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Edit Distributed Request
Original Request
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Request ID:
8396
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Date Submitted:
March 16, 2020
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Requested By: RYAN GISSAL
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Code:
Residential
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Edition:
2017
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Chapter:
Chapter 3 Building Planning
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Section:
Table R301.2(2)
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Topic:
Component and Cladding Design Pressures
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Question:
Is it the intent of Table R301.2(2) to permit slightly lower component and cladding negative pressures than as specified in ASCE 7-10, Figure 30.5-1 by permitting the ASD pressures to be truncated to the nearest integer?
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Comments:
When comparing ASCE 7-10 Figure 30.5-1 pressures to the pressures shown in FBC-R, Table R301.2(2), we noticed that the negative ASD pressures were slightly lower in FBC-R. The discrepancy appears to be caused when the FBC-R table truncates negative pressures to the nearest integer. This discrepancy grows when applying the height and exposure adjustment coefficients in Table 301.2(3).
For example:
ASCE 7-10, Figure 30.5-1, Vult = 140 mph, Exposure C, Zone 4, 10 SF, MRH = 30ft:
+35.3 / -38.2 psf (Fig 30.5-1) x 0.6 = +21.2 / -22.9 psf (ASD) x 1.40 = +29.7 / -32.1 psf
From FBC-R, same pressures would work out to be:
+21.2 / -22.0 psf (Table 301.2(2)) x 1.4 = +29.7 / -30.8 psf
Please see attached for additional comparison. Is this difference intentional? This may be a moot point as 140 mph wind speed would fall back to ASCE 7 per R301.2.1.1, but the difference is still confusing, and sometimes causes rejection comments from plan reviewers.
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Attachment 1: Download
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