DOI : 10.17577/IJERTV5IS070483
- Open Access
- Total Downloads : 191
- Authors : Kazi Muhammed Mustaqeem, Md. Mansooor Ahmed
- Paper ID : IJERTV5IS070483
- Volume & Issue : Volume 05, Issue 07 (July 2016)
- DOI : http://dx.doi.org/10.17577/IJERTV5IS070483
- Published (First Online): 26-07-2016
- ISSN (Online) : 2278-0181
- Publisher Name : IJERT
- License:
This work is licensed under a Creative Commons Attribution 4.0 International License
Impact of Intermittent Diaphragm and Re-entrant corners on Seismic Response of Multistoried RC framed Buildings
Kazi Muhammed Mustaqeem,
PG Student,
Dept of Civil Engineering, KBN college of Engineering Gulbarga,Karnataka.
Md. Mansoor Ahmed,
Assistant Professor, Department of civil Engineering,
KBN college of Engineering, Gulbarga, Karnataka.
Abstract -In multi-storied framed building, harms from seismic tremor by and large start at areas of structural weakness present in the lateral load resisting frames. Diaphragms with unexpected discontinuities or varieties in stiffness, which incorporates those having removed or open regions more prominent than 50 percent of the gross encased diaphragm area, or changes in viable diaphragm stiffness of more than 50 percent starting with one story then onto the next. In structural designing, a diaphragm is a basic framework used to exchange horizontal loads to shear walls or frames essentially through in-plane shear stress. Lateral loads are normally wind and seismic tremor loads.
In this paper attempt has been made to study two sorts of arrangement namely diaphragm discontinuity and re-entrant corners in the structure. These irregularities are made according to provision 7.1 of IS 1893:2002(part1) code. Different irregular models were considered having diaphragm irregularity and re- entrant corners which were analyzed utilizing ETABS to decide the seismic reaction of the building. The models were investigated utilizing static, dynamic and pushover analysis and parameters considered being displacement, maximum drift, base shear, and time period. From the present study the model which is most vulnerable to failure under exceptionally extreme seismic zone is discovered.
Keywords – Diaphragm discontinuity, equivalent static, Response spectrum, pushover analysis, displacement, drift, base shear and time period.
1. INTRODUCTION
For a structure to perform well during earthquake, the structure ought to have four fundamental traits, in particular basic and general design, sufficient lateral strength, stiffness and ductility. Structures with straightforward normal geometry and consistently distributed mass and stiffness in plan and in addition in rise are considered to endure much lesser harm than structures with irregular designs. However, these days, with the progression in fast development of urbanization and for aesthetic reason structures with irregular arrangements are broadly built. These setups in structures prompt non-uniform appropriations in their masses, stiffness and strength accordingly they are inclined to damage amid tremors. Henceforth in present study an attempt has been made to think about the conduct of such structures situated in serious seismic zone.
The segment 7 of IS 1893(part1):2002 enrolls the abnormality in structures. These abnormalities are sorted as takes after
-
Vertical irregularities alluding to sudden change of strength, stiffness, geometry and mass results in unpredictable dissemination of strengths or conveyance over the stature of the building.
-
Plan abnormalities which allude to uneven arrangement shapes (L-, T-, U- and F-) or discontinuities in the horizontal resting components (diaphragm), for example, cut-outs, huge openings, re-entrant corners and other unexpected changes bringing about torsion, diaphragm disfigurements and stress concentration.
As said above plan abnormalities might be because of intermittent diaphragm or nearness of re-entrant corners in the structures. The diaphragm is a horizontal component that exchanges forces between vertical resistance components. The diaphragm intermittence may happen with unexpected varieties in stiffness, including those having removed or open ranges more than half of the gross encased diaphragm area, or change in viable diaphragm stiffness of more than half starting with one story then onto the next story. The re- entrant corners, where projections of the structure past the re-entrant corner are more than 15 percent of its plan measurement in the given direction is accepted in shapes like L, T, H, C, + shapes.
-
OBJECTIVE OF THE STUDY
To study the impact of intermittent diaphragm and re-entrant corners in tall structures under serious seismic zone considering parameters like displacement, drift, base shear and time period.
-
METHODOLOGY
-
Select the buildings with intermittent diaphragm and re- entrant corners.
-
Design the building as per prevailing Indian standards for dead load, live load and earth quake load in Etabs.
-
Analyze the building using, Equivalent static, Response spectrum, Pushover analysis methods.
-
Analyze the results and arrive at conclusions.
-
-
DETAILS OF THE BUILDING
For study purpose, the layout of the plan having 5X5 bays of equal length of 4m is considered.. The building parameters are as follows,
-
Type of building: Ordinary moment resisting frame
-
Number of stories: 20
-
Seismic zone: V
-
Floor height: 3 m
-
Grade of Concrete: 30 Mpa
-
Grade of steel: Fe500
-
Beam dimension : 450mm x 850mm
-
Column dimension: 350mm x 650mm
-
Slab depth: 150mm
-
Dead load: 1.5 Kn/m2
-
Live load : 2 Kn/m2
-
Importance factor(IF): 1.5
-
Response reduction factor:3
-
-
MODELS
MODEL R-REGULAR
MODEL D1-H SHAPED
MODEL D2-C SHAPED
MODEL D3-PLUS (+) SHAPED
MODEL L1-40%
MODEL L2-60%
MODEL L3-80%
Model Description
The arrangement setup comprises of, MODEL R -Building in square shape.
MODEL D1 – Intermittent Diaphragm H in shape. MODEL D2 – Intermittent Diaphragm C in shape. MODEL D3 – Intermittent Diaphragm + in shape.
MODEL L1 – Re-entrant corners 40% in X course and 40% in Y heading.
MODEL L2 – Re-entrant corners 60% in X course and 40% in Y heading.
MODEL L3 Re-entrant corners 80% in X course and 40% in Y heading.
MAX.DRIFT(mm)
MAX.DRIFT(mm)
-
RESULTS
14
12
11.869
14
12
11.869
10
8
6
4
2
0
7.806
8.269
7.39
EQX
10
8
6
4
2
0
7.806
8.269
7.39
EQX
MODELS
MODELS
2.587
2.587
2.687
2.687
2.567
2.567
2.613
2.613
SPECX
PUSHX
SPECX
PUSHX
1.003
R
1.003
R
0.964
0.964
D1
D1
0.951
0.951
D2
D2
0.971
D3
0.971
D3
FIG 1: Plot of Maximum Drift VS Models for static, dynamic and pushover analysis in X direction.
5.146
5.339
5.234
2.241
2.29
2.363
2.304
0.871
0.831
0.823
0.852
R
D1
D2
D3
5.146
5.339
5.234
2.241
2.29
2.363
2.304
0.871
.831
0.823
0.852
R
D1
D2
D3
6 5.503
MAX.DRIFT(mm)
MAX.DRIFT(mm)
5
4
3
2
1
0
MODELS
EQY SPECY PUSHY
9
8
7
6
5
4
3
2
1
0
9
8
7
6
5
4
3
2
1
0
7.806
7.806
7.04
7.04
7.435 7.332
7.435 7.332
2.587
2.587
2.757
2.757
2.765 2.771
2.765 2.771
EQX
SPECX PUSHX
EQX
SPECX PUSHX
MAX.
DRIFT(mm)
MAX.
DRIFT(mm)
FIG 2: Plot of Maximum Drift VS Models for static, dynamic and pushover analysis in Y direction.
1.003
R
1.003
R
0.948
L1
0.948
L1
0.962
L2
0.962
L2
MODELS
MODELS
0.979
L3
RE-ENTRANT
0.979
L3
RE-ENTRANT
5
4
5
4
3
3
2.241
2.241
2.288
2.288
2.351
2.351
2.421
2.421
EQY
SPECY PUSHY
EQY
SPECY PUSHY
MAX.DRIFT(mm)
MAX.DRIFT(mm)
FIG 3: Plot of Maximum Drift vs Models for static, dynamic and pushover analysis in X direction
6
5.146
4.844
4.904
4.911
6
5.146
4.844
4.904
4.911
R
L1
L2
R
L1
L2
MODEL
MODEL
2
2
0.871
0.871
0.965
0.965
1.015
1.015
1.051
1.051
1
0
1
0
L3
RE-ENTRANT
L3
RE-ENTRANT
FIG 4: Plot of Maximum Drift vs. Models for static, dynamic and pushover analysis in Y direction
450
DISPLACEMENT(mm)
DISPLACEMENT(mm)
400
350
300
250
200
150
100
50
0
411.9
274.8
291.9
127.4
133.4
127.5
129.7
42.4
42.8
41.5
42.3
R
D1
D2
D3
274.8
291.9
127.4
133.4
127.5
129.7
42.4
42.8
41.5
42.3
R
D1
D2
D3
321.6
EQX SPECX PUSHX
Note: Displacement increases with the increase in story, maximum value of the displacement which occurs at top story (20th story) is taken into account.
MODELS
FIG 5: Plot of displacement vs Models for static, dynamic and pushover analysis in X direction
DISPLACEMENT(mm)
DISPLACEMENT(mm)
234.8
243.2
253.1
238.5
109.7
113.3
116.1
113.6
37.8
37.6
37.4
38
R
D1
D2
D3
234.8
243.2
253.1
238.5
109.7
113.3
116.1
113.6
37.8
37.6
37.4
38
R
D1
D2
D3
300
250
200
150
100
50
0
MODELS
EQY
SPECY PUSHY
FIG 6: Plot of displacement vs. Models for static, dynamic and pushover analysis in Y direction.
350
DISPLACEMENT(mm)
DISPLACEMENT(mm)
300
250
200
150
100
50
0
274.8
273.4
288.2
292.1
127.4
136.2
137.2
137.5
42.4
40.9
42.3
43.8
274.8
273.4
288.2
292.1
127.4
136.2
137.2
137.5
42.4
40.9
42.3
43.8
R L1 L2 L3
EQX SPECX PUSHX
MODELS RE-ENTRANT
FIG 7: Plot of displacement vs Models for static, dynamic and pushover analysis in X direction
250 234.8 221.3 225.7 228
DISPLACEMENT(mm)
DISPLACEMENT(mm)
200
150
100
50
109.7 113.1 116.8 120.8
37.8 42.9 45.9 48.3
EQY SPECY PUSHY
0
R L1 L2 L3
MODELS RE-ENTRANT
BASE SHEAR (KN)
BASE SHEAR (KN)
FIG 8: Plot of displacement vs Models for static, dynamic and pushover analysis in Y direction
10000
8000
6000
4000
2000
EQX
SPECX PUSHX
MODEL
EQX
SPECX
PUSHX
R
7223.0472
2605.5461
9224.6186
D1
6140.0578
2215.1355
9272.4735
D2
6362.1965
2302.2275
8476.1454
D3
6546.9746
2365.017
8397.0863
L1
6199.44
2229.199
7653.1025
L2
5682.7961
2034.4815
7203.4801
L3
5183.3865
1843.4653
6581.4949
10000
8000
6000
4000
2000
EQX
SPECX PUSHX
MODEL
EQX
SPECX
PUSHX
R
7223.0472
2605.5461
9224.6186
D1
6140.0578
2215.1355
9272.4735
D2
6362.1965
2302.2275
8476.1454
D3
6546.9746
2365.017
8397.0863
L1
6199.44
2229.199
7653.1025
L2
5682.7961
2034.4815
7203.4801
L3
5183.3865
1843.4653
6581.4949
0
0
R
D1 D2 D3
MODELS
L1 L2 L3
R
D1 D2 D3
MODELS
L1 L2 L3
BASE SHEAR(KN)
BASE SHEAR(KN)
Fig 9: Plot of Base Shear vs Models for static, dynamic and pushover analysis in X direction
14000
12000
10000
8000
6000
4000
2000
0
EQY
SPECY PUSHY
MODEL
EQY
SPECY
PUSHY
R
8371.7342
2997.5188
11968.0996
D1
7228.8852
2594.3637
9915.982
D2
6986.4978
2512.1483
9589.6261
D3
7504.5397
2694.0241
10288.5349
L1
7138.9033
2528.4777
9761.4323
L2
6486.8397
2264.2554
8933.4812
L3
5841.3677
2012.9565
8046.9711
14000
12000
10000
8000
6000
4000
2000
0
EQY
SPECY PUSHY
MODEL
EQY
SPECY
PUSHY
R
8371.7342
2997.5188
11968.0996
D1
7228.8852
2594.3637
9915.982
D2
6986.4978
2512.1483
9589.6261
D3
7504.5397
2694.0241
10288.5349
L1
7138.9033
2528.4777
9761.4323
L2
6486.8397
2264.2554
8933.4812
L3
5841.3677
2012.9565
8046.9711
R D1 D2 D3 L1 L2 L3
MODELS
R D1 D2 D3 L1 L2 L3
MODELS
Fig 10: Plot of Base Shear vs Models for static, dynamic and pushover analysis in Y direction.
3
3
2.5 2.415
2.392
2.379 2.409
2.401 2.41
2.5 2.415
2.392
2.379 2.409
2.401 2.41
R
D1 D2 D3
Models
L1 L2 L3
R
D1 D2 D3
Models
L1 L2 L3
2.332
2.332
2
2
1.617
1.617
1.5
1
1.5
1
ANALYTICAL
CODAL
ANALYTICAL
CODAL
0.5
0
0.5
0
Fundamental time peroid (s)
Fundamental time peroid (s)
Fig 11.Plot of time period vs. Models for analytical and codal method.
-
CONCLUSIONS
-
-
When comparing the results of static and response spectrum method, the magnitude of displacement is more in static method as the response of the building is assumed to behave in a linear elastic manner.
-
Results of response spectrum method are more accurate. Response spectrum is based on known seismic activity. Static analysis is base shear analysis.
-
Pushover analysis gives higher value as compared to static and response spectrum method because in this method building is analyzed until the maximum capacity is reached.
-
Dynamic loads are applied as a function of time, this time varying load application induces time varying response (displacement, drift, forces and stresses), and these time varying characteristics make dynamic analysis more complicated and more realistic then static analysis.
-
From Fig.1&2, it is observed that the drift values are maximum for model D1 than the rest of the models hence is more susceptible for seismic forces.
-
From Fig.3&4, model L3 has maximum drifts as compared to the other models because of more re-entrant corners more (80%in X direction & 40% in y direction).
-
From Fig.5 & 6, it is observed that the displacement values remained almost same in static and response spectrum analysis for all models, whereas in pushover analysis model D1 gave higher displacement value as compared to rest of the models. Therefore model D1 is most vulnerable.
-
From Fig. 7&8, when comparing the re-entrant modes with regular model, it is seen that mode L3 is most vulnerable as re entrant corners are more (80%in X direction & 40% in y direction.
-
From Fig. 9 & 10 the magnitude of base shear is maximum for regular mode R and minimum for re- entrant model L3, more the base shear of the building more will the member attract seismic forces. The influence of diaphragm opening played a major role in reducing the base shear hence attracting less seismic forces.
-
From Fig 11, results of fundamental natural period have proved that code IS 1893 does not consider the irregularity of buildings. The analytical method gives more accurate results as the time period is calculated on the basis of mass and stiffness of the building whereas the codal empirical formula depends only on the height of the building.
ACKNOWLEDGMENT
Above all else, acclaim and much gratitude go to God for the blessing that has been bestowed upon me in every one of my endeavors.
I am profoundly obligated to Md Mansoor Ahmed sir, assistant Professor of Structural Engineering department, my counsel and guide, for the inspiration, direction, tutelage and persistence all through the project work. I might want thank my Parents without their affection, persistence and bolster, I could not have finished this work.
At last, I wish to thank numerous friends for the encouragement and support.
REFERENCES
-
Indian Standard code IS 18932-2002
-
Turgut O. (2011) : A study of the effect of slab gaps in buildings on seismic response according to three different codes (Scientific research and essays vol 6)
-
Moehle, J. P. (1984), Seismic Response of Vertically Irregular Structures, JOSE (ASCE), Vol. 110. No. 9, 2002-2014.
-
J. H. Cassis and E-Cornejo, Influence of Vertical Irregularities in the Response of Earthquake Resistant Structures.
-
FEMA 356 Pre-standard and Commentary for the Seismic Rehabilitation of Buildings Nov-2000.
-
FEMA 440 Improvement of Nonlinear Static Seismic Analysis Procedures June-2005.
-
IS 456 : 2000 Plain and Reinforced Concrete Code of Practice ( Fourth Revision )
-
Amin A. and Prof. P.S. Rao (2013) : Influence of torsional irregularities of RC buildings in High Seismic Zone (Australian journal of basic and applied sciences)
-
Ravikumar C.M and Sujith B V l (2012) : Effect of irregular configurations on seismic vulnerability of RC building (Architecture Reasearch)