Wood Ledger Bolted to CMU Wall - 45 year old building
Wood Ledger Bolted to CMU Wall - 45 year old building
(OP)
I have been asked to evaluate the gravity load capacity of a wood-framed floor system within a building that was built in 1968. The floor consists partly of 3 x 12's in joist hangers mounted to a 3 x 12 wood ledger. The ledger is bolted to the CMU with 5/8" bolts at 4' o.c. Everything in this system that I have analyzed yields an allowable total floor load of more than 90 psf with the exception of this ledger connection. The wood is Douglas fir from 1968, tight-grained, clear (beautiful stuff by today's standards).
Using today's code, the allowable load per bolt per the 2005 NDS Table 11E is 610 lbs. Working backwards (the tributary floor width to this ledger is 8.5 feet) the allowable total floor load based on the ledger connection is only 18 psf (Ouch!). I know this allowable bolt load is based on 1 of 6 yield modes, all of which contain varying safety/reduction factors.
My question is: Does anyone know if back in 1968 there was significantly different allowable loads for the design of these connections? Perhaps the factors of safety were much less or there was a lack of understanding of these connections? I hate the thought of telling the owner this is a problem, even though the floor has held various occupancies throughout the last 45 years with no apparent damage whatsoever.
Thank you!
Using today's code, the allowable load per bolt per the 2005 NDS Table 11E is 610 lbs. Working backwards (the tributary floor width to this ledger is 8.5 feet) the allowable total floor load based on the ledger connection is only 18 psf (Ouch!). I know this allowable bolt load is based on 1 of 6 yield modes, all of which contain varying safety/reduction factors.
My question is: Does anyone know if back in 1968 there was significantly different allowable loads for the design of these connections? Perhaps the factors of safety were much less or there was a lack of understanding of these connections? I hate the thought of telling the owner this is a problem, even though the floor has held various occupancies throughout the last 45 years with no apparent damage whatsoever.
Thank you!






RE: Wood Ledger Bolted to CMU Wall - 45 year old building
RE: Wood Ledger Bolted to CMU Wall - 45 year old building
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
RE: Wood Ledger Bolted to CMU Wall - 45 year old building
Doubtless there are differences, but a 5/8" bolt in single shear perpendicular to grain has never been equivalent to the end reaction of two or three 3 x 12 floor joists, which I assume it is carrying.
RE: Wood Ledger Bolted to CMU Wall - 45 year old building
EIT
www.HowToEngineer.com
RE: Wood Ledger Bolted to CMU Wall - 45 year old building
EIT
www.HowToEngineer.com
RE: Wood Ledger Bolted to CMU Wall - 45 year old building
Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.
RE: Wood Ledger Bolted to CMU Wall - 45 year old building
M.S. Structural Engineering
Licensed Structural Engineer and Licensed Professional Engineer (Illinois)
RE: Wood Ledger Bolted to CMU Wall - 45 year old building
I would also make sure that the existing ledger satisfied the minimum 200#/foot lateral load for the diaphragm without goint into cross grain bending. I would be willing to bet that there are no direcct ties to the CMU other than the existing bolts thru the ledger.
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
RE: Wood Ledger Bolted to CMU Wall - 45 year old building
RE: Wood Ledger Bolted to CMU Wall - 45 year old building
The current code tells you 610#. That's about a 25% reduction, but ewill still yield only about 24 psf for the floor load, way below the 90 psf you apparently need.
You just need to add the steel angle bearing ledger.
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
RE: Wood Ledger Bolted to CMU Wall - 45 year old building
RE: Wood Ledger Bolted to CMU Wall - 45 year old building
Make sure that you consider the load to the slab if you decide to add a load bearing stud wall. If it is a floating slab, I would be hesitant. I would anchor the ledger to the wall with additional anchors using Hilti Hit Hy 70 system (which is good for hollow or solid block). I may also consider adding a tie or angle from the top of ledger to the block wall to get the out-of plane forces directly into the floor diaphragm preventing any cross grain bending of the ledger.
RE: Wood Ledger Bolted to CMU Wall - 45 year old building
No, not if you added something like a PA51 oe aimilar over the diaphragm sheathing and after-set bolted to the CMU wall. You could also do this to the side of the purlins, through the 3X ledger, and into the CMU wall, but it would be more difficult. Another op[eion , depenc=ding on the depoth of the joists and le3dger, would be to attach the tie to the bottom of the joists and after-set bolt to the wall. Just depends what works best for the situation.
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com