47.5 MB - The Whole Building Design Guide

2.3.4 RISK REDUCTION IN HURRICANESTORM SURGE AREASCoastal communities along the Atlantic and Gulf coasts are subjectto storm surge flooding generated by hurricanes and tropicalstorms. Depending on a number of variables, storm surge flooddepths may significantly exceed the BFE. In addition, waves arelikely to be larger than predicted for the base flood, and will occurin areas where significant wave action during the base flood is notexpected. Application of the minimum requirements related toelevation of the lowest floor and foundation design does not resultin flood resistance for such extreme conditions. The followingspecial considerations will provide a greater degree of protectionfor critical facilities located in areas subject to storm surges.Higher foundations: Foundations should be designed to elevatethe building so that the lowest horizontal structural members arehigher than the minimum required elevation. Additional elevationnot only reduces damage that results from lower probabilityevents, but the cost of Federal flood insurance is usually lower.However, accessibility may be affected and there will be some additionalconstruction costs that must be balanced against avoidedfuture damage and a higher likelihood that a facility can be morerapidly restored to full function.Scour and erosion: Storm surge flooding and waves can cause scourand erosion, even at locations that are some distance from theshoreline. Foundation designs for critical facilities in coastal communitiesshould account for some erosion and local scour ofsupporting soil during low probability surge events.Water-borne debris: Storm surge flooding can produce large quantitiesof floating debris, even at locations that are some distancefrom the shoreline. Debris damages nonstructural building componentsand, in some cases, prolonged battering can lead tostructural failure. Foundation designs for critical facilities incoastal communities should account for debris loads. This is especiallyimportant where damage to other buildings in the area maygenerate additional debris, thereby increasing the loads.Continuous load path: Especially in high wind regions, designersshould pay special attention to the entire roof-to-foundation load2-72 MAKING CRITICAL FACILITIES SAFE FROM Flooding