Steel Canopy 2

[Murali27]

In one of my job, architects wants to have a steel canopy projecting 6m as a pure cantilever, without any tension wires, supporting glass.

This is at the main entrance of the building.

Is there a vibration issue due to local wind gusts?

 

[csd72]

6m is not that far, I have done 9m cantilevers before.

If the cantilever is rigid enough then I would not expect vibration to be an issue.

Precamber it, and design it for a deflection of L/250 to ensure the dead load sag is not visible.

You also may need to check the rotation due to the supporting structure.

 

[Murali27]

Thanks for your reply

The cantilever (probably tapered hollow section) support is attached to a concrete beam which is running over columns.

As you said, it is better to attach on columns, if sections are ok for architect.

Design gust wind speed is around 48 m/s at this site. Vibration and reponse factor could be checked with assumed frequency range for winds. I am just to feel the numbers, hope that it is not critical

 

[csd72]

The critical item for this will be the connection into the concrete frame.

Assuming this is a new building, then it could be an embedded plate.

Dont forget the check the beams for torsion and the frames for additional sway from the wind on the canopy.

 

[Murali27]

Yes, this is a new building, 30 stories.

Columns are heavily loaded subjected to shorten around 20 mm after we attach the canopy, due to secondary effects.

Can we come out of this issue with slotted holes in embedded plate?

 

[csd72]

20mm seems high, are you sure this is not for the whole building?

Embedded plates are usually solid plates with rebar welded to the back of them, they are embedded into the concrete and then the canopy is welded to them. This is a fairly common practice with precast concrete (PC), so you should look at publications on PC for guidance.

 

[hokie66]

Agree with csd72 that your columns should not shorten 20mm at the ground floor level. This is probably the shortening over the height of the column. There should be no need for slotted holes or other means of adjustment. At any rate, I would think that the canopy would be erected late in the schedule.

As well as embedded plates, you could consider casting in anchor bolts to develop the bending moments and shear from the cantilever. Either way, be sure to fully develop the hollow section cantilever member to the end plate. Full strength welds will require backing strips.

 

[Murali27]

Apologies for that, this is a over the full height of the building.

Thanks for your input.