This document summarizes research on analyzing the progressive collapse of a reinforced concrete frame building. Progressive collapse occurs when a structural failure in one element, like a column, causes a domino effect that brings down larger parts of the structure. The researchers used linear static analysis in SAP2000 to model removal of columns and calculate demand-to-capacity ratios to evaluate structural integrity. They also conducted nonlinear dynamic analysis removing a single column to study load redistribution. The analysis found catenary action helped resist progressive collapse by redistributing loads through composite joints. Demand-to-capacity ratios above 2.0 indicated structural damage or collapse depending on the structural configuration.

1. Proceedings of the International Conference on Emerging Trends in Engineering and Management (ICETEM14)
30 – 31, December 2014, Ernakulam, India
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PROGRESSIVE COLLAPSE ANALYSIS OF A
REINFORCED CONCRETE FRAME BUILDING
Shefna L Sunamy, Binu P, Dr. Girija K
1, 2
(Civil Engineering Department, Sree Narayana Gurukulam College of Engineering, Kolenchery, Kerala, India)
3
(Civil Engineering Department, Govt. Engineering college, Bartonhill, Thiruvananthapuram, Kerala, India)
ABSTRACT
Progressive collapse in a structure occurs when major structural load carrying members are removed suddenly,
and the remaining structural elements cannot support the weight of the building. This failure usually occurs in a domino
effect and leads to a progressive collapse of the structure. The basic characteristic of progressive collapse is that the end
state of destruction is disproportionately greater than the failure that initiated the collapse.
This paper describes linear static analysis of a multi-storeyed building using SAP 2000 by static removal of a
major structural element and nonlinear dynamic analysis by removing a single column.
Keywords: Acceptance Criteria, Column Removal, Demand Capacity Ratio, Progressive Collapse, Nonlinear Analysis.
1. INTRODUCTION
The progressive collapse of building is initiated when one or more vertical load carrying members (typically
columns) is removed. When a column is removed, (due to a vehicle impact, fire, earthquake, man-made or natural
hazards) the building’s weight (gravity load) transfers to neighboring columns in the structure. If these neighboring
columns are not properly designed to resist and redistribute the additional gravity load that part of the structure fails. The
vertical load carrying elements of the structure continue to fail until the additional loading is stabilized. As a result, a
substantial part of the structure may collapse, causing greater damage to the structure than the initial impact. Progressive
collapse occurs when a structure has its loading pattern or boundary conditions changed such that some members are
loaded beyond their intended capacities. The residual structure is then forced to seek alternate load paths to redistribute
the out-of balance loads from damaged members. As a result, other neighboring members surrounding the residual
structure may also fail shedding some applied loads. The redistribution of loads is a dynamic process and will continue
until a new equilibrium position is reached by the residual structure, either through finding a stable alternate load path or
through further shedding of loads as a consequence of collapsed members
2. LITERATURE REVIEW
Rakshith K G and Radhakrishna, (2013), studied about progressive collapse which 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. 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. The adequate reinforcement
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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.
Lanhui Guo and Shan Gao, Feng Fu, (2013) studied about Partial or full range progressive collapse of structures
which is triggered by a local damage due to abnormal events such a gas explosion, bombing attack or vehicle collision
may lead to terrible causalities and severe economic loss. It is mainly because that the loads on superstructures cannot be
transferred downwards when a vertical load carrying component fails. However, in the process of column failure,
“catenary action” plays an important role in redistributing the internal load and preventing progressive collapses of the
structure. Rigid composite joints exert great influence in catenary action. Therefore, an experiment related to a 1/3 scale
progressive collapse resistance with the use of rigid composite joints was conducted, and the results of the experiment
were analyzed. In catenary stage, catenary action evidently enhanced the resistance to the progressive collapse of the
frames. The steel–concrete composite frame with rigid connections designed in accordance to current design standards
showed a good resistance to progressive collapse. It is also found that horizontal restraining stiffness of the frame exerted
great influence on the resistance in catenary stage.
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).
Acceptance criteria for the primary and secondary structural components shall be determined as:
D.C.R= QUD/ QCE (1)
where,
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.
The allowable DCR values for primary and secondary structural elements are:
• DCR < 2.0 for typical structural configurations
• DCR < 1.5 for atypical structural configurations
4. SAP2000 MODELLING AND ANALYSIS
The building considered for the study is twelve storey symmetrical R.C. building. The structure consists of six
bays of 5 m in the longitudinal direction and four bays of 5 m in the transverse direction. Typical floor-to-floor height is
3.1 m and for the first story it is 3.4 m. Wall having 115 mm thickness is considered on all the beams. Slab thickness
considered is 150 mm. Beam size is taken for twelve storey’s as 300 × 550 mm. Column sizes are 500x500, 600x600 &
900x900 mm are considered for building. Loading considered on the building for the study are as follows.
• Dead load
• Live load
• Seismic loading as per IS: 1893
Fig.1: Plan of the building

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4.1. Linear static progressive collapse analysis
To evaluate the potential for progressive collapse of a twelve storey symmetrical reinforced concrete building
using the linear static analysis three column removal conditions is considered. First building is designed in SAP 2000 for
the IS 1893 load combinations. Then separate linear static analysis is performed for each case of column removal.
Fig. 2: 3D model generated in SAP 2000
4.2. Calculation of Demand Capacity Ratio
Demand capacity ratio for flexure at all storeys is calculated for all three cases of column failure..Capacity of
the member at any section is calculated as per IS456:2000 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 SAP 2000.
4.3. Graphical Representation of DCR
After getting all the DCR values for critical cases of column removal, for all zones graph is plotted DCR Vs
Storeys.
Fig.3: Graphical representation of DCR when Long side column removed

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Fig.4: Graphical representation of DCR when Short side column removed
Fig.5: Graphical representation of DCR when Corner column removed
5. NONLINEAR STATIC PROGRESSIVE COLLAPSE ANALYSIS
Nonlinear static analysis is widely used to analyze a building for a lateral load and is known as pushover
analysis. It increases applied loads step-by-step until maximum load is attained (load controlled) or maximum
displacement is attained (displacement controlled). This method can be used to determine the ductility measure of the
structure for lateral loading. Ductility is measured as a ratio of maximum displacement and yield displacement.
Generally, the ability of the structure to attain large ductility results in better performance under earthquake
loading. For nonlinear analysis automatic hinge properties and user-defined hinge properties can be assigned to frame
elements. When automatic or user-defined hinge properties are assigned to a frame element, the program automatically
creates a generated hinge property for each and every hinge. There are five default hinge options are available, Axial (P),

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Torsion (T), Moment (M2 or M3),Shear (V2 or V3), and Coupled (P-M2-M3). The hinge properties are calculated by the
program for the cross section and reinforcement details provided. For default moment hinges, SAP2000 uses Tables 6-7
and 6-8 of FEMA 356.
Fig.6: Pushover curve: 3D Frame without column removed case
Fig.7: Pushover curve: 3D Frame when long side column removed
6. CONCLUSIONS
Seismically Designed building has inherent ability to resist progressive collapse. Nonlinear static analysis
reveals that hinge formation starts from the location having maximum demand capacity ratio. 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. To mitigate progressive collapse an alternate load path has to be provided. The
alternate load path like, providing bracing at floor level and increasing size of column at the outer face can be adopted
advantageously.
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