47.5 MB - The Whole Building Design Guide

2.3.5.4 Storage Tank InstallationsAboveground and underground storage tanks located in floodhazard areas must be designed to resist flotation, collapse, andlateral movement. ASCE 24 specifies that aboveground tanks areto be elevated or constructed, installed and anchored to resistat least 1.5 times the potential buoyant and other flood forcesunder design flood conditions, assuming the tanks are empty.Similarly, underground tanks are to be anchored to resist atleast 1.5 times the potential buoyant forces under design floodconditions, assuming the tanks are empty. In all cases, designersare cautioned to address hydrodynamic loads and debris impactloads that may affect tanks that are exposed to floodwaters.Vents and fill openings or cleanouts should be elevated abovethe DFE or designed to prevent the inflow of floodwaters or outflowof the contents of tanks.2.3.5.5 Accessory StructuresDepending on the type of accessory structures, full compliancewith floodplain management regulations is appropriate and maybe required. For example, buildings or portable classrooms thatserve educational purposes (e.g., offices, classrooms), even if detachedfrom the primary school building, are not considered tobe accessory in nature and must be elevated and protected to thesame standards as other buildings.Some minor accessory structures need not fully comply, but maybe “wet floodproofed” using techniques that allow them to floodwhile minimizing damage. Examples include small storage sheds,garages, and restrooms. Accessory structures must be anchoredto resist flotation, collapse, and lateral movement. Flood-resistantmaterials must be used and utilities must be elevated abovethe DFE (plus freeboard, if required). Openings in walls must beprovided to allow the free inflow and outflow of floodwaters tominimize the hydrostatic loads that can cause structural damage.Because wet floodproofed accessory buildings are designed toflood, critical facility staff must be aware that contents will bedamaged.MAKING CRITICAL FACILITIES SAFE FROM Flooding2-77