| Popis: |
A statistical study of National Fallout Shelter Survey (NFSS) Phase 2 building structural characteristics extracted from OCD files is reported. A total of 844 buildings of the original Phase 1 sample of 1541 was surveyed by AR's in the NFSS Phase 2. Included in these buildings are 1030 basement shelter areas, 262 first story shelter areas, and 838 upper story shelter areas. The modal value for basement sill heights is 5 feet; whereas 80% of the sill heights of the first stories are from 2 to 3 feet, and for upper stories 90% are from 2 to 3 feet. Parallel partitions occur in 51% of the basement shelter areas, 68% of the first story shelter areab, and 78% of the upper story shelter areas. Cross partitions occur in 761 of the 2130 shelter areas. ''Area factors'' are multipliers used to estimate the fraction of the total floor area offering protection greater than a predetermined value. A unique set of area factors which do not vary with structural details of the building are used in the NFSS. Several shortcomings of these approximate area factors are discussed: cases in which center PF's are lower than off-center PF's; the effect of interior partitions, floor thickness, and apertures; and shelters with predominantly roof contribution. Analyses of shelters with only roof contribution and of shelters with both ground and roof contribution are presented. Methods of determining more nearly correct area factors for each situation are given. For more exact computations, it is recommended that the shelter area be calculated by computing PF's at several offcenter locations and determining graphically the areas which reach a prescribed PF. |
