Bolting bracket to concrete wall
Bolting bracket to concrete wall
(OP)
Hello
I have a bracket, 50" horizontal with a 24" vetical leg that I want to bolt to a concrete wall. The approximate load on this (spread evenly over the horizontal member)will be ~1000 pounds.
I plan to use (2) 3/4" bolts passing through the concrete and vertical leg.
My question... common sense would indicate the higher (closer to the horizontal)the better for the first hole. But.... what would be the minimum distance from this first hole to the second.
Both bolts will share the shear forces but the top one will see most of the tensile force. The farther away the second bolt is the less tensile it will see so it would seem to me that it should be as close as possible to the first. But the strength of the concrete with 2 holes drilled in close proximity concerns me..
Anyone with any thoughts... advise??
Thanks
Ralph
I have a bracket, 50" horizontal with a 24" vetical leg that I want to bolt to a concrete wall. The approximate load on this (spread evenly over the horizontal member)will be ~1000 pounds.
I plan to use (2) 3/4" bolts passing through the concrete and vertical leg.
My question... common sense would indicate the higher (closer to the horizontal)the better for the first hole. But.... what would be the minimum distance from this first hole to the second.
Both bolts will share the shear forces but the top one will see most of the tensile force. The farther away the second bolt is the less tensile it will see so it would seem to me that it should be as close as possible to the first. But the strength of the concrete with 2 holes drilled in close proximity concerns me..
Anyone with any thoughts... advise??
Thanks
Ralph






RE: Bolting bracket to concrete wall
Will you have some sort of bracing or something to make the bracket rigid enough that you will not also have forces due to the bracket moving out-of-plane?
It is up to you to either calculate the forces and bolt capacities or hire someone who can. We cannot do that part, of course.
RE: Bolting bracket to concrete wall
Are you bolting the 50" horizontal part of the bracket anywhere? That seems like a bit of a long span to go without any bolts.
RE: Bolting bracket to concrete wall
The horizontal portion will have a diagonal brace.. from 2/3 the distance (at a 30 degree angle.. mating with the vertical at 60 degrees. The bracket will be 4x4 x .375 structural steel angle, welded .. There will be 4 of these to support a 10 foot x ~50 inch wide addition to my house.. Making room for a main floor laundry, part of which will be within the current walls.
The comment about "Hilti" I will look into, but this is not quite like a pullout cone as I am drilling through.. and with a back up plate / washer..
Ralph
RE: Bolting bracket to concrete wall
Sounds to me your structure will be plenty strong enough, I would guess the top bolt should go somewhere near the top of the 24" L and the bottom bolt approx 12" below it.
RE: Bolting bracket to concrete wall
The determining factor will be how close to the top of the concrete wall I can have the top hole.. Tenativly I had thought a minimum of 8 inches.. then the next one 10 inches below that.
My basement wall thickness is unknown at the moment.. I am assuming a standard 8 inches.. which seems to be the norm around here.
RE: Bolting bracket to concrete wall
Don't arbitarily set distances between bolts. The distance between bolts affects the tension each bolt gets. Too little distance will give you large forces. Too much and you may adversely affect your frame.
Again, you should make sure you check all of your numbers thoroughly and sufficiently or hire someone who can.
RE: Bolting bracket to concrete wall
The "steel" numbers have been worked out and verified as being sufficient with ample safety margin...
But the.. "So you still have to check the strength of the concrete".. part concerns me. The only tests I have ever seen on concrete are essentially compression factors. How much sideways force a concrete wall can sustain is kind of an unknown as there are many variables which are pretty hard to quantify.
Using simple geometry.. I assume a 1000 pound load at 32 inches from the wall then one bolt would have to hold 32000 pounds, if this bolt was lowered 8 inches the force would increase to 48,000 pounds (assuming a pivot point at the bottom of my 24 inch leg)which is not true as there will be another bolt to assist... but that calculation exceeds my simple geometry skill...
There will be 4 brackets spread over 10 feet. My basement wall is ~30 feet long and a standard 8 feet deep. Grade is some 12 inches from the top of the wall.The addition will be centered on this wall
My gut feeling is... the wall can handle it.
(should I be worried??)
RE: Bolting bracket to concrete wall
Again, you should make sure you check all of your numbers thoroughly and sufficiently or hire a registered professional engineer in your area who can. If you are not a strucutral engineer yourself, and you do not have the proper knowledge to actually check everything and not just the few things you know, then you need to hire someone. We're not going to check it for you or give you a "yay or nay". That is neither our purpose nor the function of this site.
RE: Bolting bracket to concrete wall
ZCP
www.phoenix-engineer.com
RE: Bolting bracket to concrete wall
I think the guidance produced by the Hilti corporation is worth reading for your first question, but I think there are questions that need answers of which you haven't even considered.
Good Luck.
RE: Bolting bracket to concrete wall
RE: Bolting bracket to concrete wall
After I shut my computer off I realized I had made some major errors in my calculations.. What I have is moments of force around a pivot point. So 1000 pounds at 32 inches to the pivot= a reaction of 1333 pounds at 24 inches. Considering then only the vertical leg a force of 1333 pounds at 24 inches = 1999 at 16"
Much more reasonable numbers and I am sure the wall can handle that.
Thanks again for all the advice and concerns. For what it is worth... the city did require a PEng to approve this design.. but the matter of spacing the attaching holes was not specified.. nor was the wall inspected. It is still currently covered over (finished basement) and there may be some surprises when I remove the wall covering for access.. The whole thing may go back to the drawing board if I find large existing cracks in my wall.
Ralph
RE: Bolting bracket to concrete wall
I agree with Dinosaur, follow this advice.
I highly suggest you get a local structural engineer to check this out. You should be able to find one by calling a local land surveyor or civil engineer. They usually have a structural engineer that they use.
I prescribe to an analysis of ---"is the risk worth the reward?" In this case the risk of failure is high and after the fact the fix could be expensive!
Also you might have trouble getting a building permit without engineering sign-off.
RE: Bolting bracket to concrete wall
To keep my costs reasonable this is a one person project.. me..
As I can not get mechanical equipment into the back of the house I would have to drill the footing holes by hand... not something I fancy when the depth has to be in the 12 foot deep range. Then, placing the concrete into those holes would also be a problem..
And... in my limited experience an addition resting on footings seperate from the house will forever cause cracking. The house moves the footings move and the walls crack.
So... As I work in the steel industry.. my materials are at cost and my labor is free it "seemed" like a reasonable solution.. If.. in the end it did not work.. it will be an expensive repair.. but that is the risk I am taking