Portal Frame 1

[BadgerPE]

Hi all. I am working on a project in which we are designing a large addition to be added to an existing two story building. The new addition will be built in such a fashion that it matches up with the roof line, exterior walls, etc. The wall dividing the new and old portions of the building is currently a shear carrying wall. However, the architect is proposing to remove the first floor wall to create a large open room between the new and old structures. Without any interior walls capable of picking up the shear, it has been decided that the best course of action may be to install a steel moment resisting frame inside the first floor wall opening. My question is, how do you properly model the columns of the frame for the wind loading applied? Do you apply the resultant wind load from the tributary area of the frame to a specific point, or do you model it as a distributed load acting over the full length of the column. Any help would be greatly appreciated!

 

[ToadJones]

A lot will depend on how the new frame is detailed and attached to the existing structure. Most frames like this I analyze with a distributed wind load along the column even though, in most cases for me, there are girts attached every 5-8 feet.

 

[ToadJones]

....because in the design stage, you sometimes dont know where the girts or facade will attach. In your case, you probably will.

 

[paddingtongreen]

On a similar situation, I designed the end of the new building to take the shear from the old building as well as the new. The new frame was tied to the old building with diagonals, tension and compression, with a long,side-to-side dimension and a short, end-to-end dimension.

If say the old and new bents were 4'-0" apart, I made the connections at least 20'-0" apart. Using tension and compression meant no net longitudinal transfer, just the shear and the resulting moment from that shear, in the new building.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[ToadJones]

Pad-
Your post is hard to follow, but has me interested.
Can you clarify?

 

[BAretired]

If it looks anything like the attached sketch, I would apply the wind force at the Second Floor level.

BA

 

[apsix]

If the walls are predominantly spanning between floors/roof (and not between columns) then wind load should be applied as a point load at floor/roof level.

 

[Ron]

How you apply the load to the portal frame depends on how the existing wall is framed. If it is acting as a shear diaphragm, then you can probably distribute the load on the column. If it is a shear frame, then a resultant at the top of the column would be more appropriate, with girts or struts to the shear frame, as ToadJones noted.