cross grain bending

[msquared48]

cross grain bending

thread337-246096

I posted to in 09 that I never got beyond my first post. A little late, but here goes...

Cross grain bending was mentioned in the '79 UBC in section 2312(j)3A and states that it should not be used, specifically for concrete to wood connections in a seismic area.

It is also referred to in ASCE 7-05 in section 12.1.2.2.3 and also placed in the seismic section as a nono.

That being said, I could find no reference to wind limitations in the code except for that implied in ASCE section 1.4, General Structural Integrity, where the direct reference to providing multiple load paths in the design is mentioned.

Therefore, considering the failure mechanism of cross grain bending, even for the wind application, the implication is to provide a second means of transfer of any lateral force to a ledger, or a sill plate for that matter, as it is just a ledger rotated 90 degrees. The force diagram is the same. Hencew the need for direct wall ties of a wood diaphragm to a tilt-up concrete wall, or the use of holddowns at the ends of shear walls instead of relying on the tension force in the anchor bolts against the sill plate,



Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[BAretired]

Why would anyone want to consider cross grain bending as a valid strength? The wood could crack at any time with or without stress.

BA

 

[azcats]

IMO, the implication is to provide a direct attachment for out of plane forces (w/o using cross grain bending) from wall to diaphragm where the wall is supported by the diaphragm. The forces are in different directions in a shear wall sill plate and the comparison doesn't equate in my head. Were shear wall anchor bolts ever used in tension in lieu of a holddown? I've never seen that. Are you implying that holddowns are required even if no uplift exists at the end of a shear wall?

 

[msquared48]

In response to your last question, no, not at all - I have done that for years.

However, I do make a point here that the use of only sill plate anchor bolts to resist the uplift of a shearwall is not an acceptible alternative to holddowns at the ends of the shearwalls, at least not to me.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[azcats]

I completely agree with that.

Although, I guess for some really light loads if you plate-washered the anchor bolt to eliminate CG bending, you could fashion some sort of detail with tension capacity.

 

[msquared48]

Well, that gets into the failure seen in California a few years ago where the plates split at the anchor bolt line, and then washers were required. I thought about that too, bot to work, I feel that the washers would have to be much larger than what is currently required, and more often, to stiffen the plate properly.

That being said too, I think the holddowns would be cheaper at some point, if not sooner.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[azcats]

I'd probably only try the AB tension detail in a situation where a holddown anchor was mis-located or I was dealing with an existing condition.

 

[BAretired]

Could use a rectangular steel plate over the sill. The problem then becomes anchoring the studs to the sill for tension.

BA

 

[msquared48]

In that end and toenailing are presently used, in combination with the shear nailing of the plywood to the side of the sill plate, this becomes a problem.

The stud is transmitting some uplift since the shearwall is nailed to it, through the nailing of it to the plate, causing little eccentricity to induce splitting of the plate. However, the nailing of the plywood to the side of the plate is generating a cross-grain moment that is inducing the tension forces to be reckoned with. This side nailing to me is the primary problem driving the splitting of the sole plate.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[azcats]

How about an H3 from stud to plate? Or 2. Heck you could fit 4.

If the anchorage of the shearwall material to the stud (edge nailing) - and the stud to the plate is relatively rigid, it should absorb and transfer the load to the plated AB before putting too much tension on the sill plate thru sheathing. The stud(s) would need to be in close proximity to the AB you're trying to use in tension.