Joints in concrete footings 2

[WWTEng]

I have seen general notes specifying the maximum spacing of joints in slabs and walls but I guess I have never really paid attention if the same applies to footings. How do you specify the spacing of joints in trench footings (so no foundation wall)? Does the typical maximum spacing of 20’-0” apply to these footings?

 

[Ron]

No. Footings rarely have a need for joints as there is little thermal cycling that occurs. You can match footing joints to other structural control joints, but it usually isn't necessary. There is certainly no need to match footing joints to slab joints unless the footings are monolithic with the slab, then several considerations have to be made for restraint, particularly if the monolithic placement is anything other than a turn-down slab edge.

 

[denoid]

Most of the time, trench footings are buried and out of sight, so no one cares if they have shrinkage cracks, as long as they are strong enough.

 

[WWTEng]

Ron, denoid

Thanks for the input. So how does section 22.3 of ACI-318 apply to trench footings, if at all?

 

[denoid]

Read the last sentence of the Commentary, R22.3:

"Where random cracking due to creep, shrinkage, and temperature effects will not affect the structural integrity, and is otherwise aceptable, such as transverse cracks in a continuous wall footing, transverse contraction or isolation joints are not necessary".

 

[WWTEng]

Deniod, thanks, should have seen that.

I have a significant size trench footing. 6'x3'wide, so wanted to get clarification on the issue.