Progressive collapse analysis of reinforced concrete

IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
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IC-RICE Conference Issue | Nov-2013, Available @ http://www.ijret.org 36
PROGRESSIVE COLLAPSE ANALYSIS OF REINFORCED CONCRETE
FRAMED STRUCTURE
Rakshith K G1
, Radhakrishna2
1
PG student, 2
Associate Dean, Department of Civil Engineering, RV college of Engineering, Bangalore-560059
raks23.kg@gmail.com.
Abstract
The progressive collapse of reinforced concrete structures is initiated when one or more vertical load carrying members are removed
due to man-made or natural hazards. The building’s weight transfers to neighboring columns in the structure, leads to the failure of
adjoining members and finally to the failure of partial or whole structure system. In which the collapsing system continually seeks
alternative load paths in order to survive. In the present study the demand capacity ratio (DCR) of reinforced concrete twelve storey
framed structure are evaluated as per U.S. General Services Administration (GSA) guidelines. The Linear static analysis is carried
out using software, ETABS V9.7. The structural behavior of the building for progressive collapse, a finite element model is considered
using the preprocessing function of structural analysis program. Further loading are assigned to model according to IS codes.
Analysis is carried out for member forces and reinforcement details. The obtained DCR values show that columns are safe and beams
to be reinforced additionally.
Key words: Progressive collapse, ETABS, Finite element model, Column removal.
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1. INTRODUCTION
The robustness of a structure is the ability of the structure to
withstand local damage that may arise by accidental actions
without disproportional failure that is disproportionate to the
triggering cause. Progressive collapse is such a disproportional
failure, which refers to the condition when the failure of a
local component (or localized region) leads to global system
failure. [1] The terminology of progressive collapse is defined
as ``the spread of an initial local failure from element to
element, eventually resulting in the collapse of an entire
structure or a disproportionately large part of it'' [2]. After the
event of 11 September 2001, more and more researchers have
started to refocus on the causes of progressive collapse in
building structures, seeking ultimately the establishment of
rational methods for the assessment and enhancement of
structural robustness under extreme accidental events. [3]
Progressive collapse of a structure takes place when the
structure has its loading pattern or boundary conditions
changed such that structural elements are loaded beyond their
ultimate capacities and fail. When any element fails, the
remaining elements of the structure seek alternative load paths
to redistribute the load applied to it. As a result, other elements
may fail, causing failure mechanism. It is a dynamic process,
usually accompanied by large deformations, in which the
collapsing system continually seeks alternative load paths in
order to survive. [4 and 5] One of the important characteristics
of progressive collapse is that the final damage is not
proportional to the initial damage.
2. GUIDELINES PROVIDED BY THE U.S.
GENERAL SERVICES ADMINISTRATION (GSA)
The purpose of these Guidelines is to [6]:
• Assist in the reduction of the potential for progressive
collapse in new Buildings
• Assist in the assessment of the potential for progressive
collapse in existing Buildings
• Assist in the development of potential upgrades to
facilities if required
2.1 Linear Static Analysis
In the linear static analysis column is removed from the
location being considered and linear static analysis with the
gravity load imposed on the structure has been carried out.
From the analysis results demand at critical locations are
obtained and from the original seismically designed section
the capacity of the member is determined. [8] Check for the
DCR in each structural member is carried out. If the DCR of a
member exceeds the acceptance criteria, the member is
considered as failed. The demand capacity ratio calculated
from linear static procedure helps to determine the potential
for progressive collapse of building.
2.2 Analysis Loading
For static analysis purposes the following vertical load shall be
applied downward to the structure under investigation:
Load = 2(DL + 0.25LL)

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Where,
DL = dead load
LL = live load
2.3 Acceptance Criteria
An examination of the linear elastic analysis results shall be
performed to identify the magnitudes and distribution of
potential demands on both the primary and secondary
structural elements for quantifying potential collapse areas.
The magnitude and distribution of these demands will be
indicated by Demand-Capacity Ratios (DCR) as Eqn. 1. [8]
(1)
Q
UD
= Acting force (demand) determined in component or
connection/joint (moment, axial force, shear, and possible
combined forces)
Q
CE
= Expected ultimate, un-factored capacity of the
component and/or connection/joint (moment, axial force,
shear and possible combined forces)
Using the DCR criteria of the linear elastic approach,
structural elements and connections that have DCR values that
exceed the following allowable values are considered to be
severely damaged or collapsed. [8]
The allowable DCR values for primary and secondary
structural elements are:
• DCR < 2.0 for typical structural configurations.
2.4 Scope
For the study twelve story reinforced concrete structure is
considered. The progressive collapse is initiated by removing
vertical load carrying members.
3. MODELING OF BUILDING
For the analysis, a typical frame model of plan as shown in
Fig.1 and of height 37.5 m is modeled using ETABS v9.7
software. The ground storey height is taken as 3.4 m and the
rest of the storey are taken to be 3.1 m high. The column cross
section is taken as 0.60m x 0.30m. Beam size is taken as 0.3m
x 0.3 m. The floor slabs are modeled as plates of 0.15m
thickness. Wall having 200 mm thickness is considered on all
the beams. All the supports are modeled as fixed supports.
Linear analysis is conducted on each of these models.
Fig.1 Plan of framed structure
Dead load [9]
Self weight of the structural elements
Floor finish = 1.5 kN/m2
and
Wall load on all beams is 11.16 kN/m2
Live load
On roof 1.5 kN/m2
, and on floors 3.0 kN/m2
Seismic loading as per IS: 1893 [10]
Zone II, III, IV &V
Soil type II, Response Reduction Factor = 3
Importance factor =1
The characteristic compressive strength of concrete (fck) is 30
N/mm2 and yield strength of reinforcing steel (fy) is 415
N/mm2. Analysis and design of building for the loading is
performed in the ETABS 9.7.Twelve storey building is
designed for seismic loading in ETABS 9.7 according to the
IS 456:2000.
4. ANALYSIS
To evaluate the potential for progressive collapse of a twelve
storey symmetrical reinforced concrete building using the
linear static analysis four column removal conditions is
considered. First building is designed in ETABS v9.7 [11] for
the IS 1893 load combinations. Then separate linear static
analysis is performed for each case of column removal.
Demand capacity ratio for flexure at all storeys is calculated
for three cases of column failure. Column C1, C16 and C18
are removed for progressive collapse analysis in different
cases.

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4.1 Calculation of Demand Capacity Ratio:
Capacity of the member at any section is calculated as per IS
456:2000 from the obtained reinforcement details after
analysis and design. Demand capacity ratio after removal of
column is found out considering the member force for the load
combination as per GSA guidelines. Member forces are
obtained by analysis results carried out in ETABS 9.7.
5. RESULTS AND DISCUSSION
The DCR values for the columns in all three cases do not
exceed the acceptance criteria value suggested by GSA
guidelines and hence columns are safe against progressive
collapse. But for a removed column adjacent beams DCR
values exceed the acceptance criteria value suggested by GSA
guidelines. The DCR values of unsafe beams in all seismic
zones are graphically represented.
5.1 Graphical Representation of DCR
After getting all the DCR values for all cases of column
removal, for all zones graph is plotted DCR Vs Storeys
For column C1 removed beam B1 and B5 exceed acceptance
criteria value suggested by GSA for progressive collapse
guidelines as in Fig.2 and Fig.3 respectively.
Fig.2 B1 beams DCR Fig.3 B5 beams DCR
For column C16 removed beam B23 and B24 exceed
acceptance criteria value suggested by GSA for progressive
collapse guidelines as in Fig.4 and Fig.5 respectively.

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For column C18 removed beam B25 and B26 exceed
acceptance criteria value suggested by GSA for progressive
collapse guidelines as in Fig.6 and Fig.7 respectively.
CONCLUSIONS
Based on the limited study of progressive collapse on
reinforced framed structure the following broad conclusions
can be made.
1. The DCR values of columns are less than two; it
suggests that columns are safe as per GSA guidelines
for progressive collapse analysis. Hence seismically
designed building columns have inherent ability to
resist progressive collapse.
2. The beams whose DCR values are more than
acceptance criteria value suggested by GSA for
progressive collapse guidelines are unsafe. That
beams were found to be adjacent to the removed
column in respective cases.
3. To avoid the progressive failure of beams and
columns, caused by failure of particular column,
adequate reinforcement is required to limit the DCR
within the acceptance criteria.
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.
REFERENCES
[1] Feng Fu Progressive collapse analysis of high-rise
building with 3-D finite element modeling method.
Journal of Constructional Steel Research 65 (2009)
1269_1278.
[2] B.A. Izzuddin, A.G. Vlassis, A.Y. Elghazouli, D.A.
Nethercot - Progressive collapse of multi-storey
buildings due to sudden column loss Part I: Simplified
assessment framework. Engineering Structures 30
(2008) 1308–1318.
[3] Jae-hyouk Choi, Dong-kuk Chang - Prevention of
progressive collapse for building structures to member
disappearance by accidental actions. Journal of Loss
Prevention in the Process Industries 22 (2009) 1016–
1019.
[4] Kapil Khandelwal, Sherif El-Tawil - Pushdown
resistance as a measure of robustness in progressive
collapse analysis. Engineering Structures 33 (2011)
2653–2661.
[5] Hyun-Su Kim, Jinkoo Kim, Da-WoonAn -
Development of integrated system for progressive
collapse analysis of building structures considering
dynamic effects. Advances in Engineering Software 40
(2009) 1–8.

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[6] H.M. Salema, A.K. El-Fouly , H.S. Tagel-Din - Toward
an economic design of reinforced concrete structures
against progressive collapse Engineering Structures 33
(2011) 3341–3350.
[7] Seweryn Kokot ,ArmelleAnthoine, Paolo Negro,
George Solomos - Static and dynamic analysis of a
reinforced concrete flat slab frame building for
progressive collapse. Engineering Structures 40 (2012)
205–217.
[8] General Services Administration (GSA). (2003).
Progressive collapse analysis and design guidelines for
new federal office buildings and major modernization
projects, GSA.
[9] IS 456:2000 (2005). Plain and reinforced concrete code
of practice, 4th Revision, 7th Reprint, Bureau of Indian
Standards, New Delhi.
[10] IS 1893 (Part 1):2002 (2006). Criteria for earthquake
resistant design of structures.5th
Revision, 3rd Reprint,
Bureau of Indian Standards, New Delhi.
[11] ETAB v 9.6 analysis reference manual, Computers and
Structures, Inc., Berkeley.
[12] Yanchao Shi, Zhong-Xian Li, Hong Haoa, - A new
method for progressive collapse analysis of RC frames
under blast loading. Engineering Structures 32 (2010)
1691_1703.

Progressive collapse analysis of reinforced concrete

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