Support strip and weight on shelf

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I have a shelf made of glued laminated timber from Byggmax. It is 109 cm long (wide). I have two brackets that I plan to place quite far out on the sides below to make room for lighting between them under the shelf.

Question 1: How much weight can such a shelf approximately hold?

Question 2: Can I attach a support strip to the wall against the shelf to support the middle with nail plugs? If so, what dimension, a standard stud? The shelf is 19 cm deep.

 

[AskeHolst]

Without knowing how thick it is, nothing can be said about the durability.

 

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Glued laminated 18 mm thick it seems to be.