ABSTRACT:-
At the time of Earthquake RC (Reinforced Concrete) framed structures are
subjected to lateral loadings. Most of the RC structures are design to resist
the gravity loading only by neglecting the effect of lateral loading on it at
the time of earthquake. This study is concentrated on the comparison of cost
for both earthquake resistant building (Special Moment Resisting Frame, SMRF)
and Non-earthquake resisting building (Ordinary Building). This study has been
carried out using STAAD PRO software, IS 1893:2002, IS456:2000 and IS13920:1996
for designing of structure and SOR for analysis of rates for cost comparison of
both structures. The building under analysis consist of 5 floors and has 4 bays
along both X and Z direction with a span of 3m each, floor to floor height is
3m throughout the structure height.  The
building has been located in seismic city AGRA, Uttar Pradesh.

Key Words:
Seismic Force, IS1893, Staad Pro v8i, Grade of Material, ADA, SOR

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1.INTRODUCTION

A
Building or edifice is an RC framed structure mainly consists of Beam, Column
and Slabs standing more or less permanently in one place. Buildings have
different shapes, size and functions and have been adapted throughout history
for a wide numbers of factors such as Weather condition, Ground condition (Seismic
Zone, Bearing Capacity of Soil, Availability of material), Specific use and
aesthatic appearance. Normally building is designed to withstand against the
vertical of loads but there are so many loads which have to be exerts in
lateral direction on a structures. Earthquake resistant structures are the
structures designed to withstand earthquakes, while no structure is completely
immune to damage due to earthquake. The specified goal of earthquake resistant
construction is to erect structure that behaves better during seismic activity
and their conventional counterparts. According to IS 1893 Part-I:2000,
earthquake resistant structures are intended to withstand the largest
earthquake of a certain probability that is likely to occur at their location,
which means that the loss of life should be minimized by preventing the
collapse from earthquake. Currently there are several design philosophies for
designing of structures but  in INDIA IS
456:2000 is generally used for design of structural elements like Beams,
Columns and Slabs while IS 1893:2000 is used for design of structure for
earthquake considerations. In this Study we use STAAD Pro v8i for the designing
of structure as per Indian Standards by BIS and determine the change in the
value of Quantity of material used for the structure in both cases as follows:

a)      Structural
Design of  Building due to Vertical loads
only

b)      Structural
Design of Building due to Vertical and Lateral Load ( Earthquake Loading)

Finally, we analyze the rate of material
used in both structures as per SOR (Schedule of Rates) by ADA (Agra Development
Authority).     

 

2.STRUCTURAL PROPERTIES
OF RC (Reinforced Concrete) FRAMED BUILDING

 

·        
No. of Stories: G+4

·        
Storey Height: 3.0 m

·        
Beam Dimensions: 230mm
x 450mm

·        
Column Dimension for
Ground and First Stories: 450mm x 450mm

·        
Column Dimension for
above Stories:   300mm x 300mm

·        
Grade of Concrete: M20

·        
Grade of Steel: Fe415

·        
Fck : 25N/mm2

·        
Fy : 415N/mm2

·        
Slab Thickness: 120mm

·        
Zone Factor: 0.16

·        
Importance Factor: 1.0

·        
Response reduction
Spectrum: 5.0

·        
Rock/Soil factor: 1.0

·        
Damping
Ratio: 5%

Fig 2.1 – Structural
dimensions

 

3.  
LOADING
SPECIFICATION USED:

As
we consider the structure is a residential one, so there are following loadings
which we consider as per IS 875 (Part 1, Part 2, Part 3). IS875 Part 1 for Dead
Loads, IS875 Part 2 for Imposed Loads and IS875 Part 3 for Earthquake
considerations.

Here
Loading is as Follows:

a)      Dead
Load

i)       
Self Weight of Frame

ii)      UDL
due outer walls        – 12.42 kN/m

iii)    UDL
due inner walls        – 6.21 kN/m

iv)    UDL
due to Parapet walls – 3 kN/m

b)      Live
Load

i)       
Floor load of intensity
– 3.5 kN/m2

c)      Seismic
Load as per IS875 Part 3 for city AGRA in Zone III including all accidental
loads.

Fig 3.1 – Seismic Zones
in INDIA

 

 

4. TERMINOLOGIES USED FOR
 ANALYSIS   OF EARTHQUAKE

Analysis
of Structure for vertical structures load only and for both vertical load and
earthquake considerations is done by
STAADPRO v8i software. Data used in
software for earthquake analysis as per IS 1893 part 1.

a)      Horizontal
acceleration coefficient (Ah)

b)      Modal
Mass

c)      Modal
Participation factor

d)     Zone
Factor

e)      Moment
resisting frames

·  
OMRF (Ordinary moment
resisting Reinforced Concrete frame)

·  
SMRF (Special moment
resisting Reinforced Concrete frame)

f)       Design
eccentricity(ed)

g)      Design
Spectrum (Clause 6.4 IS1893 PartI:2002)

h)      Zone
Factor (Z): Clause 6.4.2 IS1893 Part I:2002

Seismic Zone

II

III

IV

V

Seismic Intensity

Low

Moderate

Severe

Very
Severe

Z

0.10

0.16

0.24

0.36

 

4.1  Dynamic Analysis as per IS 1893 :2002

To
obtain the design seismic force and their distribution to different levels
along the height of the building and to various load resisting elements Dynamic
analysis is performed as per IS1893 Part I for the following buildings:

a)     
Regular
Buildings
– Buildings those have heights greater than 40m in Zone IV and V, and those
whose height is greater than 90m in Zone II and III. Modeling is done as per Clause 7.8.4.5 of IS1893 Part I.

b)     
Irregular
Buildings
( as Per Clause 7.1 IS 1893:2002) –  All
RC Framed Building having height greater than 12m in Zone IV and V, and for
frames having height greater than 30m in Zone II and Zone III.

 

4.2     Building with Soft Storey

a)      Buildings
those have Flexible storey consisting of an open space for parking needs
special arrangements to increase the lateral strength and the stiffness of
soft/open storey.

b)      In
Dynamic analysis as per IS 1893 part 4 is carried out by considering the
strength and stiffness effects of infills and deformation which is inelastic in
nature, particularly members designed accordingly in case of soft storey.

c)      Design
criteria which is going to be adopted to carrying out the analysis due to
earthquake, which is already a function in STADD
PRO v8i. This software analyze the structure for earth quake as per IS 1893
also by considering accidental loads.

d)     Following
design criteria is to be adopted after analysis of earthquake by neglecting the
effect of infill as follows:

·     
Columns and beams of soft storey is
designed for 2.5 times the shear and moment calculated under seismic loading.

·     
Shear wall placed symmetrically in both
direction of the building as feasible from the centre of the building.

 

5. DESIGN OF STRUCTURE WITHOUT EARTHQUAKE

 

In this analysis by STAAD PRO,
structure of specified dimension is to be designed only for vertical loadings
consist of Dead loads and Live load only( No Lateral forces is considered while
designing the structure).

Here due to application of live
load and dead load following load combinations is generated as per IS456:2000
for designing of structure as follows:

a)     
1.5 Dead Load + 1.5 Live Load

b)      1.2
Dead Load + 1.2 Live Load

c)      1.5
Dead Load

d)    
0.9 Dead Load

The above load combination with
is generated by STAAD PRO v8i is as per IS456:2000, which is auto generated for
general structures.

Fig 5.1 – Deflected Shape of Structure

 

 

6. DESIGN OF STRUCTURE WITH EARTHQUAKE

 

In this analysis by STAAD PRO,
structure of specified dimension is to be designed only for vertical loadings
consist of Dead loads and Live load and Seismic loads for City AGRA which is in
Zone III as specified by GOI.

Here due to application of dead
load, live load ans seismic load following load combinations is generated as
per IS456:2000 for designing of structure as follows:

a)     
1.5 Dead Load + 1.5 Live Load

b)      1.2
Dead Load + 1.2 Live Load

c)      1.2
Dead Load + 1.2 Live Load + 1.2 Earthquake load

d)     1.2
Dead Load + 1.2 Live Load – 1.2 Earthquake load

e)      1.5
Dead Load

f)       1.5
Dead Load + 1.5 Earthquake Load

g)      1.5
Dead Load – 1.5 Earthquake Load

h)      0.9
Dead Load + 1.5 Earthquake Load

i)       
0.9 Dead Load – 1.5 Earthquake Load

 

The above load combination with
is generated by STAAD PRO v8i is as per IS456:2000, which is auto generated for
general structures and includes all repeat load cases.

Here,
in the Seismic analysis we see the deflection of large magnitude in comparison
to the design of structure for only Dead Loads and Live Load. Fig 5.1 shows the
deflected shape of the structure which is designed only for vertical loads,
while Fig 6.1 shows the deflection of the same structure when it is designed
for vertical loads and lateral load(Seismic) both. In comparative analysis we
consider the same scale for the representation of Deflection, BMD, SFD
etc.  Here we also compare with the
design of a column (Fig 7.1) which is at ground floor and see the variation in
reinforcements.

Fig 6.1 – Deflected Shape of Structure

 

7. COMPARISION OF REINFORCEMENT
SPECIFICATIONS:

As
we know that by analyzing the structure for different load conditions , there
is a change in reinforcement and amount of concrete for the same geometry of
the sections. Here we Compare the change in area of reinforcement for both
conditions section 5 and section 6.Here we choose a single column then see the
variation in the reinforcement for different load conditions.

 

 

 

 

 

Fig7.1
Selected Column

Fig7.2:  As required without EQ analysis

Fig7.3:  As required without EQ analysis

Here
we see from Fig7.2 and Fig7.3 that for the same geometry of the section but for
the different load conditions there is a diverse change in the quantity of the
reinforcement. When we analyze only for vertical loads total area of
reinforcement required As is 458 mm2, so we provide 8-12 mm
dia. But in case of earthquake analysis (combination of vertical loads and
earthquake load) total area of reinforcement required As is 7731 mm2,
so we provide 16-25 mm dia. as main reinforcement.

8.
COMPARISION OF QUANTITY AND COST

As
seen in the previous section that even in a single element there is a huge
change in quantity of the steel reinforcement, as on large sacle the amount of
the material required is of a large value which directly affects the cost of
the structure. Here for designing of the structure we use M25 grade of concrete
from LAFARGE CEMENTS which costs Rs. 5640 per cubic meter, and Fe415
grade of steel from Amba Shakti TMT which costs Rs. 30500 per 930 Kgs.
Following is the Quantity analysis for both structures ( Normal Building
subjected to vertical loads and Earthquake resisting building).

Table
8.1 – Quantity and Rate analysis for the Building subjected to vertical loads
only.

Material

Total Quantity

Cost per unit

Total Cost

Concrete (M25)

112.7 m3

Rs.
5640/m3

Rs.692028

Steel (Fe415)

64927 Kgs

Rs.30500
per 930 Kgs

Rs.2129327

Total Cost of structural material

Rs.
2821355

 

Table
8.2 – Quantity and Rate analysis for the Building subjected to vertical loads and
Earthquake loads.

Material

Total Quantity

Cost per unit

Total Cost

Concrete (M25)

89.6 m3

Rs.
5640/m3

Rs.505344

Steel (Fe415)

136486 Kgs

Rs.30500
per 930 Kgs

Rs.4476154

Total Cost of structural material

Rs.
4981498

.

9.
RESULT AND CONCLUSION

 

Finally we know the total amount of
reinforcement for both the structures and see the variation in cost for the
structures. But we also see the variation in the values of deflection which is
the basic need for the stability of the structure at the time of earthquake.
Here cost is nearly increased by 1.76 times the cost of the bulding subjected
to the vertical loads only, which concludes that Ductility of the framed
structure is high because increase in cost is generally lies between 33% to 87%
as the ductility of the structures varies from low to high respectively. So,
finally after results we says that the structure designed for earthquake is DCH
(High Ductility).

Finally we have to work for
reducing the cost of the structures having capability to resist the Earthquake
loadings.