47.5 MB - The Whole Building Design Guide

locities greater than 10 feet per second cannot be converted toequivalent hydrostatic loads. Instead, they must be determined accordingto the principles of fluid mechanics or hydraulic models.Hydrodynamic loads become important when flow reachesmoderate velocities of 5 feet per second. The components of hydrodynamicloads are laterally imposed, caused by the impact ofthe mass of water against the building, and drag forces along thewetted surfaces. Drag coefficients for common building elements,such as columns and piers, can be found in a number of sources.ASCE 7 recommends values for a variety of conditions.Another component of hydrodynamic loads is wave loads. As describedin ASCE 7, “design and construction of buildings andother structures subject to wave loads shall account for the followingloads: waves breaking on any portion of the buildingor structure; uplift forces caused by shoaling waves beneath abuilding or structure, or portion thereof; wave runup striking anyportion of the building or structure; wave-induced drag and inertiaforces; and wave-induced scour at the base of a building orstructure, or its foundation.”Wave forces striking buildings and building elements can be 10to 100 or more times higher than wind forces and other forces.Forces of this magnitude can be substantial, even when actingover the relatively small surface area of the supporting structureof elevated buildings. Post-storm damage inspections show thatbreaking wave loads overwhelm virtually all wood-frame and unreinforcedmasonry walls below the wave crest elevation. Onlyengineered and massive structural elements are capable of withstandingbreaking wave loads. The magnitude of wave forces isthe rationale behind the floodplain management requirement forthe bottom of the lowest horizontal structural member to be ator above the design flood elevation in environments where wavesare predicted to be 3 feet or higher (V Zones). Because waves aslow as 1.5 feet can impose considerable loads, there is a growingawareness of the value of accounting for waves in areas that are referredto as “Coastal A Zones.”Computation of wave loads depends on the determination of waveheight. Equations for wave height are based on the assumptionthat waves are depth-limited (on the order of 75 to 80 percent of2-24 MAKING CRITICAL FACILITIES SAFE FROM Flooding