Cantilever Canopy Seems ok....can anyone confirm? 1

[Hemi79]

So Im attaching a cantilever canopy I'm running. It seems to good to be true and I was wondering whether anyone might look at it and give me some pointers. The canopy only extends (cantilevers) 5 ft and is attached to a masonry wall that has vertical reinforced concrete fill every 32 inches on center. I was hoping the architect would want aluminum but he put it on us to do with steel. Im using a channel against the masonry wall (2 A325 bolts @ 32"O.C.) and Wide Flange beams extending 5 ft. @ 5 ft. O.C. and standing seam panel over them. Any help is appreciated.

Thanks!

ps. I tried using pin connection for the beam connectors and always got instabilities at every cantilevered joint. I figures I'd allow the moment at the connecting end instead (Weld, is this the best approach?

 

[Hemi79]

sorry here is the file.

 

[JoshPlumSE]

1) You're using the "open structure" wind loads. This feature only applies load to the cross sectional area of your members. If you've got a steel deck wood deck over this (heck, even if you've only got dense fabric), you'll want your wind load applied to the whole area instead.

2) You're using LRFD load combinations. However, the design code (on the Codes tab of the Global-Model Settings) is set to ASD.

3) You've got boundary conditions at the base of every one of your cantilevers. Therefore, your channel will not be taking ANY loading other than it's self weight.

4) Your channel isn't going to be 73ft long in reality. If I were you I'd break it up into smaller pieces. That way, the moment, shear and torsion diagrams RISA gives you for each member will have a bit more granularity.... Meaning the program only uses a certain number of data points (approximately 100 for your file) when plotting these diagrams. That way you will not longer have diagrams that look like this:

I hope that helped!

Josh

 

[jayrod12]

edited: Josh's review is much more comprehensive than mine.

 

[Hemi79]

@joshplum Thanks for that break down. Very helpful! I've added plates and applied surface loads. What do you suggest for the mesh on it? When doing so I get huge deflection on the nodes of of the plates. Again , thank you.

@jayrod12 Thanks for reading.

 

[JoshPlumSE]

I would have used the regular member area loads rather than use plates. You actually applied the area load correctly. You just chose the wrong "Distribution" direction. You chose "Open Structure" when you probably wanted to choose "B-C".

It's a little confusing at first. But, when you create the area load, the 1st node is A, the 2nd is B, 3rd is, and the 4th is B. Within this context, the B-C direction means the distribution direction is parallel to a line that connects nodes B and C. That would make the distribution direction perpendicular to your cantilevers. Just like if you had metal deck spanning in that direction. You'll even get a little arrow in the model view showing you the distribution direction.

The problem with using plates is that they have stiffness and you'll get more of a two way distribution than the 1-way distribution you probably wanted. If a two way distribution is what you want, you could still use member area loads (with a distribution direction of "Two Way"). If you're really keen on using plates to model a concrete deck or something then go ahead. But, I would mesh it pretty good. I try to us a minimum of 3 plate between points of inflection. So, I'd say something like 7 plate between each cantilever.

 

[oldrunner]

I hope that someone also checks your connection to the partially filled concrete block wall. The A325 bolts make me uncomfortable. I would run any bolted connection through the block wall (thickness unknown) and have a plate on the interior of the wall. You probably can not buy A325 bolts long enough for that.

 

[Hemi79]

@joshplum thanks a bunch for all the help.. I did add the loads how you recommended and not applying to plates. And I played with a couple load distribution directions. Thanks for all the help.

@oldrunner, thanks for the recommendation. I have used A325 bolts up to 7 inches. However, for every inch after a factor on diameter you loose a percentage of its capacity by AISC. I don't remember the factor but it is considerable when using up to 7 inches. To be honest I'm not very comfortable with the plate on the other side either. I feel like once the tension capacity on the concrete is met that canopy still goes out, but I do suppose it is a lot safer. However, I'm not comfortable relying on the concrete anchor alone for a cantilevered member but everyone here calls me a rookie for insisting on adding supports on the other end even if at large on center spacing.