Plate Crushing Contribution to Long Term Shrinkage in Typical Multi-Story Light Frame Wood Buildings

Question

Plate Crushing Contribution to Long Term Shrinkage in Typical Multi-Story Light Frame Wood Buildings

Mike Mike (Structural)

(OP)

5 Aug 21 16:29

Does anyone know a good source for how much vertical deformation occurs specifically due to wood studs loading plates?

ASTM D245 establishes Fc perp by compressing a 2" wide steel plate on a 2"x2"x6" wood specimen and recording the stress at 0.04" deformation. NDS states the deformation at a stress of 0.73 x Fc perp = 0.02". NDS states "For the same stress, deformation of a joint consisting of two wood members both loaded perpendicular to grain will be approximately 2.5 times that of a metal to wood joint." I remember reading an estimation method out on the interwebs that suggested a stud bearing on a plate would experience approximately 1.75 times that of a metal to wood joint, which seems reasonable to me, but I can't find it now.

Typically plates in my structures average about 0.73 times their capacity when fully loaded, and both top and bottom plates contribute, so I'm thinking my deformation per floor due to plate crushing is like 0.02" x 2 x 1.75 = 0.07".

Canuck65 (Structural) · Answer 1 · 2021-08-05 16:58:46

The taller wood framed buildings I have seen designed specify engineered lumber (LVL) for all sill plates and top plates to reduce vertical shrinkage due to A) drying of the material and B) crushing of the sill plates. Compared to non-combustible elevator and stairwell cores, the shrinkage of the wood structure can become problematic and thus anything reasonable to reduce the differential shrinkage is considered.

I do not have any specific literature, however, would direct you towards the literature created by FP Innovations, I am guessing they have addressed this issue.

Mike Mike (Structural) · Answer 2 · 2021-08-05 22:30:50

Thanks Canuck65, I'm not seeing anything related by FP Innovations. How much do engineered plates deform under dimension lumber stud loads?

hokie66 (Structural) · Answer 3 · 2021-08-05 22:42:31

Thought I had posted this, but it seems not to be here. Canuck is correct, in that shrinkage perpendicular to grain is a larger factor than compression.

https://www.woodworks.org/experttip/wood-framing-s...

Mike Mike (Structural) · Answer 4 · 2021-08-06 01:31:27

Thanks Hokie, in the case of LSL plates kept relatively dry during construction, most engineers would consider their shrinkage perpendicular to grain to be zero. In this case plate crushing would be a larger factor. Also, there are a lot of readily available resources on shrinkage, so I'm less interested in that aspect.

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Plate Crushing Contribution to Long Term Shrinkage in Typical Multi-Story Light Frame Wood Buildings