# Calculate Equivalent Thickness

QUESTION
How can you calculate equivalent thickness if i am using top and bottom reinforcement equal 628 mm^2 and thickness of concrete = 300 mm and if i put orientation that mean the reinforcement in the perpendicular direction. (I understand that you put layer of top reinforcement and second layer is concrete and then third layer is bottom reinforcement is that OK?)

REPLIES

Erik Panos Kostson
Example for the three overlay ed shell/plate element smeared approach.

The figure below shows these overlay ed shells, with red shells being top reinforcement (reo.), blue concrete, and green bottom reinforcement (shell offset is shown).
Now say for the example here and the sake of illustration, that the top reo., has 2000 mm2 of steel, and the bottom, has 5000 mm2 of steel:

Furthermore assume that the rc slab/plate is 1000 mm x 1000 mm and (assume same reo. in both directions).

Now to calculate the equivalent thickness of the top. reo. shells: th_top = 2000 mm2 / 1000 mm = 2 mm.
In the same way for the bottom reo, it is th_bot = 5000 mm2 / 1000 mm = 5 mm.
Thus we need to match the cross. area of the plate shells for the reo (a= width*thickness) to the steel reo. that one has in reality. From this we can solve for the thickness by dividing the width, just as was done in the example above.

Hope this explains how to calculate an equivalent thickness.

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