Slotted connection for roof truss support

[LJ_]

Hello,

I was wondering if I could use a slotted connection for the roof truss support that is designed as “roller” I get a maximum horizontal displacement of 3/4 in.

Could you recommend me a guide for this? I only have found very old details that recommend using this type of connection. This is a light structure. But I am still concerned about the locking of this roller connection due to environmental causes.

I haven’t found anything related to this in AISC. Most of their information relates to frames connections.

Thank you!

 

[klaus.]

Well you have to design your so it can take the displacements.....no problem

 

[LJ_]

But, is there a guide? because I could slot my angle for like 4 inches. It could be snug tightened or hand tightened.

I just want to avoid any bad practice.

 

[r13]

You can weld a plate to the support end joist, and slot the plate. But 4" of lateral displacement, it sounds quite excessive.

 

[LJ_]

I was exagerating ! but the thing is that I see nothing in the code that can really guide me. Part 13 of the AISC manual has only a paragraph relating this issue and it is vague.

 

[r13]

The reason for lack of guidance is because this situation can be avoid through other design considerations, or methods. The practice is inexplicitly discouraged, for it can cause severe structural problem - unexpected axial force due to support jamming/locking. Do not use slot hole for sliding at location that is difficult to reach, unless you are fully confident on the functionality of your design.

 

[LJ_]

This is exactly what I am wondering. If I can’t use slots. What is the alternative? I can’t specify lightly sliding materials because it is way too expensive for the project significance. So my design does have some high degree of allowance if this was a pinned/pinned instead of pinned/roller connection for wind and dead plus live load however it does not work for temperature.

 

[r13]

How about adding insulation?

 

[LJ_]

The truss is located in the beach.

 

[r13]

Salty/moist air is your enemy, watch out.

 

[klaus.]

But, is there a guide?

well..my engineering sense is my guide
You cannot find each and every connection or detail in a Code
Codes give general guidance...but not each detail otherwise we would not need structural engineers

 

[HTURKAK]

Yes ...you can use slotted connection for the roof truss support . The slot could be 2 in. for a horizontal displacement of 3/4 in.
It should be finger tightened. and provide teflon shim to limit the horizontal load transfer.

Just for curious, what is the reason for modelling roller support ?

A sketch showing the truss and supporting structure will be helpful to get more valuable responds..

 

[LJ_]

It was a bowstring truss, just supported at the bottom chord. I did provide the slotted connection. I just try to be extra careful in connections of structures with so little redudancy.
As to why modelling roller support, if it was fixed it would be saying it can´t move and will generate internal stresses in the bottom chord (mainly, because of how it is supported). If it has a roller, all those stresses are gone. Because I am not designing this truss, I can´t provide elements that satisfy both boundary condition.