isolation joint between slab on grade and pits /cable trenches

[mezzoms]

dear engineers

i have seen lots of details of slab on grade and i noticed that there is isolation joint between it and the sump pits ,cable trenches and elevator pits......are these isolation joints mandatory or they are optional??? and why i do it in such places???

have i to make isolation joint between slab on grade and machine/equipment base??? why????

regards
m.samir

 

[thaidavid40]

The slab will tend to shrink more than the pit/trenches (as they are more restrained by their geometry), so you will need to make provision for that by using the isolation joints. The same is true for slabs adjacent to equipment foundations. And most equipment tends to vibrate. Decoupling the foundation from the slab short-circuits the vibration path, and keeps it out of the slab, where it could propagate to other areas. This leaves the soil as the only remaining path for the vibrations.
Dave

Thaidavid