Bookcase on casters, will it tip over?

[fleabag]

I was wondering, if you had a small but very tall bookcase, one that is taller than it is wide or deep but the width and depth are the same, so it has a square bottom it it goes up. So the question is, would a bookcase on 4 casters (each corner) placed in the middle of a room be more likely to tip over in an earthquake compared to one not on casters.

 

[So]

I think both would be pretty damn likely to tip over.

 

[nageov3t]

seems likely.

why would you want a large bookcase on casters?

 

[IronWing]

Find out. Place two similar bookcases in a room, one on casters. Then take the bottle jack out of your car and go down in your basement and start shaking the house.

 

[IronWing]

To answer the question in a somewhat more serious manner. Placing entire buildings on rollers is one method of "earthquake proofing" buildings. The Salt Lake City - City Hall was retrofitted with rollers for this reason.

 

[0roo0roo]

seriously bad idea.

 

[0roo0roo]

Originally posted by: ironwing
To answer the question in a somewhat more serious manner. Placing entire buildings on rollers is one method of "earthquake proofing" buildings. The Salt Lake City - City Hall was retrofitted with rollers for this reason.

well not like that though.if the building was unstable as the bookcase in the first place it would be even more dangerous with casters. buildings are far wider and have their weight more evenly distributed....casters are fine on wide furniture..like tables and desks, but he's described something really tall and thin.

 

[seemingly random]

Depending on the number of books, those casters would have to be pretty strong.

 

[fleabag]

Just keep in mind that it isn't so precarious that if you lean on it or push it on a smooth surface (w/out casters, moving men?) that it'll tip over. But for the sake of discussion, what about one that was more precarious? It just would seem like it'd roll around a lot like a car skidding on ice instead of a car skidding into a curb and flipping over.

 

[IronWing]

Originally posted by: 0roo0roo

Originally posted by: ironwing
To answer the question in a somewhat more serious manner. Placing entire buildings on rollers is one method of "earthquake proofing" buildings. The Salt Lake City - City Hall was retrofitted with rollers for this reason.

well not like that though.if the building was unstable as the bookcase in the first place it would be even more dangerous with casters. buildings are far wider and have their weight more evenly distributed....casters are fine on wide furniture..like tables and desks, but he's described something really tall and thin.

Let's break this down.

A fault slips, a component of the energy released is transmitted as acceleration in the horizontal plane. We can ignore the vertical component for this discussion for the moment (good pun, no?).

The case of the caster-less bookcase:
The floor beneath the bookcase is accelerated.
The base of the bookcase is accelerated at the same rate as the floor unless friction is overcome and floor-bookcase slippage occurs resulting in less acceleration of the base of the bookcase in the horizontal plane.
The acceleration of the base is transmitted up the case as a shear force.
If the lag in time between the acceleration of the base of the bookcase and the acceleration of the top of the bookcase due to the shear force is too long, then the center of gravity of the bookcase will pass over the trailing edge of the bookcase and the bookcase will tip. If the shear force can act quickly enough or the initial acceleration of the base is too small, the bookcase will stay vertical.

The case of the castered bookcase:
The floor beneath the bookcase is accelerated.
The base of the bookcase remains stationary to the extent the movement of the floor beneath the bookcase is decoupled from the bookcase through the action of the casters rolling. Friction in the casters will transmit some acceleration to the base of the bookcase.
The acceleration of the base is transmitted up the bookcase as a shear force but the shear force will be less than with the casterless bookcase as the decoupling lessened the energy transmitted to the base.

 

[0roo0roo]

bookshelves also have to deal with the pulling force of someone accidentally putting force on it, or a child trying to climb up to reach something. buildings are free standing, the bookshelf has to deal with the wall. if its secured at the top its doubtful its bolted on strong enough to support its full weight and compromising the footing is asking for trouble in any case.

 

[AlienCraft]

Originally posted by: fleabag
I was wondering, if you had a small but very tall bookcase, one that is taller than it is wide or deep but the width and depth are the same, so it has a square bottom it it goes up. So the question is, would a bookcase on 4 casters (each corner) placed in the middle of a room be more likely to tip over in an earthquake compared to one not on casters.

Answering strictly as written, I would guess the one on casters would "slip" easier to any lateral forces, but any perpendicular ones would surely upset it.
There are sway reduction technologies that resemble that "casters on the bottom" scenario, the giant springs under buildings come to mind, but the massive tonnage keeps them planted. Your bookcase lacks that massive-ness.

 

[alkemyst]

now the question is, if you put it on a treadmill; will it take off?

 

[us3rnotfound]

Originally posted by: alkemyst
now the question is, if you put it on a treadmill; will it take off?

Neat idea, you could guide it gently while the treadmill is going. It'll stay in the same spot.

 

[Nik]

Originally posted by: alkemyst
now the question is, if you put it on a treadmill; will it take off?

LOL

 

[IHateMyJob2004]

It matters where the feet are on the bookshelf to begin with. And where the casters touch the floor. The one that is wider and deeper where it contacts the floor is less likely to tip over.

 

[Mo0o]

yeah it's likely unless you load down the bottom w/ weight and keep the top realy light

 

[0roo0roo]

small square and very tall.. weighing down the bottom...u'd have to use lead weights or something

 

[Leros]

Screw it the floor. Problem solved.

 

[thescreensavers]

if it gets to heavy up top it will be very easy to tip.

 

[Leros]

Originally posted by: thescreensavers
if it gets to heavy up top it will be very easy to tip.

Thats a good idea. Make the bottom really heavy. Throw a few 50lb weights on the bottom shelf.

 

[feralkid]

Originally posted by: Leros

Originally posted by: thescreensavers
if it gets to heavy up top it will be very easy to tip.

Thats a good idea. Make the bottom really heavy. Throw a few 50lb weights on the bottom shelf.

Or drop them from several feet above. Throw or drop, either works just as well.