Linear Static Analysis of Regular Space Frame with & Without Fixed Base
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7/21/2019 Linear Static Analysis of Regular Space Frame with & Without Fixed Base
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I JSRD - I nternational Journal for Scientifi c Research & Development| Vol. 3, I ssue 11, 2016 | ISSN (onli ne): 2321-0613
All rights reserved by www.ijsrd.com 389
Linear Static Analysis of Regular Space Frame with & without Fixed
BaseMs. Akshaya Ghalimath1 Mr. Mantesh A.Hatti2 Ms. Sheetal More3 Ms. Chaitrali Jamadar4
1,2,3,4Department of Civil Engineering1,2,3,4A.G. Patil Institutes, Solapur, Solapur University
Abstract — Due to present increase in the world population
people in this world tends to occupy available location
present in any zone, which also includes zones falling in the
high seismic zone categories. Commonly designers considerthe building to be fixed at their bases. Flexibility of the soil
causes the decrease in stiffness resulting increasing in the
natural period of the structure. Such increases in the natural
periods, changes the seismic response of structure hence it
may be an important issue for design consideration. The
present study provides systematic guideline for determining
the natural periods of frame buildings due to the effect of
soil-flexibility and identification of spring stiffness for linear
building story and various influential parameters such as
period, displacement, base shear and column forces haveidentified for both fixed and flexible base has to be studiedfor bare frame for all types of soils.
Key words: Bare Frame, Fixed Base, Flexible Base, Base
Shear, Period, Displacement, Axial Forces In Column
I. I NTRODUCTION
Presently and majority existing of reinforced cement
concrete structure has been a tremendous increase in the
amount of tall stories in modern localities and the structures
do not need the current seismic requirement as they are
primarily designed for gravity loads only. Since the structure
being tall and slender are subjected to seismic and wind
load, if the structure is not stiff enough to resist the loadsand vibration cause. Therefore it is important for these
structures to resist lateral forces along with vertical forces.
As waves from an earthquake a reach a structure, they
produce motion in the structure. This motion depends on the
structure vibration characteristics and the layout of the
structure. For the structure to reach to the motion, it needs to
overcome its own inertia force, which results in an
interaction between the structure and the soil. The extent to
which the structural response changes the characteristics ofearthquake motions observe at the foundation level depends
on the relative mass and stiffness properties of the soil and
the structure. Thus the physical properties of the foundation
medium are an important factor in the earthquake responseof the structure supported on it. The process in which the
response of soil influences the motion of the structure and
the motion of the structure influence the response of the soil
is termed as soil structure interaction.
In the analysis work one model of R.C.C. Space
Frame G+ 10 floors are made to know the realistic behavior
of building during earthquake.
A. Bare Frame:
The in-plane stiffness of masonry infill wall is not taken into
account in bare frame. Bare frame will deflect under
horizontal loads by bending in columns and beams .Non-
structural components such as masonry that are subjected toseismic forces are not normally within the design scope of
the structural engineer, whose responsibility is to provide
the seismic safety of the building.
Fig. 1: Bare Frame
II. THEORETICAL FORMULATION
A. Objective
The main objective of this work is to carry out the effect of bases, types of soil on the seismic behavior of R.C.C.
building with linear static analysis method.
B. Methods of Seismic Analysis
Following Flow chart shows seismic analysis methods used
for Seismic evaluation:
Fig. 2: Seismic Analysis Methods
1) Linear Static Analysis
Equivalent static analysis is the indirect method of
considering the effect of ground motion and there is
incorporation of dynamic properties of the structure in terms
of fundamental period, response reduction factor, soil type,
seismic zone and importance factor. Equivalent static
analysis were carried out for all the models under the action
of Dead load (DL), Live load (LL) and earthquake load
(EQ) for different load combination as per IS 1893-2002.This method is limited to regular type of structure whose
response is governed by first mode of vibration. As per IS
1893-2002 regular structure up to 40m in height in zone IV
and V and up to 90m in zone II and III can be analyzed by
Time History and Response Spectrum analysis.
2) SMRF:Special Moment-Resisting Frame, It is a moment- resisting
frame specially detailed to provide ductile behavior and
comply with the requirements given in IS 4326 or IS13920
or SP6.For the analysis and design purpose one model has
been considered namely as bare frame (S.M.R.F frame).
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Linear Static Analysis of Regular Space Frame with & without Fixed Base
(IJSRD/Vol. 3/Issue 11/2016/092)
All rights reserved by www.ijsrd.com 390
III. DESCRIPTION OF STRUCTURES
In this paper the study has been carried out for ten Storied 3
Bay 3D RC frame building models with varying soil
conditions. The buildings are located in seismic zone II, III,
IV and V. The bottom storey height is 1.5m and upper floorsheight is taken as 3m for all buildings shown in fig. (3.2) the
buildings are kept symmetric to avoid torsional response
under pure lateral forces. The Spacing of beam is 3.2 m.
IV. METHODOLOGY
Multi storied building with fixed and flexible base subjected
to seismic forces were analyzed under different soil
condition like very soft, soft, medium, sandy, and hard. The
buildings were analyzed using linear static analysis usingsoftware E-TAB. Seismic analysis was carried out by
following IS1893:2002-PartI. Different response results
were found for fixed and flexible base buildings.
Fig. 3: Plan of frame
Fig. 4: View of frame
Material Properties Values
Grade of Concrete 25 N/mm2
Grade of steel 415 N/mm2
Modulus of Elasticity of Concrete 25000000 N/mm2
Modulus of elasticity of steel 200000 N/mm2
Unit Weight of Concrete 25 KN/m3
Unit Weight of Brick 20 KN/m3
Poisson’s Ratio for Concrete 0.2
Table 1: Material Properties
A.
Material Considered In the Study
The scientist Pais and Kausel (1988) has given different
formulae for calculation of spring stiffness for both 2D and
3D system considering rigid rectangular footing at the
ground surface which are three translational and three
rotational degree of freedom for rigid footing are given in
Table (1) below:
Degree of freedom Pais and kausel (1988)
Translation along z-axis , = 1 − 3.1(
). +1.6 Translation along y-axis , =
2 − 6.8 (). +0.8(
)+ 1.6
Translation along x-axis , = 2 − 6.8().
+2.4
Torsion about z-axis , = 4.25(). +4.06
Rocking about y-axis , = 1 − 3.73(
). + 0.27
Rocking about x-axis , = 1 − [3.2(L
B) + 0.8] Table 1: Description
Three translational and three rotational degree of freedom
for rigid footing:
Where
G= E/2(1+ )
G = Shear modulus
E = Modulus Elasticity of SoilL =Length of Rectangular footing
B = width of Rectangular footing=Poisson ratio of soil
V. A NALYSIS OF RESULTS
Ten storied building frames with fixed and flexible base
analyzed and designed to understand the behavior under
seismic forces. Various seismic responses were compared
for both the type of building frames.
FIXED FLEXIBLE
VerySoft Soft Medium Hard Sandy
VerySoft Soft Medium Hard Sandy
Period In (Sec) 1.8232 1.8232 1.8232 1.8232 1.8232 2.3066 2.1311 2.1989 1.9801 1.8583
Base Shear
In (KN)
EQX 230.82 230.82 230.82 230.82 230.82 170.19 188.04 147.29 129.96 134.31
EQY 187.13 187.13 187.13 187.13 187.13 146.70 160.09 126.35 107.07 109.64
Displacement(mm) 10 10 10 10 10 20 20 10 10 10
Corner
Column
(Pu) KN 586.50 586.50 586.50 586.50 586.50 1934.9 1860.0 1894.08 926.03 890.83
(Mu3)
KNM15.414 15.414 15.414 15.414 15.414 69.794 66.78 68.24 44.03 42.36
Table 2: ZONE II (Different Parameters for Fixed & Flexible Base of Bare Frame for 3.2
FIXED FLEXIBLE
Very
SoftSoft Medium Hard Sandy
Very
SoftSoft Medium Hard Sandy
Period In (sec) 1.8232 1.8232 1.8232 1.8232 1.8232 2.3066 2.1311 2.1989 1.9801 1.8583Base Shear EQX 230.82 230.82 230.82 230.82 230.82 273.06 300.87 235.67 207.93 214.90
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Linear Static Analysis of Regular Space Frame with & without Fixed Base
(IJSRD/Vol. 3/Issue 11/2016/092)
All rights reserved by www.ijsrd.com 391
In (KN) EQY 187.13 187.13 187.13 187.13 187.13 236.66 256.15 202.17 171.31 175.42
Displacement(mm) 10 10 10 10 10 30 30 20 10 10
CornerColumn
(Pu)
KN586.50 586.50 586.50 586.50 586.50 1934.97 1788.04 1894.08 982.36 949.815
(Mu3)
KNM15.414 15.414 15.414 15.414 15.414 69.794 116.34 68.24 46.716 42.365
Table 3: ZONE III (Different Parameters for Fixed & Flexible Base of Bare Frame for 3.2m)
FIXED FLEXIBLEVery
SoftSoft Medium Hard Sandy
Very
SoftSoft Medium Hard Sandy
Period In (sec) 1.8232 1.8232 1.8232 1.8232 1.8232 2.3066 2.1311 2.1989 1.9081 1.8583
Base ShearIn (KN)
EQX 230.82 230.82 230.82 230.82 230.82 407.35 448.85 353.50 311.90 322.36
EQY 187.13 187.13 187.13 187.13 187.13 354.99 384.23 303.25 256.96 263.14
Displacement(mm) 10 10 10 10 10 40 40 30 20 20
Corner
Column
(Pu)
KN586.50 586.50 586.50 586.50 586.50 1922.42 1906.27 1915.07 1651.2 1599.56
(Mu3)
KNM15.414 15.414 15.414 15.414 15.414 160.65 158.49 159.39 106.29 105.14
Table 4: ZONE IV (Different Parameters for Fixed & Flexible Base of Bare Frame for 3.2m)
FIXED FLEXIBLE
VerySoft
Soft Medium Hard SandyVerySoft
Soft Medium Hard Sandy
Period In (sec) 1.8232 1.8232 1.8232 1.8232 1.8232 2.3066 2.1311 2.1989 1.9081 1.8583
Base Shear
In (KN)
EQX 230.82 230.82 230.82 230.82 230.82 614.38 676.95 530.25 466.58 483.53
EQY 187.13 187.13 187.13 187.13 187.13 532.49 576.34 452.41 384.39 394.70
Displacement(mm) 10 10 10 10 10 60 60 50 30 30
Corner
Column
(Pu)
KN586.50 586.50 586.50 586.50 586.50 2079.94 2083.61 2083.87 1779.8 1735.35
(Mu3)
KNM15.414 15.414 15.414 15.414 15.414 225.46 221.74 223.32 141.82 139.65
Table 5: ZONE V (Different Parameters for Fixed & Flexible Base of Bare Frame for 3.2m)
VI.
CONCLUSION
Following Conclusion are observed from above study:
1) The natural time period increases for flexible base ascompared to fixed base for all types of soil for all
seismic zones.
2) The base shear will be reduces for flexible base as
compared to fixed base for all types of soil in both ‘X
‘and ‘Y’ direction f or II seismic zone.
3) The values of base shear in X-direction are more than
Y-direction.
4) The values of natural period and base shear are
increases zone wise i.e. Zone II and Zone V.
5) The values of top storey displacement increase for
flexible as compared to fixed base.6) The values of top storey displacement increases zone
wise from Zone II to Zone V for all types of soil.
7) The values of column forces i.e. axial force increases
for flexible base as compared to fixed base.
8) Axial force increases zone wise from Zone II to Zone
V for all types of soil.9) The values of bending moment in the column are more
for flexible base as compared to fixed base.
10) The values of bending moment in the column are more
for flexible base as compared to fixed base for Zone II
to Zone V for all type of soil.
11) Lateral loads affects not only natural period, base shear
but it also affects lateral deflection therefore lateralload and gravity load should be consider.
R EFERENCES [1] Chopra A.K. 1995. Dynamics of Structures. Prentice
Hall.
[2] IS 1893-2002 - Bureau of Indian Standards Manak
Bhavan, 9 Bahadur Shah Zafar Marg New Delhi
110002.
[3] R.M. Jenifer Priyanka Studies on Soil structure
interaction of Multi Storeyed Building with Rigid and
Flexible Foundation ISSN 2250-2459, ISO9001:2008
Certified Journal, Volume 2, and Issue12 December
2012.[4] Ramesh Baragani Performance Based Seismic
Evaluation G+6 RC Buildings Considering Soil
structure interactions Volume 14 Number 3-Aug 2014.
[5] S.G Shah Soil structure interaction analysis methods-
State of art-Review Volume 2, No 1, 2010.
[6] Shiji P.V Effect of Soil Structure Interaction inSeismic Loads of framed Structures, ISSN 2229-5518,
Volume 4, Issue 5, May-2013.
[7] Stewart, Jonathan Soil structure interaction in building
1: Analytical aspects, 01-01-1999