Connecting threaded rod to Z-purlins? 3

[Tomfh]

We have some threaded rods we need to hang from Z-purlins (5 degree incline). Load around 1kN per rod. What's the best way to attach them?

The recommendation is always to hang loads from the purlin web, however many proprietary rod clips hang from the flanges:

https://www.mynes.com.au/epc10-beam-clamp-for-m10-threaded-rod-zp.html

Hangers like these (4029706, RH1200) attach to the web, but likely wouldnt work with non vertical purlin webs. The rod would be at an angle.

https://www.unistrut.com.au/E-doc/Unistrut-AU-GEC/index.html#p=162

I'm also wondering how to assess the resultant twisting load applied to an inclined purlin.

Any advice would be appreciated...

 

[human909]

A few GP brackets and some 100Cs in bridging between your Zs would do the job.

I agree with your hesitation about hanging from the flanges. I'd be quite wary about hang much load at all from the flanges of your purling unless you want their capacity to be compromised.

 

[Tomfh]

A few GP brackets and some 100Cs in bridging between your Zs would do the job.

Could you clarify what you mean? How would you arrange them and connect the rod?

 

[human909]

I am presuming these are existing purlins and a site addition.

I would suggest the use of GP bracket to connect 100C purlins to the ZEE purlins running perpendicular between the ZEEs. I would then use a "vertical mounting plate" as linked from your unistrut catalogue or similar into the web of the C purling to be able to neatly drop the threaded rod down where you need it.

I see this solution as site flexible and simple. If you want to make life easier for the guys on site you could consider whether TEK screws (metal self tapping screws) as sufficient connection between your GP brackets and your purlins. It will save alot of drilling of holes.

At a guess all this would be suitable for a 1kN load.

 

[Tomfh]

It’s all new construction, so we can do what we need. There will be lots of rods, as per normal ceiling construction.

The issue is the ceiling has some heavy stuff hanging from it that would overload a normal ceiling system (unless there’s some very heavy duty suspended ceiling system I’m not aware of).

 

[human909]

In that case I'm not sure. I'd consider going with CEEs and just make everybody's life easier. Sure ZEEs are more efficient but by the time you include the lapping distance and the time to install the difference isn't as significant as you'd think.

Anyway that is my 2cents. I've never specified suspended ceilings at all as I work with industrial construction.

 

[hokie66]

Whether C's or Z's, I think hanging the rods from bridging between the purlins is a good solution.

 

[Tomfh]

Hokie, do you agree with using one of those proprietary clips fixed to the purlin/bridging web?

 

[SandwichEngine]

If you download the Metal Building Manufacturers Association (MBMA) manual, it has guidance on how to attach hanging loads to cold formed members. Of course it recommends attaching to the web. It specifically says not to clamp to the toe of a cold formed member. It does allow for a clamp that attaches near the web but to analyze that along with all the other distortional buckling states that need to be checked for cold formed steel seems like a fools errand.

The MBMA manual also recommends using a spreader beam for large loads.

 

[Tomfh]

Thanks SandwichEngine. Useful info. I’ll probably end up using that approach, with lightweight spreaders attached to the underside.

 

[hokie66]

Tomfh,

I was thinking of going between the webs with the spreader, but the detail which Sandwich Engine posted is better.

 

[dhengr]

Tomfh:
Some attachment hardware supplier will allow you to bend their hardware, once, a little bit, to make it work, without significant loss of cap’y. That doesn’t mean you can straighten out one of their 90° corner bends, or make a new 120° bend, and they don’t want you to bend the material back and forth at one location. Something like (similar to) that RH1200 Rod Hanger, might be bent 5° btwn. the lower screw hole and the rod holder to match the purlin web slope, without appreciably affecting the strength of the hardware. Give that manuf’er. a call, and see what they have to say. Although, the spreader beam btwn. purlins is really a good solution.

 

[GC_Hopi]

For what its worth, I was told by a PEMB designer that they prefer to attach to the webs of the purlins, see the snip. The designer was a bit conservative so...

 

[GC_Hopi]

Also its recommended to avoid hanger attachments to the webs of the purlins if the roof slope is greater that 4:12 and to block purlins if the load exceeds 250 lbs to prevent purlin rotation.

 

[rowingengineer]

A few years ago I was retained as a ceiling failures engineer. Basically I was on call to some large super market outlets that would ask me to help out everytime a ceiling failed. I would get between 4 to 5 failures per year.

My recommendations are:
1. Never trust a manufacturer, they don't do very good testing for unintended situations. What I found was generally the manufacturer connections work well at a vertical situation, but if you incline the rod by more than 5 deg and your capacity is halved. I used to aduit my sites and in most cases the rods were not vertical and generally 20% or more were above 5 deg and this was always in the locations the elecs had installed lights, plumbers pipes or AC guys AC.

2.thru fix always. Fixing as a hanging arrangements to the lip is not a great practice, often a good wind load can have the ceiling falling. Always fix thru the flange or off the web with an angle. While this might cause some issues for the purlin designer, at least the failure isn't for the ceiling to fall on people.

3. Tradies are not engineers, if they can manually relocate a dropper to miss a AC duct or similar they will, have an inspection requirement after installation of all services.

4. Earthquakes are real and they happen in Australia, make sure you have correct horizontal designs. Often unintended horizontal loading occurs like people lifting stuff and hitting ceilings.

 

[Ron247]

The "proprietary clip" attaching to the tip of the flange is not stating the purlin works, it just states their clip works. They have no idea how thin the purlin is, if there is a stiffening lip present and if so, what is its' strength. Do the moment calc of 50 pounds across 2.5" of .06" flange and you will see the diving board affect is substantial.

Any of the "trapeze" type connection cost more but are worth it. I had to go to project once with a collapsing Z-purlin roof in a main electrical building. The specs said they could use the c-clamp type connections for 35 lbs or less. It gave no requirements about how far you had to go before you could put another one. So to hang 350 lbs, they put 10 of them side by side. Everyone did that to support their cable trays, large amp electrical cable and HVAC.