Girder Truss Supports 1

[531234]

I am involve in a project where we need to design a 80 feet clear span girder truss that will have wide flange members. The girder will support a three storey wood frame for dwelling. We are going to restrain the girder with pin on one end and roller on the other. My question is the roller support, should a slotted bolt connection (to allow translation in horizontal axis) at bearing point considered as roller? s there any problem with this connection?

 

[briancpotter]

What's the reason for specifically requiring a connection that allows translation?

Brian C Potter, PE

http://simplesupports.wordpress.com

 

[JedClampett]

If you're just trying to match the analysis, it's not commonly done. This is for several reasons:

Expense.
You can't really match the analytical case. There's friction, corrosion, misalignments, etc.
It only changes the analysis slightly and in a conservative way.
You need the fixity to support the top of the walls.

This is done on bridges, but they're outdoor structures, with more temperature effects.

 

[531234]

Thanks for the replies. The translation is for the expansion and contraction of steel.

 

[nac521]

Be careful with that type of connection. Research the David L Lawrence Convention Center collapse. Along with other factors, the inability of the bolts to slide freely within the slotted holes was determined to be one of the main causes.

 

[msquared48]

You might consider bearing on teflon pads on one end, but even that gets dicey. Somehow, the truss to wall connection needs to be limited for lateral stability of the wall and support of the truss, especially in a seismic event.

Mike McCann
MMC Engineering

 

[hokie66]

nac521 is correct. Slotted bolts bind, and should never be used for heavily loaded connections. The reference he gave for the Pittsburgh collapse should be required reading for structural engineers.

Use guided slide bearings. Try this company:

http://www.sepbearings.com/fluorogold-slide-bearings.html

 

[BAretired]

An eighty foot long truss is likely to be at least 8' deep. Why not hinge one end at the bottom chord and support the other end at the top chord on a column hinged top and bottom so that temperature strains can be accommodated? That would be equivalent to using a hinge and roller.

BA

 

[paddingtongreen]

If the supports are columns, what is the need for a sliding bearing? both ends pinned for the girder and one of the columns will fit the model. If on rigid foundations, then yes, use guided slide bearings.

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

 

[531234]

Thanks to for all the comments. Yes the girder sits on a rigid foundation.

 

[BAretired]

How deep is the truss?

BA

 

[531234]

The girder is around 10 feet deep, top and bottom chords are fully braced.

 

[BAretired]

Carry the bottom chord to the end vertical at one end. On the other end, use a top bearing truss with a 10' high column under the shoe. The column can be hinged top and bottom but braced perpendicular to the truss. Do not attach the bottom chord to the column. No need for slide bearing or slotted connections which fill up with dirt.

BA

 

[531234]

BAretired, you are a genius! thanks a lot.