Structural engineer type question.
 

Hi Guys.

I'm planning on building a per pergola type structure with a glass roof. I'll have six rolled Steel Joists 100mm x 45mm each doing a 5m span. They will be supporting six sheets of glass weighing about 50kg each. So each RSJ (I-Beam) will be supporting about 125kg.

The question... Is a five meter span OK for this amount of weight?

It will look something like the below pic' but bigger and different. I just googled for the pic to help explain the structure.

LOL sorry, here is the pic'.

http://forums.pelicanparts.com/uploa...1598752127.jpg

must be all glass...can't see it.

That works! Looks nice. What about cleaning the glass?

I won't get too fussy about the glass. It's a bit stained anyway. They were windows in an office building in town that had a failure of the e-coating or something. They are two square meter sheets 10mm thick and safety glass. I made a smaller six square meter patio roof for over the front door a a few years ago and love it. Light pours into the house while keeping rain and wind away.

I’d need to see the cross section of the rafters to make a determination of whether you are in the ball park. I’m guessing no snow load to consider...

The rafters are an I-Beam shape. 45mm across the top and bottom. 100mm from top to bottom with a thickness of 4mm.

And no snow. A run off for rain so angled about 15 degrees.

Thanks for taking an interest you guys!

Steel or aluminum?

Steel.

That changes a lot. You got it easy.

So only thing to worry about is wind shear.
What is the kit rated for?

You want the attachment points to be tight. Grade 5 or even Grade 8 bolts through both runs.
Some angle braces to keep it square.
Washers to spread the load.
The base bolts into concrete and/or backed up with deep ground implants using cables.

Steel will rust eventually.
Give all the pieces a few extra coats of enamel in your preferred color before installing it.

It's sounding quite positive :)

It's windy here, but one side will be bolted to the house and another side to a concrete wall. The other side will have a large (high density PSI concrete) foundation sitting on the hard rock pan a couple of meters underground. I'll use 304 stainless steel 12mm bolts to hold it together and get it all hot dipped galvanized.

Things really rust here John. I get extra thick galvanizing done and use stainless fasteners wherever I can.

Around here, S.E. Michigan is all heavy clay soil which buckles and heaves with the snow and cold.
So nothing external attached to any solid foundation would be considered "permanent".

We also get the occasional 100degF summer and the -20degF winter.
(Probably less than Chicago and NYC or the upper East Coast though).

Sitting in sand, you probably want the frame pieces to be attached solid into the ground.
Make the flat sections disposable.
Any new drilling needs a shot of sealant spray.

Will the sides be open or closed up?

If they're open...
The Steel should be strong enough to hold the weight but I'd be concerned about the wind load.

We're pretty lucky here. In winter it doesn't get below 46degF and summer doesn't get much above 78degF.

There is a very weird hard rock pan a couple of meters down. It's like solidified iron sand that I can barely scuff the surface of with a crow bar. GF has engineers specs for a deck she is getting made for her house, so I thought I'd just copy then double the spec's for the footprint of the foundation. And have it on the rock pan.

Wind load and possibly seismic are concerns. How are you addressing shear / lateral forces?

Nope. I wouldn't have a clue.

In extreme cases of wind:

If the vertical posts are very hollow and weak, add curved braces/brackets which extend below center-line of the post. Or at least a 1/3 down the post.
These can be made of 1/2" steel for example. Or 2x16 wood cut down. Or LVL. Whatever works. Anything is better than no triangulation.
The world is your oyster as to design.
Very strong but also decorative.

That will help keep things square to lateral/side forces.

An open top such as lattice will let air flow through but provide some shade.
A solid top will provide rain cover but might act as a sail and try to pull on the entire structure.

I bought some used steel that had come from powerline pylons. it's already galvanized too. It's U-Channel steel 150mm x 75mm and 7mm thick in the web. i'll be using this for the posts.

And with one side of the pergola attached to the house, the other to a concrete wall, i'm guessing it's good for lateral/side forces.

Just remember that new posts will probably want to sink a bit at first, and pull attached structure such as the house with it.

Boxed steel is much stronger.
U-Channel is open and tends to dig itself into the ground. Be warned.
You could weld brace tabs on later I suppose. Cut them fashionable.

Any vertical posts should sit on top of concrete-filled sono-tubes 4' below ground at the very least in frost/cold zones.
Something solid. Foundation is everything.
There will still be some minor shifting though.

I've got some 100mm flat steel that I was going to weld on the ends as "feet" then use 12mm SS bolts to gal' steel set in the concrete foundation.

I was planning on making the thing, fine tuning it, then pulling it to bits and getting the RSJ joists/rafters galvanized. So hopefully the bedding down would happen before everything was finished.

Thanks for being so helpful and sharing your knowledge John. Are you a structural engineer to know this stuff?

No not an engineer. Sorry to pretend to be knowledgeable on the internet.
(Please disregard this fool.)
I've learned from my many house mistakes twice-over, having been through it, and just trying to help out another.

Well, your help is much appreciated. Very much appreciated.

I had to google 5 meters:)

That steel is 100mm, so that's about 4+ inches. The span is 16'. That's a bit long but I am not an engineer. My fear is flex and sag. Only 3/16 thick or 4mm? Im not an engineer so I am waiting for the smart folks for their calc

I was looking at some car ports on the internet.
-One was rated at 75mph wind.

-A similar looking one from a major box store was rated at 25 mph.
(Yeah you read that correct. US Government federally-approved. 25mph.)
Your car might have mandated crumple zones and seat belts and airbags and and tire pressure monitors and computer ABS, but you will still get crushed just sitting there in the driveway.

-A good looking chinese knock-off was rated at 7mph after much digging at the specs.
The metal pieces were paper-thin upon further visual inspection.
Serious WTF territory.

The manufacturer should have a quick answer if that I-beam will span that distance.
And what the spacing should be.
I would email them.

5 meters = 5 yards and a bit haha.

Good thinking re email the manufacturer.

Or I could up size it a little from 100mm to 125mm web (height).

Judging from those numbers, I would up size a bit jsut to take the flex out. Glass do not like to be flexed, well, not that much. Get Low E glass.

Yes, this particular glass is weird stuff, it's old windows from a tower type office building in town. I accidentally broke a couple a couple of sheets and they sounded like a pistol bullet going off and broke up into dice sized pieces like car windows used to.

Either that or the neighbor was shooting at me and got the glass instead.

How did you break it? Must be tempered glass. Did you sit the edge on concrete and it shattered? Ask me how I found out.

I am not sure about putting that glass on top especially if its 16' or 5 meter span? That's a lot of glass if it goes. I know you already have it on hand, but I would seriously consider new pieces like a laminated glass like a windshield. I wouldn't put that in someone's house. Too much liability especially without engineering or stamping their name in blood on this one.

One sheet I had the glass clamps (things you pick up sheets of glass with) too close to the edge and I think it put a slight bend i the glass and created a weak point on the edge. the other one I very slightly tapped it on the edge with a hammer. LOL although it was a hammer I barely tapped it.

We are pretty rough here in NZ. We re use a lot of stuff to save money - and to make projects happen that would otherwise be unaffordable.

I am in a different situation then you, Bill. I have to delivery a safe product or else I will be in some deep poo. You should see when I bought my home 20 years ago at age 29, a total fixer. I used whatever possible knowing is good enough for a few years, I did it. Do it again or right when the money comes through at a later day. Got married a few years later, then I got serious because there's someone else in the house and kids will be coming, so I tore it out and rebuild everything taking out the sharp edges. I rebuild about 90 % of my house because of "Those people"

What do you mean by pretty rough? The economy is still strong down there before covid?

Sounds like tempered glass. It exploded into a thousand little pieces?

Early Pyrex baking dishes did that. I had that happen.

Maybe I should describe us as "overly practical".

Yes, the economy is fine, were doing OK. A good standard of living around the place.

Maybe it is tempered glass. It broke like car windscreens used to break back in the 1970's. Yes a thousand little squares.

You must watch too much American TV. We are portrayed as living large in million dollars beach front properties. That's not true at all. Across the nation, we are a pretty practical group.

Haha, we grew up on American TV. Walt Disney comics...

GF watches Million Dollar listings (Altman brothers) I have real trouble explaining to her that not all of the US is like that. I've been to about 12 states, and stepped foot in Mexico and Canada, so I'm pretty realistic about what goes on in the place.

Design factor in some cases:
I have a similar structure on my ocean front home in Baja MX.(Solarium)
Had to take into consideration the condensation that occurs on the inside surface certain times of the year (foggy/sunny days)
Installed evaporation trays on low end of properly angled panes, to low a pane install angle leads to dripping instead of laminar flow on inside glass surface. Condensate flows into trays and evaporates instead of drip marks on wood tile.

No bad days in Baja, peace, love & fish tacos

I would make the feet adjustable or shimable.

There are span and load charts online...and formulae...

Yes, find and use those like a professional would.

Notice closely the "T" brackets at the top of the columns in the original post as well. These eliminate need for diagonal bracing.

At the bottom of the column will be equal measures as well.

These not only laterally stabilize the structure they work to transfer UPLIFT loads.

The roof acts like an airplane wing, hence the reason for tie-down straps and brackets in the building code.

Oshkosh Archives - Arizona Flight Training Workgroup
http://forums.pelicanparts.com/uploa...1598825848.jpg

Precautions taken at the Oshkosh Airventure to tie aircraft down and ballast them may serve as a reminder.

Similarly your footings should be sized not only for gravity loads but for uplift as well.

If you pay a structural engineer for a couple hours of review time it will be well worth the $120 an hour in my opinion.