47.5 MB - The Whole Building Design Guide

cult to estimate the potential for debris in riverine flood hazardareas. Any riverine waterway, whether a large river or smallerurban stream, can carry large quantities of debris, especiallyuprooted trees.Figure 2-10:The South CameronMemorial Hospital,Cameron, LA, wasdamaged by debriscarried by HurricaneKatrina’s storm surge(2005).Source: LSU AGCENTERThe basic equation for estimating the magnitude of impact loadsdepends on several variables that must be selected by the designer.These variables include several coefficients, building or buildingelement stiffness, debris weight, debris velocity, and duration ofimpact. The latter three variables, described in more detail inASCE 7, are briefly described below.Debris weight: Debris weight is one of the more difficult variablesto estimate. Unless otherwise indicated by field conditions, ASCE7 recommends using an average object weight of 1,000 pounds.This weight corresponds to a 30-foot long log only 1 foot in diameter,small in comparison to large trees that may be uprootedduring a flood. In coastal areas, expected debris weights dependon the nature of the debris. In the Pacific Northwest, large treesand logs are common, with weights in excess of 4,000 pounds. Inareas where piers and pilings are likely to become debris, 1,000pounds is reasonable. In areas where most debris is likely to resultfrom building damage (failed decks, steps, failed walls, propanetanks), the average debris weight may be less than 500 pounds.2-26 MAKING CRITICAL FACILITIES SAFE FROM Flooding