Strengthening a Slab

"So no load is transferred to slab" ?!?!?!?!

How do you figure?

Can you provide a sketch of what you are proposing?

You are proposing to use the I-sections as piling. Were you intending to drive the piling through the holes in the floor?

I think that there might be better approaches to distributing the load over the existing floor.

ahhhhhhhhh - I get it now - "no load on slab".

Yeah - how about building a frame to distribute the load over more area?

Pour an additional slab over existing one. This should be :thicker, reinforced with mesh and generally : larger, so as to spread the load more evenly ( and intimately) on the existing slab. Thick underlay will garantee that when you want to remove your load in the future there will not be any noticeable marks where the additional slab is eventuallky set down.

To complement good planning allow fittings ( ferrules ) in the concrete so that if required the new additional slab can be removed effortlessly with a fork-lift or other mode of transport off the site.

Labor Omnia Vincit.

I think distributing the load is the way to go. Is the allowable load the combination of Dead and Live loads. If not there may be some extra capacity that you can use if you ensure that no other live loads can occur. In a situation where you control the load you also may be able to use a reduced safety factor.

GA! Extrapolating from your 4 hefty people and filing cabinet examples, what about even one small person (standing close together), say 60 Kg on 600 cm²: works out at 1000Kg/m². One hefty person standing on one leg or running doesn't bear thinking about.

I agree that the slab loading is very low. Is this a suspended slab, perhaps a mezzanine floor or a roof slab? How is the slab currently supported? Without having any detail the only advice one can really give is that you contact a structural engineer for advice.

When I first read this string I assumed a slab on grade, and the original proposal was to use steel sections as piles. Given the extremely low load capacity, I wonder if that assumption is correct. We must know if the slab is a raised slab or not (is this slab cast on the ground, or is it supported by something else?)

If this is a raised slab perhaps we will simply need to add mid-span supports to increase the capacity of the slab (or to decrease the stress induced in the slab by these loads, however you wish to look at it!)

Build a structural steel platform to distribute the load over the necessary floor area. Another option is to place each individual battery on a piece of 1" plate that will distribute the 1000kg load over and area large enough to bring the load down to 400kg/M2, grout the plate.

1000kg/m2= less than 1.5 psi. That's less force than a person standing on one foot, and I doubt that they'd fall through the slab. This is a slab on grade? What is the real problem? Do you think the slab will deflect under the weight? I just don't see the issue.

Hi!

I'll assume it is a slab on grade, however additional information is required, i.e. concrete strength, thickness, reinforcement strategy and UPS dimensions etc. Commerical driveways, 28MPa concrete, 200mm thick, reinforced by 2 layers of 10x10x6 welded wire mesh on compacted 20mm minus crush gravel 200mm thick on prepared subgrade is a city standard (Calgary, AB) that will take truck traffic and would be suitable for your equipment requirements.

The most important part of any pavement or slab is the preparation beneath it.

Drilling the holes in the slab may cause potential problems down the road. It may affect the existing slab by creating focus points for cracking, but the moisture barrier in your building interior will be breached which is not a good thing in cold or wet climates. Drilling holes could also breach any conduits in the slab creating headaches later.

Putting I-beam 'Piles' to the gravel below won't help as the Point Bearing capacity of gravel is significantly less than concrete, and will eventually settle, unless the horizontal member is already on the slab - which would then be carrying the distributed load already, and has already been addressed by others; re plates, beams, additional concrete slab. These are the best economical solutions.

Your builder should have good ideas. I'd hope that it isn't a 50mm slab that is being poured. If you really want to sleep at night talk to your engineer or architect.

There is also a solution to his problems that might be a little "left field" for some.

Hang the UPS and such from the ceiling girders and thus the load is transferred directly to the foundations without adding load to the floor.

As a Contractor who has had to solve similar problems, I shall not assume anything. Describe in detail if the existing concrete is supported, unsupported, , how thick whether or not it is reinforced by any means and any other applicable info available. I cannot guess at these unknown conditions and no one else should either.

TMF

Some see the existing slab as a supporting surface. "I", on the other hand see the slab for what it really is, as a load on another means of support. The problem poster seems to have no knowledge of the fact that what ever is supporting the existing slab may not be suitable for supporting any additional load.

If this slab were placed on a compacted material that was only 6" thick, and therefore suitable for the original designed need. That does not mean that together the 4" slab and the 6" compacted fill together can support the new intended load. It could be that the best way to resolve this matter will be to section and remove the effected area of the slab and the existing compacted fill and replace the fill with a much thicker quantity of fill compacted in layers to achieve the overall all strength needed to support the new total load and to undermine the existing edges of the 4" slab to accept a footing designed to support the new edges created by the removal of unsuitable area.

This original poster needs an Engineer.

TMF

I agree, the original poster has to involve an engineer. The original question regarding the impact to the building as well as the slab strengthening needs the attention of an engineer capable of looking at the structural as well as envelope elements.

One of the first slab jobs I did was installing a printing press foundation in a commercial building unit. It was a heavy piece of equipment and with the vibration, required that the original slab be removed, fill below excavated and a new isolated base be poured, more than 5x the thickness of the surrounding slab.

friend:

you have mentioned only a slab. it would be relevant to consider how the slab itself is supported. is it a roof slab? is it a slab projecting from wall as a cantilever? is the slab supported on all the four sides? if so, can the existing wall/column/beam support the load required by you? a sketch detailing the structure with span dimensions would help

shankar, bangalore, india -mallipatna@yahoo.com

Actual dear i dont know if there is about 10KN/m^2 weight like this.

are u sure dear about 10 Kn/m^2>>> i dont remember what is the max, load in 1m^2.

But i remeber that my friend has a problem with building that the owner want the load 10 KN/m^2 and it is not posible to to open long spans with this load in structural steel. and this weight is just avillable when you put water in the bulding.

Plz make sure about this dear :)

thanx

Hi Aruna

I disagree to make holes in the slab thats already casted; anyway your I-Beam-holes method seems to be weakening the slab rather than strenghtening it. Since you can transfer the loads [meaning you have chance to erect colums below the slab] why not do it without making the holes. Design bearing plates and let the slab / portion of the RCC slab be supported by these additional columns with plate ends supporting the slab. Also, the thickness and the flextrural strength of this slab has to be verified.

I'd gladly go with a double plate, say 400x400mmx10thk, fillet welded and gussetted to the I-Beam column ends supporting the slab; numbers of these supports will be based on the space available... what do you say..? But NO to making holes please.

Dear we have very simple logic to handel this types of issue i also work MSC and several time we meet this issue. what a solution just calculate how much base area required to meet your exsiting slab load and povide wood base of that much area. by this way you can handle this issue.

if you secceed please infrom me furqan265engr@gmail.com

thanks