47.5 MB - The Whole Building Design Guide

stillwater depth) and that waves propagating into shallow waterbreak when the wave height reaches a certain proportion of theunderlying stillwater depth. These assumptions are used by FEMAto determine coastal high hazard areas (V Zones) where breakingwaves are predicted to be 3 feet or higher. At any given site, waveheights may be moderated by other factors. Designers should referto ASCE 7 for detailed discussion and computation procedures.Breaking wave loads on vertical walls or supporting structuralmembers reach a maximum when the direction of wave approachis perpendicular to the wall. The duration of individual loads isbrief, with peak pressures probably occurring within 0.1 to 0.3seconds after the wave breaks. It is common to assume that thedirection of approach will be perpendicular to the shoreline, inwhich case the orientation of the wall to the shoreline will influencethe magnitude of the load placed on the wall. ASCE 7provides a method for reducing breaking wave loads on verticalwalls for waves that approach a building from a direction otherthan straight on. Structures should be designed for repetitive impactloads that occur during a storm. Some storms may last for justa few hours, as hurricanes move through the area, or for severaldays, as during some winter coastal storms (nor’easters) that affectthe Mid-Atlantic and northeastern States.2.1.2.6 Debris Impact LoadsDebris impact loads are imposed on a building or building elementsby objects carried by moving water. Objects commonlycarried by floodwaters include trees, dislodged tanks, and remnantsof manmade structures such as docks and buildings (seeFigure 2-10). Extreme impact loads result from less commonsources, such as shipping containers, boats, and barges. Themagnitude of these loads is very difficult to predict, yet some reasonableallowance should be made during the design process.Impact loads are influenced by the location of the building inthe potential debris stream. The potential for debris impacts issignificant if a building is located immediately adjacent to, ordownstream from, other buildings, among closely-spaced buildings,or downstream from large floatable objects. While theseconditions may be observable in coastal areas, it is more diffi-MAKING CRITICAL FACILITIES SAFE FROM Flooding2-25