Joints in a steel structural system - Conceptual design

[SuG89]

Hello,

Please ignore the question if it sounds stupid.
Given a large steel structural system, is there a method to figure out the optimal layout of the pin and rigid joints? For example, if a structural system has 10 joints, how to decide which of them need to be rigid/pinned. I know that this depends on the structural system geometry, type of loading/load path and whether the structure is attached to something or stand-alone. But I was just wondering if anyone did some research work on this theme and came up with some general rules.

Regards,
Su

 

[klaus.]

Well I would say the question is not stupid but also the question cannot be answered very easy because it depends on many many 'boundary ' conditions ... not only structural....

 

[MotorCity]

The number of fixed or pinned joints depends on your lateral system. If you are referring to "joints", that eliminates shear wall systems and you are left with moment frames or braced frames (its generally not a good idea to use moment frames and braced frames in the same line of resistance). So, say you choose moment frames. You will most likely have two moment connections per moment frame (upper left and right corners). By default, the remaining upper joints are pinned (i.e. not part of a moment frame). Now lets say you choose braced frames. In this case, all joints will be pinned (if any of them were fixed, you would have a moment frame). So the general answer is that the layout of pinned or rigid joints depends mostly on what lateral system you select. Also, you need to define what "optimal" is. Is it the least cost? Is it the least story deflection? Is it the easiest to construct?

 

[cal91]

Yes, define "optimal". Is it minimum number of fixed joints?

 

[Once20036]

If I had a structural system (not sure exactly what type of system we're talking about) with 10 joints, all of the joints would start as pinned.
I would change the pins to rigid only if I had very good reason, as a rigid connection is much more expensive than a pinned connection.

 

[mike20793]

Sounds like a homework problem.

 

[JLNJ]

Fix as few as possible, because fixity is difficult and expensive to achieve.

Of course, the structure still need to be stable and smart.

 

[SuG89]

Thank you very much (to everyone) for responding to my question!
I would define optimal as minimum number of fixed joints in the structure. And this should not lead to a strength, serviceability or stability failure.
My takeaways would be:
1. It is a multi-variable problem and does not have a direct answer
2. Depends on what type of lateral system is selected
3. Start with all pinned and change individual joint to fixed until the set design criteria is fulfilled

Regards,
Su

 

[jayrod12]

You've posed an extremely vague question. I can frame a steel structure using absolutely zero fixed joints depending on the geometry and the ability to put in bracing. Sometimes fixed joints are unavoidable, but without an actual situation to look at, there's no right answer.