basement joint 1

[swelm]

hi everybody

we have basement for building has 3 floors.

the area of basement is 300 meters by 200 meters.

foundation should be raft the ground water table is under natural ground level by 1.5 meter.

we suggest to make construction joint every 100 meter in two direction is that enough.
or we need make joint to separate that huge area of concrete.

also the wall of basement has height 4.5 meter clear height.
do you think it need also joint or not?

we use ACI-05 and IBC 2003.

 

[msquared48]

With earth on one side of the wall and a heated(?) basement on the other side, I do not see the potential for much temperature fluctuation. I would be mainly concerned with the initial shrinkage.

I think joints to match the raft joints would be a good idea, but the wall would have to be keyed, and a waterstop inserted at the vertical wall joint, and at the base of the wall to the raft foundation.

With the high watertable, I hope it doesn't float! I also assume that you do not forsee any liquefaction problems.

Mike McCann
McCann Engineering

 

[hokie66]

The basement is 4.5 metres clear height, and the water table is 1.5 metres below natural ground. So I take it that the building will have to be heavy enough to resist 3 metres of hydrostatic uplift, or 30 kPa. Is this correct or could the water level conceivably be higher at some stage?

The raft slab will have to be quite thick to both provide ballast and resist the uplift pressure, spanning between the columns. This will doubtless require a heavy mat of reinforcement both top and bottom. So the flexural reinforcement in this type foundation slab will probably easily meet the requirements for restraint shrinkage reinforcement.

My approach would be to cast the entire slab with no other joints other than construction joints. These would be located roughly at midspan between columns where slab shear is mimimal. All reinforcement would be continuous through the joints.

Casting 100 m x 100 m sections of a raft slab is a mammoth undertaking, so I think for practical reasons you would have a lot more joints. The slab thickness will depend on column spacing, so after this is determined, you can decide on comfortable size pours.

I would joint the wall at regular intervals, probably not exceeding 10 metres. You can get a lot of undesirable cracking in walls cast on a heavy slab or footing because of restraint. So go heavy on the horizontal reinforcement near the bottom of these walls. Reinforcement would not be continuous through the wall joints.

The waterproofing system is crucial to creating a dry basement. Don't know if that is your responsibility, but you need to be involved

 

[swelm]

dear gentlemen

many thanks for your valuable information