Library Stack Weight towards Seismic Dead Load 1

[lweiss4]

Does anybody know of a good reference to the percentage of library stack loading that should be counted towards the Seismic Dead Load? I could take 25%, as the Codes suggest for storage, but this seems to be a bit more specific, and permanent of a case. Thanks!

Lenny

 

[JAE]

I see it as more permanent - perhaps 75% of the stacks full at the time of the seismic event?

 

[lweiss4]

Thanks - it does seem to warrant more than 25%, and 75% of the stacks full seems like a good suggestion, but I can't find any literature to back this up. So it may just come down to engineering judgment. Have you seen any manuals or references that might point us to that number?

 

[JAE]

Nope - but there probably are - I've just never designed a library in a seismic condition before so never looked. Have you searched "wall-to-wall" in the ASCE 7?

 

[lweiss4]

I have, but it doesn't specify. An interesting point comes up in the literature I've searched: A seismic event seems to affect the equipment/components that are permanently attached to the building. So the bookshelves are attached, but what about the books? Any thoughts? Storage of course isn't attached either, though I suppose that it could have friction enough to "move with the building". Books however, may not...

 

[JAE]

Well, some library rack-shelves are attached to the building directly, extending multiple stories through open floors. And the shelves have edges that keep books from sliding off -

For loose shelves, that would rock around in a seismic event, their mass participation in the seismic load could definitely be different.

 

[phuduhudu]

As I understand it the 25% doesn't refer to the likelihood of the mass being there or not but refers to it's participation in the seismic oscillation. So I would say 25% might even be high. The books can just be thrown off the shelves in a seismic event. Even if there is an upstand edge to the shelves the books if sliding back and forward would not be participating in the building critical modes.

 

[lweiss4]

Thanks; this makes good sense for forces perpendicular to the racks, but if books are tight to the rack in the direction parallel to the rack, perhaps they could participate more with the racks. Any thoughts or references?

 

[IJR]

phuduhudu

When one considers that durations of killer earthquakes are in the order of 30-45seconds(I was once in a country that suffered a bad 45second one), then one may appreciate that the books may not have time to slide over each other and gain enough momentum to fly over the room.

I would go with JAE's number, 70-75%. In the code I am using(highly seismic location) it is 80% for warehouses and 60% for a shopping mall). So JAE's number makes good sense for a library

respects
ijr