Study of P-Delta Effect on Regular and Irregular RCC Buildings
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During earthquake, the building undergoes various random motions of the ground at its base, which induces inertia forces in the structure. Different types of irregularities are considered in the building viz. Mass irregularities and geometric irregularities in urban India, which are subjected to several types of forces. Earthquake load mainly induce lateral forces which causes lateral displacement of the structure. The effect of gravity load acting on the structures lateral displacement is called the P-delta effect. Due to P-delta effect, geometric nonlinearity induces in the building which creates additional moment and shear. It is generally observed that the regular buildings have a dominant fundamental results participation in their seismic responses and as the irregularity increases the contribution of it. Hence, In the present study, modelling and analysis of Regular and Irregular RCC building is carried out in SAP2000V16 considering P-delta effect using Time history analysis. Various parameters such as base shear, storey drift and overturning moment are obtained. It is found that p delta effect in building needs to be considered and controlled.
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IOSR Journal of Mechanical and Civil Engineering (IOSR-JMCE)
e-ISSN: 2278-1684,p-ISSN: 2320-334X, Volume 15, Issue 4 Ver. II (Jul. - Aug. 2018), PP 01-04
www.iosrjournals.org
Study of P-Delta Effect on Regular and Irregular RCC Buildings
Payal Shah1, V.G.Jadhav2
1
(ME (Structure) Student, Department of CIVIL, Jawaharlal Nehru Engineering College, India)
2(Asst. Professor, Department of CIVIL, Jawaharlal Nehru Engineering College, India)
Abstract: During earthquake, the building undergoes various random motions of the ground at its base, which
induces inertia forces in the structure. Different types of irregularities are considered in the building viz. Mass
irregularities and geometric irregularities in urban India, which are subjected to several types of forces.
Earthquake load mainly induce lateral forces which causes lateral displacement of the structure. The effect of
gravity load acting on the structures lateral displacement is called the P-delta effect. Due to P-delta effect,
geometric nonlinearity induces in the building which creates additional moment and shear. It is generally
observed that the regular buildings have a dominant fundamental results participation in their seismic
responses and as the irregularity increases the contribution of it. Hence, In the present study, modelling and
analysis of Regular and Irregular RCC building is carried out in SAP2000V16 considering P-delta effect using
Time history analysis. Various parameters such as base shear, storey drift and overturning moment are
obtained. It is found that p delta effect in building needs to be considered and controlled.
Keywords: P-delta effect, Regular buildings, Irregular buildings, Time history analysis, SAP.
----------------------------------------------------------------------------------------------------------------------------- ---------Date of Submission: 02-07-2018
Date of acceptance: 21-07-2018
----------------------------------------------------------------------------------------------------------------------------- ----------
I. Introduction
The engineers do not attempt to make earthquake proof buildings that will not get damaged even
during the rare but strong earthquake; such buildings will be too robust and also too expensive. Instead, the
engineering intention is to make buildings earthquake resistant; such buildings resist the effects of ground
shaking, although they may get damaged severely but would not collapse during the strong earthquake. Thus,
safety of people and contents is assured in earthquake-resistant buildings, and thereby a disaster is avoided. This
is a major objective of seismic design codes throughout the world.
After minor shaking, the building will be fully operational within a short time and the repair costs will
be small. And, after moderate shaking, the building will be operational once the repair and strengthening of the
damaged main members is completed. But, after a strong earthquake, the building may become dysfunctional
for further use, but will stand so that people can be evacuated and property recovered. The consequences of
damage have to be kept in view in the design philosophy.
Time history analysis refers to dynamic response of the structure at each increment of time, when its
base is subjected to a specific ground motion time history. Alternatively, recorded ground motions database
from past natural events can be a reliable source for time histories but they are not recorded in any given site to
include all seismological characteristics suitable for that site. Recorded ground motions are randomly selected
from analogous magnitude; distance and soil condition category are the three main parameters in time history
generation.
P-Delta effect, also known as geometric nonlinearity, involves the equilibrium and compatibility
relationships of a structural system loaded about its deflected configuration of particular concern. It is the
application of gravity load on laterally displaced multi-storey building structures. This condition magnifies story
drift and certain mechanical behaviours while reducing deformation capacity. In structural engineering, the
P-Delta effect refers to the abrupt changes in ground shear, overturning moment, and the axial forcedistribution
at the base of a sufficiently tall structure or structural component when it is subjected to a critical lateral
displacement.
Several researchers have presented their study in area of effect of p-delta analysis on various structures
in several papers. Akshay Gupta and Helmut Krawinkler investigated the inelastic response of steel moment
resisting frame. P-delta effect induces negative post yield storey stiffness as seen from pushover curve.The
results lead on to the belief that P-delta problem is indeed a potential collapse hazards that needs to be
considered in the present design process. EF Black introduced and evaluated two stability coefficients that can
be used to quantify the P-delta effect during elastic and inelastic lateral displacement of regular steel SMRF.
The study shows that the combined use of these two coefficients permit the accurate prediction of the load
deformation curve of the SMRF affected by P-delta phenomena.H. Scholz studied a novel method to allow for
the P-Delta effect of steel sway frames analyzed by elastic methods.A numerical example suggests that more
DOI: 10.9790/1684-1504020104
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Study Of P-Delta Effect On Regular And Irregular RCC Buildings
economical designs may be obtained, but a further comprehensive parametric study will be required to confirm
this for the general case.
II. Frame Structure Details And Problem Statement
In the present study, effect of nonlinearity on the response of G+14 Regular RC building and G+14
Irregular Stepped RC building has been investigated. Nonlinearity is considered in terms of P-delta effect. In
Regular building, the structure has 4 bays in both X and Y direction of 4m each with constant storey height of
3m. In Irregular building, the structure has 2 bays in X direction and 4 bays in Y direction in the 1 st step, 3 bays
in X direction and 4 bays in Y direction in the 2 nd step and 4 bays in X direction and 4 bays in Y direction in the
3rd step from top to bottom. Width of bay is 4 m with constant storey height of 3.0m.
Table 1: Specification of Models
Type of structure
Seismic zone
Importance Factor
Damping Ratio
Imposed load for residential floor
Imposed load for commercial floor
Storey Height
Specific Weight of RCC
Specific Weight of Brick infill
Infill Wall
Column size
Beam size
G+14 storied
(RC moment resisting frame)
V, As per IS 1893 Part I, Z=0.36
1
0.05
2 KN/m2
3.5 KN/m2
3.0m
25KN/m3
20 KN/m3
230mm
300X600
230X600
Fig. No.1: Front elevation of Regular building Fig. No.2: Front elevation of Irregular building
III. Methodology
In this paper, fourteen storied regular and irregular building frame is under the action of Imperial
Valley (El-Centro) (1940) earthquake. Both RCC buildings are considered with the provision of lift and
staircase for performing time history method of dynamic analysis. The building is analyzed for two
combinations such as i) Without P-delta effect and ii) with P-delta effect modelled and designed in SAP2000
v16 using time history analysis and response quantities viz. displacement, base shear and overturning moment
are obtained under considered earthquake.
DOI: 10.9790/1684-1504020104
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Study Of P-Delta Effect On Regular And Irregular RCC Buildings
IV. Results
The following table no.2 represents the value for Base shear, Displacement and overturning
moment without P-delta effect for the two cases, i) Regular building ii) Irregular building
Table No 2: Represents without P-delta effect
Parameter
Base Shear
Displacement
Overturning Moment
Regular Building
143225.263
0.165124
5432.56
Irregular Building
98378.236
0.58436
6436.884
The following table no.3 represents the value for Base shear, Displacement and overturning moment with
P-delta effect for the two cases, i) Regular building ii) Irregular building
Table No 3: Represents with P-delta effect
Base shear
Parameter
Base Shear (KN)
Displacement (mm)
Overturning Moment(KN.m)
Regular Building
148954.771
0.2028
6812.91
160000
140000
120000
100000
80000
60000
40000
20000
0
Irregular Building
103116.358
0.7112
7762.86
with P-delta
without P-delta
Regular
Building
Irregular
Building
Fig. 3: Shows the difference between the Base Shear values for regular and irregular building for the two cases
i) Without P-delta effect and ii) with P-delta effect
0.8
0.7
0.6
0.5
with p-delta
0.4
without p-delta
0.3
0.2
0.1
0
Regular Building
Irregular Building
Fig. 4: Shows the difference between the Displacement values for regular and irregular building for two cases
i) Without P-delta effect and ii) with P-delta effect
DOI: 10.9790/1684-1504020104
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Study Of P-Delta Effect On Regular And Irregular RCC Buildings
8000
7000
6000
5000
4000
3000
2000
1000
0
with p-delta
without p-delta
Regular Building
Irregular Building
Fig. 5: Shows the difference between the Overturning moment values for regular and irregular building for two
cases i) Without P-delta effect and ii) with P-delta effect
V. Conclusion
1)
2)
3)
4)
The Displacement values increases in case of irregular buildings along with p-delta effect.
Effect of non-linearity due to p-delta is predominant than that of the normal effect.
Base shear increases in case of p-delta consideration in both regular and irregular buildings.
It can be concluded that the performance of the building under P-delta effect should be considered and
remedial measures should be taken.
References
[1].
[2].
[3].
[4].
[5].
[6].
[7].
[8].
[9].
[10].
A. Gupta and H. Krawinkler, “Dynamic P-delta effect for flexible inelastic steel structure,” Journal of Structural Engineering,
Vol. 126, No. 1, January 2000, pp 145-154.
E. F. Black, “Use of stability coefficient for evaluating the P-delta effect in regular steel moment resisting frames,” Engineering
Structures, Vol. 33, February 2011, pp 1205-1216.
H. Scholz, “P-delta effect in elastic analysis of sway frames,” Journal of Structural Engineering, Vol. 113, No. 3, March 1987,
pp 534-545.
H. Kwak, and J. Kim, “P-delta effect on slender RC column under seismic load,” Engineering Structures, Vol. 29, April 2007,
pp 3121-3133.
M. Aschheim, and E. H. Montes, “The representation of P-delta effect using yield point spectra,” Engineering Structures,
Vol.
25, April 2003, pp 1387-1396.
R. Gaiotti, and B. S. Smith, “P-delta analysis of building structures,” Journal of Structural Engineering, Vol. 115, No. 4, April
1989, pp 755-770.
A. Wibowo, J. L.Wilson, N. T.K. Lam, E. F. Gad, “Collapse modeling analysis of a precast soft storey building in Australia,”
Engineering Structures, Vol. 32, 30 March 2010, pp 1925-1936.
H. B. Kaushik, D. C. Rai, and S. K. Jain, “Effectiveness of some strengthening options for masonry-Infilled RC frames with open
first story,” Journal of Structural Engineering, Vol. 135, No. 8, July 2009, pp 925-937.
I. S. Misir, “Potential use of locked brick infill walls to decrease soft-story formation in frame buildings,” Journal of Performance
of Constructed Facilities, September 2014, pp 1-10.
K. Patel, S. Thakkar, “Analysis of CFT, RCC and steel building subjected to lateral loading,” 3rd Nirma University International
Conference on Engineering, Nirma University, Ahmedabad, 2013, Paper No. 51, pp 259 – 265.
Payal Shah1, V.G.Jadhav.’’Study of P-Delta Effect on Regular And Irregular RCC Buildings .”
IOSR Journal of Mechanical and Civil Engineering (IOSR-JMCE) , vol. 15, no. 4, 2018, pp.
01-04
DOI: 10.9790/1684-1504020104
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4 | Page
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