Elastomeric bearings under beams

[ImSparticus]

I am looking at designing a roof beam spanning between two independant buildings in a seismic zone. Its not soemthing we normally have to do in the UK, so have some very basic questions.

The movement is to be 120mm. It has been suggested I use 2No 60mm bearings at each end. How would I ensure that the beam does not move the whole 120mm when wind load is applied?

Is this a normal detail?

I am assuming the movement will have to be allowed in all direction and not just in the direction of the span.

Thanks for your help.

 

[paddingtongreen]

It sounds as if you need teflon/elastomeric bearings.

http://pretread.com/neoslidepads.html

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[rscassar]

How far does the beam have to span and where does the movement come from? It is possible to use an elastomeric bearing which allows 120mm movement.

 

[JAE]

For a one way expansion joint bearing detail, you would normally do this:

1. Use a lower and upper plate assembly.
2 The upper assembly would be a steel plate covered with a teflon or other glide coating with the glide coating facing down.
3. The lower assembly would be a steel plate with an elastomeric pad with a bonded glide coating, with the glide coating facing up.
4. The glide/teflon coatings would of course be in contact.
5. Use a vertical shear dowel extending from the lower seat structure pointing up into the beam above which would have a slotted hole to allow the movement.
6. The upper assembly should be larger than the lower assembly such that any lateral movement would not expose the upward facing glide surface where dust or debris could accumulate.
7. The thickness of the elastomeric pad depends upon the load and size of pad. The pad manufacturers have design guidance available. Also your local DOT might have design guides for this as they do bearings similar in bridges.
8. If the load is large enough, you might have to reinforce the pad with intermittent steel shim plates between layers of the elastomer. This reduces the bulging strain on pad and allows for larger loads.

The elastomeric pad allows rotation in the beam and the teflon/glide surface allows lateral movement. This kind of assembly is primarily for one-way movement only. Not sure what you'd do to allow two-way movement.

Try this site for starters: Fabreeka site

Or this one: SEP site

 

[paddingtongreen]

@JAE,
I have used them with guides, in two layers at right angles. I have used some that only allow rotation at one end and bi-lateral movement at the other.

Generally when any direction of movement was possible, I tried to allow only rotation and one direction movement at each end, the directions being at right angles to each other.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[BAretired]

Permit rotation about a vertical axis at both supports and permit expansion or contraction at only one support.

BA