What is reason for Top & Bottom Reinf. in simply supported covers 2

[ScratchyFilm]

Say we have an 8" over slab on a junction box (10'x10' or so). The cover sits on top of the walls, so it is simply supported all around. What is the reason for bottom and top steel reinforcement if there is no negative moment in the slab? Is it just conservative for T&S reinforcement or is there a basis of design?

Thanks!

 

[HTURKAK]

I think the cover slab precast.. in this case, depending on the formwork, stripping and handling, top reinforcement could be necessary.. The top rebar will help to reduce the deflection, shrinkage and temperature effects..

If the slab is cast in place and indoor , i do not see any reason .. if necessary increase the thickness of the slab rather than compression steel..

 

[ScratchyFilm]

That makes a lot of sense based on shop drawings I have seen. Thanks for the reply!

 

[molibden]

You do kind of need top reinforement in the corners of the slab, if supports prevent movement (torsional moment m_xy).

 

[JoshPlumSE]

To lessen cracking.

To allow for the cover to be picked up / removed or placed.