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Book shelves (like aquariums) are heavy.

My concern would be traffic and weight. Public buildings are designed with thicker/wider and more numerous structural elements compared to residential buildings.

I believe the residential standard for concrete structures in India (where I am) specifies a minimum live load bearing capacity of 2kN/m2 (approx 200 kg/m2). This is much higher for schools/colleges/libraries/auditoriums etc.

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Most shelving materials as well as paper itself floats, so bookshelves can't be anywhere near as heavy as an aquarium even if you have them packed impossibly dense.

Edit:

Some one deleted their reply to you listing densities of paper and water. Here are some figures from Wikipedia

- The density of paper ranges from 250 kg/m3 (16 lb/cu ft) for tissue paper to 1500 kg/m3 (94 lb/cu ft) for some specialty paper. Printing paper is about 800 kg/m3 (50 lb/cu ft).

- Water: 1000 kg/m3

So they are not that far apart when you consider that the average bookshelf is often bigger than the average aquarium.

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