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

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.