Study of RC Framed Structure using Push over · PDF filePush over analysis is an approximate...

International Journal of Engineering Technology, Management and Applied Sciences

www.ijetmas.com May 2017, Volume 5, Issue 5, ISSN 2349-4476

436 Mr. Gaurav Pratap Singh, Mr. Mohd. Zain,Er. Shubham Srivastava

Study of RC Framed Structure using Push over Analysis

Mr. Gaurav Pratap Singh1, Mr. Mohd. Zain

2,Er. Shubham Srivastava

3,

1M.tech (structural engineering), Shri RamswaroopMemorial University,LUCKNOW

2Assistant Professor, Shri RamswaroopMemorial University,LUCKNOW

3Assistant Professor, Shri Ramswaroop Memorial University,LUCKNOW

Abstract:

Recent earthquakes in which many concrete structures have been severely damaged or collapsed, have indicated the

need for evaluating the seismic adequacy of buildings. About 60% of the land area of our country is susceptible to

damaging levels of seismic hazard. We can’t avoid future earthquakes, but safe building construction practices can

certainly reduce the extent of damage and loss. To evaluate the performance of framed building under future expected

earthquakes, a non-linear static pushover analysis has been conducted.

The main aim of this study is to understand the behaviour of Reinforced Concrete framed structures by using nonlinear

static procedure (NSP) or pushover analysis in finite element software “SAP2000”.and the Comparative study made for

different models in terms of base shear, displacement, performance point

Keywords: push over analysis, non linear static procedure, seismic hazard

INTRODUCTION

This analysis of the non linear response of RC

structures to be carried out in a routine fashion. It

helps in the investigation of the behavior of the

structure under different loading conditions, its load

deflection behavior and the cracks pattern.

In the present study, the non-linear response of RCC

frame using SAP2000 under the loading has been

carried out with the intention to investigate the

relative importance of several factors in the non-

linear analysis of RCC frames. This includes the

variation in load displacement graph.

Push over analysis is an approximate analysis

method in this we monotonically increase forces

with an invariant height wise distribution on a

structure until we achieve a target displacement.

Push over analysis comprises of series of step wise

elastic analysis, superimposed to approximate a

force displacement curve of the overall structure. A

2D or 3D model with bilinear or trilinear load

deformation diagram of all lateral force resisting

element is first created and gravity loads are applied

initially. Then lateral load which is predefined and

distributed along the building height is then applied.

The lateral forces are increased until some members

yield. The structure model is modified to deal with

the reduced stiffness of yielded members and

lateral forces are again increased until another

member yield. This process is continued until

structure under consideration becomes unstable and

a control displacement at the top of building is

achieved. To get the global capacity curve, the roof

displacement is plotted with base shear

the next key component of seismic hazard we create

the seismic models, forwhich we need translating

seismotectonic information into a spatial

approximation of earthquake localisation and

temporal recurrence. For this we need to compile

and view all the available data on neo-tectonics,

geodynamics, morph structures etc, on a seismicity

map. These maps then need to be carefully studied

for defining areal seismic source zones and active

faults. For defining the parameters that characterise

the seismicity of the sources region, on earthquake

recurrence model is then put on these source zone,

which can be used as inputs to the algorithm for the

computation of seismic hazard viz. fig.1.1 gives a

flow chart that represents the important steps in

performance-based design process. This process is

iterative which begins with the selection of

performance objective, followed by the

development of a preliminary design an assessment,

as to whether or not the design meets the

performance objective and finally redesign and

reassessment , if required ,until our design




performance level is achieved (ATC,1977a)

Figure 1.1Performance-Based Design Flow

Diagram

GENERAL DESCRIPTION OF THE

STRUCTURE

Our major objective of this work was to check a

real-life structure under pushover loads. For no

special design of the structure as such war

performed we use choose a portion of real life

existing office building to keep the structure as close

to reality as possible. In this, we check a replica of a

part of an existing office building. The portion was

selected in such a way that it had certain

eccentricities and was un-symmetric in plan

MATERIAL PROPERTIES

We are using material for concrete with M-20 grade

concrete and fe-415 grade reinforcing steel for

construction. The stress-strain relationship will be

same as per IS456:2000. The basic material

properties used are as follows;

Modulus of elasticity of steel, Es=21,0000MPa

Modulus of elasticity of concrete,

EC=22,360.68Mpa

Characteristic strength of concrete, fck=20MPa

Yield stress for steel, fy=415MPa

Ultimate strain in bending, ϵcu=0.0035

MODEL GEOMETRY

The structure used for analysis is a five-storied, two

bays along X-direction and two bays along Y-

direction moment-resisting frame of reinforced

concrete with properties as specified above.

We will use rigid concrete floor. The detail of

model are given as;

Number of stories=5

Number of bays along X-direction=2

Number of bays along Y-direction=2

Story height=3

Bay width along X-direction=4 meters

Bay width along Y-direction=4 meters

3D Model of the Structure

Fig 1.2 3D model of five storey building for push

over analysis

Result and Analysis

COMPARISON BETWEEN THE SAP2000

ANALYSIS AND THE EXPERIMENTAL

RESULTS OF THE FRAME

FIG.1.34 combined pushover curve from

experimental data (reddy. Et.al,2010)




The behaviour of the frame has been observed to be

linear up to the value of base shear around 230 KN,

whereas the structure has been found to be linear up

to the value of base shear 300 KN in case of

experiment. At this point the flexural tension cracks

at the base of the columns depicting reduction in

stiffness have been observed.

After reaching a base shear value of approximately

425 KN, the cracks at the base of the columns have

been found to open wider and failures at other

location like beams and beam – column joints

started. Whereas in case of experiment at a base

shear value of approximately 500 KN, the cracks at

the base of the columns have been observed and

failures at beam – column joints start to show up.

As a result the stiffness of the frame further goes

down, as can be seen from the pushover curve.

After reaching the base shear values of 660 KN,

displacements have found to be increasing at fast

rate whereas in case of experiment at the base shear

values of 700 KN, the joints of the frame have

found to be displaying rapid degradation and the

inter storey drift increasing rapidly.

Maximum deflection has been found to be more

than 600mm at 902 KN. Maximum deflection is

more than 770mm at 880KN experimentally.

Variety of failures like beam-column joint failure,

flexural failures and shear failures have been

observed almost in the same way as seen in the case

of experiment.

Prominent failures shown by both models have been

the joint failures. Also the severe damages have

been observed at joints of lower floors whereas

moderate damages have been observed in first and

second floors. Minor damage is seen at floor level

in both the cases.

Fig.1.4Graph between resultant base shear

&Monitored Displacement

Fig 1.5 fema 440 equivalent linearization graph

between spectral acceleration & spectral

displacement

Fig 1.6fema 440 displacement modification

graph between base reaction &displacement

Fig 1.7ATC-40 capacity spectram graphbetween

spectral acceleration & spectral displacement




Fig 1.8fema 356 coefficient method

graphbetweenbase reaction & displacement

Step by step deformation for pushover

Fig 1.8(a) step 1

Fig 1.8(b) step 2

Fig 1.8(c) step 3

Fig 1.8 (d) step 4




Fig 1.8 (e) step 5

Fig 1.8 (f) step 6

Fig 1.8 (g) step 7

Fig 1.8 (h) step 8

Fig 1.8 (i) step 9

Fig 1.8 (j) step 10




Fig 1.8 (k) step 11

Fig 1.8 (l) step 12

Fig 1.8 (m) step 13

Fig 1.8 (n) step 14

Fig 1.8 (o) step 15

Fig 1.8 (p) step 16




Fig 1.8 (q) step 17

Fig 1.8 (r) step 18

Fig 1.8 (s) step 19

CONCLUSIONS

The main observations and conclusions drawn are

summarized below:

The frame behaved linearly elastic up to a base

shear value of around 230 KN. At the value of base-

shear 660KN, it depicted non-linearity in its

behaviour. Increase in deflection has been observed

to be more with load increments at base-shear of

660 KN showing the elasto-plastic behaviour.

The joints of the structure have displayed rapid

degradation and the inter storey deflections have

increased rapidly in nonlinear zone. Severe

damages have occurred at joints at lower floors

whereas moderate damages have been observed in

the first and second floors. Minor damage has been

observed at roof level.

The frame has shown variety of failures like beam-

column joint failure, flexural failures and shear

failures. Prominent failures are joint failures.

Flexural failures have been seen in beams due to X-

directional loading.

It has been observed that the top storey experienced

major damages in this case opposite to the case of

frame.

Micro cracks have been observed to appear even

when the frame is in its elastic zone. The cracks

have been found increasing with the increase in

deflections

REFERENCES KonuralpGirgin and KutluDarılmaz. Seismic

Response of Infilled Framed Buildings Using

Pushover Analysis. Department of Civil

Engineering, Istanbul Technical University, 34469,

Maslak, Istanbul, Turkey. VOLUME 54, NUMBER

5. 5 December 2007.

Mehmet Inel, HayriBaytanOzmen. Effects of plastic

hinge properties in nonlinear analysis of

reinforced concrete buildings. Department of Civil

Engineering, Pamukkale University, 20070 Denizli,

Turkey. Available online 30 March 2006.

Moehle JP, Mahin SA. Observations on the

behavior of reinforced concrete buildings during

earthquakes. In: Ghosh SK, editor. Earthquake-

resistant concrete structures—inelastic response

and design. American Concrete Institute SP-127;

1991.

Oscar Möller, Ricardo O. Foschi, Laura M. Quiroz,

Marcelo Rubinstein. Structural optimization for

performance-based design in earthquake




engineering: Applications of neural networks.

Structural Safety 31, 490–499. (2009).

Priestley, M. J. N. & Park, R. Strenght and

Ductility of Concrete Bridge Columns Under

Seismic Loading. ACI Structural Journal, Technical

paper, Title n° 84-S8, 79(1), pp. 61-76, January-

February, 1987.

Zou XK. Optimal seismic performance-based

design of reinforced concrete buildings. Ph.D.

dissertation. Hong Kong (PR China): Hong Kong

University of Science and Technology; 2002.

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