1
“DYNAMIC ANALYSIS OF RECTANGULAR AND
CIRCULAR RCC SILOS” Chetan Borase
1*, Rohan K. Choudhary
2
1MTech Student, Department of civil engineering, Sandip University, Nashik, India.
2Assistant professor, Department of civil engineering, Sandip University, Nashik, India.
Abstract: Silo is one of the storage structure which is required for industrial plants to store
various kinds of materials such as cement, coal, grains, etc. Hence it is necessary to judge
regarding the design procedures for such structures, which includes the study of codal
provisions leading to analysis and design along with detailing of the same. In order to reveal
the dynamic response mechanism of silo-storage-foundation system under seismic wave
loading, the silo is simplified as a thin-walled cylindrical shell structure with fixed bottom
and free upper part. The various load intensity and structural parameters calculate using
Janssen’s theory as per IS: 4995 (Part I and Part II): 1974. Analysis of silo done using
Response Spectrum Method and Wind Analysis. The considered silos are studied for seismic
zone-III as per IS: 1893 (Part-I):2016 and wind analysis is carried out as per IS: 875 (Part-
III): 2015. The circular and rectangular silo is model and analysis is carried out in STAAD
Pro. Result are obtained in the form of lateral displacement and base shear. Base shear is
increases with height to diameter ratio increase and also for the higher seismic zone.
1.1 INTRODUCTION
Storage structure likes bins are basically called as silos and bunkers for storing
different type of material. Classification of silo and bunker is depending upon the plane of the
rupture. As per the IS code 4995(Part I):1974 Height/Diameter ratio greater than or equal to
two for the reduction of lateral pressure over the large height takes place. Basic shape of silo
is circular but as per requirement it could be square, rectangular or polygonal shape and it is
provided with roof and bottom which may be conical, pyramidal or flat.[2] Silos are generally
supported with number of column, total structure wall, hopper bottom and column is
connected by the ring beam to distribute the load. Silo basically design for both vertical and
horizontal pressure. The exact pressure calculation is difficult due to the many factor acts
during the emptying and filling of material. Silo, bins, or bunker are container used for
storing bulk solids. Silo structure may be elevated or rest on ground have circular, square or
rectangular in shape. Rectangular or Square silos usually have single outlet with pyramidal
bottom, but sometimes a trough bottom is used with a single elongated outlet or two or more
circular or square outlet. Silo which is in circular shape have flat bottom or conical bottom
with single outlet. Material used for construction of silo may be RCC & steel.[5]
Governing factor in design of silos are the type of material stored in it and there
properties. Bulk material density, frictional properties & pattern of material flow varies
generously, the applied loads and load caring system different in structure like silo than other
traditional structure. Silos are designed as special structure & also design is based on the
strength design method.[3]
Storage container & silo fails because of many reason. Failure of silo categories depend on
silo failure causes which are as follows,
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Failure due to design
Failure due to construction
Failure due to usage
Failure due to maintenance
An earthquake analysis effective components acting on silo due to structural loading are the
two horizontal and one vertical direction. Silos have effect of seismic vertical loads is small,
compare to lateral seismic loads on the tall silos storing heavy material. Seismic load
magnitude in lateral direction directly related to the weight of silo. In earthquake analysis
increase of lateral load bending moment also increases result of this non uniform pressure at
bottom of silo increase as compare to pressure due gravity load.
Fig.No. 1.a Undamaged silos [2] Fig.No. 1.b silos damaged at SEKA paper
mill during 1999 Kocaeli [2]
2.1 METHODOLOGY
Dynamic analysis and seismic behavior of RCC silo and avoid failure of RCC silo
during earthquake seismic force calculated by using IS code. Results will cross check by
using structure design software.
1. Calculation of pressure acting on the wall of silo using height to diameter ratio and
angle of internal friction by using Janssen’s theory.
2. Design of silo using IS specifications.
3. Modeling and analysis of different shapes of silo by using Staad pro software..
4. Calculation and comparison of natural frequency, time period and displacement for
different mode shapes.
5. Calculation and validation of natural frequency, time period using Rayleigh ritz
method.
2.2.1 LOAD CONSIDER FOR SILO DESIGN
Loads should be applied to the structural design of a silo according to its intended use, size,
structure type, materials, design lifetime, location and environment, in order to assure life
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safety and to maintain its essential functions.
The applied loads should be as follows, and their combinations should be defined considering
the actual probability of occurrence.
Dead loads
Live loads
Snow loads
Wind loads
Seismic loads
Impulse and suction due to content sloshing, and pressure due to content
Thermal stresses
Shock,
Fatigue loads
Soil and water pressures
Others
2.2.2 PROBLEM STATEMENTS
In this paper RCC single hopper silos and double hopper silo is analyzed using
STAAD-PRO V8i.
1. Self weight
DL/m2=Thickness x Density = 25x0.2= 0.5 KN/m2
2. Load on vertical walls
Ph=γhk
=25x12x0.4
=120kN/m2
Where k is 0.25 ≤ k ≤ 0.6(Ref. Janssen’s theory )
3. Earthquake load
Zone-III
Zone factor-0.16
Soil Condition-Medium
Time Period-Ta=0.09h/√d=0.62sec
Sa/g-2.5
Damping Ratio=0.05
Type of support-Fixed support
2.2.3 ANALYSIS OF SILO
For calculation of static pressure on silo wall parameter consider for silo design as per
IS code. While calculation done for seismic force parameter used for calculation of seismic
force will varies with their respective code condition that parameter. Following data consider
for calculation of silo pressure
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Table No. 1 Problem statement
Type RCC silo RCC silo RCC silo
Purpose of silo Storage of cement Storage of cement Storage of cement
Configuration
A single free
standing
rectangular shape
Double free
standing
rectangular shape
Double free
standing circular
shape
Height of silo 12m 12m 12m
Length 3m 1.5m 3.38(Dia)
Width 3m 1.5m 3.38(Dia)
Thickness of silo 200mm 200mm 200mm
Storage product density 15.50kN/m3 15.50kN/m3 15.50kN/m3
Angle of internal
friction 25 25 25
Friction coefficient of
tank wall 0.46 0.46 0.46
coefficient of wall
friction(ȝ) Tan𝜑 tan𝜑 tan𝜑
Seismic zone III III III
Grade of RCC 20 20 20
3 RESULT AND CONCLUSION
3.1 Rectangular silo full condition
Figure no-.2 (Displacement for rectangular silo)
02468
10
X Y Z
8.01
0.0186 0.00172
X Y Z
Series1 8.01 0.0186 0.00172
Displacement for rectangular silo
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Figure No-3 (Velocity forrectangular silo)
Figure no-4 (Acceleration for rectangular silo)
3.2. Circular Silo Full Condition
Figure no-5 (Displacement for circular silo)
0102030405060
X Y Z
57.8
0.0134 0.00131
X Y Z
Series1 57.8 0.0134 0.00131
Velocity for rectangular silo
Series1
00.10.20.30.40.50.6
X Y Z
0.525
0.00122 0.000102
X Y Z
Series1 0.525 0.00122 0.000102
Acceleraction for rectangular silo
0
2
4
6
8
X Y Z
6.86
0.0315 0.117
X Y Z
Series1 6.86 0.0315 0.117
Displacement for circular silo
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Figure No-6 (Velocity for circular silo)
Figure no-7 (Acceleration for circular silo)
3.3 Comparison For Empty And Full Condition
3.3.1 Rectangular silo
Table no-2 (Time-Displacement for rectangular silo)
TIME-DISPLACEMENT
Full condition Empty Condition
X Y Z X Y Z
At top
nodes 8.01 0.0186 0.00172 10.1 0.0163 0.00118
At middle
nodes 7.97 0.0176 0.00164 10.1 0.0156 0.00116
At bottom
nodes 7.96 0.00294 0.00161 10 0.00259 0.00113
0
20
40
60
80
X Y Z
68.3
0.314 1.1
X Y Z
Series1 68.3 0.314 1.1
Velocity for circular silo
Series1
00.10.20.30.40.50.6
X Y Z
0.561
0.00258 0.0106
X Y Z
Series1 0.561 0.00258 0.0106
Acceleration for circular silo
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Table no-3 (Time-velocity for rectangular silo)
TIME-VELOCITY
Empty condition Full Condition
X Y Z X Y Z
At top
nodes 57.1 0.0921 0.00669 57.8 0.0134 0.00131
At middle
nodes
56.9
0.0883 0.00645 57.6 0.00127 0.00126
At bottom
nodes
56.9
0.0147 0.00609 57.5 0.0212 0.00124
Table no- 4 (Time-Acceleration for rectangular silo)
TIME-ACCELERATION
Empty condition Full Condition
X Y Z X Y Z
At top
nodes 0.506 0.00082 0.0000406 0.525 0.00122 0.000102
At middle
nodes 0.505 0.00079 0.000034 0.522 0.00116 0.000973
At bottom
nodes 0.504 0.00013 0.0000338 0.521 0.00194 0.000962
3.3.2 Circular silo
Table no-5 (Time displacement for circular silo)
TIME-DISPLACEMENT
Empty condition Full Condition
X Y Z X Y Z
At top
nodes 7.07 0.0325 0.118 6.86 0.0135 0.117
At middle
nodes 7 0.032 0.118 6.79 0.0311 0.117
At bottom
nodes 6.96 0.096 0.113 6.75 0.0931 0.118
Table no-6 (Time Velocity for circular silo)
TIME-velocity
Empty condition Full Condition
X Y Z X Y Z
At top
nodes 69.4 0.319 1.15 68.3 0.134 1.1
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At middle
nodes 68.7 0.314 1.12 67.6 0.310 1.12
At bottom
nodes 68.3 0.0943 1.21 67.2 0.0923 1.13
Table no-7 (Time Acceleration for circular silo)
TIME-ACCELERATION
Empty condition Full Condition
X Y Z X Y Z
At top
nodes 0.668 0.00314 0.0112 0.561 0.00258 0.0106
At middle
nodes 0.661 0.00309 0.0109 0.555 0.00255 0.0107
At bottom
nodes 0.657 0.00972 0.0102 0.552 0.00076 0.0108
6.6 ABSOLUTE STRESSES
6.6.1 RECTANGULAR SILO
6.6.1.1 Absolute stresses of rectangular silo for empty condition
Fig no-8 (Absolute stresses of rectangular silo empty condition)
6.6.1.2 Absolute stresses of rectangular silo for partially full condition
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Fig no-9(Absolute stresses of rectangular silo partial condition)
6.6.1.3 Absolute stresses of rectangular silo for full condition
Fig no-10 (Absolute stresses of rectangular silo full condition)
6.6.1.4 Absolute stresses of rectangular silo comparison
Figure no- 11 (Absolute stresses of rectangular silo)
max stresses min stresses
empty condition 0.196 0.024
partial condition 4.94 0.549
full condition 9.86 1.07
0
2
4
6
8
10
12
Absolute stresses of rectangular silo
empty condition partial condition full condition
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6.6.2 ABSOLUTE STRESSES FOR CIRCULAR SILO
6.6.2.1 Absolute stresses for circular empty condition
Fig no-12(Absolute stresses of circular silo empty condition)
6.6.2.2 Absolute stresses for circular partially full condition
Fig no-13(Absolute stresses of circular silo partial condition)
6.6.2.3 Absolute stresses for circular full condition
Fig no-14(Absolute stresses of circular silo full condition)
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6.6.2.4Absolute stresses of circular silo comparison
Figure no-15 (Absolute stresses of circular silo)
Fig No.16. Shear stress develop at edge of single hopper silos
Fig No17 Shear stress develop at edge of double hopper silos
max stresses min stresses
empty condition 0.257 0.041
partial condition 1.03 0.156
full condition 5.52 0.583
0
1
2
3
4
5
6
Absolute stresses of circular silo
empty condition partial condition full condition
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CONCLUSION
1. For rectangular silos, Time-displacement, time-velocity, Time-acceleration is high at
topside and decreases towards downside same results to be appear for circular silos
also.
2. Absolute stress are decreases for empty condition whereas for in full condition
stresses are constant in both rectangular and circular silos.
3. Shear stresses are generating at edges due to heavy loading at bottom side so
accordingly thickness of plate should be decided.
REFERENCES
1. Uzma Wani, “Dynamic Analysis of Steel Silo using Wind Load As Per Indian
Standard” November 2019, pp. 402-405.
2. Akshita Meshram, “Analysis and Design of Rcc Silo Structure by Considering Indian
Seismic Zones”, 2019, pp. 49-52.
3. Sagar R. Aambat, 2 Sunil M. Rangari and 3 Priyanka A. Jadhav 'Effect of Height to
Lateral Dimension Ratio on Dynamic Behaviour of Rcc Circular Silo' Volume 7 Issue
6 Ver I || June 2018,pp. 62-68.
4. Anurag R.Warade, “Analysis and Design of LongConcrete Silo Having Different
Height and Diameter under Earthquake Effect” 2018, pp. 145-154.
5. Christoph Butenweg 1, Julia Rosin 1, and Stefan Holler 2 'Analysis of Cylindrical
Granular Material Silos under Seismic Excitation' July 2017, pp. 1-12.
6. Pradnya P.Dhamdhere, Y.R.Suryawanshi 'A Study of Comparison of RCC Silos
under Influence of Dynamic Loading In Accordance With Is-1893:2002'
volume1,Issue2,June 2017
7. Ms Rini Riyansi.E1; Mrs. Abida Justus2 'Comparative Study of Silo Supporting
Structure Using RCC & RCC' Vol. 3, Issue 35, April 2017, pp. 133-145.
8. Chirag L. Korat1 ,Jasmin A. Gadhiya2 ,Hardik A. Patel 'A Review on Parametric
Study of Circular RCC Silo having Hopper Bottom' Volume 4, Issue 11, November -
2017,pp 495-499.
9. Pooja. B. Suryawanshi Prof. H. G. Sonkusare 'Review Paper on Collapse Analysis of
Seismically Designed RCC Braced Frame'Volume 2 | Issue 07 | January 2016, pp.
118-119.
10. K.Dharani, D.Jeyakumar 'A Brief Review on Bunkers and Silos' Volume 4 Issue X,
October 2016, pp. 323-327.
11. Afzal Ansari1, Kashif Armaghan2, Sachin S. Kulkarni3 ' Design and Optimization of
RCC Silo' Volume 4 Issue VI, June 2016, pp. 458-466.
12. Sagar Belgaonkar, “Behavior of Circular RCC Silo under Earthquake Forces”, August
2016, pp. 67-71.
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13. IS 875 (Part 1):1987, “Code of practice for design loads (other than earthquake) for
building and structures- Dead Loads- Unit weights of building materials and stored
materials”, BIS, New Delhi
14. IS 875 (Part 2):1987, “Code of practice for design loads (other than earthquake) for
building and structures- Imposed Load”, BIS, New Delhi
15. IS 875 (Part 3):2015, “Code of practice for design loads (other than earthquake) for
building and structures- Wind Load”, BIS, New Delhi
16. IS 1893 (Part 1): 2016, “Criteria for earthquake resistant design of structure”, BIS,
New Delhi
17. IS 4995(Part 1): 1974, “Criteria for design of reinforced concrete bins for the storage
of granular and powdery materials- General requirement and assessment of bin
loads”, BIS, New Delhi
18. IS 4995(Part 2): 1974, “Criteria for design of reinforced concrete bins for the storage
of granular and powdery materials- Design criteria”, BIS, New Delhi
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