dynamic analysis of rectangular and circular rcc silos

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


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


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


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


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


building and structures- Imposed Load”, BIS, New Delhi


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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dynamic analysis of rectangular and circular rcc silos

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