Shear on bolts in brickwork

[tony1851]

I have to beef up the support to a domestic timber floor due to increased loading.
My idea is to resin-bolt a 3"x3" steel angle to the brickwork immediately below the floor, using 3/8" bolts or threaded bar. I believe the shear on the bolts will not be the governing factor, it will more likely be the strength of the brickwork. The bricks are old
(+ 100 years) and of crushing strength probably around 1000 psi, in soft lime mortar.
Does anyone know of a method for evaluating the limiting shear on each fixing, or know of any publication
covering this?
thanks.

 

[Screwman1]

Not sure I understand. The 3 X 3 will be face bonded onto the brick or will the leg be inlet into the bricks?

 

[tony1851]

this is what I was proposing.

 

[davek671]

In the UK I use manufacturers recommended allowances for fixings (Hilti in most cases).

A simple approach would be to use the same fixings and spacings as the timber which is currently fixed to the masonry. You will be more than doubling the shear strength since the capacity of the bolt in steel+masonry will be higher than the timber+masonry.

 

[msquared48]

If not already present, you will also need to tie the floor joists to the brick wall with thru-bpplts, strap ties and metal rosettes on the outside of the brick wall at 4 to 8 foot spacings.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[haynewp]

I talked to Hilti and Simpson a long time before about this and they were not able to help much since we didn't know a starting point for the strength of the old brick. It was a 100 year old building also, I think I ended up assuming a very low brick strength value. I have noticed some bricks appear to get softer with age/exposure to elements. I would talk to someone at the BIA on what decreased strength you might be looking given the time of construction of the building and then talk to Hilti/Simpson. You could approach it as doubling the capacity of the floor by doubling the original connections (if you have an original load capacity listed on the drawings) but I don't know how the brick being 100 years old would figure into the actual brick strength you have now (ask BIA).

You could also check into testing the brick to determine the compressive strength which is the better way.

 

[dhengr]

Tony:
I believe there are methods to test that brick and mortar insitu, particularly for general compressive strength. Ask some local testing labs who do this kind of testing and work. The problem with your detail, bolts in shear and point bearing on the brick, is that that old brick and mortar are usually pretty soft, so it crumbles when you drill it and under those kinds of concentrated loads, or splits from the point bearing, or it literally vibrates loose during the drilling. Someone has to make a general assessment of the condition of the entire wall system, its strength and stability. Then, why not grout one angle 3x3x12", or some such, with one leg into a mortar joint. Then you have some substantial bearing area, not point bearing. Another angle above, with its horiz. leg outward is welded vert. leg to vert. leg and pushed up under the ledger. The original floor framing likely did provide lateral support for the wall, so you should some pay attention to that too, along with eccentricity of the above detail.

 

[slickdeals]

This might be an offbeat idea, but can you fabricate precast concert blocks slightly smaller than original brick, remove an existing brick and pack this block in. You can the dry pack the gap with nonshrink grout. This concrete block can serve as a corbel.

 

[tony1851]

Thanks, guys, for all your comments, which have been taken on board. My problem is that I am trying to rectify identical floor-support issues on 10 houses which were 're-furbished' 2 years ago by a developer who cut corners to say the least. The floor I showed in the sketch is only casually fixed to the wall by a few screws along the length of the wall plate, and the Building Inspector has asked for proper support. The brick wall terminates only about 2 feet above the floor, so drilling or cutting-out could shake it too much. After thinking and considering the responses,I will probably play safe and put a steel beam under the floor instead. This will be much more disruptive and expensive but at the end of the day that's not my problem!. Thanks again.

 

[BadgerPE]

We are working on a fix similar to what Dhengr proposed. It appears to be a cheap, quick fix and will allow for a good comfort factor knowing the load is carried by bearing of an angle versus bearing of bolts on clay masonry.

 

[Archie264]

I think 1,000 psi for the old brick might be way high. It might well be around 100 psi to 200 psi. I suggest checking with the Brick Institute or having it tested, both as noted above.