Hanging porch swing bed from purlin?

[titus211]

Hello folks,

My wife saw an idea for a porch swing bed online, and over the weekend we built one out of some pine. After building it, it seems to have grown - this monstrosity is about 8' wide and 3.5' deep and can seat 4 people.

Our house is a normal red-iron metal shop building with an area enclosed for a living space. We would like to hang it under our porch from the purlins. My question is - am I going to cave in the roof hanging this thing?

It will attach with forged eye bolts and chains from each corner of the swing. The layout of our porch is 20'x20' with I-beams on each end, and 8"x2.5"x14ga C purlin perpendicular to the I-beams every 4 feet. The swing would be attached to 2 separate purlins, each with one attachment point 2' from the end and another 10' from the end. My crappy drawing in mspaint below probably describes this better.

My guess is that the maximum weight would be about 220# x4 people, plus another 200# for the swing for a total of 1080 pounds. All the hardware hanging it is more than sufficient - just worried about the purlins.

Any thoughts? Or pointers on how to calculate this? Thanks for helping a lurker out!

Ryan

 

[readhead]

I'm in the metal building biz and I would say absolutely no. You could install another purlin back to back and screw them together to create a beam. You cannot attach this much weight to the bottom flange. You will have to attach to the web of the purlin.

 

[Kaizen]

Agree no way. Also what did you make the support structure for that out of?
Meaning under the seat that you will hang it from

 

[NUTTSGT]

I'd listen to what redhead mentions about doubling up the purlins.

We have a regular porch swing on our front porch and when I built the front porch, I planned for it. The porch rafters are 2x6 and the one that holds the swing is doubled up and I used carriage bolts to bolt them together so they would spread apart. Once that was done, I drilled vertically between the 2x6s for the eye bolts. Not only do the bolts run through the 2x6s, I also put a 2x4 horizontally spanning 3 more rafters to help spread the weight and some large washers to spread the weight of the nut on top.

In the 12 years or so, the porch swing has never made an inkling of hurting the front porch at all. So what I'd suggest is that maybe in addition to the doubling of the purlins is to add something across the top to help distribute the weight too.

 

[titus211]

The swing itself is made of 2x6s, and then wrapped with 1-by boards. I've supported it from the hanging points with a couple of floor dollies and had some people sit on it - no signs of flexing, so I'd say the swing itself is structurally sound.

Sounds like if I sistered each of these purlins with another purlin, back to back, and then added a plate between them (bolted to the web), I could then attach my chain to that plate. Something like the attached drawing.

Thanks all for the help and suggestions!

 

[readhead]

Yes. That would be the way to go. However the two purlins need to be bolted probably a foot on center, not just at the hangers. Make some shims the same thickness as the hangers and bolt away.

 

[titus211]

Any recommendation on shim or bracket thickness? Think 3/16" would be sufficient?

 

[readhead]

I would go with 1/4".