Cantilever/Moment Connection

[hemal1214]

I am designing a couple of cantilever connection for a parking structure. The design of beams and columns are not very complicated. However, the connections design is very interesting. I have attached a .pdf file for reference. I need:

1) A design guide for beam to beam moment connection.
2) The cantilever connection between column and beam has two options:
a) Main beam (one piece)going over the top of column and cantilevered each side
b) Main beam(two pieces)are connected to the column flange as moment connection.
The question is which is a better connection design approach and why?

Any other suggestions for member and their connection design? I was thinking to design main cantilevered beams as plate girder tapered cantilever end to support end.

Thanks

 

[msquared48]

12 stall parking structure?

"a." is the better option if for nothing else than inherent continuity and fewer pieces.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[Keneng99]

I agree with Mike, a is a better detail. Would look to "haunch" the top of the column to get additional strength / stiffness at this critical location
If the structure only has one row of columns I am surprised that columns are not box sections (would examine torsional rigidity /strength of the structure which could be another issue)

 

[rowingengineer]

I agree with Mike, I will also hope you have vibrations & unequal loadings covered. A cantilever on a cantilever in a carpark structure is always interesting unless it is the roof.

ANY FOOL CAN DESIGN A STRUCTURE. IT TAKES AN ENGINEER TO DESIGN A CONNECTION.”

 

[RFreund]

Not to take away from the OP but...
Keneng99 what are you referring to when you say the torsional strength/rigidity. Would you mind expanding on this? Are you referring to wind/EQ causing a torsional loading in the plane of the diaphragm? Wouldn't this just resolve in to T-C couples?

Thanks!

EIT

 

[ztengguy]

For a canopy you will also have uplift too? That could change things. Also, how are you handling redundancy with just one set of columns, any provisions for impact on the columns?

 

[SteelPE]

I agree with m^2.

About a year ago I designed a similar structure for some people who wanted to use it to support solar panels in parking lots. I went through the conceptual design and prepared some preliminary sketches for pricing. About 6 months later, I found out the company I did the work for took my design (that I never got paid for) tweaked it a little bit and then took it to the construction phase. I am still not happy with that one.

Anyway, with my design we had a cantilever column and cantilever primary beams. However, the roof was slopped to the center line of columns, so we had a beam that was split and moment connected back together in the shop to form the slopped roof.

One thing we did was use single piece secondary roof beams that framed over the top of the primary roof beams. This eliminated the beam to beam moment connection you are referring to above. You can save some money and end up with a better structure by eliminating that connection.

 

[hemal1214]

@SteelPE:

When you designed your structure you had cantilever primary beam on both side of the column or just on one side? I have cantilever sloped beam on both sides. As I have cantilever primary beams on both sides of columns, I am getting a large moment at column base for unbalanced snow load. So, I will need to design the base plate and anchor bolt for small axial load and large moment. I am using the AISC guide 1 for base plate and anchor bolt design (design example 4.7 for reference). When I tried to solve for Y, I am getting two answers as per the example. The answers didn't make a sense to me as one was almost double the actual plate size (e.g. 46" for 24" plate size) and the second was (3" for the same 24" plate size). Is it a possible answer?

I am sure if you have cantilever beam on one side only you must have designed the column, base plate, anchor bolts, piers and footing for moment connections and you might have come across the same issues that I am dealing with.

I am using the secondary beam on top of primary cantilevered beams.

 

[SteelPE]

hemal1214,

Basically what I was going to have the fabricator cut a beam in the shop and weld it back together to get the bend the client wanted. I was then going have a moment connection from the column to the primary cantilever beams. Everything was prepared as to allow for field bolting only (no welding).

I did this work for a fabricator who sent the information to the client. The client took most of what I did and then finished up the details. I never got down to foundation or base plate size. I only had a loose idea on what I was going to do.

I would expect the forces to be large at the base. I have written spreadsheets for DG1 (now they are very dated) and I use other programs that help with the design at the base so I was not to worried.