This study was conducted by the National Institute of Building Sciences’ Building Seismic Safety Council (BSSC). The goal was to develop standardized categories for older concrete buildings that incorporate more detail than those included in the standard set of Federal Emergency Management Agency (FEMA) Concrete Model Building Types – namely, C1-frames, C2-shear walls, C3-concrete frames with masonry infill, and PC2-precast frames. The recommended “subtypes” generally can be identified without extensive engineering evaluation and therefore can document the inventory of older concrete buildings in an effort to better quantify how many structures might require mitigation. The identification of these subtypes also contributes to determination of the highest priority research needed to enable rapid implementation of performance-based seismic design for mitigation.
For initial collection of inventory data, building age, height, and occupancy should be documented. Data on additional attributes that affect risk of high damage levels or collapse would require engineering evaluation and cannot be collected reliably using typical inventory-collection techniques; however, additional attributes that may be important for identifying a high-risk concrete building are discussed.
The primary attribute suggested for initial classification is occupancy and 13 different occupancies are recommended. The structural systems typically, but not exclusively, used for each occupancy are described as are potential seismic deficiencies. Also described are the many variations that can affect the risk levels of each of the FEMA Concrete Model Building Types (C1, C2, C3, and PC2) including strength, stiffness, configuration irregularities, and gravity frame type. These descriptions are organized into Structural Type Families based on the four primary model building types.
Without further understanding of the collapse mechanisms of older concrete buildings, building subtypes that can reliably distinguish seismic risk levels cannot be established