Building comments 3.pdfMiller, Chuck
From: Miller, Chuck
Sent: Wednesday, April 24, 2013 4:52 PM
To: 'waitearch@comcast.net'
Subject: BLD2013-0240 Waite carport conversion -garage addition plan review comments
Good afternoon,
The IRC live load defection allowance (per Table R301.7) for 'all other structural members' (those that .are not 'floors and
plastered ceilings' or 'rafters having slopes greater than 3:12 with no finished ceiling attached to rafters') is L/240. Table
footnote 'b' notes 'For cantilever members, L shall be taken as twice the length of the cantilever' — for this project the
one foot cantilever would be calculated at two feet in the beam calculations.
The beam calculations provided as part of the submittal documents (see attachment #1) properly reflect the size,
species, grade, spacing, span, cantilever, and number of framing members and indicate a deflection at the cantilever
(reverse camber as you called it in an earlier email) of 0.362 inches. Without any limitations on the allowable amount of
deflection, the analysis seems to indicate that the beam design is OK. However, the total load deflection ratio
(Length/Deflection - highlighted) is 132.7, and a good portion of that load is live load.
Using a different beam calculation software, and entering the same information, the analysis indicates a failure due to
the stress developed at the top of the rafters (tension side) at the bearing end supporting half of the span plus the
cantilever as a result of the cantilever (see attachment #2). The total load deflection at the cantilever is comparable at
0.38 inches, as is the deflection ratio at L/126. However, the live load deflection ratio, L/202, does not meet the limits of
Table R301.7. A similar failure is indicated even with one foot entered for the length of cantilever in the analysis (see
attachment #3) —just in case there was any question about the program 'automatically' doubling the cantilever to meet
the footnote requirement.
t
t
t
attachment
attachment
attachment
1,pdf
2.pdf
3.pdf
Therefore, review comment #1, dated April 5, 2013, still applies, and another method must be proposed for the framing
of the roof structure additions to the existing roof structure.
Feel free to contact me if you have any questions or wish to discuss this further.
Chuck Miller
City of Edmonds
Plans Examiner
chuck.miller(cDedmondswa.aov
425-771-0220 x 1314