 7

8 Volume: Issue: June 8 (IJRIER) D Modeling of water tank for m with m height in zone II, III, IV, V IV. RESULTS AND DISCUSSIONS RESULTS FOR m TANK:-. Result for m capacity of water tank with m staging height in Empty condition Time period.... Base shear(kn) Over strength factor(rs)..8.. Ductility factor(rµ).... Redundancy factor(rr) Response reduction factor(r) Result for m capacity of water tank with m staging height in Full condition Time period Base shear(kn) Over strength factor(rs) Ductility factor(rµ) Redundancy factor(rr) Response reduction factor(r) Result for m capacity of water tank with m staging height in Empty condition Time period Base shear(kn) 7 Over strength factor(rs)...7. Ductility factor(rµ) Redundancy factor(rr) Response reduction factor(r) Result for m capacity of water tank with m staging height in Full condition Time period Base shear(kn) Over strength factor(rs)...7. Ductility factor(rµ).... Available Online at: Page 8

9 Volume: Issue: June 8 (IJRIER) Redundancy factor(rr) Response reduction factor(r) Result for m capacity of water tank with m staging height in Empty condition Time period Base shear(kn) 9 Over strength factor(rs)....9 Ductility factor(rµ)...9. Redundancy factor(rr) Response reduction factor(r) Result for m capacity of water tank with m staging height in Full condition Time period.... Base shear(kn) 7 8 Over strength factor(rs) Ductility factor(rµ).7... Redundancy factor(rr) Response reduction factor(r) BASE SHEAR FOR m TANK CAPACITY (Empty and Full) 7 7 Empty Full Empty Full Figure : graph of Base shear v/s seismic zones for different Tank condition 7 Empty Full Figure : graph of Base shear v/s seismic zones for different Tank condition Available Online at: Page 9

10 Volume: Issue: June 8 (IJRIER).8 RESPONSE REDUCTION (a) Variation of Response reduction factor for m: m m m m m m Figure : graph of R factor v/s seismic zones for different staging of water tank Graph shows the comparison of staging height with three factors redundancy, ductility, and over strength. Results are taken for m full and empty conditions. Results show that R factor decrease with increase in staging height. Redundancy depends upon number of vertical framing, so Redundancy factor is remaining same for all height. Over strength factor is decreasing by increasing staging height. It shows that reserve strength of tank is decreasing by increasing height. TANK EMPTY TANK FULL 7. OVERSTRE NGTH.... OVERSTRE NGTH Figure : graph of Factors v/s seismic zones for m staging of water tank Available Online at: Page

11 Volume: Issue: June 8 (IJRIER) OVERSTR ENGTH... OVERSTRE NGTH.. Figure : graph of Factors v/s seismic zones for m staging of water tank... OVERSTR ENGHTH Figure : graph of Factors v/s seismic zones for m staging of water tank OVERSTR ENGTH.9 TIME PERIOD: (a) Variation of Time Period for m: EMPTY FULL EMPTY FULL EMPTY FULL Zone Zone Zone Zone m m m Figure 7: bar graph of Time period v/s different for different zones and tank condition of water tank V. RESULTS FOR m TANK. Result for m capacity of water tank with m staging height in Empty condition Time period.... Base shear(kn) 7 7 Over strength factor(rs) Ductility factor(rµ)....9 Available Online at: Page

12 Volume: Issue: June 8 (IJRIER) Redundancy factor(rr) Response reduction factor(r) Result for m capacity of water tank with m staging height in Full condition Time period Base shear(kn) 7 9 Over strength factor(rs) Ductility factor(rµ) Redundancy factor(rr) Response reduction factor(r)...8. Result for m capacity of water tank with m staging height in Empty condition Time period Base shear(kn) Over strength factor(rs)....7 Ductility factor(rµ)..9.. Redundancy factor(rr) Response reduction factor(r) Result for m capacity of water tank with m staging height in Full condition Time period Base shear(kn) Over strength factor(rs) Ductility factor(rµ)....8 Redundancy factor(rr) Response reduction factor(r) Result for m capacity of water tank with m staging height in Empty condition Time period.... Base shear(kn) Over strength factor(rs).... Ductility factor(rµ)...7. Redundancy factor(rr) Response reduction factor(r)..... Result for m capacity of water tank with m staging height in Full condition Time period.... Base shear(kn) 7 8 Over strength factor(rs) Ductility factor(rµ) Redundancy factor(rr) Response reduction factor(r) Available Online at: Page

13 Volume: Issue: June 8 (IJRIER).7 BASE SHEAR FOR m TANK CAPACITY (Empty and Full) 7 7 Empty Full Empty Full Figure 8: graph of Base shear v/s seismic zones for different Tank condition 7 Empty Full Figure 9: graph of Base shear v/s seismic zones for different Tank condition.8 RESPONSE REDUCTION (a) Variation of Response reduction factor for m: 8 7 m m m Figure : graph of R factor v/s seismic zones for different staging of water tank 7 m m m Available Online at: Page

14 Volume: Issue: June 8 (IJRIER) Graph shows the comparison of staging height with three factors redundancy, ductility, and over strength. Results are taken for m full and empty condition. Results shows that R factor decrease with increase in staging height. Redundancy depends upon number of vertical framing, so Redundancy factor is remaining same for all height. Over strength factor is decreasing by increasing staging height. It shows that reserve strength of tank is decreasing by increasing height. TANK EMPTY OVERSTR ENGTH TANK FULL Figure : graph of Factors v/s seismic zones for m staging of water tank Figure : graph of Factors v/s seismic zones for m staging of water tank OVERSTR ENGTH DUCTILIT Y OVERSTRE NGTH Figure : graph of Factors v/s seismic zones for m staging of water tank OVERSTRE NGTH N CY OVERSTRE NGTH N CY OVERSTRE NGTH Available Online at: Page

15 Volume: Issue: June 8 (IJRIER).9 TIME PERIOD:- (a) Variation of Time Period for m: Zone Zone Zone Zone EMPTY FULL EMPTY FULL EMPTY FULL m m m Figure : bar graph of Time period v/s different for different zones and tank condition of water tank V. CONCLUSION. The response reduction factor is considerably affected by the staging height of water tank. It reduces as the of water tank is increasing.. R factor is highly dependent on seismic zones. For various seismic zones R factor also changes.. Time period and Redundancy of elevated tank will remaining same for all zones of same height of tank.. Base shear will increasing by changing the zone from II to V for the same height of elevated tank.. The Time period is considerably affected by the staging height of water tanks. It increases as the height of water tank is increasing.. Over strength factor of elevated tank is decreased by increasing zone factor. So, it shows that reserved strength of water tank is decreasing by increasing the zone factor. 7. R factor is decreasing by changing the condition of water tank from full to empty. 8. Time period and base shear of elevated tank is also increased in full condition of tank. REFERENCES [] ATC-9, Structural response modification Factors, 99 [] ATC (99): Seismic Evaluation and Retrofit of Concrete Buildings, Volume, ATC- Report, Applied Technology Council, Redwood City, California [] IS 89 (Part I), Criteria for Earthquake Resistant Design of Structures [] Jinkoo Kim, Hyunhoon Choi., Response modification factors of chevron-braced frames Engineering Structures 7 () 8 (). [] Bhavin Patel and Dhara Shah., Formulation of Response Reduction Factor for RCC Framed of Elevated Water Tank Proceedings of the World Congress on Engineering Vol III WCE, June - July,, London, U.K. [] SoheilSoroushnia, TavousiTafreshi, Omidinasab SH, Beheshtian F, SajadSoroushnia N., Seismic Performance of RC Elevated Water Tanks with Frame and Exhibition Damage Pattern The Twelfth East Asia-Pacific Conference on Structural Engineering and Construction(Procedia Engineering () 7 87). [7] Moslemi M, Kianoush M R, Pogorzelski W., Seismic response of liquid-filled elevated tanks Engineering Structures () 7 8 () [8] Estekanchi H E, Alembagheri M., Seismic analysis of steel liquid storage tanks by Endurance Time method Thin- Walled Structures (). Available Online at: Page