ASCE 7-10 Exposure D – How Does it Work?

We’ve created a few quick steps that will help any design professional understand how and when to apply an exposure D condition.

 

1.      CONFIRM SURFACE ROUGHNESS DISTANCE AND THE INITIATION POINT OF EXPOSURE D: THE INITIATION POINT (Ip) OF EXPOSURE D OCCURS AT THE POINT ON LAND WHERE “SURFACE ROUGHNESS D” PREVAILS IN THE UPWIND DIRECTION FOR A DISTANCE OF 5000 FEET MINIMUM.

 

INITIATION POINT (Ip) = SURFACE ROUGHNESS > 5000FT

 

2.      DETERMINE DISTANCE OF STRUCTURE FROM THE INITIATION POINT (Sdist).

 

3.      CONFIRM PRIMARY EXPOSURE D REGION: THE PRIMARY EXPOSURE D CONDITION OCCURS (FOR ALL STRUCTURES) FROM THE EXPOSURE D NITIATION POINT AT THE DIRECTLY EXPOSED COASTLINE AREA,  RUNNING INLAND FOR A DISTANCE OF 600 FEET (Dprimary = 600 FT).

 

IF (Sdist) < (Dprimary) THEN EXPOSURE D APPLIES

 

4.      CONFIRM BUILDING-SPECIFIC EXPOSURE D REGION: A SECONDARY EXPOSURE D CONDITION MAY OCCUR BASED ON THE STRUCTURE ITSELF. TO DETERMINE THE BUILDING-SPECIFIC EXPOSURE D REGION, MULTIPLY THE MEAN ROOF HEIGHT (MRH) OF THE STRUCTURE BY 20 (Dsecondary=MRH*20). COMPARE Dsecondary TO THE Sdist.

 

IF (Sdist) < (Dsecondary) THEN EXPOSURE D APPLIES

 

Click the image below to enlarge the diagram:

 

 

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