Evaluation of Various-Shaped Elevated RCC Water Storage

Vessels in Zone V
S.W. Dhengarea, U.P.Wagheb, Abhishek Dakholec, R.M.Bhagatd

Civil Engineering Department, Yeshwantrao Chavan College of Engineering, Nagpur, India

a)
Corresponding author:swdhengare@ycce.edu
b
principal@ycce.edu, cabhidakhole123@gmail.com, drmbhagat@ycce.edu

Abstract. This study examines the structural performance of different Elevated Storage Reservoirs (ESRs) under static
earthquake conditions, focusing on Zone V, a severe earthquake zone, to provide water for human habitation and
industry. The study analyses axial forces, bending moments, staging displacement, and horizontal bending moments in
columns, beams, and tank walls, revealing significant structural variations among different shapes. This comparative
analysis enhances ESR design philosophy for economical, safer, and cost-effective solutions, enhancing resilience in
earthquake-prone areas for essential water supply.

Keywords: Elevated storage reservoir, convective hydrodynamic pressure, impulsive hydrodynamic pressure, equivalent
static and dynamic analysis, etc.

INTRODUCTION

The Indian subcontinent faces high vulnerability to natural disasters, including earthquakes, cyclones, floods, and
droughts, based on seismology data. Most states and union territories in India are susceptible to one or more of these
disasters, resulting in significant losses in terms of life, property, and wealth annually. Earthquakes, due to their
impact on structural stability, are particularly concerning, often causing irreversible loss of life. Poorly designed or
constructed structures contribute to these losses, as many buildings are not designed to withstand seismic activity.

The Indian code IS: 1893 (Part 1): 2016 highlights that over 60-70% of the country is in mild to severe earthquake
zones, emphasizing the need to analyse structures within specified seismic zones. Elevated water tanks, crucial for
human life sustainability, are a major component of water supply systems in Indian states. These tanks, known as
elevated storage reservoirs (ESRs), face vulnerability to horizontal forces like earthquakes, necessitating a thorough
assessment of seismic effects.

ESRs consist of a tank supported by a staging framework, including foundations, columns, and braces. Despite their
importance for daily water needs, ESRs have experienced failures during earthquakes. To address this, new
development strategies are crucial, involving the retrofitting of structures with control devices to reduce stresses and
enhance seismic resistance while keeping construction and maintenance costs low. Scientists and researchers have
proposed separate spring-mass models for different types of tanks, suggesting the use of a single spring-mass model
for tanks with rigid and flexible walls. Updated expressions for convective hydrodynamic pressure and simplified
representations of sloshing wave height have been introduced. For elevated water tanks with framed-type staging,
new provisions account for earthquake loading direction and vertical excitation effects .
 METHODOLOGY
The goal of this project is to use the finite element method to conduct seismic analysis under severe seismic
conditions on square and circular elevated storage reservoirs (ESRs). Static seismic analysis is used in this work to
analyse the RC walls, beams, columns, and slabs that make up the ESR structural system. According to IS code
1893—Parts 1 and 2 and the IITK-GSDMA guidelines for the seismic design of liquid storage tanks, the various
pressure and force coefficients are calculated. With STAAD-Pro, modelling, and analysis are carried out. The two
distinct cases that are taken into account in this work are seismic analysis and the behaviour of ESR structures with
the same capacity but different shapes. There are four distinct ways that the ESRs are modelled:

M1: Static seismic analysis of a circular water tank.

M2: Static seismic analysis of a square water tank.

Table 1. Geometry Parameter considered for M1 models

Tank Parameters Details

Type of Structure Square E.S. R

Stagging Height 12.00 m

Nos. of Stagging 03 Nos

Square Side Dimensions 5.30 m

Depth of water 03.60 m

Free-Board 00.30 m

Tank Height 04.30 m

Grade of concrete M30

Grade of Steel Fe500

Table 2. Geometry Parameter considered for M2 models

Tank Parameters Details

Type of Structure Square E.S. R

Stagging Height 12.00 m

Nos. of Stagging 03 Nos

Square Side Dimensions 5.30 m

Depth of water 03.60 m

Free-Board 00.30 m

Tank Height 04.30 m

Grade of concrete M30

Grade of Steel Fe500

 Table 3. Gravity Load Consideration

Loads Intensity Unit Remarks

Water Density 10 kN/m3 As per Standard Practice

Live load on Roof 1.5 kN/m2 As per IS 875 Part 2

Live load on Gallery 2 kN/m2 As per IS 875 Part 1

Density of Concrete 25 kN/m3 As per IS 875 Part 1

Table 4. Table Seismic Loading Parameter

Parameter Factor Remark

Seismic Zone V As per Site Location

seismic Coefficient 0.36 As per IS 1893:2016 part I

Response Reduction Factor 4 As per IS 1893:2014 part IV

Importance Factor 1.4 As per IS 1893:2014 part IV

Table 5: Earthquake calculations for M1 & M2 Models

Member Length(m) Nos Width/Area2 Ht.(m) Member(kN)

Roof Beams 4.243 4 0.25 0.25 26.52

Roof Slab Area 1 28.26 0.15 105.98

Circular Wall 18.85 1 0.2 4.3 405.27

Base Slab Area 1 28.26 0.2 141.3

Cantilever Gallery Area 1 27.13 0.15 101.79

Base Slab beams 4.243 4 0.3 0.4 50.92

Staging beams 50.916 1 0.25 0.4 127.29

Staging Columns Area 4 0.12566 12 150.72

Water Volume 100cu.m 1000.00

 Table 6: Earthquake calculations for M3 & M4 models Liquid

Member Length(m) Nos Width/Area2 Ht.(m) Member(kN)

Roof Beams 5.3 2 0.25 0.25 26.52

Roof Slab Area 1 28.09 0.15 105.98

Wall 21.2 1 0.2 4.3 405.27

Base Slab Area 1 28.09 0.2 141.3

Cantilever Area 1 25.2 0.15 101.79

Gallery

Base Slab beams 5.3 4 0.3 0.4 50.92

Staging beams 5.3 12 0.25 0.4 127.29

Staging Columns Area 4 0.1257 12 150.72

Water Volume 100cu.m 1000.00

STAAD MODELS

Figure 1. Circular ESR model and Square ESR model

Models for seismic load combinations were analysed using references to IS 456:2000 and IS 1893 Part II: 20161.
View the load combinations for in the table below. STAAD Pro software was used to analyse the models. The load
combination's notation is as follows: WL stands for water load, DL for dead load, LL for live load, EQ for
earthquake load, WLEQ for earthquake water load, and IMP&CON for impulsive and convective
 Table 7. Seismic Weight Comparison between STAAD Pro & Manual Calculation

Seismic Weight Comparison between STAAD Pro & Manual Calculation

Circular Tank Rectangular Tank
Level STAAD Manual Difference STAAD Manual (kN) Difference
Pro.(kN) (kN) (kN) Pro. (kN) (kN)
Plinth Level 2.0 m 20.817 20.817 0 23.46 23.46 0
Staging level - 6.5 m 24.744 24.744 0 27.387 27.387 0
Staging level - 11.0m 22.388 22.388 0 25.031 25.031 0
Staging level - 14.0m 500.294 492.05 8.246 535.401 519.331 16.070

Seismic weight calculations in STAAD Pro, a structural analysis and design software, involve utilizing advanced
algorithms to determine the seismic forces acting on a structure based on code provisions. This automated process
considers the structure's geometry, material properties, and seismic parameters, providing accurate results
efficiently. In contrast, manual seismic weight calculations involve more labour-intensive procedures, where
engineers manually apply seismic coefficients and consider various factors to determine seismic loads. While both
methods aim to ensure structural integrity, STAAD Pro offers a quicker and more precise solution, leveraging
computational power for complex seismic analyses compared to the time-consuming nature of manual calculation.
On the other hand, manual calculation involves the application of engineering principles and formulas by hand.
Engineers perform calculations for seismic forces based on seismic coefficients, modal analysis, and response
spectrum methods. This process is time-consuming and prone to human error, but it offers a deeper understanding of
the underlying calculations and assumptions. The seismic weight comparison aims to assess the consistency and
reliability of results obtained from STAAD Pro and manual calculations. Engineers may use both methods to cross-
verify their findings, ensuring that the structure meets safety standards and regulatory requirements. While STAAD
Pro streamlines the process and reduces the likelihood of errors, manual calculations offer a valuable check to
validate the software-generated results and ensure the structural integrity and safety of the design. Ultimately, the
choice between STAAD Pro and manual calculation depends on the project requirements, the complexity of the
structure, and the engineer's preferences for validation and verification processes.

Table 8: Load Combination for Static Analysis

Load Case Load Combination for Static Analysis

101 1.5(DL+LL+WL)
102 1.2(DL+WLEQ+EQX)
103 1.2(DL+WLEQ-EQX)
104 1.2(DL+WLEQ+EQZ)
105 1.2(DL+WLEQ-EQZ)
106 0.9DL+1.5(WLEQ+EQX)
107 0.9DL+1.5(WLEQ-EQX)
108 0.9DL+1.5(WLEQ+EQZ)
109 0.9DL+1.5(WLEQ-EQZ)
110 1.5(DL+WLEQ+IMP)
111 1.5(DL+WLEQ+CONV)
112 1.2(DL+LL+WLEQ+IMP)
113 1.2(DL+LL+WLEQ+CONV)
114 0.9DL+1.5(WLEQ+IMP)
115 0.9DL+1.5(WLEQ+CONV)
Load combinations in structural engineering involve considering various combinations of different types of loads to
assess the structural response accurately. These combinations typically include factors for dead loads, live loads,
snow loads, wind loads, and other relevant forces. These load combinations help ensure that the structure is designed
to withstand a range of potential loading scenarios, enhancing overall safety and performance .

RESULTS AND DISCUSSION

STAAD-Pro software is used to analyse the models following the preparation of the modelling and application of
loads in accordance with IIT guidelines for liquid storage tanks. Following examination of two the results are
extracted from various shapes models using a static seismic analysis process. The outcomes are extracted and
compared for the various parameters that are being considered. Four distinct ESR models are being considered, and
the schematic representation of the results is plotted in tables and graphical format for each.

Circular Water tank using Static-ESR Square Water tank using Static -ESR

Figure 2: critical horizontal displacement of staging in x- direction for both circular esr’s
& square esr’s

Figure 3. Comparison of Maximum Bending Moment in columns for Circular ESR’s & Square ESR’s in Static
condition.
 Figure 4. Comparison of Maximum Axial Forces in Columns for both Circular ESR’s & Square ESR’s in Static
condition

Bending Moment in Staging Beams

380
360
340
320
300
280
Max moment in column

Square ESR- Static Circular ESR- Static

Fig. 5: Comparison of Maximum Bending Moment in Staging Beams for both Circular ESR’s & Square ESR’s in
Static condition

Bending Moment in Base Slab Beams

141
140
139
138
137
136
135
134
133
Max moment in column

Square ESR- Static Circular ESR- Static

Fig.6: Comparison of Maximum Bending Moment in Base Slab Beams for both Circular ESR’s & Square ESR’s in
Static condition
 Horizontal Moment in Tank wall
45
40
35
30
25
20
15
10
5
0
Square ESR- Circular ESR-
Static Static

Fig.7: Comparison of Maximum Bending Moment in Staging Beams for both Circular ESR’s & Square ESR’s in
Static condition

Vertical Moment in Tank wall

45
40
35
30
25
20
15
10
5
0
Square ESR- Circular ESR-
Static Static
Fig. 8: Comparison of Maximum Vertical Bending Moment in Tank wall for both Circular ESR’s & Square ESR’s
for Static condition

Displacement in frame at stagging levels

200

150

100

50

0
Max moment in
column

Square ESR- Static Circular ESR- Static

Fig. 9: Comparison of displacement in frame at staging level for both Circular ESR’s & Square ESR’s in Static
condition
 Base shear at different stagging levels
2250

2000

1750

1500

1250

1000

750

500

250

0
At E.L. At E.L. At E.L. At E.L. At E.L.
0.0 M 2.0 M 6.5 M 11.0 M 14.0 M
Square ESR (kN) 0 83.268 98.976 89.552 2001.176
Circular ESR (kN) 0 93.84 109.548 100.124 2141.604

Fig. 10: Comparison of Base shear at different staging level for both Circular ESR’s & Square ESR’s

The graph above demonstrates that, in static conditions, the base shear values for both square and circular ESRs are
almost equal at various staging levels. The reason for this is that the With the exception of the tank section, both
models' geometry is very similar. That for the square ESR model, there is a modest increase in base shear.

CONCLUSION
After comparing the data, it is discovered that while there is very little difference in the axial forces in the
columns, there is a noticeable difference in the bending moments of the columns for circular ESR compared to
circular ESR. Additionally, for both models, the percentage of steel needed in columns is higher in dynamic than in
static conditions. Therefore, compared to circular ESR, the percentage of steel needed for square ESR in columns is
higher. After comparing the data, it is also discovered that, in the static condition, there is a significant difference in
the bending moments of the beams for the Square and Circular ESRs. Therefore, compared to circular ESR, the
percentage of steel needed for square ESR in beams is higher. Compared to circular shapes, the displacement for
ESRs with square shapes at various staging heights is continuously increasing. This suggests that, when taking the
seismic effect into account, the circular ESR is more stable than the square ESR. In addition, compared to circular
ESR, the results of horizontal bending moments in the tank wall for square ESR models are noticeably higher.
Which suggests that the square shape of a wall's junction places more stress on it than a circular one does. Which
lead to an additional steel provision at the corner junction. Circular ESRs are preferable over square or rectangular
ESRs from an economic and stability standpoint after the analysis process is completed, the results are extracted,
and they are compared.

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