2x12 Ledger to Concrete Wall - what am I missing?

[ctcray]

Situation: 2x12 SPF #2 Ledger fastened to concrete wall with 3/4" bolt @ 12"oc at the centerline of the ledger, supporting 336 plf total load. From 2005 NDS Table 11E, I get a Zperp of 450 lbs. Assuming all Adjustment factors are 1.0, is there something else that needs to be checked?

I ask because Woodworks Connection is telling me that the capacity of my connection is 157.9 plf, while reporting the controlling yield limit is 450 lbs, and all adjustment values =1.0. I can't figure out where it's getting the big reduction.

Any ideas?

Thanks,
Chuck

 

[CJJS]

Have you checked tension perpendicular to the grain for your ledger?

 

[ctcray]

I can't find where the NDS describes how to check that, other than to say it's not good.

Seems to me that any bolt that is loaded perp to grain is essentially loading the wood with tension perp to grain.

Any idea how you evaluate a wood member for tension perp to grain?

 

[msquared48]

You might try calculating it by hand.

In the 1994 AITC, Fourth Edition, page 454, at the bottom of the page, it tells how to calc the connection using the six Mode equations.

I also looked in table 7.12 in the same AITC for 1.5" wood with 1/4" side plates (different than your case) and got 300 plf perpendicular for a 3/4" bolt SPF.

In Table 7.15, with two 1.5" members SPF and 3/4" bolts, the falues for Z perp were 900 for Zs perp and 450 for Zm perp.

As a further note for comparison, the 1985 UBC in table 25-F shows 270 #/ft for 1.5" SPF member in SS.

Mike McCann
McCann Engineering

 

[Lion06]

I believe the NDS says that tension perpindicular to the grain is not allowed in the wood. You will need to provide some other mechanism to transfer that load.
How is a ledger with bolts through its center and taking load into the bolts through shear only seeing any tension perpindicular to the grain? I'm not seeing that unless the ledger is loaded below the bolts or you have some unusual eccentricity.

 

[ctcray]

Footnote 2 in Table 11.5.1a discusses concentrated loads and states that they "shall not be suspended below the neutral axis of a single sawn lumber....beam except where mechanical or equivalent reinforcement is provided to resist tension stresses perpendicular to grain (see 3.8.2 and 10.1.3)." In this case, i'm not below the neutral axis, but I looked at the other sections mentioned anyway.

Section 3.8.2 suggests avoiding Tension perp to grain, but when unavoidable, to use mech. reinforcement. The references cited in this section don't look to explicitly deal with tension perp to grain.

I then checked 10.1.3 and this section talks about the reduced shear capacity of the beam due to the bolt location, but when i check the value in my 2x12, it's greater than the controlling Yield Limit Value for the bolt.


Incidentally, Woodworks technical support emailed me back that the reduction I encountered was a bug, and they are going to look into it.

I also called AF&PA Helpdesk, and they thought the correct value for my ledger situation should be the 450 lbs that is shown in Table 11E.


BUT, I've still not discovered any way to analyze/evaluate the capacity of a wood member for tension perp. to grain. I know USP and Simpson provide reduced capacities for their hangers for when, say you have a 2x4 hanger suspended from the bottom of a 2x12 beam. But again, i can't find how they calculate this reduction.

 

[CJJS]

I have never found a reference for how to calculate tension perp. to grain either. I brought it up hoping that someone would be able to provide a way to do this. I usually reference Simpson's technical bulletin for reduced capacities. Or I use a fastener that transfers the force above the neutral axis.

It depends on how your ledger is loaded and the location of the anchor bolts as to whether or not you will have tension perp. to grain. I would suggest staggering the bolts (above and below the neutral axis). Also check the Simpson tech. bulletin for reduced values using hangers.

 

[UcfSE]

Simpson and USP probably get their values from tests, not calculations. Will this ledger be transferring the out-of-plane wall reaction to a diphragm?

 

[FSS]

I used handy connection calculator from awc.org website and got 450# as well. By the way, are you able to get spf 2x12's? Usually anything over a 2x6 is going to be pine or doug fir, at least in my area.

 

[AlmostPE]

I think simpson get their values for top flange hangers with tests, face mount hangers from calculations.

Not almost anymore!

 

[ctcray]

I work at a lumber company in central maryland. We stock up to 24' 2x12 SPF. All of our framing is SPF.