max stress due to point load on concrete?
max stress due to point load on concrete?
(OP)
Is there an easy way to check for the maximum allowable point load force on concrete?
Situation is as follows: a heavy workbench will be resting on the floor, supported on four bolts (bolted head down in the feet of the bench).
The bolts will enable to level the workbench. So all the weight of the bench rests on the four bolt heads.
Each bolt will see a max. load of 12.5 kN (static load), x2 (safety) = 25 kN. (situation in which the bench rests on three points is foreseen in this).
Area of the bolt head is around 520 mm², so a local 50 Mpa.
Concrete will be poured 20 cm (8") thick, of the (european) C25/30 quality, and will be reinforced with fibres.
If necesssary, I can still adjust the bolt sizes, I doubt I can change the prescribed concrete...
Could someone point me into the right direction for this?
If anymore information in needed, please do ask...
I'd like to see the method instead of a ready answer, so I can refer to this if later ever necessary.
Putting metal plates under the bolt heads to distribute the load is not an option as the bench will also have four casters, and will be rolled around regularly. The bolts will always be used whenever (and wherever) the bench remains stationary.
Situation is as follows: a heavy workbench will be resting on the floor, supported on four bolts (bolted head down in the feet of the bench).
The bolts will enable to level the workbench. So all the weight of the bench rests on the four bolt heads.
Each bolt will see a max. load of 12.5 kN (static load), x2 (safety) = 25 kN. (situation in which the bench rests on three points is foreseen in this).
Area of the bolt head is around 520 mm², so a local 50 Mpa.
Concrete will be poured 20 cm (8") thick, of the (european) C25/30 quality, and will be reinforced with fibres.
If necesssary, I can still adjust the bolt sizes, I doubt I can change the prescribed concrete...
Could someone point me into the right direction for this?
If anymore information in needed, please do ask...
I'd like to see the method instead of a ready answer, so I can refer to this if later ever necessary.
Putting metal plates under the bolt heads to distribute the load is not an option as the bench will also have four casters, and will be rolled around regularly. The bolts will always be used whenever (and wherever) the bench remains stationary.






RE: max stress due to point load on concrete?
RE: max stress due to point load on concrete?
The bench is moveable on four castors, however when stationary the four bolts will be unscrewed so that the bench rests at the bolt heads.
So disregard the castors, and suppose that the weight on the worktable rests at the four bolt heads.
see attached image ...
RE: max stress due to point load on concrete?
I would just take the area of the bolt head and divide it into the force in each bolt, thats the pressure on the concrete, then compare that value with the concrete's safe stress.
desertfox
RE: max stress due to point load on concrete?
This is for column bases and so in theory is relevant for your application.
Therefore your allowable bearing stress is 0.6*30 = 18N/mm2
The only thing you would need to look at then is your punching shear, which will depend on your reinforcement, cover and whether the slab is suspended or ground bearing and if ground bearing what the sub-strata is.
Though I may be over thinking the last bit.
RE: max stress due to point load on concrete?
Kieran
RE: max stress due to point load on concrete?
As I said before, bearing plates are not an option as there is no way to make sure the operators will actually use them.
Grahammachine, If I should stay below 18 Mpa, and I've got a local 50 Mpa, that means I should enlarge the bolt area by about 3.
I am already using an M30 (typo in my first post), I'll have to see if I can accomodate an even larger bolt (d > 42 mm).
RE: max stress due to point load on concrete?
Dik
RE: max stress due to point load on concrete?
An M24 gives a head area of 1122mm2 (36mm across the flats and 42mm from corner to corner) giving a bearing pressure of 22.3N/mm2
The sizes can be found here http://www
So you may want to check the values.
Graham
RE: max stress due to point load on concrete?
There must also be many newer code equations that I'm not familiar with.
tg
RE: max stress due to point load on concrete?
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: max stress due to point load on concrete?
key width is 46, so circular area of 1662 mm².
So the bearing pressure is below 18 Mpa.
Should I worry about shear/punch through? I really doubt that, as it's 8" thick on stabilised soil (not dug out).
@ msquared48: If I welded the bearing plates to the bolt heads, I would also have trouble adjusting the bolts... the feet are threaded for the bolts, it isn't a plate with a hole, and two nuts (so the bolt would remain in the same position).
Thanks everybody for your replies...
RE: max stress due to point load on concrete?
Wouldn't hurt to increase the bearing area to 620 mm^2.
BA
RE: max stress due to point load on concrete?
Could you get the 4 legs loaded at once, each with 25kN factored load?
Punching may not occur, but isn't it your job to prove, by calculation, that it doesn't?
tg
RE: max stress due to point load on concrete?
RE: max stress due to point load on concrete?
What is represented by A1 and A2?
@ Trainguy:
cc distance is about a 3 by 1 meter rectangle. perhaps give or take an inch.
And No that is not possible, 25 kN is if the table should balance on two diagonal opposite feet.
Yes and no, I do not have to prove it but would still like to check. This isn't exactly for work, I'm doing a friend a favor after hours but I still want to make sure everything is done as correctly as possible. I do know there are risks involved hence the checking.