Sill Plate Crushing at Girders
Sill Plate Crushing at Girders
(OP)
I've read at least (2) past posts regarding "Crushing of Plywood" and "Wood Bearing Plate at Trusses".
Now what about sill plate crushing at heavy girder reactions?
After reading the prior threads, i can be comfortable with a slight over-stress of perpendicular compression. But when i have a 16K reaction bearing on a 3.5x3.5 parallam, the compression perp exceeds 1,000 psi! I don't want to ignore that!
With one commercial general contractor, for over a decade, i've been specifying that the column shall interrupt both the top plates and sill plate and bear on a steel plate on concrete foundation wall. I've had no problem with that contractor. Did they actually comply in the field? As reputable as they are, i trust they do.
A different contractor, for a multi-family developer, is questioning this specification. After meeting and hearing my defense, they do understand and will comply for at least one particular heavy reaction location. Desiring to please the client, i am considering to raise my threshold of compression perp, but i must stay within reason.
After reading the aforementioned posts, i can conclude that crushing, WITHIN REASON, is not a major issue. But, where is that threshold? Do i accept nothing higher than 425 for SPF and likewise 625 for DFL or how much can i be comfortable exceeding this?
Related to this topic, in a prior post, i inquired, without a reply:
If the wood actually DID begin to crush, wouldn't the allowable compression perpendicular actually increase as the wood is crushing, and thus, soon terminate the crushing? Any opinions?
Another consideration is that if crushing DID occur, if brittle finishes, such as gypsum, are on that wall, cracking of that finish will also occur.
Another other thoughts?
Thank you!
Now what about sill plate crushing at heavy girder reactions?
After reading the prior threads, i can be comfortable with a slight over-stress of perpendicular compression. But when i have a 16K reaction bearing on a 3.5x3.5 parallam, the compression perp exceeds 1,000 psi! I don't want to ignore that!
With one commercial general contractor, for over a decade, i've been specifying that the column shall interrupt both the top plates and sill plate and bear on a steel plate on concrete foundation wall. I've had no problem with that contractor. Did they actually comply in the field? As reputable as they are, i trust they do.
A different contractor, for a multi-family developer, is questioning this specification. After meeting and hearing my defense, they do understand and will comply for at least one particular heavy reaction location. Desiring to please the client, i am considering to raise my threshold of compression perp, but i must stay within reason.
After reading the aforementioned posts, i can conclude that crushing, WITHIN REASON, is not a major issue. But, where is that threshold? Do i accept nothing higher than 425 for SPF and likewise 625 for DFL or how much can i be comfortable exceeding this?
Related to this topic, in a prior post, i inquired, without a reply:
If the wood actually DID begin to crush, wouldn't the allowable compression perpendicular actually increase as the wood is crushing, and thus, soon terminate the crushing? Any opinions?
Another consideration is that if crushing DID occur, if brittle finishes, such as gypsum, are on that wall, cracking of that finish will also occur.
Another other thoughts?
Thank you!






RE: Sill Plate Crushing at Girders
In practice I've often ignored perp. compression if I didn't have a serviceability or performance issue. Metal bearing plates can also get you out of these failure modes pretty easily as well.
Professional and Structural Engineer (ME, NH)
American Concrete Industries
www.americanconcrete.com
RE: Sill Plate Crushing at Girders
This doesn't really answer your question, but gives some places to look.
RE: Sill Plate Crushing at Girders
RE: Sill Plate Crushing at Girders
As noted, too, the plate will crush to a certain extent to achieve the load seen, similar to what soil does in bearing. The larger and thicker the plate, the less crushing.
Mike McCann, PE, SE (WA)
RE: Sill Plate Crushing at Girders
I usually limit my stresses at 400 for SPF plates, if over i switch to SYP plates. And i actually have never been over 600 knowingly...
RE: Sill Plate Crushing at Girders
Something i forgot:
I would not specify SPF or DFL for sill plates. Since sill plates (typically) bear on concrete, unless we provide a separation barrier, i should only be specifying preservative treated SYP sill plates. Apparently, for the heavy girder situations, that is why i've specified the steel base plates. Through my research, SYP is the only species that is preservative treated in this area.
Thank you all!
RE: Sill Plate Crushing at Girders
RE: Sill Plate Crushing at Girders
RE: Sill Plate Crushing at Girders
I don't know anything about the legality of taking the wind tables from the NBCC and creating an interactive map out of them. You'd have to talk to an intellectual rights lawyer about that.
RE: Sill Plate Crushing at Girders
http://www.strongtie.com/ftp/catalogs/C-L-SWSB13/C...
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Sill Plate Crushing at Girders
The steel plate can be loose, otherwise fasten it to concrete with tapcon screws or other. I have previously specified the following:
A STAINLESS OR GALVANIZED 1/2" x 8" THREADED ROD WITH 4" PROJECTION MUST BE CAST IN PLACE INTO CONCRETE FOOTING CENTERED ON WOOD COLUMN AND PROJECT 4" UP THROUGH BASE PLATE AND BOTTOM OF WOOD COLUMN.
You could also specify to have the threaded rod installed, with epoxy, after the concrete pour.
To anchor the wood column to prevent uplift, specify any of the Simpson Holdowns or Tension-Ties. The accompanying anchor, required to fasten the Holdown or Tension-Tie to concrete, would be installed above the adjacent wood sill plate (which is interrupted by the steel bearing plate), penetrate and go through the sill plate and anchor to the concrete.
RE: Sill Plate Crushing at Girders
When I am working on a problem, I never think about beauty but when I have finished, if the solution is not beautiful, I know it is wrong.
-R. Buckminster Fuller