|
|
re: strengthen a header?
14 aug 2005
rick wrote:
>...at first glance i'd say they calculated the load capacity of the
>existing configuration and used that to spec a clear span.
well, if two 9' 2x10s have s = 3x9.25^2/6 = 42.8 in^3 and m = 1000s
= 42800 in-lb = w9x12/8, w = 3169 pounds, it looks like the 2x4 post
(it might support 5250 pounds) isn't the limiting factor. the uniform
load on an 18' beam would be 2x3169/18 = 352 pounds per foot.
the 1981 nahb ap note says an 18' 2x10 hem fir beam with a 1/2"x9" plate
can support 215 lb/ft of uniform load, so a 0.5x352/215 = 0.82" plate
(or 2 246 pound 7/16" plates) might support 352 lb/ft. they suggest
1/2" bolts every 20" near the top and every 40" near the bottom and
something like 2 2x6 jack posts with 3/4" plywood plates at each end.
please apply the usual disclaimers.
nick
|
|
