A structure experiences progressive collapse when the following conditions occur: a primary structural member fails due to manmade or natural causes, the loads from the lost member are transferred to adjoining members, adjoining members fail due to the redistributed loads, and the process repeats until a disproportionate amount of the structure is damaged or collapses. This study investigates methods of collecting data from a test structure, modeling a structure, performing analysis, and ultimately developing a process to create a simplified model for engineers to use for fast and easy progressive collapse analysis of a structure.
In this research, a reinforced concrete structure is tested and modeled for analysis. The building consisted of three above ground floors and a basement in a regular rectangular layout, thick reinforced concrete slabs with no beams on the lower floors, and circular columns with drop panels. 14 strain gauges were placed strategically on three of the first story columns near the same corner of the building prior to its demolition. Strain data was collected and monitored from the gauges during the demolition process where three external columns, including the corner column, were removed by a processor. This was done to simulate a multiple column loss triggering event for progressive collapse.
Using the SAP2000 program, a detailed model is developed to represent the building and its behavior as accurately as possible. Various factors such as the loading conditions, development of structural elements with proper dimensions, and end constraints are modeled according to the building plans. Analysis is performed on the model and compared to the test data to verify that the model accurately represents the measured behavior of the structure. Various simplifications are then made to the detailed model including a reduction in the number of floors, a reduction in the number of bays, and replacing the thick slabs with equivalent beams. A series of sensitivity analyses are performed to investigate and justify all simplification steps made to the models. The test data is compared to the calculated results from the models after each major simplification is made to ensure relative accuracy is maintained. Ultimately, a procedure for creating a final simplified model consisting of only a few structural elements is developed. A spring model is also developed from the final simplified model which can be used in future research to perfect the proposed model.
The research results provide valuable information to the study of progressive collapse as the behavior and response of a reinforced concrete structure subjected to multiple column losses is investigated and discussed at length. The proposed procedure and model are suggested for use by engineers for the quick and simple check of a structure’s ability to resist progressive collapse. The final simplified model consists of only a few frame elements and is developed for general use of analyzing different types of building structures.