A study on response reduction factor of RC wter tank

A STUDY ON RESPONSE REDUCTION FACTOR OF RC WATER TANK

By

MILAN H MANEK

(Enrolment No. 130540720006)

Guided By

Prof. D.K.JIVANI (M.E. CASAD)

Prof. Civil Engg. Dept., DIET, Hadala

A Thesis Submitted to

Gujarat Technological University

In partial Fulfilment of the Requirements for

The Degree of Master of Engineering

In Civil-Structural Engineering

MAY-2015

DARSHAN INSTITUTE OF ENGINEERING & TECHNOLOGY, RAJKOT-

MORBI HIGHWAY, HADALA.

CHAPTER-1 INTRODUCTION

1.1 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.

Water tanks are the structure which are used to store a water. Broadly water tanks are

classified in to different categories as given below.

Underground water tanks.

Partial underground water tanks.

Water tanks resting on ground.

Elevated water tanks.

In India, most municipalities have water supply which depends on elevated tanks for

storage. Elevated water tank is a large elevated water storage container constructed for

the purpose of holding a water supply at a height sufficient to pressurize a water

distribution system. Thats why Elevated water tanks are one of the most important

components of water distribution system in India. To support the elevated vessel, a

concrete shaft or a framed assembly has been used. The detailed classification chart of

Elevated service reservoir is shown in Figure-1.1.

Figure-1.1 Classification of Elevated service reservoir

According to shape of container According to supporting structure

Rectangular Conical Circular Intze type

Shaft supported Column supported

Elevated Service Reservoir

For the study purpose an elevated Intze type water tank has been considered, because

intze tank is the most common type of concrete water tanks and widely used in India for

water storage. The reason for widely used is its shape, which helps to achieve an economy

particularly for large storage capacity. To support intze shape container column with

braces are provided. These bracings shorten the length of column and thus add the better

margin of safety to the water tank. Figure 1.2 shows elevted intze type water tank.

Figure 1.2 elevted intze type water tank.

1.2 NEED OF STUDY:

Majority of Gujarat portion comes in to higher seismic zone. So, it is important that

whatever water tank constructed in higher seismic zone should not collapse after

earthquake as the demand of water highly increases after earthquake to cater need of

drinking, firefighting etc.

Elevated water tanks consist of large water mass at the top supported on staging which

makes it more crucial and concern for the collapse of the tank during earthquakes. Due

to lack of knowledge of supporting system some of the tanks were heavily damaged or

collapsed. Part earthquake like Bhuj earthquake, are evidences of water tank collapse due

to failure of staging. So there is need to focus on seismic safety of water tank structure.

The figure 1.3 shows some of collapse of water tank due to earthquake forces.

The figure 1.3 collapse of water tank

Current seismic code criteria for water tank was inadequate. So, After the Bhuj

earthquake, revision of current Indian code became inevitable. Hence Indian Institute of

Technology, Kanpur has proposed guidelines along with commentary and explanatory

examples for seismic analysis of liquid storage tanks in association with GSDMA

(Gujarat State Disaster Management Authority). These publications cover seismic

analysis and design of ground supported as well as elevated tanks.

For behavior and performance of water tank during earthquake highly depends on

Response Reduction Factor (R). Which, Reflects the Capacity Of Structure to Dissipate

Energy By Inelastic Behavior.

The values of response reduction factor (R) of RC elevated water tank are given in IS:

1893 draft code or GSDMA Guideline, which is calculated at empirically based on

engineering judgment. The values of response reduction factor of elevated water tank

adopted by difference codes/standards are summaries in Table 1.1. From the comparison

it is clear our codes suggested somewhat conservative values for Response reduction

factor. So, here we tries to find out actual values of response reduction factor for elevated

water tank by static nonlinear analysis.

Table 1.1 R as Per International Standards for Elevated Tanks

Codes/standards R Factor

IBC 2000/ FEMA 368 1.5 to 3.0

ACI 350.3 2.0 to 4.75

IS:1893-2002(Part -2) RCC frame support (draft code)

Or GSDMA Guideline

1.8 (OMRF)

2.5 (SMRF)

Also the Value of R-Factor Is Fixed 2.5 for staging Supported RC Elevated Tank. One

Constant R-Value For Elevated Water Tank Cannot Reflect The Expected Inelastic

Behavior Of All Elevated Water Tanks Located In Different Seismic Zone And Having

Different Capacities. So It Is Required to Find out Perfect Value of R factor For Various

Type of RC Elevated Tank Individually.

1.3 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

Prepare a spreadsheet to design elevated tank

Compare the calculated r factor with the assumed r factor.

Evaluate ductility, redundancy and over strength factor of elevated Intze 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).

1.4 SCOPE OF WORK:

The main scope of work is to study the Response Reduction factor for the elevated Intze

type of water tank and other scope of Present work is summarized as below,

To prepare a spreadsheet and design water tank as per is- 3370:2009 (limit state

method).

Understand the procedure of water tank modelling and pushover analyses in sap

software considering hydrodynamic pressure as per iitk-gsdma guidelines.

To perform pushover analysis of elevated water tank for different capacity, height,

zone and compare the results.

Perform a comparative study between different staging patterns in form of variation

in ductility, redundancy and over strength factor etc.

Calculated and compare the calculated response reduction factor with the assumed r

factor

CHAPTER-2 LITERATURE REVIEW

2.1 GENERAL:

Literature survey is always an important as it helps in finalization the scope and objective

of work. For literature survey different relevant research papers, and codes has been

referred. Various research papers have been studied and brief review of the same has been

discussed below.

2.2 LITERATURE REVIEW

2.2.1 Seismic behavior of water tank:

Patricia Pappa, Daniel Vasilikis, Polynikis Vazouras, and Spyros A. Karamanos

(2011): In this paper some special issues on the structural behavior of upright-cylindrical

liquid storage tanks are examines, which are widely used in industrial facilities and for

water storage. The structural response of liquid storage tanks under strong seismic

loading constitutes an important issue for safeguarding the structural integrity of

industrial facilities, especially in refineries and power plants. The mode of tank failure is

in the form of elephants foot buckling at the tank base. Other types of earthquake

damages include buckling of the top of the tank shell, base plate failure due to uplifting,

roof damage due to excessive sloshing, or shell damage at nozzle areas due to non-flexible

connections with piping. Current design practice is based on the application of the API

650 provisions [3]. For the majority of tanks, consideration of only one sloshing

(convective) mode is adequate for the calculation of the total seismic force.

Ahmed Hafez (2012): In This paper study is focused on the nonlinear behavior of

ground-supported open top circular concrete tanks under the effect of seismic loads. The

tank support conditions are considered in this study where both flexible and nonflexible

supports are investigated. A comparison between the behavior of RC and prestressed

concrete tanks is undertaken for flexible base condition. The finite element method is

used to study the nonlinear response of circular tanks under dynamic time-history and

push-over analysis. Further, the response modification factors included in current practice

are evaluated based on the results of nonlinear dynamic and push-over analysis. Several

tank configurations with different aspect ratios, construction method, and base conditions

are used in this study to attain reliable results and to validate the R-values. The behavior

of circular RC tanks under shrinkage effect is also investigated.

MANORANJAN SAHOO and TANDRITA BISWAS (2007): 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: 1893-1984/2002 for seismic design and IS: 875-1987(Part III)

for wind load has been referred. Then checked the Design of Intze Tank by using the

software STAAD PRO. Conclusion of this paper is that the Ratio of Base Shear of tank

and building is 6 to 7 for low ductility tanks and 3 to 4 for high ductility tanks. Convective

Mode Base Shear values obtained from API 650 and Euro Code 8 are similar but those

obtained from ACI 350.3 is 2.5 times greater than that of ACI 370. Based on the review

of various International Codes, it is recommended that IS 1893 should have values of R

in range of 1.1 to 2.25 for different types of tanks. Base Shear and Base Moment increases

from Zone 3 to Zone 4 to Zone 5.

Review of Code Provisions on Design Seismic Forces for Liquid Storage Tanks

It Is Well Recognized That Liquid Storage Tanks Possess Low Ductility And Energy

Absorbing Capacity As Compared To The Conventional Buildings. Accordingly, Various

Design Codes Provide Higher Level Of Design Seismic Forces For Tanks. In This

Article, Provisions Of IBC 2000, ACI, AWWA, API, Euro code 8 And NZSEE

Guidelines Are Reviewed, To Assess The Severity Of Design Seismic Forces For Tanks

Vis--Vis Those For Buildings. It Is Seen That, Depending On The Type Of Tank,

Design Seismic Force For Tanks Can Be 3 To 7 Times Higher Than That For Buildings.

Based On The Comparison Of Provisions In These Documents, Various Similarities,

Discrepancies And Limitations In Their Provisions Are Brought Out.

This Article Presents An Assessment Of Design Seismic Force For Tanks Vis- -Vis

Design Seismic Force For Buildings As Mentioned In The Following Documents:

(A) IBC 2000

(B) ACI Standards ACI 371 (1998) and ACI 350.3 (2001)

(C) AWWA D-100 (1996), AWWA D-103 (1997), AWWA D-110 (1995) and AWWA

D-115 (1995)

(D) API 650 (1998)

(E) Euro code 8 (1998)

2.2.2 Response Reduction Factor of Water Tank:

Tejash patel, jignesh amin, bhavin patel (2014): Main objective of this paper is

perform Nonlinear static pushover analysis is done by using ETABS. Moment-rotation

(M-) and load-bending moment (P-M) relationship for flexural and compression

members have been developed. From result it is observed that the first hinge is formed at

8th step. The maximum number of hinges formed in elastic range only. Hence, it

indicates that there is a need of retrofitting for members.

Dr. S. N. Tande and R. V. Ambekar(2013): The present study estimates the seismic

Response reduction factor (R) of reinforced concrete special moment Resisting frame

(SMRF) with and without shear wall using static nonlinear (pushover) analysis.

Calculation of factor(R) is done as per the new formulation of Response reduction factor

(R) given by Applied Technology Council (ATC)-19 which is the product of Strength

factor (Rs), Ductility factor (R) and Redundancy factor (RR). The analysis revealed that

these three factors affects the actual value of response reduction factor (R) and therefore

they must be taken into consideration while determining the appropriate response

reduction factor to be used during the seismic design process. Conclusion of this paper is

that the Response reduction factor without shear wall is almost reduced by 50%

considering displacement ductility ratio as compared to IS Code values. Response

reduction factor with shear wall are almost doubled considering rotational ductility ratio

as compared to IS code values.

Mostafa Masoudi, Sassan Eshghi, Mohsen Ghafory-Ashtiany (2012): This paper

discusses the failure mechanism of elevated concrete tanks with shaft and frame staging

(supporting system) along with seismic behavior of these construction types. In order to

modify the current code-based seismic design methodology, computer models have been

established to determine the R, of the shaft and frame staging elevated tanks. The

computational models have been subjected to an ensemble of earthquake ground motions.

The effects of multi-component earthquakes, fluidstructure interaction and the PD

effects on the inelastic response of elevated tanks have been studied by conducting linear

and nonlinear response history analyses.

R. Sadjadi1 and M.R. Kianoush (2008): Reinforced concrete liquid storage tanks have

been extensively used as a part of environmental engineering facilities. Since

functionality of these structures after an earthquake is very important to meet the

emergency state requirements, seismic damage of these structures is of main concern.

One of the main parameters used in the seismic design of structures is the Response

Modification Factor (R). The values of R for different structural systems and materials

for buildings are well defined and included in the building Codes. For liquid containing

structures (LCS), there has not been a justifiable guideline for determination of the R

and the empirical values have been implemented in the design of such structures. While

the seismic design criteria for the buildings are mainly based on life safety and prevention

of collapse, the concrete storage tanks should be designed to meet the serviceability limits

such as leakage. In this paper the mechanism of leakage in (RC) tanks is discussed. The

response modification factor for (LCS) along with the corresponding experimental tests

will also be discussed. It is concluded that the use of period independent R factor for the

(LCS) may not be appropriate. The current values of R might need to be adjusted as no

leakage was observed prior to the yielding of the wall reinforcement.

Mr. Bhavin Patel and Mrs. Dhara Shah (2010): The present study investigates the

formulation of key factors for seismic response modification factor of RCC framed

staging of elevated water tank. The analysis revealed that three major factors, called

reserved strength, ductility and redundancy affects the actual value of response

modification factor and therefore they must be taken into consideration while determining

the appropriate response modification to be used during the seismic design process. The

evaluation of response modification factor is done using static nonlinear pushover

analysis. Pushover analysis is an advanced tool to carry out static nonlinear analysis of

framed structures. It is used to evaluate nonlinear behavior and gives the sequence and

mechanism of plastic hinge formation. Here displacement controlled pushover analysis

is used to apply the earthquake forces at C.G. of container.

Yi-Hsuan Tu, Shyh-Jiann Hwang and Tsung-Chih Chiou (2006): In Taiwan, many

school buildings suffer severe damage in earthquakes due to their typical architectural

pattern. 4 in-site push over tests of school buildings were carried out to study the effects

of different retrofitting measures and to verify the seismic assessment methods. The

specimens include a 2-floor building with 3 classrooms of Hsin-Cheng Junior High

School, Hualien, and a 2- floor school building of Kouhu Elementary School, Yulin. The

latter was consists of 8 classrooms and cut into 3 specimens, each has 2 classrooms, while

the rest 2 classrooms reinforced by steel bracing to provide reacting support. Specimen

in Hualien was a typical school building with no walls in the longitudinal direction, while

specimens in Yulin has an typical one, one with original brick wing walls, and one with

new RC wing walls as retrofit in the longitudinal direction. 6 hydraulic actuators were

placed at the top of each floor of each specimen to provide lateral loading along the

longitudinal direction. While being lateral loaded, some of the specimens were subjected

to extra vertical loads by added weights on the slabs. The test results show that wing walls

can efficiently improve lateral strength of school buildings.

2.2.3 Push over analysis:

Aditi Patidar* and Swatilekha Guha Bodh (2014): In this paper the lateral loading

pattern for waffle slab structure is adapted to the pushover analysis. The seismic collapse

capacity of waffle slab is to be determined with the help of pushover by using ETAB

9.Main objective of this study is to determine the collapse capacity of waffle slab by

pushover analysis and to analyze the waffle slab with panel and without panels by using

ETAB9. Waffle slab is defined as combination of flat flange plate or deck and equally

spaced ribs. Two way floor roof systems consisting of a reinforced concrete slab poured

with integral joists or ribs in two directions beneath it. The system has a waffle-like

pattern when a reinforced concrete slab with equally spaced ribs parallel to the sides,

having a waffle appearance from below. This system is an efficient and better way of

constructing slabs for new homes or industrial buildings.

Rahul RANA, Limin JIN and Atila ZEKIOGLU (2004): Pushover analysis was

performed on a nineteen story, slender concrete tower building located in San Francisco

with a gross area of 430,000 square feet. Lateral system of the building consists of

concrete shear walls. The building is newly designed conforming to 1997 Uniform

Building Code, and pushover analysis was performed to verify code's underlying intent

of Life Safety performance under design earthquake. Procedure followed for carrying out

the analysis and results are presented in this paper. Building analyzed is a nineteen story

(18 story + basement), 240 feet tall slender concrete tower located in San Francisco with

a gross area of 430,000 square feet. Unique features of the slender concrete tower

presented challenges for seismic design. Typically, a 240 feet tall concrete building in

seismic zone 4 would have a lateral system that combines shear walls and moment

frames. However, two architectural features made the use of moment frames difficult.

First, the 60 feet long open bays limited the number of possible moment frames. Second,

on the southeast side two of the perimeter columns are discontinued at the 6th story and

six new columns are introduced that slope for the lowest six stories at an angle of about

20 degrees from vertical. These sloped columns connect to transverse walls through

horizontal transfer elements at the 6th story and put considerable gravity-induced

horizontal loads on the lateral system at that level. Software SAP2000 version 7 [13] and

ETABS version 7 [14] were used for analysis. SAP2000 was used to perform pushover

analysis and ETABS was used to calculate hinge properties of shear wall and elastic

analysis.

CHAPTER-3 SEISMIC ANALYSIS AND DESIGN

OF ELEVATED TANK

3.1 General:

The main purpose of earthquake resisting design is that the structure should not permitted

to collapse but damage is allowed during earthquake. Water tank is important structure.

Staging type of tanks are generally collapse during earthquake, so it is required to

calculate earthquake load perfectly. Past evidence has shown that the elevated tanks are

vulnerable due to earthquake. The tanks are designed based on linear elastic methods

which are considered only elastic range. In this chapter concept of response reduction

factor and basic component of R factor is discussed with the pushover analysis

methodology.

3.2 Review of basic component of response reduction factor:

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 behavior. 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 as mentioned below and also shown in Figure---------.

1) Over strength factor

2) Ductility factor

3) Redundancy factor

Over Strength Factor Accounts For The Yielding Of A Structure At Load Higher Than

The Design Load Due To Various Partial Safety Factors, Strain Hardening, Oversized

Members, Confinement Of Concrete. Non-Structural Elements Also Contribute To The

Over Strength. Nonlinear static analysis (also termed pushover analysis) can be used to

estimate the strength of a building or framing system. The procedure used to estimate the

strength of a building is requires to select a limiting state of response in form of maximum

inter story drift and maximum plastic hinge rotation.

Ductility factor (R) is ratio of ultimate displacement or code specified permissible

displacement to the yield displacement. Higher ductility implies that the structure can

withstand stronger shaking without collapse.

A redundant seismic framing system should be composed of multiple vertical lines of

framing, each designed and detailed to transfer seismic-induced inertial forces to the

foundation. Yielding at one location in the structure does not imply yielding of the

structure as a whole. Hence the load distribution, due to redundancy of the structure,

provides additional safety margin.

Figure 3.1 Horizontal force verses roof displacement.

The ATC-19 Describes the Calculation procedure of response reduction factor (R).The

response reduction factor (R) is depends on Over strength (Rs), Ductility (R),

Redundancy (RR). According to ATC-19, it is described Response Reduction factor (R)

as,

R = Rs * RR * R

Estimation of over strength (Rs) factor:

The Over strength (Rs) factor is the ratio of Maximum Base Shear (from pushover

curve) VO to Design Base shear (as per EQ calculation) Vd.

Rs = Vo / Vd

Estimation of ductility factor:

Equations for estimation of ductility factor is as below:

R = {( - 1 / ) + 1}

Where, R = Ductility Factor

= 1+ {1 / (10T -T)}{(1 / 2T)*e^ (-2(ln (T) 0.6) ^2)} for rock sites

= 1+ {1 / (12T -T)}{(2 / 5T)*e^ (-2(ln (T) 0.2) ^2)} for alluvium sites

= m / y

m = Maximum drift capacity (0.004 H as per IS 1893:2002)

y = Yield drift (from pushover curve)

Estimation of redundancy factor:

The value of redundancy factor as suggested in ATC-19 is summaries in Table 3.

Table 3.1 Redundancy Factor as per ATC-19

Lines of vertical seismic framing Drift redundancy factor

2 0.71

3 0.86

4 1

3.3 TWO MASS MODAL METHOD

Housner developed a two mass model for elevated tank in 1963, which is more

appropriate and is being commonly used in most of the international codes including

IITK-GSDMA guidelines. As per this theory, the pressure is generated within the water

due to the dynamic motion of the tank can be separated into two parts, impulsive and

convective. An elevated tank containing liquid with a free surface is subjected to

horizontal earthquake ground motion, tank wall and liquid are subjected to the

horizontal acceleration. The liquid in the lower region of tank acts as a mass that is

rigidly connected to tank wall. This mass is defined as impulsive mass and which

accelerates along with the wall and generates impulsive hydrodynamic pressure on tank

wall and similarly on base liquid mass in the upper region of tank undergoes sloshing

motion, this mass is defined as convective mass and it induces 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, two-mass

model will take for elevated tanks. In this study two mass model is considered. The

parameters of this model depend on geometry of the tank and its flexibility. The

response of two degree of freedom system can be achieved by structural dynamics. For

most of elevated tanks it is observed that both the time periods are well separated. So,

the two mass idealizations can be treated as two uncoupled single degree of freedom

system. Figure 3.2 shows two mass model system for water tank.

(a) Two mass idealization (d) equivalent uncoupled system

Figure 3.2 Two mass idealization of elevated tank

For the modelling of convective and impulsive, two mass model system is used and

Figure 3.2shows the modelling system used in present study for impulsive and

convective mass of water tank. In the below figure 3.3 Mi is the Impulsive mass and

shall be added to the wall equally on periphery. While Mc is the convective mass which

includes sloshing mass of water which is provided in cylinder and connected with the

side wall with stiffness Kc. The convective mass, impulsive mass and stiff nesses are

calculated as per GSDMA Guideline and equations for same are mentioned in Table

3.2.

Figure 3.3 Two mass computational model of elevated tank

Table-3.2 Expression of Mass and Height for Impulsive & Convective

mode

Impulsive mode Convective mode

Mass mim

=tanh (0.866

Dh)

0.866 (Dh)

mcm

=0.23 tanh (3.68

hD)

hD

Height of

mass

from

Container

Bottom

hih

= 0.375 for h/D 0.75

= 0.5 0.09375

h/D for h/D > 0.75

hch

= 1 cosh (3.68

hD) 1.0

3.68hD sinh (3.68

hD)

hi

h=

0.866Dh

2 tanh (0.866Dh)

0.125 for h/D 1.33

= 0.45 for h/D > 1.33

hc

h= 1

cosh(3.68h/D) 2.01

3.68hD sinh (3.68

hD)

Stiffness ---------------------------------- Kc = 0.836 mg

htanh2(3.68

h

D)

3.4 Material Properties:

Property of concrete and steel which is used in water tank is as below:

Grade of concrete: 30N/mm^2

Grade of steel: 415N/mm^2

Density of concrete: 25000N/m^3

Density of liquid: 9810N/m^3

Modulus of elasticity: 27386N/m^2

Permissible stress in concrete:

Direct compression (cc): 8N/mm^2

Bending Compression (cb): 10 N/mm^2

Modular Ratio (m): 9.33

Direct tension (ct): 1.5 N/mm^2

Bending (cb): 2 N/mm^2

Permissible stresses in steel:

Direct Tension (st): 30N/mm^2

Tensile stress (0.87*fy): 361N/mm^2

k = (1/(1+(st/(m*cbc)))): 0.42

j = 1-(k/3): 0.86

3.5 Hinge formation:

The RC beams and columns are modeled as 3-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 (M3),

axial biaxial moment (P-M2-M3) and axial compressive shear force (V) hinges are

assigned at the face of beam, column, and bracing respectively using the static pushover

analysis.

3.6 Design methodology:

3.6.1 General:

Storage reservoirs are used to store water, liquid petroleum, petroleum products and

similar liquids. The force analysis of the reservoirs or tanks is about the same

irrespective of the chemical nature of the product. All tanks are designed as crack free

structures for neglecting any leakages. Elevated tanks are mainly designed by two

methods. 1) Limit state method 2) Working stress method.

We have used limit state method for the designing of elevated water tank. In the water

retaining structures a dense impermeable concrete is required so, proportion of fine and

course aggregates to cement should be such as to give higher quality of concrete.

Concrete mix weaker than M30 is not used for the water retaining structure as per IS:

3370. The minimum quantity of cement in the concrete mix shall be not less than 30

kN/m3. The design of the concrete mix will be sufficiently impervious.

Design of liquid retaining structure is different from ordinary R.C.C, structures as it

requires that concrete should not crack and so the tensile stresses in concrete should be

within permissible limits. It should be conform that tensile stress on the liquid face of

the elevated tank of equivalent concrete section does not exceed the permissible tensile

strength of concrete which is given in material property.

After the manual design of elevated tank, a model is prepared in SAP2000 for the

nonlinear analysis of elevated water tank. Model is prepared and analyzed in SAP2000

and pushover curve is generated.

Using pushover curve, over strength, ductility factors are calculated. And finally

Response reduction factor is calculated for elevated water tank.

Methodology of work is shown in flow diagram below.

Figure 3.4 Flow chart of work.

This is the work flow chart of our work. We have taken height variation, zone variation

and staging type variation. In the height variation, taking the height 12m, 16m, 20m.For

the height variation zone 4 and staging pattern of 6 columns is fixed. For the zone

variation zone 2, 3, 4, 5 are taken for the study. For the variation in zone staging height

20m and staging pattern of 6 columns is fixed. Variation in staging type is shown in

1 Selection of Water tank for Response reduction factor study

2 Manual analysis and design of Tank as per IS 3370:2009 considering hydrodynamic pressure using

spread sheet

3 Pushover analysis using SAP software

4 Calculate over strength factor (over strength + redundancy) and Ductility factor R

5 Calculate Response Reduction factor

R = x R

6 Interpretation of Results in form of

- Redundancy, Over strength , Ductility, Time period etc.

7 Conclusion

3.7 bench mark problem study:

3.7.1 General:

Accuracy of any results are depends on its correct modelling procedure and software

capability for particular problems. For that a benchmark problem, it is considered to

checks the capabilities of the SAP Program and it proves the accuracy of modelling and

analysis in SAP for further applications.

3.7.2 Problem Description:

We take an example-3 from GSDMA guidelines for the validation of software.

Following data is given in example-3. This is analyzed in SAP and results of SAP is

compared with the results given in GSDMA guidelines.

Table-3.3 Data of Ex-3 from GSDMA guidelines

component Size

Top Dome 120 mm thick

Top dome Rise 1.75 MT

Cylindrical dia i/i 8.60 MT

Top Ring Beam 250 X300

Cylindrical wall 200 mm thick

wall height 3.7 MT

free board 300 mm

Middle Ring Beam 500 X300

Bottom Ring Beam 500 X600

Bottom Dome 200 mm thick

conical Dome Rise 1.5 MT

Bottom Dome Rise 1.5 MT

Staging dia 5.78 MT

Conical Dome 250mm thick

Braces 300 X600

Column 650 mm dia

Ht. of Staging 12, 16, 20 MT

No. of Column 6

Figure 3.5 Members and its size of elevated water tank.

3.7.3 Loading

A three dimensional finite element model is used for modeling, the elevated water tank

are based on the fixed base condition as shown in Figure 3.6. Beams and columns are

modelled as frame elements the walls container and slabs are modelled with

quadrilateral shell elements. In according to draft code water tank model the impulsive

and the convective water mass components and their respective heights are given by

the expressions shown in Table 3.2 These calculated impulsive and convective masses

are applied to the three dimension model which is prepared in SAP2000, at their

respective heights of impulsive and convective height. The static analysis was carried

out using the finite element structural analysis software, SAP2000.

Figure 3.6 Rendering model of elevated tank in SAP.

3.7.4 Results and Discussion:

Comparison of Base-shear and Base-moment of the Draft code and the SAP2000

software has been given in the Table 3.3. It is observed that the Base shear and Base

moment of the elevated water tank obtained from the SAP software and the Draft code

are in good agreement. This indicates that the SAP software can provide acceptable

results.

Table shows the comparison of results of SAP and results of example given in GSDMA

guidelines

Table 3.4 Percentage of error of result in SAP:

Figure 3.5 Comparison of time period of eater tank of SAP and IITK guidelines.

Figure 3.6 Comparison of base shear and base moment of eater tank of SAP and

IITK guidelines.

0.8

0.85

0.9

0.95

IITK Guideline SAP

Time Period (sec)

Time Period

277

5381

280

5230

0

1000

2000

3000

4000

5000

6000

Base Shear (kN) Base Moment (kN-m)

IITK Guideline SAP

Fluid

Level

Time Period Base Shear (Kn) Base Moment (Kn-M)

IITK

Guideline SAP

Percentage

Difference

(%)

IITK

Guideline SAP

Percentage

Difference

(%)

IITK

Guideline SAP

Percentage

Difference

(%)

Tankful 0.86 0.9 4.44 277 280 1.07 5381 5230 -2.89

Graph shows the percentage of difference in results of time period, base shear and base

moment. There is 4.44% difference in the result of time period, 2.89% difference in

result of base moment and 1.07% difference in result of base shear.

3.8 Summary:

In this chapter two mass model method is described and with reference of that theory,

Model of elevated water tank is prepared in SAP-2000 software. Capability of SAP is

Checked with bench mark problem mentioned in IITK GSDMA guideline and results

Were compared and matched. Another important thing, Concept of Response reduction

factor and calculation for R factor is described. Material property of steel and concrete

which is used in water tank is mentioned.

CHAPTER-4 NONLINEAR ANALYSIS AND

FORMULATION OF RESPONSE REDUCTION FACTOR

4.1 General:

The tanks are designed based on linear elastic methods which are considered only

elastic range. Factor shows the reserved strength of water tank.in IS 1893-2002(part-2)

value of R factor for RC elevated shaft supported tank is 1.8 and for column supported

2.5.Values of R factor changes by change in height of water tank. In this chapter value

of R is calculated by nonlinear static analysis of 250m^3 and 500 m^3 of water tanks

with varying height of 12m, 16m, and 20m.Nnlinear analysis is done by using SAP

2000.

SAP, Structural Analysis Program, is user friendly widely used, generalized analysis

and design software developed for all kind of structures like buildings, water tanks,

bridges etc. SAP Version 15.1.0 has a powerful graphical interface with modeling,

analytical, and design procedures. It is a full-featured program that can be used for the

simplest problems or the most complex projects, including a wide range of nonlinear

behaviors.

4.2 Description of problem:

A Reinforced concrete elevated tanks with different capacity of 250 m3 and 500 m3

has been considered in this study. These elevated tanks are placed on column supported

framed structure with different staging height of 12m, 16m and 20m, respectively, Zone

4 and staging type of 6 columns is fixed for the varying height. In this study, the column

staging supports are assumed as a fixed while the simple circular tie bracing has been

considered. Since the tank vessel is Intze, there is a symmetric in the loading and shape

of the vessel. This type of tank and supporting system has been widely used in the recent

years around the world.

Figure 4.1 Staging type 6 columns

Table 4.1 Water tank Specification for 250m3 capacity

Table 4.2 Water tank Specification for 500m3 capacity:

A three dimensional model is prepared in SAP2000 for static nonlinear

analysis.

4.3 Static nonlinear analysis of tank:

SAP software is used to perform the nonlinear static pushover analysis. The RC beams

and columns are modeled as 3-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 (M3), axial biaxial moment

(P-M2-M3) 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 0.5% considered.

4.3.1 Steps for Static nonlinear analysis of tank:

The following steps for the pushover analysis. Steps 1 through 4 discussing how to

creating the computer model, step 5 runs the analysis, and steps 6 through 10 review

the pushover analysis results.

1. Create the basic computer model (without the pushover data) in the usual manner use

of graphical interface of SAP-2000 makes this a quick and easy.

2. The program includes several built-in default hinge properties that are based on

average values from ATC-40 for concrete members and average values from FEMA-

273 for steel members. These built in properties can be useful for preliminary analyses,

but user-defined properties are recommended for final analyses. Uses default

properties.

3. Locate the pushover hinges on the model by selecting one or more frame members

and assigning them one or more hinge properties and hinge locations, locate at 0 and 1.

4. Define the push-over load case. Push-over load case can start from the final

conditions of other pushover load-case that was previously run in the same analysis.

Typically the first pushover load case is used to apply gravity load and then subsequent

lateral pushover load cases are specified to start from the final conditions of the gravity

pushover. Pushover load cases can be force controlled, that is, pushed to a certain

defined force level, or they can be displacement controlled, that is, pushed to a specified

displacement. Typically a gravity load pushover is force controlled and lateral

pushovers are displacement controlled. SAP2000 allows the distribution of lateral force

used in the pushover to be based on a uniform acceleration in a specified direction, a

specified mode shape, or a user-defined static load case. Here how the displacement

controlled lateral pushover case that is based on a user defined static lateral load pattern

named PUSH is defined for this example.

5. Run the basic static analysis and, if desired, dynamic analysis. Then run the static

nonlinear pushover analysis.

6. Display the pushover curve. The File menu shown in this display window allows you

to view and if desired, print to either a printer or an ASCII file, a table which gives the

coordinates of each step of the pushover curve and summarizes the number of hinges

in each state.

7. Display the capacity spectrum curve. Note that you can interactively modify the

magnitude of the earthquake and the damping information on this form and

immediately see the new capacity spectrum plot. The performance point for a given set

of values is defined by the intersection of the capacity curve (green) and the single

demand spectrum curve (yellow). Also, the file menu in this display allows you to print

the coordinates of the capacity curve and the demand curve as well as other information

used to convert the pushover curve to Acceleration-Displacement Response Spectrum

format.

8. Review the pushover displaced shape and sequence of hinge formation on a step-by

step basis. The arrows in the bottom right-hand corner of the screen allow you to move

through the pushover step-by- step. Hinges appear when they yield and are color coded

based on their state

9. Review member forces on a step-by-step basis. Often it is useful to view the model

in two side-by-side windows with the step-by-step displaced shape in one window and

the step-by-step member forces in the other. These windows can be synchronized to the

same step, and can thus greatly enhance the understanding of the pushover results.

Figure 4.2 Pushover case 1

Figure 4.3 Pushover case 2

Figure 4.4 Pushover curve for 12m, 250m3 water tank (full condition)

4.4 Results and Discussion:

Results of 250 M3 and 500 M3 elevated tank for varying height is as below.

4.4.1 Results for 250m3 water tank:

Table below shows the Results of R factor, Time Period, Base Shear, Ductility Factor,

Redundancy Factor, over strength Factor and R factor for 12m height, zone 4 for full

and empty both condition:

Table 4.3 Results for 12M height.

Tank Type:Intz Tank Column Size:650mm Dia

Staging Type6 Col Circular Zone IV

Staging Height 12m Full Empty

Time Period 1.46 0.58

Base Shear 401 369.25

Ductility Factor 2.23 2.29

Redundancy Factor 0.86 0.86

Over strength Factor 1.827 1.28

R 3.51 2.52









Base Shear 356.17 298



Overstrength Factor 1.92 1.89

R 1.83 4.13













R 1.87 3.01

Graphs for 250M3:

Graph shows the comparison of staging height verses three factors redundancy,

ductility, and over strength. Results are taken for 250m3 full and empty condition.

Results shows that R factor decrease with increase in staging height. 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.

Figure4.5 Comparison of staging height verses three factors for empty tank.

Figure4.6 Comparison of staging height verses three factors for full tank.

0

0.5

1

1.5

2

2.5

3

12 14 16 18 20

Fact

or

Staging Height (m)

250m3 (Tank Full)

REDUNDANCY FACTOR

OVERSTRENGTH FACTOR

R Factor

0

1

2

3

4

5

12 14 16 18 20

Fact

or

Staging Height (m)

250m3 (Empty)

REDUNDANCY FACTOR

OVERSTRENGTH FACTOR

R Factor

Graph shows the comparison of time period verses three factors redundancy, ductility,

and over strength. Results are taken for 250m3 full and empty condition. Results shows

that R factor decrease with increase in time period. Redundancy depends upon number

of vertical framing, so Redundancy factor is remaining same for all height. Over

strength factor is increasing by increasing time period.

Figure4.7 Comparison of time period verses three factors for full tank.

Figure4.8 Comparison of time period verses three factors for empty tank.

0

0.5

1

1.5

2

2.5

3

0 0.5 1 1.5

Fact

or

Time Period (sec)

250m3 (Tank Full)

REDUNDANCY FACTOR

OVERSTRENGTHFACTOR

0

1

2

3

4

5

0 0.2 0.4 0.6 0.8 1 1.2

Fact

or

Time Period (sec)

250m3 (Empty)

REDUNDANCY FACTOR

OVERSTRENGTH FACTOR

R Factor

This graph shows the comparison of staging height to time period. This graph shows

the comparison of staging height to time period. Graph shows that by increasing

staging height time period will increasing for full and empty condition of 250m3

water tank.

Figure4.9 Comparison of staging height verses time period for full tank and empty.

This graph shows the comparison of staging height to base shear. Graph shows that by

increasing staging height base shear will decreasing for full and empty condition of

250m3 water tank.

Figure4.10 Comparison of staging height verses base shear for full tank and empty.

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

12m 16m 20m

Tim

e P

eri

od

(se

c)

Staging Height (m)

FULL

EMPTY

0

50

100

150

200

250

300

350

12m 16m 20m

Bas

e S

he

ar (

kN)

Staging Height (m)

FULL

EMPTY

This graph shows the comparison of staging height to Redundancy factor. Graph

shows that by increasing staging height Redundancy factor will same for full and

empty condition of 250m3 water tank.

Figure4.11 Comparison of staging height verses redundancy factor for full tank and

empty.

This graph shows the comparison of staging height to over strength factor. Graph

shows that by increasing staging height over strength factor will decrease for full and

empty condition of 250m3 water tank.

Figure4.12 Comparison of staging height verses Overstrength Factor for full tank and

empty.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

12m 16m 20m

Re

du

nd

ancy

Fac

tor

Staging Height (m)

FULL

EMPTY

0

0.5

1

1.5

2

2.5

3

3.5

12m 16m 20m

Ove

rstr

en

gth

Fac

tor

Staging Height (m)

FULL

EMPTY

This graph shows the comparison of staging height to R factor. Graph shows that by

increasing staging height R factor will decrease for full and empty condition of

250m3 water tank.

Figure4.13 Comparison of staging height verses R factor for full tank and empty.

4.4.2 for 500m3 water tank:












Over strength Factor 1.827 1.28

R 3.51 2.52

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

12m 16m 20m

R F

acto

r

Staging Height (m)

FULL

EMPTY













R 1.83 4.13













R 1.87 3.01

Graphs for 500M3:

Graph shows the comparison of staging height with three factors redundancy, ductility,


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.

Figure4.14 Comparison of staging height verses three factor for full tank.

Figure4.15 Comparison of staging height verses three factor for empty tank.

0

0.5

1

1.5

2

2.5

3

3.5

4

12 14 16 18 20

Fact

or

Staging Height (m)

500m3 (Tank Full)

REDUNDANCY FACTOR

OVERSTRENGTH FACTOR

R Factor

0

1

2

3

4

5

12 14 16 18 20

Fact

or

Staging Height (m)

500m3 (Empty)

REDUNDANCY FACTOR

OVERSTRENGTH FACTOR

R Factor

Graph shows the comparison of time period verses three factors redundancy, ductility,


that R factor decrease with increase in time period. Redundancy depends upon number

of vertical framing, so Redundancy factor is remaining same for all height. Over

strength factor is increasing by increasing time period.

Figure4.16 Comparison of time period verses three factor for full tank.

Figure4.17 Comparison of time period verses three factor for empty tank.

This graph given below shows the comparison of staging height to time period. Graph

0

0.5

1

1.5

2

2.5

3

3.5

4

0 0.5 1 1.5 2 2.5

Fact

or

Time Period (sec)

500m3 (Tank Full)

REDUNDANCY FACTOR

OVERSTRENGTH FACTOR

R Factor

0

1

2

3

4

5

0 0.2 0.4 0.6 0.8 1 1.2

Fact

or

Time Period (sec))

500m3 (Empty)

REDUNDANCY FACTOR

OVERSTRENGTH FACTOR

R Factor

shows that by increasing staging height time period will increasing for full and empty

condition of 500m3 water tank.

Figure4.18 Comparison of staging height verses time period for full and empty tank.

This graph given below shows the comparison of staging height to base shear. Graph

shows that by increasing staging height base shear will decreasing for full and empty


Figure4.19 Comparison of staging height verses base shear for full and empty tank.

0

0.5

1

1.5

2

2.5

12m 16m 20m

Tim

e P

eri

od

(se

c)

Staging Height (m)

FULL

EMPTY

0

50

100

150

200

250

300

350

400

450

12m 16m 20m

Base

Sh

ear

(kN

)

Staging Height (m)

FULL

EMPTY

This graph given below shows the comparison of staging height to Redundancy

factor. Graph shows that by increasing staging height Redundancy factor will saame

for full and empty condition of 500m3 water tank.

Figure4.20 Comparison of staging height verses Redundancy Factor for full and

empty tank.

This graph given below shows the comparison of staging height to over strength.

Graph shows that by increasing staging height over strength will decreasing for full

and empty condition of 500m3 water tank.

Figure4.21Comparison of staging height verses Overstrength Facto for full and empty

tank

This graph given below shows the comparison of staging height to R factor. Graph

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

12m 16m 20m

Red

un

dan

cy F

act

or

Staging Height (m)

FULL

EMPTY

0

0.5

1

1.5

2

2.5

12m 16m 20m

Over

stre

ngth

Fact

or

Staging Height (m)

FULL

EMPTY

shows that by increasing staging height R factor will decreasing for full and empty


Figure4.22 Comparison of staging height verses R Facto for full and empty tank

4.5 Formulation of response reduction factor:

Response reduction factor is product of three factor 1) over strength factor 2) ductility

factor and 3) redundancy factor.

R = Rs * RR * R

For the formulation of R factor we take a 500m3(full condition) tank with 12m height,

zone 4, and staging type 6 columns.

Dimensions of all members are shown in figure below:

Static nonlinear analysis is done by using SAP with two nonlinear cases. Push 1and

Push 2. Push 1 includes dead load with full load control. Push 2 includes earthquake

load with displacement control, including multiple state in both cases.

Figure shows the pushover curve for 500m3(full), 12m height of water tank, damping

ratio is considered 5%.

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

12m 16m 20m

R F

acto

r

Staging Height (m)

FULL

EMPTY

Figure4.23 Pushover curve for 500m3(full condition) tank with 12m height.

From the pushover curve we can take yield drift (y) and maximum base shear (Vo):

y=0.024

Vo=733.65

Time period (t) = 1.45688

Design Base shear (as per EQ calculation) Vd = 401.5

Now, calculation for R:

Estimation of strength factor:

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 = 1.827

Estimation of ductility factor:

R = {( - 1 / ) + 1}

= m / y

m = Maximum drift capacity (0.004 H)

y = Yield drift (from pushover curve)

for rock sites: = 1+ {1 / (10T -T)}{(1 / 2T)*e^ (-2(ln (T) 0.6) ^2)}

Using this equations R = 2.23

Estimation of redundancy factor:

The value of redundancy factor as suggested in ATC-19 is summaries in Table 3.

Table 4.8 Results for Redundancy factor.

Lines of vertical seismic framing Drift redundancy factor

2 0.71

3 0.86

4 1

We have 3 lines of vertical framing so, RR is 0.86

Now R = Rs * RR * R

R=3.51

4.6 Summary:

In this chapter pushover analysis of 12m, 16m, and 20m height of water tank with

250m3 and 500m3 capacities with full and empty condition are done using SAP and R

factor is calculated. Calculation of R factor of 500m3(full), 12m height is shown.

Comparison of various result and its graphs are included and discussed. Effect of height

on R is studied. Comparison of R with different factors is shown with graph and

discussed about results.

CHAPTER-5 EFFECT OF

SEISMIC ZONE ON RESPONSE REDUCTION FACTOR

5.1 General:

Seismic behavior of water tank is changed in different seismic zones.so, R factor also

varies by changing the seismic zones. In this chapter effect of zones on R factor is

studied. Zone 2, 3, 4, 5 are taken for study of 20mheight of water tank. Change in R

factor for different zones is very important for the seismic design of elevated tank.

5.2 description of problem:



framed structure with different staging height of 20m, respectively, Zone 2, 3, 4, 5 and

staging type of 6 columns is fixed for the varying height. In this study, the column

staging supports are assumed as a fixed while the simple circular tie bracing has been

considered. Since the tank vessel is Intze, there is a symmetric in the loading and shape

of the vessel. This type of tank and supporting system has been widely used in the recent

years around the world.



Figure 5.1 Staging type 6 columns

5.3 Analysis of tank:

Analysis of tank is done by using SAP 2000. First of all 3D model of water tank is

generated. Now material property of concrete and loading is applied. For the loading,

dead load and earthquake load is applied for the zone 2, 3, 4, 5. Finally tank will be

analyzed.

5.4 Results and discussion:

Results of variation in zone are discussed as below. Zone varies from 2 to 5, staging

height is 20M and staging type is 6 columns tie bracing





Table 5.3 for zone II


Staging Type6 Col Circular Zone II



Base Shear 101 87




R 3.99 7.9




Table 5.4 for zone III


Staging Type6 Col Circular Zone III



Base Shear 161 141




R 3.2 4.86




Table 5.5 for zone IV





Base Shear 263 233




R 1.34 2.68




Table 5.6 for zone V


Staging Type6 Col Circular Zone V



Base Shear 280 316




R 1.23 2.68

Graphs for 250M3:

Effect of zone on different parameters is shown in graph:

This graph below shows the effect of zone on time period. Graph shows that time period will

remaining same by changing zones.

Figure 5.2 Comparison of zone verses time period for full and empty tank.

This graph below shows the effect of zone on base shear. Graph shows that base shear will

increasing by changing zones from 2 to 5.

Figure 5.3 Comparison of zone verses base shear for full and empty tank.

0

0.2

0.4

0.6

0.8

1

1.2

1.4

II III IV V

Tim

e P

eri

od

(se

c)

zone

FULL

EMPTY

0

50

100

150

200

250

300

II III IV V

Bas

e s

he

ar (

kN)

seismic zone

FULL

EMPTY

This graph below shows the effect of zone on R factor. Graph shows that base shear will

decreasing by changing zones from 2 to 5.

Figure 5.4 Comparison of zone verses R- factor for full and empty tank.

This graph below shows the effect of zone on three factor. Graph shows that R factor will

decreasing by changing zones from 2 to 5 for tank full and empty condition.

Figure 5.5 Comparison of zone verses three factor for full tank.

Figure 5.6 Comparison of zone verses three factor for empty tank.

0

2

4

6

8

10

II III IV V

R

FULL EMPTY

0

1

2

3

4

5

0 1 2 3 4 5

Fact

or

seismic zone

250m3 (Tank Full)

REDUNDANCY FACTOR

OVERSTRENGTH FACTOR

R Factor

0

2

4

6

8

10

0 1 2 3 4 5

Fact

or

seismic zone

250m3 (tank empty)

REDUNDANCY FACTOR

OVERSTRENGTH FACTOR

R Factor





Table 5.7 for zone II


Staging Type6 Col Circular Zone II



Base Shear 126.85 99.12




R 3.61 7.877




Table 5.8 for zone III


Staging Type6 Col Circular Zone III







R 2.24 4.61




Table 5.9 for zone IV









R 1.87 3.01




Table 5.10 for zone V


Staging Type6 Col Circular Zone V



Base Shear 456.68 356.77




R 1.01 2.04

Graphs for 500M3:

Effect of zone on different parameters is shown in graph:

This graph below shows the effect of zone on time period. Graph shows that time period will

remaining same by changing zones.

Figure 5.7 Comparison of zone verses time period for full and empty tank.

This graph below shows the effect of zone on base shear. Graph shows that base shear will

increasing by changing zones from 2 to 5.

Figure 5.8 Comparison of zone verses base shear for full and empty tank.

This graph below shows the effect of zone on R factor. Graph shows that base shear will

decreasing by changing zones from 2 to 5.

2.015 2.015 2.015 2.01

1.05 1.05 1.05 1.05

0

0.5

1

1.5

2

2.5

II III IV V

Tim

e P

erio

d (

sec)

zone FULL EMPTY

0

50

100

150

200

250300

350

400

450

500

II III IV V

Bas

e sh

ear

(kN

)

seismic zoneFULL EMPTY

Figure 5.9 Comparison of zone verses R-factor for full and empty tank.

This graph below shows the effect of zone on three factor. Graph shows that R factor will

decreasing by changing zones from 2 to 5 for tank full and empty condition. Over strength

decreases by changing the zone from 2 to 5. Redundancy remains same for every zone for

tank full and empty condition

Figure 5.10 Comparison of zone verses three factor for full tank.

Figure 5.11 Comparison of zone verses three factor for empty tank.

0

2

4

6

8

10

II III IV V

R

FULL EMPTY

0

1

2

3

4

5

0 1 2 3 4 5

Fact

or

seismic zone

500m3 (Tank Full)

REDUNDANCY FACTOR

OVERSTRENGTH FACTOR

R Factor

0

2

4

6

8

10

0 1 2 3 4 5

Fact

or

seismic zone

500m3 (tank empty)

REDUNDANCY FACTOR

OVERSTRENGTH FACTOR

R Factor

5.5 summary:

In this chapter pushover analysis of 20m height of water tank with 250m3 and 500m3

capacities with full and empty condition are done using SAP and R factor is calculated.

A study of variation in zone from 2 to 5 for the same height is made in this chapter.

Comparison of R with different factors and is shown using bar charts. Effect of zone on

R factor is studied and discussed.

CHAPTER-6 EFFECT OF WATER TANK STAGING

PATTERN ON RESPONSE REDUCTION FACTOR

6.1 General:

During the earthquake, bracing fails first in elevated type water tank. So, effect of

staging pattern on R is important to study.in our study, two type of staging pattern is

taken and R factor is calculated for these two staging pattern.

6.2 Description of problem:



framed structure with different staging height of 20m, respectively, Zone 4 is fixed for

the varying staging pattern. In this study, the column staging supports are assumed as a

fixed while the simple circular tie bracing and ross bracing has been considered. Since

the tank vessel is Intze, there is a symmetric in the loading and shape of the vessel. This

type of tank and supporting system has been widely used in the recent years around the

world.

Water tank Specification for 250m3 capacity:


These two staging pattern are taken:

Figure 6.1 Figure 6.2

Staging Type 1(tie bracing) Staging Type 2 (Ross bracing)


6.3 Analysis of tank:

Analysis of tank is done by using SAP 2000. First of all 3D model of water tank is

generated. Now material property of concrete and loading is applied. For the loading,

dead load and earthquake load is applied for the zone 4. Finally tank will be analyzed.

Height of tank is 20m.Ross bracing and Tie bracing is taken for analysis.

6.4 Results and discussion:

Result of staging effect on response reduction factor is discussed as below. Here height

of water tank is 20M and zone 4 is used. Two types of staging type tie bracing and Ross

bracing is studied for full and empty conditions.


Table 6.3 for tie bracing.





Base Shear 263 233




R 1.34 2.68

Table 6.4 For Ross bracing.





Base Shear 309 258




R 1.6 2.86


Table 6.5 for tie bracing.









R 1.87 3.01

Table 6.6 for Ross bracing.









R 1.34 2.74

6.5Summary:

In this chapter pushover analysis of 20m height of water tank with 250m3 and 500m3

capacities with full and empty condition are done using SAP and R factor is calculated.

A study of variation in staging type of 6 columns for the same height is made in this

chapter. Comparison of R with different factors and is shown using bar charts. Effect

staging R factor is studied and discussed.

CHAPTER-7 CONCLUSION

The water tanks Fundamental time period increases with increasing in staging

height. Also time period increases with the tank filling condition (full or empty).

The critical response is occurs in case of full tank conditions. This result may

be due to the fact that the hydrodynamic pressures higher in tank full case as

compared to empty water tank.

The Base shear is decreases as the staging height increases that is due to increase

in Time period and the dispersion of base shear is increased when the percentage

of the filling in the storage tanks are increasing.

The response reduction factor is considerably affected by the

fundamental time period of water tanks. It reduces as the fundamental time

period increases.

Estimation of response reduction factor with exact analysis will help in an

economical design.

It is observed that response reduction varies from 1.5 to 4 for tank in full

condition in seismic zone IV.

The response reduction factor is considerably affected by the staging height of

water tanks. It reduces as the height of water tank is increasing.

By changing the pattern of bracing from tie bracing to Ross bracing than R

factor is decreasing. So R-factor is affected by the type of bracing.