Calculating Load On Brick Mounted Cantilever Gym Equip

[clintonallen23]

Hello All,
I work for a Fluidpower company however have a fastener related question for something I'm trying to do at home and was hoping someone could assist me with some basic (for the right person) calculations.

I'm trying to ascertain the load on a pull up bar I want to install so see how many anchors I need.It has 12 possible mount points but I don't think I'll need them all.

The bar sits 0.84mt from the pivot point/wall and I weigh 75gks so will exert 735 newtons onto the bar in a downward motion. each of the three sets of holes are spaced 0.26mt apart so the farthest anchors will be 052mt from the pivot point vertically. Weight of the unit itself is 13kg.

Is anyone able to help me calculate the effective tension on each of the 3 vertical mounting points? I'm assuming the bottom mount holes effectively do nothing other than hold some shear load?

Side information: The manufacturer states a weight rating of 900kg's and supplys with 10X M10 dynabolts however a)I am thinking of using Chemical anchors as I have hollow bricks and b) It's a gym standard unit designed for big blokes doing kipping pull ups etc which I aint gonna do.

I don't really want to drill a dozen 16mm holes to fit 10mm chemical anchors if I can help it but want to make sure I am safe.

If anyone can help me it would be greatly appreciated, I'd really like to understand the calculation behind it too if possible?

 

[clintonallen23]

Sorry there are 18 mounting points in total. As there are 10 fasteners I assume the intention was to use 2 on either side of the top two tier and a single anchor each side on the bottom tier.

 

[Tmoose]

How thick is the plate that contains the mounting holes ?

The manufacturer has //probably//"done his homework", but If it is not thick enough then it will tend to bend locally at the uppermost bolt(s) and exert a prying force larger than the simple withdrawal force calculated from a statics diagram.

Something along the lines of this -

http://i248.photobucket.com/albums/gg170/mm5aho/Sailing/winter 11 12 mtce/IMG_5250.jpg

It looks like each pair of mounting holes is in a short strap bent to conform and jog over the main vertical strap.
That suggests to me the straps are relatively thin in order to conform tightly to the vertical strap.

 

[clintonallen23]

Hi Moose,
I think it's pretty strong in itself. I don't have it here with me now but both the horizontals are 50mm SHS and the cantilever is also SHS as opposed the picture which is pipe on the cantilever.

I need to check when I get home but I'd say both the vertical plate and those straps are at least 4mm plate. You can actually mount straight through the centre as well which goes through the strap AND the plate.

If in doubt I'm thinking the safest is to use chemical anchors with the dispersal sleeve to push the resin into the brick hollows and M10 grade 5.8 studs in 10-12 of the mount holes but I'd rather have some science behind it.

I may be overthinking but I'm hanging myself and my wife off it (not at the same time) not an inanimate object so want to make sure it's right.

Thanks for the help so far.

 

[desertfox]

Hi

Try this site and scroll down till you see the title "bolts withstanding bending forces"

http://www.roymech.co.uk/Useful_Tables/Screws/Bolted_Joint.html

 

[Ron]

The simple way is to assume the middle attachments don't exist. You have a resisting moment from the pull-up bar (assume 2x for the safety factor). Resolve the moment to a couple and that will give you the pullout for the top fasteners....make all the others the same.

Check unity for shear and tension in the top fasteners.

 

[hokie66]

I would be more concerned with the brick wall than with the fasteners. Is this just a free standing brick wall, a reinforced wall, or a brick veneer?

 

[clintonallen23]

It's a single brick wall however I was planning to screw into the pillars in front of the wall which must be bearing the load of the roof, as such bricks will be in compression.

Here is a photo.

https://onedrive.live.com/redir?res...authkey=!AFtGZRZRUvHywQw&v=3&ithint=photo,jpg

Tha plate the mounting points are made from are def 4mm.

 

[drawoh]

I would be more concerned with the brick wall than with the fasteners. Is this just a free standing brick wall, a reinforced wall, or a brick veneer?

I was waiting for someone to ask about the brick wall. My understanding from reading one of J.E.Gordon's books is that bricks are regarded as having no tensile strength whatsoever. The cantilever loading will create tensile stresses. The OP really need to screw this thing into wall studs.

Please note that I am mechanical, not civil or structural.

--
JHG

 

[chicopee]

See the attachment for a typical analysis of the system shown in your OP. Certain assumptions were made. Your requirement will be to fill in the numbers and pay attention to the concerns mentioned above and that within the attachment.

 

[hokie66]

Based on the photo of the wall, it looks as if those "pillars" are just bricks stacked in front of the single skin brickwork. Unless they are well tied into the single skin, they are not to be depended on for strength. I always cringe at attaching cantilevered elements to brickwork...every year or so, I see a report of a death caused by a basketball backboard connected to a garage wall.

 

[clintonallen23]

Thank you for the advice and in particular chicopee for going well above and beyond with that free body diagram. Amazing!

It may sound ridiculous but I think I'm going to see if I can find a local structural eng (near Melbourne AUS) who may be willing to look at it first hand. Will cost me I'm sure and it's a pissy job but I want to be sure and it's not worth risking peoples safety.

 

[hokie66]

Good decision. There are plenty of structural engineers in Melbourne.

 

[clintonallen23]

Hi Guys,
I just about gave up on this but have had another thought. Unfortunately nobody is really interested in such a fgiddly small job (to be expected).

I was speaking to my step father and he was thinking we can get two pieces of 75X75 SHS the height of the wall and anchor this to the brickwork with the bottom of the SHS resting on the concrete floor. I'm thinking 4X 12mm chem anchors on each piece of SHS so one every 750mm or so.

Obviously this distributes load over a far greater area and also some is transmitted into the floor. I assume the major bending moment is still at the top trying to pull from the wall though.

I also thought I could run a piece of timber parrallel to the wall 900mm out spanning 4 ceiling joists and run 2 short lengths of steel rop down to the tips of the bar. This would effectively place most of my 75kg's on those 4 joists. They are not designed to bear load but 20kg per joist is not a lot either.

Any thoughts?

 

[clintonallen23]

I guess the other question is how would having the SHS touching the ground affect chicopee's fantastic diagram?

I really I am asking a lot here guys so sorry to be a pain. Just a bit paranoid as I don't wan to hurt anyone. I'd rather it be overengineered.