mixing 15 and 20ft bays

[dannewhouse]

We are thinking of moving some 30ft spans 15ft bays to create a 125ft long 30ft wide shed (probably stand it up at 16ft to eaves) I want to put a side door in but I think 15ft is too small so was thinking of putting a 20ft bay in where the door is. I prefer timber purlins and fibre cement roof as the shed may be used for cattle at some point in its life. the 15 foot spans are all on 7" x 3" purlins but the 20 ft would want to be on 9" x 3" purlins.

has anyone done something similar?
I have debated having the 2 rafters (either side of the 20ft bay) equivalent of 2" lower and just putting something 2" under the 7" timbers such as a piece of box welded on the rafter but think this will look crap.
I have thought about leaving the rafters the same and notching 2" off the 9 x 3 s so they fit to the same level and then possibly put a piece of angle 150 x 75 x 6/8 to carry the rest ie welded onto the web of the rafter 2" below the flange.
I debated doubling up and just using 7 x 3 but put 2 in every spot? or even just 1 and risk it? (we have a telegraph pole building been up 60 year 15 foot bays 20 foot span (7x3 purlins on 9x3 rafters!) how much are our buildings over engineered?
less preferred option use a 7" Z purlin for the 20 ft bay but it will look like a miss match!

the two portals either side of the 20 ft bay are larger steel yet to be cut and welded etc there actually gable posts from a second hand building. 203 x 133.
the existing buildings are on smaller rafters so I don't want to go to all 20ft bays (180 x 100 legs 155 x 88 rafters)
thanks

 

[RWG Contracts]

use 9x3 notch the end end out, then weld a piece of angle iron in your web about 18 inch long for the 9x3 to sit on, this will reduce your purlin span to 17' and stop it sagging

 

[dannewhouse]

never thought of welding angle iron that direction would you use like a 75 x 75 x 8 or keep to the 150 and have the 150 length pointing down to give strength.

 

[multi power]

There is a few here with 20 ft bay on the end, bigger timber, they have sagged less than the rest of the bays

 

[RWG Contracts]

 

[RWG Contracts]

125x75x8 should be ample 150x75x10 is probably a bit over spec

 

[dannewhouse]

I was thinking by pointing the longer flange down it avoids having to notch out for the flange of the rafter or would you just use the angle as the cleat (even extend it to the other side of the rafter for the 7 x 3 from other side) not a bad idea seen as I have the cleats to put on all this steel work any way

 

[RWG Contracts]

Yeah can go other way up I just like it that way up because it stood them sagging down then roof if that makes sense. I know the ridge capping does that to a point

 

[Frank_farmer]

If you want it to look the same do them all 15ft. Then use one of those beams to miss out a column where the door is. You should be able to calculate beam with it new degree. Nice uniform shed then.

 

[Frank_farmer]

rwg have you done any of those beam sheds? Do they work ok?

 

[dannewhouse]

I debated doing that using a carrier beam to miss 1 column out but figure id be putting a column in at 20 ft any way and how I want to divide the shed up into straights bays fits better to a 20ft bay rather than a carrier beam idea

 

[RWG Contracts]

rwg have you done any of those beam sheds? Do they work ok?

Yeah done a few. They work fine makes a nice big space

 

[RWG Contracts]

just doing one now

I keep looking at drawing thinking there must be a more cost effective way of doing it but, this is how the customer wants it and he is right

 

[dannewhouse]

What's that drawn up on? does it scale etc or does it just give a rough image in its surroundings?
We use Autodesk Revit to do most stuff and can run the robot part extra to check hand calculations. you can pull sections out and dimension fully such as end plate or gusset dimensions etc

 

[RWG Contracts]

What's that drawn up on? does it scale etc or does it just give a rough image in its surroundings?
We use Autodesk Revit to do most stuff and can run the robot part extra to check hand calculations. you can pull sections out and dimension fully such as end plate or gusset dimensions etc

Google sketch up. It's free to download and it does everything. You can add a geo-location in to make sure the building you want will fit where you want it. Had one last week and he wanted it in a gap, got sketch up on laptop and drew the footprint out and kept moving it till he was happy. Could even see the black boxes over water pipes to avoid them.

You can take cross sections, does dimensions there's not a lot it doesn't do. For steel drawing I have stru cad as well but just for general cad work for planning ect and making gates sketch up is spot on

 

[SF1]

just doing one now

I keep looking at drawing thinking there must be a more cost effective way of doing it but, this is how the customer wants it and he is right
View attachment 272852

What size would the carrier beam have to be,quite alot of stress on it.
TIA. SF

 

[RWG Contracts]

What size would the carrier beam have to be,quite alot of stress on it.
TIA. SF

Depends on size of building.

There’s a load of extra tube bracing goes in roof to hold it as well

 

[SF1]

Yes i can imagine,more than 2 sets of braces either end.

 

[BobGreen]

What size would the carrier beam have to be,quite alot of stress on it.
TIA. SF

We did one to give a 40ft opening
Beam was bigger than the stanchions it was bolted to I seem to recall
Engineer design is the way to go

 

[Mrs Brown]

Keep it simple and use all 9"x3" purlins