Seismic analysis performed on RCC and Steel frame in

Seismic analysis performed on RCC and Steel frame in various

zones using STADD Pro

Monali Bhakare1, Meghna Patankar

*2

Assistance Professor .Civil Engineering Department, GSMCOE, Savitribai Phule Pune University

Assistance Professor .Civil Engineering Department, GSMCOE, Savitribai Phule Pune University

ABSTRACT- At the present era of the construction industry RCC is the famous material which is being used as construction

material. RCC gives many structural advantages like lesser deflection, very high compressive strength etc. and it also gives

economical advantage as well. Steel material can also be used as construction material because steel also have some very useful

advantages like increment in speed of construction, increase in ductility of structure. Now earthquake is very important factor

that must considered while designing of building otherwise it can be very hazardous to the building in safety point of view. Due

to earthquake, buildings get subjected to loading causes building to deflect. Therefore comparative seismic study will be very

useful for evaluating the performance of those buildings under the application of earthquake loads. So the main parameters

which can used for study the performance are base shear, storey drift, maximum storey deflection, mode shapes and time period.

For calculating those parameter IS 1893 has given different methods and these methods are neatly programmed in STAAD PRO

software which is commonly used for structural designing purpose.

Keywords: Base shear, Storey drift, Node deflection, Equivalent static, Response spectrum.

I. Introduction

Worldwide different types of RC and steel structures with various floor systems are being used for multi-storey buildings. In the past,

masonry structures were widely used for building construction. Day by day technology has developed. Later, steel structural systems

were started for multi-storey buildings. With the introduction of reinforced concrete, RC structural systems started for multi-storey

building construction. RC floor system supported on steel beam was historically designed as non composite. With the advent of welding,

it became practical to provide mechanical shear connectors to consider composite action. Due to failure of many multi-storied and low-

rise RC and masonry buildings due to earthquake, structural engineers are looking for the alternative methods of construction. Use of

composite or hybrid material is of particular interest. Bare steel structure is sensitive to fire. Now a day, different fire proofing system

has developed significantly. In India, mostly masonry and RC structures were being used. During last decade, steel structural systems are

being popular. So, alternative structural systems are gradually developing to compete with RC structural systems. Now a day, use of

masonry structure is very limited. RC structure is dominating and steel structure is entering gradually for multi-storey building structures

in India. So, comparative study is required to identify most effective structural system for a particular building.

II. METHODOLOGY

General

Different researchers have comparative seismic analysis of RCC and Steel. The method which is adopted for the study is explained in

this chapter.

1. Methodology

Following step by step procedure for seismic analysis of RCC and steel frame.

1.1 Selection of Plan

INTERNATIONAL JOURNAL OF INFORMATION AND COMPUTING SCIENCE

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Fig.No.1: Plan Fig.No.2: Elevation

[1] Above plan is same for RCC and steel frame.

[2] Stiffness of the wall is not considered.

[3] Plan dimensions-

I. Plan area – 32m X 32m

II. Height of each storey – 3.2m

III. No of floors – G+7

2: Loading

2.1 Loads Acting on Frames

Loads acting on frames are mainly of gravity loads and lateral loads.

1) Gravity Loads

Gravity loads include self-weight of frame, floor finish which is taken as 1.5 kN/m2 and live load which is taken as 3 kN/m2 as per IS

875(part-II) for a residential frame that would be acting on the structure in its working period. We have also considered wall load as

imposed load on beams as 12.65 kN/m2. Wall load is calculated by the multiplying the density of wall material to the cross sectional area

of the wall which is perpendicular to the length of the wall.

2) Earthquake Load

Earthquake loading is a result of the dynamic response of the structure to the shaking if the ground. Earthquake loads are another lateral

live load. They are very complex, uncertain and potentially more damaging than wind loads. It is quite fortunate that they do not occur

frequently. The Earthquake creates ground movements that can be categorized as a “shake”, “rattle” and “roll”. Every structure in an

Earthquake zone must be able to withstand all of these loadings of different intensities. Although the ground under a structure may shift

in any direction, only the horizontal components of this movement are usually considered critical in analysis

The magnitude of horizontal inertia forces induced by earthquakes depends upon the mass of structure, stiffness of the structural system

and ground acceleration.

In the presented study the magnitude of wind load is negligible as compared to the seismic load hence the value of wind load is neglected

only seismic load is considered.

The structural system of a frame consists of two components, one is horizontal framing system (beam and slab) and other is vertical

framing system (walls and columns). Horizontal framing system is primarily responsible for transfer of vertical loads to vertical framing

systems that is responsible for transferring the vertical loads and lateral forces to the footing.

3. Design of beam and column section

The frame is analyzed with dead load and live loads for RCC sections for beams and columns in STAAD.Pro.

The maximum forces in columns and beams are determined from output file.

Optimum section for beam and column is selected by trial and error method.

Same procedure is adopted for steel section.

Table 1: Beam and Column Section



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Structural Component RCC

Steel Width Depth

Beam 230mm 450mm ISMB350

Column 450mm 550mm ISHB450 with 20mm additional plate on both flanges

of I-section

Slab 125mm 125mm

4. Seismic Input Parameters

Zone factor (Z):

It is a factor to obtain the design spectrum depending on the perceived maximum seismic risk characterized by Maximum Considered

Earthquake (MCE) in the zone in which the structure is located. The basic zone factors included in this structure are reasonable estimate

of effective peak ground acceleration.

Z = Zone factor given in Table 2 of IS 1893:2002

Seismic Zone Factors

Seismic Zone II III IV V

Seismic Intensity Low Moderate Severe Very Severe

Z 0.10 0.16 0.24 0.36

Importance Factor (I):

It is a factor used to obtain the design seismic force depending on the functional use of the structure, characterized by hazardous

consequences of its failure, its post-earthquake functional need, historic value, or economic importance.

I = Importance factor, depending upon the functional use of the structures, as per IS

1893 table 6 clauses 6.4.2.

Importance Factor (IS 1893: 2002, Table No. 6)

Sr. No. Structure Importance Factor (I)

1 Important service and community frames, such as hospitals, schools,

monumental structures, emergency frames like telephone exchange, television

stations, radio stations, railway stations, fire station frames, large community

halls like cinemas, assembly halls and subway stations, power station

1.5

2 All other frames 1.0

Response Reduction Factor (R):

It is the factor by which the actual base shear force, which would be generated if the structures were to remain elastic during its response

to the Design Basis Earthquake (DBE) shaking, shall be reduced to obtain the design lateral force.

R = Response reduction factor, depending on the perceived seismic damage, Performance of the structure, characterized by ductile or

brittle deformations.

However, the ratio (I/R) shall not be greater than 1.0. The values of R for frames are given in Table 7.

Response Reduction Factor R (IS 1893: 2002, Table No.7)



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Fig.No.2: Response Reduction Factor

Structural Response Factors (Sa/g):

It is a factor denoting the acceleration response spectrum of the structure subjected to earthquake ground vibrations, and depends on

natural period of vibration and damping of the structure.

Fig.No.3: Structural Response Factors

Natural Period (T):

Natural period of a structure is its fundamental time period of undamped free vibration. The approximate fundamental natural period of

vibration (Ta) in seconds of a moment resisting frame without brick infill panels may be estimated by the empirical expression:

[Clause 7.6.1, IS-1893-2002]

Ta = 0.075 h0.75 ……For RC Frame

Ta = 0.085 h0.75 ……For Steel Frame

The approximate fundamental natural period of vibration (Ta) in seconds of all other frames, including moment-resisting frame frames

with brick infill panels, may be estimated by the empirical expression: [Clause 7.6.2, IS-1893-2002]

d

Tah09.0

Where,

h = Height of frame in m. This excludes the basement storey, where basement walls are connected with the ground floor deck or fitted

between the frame columns. But, it includes the basement storey when they are not so connected.

d = Base dimension of the frame at the plinth level in m along the considered direction of the lateral force.

Seismic Weight (W): It is the total dead load plus appropriate amounts of specified imposed load.



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5. Acceptance of Software

Since the present study uses the STAAD.PRO and ETABS as a software tool for carrying out seismic analysis, the method of analysis in

the STAAD.PRO is verified at the beginning by comparing STAAD.PRO results with classical method for symmetrical frame.

Q. The plan and elevation of three storey RCC school frame is shown in fig. The frame is located in seismic zone V. The type of

soil encountered is medium stiff and it is proposed to design the frame with special moment resisting frame. The intensity of DL

is 10 KN/m2 and the floors are to cater to an imposed load of 3 KN/m2. Determine the design seismic load on the structure by

static analysis.

Solution:

Design parameters:

For seismic zone V, zone factor, Z=0.36

Importance factor, I=1.5

Response reduction factor, R=5

Fig.No.4: Plan & Elevation

Seismic weight:

Floor area= 8 x 8= 64 m2

For LL up to and including 3 KN/m2,

Percentage of LL to be considered = 25%

The total seismic weight on the floors is

W= ∑Wi

Where Wi is sum of loads from all the floors which include DL and appropriate % of LL.

Seismic wt contribution from one floor = 64 x (10+0.25x3)= 688 KN

Load from Roof = 64x10 =640 KN

Hence, the seismic wt of the structure= 2 x 688+640 = 2016 KN

Fundamental natural period of vibration, Ta, is given as

d

Tah09.0



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Where h is ht of frame in meters and d is the base dimension in meters at plinth level along the direction of the lateral loa d.

8

10.5 x 09.0Ta

Ta = 0.334 Sec

Since the frame is symmetrical in plan, the fundamental natural period of vibration will be the same in the both directions.

For medium stiff soil and Ta= 0.334 Sec

(Sa/g) = 2.5

g

S

R

IZA a

h2

135.052

5.25.136.0

X

XXAh

Design base shear VB, is given as

VB= AhxW = 0.135x2016 = 272.16 KN

The force distribution with frame ht is given in table and shown in fig

Fig.No.5: Design Seismic Forces by Static Analysis

Table 2: Lateral Loads Distribution With Height

Storey Level Wi (KN) Hi (m) WiHi2

)KN(

hW

hWVQ

n

1j

2

jj

2

iiBi

3 640 10.5 70560 170.37

2 688 7 33712 81.38

1 688 3.5 8428 20.41

∑ WiHi2= 112700 ∑Vi = 272.16

Screenshot of Results Given by Softwares

1. STADD.PRO



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Fig.No.6: Lateral Loads (STAAD.PRO)

Conclusion:

It is found that

i. All results from STAAD.PRO matches with the manual approach.

ii. STAAD.PRO isvery convenient to perform seismic analysis.

iii. STAAD.PRO gives Base shear and story shear at the floor level which is essential for economic design.

6 Structural Modeling and Analysis

This section deals with structural modeling, assigning member properties, assigning basic loads, generation of load combinations

6.1 Generation of Model

Following design of column, beam and slab section and seismic input parameter. To make three dimensional structural models in

STAAD.PRO .

6.2 Assigning Member Properties

Member properties are primarily assigned based on preliminary analysis and design for beam elements, surface and plate elements.

Finally member properties are corrected as per final design and checked by STAAD.PRO whether the final design is correct or not.

Sr.No Particulars RCC Steel

1 Model G+7 G+7

2 Type of Frame Residential Residential

3 Type of Frame SMRF SMRF

4 Plan Dimension 30mx30m 30mx30m

5 Height of Frame 25.6 m 25.6 m

6 Height of Each Storey 3.2 m 3.2 m

7 Size of Beam 230mm x 450mm ISMB350

8 Size of Column 450mm x550mm ISHB450 TB

9 Thickness of Slab 125mm 125mm

10 Thickness of Wall 0.23 m 0.23 m

11 Seismic Zones

II II

III III

IV IV

V V

12 Soil Condition Medium Medium

13 Importance Factor (IS1893-2002 T-6) 1 1

14 Zone Factor 0.1 0.1



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(As per IS1893-2002 clause 6.4.2 T-2) 0.16 0.16

0.24 0.24

0.36 0.36

15

Response Reduction Factor

5 5 (IS1893-2002, T-7)

16 Floor Finish Load 1.5 KN/m2 1.5 KN/m2

17 Live Load 3 KN/m2 3 KN/m2

18 Live Load (For Roof) 1.5 KN/m2 1.5 KN/m2

19 Grade of Concrete (fck) M30 N/mm2 M30 N/mm2

20 Grade of Steel 415 N/mm2 415 N/mm2

21 Yield Strength of Steel (fy) - 250 N/mm2

22 Density of Concrete 25 KN/m3 25 KN/m3

23 Density Of Brick 20 KN/m3 20 KN/m3

24 Damping Ratio 5% 2%

25 Software STAAD.PRO STAAD.PRO

ETAB ETAB

Fig.No.8: STAAD.PRO Models for RC Structures

6.3 Assigning Basic Loads

Gravity loads and lateral loads are assigned in all models generated & Earthquake loads are generated as nodal loads taking the

calculated point loads at different heights in section for earthquake load considerations. Nodal loads are assigned at column beam

connections at story level

Live loads and dead loads are assigned according to available data of section. Basic loads assigned are listed below. Some basic

loads assigned in STAAD.Pro models

[1] D=Dead loads

[2] L=Live loads

[3] EX+ = Earthquake loads towards X direction.

[4] EX- = Earthquake loads opposite to X direction.

[5] EZ+ = Earthquake loads towards Z direction.

[6] EZ- = Earthquake loads opposite to Z direction

6.4 Generation of Load Combinations



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Load combinations are generated using assigned basic loads. IS 1893-2002 is followed for load combinations of steel and RC structure

Table 3: Load Combinations

Sr.No. Load Combination

RCC Steel

1 1.5(DL+LL+SDL) 1.5(DL+LL+SDL)

2 1.2(DL+LL+SDL+EQX) 1.2(DL+LL+SDL+EQX)

3 1.2(DL+LL+SDL+EQY) 1.2(DL+LL+SDL+EQY)

4 1.2(DL+LL+SDL-EQX) 1.2(DL+LL+SDL-EQX)

5 1.2(DL+LL+SDL-EQY) 1.2(DL+LL+SDL-EQY)

6 1.5(DL+SDL+EQX) 1.5(DL+SDL+EQX)

7 1.5(DL+SDL+EQY) 1.5(DL+SDL+EQY)

8 1.5(DL+SDL-EQX) 1.5(DL+SDL-EQX)

9 1.5(DL+SDL-EQY) 1.5(DL+SDL-EQY)

10 0.9(DL+SDL)+1.5EQX 0.9(DL+SDL)+1.5EQX

11 0.9(DL+SDL)+1.5EQY 0.9(DL+SDL)+1.5EQY

12 0.9(DL+SDL)-1.5EQX 0.9(DL+SDL)-1.5EQX

13 0.9(DL+SDL)-1.5EQY 0.9(DL+SDL)-1.5EQY

6.5 Structural Analysis

After completion of generation of load combinations; the structural models, member properties, basic loads and load

combinations are checked thoroughly. After that, static analysis is performed for which equivalent static and response spectrum method

is used. Analysis results are preserved for structural design.

After analysis following parameters are obtained

Base shear

Story drift

Maximum story deflection

Fundamental time period and natural frequency

No. of mode shapes

Comparison of Various Parameter Obtained

To compare the analytical results of RCC & steel framed structures such as base shear in STADD.PRO software.

RESULTS AND DISCUSSION

In this study results are obtained from the seismic analysis performed on RCC and Steel frame in various zones using STADD Pro is

discussed below.

The variation of seismic parameters in various zones is given below.The results of seismic parameters for RCC and Steel are also

discussed in this chapter. Comparison of the various parameters obtained from seismic analysis for different seismic zones is also

discussed in this chapter.

Results and discussion

1 Results and discussion on output given by STADD.PRO



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1.1 Variation of Base Shear with Zone

1.1.1 Results

After the seismic analysis by Equivalent static method following result of base shear were obtained

1) RCC frame:

Base shear for various zones for RCC

Graph No 1: Base Shear for various zones for RCC

2) Steel frame:

Base shear for various zones for Steel

: Base shear for various zones for Steel

3) Comparison of RCC and Steel for base shear

BASE SHEAR FOR VARIOUS

ZONES

ZONES BASE SHEAR

KN

ZONE-II 1974.037

ZONE-III 3158.459

ZONE-IV 4737.689

ZONE-V 7106.534

BASE SHEAR FOR VARIOUS

ZONES

ZONES BASE SHEAR

KN

ZONE-II 1487.366

ZONE-III 2379.318

ZONE-IV 3568.977

ZONE-V 5353.466

ZONES BASE SHEAR FOR STEEL BASE SHEAR FOR RCC

KN KN

ZONE-II 1487.366 1974.037

ZONE-III 2379.318 3158.459

ZONE-IV 3568.977 4737.689

ZONE-V 5353.466 7106.534

BASE SHEAR FOR VARIOUS ZONES

Comparison of RCC and Steel for

base shear



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CONCLUSION

After performing the seismic analysis using Equivalent Static and Response spectrum method on RCC and steel frame by using STADD

Pro software results obtained are discussed in previous chapter. From analysis of the result, some conclusions are obtained which are

discussed in this chapter as follows:

Conclusions for Base shear

The value of base shear increases when we moves from zone II to zone v

The increment in base shear is exactly same as increment in zone factor

RCC frame has higher value of base shear than that of Steel frame by equal amount in all zones

REFERENCES

[1] Shashikala Koppad, Dr. S.V. Itti, “Comparative Study of RCC and Composite Multistorey Building.”International Journal of

Engineering and Innovative Technology, Vol 3, No 5, 2013.

[2] Prof. S. S. Charantimath, Prof. Swapnil .B. Cholekar, Manjunath M. Birje, “Comparative Study on Structural Parameter of

R.C.C and Composite Building.”International Institute for Science Technology and Education, Vol.6, No.6, 2014.

[3] D.R. Panchal, P.M. Marathe, “Comparative Study of RCC, Steeland Composite (G+30 Storey) Building.”International Journal

of Civil and Structure Engineering, Volume 6, No 1, 2015.

[4] Varsha Patil, Shilpa Kewate, “Comparative Study on Dynamic Analysis of Composite, RCC & Steel Structure.” International

Journal of Engineering Technology Management and Applied Sciences, Vol 5, No8, 2015.

[5] Ch Geetha Bhavani, Dr. Dumpa Venkateshwarlu, “ComparativSe Seismic Analysis of RCC, Steel and Steel-Concrete

Composite Frame.” International Journal of Research Science and Advanced Engineering, Vol 2, No.15, 2016.

[6] IS 1893: 2002, “Code for Earthquake Resistant Design of Structures-General Provisions for Buildings, Part I, Bureau of Indian

Standards.” New Delhi.

[7] IS 456: 2000, “Code for Practice of Plain and Reinforced Concrete Code of Practice, Bureau of Indian Standards.” New Delhi.

Graph No 3: Comparison of RCC and Steel for base shear



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Documents

Seismic analysis performed on RCC and Steel frame in