Overview of Progressive Collapse Analysis and Design: A structure may experience progressive collapse when one of the primary elements fails due to the failure of adjacent structural elements, resulting in further failure of the structure.
To avoid such errors, identifying the critical/primary element is the most important task in the design phase.
Vertical member failure is primarily the cause of progressive collapse of a structure.
Damage to a column caused by sheet metal loads, an accident, or intentional damage can cause the column to fail.
Such errors would lead to the collapse of the structure.
The following procedure is suggested in the GSA manual for progressive collapse analysis of a new structure.
- Analysis of the immediate loss of a pillar in the middle of the shortest direction of the building above the first floor
- Analysis of the immediate loss of a pillar in the middle of the longest direction of the building above the first floor
- Analysis of the immediate loss of a pillar on the corner of the first floor building
- Analysis of the immediate loss of an interior pillar from the basement or uncontrolled public area on the ground floor (for buildings with an underground passage or uncontrolled public access)
A similar procedure is used for load-bearing walls and shear walls.
The static calculation takes into account twice the self-weight and 50% of the payload.
Load = 2 (DL + 0.25 LL);
DL = dead load
LL = payload
GSA guidelines for dynamic analysis suggest different load combinations.
Load = DL + 0.25 LL
According to the GSA manual, structure analysis can be done by three different methods
- Linear-elastic static analysis
- Nonlinear static analysis
- Nonlinear dynamic analysis
Due to its simplicity, linear elastic static analysis is often used by designers.
According to GSA guidelines, 3D modeling is the most appropriate method to analyze the structure.
However, depending on the situation, the 2D model can also be used for analysis. The framework acceptance criteria are based on the limits of the demand capacity index.
DCR = Member Demand/Capacity
DCR = direct current;
D = requirement (moment, axial or shear forces acting on the element in static elastic analysis)
C = Capacity of the element (moment, axial or shear force that the element can withstand)
If the DCR value determined from linear static analysis exceeds the following values, the structural elements are considered severely damaged or collapsed.
DCR <= 2.0 for normal buildings
DCR <= 1.5 for irregular buildings
Furthermore, GSA guidelines allow for an increase in the strength of materials, such as the characteristic strength of concrete and the yield strength of reinforcement. Click here for more information on increasing material strength.
