Assessment of Progressive Collapse Requirements for Precast Concrete Buildings

Threat evaluations due to bombing and progressive collapse of precast concrete building systems are examined and presented in this report. A prototype structure based on the moment frame building system from PCI-Seismic Design for Precast/Prestressed Concrete Structures is used for these evaluations. Two distinct studies are conducted. The first examines the potential for abrupt failure of the ground level columns due to intentional detonation of explosives; the second examines the potential for progressive collapse of the building system as a result of this loss. Three types of column failures, including brisance failure, flexural failure, and direct shear failure are discussed and evaluated based on blast load effects. For each failure case, the number of failed columns respect to stand-off ranges with specified weight of charges is determined by employing UFC-3-340-02. A pictorial representation of the stand-off distances and number of failed columns are provided to assess the combined effects of blast load types with a specified charge weight. The generalized image provides a safe-range for each failure type. This methodology can be used to guide engineers in making enhancement to columns based or safe standoff ranges to ensure that safe operating levels are satisfied. In progressive collapse analysis section, the structure is examined using the procedures of the Unified Facilities Criteria (UFC) and the General Services Administration (GSA). Three model cases are compared: original model, modified model with cantilever continuous beam, and modified model with fixed-fixed continuous beam, analyze progressive collapse responses and make modifications by employing linear static procedure. The current GSA progressive collapse guidelines and UFC progressive collapse design are used for evaluations, and the commercially available structural analysis program ETABS Nonlinear V9.7.1 is utilized to perform example analyses. The evaluations show that UFC provides more conservative requirements in progressive collapse resistance than GSA does. Additionally, the deflections directly above the removed column are evaluated in the modified models with adequate strength, since the original model shows insufficient progressive collapse resistance due to inadequate strength of steel plates and anchorage bars. Consequently, the fixed-fixed continuous beam model, which is modified as simply-supported beam, is preferable due to smaller deflection evaluated.