Slotted Holes and roller connection

[SemiPE]

Hi All, from what I have read, the main purpose of a over-sized/slotted holes are for ease in installation. I also heard that it can be used when a connecting member (ie one end of a simply supported truss) was designed assuming a roller support, the slot size being equivalent to the lateral displacement of the roller. I know the former is a fact, while i'm unsure about the latter. However, if the latter isn't really how a roller support is detailed then how is it usually detailed (say a for a 60ft truss)

 

[KootK]

You may be interested in this: Link

In general, slotted holes do not make good "rollers". They lock up under significant vertical load and/or rust. I'd recommend a true sliding joint with PTFE layers etc. Google Fabreeka for som ideas.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[TLHS]

It also depends on what you mean by a roller, though. You may be talking about a theoretical roller on a simplified model of a simply supported beam that keeps the calculation straightforward and releases inconsequential secondary forces. That release in the gravity case is generally just assumed to exist due to flex in the frame, small movement in the bolt holes, and the fact that the induced forces due to that roller not existing are small. This very much depends on the connection detail, though. If you start fastening both chords of a truss to a stiff column your gravity case will transfer all sorts of axial loads from those chords due to the bending moment couple.

If you actually need movement to account for significant expansions/contractions or to ensure you've isolated something from lateral forces, then you want a proper sliding joint as mentioned above.