repair of foundation 1

[swelm]

i have isolated footing has working load 52 ton and the size of cloumn is 550mmx550mm bearing capacty for soil is
1.5kg/cm2 from soil report
they casted this footing in site by dimension 1500x1500 reinforcement concerte with plan concerte 1700x1700 thickness 100 mm
but from my design i see this footing should be
1900x1900 plan con
1700x1700 RC
but i can not take decsion to make repair or not
or ask contractor to remove and cast again

 

[csd72]

I assume that you are in the UK, due to the wierd kg/cm^2 bearing capacity (what if it is an impact load or a wind load, does the soil still work if it is not a weight?)

Anyhow, you really need to justify to yourself that repairs will work. As the reinforcement is on the bottom and your main area of stress is under the column, it would be very difficult to repair if there is not sufficient reinforcement already under the column.

That said I do not like to ask the builder to demolish something unless I have no other option. Do you have sufficient room (i.e. soil cover) above the footing in order to put a beam in over to spread the load to footing extensions? Or if there is sufficient reinforcement in the centre for the larger pad, can you epoxy bars into the sides to cantilever the additional distance?

If you are not 100% sure that these options will work, then get them to demolish.

 

[morokanu]

Hi,

I agree with csd72 about not going for demolition unless that is the only option.

You still have some options before asking the builder to demolish.
- Check the loads, they may be overestimated;
- Check with Geo people to see if you can get more than 1.5kg/cm2 for your loads (permanent + variable);
- Check to see if there is any other way of partly "unloading" the column by supplementary beam(s) in superstructure. take the additional load to other vertical elements where foundations were not cast yet or have more margin in bearing capacity.

Can't think of anything else now, but it is worth to give it a try (make friends with the builder )

 

[dik]

Why would the size of the footing differ if it is plain concrete or reinforced? 100 mm thickness is only 4"; is this correct?

Dik

 

[SperlingPE]

Speak with Geotechnical consultant.
Ask for higher bearing capacity.
Discuss design of footing using full dead load and a percentage of live load.
The second suggestion above involves evaluating risk and should only be undertaken after thorough review of risk and use of building.

 

[COEngineeer]

I dont know about i UK but the geotech report in the US is getting more and more conservative. I keep getting lower bearing pressures and higer lateral forces compared to soil report for the same soil a while back.

 

[xxpegasus11]

I assume you have a reinforced footing 1500x1500 on 1700x1700x100mm plain concrete as opposed to your original design of 1700x1700 rc on 1900x1900x100 plain concrete?

If so, your allowable safe bearing pressure is now 1.8kg/m2 instead of 1.5 kg/m2. This does not appear that prohibitive but presumably backed up by Geo.

I think your options have already been given. If you had 1.8kg/m2 would everything else comply? Rebar, shear checks etc? If so, and the rest of the design is ok, then refer to Geo - perhaps the 1.5kg/m2 was too conservative.

 

[swelm]

thanks for all
iam very happy beacuse iam feel iam not alone in this country
and have freiends help me form all the world

thanks

 

[Zambo]

the units used do not suggest the post is from the UK. One clue is that in the UK the native language is English, the fact is that most of the world use metric units.

4" is just over 100mm (25.4mm = 1"). The correct units for bearing capacity are KN/m2.

 

[dik]

Sorry... just realized that the larger footing is a plain concrete 'skim slab' as known in these environs. We usually use a 2" layer on unsuitable bearing (usually to displace water). Using the 4" thickness as part of the bearing (if not already considered, can help).

The geotech option suggested is good... since repair in future , if necessary, could be costly due to added costs of damages to finishes, disruption of business, etc. From a legal point of view, can your geotechnical expertise withstand any scrutiny if problems develop? (COEngineer: geotekkies are likely sued more often than other consultants and clients are more likely to sue, hence, more conservative.)

Dik