Truss Support Detail

[abusementpark]

When you have a long span structural steel truss, how does your end support detail usually look if you are supporting it with a wide flange column?

Also, when you design a structural steel truss, do you design the end conditions as pin-roller, even though that is difficult to achieve the field?

 

[jike]

I can envision a number of different details depending upon whether: the truss is a roof or a floor, continuous/fixed or pinned connection, underslung, square end, beam purlins or bar joists, etc.

If a roof, I suggest that the truss bear on top of the column similar to manufacturered joist girders if possible. Details should be used to make erection as safe and to achieve overall stability as quickly as possible.

 

[Lion06]

I would figure out the detail and then model the truss based on your detail. The reason is that you'll never get a pin roller situation. It's ok to ignore this for beams because the end restraint is so small that the end moment is also small - this isn't as big of a deal for a doubly symmetric section. For a truss, in which the bottom chord is designed for tension only in the pin-roller scenario (and very little tension at the ends), any end restraint at all will cause the bottom (tension) chord to go to into compression. This is a bad thing if not designed for.

You could be conservative (for the truss's sake) and design the bottom chord as though it is pinned-pinned, and not pinned-roller....... then design the top chord as though it's a pin-roller support. I would also look at the pin-roller condition to determine the maximum horizontal movement you need to detail for. You know it will be less than that.

 

[ARLORD]

Yes, model the truss as pin-roller. As a check, the members on each side of the centerline should have the same tensile or compressive force, if the truss is symetric.

 

[BAretired]

There are too many possible variations to provide a cogent answer. A sketch would be best.

If the truss is a parallel chord floor truss you could connect the top chord and end diagonal to the flange of the column with an end plate and bolts. If you want continuity, you could connect the bottom chord the same way.

If you don't require continuity, you could terminate the bottom chord at the first panel point or, as is sometimes done, continue it to the column to provide erection stability but use a slotted connection such that the truss can develop full simple span rotation at each end.

BA