# Forum Home Renovation Structural Renovation  Steel brackets to hold bench seat up

## frogger

Hi,  
Just wondering if someone can help.
I want to get 3 steel L brackets build to support a bench seat I have built. I need the brackets to support up to 200kg. The vertical plate will be held into the double brick wall using dinabolts. I dont want the plate too large so that you can not see it below. My questions are.
Seat size is 1400mm x 560mm with 45mm support frame. 
My question is how think and what type of steel I will need to support this weight ? I will have the horizontal peice weldered to the vertical plate. Also what type of steel should I be using. ie thickness, solid, hollow etc.
I hope thats enough info for someone to help.
Frogger

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## wheelinround

Thats a fair weight Frogger plus the weight of the bench
I'd be looking at Gal angle 60mmx60mmx6mm width of the bench with and same down the wall under the bench.

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## Jacksin

The seat looks a fair weight in itself plus allowing for a couple of perhaps heavy weight adults (or kids jumping around) and you are asking an awful lot on the brackets.  
I think Wheelinround's steel size could be under-gauge. I would think 10mm minimum thickness with a 45deg welded bracing with the whole thing galvanised. 
Have you considered Frogger, dyna-bolting through the back framing into the wall and installing a couple of fancy (turned) legs under the front corners?

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## Ivan in Oz

Or go Square Section Gal,
with the 45* Bracing 
Galvit, Then Silver Frost the cleaned up Welds?

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## frogger

Thanks for all your suggestions. Yes the bench is pretty heavy and with 2 adults plus kids on it it will need some support. 10mm thickness does sound solid but im sure with the weight invloved maybe not. When your talking that type of steel. Is it best to have a post type eg 60mm x 60mm with 6mm thickness or a solit peice of steel being 10mm thick ? Also when I get it welded is that very stong and not likely to come apart ? In regards to Jacksin comment I want to bench to be floating hence why i need such huge supports.

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## MrFixIt

Hi  

> Thanks for all your suggestions. Yes the bench is pretty heavy and with 2 adults plus kids on it it will need some support. 10mm thickness does sound solid but im sure with the weight invloved maybe not.

  The "thickness" is not the critical part. The most important part is to have a 45º between (or very near) the *ends* of the "L" bracket. 
Provided that YOUR method of mounting the bracket will support 200kg, a pair of 6mm thick brackets (with the 45º support) will EASILY support 200kg weight.

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## frogger

ok thanks. With the "L" bracket I only want it to come down the wall around 150mm. The other part of the "L" bracket can be 500mm long. Ill use 2 x 12mm dinabolts to hold it in. Will the '"L" bracket need a 45degree support or the weld should be enough to hold it ?

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## DJ's Timber

I don't think you'll get away with 150mm part of the "L" it's too short, the amount of leverage at the end of the 500mm bit will either pull the bolts out or crack the bricks.  
And yes you'll need a 45° support on it unless you're using box tubing or angle, flat bar won't be able to support itself.

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## Yonnee

Agreed,
Structurally you would get away with something like a piece of 150mm x 50mm x 6mm RHS the length of the bench and butt weld 3 outriggers the depth of the bench of say 50mm x 50mm x 6mm. Weld them with a 3 phase MIG and they would certainly be strong enough, but its the fixings into the bricks and the bricks themselves I'd be concerned about. If you wanted to persevere, I'd dyna-bolt every brick along the length of the bench as well as construction adhesive.

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## Ivan in Oz

Perhaps Chem-Set Type :2thumbsup: 
rather than Dyna Bolt......Or should I say "Mechanicaly Fixing" them. 
Also,
Yes,
I agree,
the 150mm Vertical is a Bit short.....Quite a Bit Short :No:  :No:

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## frogger

Thats great. Thanks for your help with that. What would be best. Using boxing or flat steel. If boxing what size would be the best ? Using maybe the 50mm x 50mm ?

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## DJ's Timber

Here's a drawing of how I would make it, using 50mm x 50mm x 2.5mm tube.    
With the holes for the dynabolts, I would have them as far apart as possible with the top one inside the gusset area drilling a 25mm hole on that side with a 12mm hole on the brick side and the the bottom 12mm hole hole can be in the 45° cutout section. Would located the holes so they line up with the middle of the bricks as long as they are solid bricks. If not solid bricks, would be even better to drill right through the double skin brick wall and use all thread and put a 5mm flat bar with holes to line up with the ones in the bracket on the other side of the wall 
Same for the long leg, say 3 holes to take a wood screw, so would need say 3 - 5mm holes on top and 2 - 12mm holes on the bottom side with the last 5mm hole in the 45° cutout section.

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## frogger

DJ. You are a super star. Thank you so much for that. That is a huge help. Thank you so much to everyone who has helped. I think your diagram more than answers my needs. Thanks again.
Frogger   :Biggrin:  :Biggrin:

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## MrFixIt

Hi  

> ok thanks. With the "L" bracket I only want it to come down the wall around 150mm.

  This is *REALLY TOO short*  

> The other part of the "L" bracket can be 500mm long.

  For THIS length. The *leverage* is very high on the top dyna bolt. Fixing the bracket mechanically or chemically will not make any difference to the load/stress on the top bolt, however the chemical based fastener is less likely to pull out. 
Think of the leverage like that of a claw hammer when used to pull out nails. Your bracket will be "pulling" on the top bolt. Any "jumping" up and down on the seat by kids (et al) will be like tapping out the dynabolts. They may hold, they may not  :Shock:    

> Ill use 2 x 12mm dinabolts to hold it in. Will the '"L" bracket need a 45degree support

  Absolutely   

> or the weld should be enough to hold it ?

  No, it won't. 
If you really *must* have a *SHORT* bracket then if *you* are making the brackets or are having them made to suit your needs then consider having a "leg" above the horizontal leg, (see rough image below) but still invisible behind the seat itself. A dyna bolt though THIS short leg will help the structural strength against being pulled  out.  
It will "transfer" the load to a point between the two top bolts and will therefore act less like a lever (claw hammer) on thetop bolt. 
The angled support arm does not *HAVE* to be 45º, *it needs to be from the outer end of the horizontal arm* to the lowest convenient point on the arm attached to the wall the very bottom is ok with the lower dyna bolt mounted just above - make sure you have enough room to fit the bolt and nut  :Smilie: .
It will not be as strong though as a longer downward leg. 
HTH

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## Pulse

...sure are a lot of amateur structural engineers on this forum... we really need a real one. 
On the rams et website:
A 6mm dynabolt only 25mm embedded into 20Mpa concrete has a tension working limit of 2200 N or about 220kg per anchor. Depending on the size of the bracket two of these should be plently... 
10mm steel, dynabolts into every brick and 12mm dynabolts really are overkill....  
The longer the leg attached to the wall, the smaller the fastener you could use. The bench is 560mm deep so a 560mm leg attached to the wall means the weight of the person (if represented by a point load 560mm from the wall) is equal to the tension on the fastener. If the vertical leg is halved then the tension in the anchor is doubled. Therefore a 140mm vertical leg against the wall with two brackets supporting 100kg each would require a 4kN anchor eg a 10mm dynabolt 45mm embedded into 20Mpa or two 6mm dynabolts adequately spaced. 
cheers
Pulse

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## Dirty Doogie

Pulse - would you get 20mpa out of bricks? 
I was going to suggest knocking the mortar out of the corner of a few bricks and inserting 50 x 50 x 8 mm angle steel into the brick work and repointing with epoxy mortar.  But there are too many variables to be sure it would work. 
I have fitted wall mounted a laminated beam benchtop (Weight approx 120 kg) into a standard brick wall by knocking out a row of bricks - making a metal plate with extending arms from angle section and then epoxy mortaring the whole missing brick section. The benchtop was 2400 long and has been carrying about 1000 kg (I stored bags of gyprock stuff and cement on it)

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## Pulse

true.... better overengineer then 
but then again that's the fun in DIY... do it so well that it obviously wasn't a real builder... 
Pulse

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## frogger

Thanks MrFixIt, Pulse and Dirty Doogie. I think ill use 10 to 12mm dynabolts to be safe. Not sure if I will take out bricks etc as DD mentioned. Ill see how it goes with the 2 "L" brakcets suggested by MrFixIt and DJ  . Just one more question do you feel this bench will need 3 brackets or 2 should be fine ?

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## DvdHntr

200kg is very light. That is less than 2 people in engineering terms. You also have to take into account that the weight will come on as an impact and may be at the edge of the seat so that will create a moment. The ratio of the distance between your bolts to the width of the ratio of the loads. Also, I would make it 250kg or 2.5kN and muliply that by 1.2 for the dynamic action to give you a total imposed load of 3.75kN And then the ratio of the 560mm to the spacing of the bolts will increase the load again. The actual weight of the seat will be assumed to act at 560/2 (280) away from the wall so the ratio must be used for that weight. And then adding the two loads will give the pull out force but you must multiply that by 1.3 as it is a prying force (just an engineering requirement). You then can divide by the number of brackets to get the required load per bolt in tension. The shear load will be the sum of the loads without multiplying by the ratio.
If you are using the limit state design tables by ramset the seat load is muliplied by 1.2 and the person load by 1.5. 
Check out ramset and Hilti as they have different connectors for hollow and cored filled brickwork. 
If I have confused you then please tell me.

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## MrFixIt

Hi   

> A 6mm dynabolt only 25mm embedded into 20Mpa concrete has a tension working limit of 2200 N or about 220kg per anchor. Depending on the size of the bracket two of these should be plenty...

  In a perfect world yes  :Smilie:  
That is CONCRETE, however into the mortar between the bricks is severely lacking in grip. Consider that there will most likely be some depth lost due to the finish of the mortar joint rolled or raked etc. 
Concrete generally is a good mix and the chances of gaps around the dynabolt in concrete are much less than in a (potentially quickly built) brick wall. 
There are pros and cons of using mortar or bricks in which to mount the dynabolt - this has been discussed at length in another thread somewhere on this forum. 
If *I* was mounting this bracket and seat, I would use 10mm dynabolts and drill into the mortar. The reasoning behind this is that *if* there are gaps in the mortar you will at least obtain some grip between the layers of brick. Fastening dyna bolts into the brick runs the risk of drilling into the (manufactured) holes in the brick - in which case you may get NO grip at all!  *Frogger*, I missed the comment about you wanting the seat to appear "*floating*". 
If access to the other side of the double brick wall is readily available and it is not too much of a problem to work on or "patch up" etc, A potential alternative for you then is this... 
Buy a long 10mm masonry drill, long enough to drill through both leaves of the double brick wall. Purchase some 50mm x 10mm flat bar and use this to support your seat. 
Drill (or otherwise) create a 50mm high x 10mm wide slot in the double brick wall. This slot is to go all the way through both leaves of the db wall. Insert the 50mm x 10mm flat bar into these (vertical) slots so we now have two pieces of 50mm x 10mm steel flat bar on edge to support the seat. Obviously you will need to cut slots in the  seat for these pieces of flat bar to pass though. 
Obviously these slots will be MUCH easier to create in the perpendicular mortar joints. This will (most likely) mean that you will need to add some additional timber to your seat to which you can fasten the flat bar, as it is unlikely that your seat timber "ends" will line up with the mortar joints. 
You can use a piece of flat bar - cut in to a long "wedge" shape to clean up/remove the mortar from the drilled holes, to help create the "slot" required  :2thumbsup:  
When the steel is in position and held there by some convenient means (your choice). Mount the seat and bolt/screw into the flat bar. The seat will really appear to "float" and will exceed your wildest expectations for load carrying capacity  :2thumbsup:  
See rough sketches below  :Biggrin:  
HTH
.

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## DvdHntr

I would create a frame with a 100x100x6EA into the wall and a series of angles welded on under the seat perp. to the wall and a trimmer length at the other end. But you are going to need a really solid connection. The other solution would be to drill through the double brick and put a series of bolts with large washers.

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## Ivan in Oz

G'Day,
Just wondering what was the result with the mounting of the seat. :Confused:

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## frogger

Hi Ivan, 
Well as you could imagine this time of year takes everyone a while to get back to work. Im seeing someone next week about making the steel brackets. When I all have it put together Ill post a picture of the seat / master peace.
Thanks
Frogger

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## DvdHntr

> Hi Ivan, 
> Well as you could imagine this time of year takes everyone a while to get back to work. Im seeing someone next week about making the steel brackets. When I all have it put together Ill post a picture of the seat / master peace.
> Thanks
> Frogger

  I hope you took my advice and went with a much heavier connection.

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## frogger

Well I finially got the brackets made and they work well. 
Might be hard to see as I have put one coat of paint on but they are extremely strong.
Thanks for everyones help

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## DvdHntr

They do look quite strong.

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