The International Journal Of Science & Technoledge
(ISSN 2321 – 919X)
www.theijst.com
THE INTERNATIONAL JOURNAL OF
SCIENCE & TECHNOLEDGE
Comparative Study of Seismic Base Shear of
Reinforced Concrete Framed Structures in Different Seismic Zone
Sunayana Varma
B.Tech Final Year Student, Panimalar Engineering College, India
A. Malar
B.Tech Final Year Student, Panimalar Engineering College, India
S. Thenmozhi
B.Tech Final Year Student, Panimalar Engineering College, India
T. Suriya
B.Tech Final Year Student, Panimalar Engineering College, India
G. Murali
Assistant Professor, Panimalar Engineering College, India
B. Venugopal
Assistant Professor, Panimalar Engineering College, India
K. Karthikeyan
Assistant Professor, VIT University, India
Abstract:
In the seismic design of reinforced concrete framed structure it is important to know the order of magnitude of the probable
maximum base shear as related with the mass of structures. In this study, a comparison has been made between the base
shear of RC frame located at various zones. For this purpose four building models are developed, corresponding to the
structures constructed on rock soil of seismic zones II, III, IV and V of India (as per IS: 1893-2002). The base shear for the
four models was calculated manually as well as using Staad Pro and Etabs software package and was compared with each
other. When calculated manually the base shear of zone III, IV and V was1640.49, 2460.74 and 3691.12 kN respectively
and it was increased up to 1.07% and 18.67% in case of Staad pro and Etabs respectively.
Keywords: Base shear, seismic zones
1. Introduction
Earthquakes are a natural hazard which causes great ruin to structures. They occur due release of energy accumulated in the
earth’s crust overtime causing damage not only limited to buildings but also to the life they sustain. The unpredictable nature of
earthquakes has presented itself to be a mind boggler to civil engineers all around the globe and the target to build earthquake
resistant buildings still remains. Equivalent lateral force method is the most common procedure adopted, wherein the base shear is
computed as a whole and then distributed along the height of the structure. In case of a rigid frame, the total shear on any one
plane is distributed to the various elements on the plane with respect to their relative rigidity. It becomes an absolute necessity that
structures with limited height must at least cross the threshold of safety with reference to the static load method. The basic concept
of earthquake resistance design of reinforced concrete structures is to make strong column- weak beam construction to make sure
safety of user means during [1-3]. Analysis was carried out the existing slender RC brick with brick infill with openings for
windows and doors, for different zones like II, III, IV and V [4]. The evaluation of the storey stiffness of buildings with soft storey
was analysed using MIDAS GEN software [5].
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Vol 2 Issue 8
August, 2014
The International Journal Of Science & Technoledge
(ISSN 2321 – 919X)
www.theijst.com
Figure 1: Key plan of the building.
Figure 2: Three dimensional line diagram of the building.
In this paper, three dimensional analyses had been carried out on typical frame of four storey RC building. The frame was
assumed to be designed for institutional building with nine and two bays in x and z direction and typical storey height of 3.5 m
was considered as shown in Fig. 1 and 2. The three dimensional view of the building which was modeled in Staad Pro and Etabs
was shown in Fig 3. The dimension of the beam and column was obtained by optimization and the preliminary datas which was
assumed for this investigation was presented in table1.
Figure 3: Three dimensional rendered view of the building from Staad pro and Etabs
1
2
3
4
5
6
7
8
9
10
11
12
13
Type of structure
Multi – storey rigid jointed RC moment resisting frame
Seismic Zone
II,III,IV,V (Table 2, IS 1893 (Part I): 2002)
Number of stories
4, (G+3)
Floor Height
3.5m
Infill Wall
250 mm thick including plaster in longitudinal and transverse directions.
Imposed Load
5 kN/m2 as per [6]
Materials
Concrete (M25) and Reinforcement (Fe415)
Size of columns
0.45m * 0.45m
Size of beams
0.35m * 0.6m
Depth of slab
0.25m (including finishes)
Specific weight of RCC
25 kN/m3
Specific weight of Infill
20 kN/m3
Type of soil
Medium soil site
Table 1: Preliminary data’s for the investigation
2. Calculation of Lumped Masses to Various Floor Levels
The earthquake forces shall be calculated for the full dead load plus the percentage of imposed load as given in Table 8 IS 1893
(Part I): 2002.The imposed load on the roof is assumed to be zero. The lumped masses of each floor are worked out as follows:
2.1. Roof
Mass of infill + Mass of columns + Mass of beams + Mass of slabs + Imposed load of that floor if permissible.
= (0.25*36*2*(3.5/2)) + (0.25*9.3*2*(3.5/2)*20) + (0.45*0.45*(3.5/2)*30*25) + ((0.35*0.6*4*(9+9+9)) +
(0.35*0.6*(12.8*10))*25) + (0.25*36*12.8*25) + 0
=792.75 + 265.781 + 1239 + 2880 = 5177.531 KN (weight) = 527.78 ton (mass)
2.2. III, II, I Floors
= (0.25*36*2*3.5) + (0.25*9.3*2*3.5*20) + (0.45*0.45*3.5*30*25) + ((0.35*0.6*4*(9+9+9)) + (0.35*0.6*(12.8*10))*25 ) +
(0.25*36*12.8*25) + (5*36*12.8*0.5**)
**50% of imposed load, if imposed load is greater than 3 KN/m2
=1585.5 + 531.5625 + 1239 + 2880 + 1152 = 7388.0625 KN (weight) = 753.115 ton (mass)
2.3. Seismic Weight of the Building
= M1+M2+M3+M4 = 527.78 + (3*753.115) = 2787.125 ton
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Vol 2 Issue 8
August, 2014
The International Journal Of Science & Technoledge
(ISSN 2321 – 919X)
www.theijst.com
Any weight supported in between stories shall be distributed to the floors above and below in inverse proportion to its distance
from the floors.
2.4. Determination of Design Base Shear for Zone II
Design seismic base shear
2.5. Earthquake Forces Data
Earthquake load for the building has been calculated as per IS-1893-2002:
Zone (Z) = II
Response Reduction Factor ( RF ) = 5.0
Importance Factor ( I ) = 1.5
Rock and soil site factor ( SS ) = 1
Type of Structures = 1
Damping Ratio ( DM ) = 0.05
From Clause 6.4.5,
For rock soil sites (Sa/g) = 2.5 (0.1<T<0.55)
Ah = (0.1/2)*0.3*2.5 = 0.0375
Design seismic base shear VB = 0.0375*2456.217*9.81 = 1025.313 KN
2.6. Vertical Distribution of Base Shear
The design lateral force Qi, computed shall be distributed along the height of the building as per the following expression,
Where, Qi = Design lateral forces at floor i, Wi = Seismic weights of the floor i, hi = Height of the floor i measured from base,
Base shear is distributed as follows,
Q1 = (1025.313*7388.0625*3.52 ) / (7388.0625*3.52)+( 7388.0625*72)+( 7388.0625*10.52)+
( 7388.0625*142) = 40.666KN.
Similarly the lateral force was calculated for the top three floors;
Q2 = 162.665 KN
Q3 = 365.998 KN
Q4 = 455.98 KN
Figure 4: Shear Diagram for the different seismic zone
The value of lateral forces was significantly increased from bottom floor to top floor in the equivalent lateral force method in all
four Zones. The base shear was obtained by equivalent lateral force method was more for lower floors and are less for upper
floors and the variation of base shear for all the zones was shown in Fig 4.
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The International Journal Of Science & Technoledge
S.No
Zone
1
2
3
4
II
III
IV
V
Results from Manual
Results from
calculation
Staad pro
1025.30
1081.19
1640.49
1622.87
2460.74
2434.30
3691.12
3651.46
Table 2: Base shear (kN) results
5000
BASE SHEAR (kN)
(ISSN 2321 – 919X)
4000
3000
www.theijst.com
Results from
Etabs
1216.75
1946.80
2920.20
4380.30
MANUAL
STAAD
PRO
2000
1000
0
II
III
ZONES
IV
V
Figure 5
3. Results and discussion
In this study the seismic base shear was determined using Staad pro and Etabs software package and the values obtained from
Staad pro and Etabs were compared with manual results. It can be seen from Table 2 and Fig 5 that the base shear of zone II was
1025.30 kN in case of manual calculation and its has been increased to 5.45% and 18.67% in case of Staad pro and Etabs
respectively. Similarly for the zones III, IV and V the base shear was1640.49, 2460.74 and 3691.12 kN respectively in case of
manual calculation and it has been increased to 1.07% and 18.67% in case of Staad pro and Etabs respectively.
4. Conclusion
Comparative study of seismic base shear of the RC buildings in different seismic zones was carried out using Software package.
The following conclusions may be drawn from this study.
1. The base shear is high in Etabs when compared to Staad pro and manual calculation, whereas a less difference was observed
between the Staad pro and manual calculation and it is suggested that the Staad pro software package is more reliable than Etabs.
5. References
1. IS 1893(Part1):2002, Criteria for earthquake resistant design of structures, Part 1 General provisions and buildings,
Bureau of Indian Standard.
2. Pankaj Agarwal, Manish Shrikhande, Earthquake Resistant design of Structures (Prentice Hall India Publication).
3. Amadio, C.; Fragiacomo, M.; and Rajgelj, S. (2003). The effects of repeated earthquake ground motions on the nonlinear response of SDOF systems. Journal of Earthquake Engineering and Structural Dynamics, 32(2), 291-308.
4. Jayaramappa.N, and Santhosh.D, (2014) “Case study on slender multi-storey RC building with brick infill” IJRET:
International Journal of Research in Engineering and Technology, Volume: 03 Special Issue: 06 | May.
5. Hiten L. Kheni, Anuj K. Chandiwala (2014) “Seismic Response of RC Building with Soft Stories” International Journal
of Engineering Trends and Technology (IJETT) – Volume 10 Number 12 - Apr.
6. IS 875 (Part 2): Code of Practice for Design Loads (Other Than Earthquake) For Buildings and Structures. Part 2:
Imposed Loads (Second Revision) (1987)
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