purlin sizes

[LD1]

It seems for the CEE purlins they are allowing a good bit more than L/360 deflection.

I will attach a chart that I found that lists some allowable spans.

So back to my earlier #'s, the purlin is going to need to endure about 80lb per foot across its length.

Looking at the chart, A 4.0 x 2.5 16ga c-purlin will span 13 feet and be allowed 87 lb per foot. With a max deflection of about 1.5". That is like a L/100 deflection. Probabally a lot more deflection than I would like, but it is not my chart. 1.5" deflection over 13' seems a bunch to me, but????

The purlins are still going to be placing ~550lbs in two points are the outer "beams" and 1100lbs in two points on the middle beams. For this, I would use a 5" x 9 lb per foot structural c-channel.

There are some ligher CEE-purlins that would be strong enough to carry the load, but they dont offer as much lateral or torsional strangth. And they are also thinner, You will be able to get a much better weld using structural steel for the "beams" IMO.

Look this chart over. You have to change sections using the index to the left. Mainly look at the gross section properties and the simple span capacities.

Access LGSI

 

[bdog]

Maybe he's planning an indoor maze??

-Jer.

I know you are just poking fun but really I don't think they will be in the way?

Attached is an aerial view. Green will be the trailers, black is the sheeted sidewalls, and red is posts. Again sorry for my awesome paint skills.

 

[bdog]

What is going to be your material of choice for the "beams". The ones that span the 12' and carry the 13' purlins??

Are you going to use structural steel like c-channel or are you wanting to us a larger CEE type purlin like you are using for the purlins??

I was thinking of using all C-purlins - 14 guage is what I believe they are locally.

A heavier c channel might be a better choice though.

I will look over the table you posted.

 

[LD1]

I was thinking of using all C-purlins - 14 guage is what I believe they are locally.

A heavier c channel might be a better choice though.

I will look over the table you posted.

While a 8" 14ga c-purlin will probabally work, I am more concerned about the connection between it and the posts. Not to mention the structural channel will offer far better lateral and torsion strength. Cost difference is probabally nil.

Now you sut have to find a way to hold things in place while you weld

 

[wroughtn_harv]

You may remember my thread on I-beams. Well I got a good deal on a semi load of 2 3/8" pipe so my plans on constructing my shed have changed. Instead of trying to make it clear span i have set 16 pipes in the ground to support the structure. I have attached a horrible drawing of what my plan is.

Basically the shed will be 36' wide and 39' feet deep. The pitch is in the 36' direction. With the 16 posts I have set in the ground (black on the drawing) the longest span for the purlin will be 13'. I plan on putting the purlins that the R panels will screw (green on my drawing) to on 4' centers so there will be a purlin centered over the pipes then two suspened in between the pipes by the purlins running in the direction of the pitch (yellow on the drawing).

I am guessing 4" purlins for the green ones will be plenty but I am wondering about the yellow ones if they need to be larger.

You can go thirteen feet spans with six inch fourteen gauge purlins without any problems.

Since you have two and three eighths posts I suggest you consider a method of construction that I've had good luck with. I would go with eight inch purlins and here's how I would do it.

I would cut off my posts to their finished height. Then I would drill through one edge of the eight inch purlin. Let's say you're looking at the purlin from the end. What you see is the C. Now imagine a piece of pipe coming through the bottom flange of the C to rest on the inside of the top flange of the C. This connection gives you an added mechanical advantage if the welding skills aren't as good as they could be. The most difficult part is lining up the holes to be drilled.

Drilling the holes is not an easy operation. What I use is a half inch DeWalt drill that's big and has two handles. Even with that leverage when the hole saw makes that last spin a lot of the time it will want to bind up and wrap you around the purlin. So don't tackle this with a small drill and whatever you do, make sure you're braced when doing it.

You can also use an old method of mine for doing the side walls using the same drilling process. You go through the four inch piece of the four inch purlin with the drill bit. Then you can slide the purlins down the pipes. Again, you get a mechanical advantage.

The four inch purlin with the four inch in a horizontal position gives you a couple of things the conventional four inch vertical location doesn't offer. One is it more than doubles your lateral strength. Vertical strength isn't a critical consideration because when your attach your metal sheeting to the purlin you've picked up ungawdly vertical strength. What you're wanting is lateral, in and out, strength.

Another thing is offers is an easier way to frame in windows and doors if desired. What's really cool about this is you don't have to go to a steel supply and pay their price for a pre-hung door or window. The horizontal orientation enables you to frame up a box store pre-hung door or window at a fraction of the price.

It's also great to have a wall framed this way if you're wanting to insulate or add sheeting on the inside. You can attach the siding to the outside edge of the purlin and then place standard insulation between the wall and your inside sheeting whether it's wood or metal.

You can click on my signature and search my site for some examples of what I'm talking about. You can also do some searches here on TBN and see more examples of it.

Keep in mind that engineers are like attorneys. Sometimes you need them.

 

[jgrreed]

I know you are just poking fun but really I don't think they will be in the way?

Attached is an aerial view. Green will be the trailers, black is the sheeted sidewalls, and red is posts. Again sorry for my awesome paint skills.

Should be ok if you're careful. Just worried that if you bump one. It might push the others to failure, and that'd be bad....

 

[rjmack]

i'd take the pipe and build trusses.

you don't have to go to elaborate lengths fitting them up, just cut the angles, heat and hammer the ends partly flat, trim the heels of the flattened 45*s and weld them up

the first one is the toughest, after that just make copies right on top of the first one.:thumbsup:

you're going to have to a bit of cross bracing on the roof and the walls anyway. this way you can cross brace the underside of the trusses and the back corners of the building and the roof will hold the front corners and the ends true.

2cents

 

[powerstroke444e]

I did something along same lines I got a rail car full of metal cheap so I built a shed out of it. I think you will be fine with the posts in the middle and you may need to add a few extra braces. I used Z perlins and welded plates to attach them to the beams. You will have many people that don't understand why you built your way but it your happy with the set up build it.:thumbsup:

 

[bdog]

Thanks for the replies. Thinking of either going Harv's route with the 8" drilled purlins or LD1's idea of the channel iron. I don't have a drill big enough (or a hole saw) to drill the purlin so by the time I buy those I could probably have paid for the channel iron. Been busy welding my fence up so still thinking on this one. Me and a helper have burned 75 pounds of welding rods in the last couple weeks so we might be able to make what ever we put up stick.

 

[davo727]

I also like Harvs idea that 6 inch purlins would be great for you.

6 in by 2.5 inch 14 gauge purlins weigh about 3.22 lb per foot so since steel is sold by weight they will cost a little over 1/3 of what the 9lb per foot channel someone mentioned will.

You would have to hit those poles with a truck going 50 miles an hour to knock that building down, a little bump is not gonna do it.

Edit: Harvs method on the 8in purlins would be even better overkill.