Well, some would say, “Nothing.” (Apparently all those who went before me thought so.) The wall is framed with 2 x 4 @ 16 in. o.c. DF-L `Stud’ grade studs. The studs themselves are 84 in. long (tall). The openings have 2 x 4 headers and are about 38 in. wide (clear). The wall supports continuous floor joists that span 10 ft one direction and 14 ft the other. The floor is light frame wood construction, and the use is `office’ or `commercial’ of some sort or another (or perhaps light manufacturing or storage).
I assume that the wall was intended to be a bearing wall. (The span would be too large for the joists for even the lightest use otherwise.) Intended or not – once framed tight, and loaded, the wall will take on load.
The situation is this: the wall shown does not have any sheathing or wall covering. Thus, the studs are not braced laterally in either direction – most importantly – their `weak’ direction. For `2 x’ studs that are 84 in. tall the `weak direction’ slenderness ratio is 84 divided by 1.5 (2 in. nominal is 1.5 in. actual, remember) = 56. The maximum slenderness ratio for wood compression members (that’s what a stud in a wall is) ... is ... 50. This is addressed, for example, in the International Building Code Sec 2308.9.9 Bridging. It is also addressed in the National Design Specification for Wood Construction (NDS). The NDS allows a slenderness ratio of up to 75 during construction ... but once the building is finished, and ready for occupancy, something must be done to keep the ratio down to or below 50. This is typically (and simply) done with the application of wall covering or sheathing. It may also be accomplished by `bridging’.
From a structural standpoint – studs unbraced in their weak direction have a greater potential of buckling (becoming unstable). Why is the wall still standing? Well, because the supported area above has only been recently occupied ... and thus loaded only `lightly’.
GET SOME SHEETROCK OR WOOD PANEL SHEATHING ON AT LEAST ONE SIDE OF THIS WALL!!! (That’s what I communicated to my client – though in a different tone.)
WHAT ELSE !!! ...???
The 2 x 4 headers, silly!!!
Under design loads I calculate that this wall will have to service a total load of over 2000 lb per linear foot (of wall). That’s over 6000 lb over a 3 ft opening.
AND GET SOME DOUBLE 2 X 10 HEADERS IN THERE OVER THOSE OPENINGS!!!
(Also communicated to my client, and also in different tone.)
It’s fun!!!
...
1 comments:
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A bridge is built for us to pass over; it is a work of utility, and which should endure. It should be in keeping with its object, solid, clean, simple, well executed without vain ornament.
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