Slab Reinforcement Design in panel with multiple openings and loaded edges

[andrew_wiggett]

I am designing a slab to cover a shaft. The slab is to be ~11m diameter and 750mm thick. There are multiple openings (see attached) which mostly (but not all) are aligned on the cartesian grid.

The openings are covered by manhole covers which will transfer any load on them to the edges - so I have a line load around the edges of each opening.

This (and the square edges to the openings) gives high local stresses and moments right at the edges of the openings - up to about 100mm from the edge - which I can see using RESULTS - MAPS. This means when I use the required area of reinforcement it suggests very high values for the reinforcement at the edges eg. 3000mm2/m for the areas at the corners

When I go to RC DESIGN - SLAB REINFORCEMENT, I do not know how to use this tool to design the reinforcement in a slab. It has automatically selected a silly reinforcement direction about 5 degrees off straight which I cannot change, and when running the calculation, it objects to the cover being too low (30mm) when I believe I have set it to 50mm in the slab properties.

How should I proceed?

(this may be an impossible design - it may require thickening of the slab or drop beams inserted beneath it)

Regards

Andrew

[Rafacascudo]

Menu Design/Required reinforcement for slabs and walls - options/Code parameters... 

On general tab you set the reinforcement main directions . If you leave on automatic it will obbey your local panel direction which has the silly 5 degrees you mentioned.

On reinforcement tab you set the cover values.

Don´t forget to assign your panel with the code parameters type you created

[andrew_wiggett]

Still does not work.

Thanks for the reinforcement direction tip, did not know about that.

My cover was already set to 50mm (default or I had changed it somewhere else yesterday?). But having rerun it, I am still getting the same problems (rotated rebar and error about cover being 30mm)

My slab has reinforcement type = shaft cover which is the same as before.

Regards, Andrew

[Artur.Kosakowski]

Could you make a sketch that shows your intended reinforcement arrangement in the panel?

[andrew_wiggett]

Initial idea was to have "beams" as shown in orange. Was expecting to have 25 or 32mm bar as the main reinforcement in these areas, and hopefully lower weight of reinforcement in the other areas which I've left blank on the sketch.

Though with all the openings I was hoping the FE modelling would suggest something better.

Slab is simply supported so all this in the bottom. top reinforcement is mainly for crack control

[Artur.Kosakowski · Accepted solution]

I would try to 'divide' the panel into smaller parts (panels) with appreciate reinforcement directions assigned to each of them.

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