Progressive Collapse Analysis of RC Multi-Story Building

IJSRD - International Journal for Scientific Research & Development| Vol. 4, Issue 01, 2016 | ISSN (online): 2321-0613

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Progressive Collapse Analysis of RC Multi-Story Building B. Ragavendar1 G. Saravanan2 1PG Student 2Assistant Professor

1,2Department of Civil Engineering 1,2Adhiyamaan College of Engineering, Hosur, Krishnagiri, Tamilnadu, India

Abstract— The term “progressive collapse” is the spread of

local failure from an element to other element within the

structure ultimately causing total collapse of the build-ing. It

is caused due to abnormal loading being induced in the

building. The abnormal loading may be induced by

earthquake, bomb blasting, tsunami, aircraft impact, any

other man-made intentional or unintentional activi-ties and

other natural hazards. These loadings causes change in the

loading pattern and boundary condition of the structure, this

result in other structural elements within the structure to load

beyond their capacity and fail. Thus the failed structure is

required to seek alternate load path in order to redistribute its

load. This process continues until the structure finds the

equilibrium by element failing or by finding alternate load

path to dis-tribute the load. In this project a multi-story

building designed, using IS codes is considered for

progressive collapse analysis. Linear static analysis is carried

out by using ETABS as per GSA guidelines. Story shear and

story drift are calculated to know the potential for progressive

collapse.

Key words: Progressive collapse, Demand Capacity ratio,

linear stat-ic analysis, column removal

I. INTRODUCTION

According to GSA guidelines (2013) (Alternate Path

Analysis and Design Guidelines for Progressive Col-lapse

Resistance), the progressive collapse is defined as “an extent

of damage or collapse that is dis-proportionate to

the magnitude of initiating event” Pro-gressive collapse is

described as ‘collapse to an extent disproportionate to the

cause”, it is frequently triggered by unanticipated extreme

events. Progressive col-lapse causes irreplaceable human

loss, financial loss to the country, public exposed to high

psychological shock due to this traumatic event. The

unanticipated extreme events cause abnormal loading in the

elements of the Structure. The abnormal loading within the

structure may be caused by manmade intentional activities or

unintentional activities, and other natural hazards. The

abnormal loading cause initial damage which propa-gates in

the structure, due to incapability of structure redistribute the

load that were carried by the initially damaged element to the

adjacent element, resulting in failure/ collapse of an entire or

part of the structure.

The progressive collapse is defined in ASCE/SEI 7

(2010) as the spread of an initial local failure from element

to element, eventually resulting in the collapse of an entire

structure or is proportionately large part of it. Initially

structural engineers did not paid attention on this issue, a

number of high profile disasters made it into consideration.

A. Objective of The Study:

To evaluate the potential for progressive col-lapse of

multi-story building using the linear dynamic analysis,

nonlinear dynamic analysis and push over analysis by

column removal condition

To find the elastic behavior of building by plotting push

over curve

To compare various results such as story shear and story

drift for bare frame model and model with removal of

column in different stories.

B. Scope of The Study:

The focus of this project is to determine if a structure is

susceptible to progressive collapse. The building is de-

signed as per IS 456- 2000, IS 1893-2002, SP6. It is modeled

using ETAB software and analyzed for progressive

collapse resistance using GSA guidelines.

C. Need for The Present Study:

The difference in performance of seismic resistant and

progressive resistant is to be examine, to help the structural

engineer to recognize which priority need to be considered to

make the structure robust, de-pending on the basic properties,

such as connection strength, stiffness and ductility as well as

frame man-agement.

It is unclear that the structures with seismic re-

inforcement and sway frames designed for seismic re-gions

are having resistance against progressive collapse.

II. MODELLING FEATURES

Three dimensional finite element model of a 7 story building

is developed in ETABS 2015. Analyses for column removal

are performed using linear static analy-sis, linear dynamic

analysis, and linear static analysis technique.

III. PRELIMINARY DATA

Length X width - 30mX32m

No of story - 7

Bottom story height - 3.1m

Rest of story height - 3.4m

Beam size - 225mmX450mm

Column size - 375mmX450mm

Slab thickness - 150mm

Support condition - Fixed

IV. DESIGN DATA

Live load = 3KN/m2 on typical floor, 1.5KN/ m2 on other

floors.

Floor finish = 1.5KN/m2

Wall load on all beams =9.54KN/m

Earthquake load – the structure is designed for zone IV as per

IS 1893-2002

Type of soil – type II (medium)

Response reduction factor – 3

Importance factor – 1.5

fck = 25N/sq.mm , fy= 415N/sq.mm

Progressive Collapse Analysis of RC Multi-Story Building

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V. PROGRESSIVE COLLAPSE ANALYSIS

To evaluate the potential for progressive collapse anal-ysis

using GSA 2003 guidelines linear static, linear dy-namic, non

linear static analysis were done using ETABS 2015. GSA

recommends removing a column from the middle of the

traverse side of the building, near the middle of the

longitudinal side of building, and at the corner of the building

for the structure to be analyzed. When analyzing the structure

for progressive collapse potential, GSA (2003) recommends

a general loading factor to be used for every structural

member in the building being tested.

Load=2.0(Dead Load +0.25(Live Load)) (1)

When vertical members are instantaneously

removed, GSA (2003) uses Demand-Capacity Ratios (DCR)

to analyze which structural members will exceed their load-

ing capacity and lead to progressive collapse. Using the linear

elastic static analysis, the DCR values are found using

Equation 2.

DCR= QUD/QCE (2)

Where, QUD꞊ Acting force (demand) determined in

component or connection/joint moment, axial force, shear,

and possible combined forces).

QCE꞊ Expected ultimate, un-factored capacity of the

component and/or connection/joint (moment, axial force,

shear and possible combined forces)

The allowable DCR values for primary and

secondary structural elements should be less than or equal to

2 for typical structural configurations. Structural elements

and connections that exceed DCR value is considered to be

severely damaged or collapsed.

VI. NONLINEAR INCREMENTAL DYNAMIC ANALYSIS

The destination of a building might be change during its

lifetime, from apartments to office building leading to

increased gravity loads. This assumes that the risk for

progressive collapse established in the initial phase of the

design could be changed from low to high. In this context, a

nonlinear incremental dynamic analysis is conducted in order

to establish the ultimate load bearing capacity to progressive

collapse of the building; thus, the maximum value of the

supplementary gravity load for which the structure will fail

through progressive collapse when subjected to suddenly

column removal will be identified.

Fig. 1: Bare frame model of 7- story building.

Fig. 2: Maximum story displacement of bare frame model




Fig. 3: Story drift of bare frame model.

Fig. 4: Story shear of bare frame model.

Fig. 5: Push over curve of bare frame model.

Fig. 6: Max story displacement for corner column

removal in longer direction.




Fig. 7: Max story drift for corner column removal in longer

direction.

Fig. 8: Story drift for corner column removal in longer

direction.

Fig. 9: Push over curve for corner column removal in longer

direction.

Fig. 10: Max story displacement for middle column

removal in longer direction.




Fig. 11: Max story drift for middle column removal in

longer direction

Fig. 12: Story drift for middle column removal in longer

direction.

Fig. 13: Push over curve for middle column removal in

longer direction.

VII. RESULTS AND DISCUSSION

Since the DCR values of columns are less than 2 in all the

cases studied, the columns are adequate and do not need

additional reinforcement to meet GSA criteria. Columns

designed for seismic forces in all Zones have inherent ability

to resist Progressive Collapse.

1) When column was removed, among the intersecting

beams the shorter span beams tend to take the extra load

and DCR values that beams were more compared to

longer span beams.

2) For removed column C6, DCR values of B1 beams

exceed 2. Decreasing pattern of DCR values is observed

has storey increases. B5 beams below storey 7 have DCR

values more than 2 and others are less than 2.

3) For C31 column removed, DCR of 1 B25 beams and 1 -

storey B24 beams exceed 2.Including adjacent B32

beams other are well within 2.

4) For C51 column removed, DCR of 1 B40 beams and B41

beams of all stories exceed 2.Including adjacent B32

beams other are well within 2.

5) For C53 column removed, DCR of B11, B12, B6 beams

of all stories exceed 2. Adjacent B16 beams have DCR

less than 2.

VIII. CONCLUSION

The adequate reinforcement provided in extra to beams which

are unsafe can develop alternative load paths and prevent

progressive collapse due to the loss of an individual

member. This study illustrates the inherent ability of

seismically designed RC beam-column frames to resist

progressive collapse. The analysis shows that a building




designed for zone IV is capable of generating an alternate

load path to transfer the loads if a vertical member fails, since

all the columns are having ac-ceptable DCR values. The

high moments generated on the beams are at the beam column

junction and hence design can be done to prevent

collapse.Story drift and story shear of both linear dynamic

analysis and non linear static analysis comparison were made

and found that linear dynamic analysis is greater than the

later.The potential for progressive collapse mechanism of the

above said modelling is studied.Push over curve is ob-tained

for bare frame model by displacement against base shear, and

also for column removal condition is done.

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Progressive Collapse Analysis of RC Multi-Story Building

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