Collector or SLRS?
Collector or SLRS?
(OP)
See the attached sketch.
The middle bay members are obviously to be designed using the 2.0 overstrength of collectors. My question is concerning the braced bays. There are varying opinions around the office that the struts are part of the SLRS and not collectors. Therefore they are not to be designed with the 2.0 overstrength.
My thoughts on it is that they are to be designed with the 2.0 overstrength.
The reasoning behind this thought is:
The connections are designed with the 2.0 overstrength factor to force the yield state of the bracing system and not the failure of the connection. If the strut were allowed to reach the yield state, it would create a K-Brace situation which is not allowed in seismic connections. Therefore, it should be designed as a collector.
Also, keep in mind, any seismic forces which are not taken out by the bracing system on one side, will be transferred across to the bracing system on the other side. In other words, if the forces at the joint don't add to zero, forces are being tranferred, therefore it is a collector.
What are your thoughts?
The middle bay members are obviously to be designed using the 2.0 overstrength of collectors. My question is concerning the braced bays. There are varying opinions around the office that the struts are part of the SLRS and not collectors. Therefore they are not to be designed with the 2.0 overstrength.
My thoughts on it is that they are to be designed with the 2.0 overstrength.
The reasoning behind this thought is:
The connections are designed with the 2.0 overstrength factor to force the yield state of the bracing system and not the failure of the connection. If the strut were allowed to reach the yield state, it would create a K-Brace situation which is not allowed in seismic connections. Therefore, it should be designed as a collector.
Also, keep in mind, any seismic forces which are not taken out by the bracing system on one side, will be transferred across to the bracing system on the other side. In other words, if the forces at the joint don't add to zero, forces are being tranferred, therefore it is a collector.
What are your thoughts?






RE: Collector or SLRS?
It seems to me that if these members "drag" forces into your braced bays then they need to be designed with the overstrength factor.
RE: Collector or SLRS?
Yes, you're looking at an elevation.
It's the struts in the braced bay that are in question whether they are collectors or part of the SLRS.
Thanks for your input,
Chip
RE: Collector or SLRS?
RE: Collector or SLRS?
Collectors themselves are designed for an overstrength factor of 2.
RE: Collector or SLRS?
I would agree with you that they are collectors. The intent is that you have a relief valve for the forces. With the diagonal braces not designed with the overstrength factor - you have created the necessary "weak-plastic" link in the system. The horizontal struts are indeed collectors and do not have to be weak links since you already have them in the diagonal braces.
RE: Collector or SLRS?
ht
RE: Collector or SLRS?
I'm not familiar with the terminology in use, but your rationale and theory are sound. For what it's worth, I agree as well: You must apply the overstrength factor to any load path in which you do not want a risk of plastic yielding.
Cheers,
YS
B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...
RE: Collector or SLRS?