Sag Rod Support
Sag Rod Support
(OP)
I am designing an industrial building to house a process plant, the frame is clad with C10 wind girts which span 20' at each bay. I have decided to use sag rods in my design.
Based on my investigations here I have found several excellent discussions regarding the use of Sag Rods for providing bracing to wind girts.
What seems to be missing from my research is information regarding the end support of the sag rods. Are they supported at the eve by a dedicated beam for the gravity and bracing loads? Are they also connected at the foundation? Or do they simply connect to adjacent steel members?
I am assuming it is supported at the eve level and I have some creative ideas for providing this support, but did not want to wander too far from typical practice.
Thank you for your time,
- bd
Based on my investigations here I have found several excellent discussions regarding the use of Sag Rods for providing bracing to wind girts.
What seems to be missing from my research is information regarding the end support of the sag rods. Are they supported at the eve by a dedicated beam for the gravity and bracing loads? Are they also connected at the foundation? Or do they simply connect to adjacent steel members?
I am assuming it is supported at the eve level and I have some creative ideas for providing this support, but did not want to wander too far from typical practice.
Thank you for your time,
- bd






RE: Sag Rod Support
RE: Sag Rod Support
Michael.
Timing has a lot to do with the outcome of a rain dance.
RE: Sag Rod Support
BA
RE: Sag Rod Support
Based on a report that offered photographs and numerical results of a full-scale test I am convinced of the bracing characteristics of a sag rod design for the wind-girts.
I'm pretty sure I found this information at Eng-Tips on another thread.
"Behavior and Design of Girts and Purlins for Negative Pressure" by Peter C. Birkemoe. Found in the Canadian Structural Engineering Conference of 1976.
RE: Sag Rod Support
You're probably correct, but I've always been a bit leery about considering the inside flange braced, particularly if the sag rod is fastened to the middle of the girt. Maybe it would be better to fasten the sag rods nearer the inside flange. The outside flange is normally braced continuously by the exterior sheeting.
BA
RE: Sag Rod Support
Now I just need to decide where to place the eve strut to act both as my collector element for lateral forces and as support for the sag rod. I was hoping to place it on the center line of the building frame columns at the knee of my bent, but that's pretty "far away" from the edge where the girts are located. I think it would generate a 10 degree angle from vertical to connect the first rod from eve strut to wind girt at their current locations.
RE: Sag Rod Support
In my experience, the bridging or sag rods are not hung from the eave strut, but rather from the eave purlin or purlin bridging, or in the case of the gable ends, from the barge.
Why would you use C girts rather than Z's? Maybe it is just local practice, but lapped Z's provide better economy.
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RE: Sag Rod Support
We used to make a composite eaves strut by connecting a channel of the same size as the girt to the bottom of the wide flange. This started before we had wide flanges and used I beams that needed the extra lateral capability. They, the I beams, often had a channel on the top flange as well.
Michael.
Timing has a lot to do with the outcome of a rain dance.
RE: Sag Rod Support
Correct me if I'm wrong, but if the girt supports the siding, even a concentric placement of sag rods will put a torque on the girt. In the case of 10" channels, the eccentricity would be 5" plus half the depth of siding.
I like hokie's idea of proprietary bridging sections supporting the siding from the bottom, but common practice in my area is to use sag rods. I don't think I have ever seen bridging sections.
BA
RE: Sag Rod Support
On the previous posts - I mentioned our method - installing the girts with a very small downward sag at the midspan. The sag rods, whether at the centroid or near the inside flange, then act as tension members coupled with the siding to form a rotational couple. Since the girt is downward sagging, any wind suction that induces compression on the inside flange will develop lateral torsional buckling downward (due to the initial sag). The sag rods are then in tension resisting the LTB.
RE: Sag Rod Support
http://www.eng-tips.com/viewthread.cfm?qid=115545
BA
RE: Sag Rod Support
thread507-236394: sag-rod supported girts (girt design)
RE: Sag Rod Support
BA
RE: Sag Rod Support
BA
RE: Sag Rod Support
RE: Sag Rod Support
RE: Sag Rod Support
RE: Sag Rod Support
RE: Sag Rod Support
Hokie66 asked where I was located. Our design firm is in the States, but the project is in mid-Oaxaca Mexico, not the middle of nowhere, but a lot of options either. We've been given a limited list of what they have available as far as structural shapes are concerned. They may have access to proprietary shapes or wind girt bridging, but I am unaware of it if they do.
ToadJones - I too had the design intent to rely little on the building skin for strength due to unknown holes in the future, but I had applied this philosophy mainly to the design of the frame bents, not to the wind girts, this is an insight that I will need to investigate further. Thank you.
JAE - It sounds like you've not relied on the wind girts for supporting the dead load of the wall skin, this is an interesting idea. How do you typically support the eve beam over the wind girts?
RE: Sag Rod Support
In some of the industrial structures I have worked on there are struts along the column line at or near the eave height. The girt line is typically 2'-0" or so. So what I would wind up with is an eave beam and a column line strut running parallel between which small sag-rod-support-beams would be run (2' long or so). Looking up at it, it looks like a ladder. This ladder also supports the gutter trough one way or the other. The eave beam would have to be supported by an outrigger in this case.
Keep in mind this situation is on heavy industrial buildings, not PEMB or the like.
RE: Sag Rod Support
RE: Sag Rod Support
DaveAtkins
RE: Sag Rod Support
BA
RE: Sag Rod Support
They typically rest on concrete grade beams and support their own weight.
For lighter panels, they still have vertical flutes, typically, so they have some ability to support their own weight provided the girt spacing isn't too far. Otherwise providing a rigid continuous edge angle that can support the vertical load - usually cantilevered off the edge beam - is used.
I'm sure there are many other approaches.
RE: Sag Rod Support
RE: Sag Rod Support