Reinforcement detail for a local thickening of a raft - Thickening on Top of Raft

[abhishekpraj]

Dear Members,

The reinforcement detail for local thickening of a raft was discussed in thread 507-416024. "

https://www.eng-tips.com/viewthread.cfm?qid=416024".

I want to know if we increase the depth of local thickness above the Raft not below the Raft. what would be the structural & construction difficulties?.

The base Raft in my case is 800MM & Local Thickness required is 800MM. Pic is attached for reference.

Kindly give your comments.

 

[KootK]

I wouldn't call those thickenings at the proportions that you're showing. More like piers.

 

[abhishekpraj]

Overlook those piers, those are pedestal modelled over Raft. It's about brown color slab.

Following are the features of Raft, as per design:-
RAFT DIM - 58M x 33M.
Thickness - 800MM, satisfying displacement & SBC criteria.

Local Thickening (800mm) required because :-
1. The flexure Reinforcement demand for design Strip is very high approx. 12000mm2/m (Although it's peak).
2. Shear Value for Strip it is showing failure.
4. The dimension of this local thk Raft would be 22M x 12M.
5. We think, increasing overall depth of raft would be uneconomical.

 

[le99]

If strength concern is the sole reason for local thickening, why not do the conventional way - thicken downward, so leave the finished floor at the same elevation. The raised pad may limit the utilization of the floor and can become a tripping hazard.

 

[dik]

Can you not do something like...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?

-Dik

 

[abhishekpraj]

Thanks for the suggestions.

It is to inform that no basement is planned. There shall be filling over the Raft.

Concern during construction is:-
1. pouring of Concrete, the 800mm part over the base would be poured last. For casting of this local thickness, manpower / machinery would roam over fresh concrete.
2. Heat of hydration and thermal cracking because of 1.6M pouring of concrete.

If Thickness increased below Raft,

The reinforcement placement would take extra effort. Pouring would be easy, but thermal cracking will be an issue.

 

[dik]

As long as the reinforcing hasn't been placed, it's actually very easy, and not a lot of effort... and no formwork.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?

-Dik

 

[le99]

The thermal effect can be minimized/eliminated by using low heat cement, adding the heat control agent, and through control of concrete placement thickness. I guess you want to use a bucket truck or front loader to place the concrete, in such case, no matter the way the thickened pad is placed, the equipment will run on the previously placed/fresh concrete. You should consider other viable placing method, such as pumping, and place working planks.