rjp1121
Structural
- Aug 30, 2016
- 3
I'm designing 9"thick x 250'long x 36'wide slab on grade for a bus station. The slab has expansion joints all around due to buildings on one side, a bridge on the other and a bus entrance and exit. My question is related to the reinforcement. If I used contraction joints following ACI they would be spaced 24 to 36 times the thickness of the slab (18' to 27' respectively) is that spacing considering I use no reinforcement? Also, while reading ACI it says to not use expansion joints due to settlement and bearing issueses at the ends due to the wide openingand water infiltration. If that's the case than the contraction joints serve two purposes one to control cracks at the contraction joints and two to help with temperature effects. For a 250' slab my expansion will be around 1.5". So in essence i need the contraction joints to crack so that on hot days when the sun is bearing down on the slab it can expand without over stressing the expansion joints at the edges of the slab. So my question is that if I use to much steel will my shrinkage be to minimal compared to my expansion and thus making the contraction joints not open up wide enough to allow for my full expansion? Will my expansion joints fail? Does steel reduce the amount of shrinkage or does the steel just distribute the shrinkage to the contraction joints?