questions about a simple canopy 2

[greznik91]

I'm designing a steel canopy with hollow sections.
I need moment frames in both directions (X, Y) since I am not allowed to use any bracing between columns a and in a roof plane. All connections between columns and beams are welded. I was thinking about using full penetration welds (butt joints) – do contractors do this kind of welds on a field?
I figured that engineers usually use pinned supports for construction/collumns like this but in this case I think about fixed supports and put some stiffeners between column and base plate. But lateral forces will be small (there willbe no walls between columns so wind forces on construction will be small, and construction is pretty light so earthquake souldnt be a problem. May as well go with pinned supports... what do you think?

Have any suggestions about this?

There are timber beams in a roof plane that are in the same plane as steel beams. How would you fix timber beams to steel? Any detail, suggestion would be appreciated.

 

[Ron]

Yes, complete penetration welds can be done in the field. For your design, you can either fix the columns at their base or use moment connections at the beams-to-column connections but you don't need both.

Not sure what codes you're designing to but make sure you require nondestructive testing of any complete penetration welds.

Also, what you have sketched is not a butt joint. You have corner and tee joints. It makes a difference.

 

[Once20036]

Why are you intending to use full pen welds? A fillet weld can develop a moment connection just the same as a full pen weld can, but its a lot less expensive. I only call for full pen when my loads are high or when I`m being lazy.

I think that the timber/steel connection is largely dependent on the aesthetics and the size of the timber. I don't have any experience with wood, but if it were my house, I'd consider a simspon joist hanger attached to the HSS with self tapping screws. If that aesthetic isn't appropriate, they have a "knife plate" column base that gets slotted into an HSS6x6 post. I'd look to see if they have published shear capacities and whether or not that would work for you.

 

[greznik91]

Once20036 - Id use fillet welds, but I dont see how since beam and column is the same width. I cant make vertical fillet welds becuse of that.

thanks for help to both.

 

[Stenbrook]

For these type of canopies I almost ALWAYS fix the base. The moment is so small that usually you don't have to do anything special with the baseplate and you avoid expensive connections at the top.

 

[Nor Cal SE]

Two thoughts:

1) There is another option that might make your connections simpler and reduce cost: ordinary cantilever column system. Are you using ASCE 7-10 as applicable code? Though your ASCE seismic R-value would be less than moment frame, leading to higher seismic load, you've already noted that seismic load should be small. And if your wind load, albeit also small, already governs over seismic by quite a bit, then the R-value reduction wouldn't penalize you. What I'm picturing in a practical sense, to create the ordinary cantilever column system, is having the column fixed for moment restraint to the base plate (similar to what you've already shown, though you might not necessarily need the gussets). These welds can all be performed in the shop. And then at the top connection you would not need any type of moment/rotation restraint like you would in the moment frame system, therefore not needing full-pen field welds.

2) For your wood beams framing into the steel beams in the same plane, you might just need to make a type of steel bent plate "seat" that bends around the sides and base of the wood beam with thru bolt through the wood, and then either screws, bolts, or weld from bent plate to steel web. This would essentially be like a custom version of a Simpson joist hanger, if that makes sense.

 

[dik]

Can you do it in timber with knee braces? If steel, can you use a 5" wide HSS ring beam at the top; it fits on a 4x4 column better and run the beam past the column and use a fillet weld around the column. Fillet weld can be as much as the 4x4, but usually go +10% of the 4x4 (CIDECT has test information that a fillet weld can be +10% and nearly provides the capacity as a full penetration weld). I usually design HSS for 70% to 80% of its load capacity to avoid the need for full penetration welds. Also have a vent hole at the bottom with a plastic plug in case water ends up in the HSS column and you have freezing conditions.

Added: Should have asked about your coating system? Is the 'box' shipped to site as a single unit?

Can you make your base plate thick enough so you can avoid gussets? Gussets can be a hazard around people walking.

Dik

 

[greznik91]

tnx for all replies. Im from EU so we use Eurocodes.
I see there are some suggestions to make a system as cantilever columns - that means supports are fixed and other connection can be pinned. It make sense since lateral loads are small and we avoid welding at column - beam connections, but what I particularly dont like in this case is making bolt connections of hollow sections - they are actually pretty uneasy to do.

dik - elements will be connected on a field. it has to be a 'clean' steel structure. thats why I was thinking about weld connections. i was thinking about gussets since they can be a hazard as dik mentioned. Well i think they can make a finishing layer (sorry for my English) 2 or 3'' thick so gussets are hidden. Beams cant pass columns, so if i want to use fillet welds my only option is to make beam width smaller than column width and weld beam to the column.

 

[mats12]

Id choose option 1 with pinned supports