Wind Driven Rain Forces on Buildings

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Wind Driven Rain Forces on Buildings
Structures

• Presented by Charles R. Norman P.E.
• Consulting Engineer

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Introduction

• Brief History
• Background

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Source 2005 Disasters in numbers. Inter-agency
Secretariat of the International Strategy for
Disaster Reduction (UN/ISDR). Press Release,
January 30, 2006.
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Defining Wind Driven Rain ForcesWDR

• Rain Drops being caught by winds
• Catch Ratio
• Rain Drop Intensity from Weather Data
• Computational Fluid Dynamics
• WDR loading the structure
• WDR infiltrating the structure

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Issues-IBC Building Codes

• Hygrothermal issues
• Including WDR as per Building Codes
• Choosing Material of Construction
• WDR forces as per Building Codes
• Importance of following Code
• Moisture Vapor Retarder
• Protection Against Decay
• Other issues

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Hygrothermal Analysis of Wall Construction

• Oak Ridge National Laboratories
• Designing for Hygrothermal issues using IBC
• Hygrothermal Analyis
• Minimizing Hygrothermal Damages from WDR

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Design Data

• Event
• Hurricane, Tropical storm, Tornado
• Wind speed
• Rainfall and raindrop intensity
• Catch ratio
• Building envelope
• Weather data after the event
• Review the available Data

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Location of Structure

• Geographic Location - Map
• Site location (City, subdivision, etc.)
• IBC and ASCE-07 requirements
• Calculating wind and WDR loads
• Temporal and spatial nature of wind

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Characteristics of Building

• Exposure A, B, C, D (IBC and ASCE-7-05)
• Envelope
• Cross section of wall
• Identify material of construction through wall,
  etc.
• Properties of material

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Material Properties

• Thermal properties
• Mechanical properties
• Physical properties
• Hygrometric Properties
• Water Absorption coefficient
• Liquid transport Coefficient
• Free water saturation

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Resistance of Home to Damage

• Determining Humidity, Air Moisture (HAM)
  Invasion
• Determining WDR and Moisture accumulation
• Base Line Evaluation
• Storm Event Evaluation

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Resistance, contd.

• Component Analysis
• Roofs
• Siding
• Windows
• Moisture Barriers
• Insulation
• Sheetrock
• Brick walls
• Engineering Analysis

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Design Assessment

• Exterior
• Interior
• Materials

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Assessment, contd.

• Interior
• Overloaded members

• Water Damages

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Assessment, contd.

• Identifying the Damages-Hygrothermal Loss of
  Use

• Structural
• Mechanical
• Cosmetic
• Safety Health Issues
• Environmental Issues
• Economic Issues

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Assessment, contd.

• Documenting the Moisture Buildup
• Analysis
• Moisture measurements
• Inspections of walls

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Damages

• Wind Flood
• Extreme Events
• Accumulation of Damages
• Remodeling

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Role of Engineer

• Evaluate WDR and Hygrothermal
• Physical Resistance to WDR
• Loads and Energy
• Establish Specifications
• More than one event
• Employ Engineering Methods

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Review of WDR Research

• Computational Fluid Dynamics
• WUF1
• Hygrothermal

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Examples
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Rain Fall Intensity
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Building Invasion
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Raindrop Size Distribution
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Computation of WDR Forces

• Ft Fasce 07 Fs x ? (lb / sq ft)
  (8)
• Ft .00256 KzKzt u2 I Fwdr Kz Kzt I
  (9)
•  
• where
•  
• Kz, Kzt, Kz, Kzt are coefficients from ASCE
  07. I is the importance factor. Kz and Kzt
  may vary from normal wind coefficients. See
  Table 6-3 of ASCE 07.

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Computation of WDR (contd)

• Fwdr Fs x ? (7)
• where
• ? no. of rain drops per unit area per unit
  time.

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Computation Model for WDR

• Purpose
• Impact forces
• Wetting Patterns
• Findings
• Minimum Design Loads

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Rain fall Data
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Summary

• Importance of WDR to Design
• Importance of WDR to Hygrothermal Issues
• Utilize Engineering Building Codes, Standards,
  and Good Engineering Practices
• Expected Results with design more resistant to
  WDR
• Future Research