47.5 MB - The Whole Building Design Guide

and debris and ice impact loads. Flood loads on shear walls are reducedif they are oriented parallel to the anticipated direction offlow. Erodible soils may be present and local scour may occur; bothmust be accounted for in designs by extending the load-bearingmembers and foundation elements well below the expected scourdepth. Depending on the total height of the elevated facility, thedesign may need to take into consideration the increased exposureto wind and uplift, particularly where breaking waves are expected.Figure 2-26:School elevated oncolumnsContinuous perimeter walls (enclosed foundations with crawlspace):Unlike stem wall foundations, continuous perimeter walls enclosean open area or crawlspace (see Figure 2-27). The perimeter wallsmust have flood openings that are intended to equalize interiorand exterior water levels automatically during changing floodconditions to prevent differential hydrostatic pressures that couldlead to structural damage. Flood openings may be engineeredand certified for the required performance level, or must meetprescriptive requirements (notably, the opening must provideat least 1 square inch of net open area for each square foot ofarea enclosed). Perimeter wall design must also account forhydrodynamic loads, and debris and ice impact loads. Enclosedcrawlspaces must not contain utilities or equipment (includingductwork) below the required elevation. Designers must provideadequate underfloor ventilation and subsurface drainage tominimize moisture problems after flooding.MAKING CRITICAL FACILITIES SAFE FROM Flooding2-61