OWSJ Analysis - End Conditions

[amecENG]

When analyzing typical OWSJ, is it wrong to assume pinned-pinned end condition as opposed to pin-roller end condition?

OWSJ are designed based on pin-roller end conditions whereby the compression in the top chord equals the tension in the bottom chord. However, in reality when the joist shoes are attached to the beam member do they not provide a pinned-pinned connection? This greatly reduces the compression load in the top chord and even introduces tension in some of the first top chord members.

I was wondering if this assumption was incorrect when analyzing existing OWSJ for additional load provided that the joist shoe connection could transfer the horizontal reaction. If the joist was designed as pin-roller then it would have a lot of extra top chord capacity as pinned-pinned.

Any thoughts would be appreciated.

 

[BAretired]

Pin-roller is the normal and more conservative assumption. It may not be 100% correct, but it is closer to reality than pin-pin. If you assume pin-pin, you could end up with zero force in the top chord.

BA

 

[Den32]

Plus you would need to check the joist end supports (beam/wall) for the lateral load (or somehow account for that horizontal load).

 

[MiketheEngineer]

Agreed