This document summarizes a study on the effect of column shapes on the earthquake resistance of reinforced concrete framed buildings. The study analyzed 10-story buildings with square and rectangular plans containing rectangular, square, and circular cross-section columns under seismic loads. It was found that using square or circular columns rather than rectangular columns resulted in a 7-8% reduction in required steel reinforcement and a cost savings of around Rs. 100,000. The study concluded that non-rectangular column shapes can improve a building's seismic performance while reducing costs.

1. PARAMETRIC STUDY OF EFFECT
OF COLUMN SHAPES ON
EARTHQUAKE RESISTANCE OF
BUILDINGS
BY: KARAN SHAH
KATHA DESAI
GUIDE :Dr. A.S SANTHI

2. INTRODUCTION
 It is estimated that by the year 2025 more than 5500 million people will live
in cities.
 Astoundingly, a significant fraction of the largest of these megacities is
located close to regions of known geological hazard, the earthquake.
 The statistics show that the risk of earthquake damage to lives and property
has more than quadrupled in the past decade, because of rise in
megacities.
 global level debate to reduce the carbon emissions in which cement ranks
2nd most hazardous material on the list.
 need to build structures which are optimum in performance under seismic
loads and have a reasonable construction cost and have carbon free
credentials.
 We experimented with the size and shape of column one of the most
important links in load transfer for the structure keeping the volume of
concrete same. The structure is to be tested with lateral loads and the
percentage of reinforcements shall be calculated.
 Our small attempt towards making globe a better and a safer place to live.

3. ABSTRACT
 The present study was carried out to study the effect of column shape on the
seismic resistance of a RCC framed structures for Ground + 10 upper stories
which consisted of rectangular shaped columns as against equivalent square
and circular shaped columns.
 Static equivalent seismic analysis was carried out for each of the two
categories of buildings
i) having three, 4m x 4m panels in both lateral directions forming a plan area
of 12m x 12m
ii) having four 4m x 4m panels in one direction and three 4m x 4m panels
forming plan area of 16m x 12m.
 All the beams were considered to be of 230mm x 450 mm in size and the
columns were of 3m height in each floor. The columns extended upto 2m
below the ground level. Cross section of columns was considered as 450mm
x 300mm for rectangular 370mm x 370mm for equivalent square columns
and 415mm dia for circular.

4.  Analysis was carried out using STAAD Pro and results were compared.
 It was concluded that there is significant decrease in steel
reinforcement requirement for square and circular cross section of
columns for both buildings when tested under seismic loads. The
quantity of steel required and concrete volume consumed is evaluated
and the structural cost is compared.
 It is concluded that the square cross section of columns give a saving
of about 7.7% and circular shape of columns show a saving of about
7.8% as that against a rectangular column shape for a square plan
building. The same values works out to be 7.6% for square and 7.3%
for circular for the rectangular shaped building

5. GEOMETRIC DEFINATION
•MODEL-1
•MODEL-2
•DIMENSIONS OF STRUCTURAL
ELEMENTS

6. MODEL-1
•plan area of 12m x 12m with
a three panel grid of 4m x 4m
in both lateral directions.
•The space frame thus
formed consists of nine
columns placed at each
panel points.
•The columns were 3m in
height for each storey and
are considered to extend for
2m below plinth level upto
foundation which was
considered to be fixed.

7. MODEL-2
• Plan area of 16m x 12m with
three panel grid of 4m x 4m in one
direction and four panel grid of
same dimension in other
direction.
•The space frame thus formed
consists of twelve columns placed
at each panel points.
•The columns were 3m in height
for each storey and were
considered to extend for 2m
below plinth level upto foundation
which was considered to be fixed.

8. DIMENSIONS OF STRUCTURAL
ELEMENTS
 Both the models had been analysed with the following
dimensions of structural elements.
 Beam size for all models was fixed as 230mmx450mm.
 All external wall of thickness 230mm
 All floor slabs of thickness 130mm
 Rectangular column size was taken as 300mmx450mm.
 Equivalent square columns were taken as 370mmx370mm.
 Equivalent circular columns were taken as 415mm in dia.

9. MODELLING

10. MODELLING
 All the supports and end of columns considered fixed in both types
of models
 Seismic load in the two lateral directions was considered as per the
equivalent static load method according to Indian standard IS:1893-
2002.
 The structure was analyzed for Zone IV with zone factor 0.24.
 Response reduction factor(IR) of 5
 Importance factor (I) of1.
 Rock soil type was taken as medium soil with factor 2.
 Damping ratio was taken as 5% .

11.  Typical Floor load
1. dead load 4.3 kN/sq.m
2. live load 2 kN/sq.m
3. wall load 11.75 kN/m
 Terrace Floor load
1. dead load 6.05 kN/sq.m (to account for water proofing).
2. live load 1.5 kN/sq.m
3. wall load 4.15 kN/m (parapet wall.)
 Analysis was carried out for 13 load combinations that were
defined based on recommendations as given in IS 456, IS
1893 and IS 13920.

12. DESIGN

13. DESIGN
 The static analysis was carried out for the given dead and live loads.
 The design was carried out by the most critical load combination of 1.5 x D.L
+ 0.9 x EQ in +X,-X,+Z,-Z directions respectively for both, rectangular and
square model.
 The following parameters were considered for design
1. Grade of concrete M25
2. Grade of steel Fe415
3. Clear cover 0.02 m
4. Maximum main reinforcement for column 25 mm
5. Maximum main reinforcement for beams 20 mm
6. Diameter of ties for beams and columns 8 mm.
 The Ast provided was checked with the Ast required for all corner and centre
columns. The columns were designed considering equal reinforcement on
all four sides for the square and rectangular shape of columns. Only one bar
diameter was used for providing the vertical steel in columns from practical
point of view.

14. RESULTS

15. TABLE-1
COLUMN SHAPES
SQUARE BAY
STEEL(TONNES) CONCRETE(M3)
COST SAVINGS COMPARED
TO RECTANGULAR
COLUMN(Rs.)
%REDUCTION OF STEEL
COMPARED TO
RECTANGULAR COLUMN
TOTAL COST OF
STEEL (Rs.)
RECTANGUAR 20.54 194.83 1232400
SQUARE 18.959 195.9 7.70 1137540 94860
CIRCULAR 18.929 232.64 7.84 1135740 96660

16. TABLE-2
COLUMN SHAPES
RECTANGULAR BAY
STEEL(TONNES) CONCRETE(M3)
%REDUCTION OF STEEL
COMPARED TO
RECTANGULAR COLUMN
TOTAL COST OF
STEEL (Rs.)
COST SAVINGS COMPARED
TO RECTANGULAR
COLUMN(Rs.)
RECTANGUAR 25.905 248.51 1554300
SQUARE 23.941 249.84 7.58 1436460 117840
CIRCULAR 24.013 274.57 7.30 1440780 113520

18. OBSERVATIONS

19. OBSERVATIONS
From Table 1, it can be observed that square shaped columns have a
definite advantage over rectangular columns in terms of steel consumption
for a regular RC building having 3 panels of 4mx4m in each lateral direction
making an overall plan size of 12m x 12m.
The Table 1 also shows that the circular shape of columns is equally good
as the square shape and performs almost the same as a square shaped
column.
The advantage of a square shaped column is slightly reduced from 7.7% to
7.58% when the overall size of the building is changed to a rectangular one
of 12m x 16m as seen in Table 2.
Table 2 also indicates that a circular shape of column is performing almost
the same as a square column with a marginal difference of 0.28% for a
rectangular building.
It is also observed from the tables that the structural cost of both the G+10
storey buildings can be reduced by nearly Rs. 1,00,000 by simply adopting
a square or circular shape of column instead of rectangular shape which is
the usual practice.

20. CONCLUSIONS
It can be concluded that the seismic
performance of RCC framed structures can be
improved by providing square or circular
shaped columns (equal stiffness members in
the principle lateral directions) instead of the
rectangular columns.

21. LIMITATIONS
 The above conclusion is drawn for only symmetric plan shaped
buildings without any reduction in the column size.
 The building is subjected to only equivalent static method of
lateral force generation which may not be the case under actual
seismic forces.
 The inclusion of infill walls may cause a deviation in the
behavior of the structure which is not modeled in the current
analysis.
 Geometric nonlinearity like the P-delta effect and large
deformations are not taken into account in the present study.

22. REFERENCES
 Bimal Shah and Jignesh Shah (2004), Performance Based Seismic
Evaluaton of RCC Framed Structures for Symmetric Plan Buildings,
Proceedings of Asia Conference on Earthquake Engineering ACEE
2004, Manila, Philippines. Vol-1, pp 165-175.
 Diptesh Das and C.V.R. Murty (2004), Brick Masonary infills in seismic
design of RC frame buildings: Part 2 – Behaviour, The Indian Concrete
Journal ICJ, August 2004.
 Naeim, F. (2001) , The Seismic Design Handbook second edition ,
Kluwer Acedemic Publishers
 Indian Standard Code of Practice IS-1893(Part 1) (2002).Criteria for
Earthquake Resistant Design Of Structures Part 1 General Provisions
and Buildings, Fifth revision.
 Chopra A. (2002) Dynamics of Structures : theory and applications to
earthquake engineering, second edition, Prentice-Hall of India Private
Limited, New Delhi.
 Indian Standard Code of Practice IS-456 (2000). Plain and reinforced
Concrete – Code of Practice (fourth Revision).

23. ACKNOWLEDGEMENTS
OUR SINCERE THANKS TO A.S SANTHI
MADAM FOR HER VALUABLE TIME AND
HER PRECIOUS INPUTS IN THE PROJECT.
THANKYOU