Is this connection doable? 4

[DanAndrews]

Hi fellows,

I have this 3.8m cantilever canopy to design. I am going to use 150SHS @ 1m spacing by using the fix connection to slab. There is 60 set down.

I am proposing the following connection to do the moment connection work. The design moment is 7.5kNm per SHS. Then I am assuming the level arm 75mm which gives me 100kN T/C to design to. Do you see any problem with this design? Is there any other way you would recommend? (note that I cannot extend the SHS to the back of the slab). Thank you.

 

[NorthCivil]

That aint gonna hold.

how about some cables to suspend the end of canopy?

alternatively, these outriggers welded to a structural box section, mounted to some sort of frame?

 

[DanAndrews]

Thank you. Can you please explain why it is not gonna work? I would expect T/C to form a moment connection here.
Cables cannot be used here unfortunately.
By box section you mean replace the EA with SHS?

 

[dik]

You have about a 12' cantilever connected to about 4" deep concrete. Can you drop the slab at the end to the underside of the HSS, put a solid 1/2" or 3/4" end plate for the full depth of the concrete slab and attach it with headed studs near the top of the slab? then weld the HSS to the end plate... how large a moment are you looking at?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[dik]

Something like:

The slab soffet on the left can go horizontal to the steel plate if formwork allows (just means the plate gets thicker)... and the headed studs can be adjusted.


Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[DanAndrews]

Thanks dik. Is this the one you are proposing?

I can make the slab thicker or have a step as what you proposed. The reason I didn't want to do this was because I have cantilever facades like this canopy that is connecting to the 150 precast walls under for this project as well. So even if I can do this for slab one it will be hard to do so for precast wall(I don't think make a step in precast wall or the end thicker is practical?).

The moment is 7.5kNm per outrigger.


(Sorry I just saw you posting a sketch as well)

 

[dik]

That can work, or if the HSS has to be below, the plate can be extended down. The plate can be thicker and the top headed stud can have 40mm or slightly less for cover.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[dik]

That works...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[dik]

The angle at the slab soffit is flexible and reduces the stiffness of the connection, and the moment is relatively small.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[DanAndrews]

Thank you dik.
Like I said, I have this scenario for my cantilever facade to 150 precast wall as well. Do you think it is practical to locally thicken my precast walls at ends or can I make a stiffer EA or other steel like I proposed at the beginning to do the same work?

Also, won't it be better if I use welded bars instead of studs so I don't have edge distance for concrete breakout / pullout issue?
Thank you.

 

[dik]

I'm not sure what you mean for the first question... as far as rebar goes, you can use headed studs or rebar... both work. If concerned about breakout then rebar is better and you can get weldable rebar 'studs', although depending on your area and welders, normal weldable rebar may be less costly.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[dik]

you can do this...

It may be a forming issue and there may be some fire resistance rating issues.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[DanAndrews]

Let's say the spacing between top & bottom studs is 70mm, leaving 40mm edge distance for the studs, which is too small? I believe for rebars we can use bond strength instead so breakout is not an issue here while it is not the case for studs/anchors?

 

[dik]

Sure... either works. I'm not sure what the minimum edge distance for studs are or what the environment is... with 40mm you should be able to get some sort of anchors into it. I think that rebar is a better solution and works better.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Tomfh]

Personally I wouldn't be happy with a 3.8m awning offset and cantilevered from a 150 slab like that.

 

[dik]

Depends on the flexibility of the connection, but the moment isn't excessive. The moment is about 6 k-ft and the resistance of the HSS is likely greater than 30 k-ft (35, I think for 1/4" wall thickness). The proposed conn had an angle at the bottom which would make the connection a lot more flexible... 3/16 fillet weld on 3 or 4 sides should give ample resistance. I'll quickly check... without a detailed check, it appears that 1/4" weld on 3 sides, or 3/16" weld on 4 sides works... just a matter of deflection and serviceablity.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Tomfh]

I’m not concerned about the tube or even the end plate per se, it’s more the arrangement of forces going into the slab edge, in particular 100kN bearing onto the bottom edge of the slab.

 

[dik]

I missed the 100kN... the moment in the slab edge was 7.5kN-m which is about 1/5 of the HSS capacity, and maybe 10kN shear I thought.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[human909]

My understanding is that it is only 50kN and that DanAndrews made a mistake with resolving the moment. But then it really depends on what his detail is. Because if you start bringing your reinforcing or studs close to then centre then yeah you get 100kN of tension. Not pretty.

 

[Tomfh]

50kN would be a 150mm lever arm. The overall slab depth is only 150mm.