Horizontal Truss in Ordinary Cantilevered Column System 1

[erictlee]

In the context of seismic design regulations, ASCE 7 allows for an exception in certain cases regarding the design of Steel Ordinary Cantilevered Column Systems. Specifically, in Seismic Design Categories D and E, ASCE 7 permits the use of provisions outlined in 12.2.5.6, typically reserved for Steel Ordinary Moment Frames. This implies that, aside from column detailing, the overall design should align with principles applicable to Ordinary Moment Frames.

Additionally, AISC 341, section B.5 (pages 9.1-10 and 9.1-11), offers guidance on incorporating a horizontal truss diaphragm within the framework of an Ordinary Moment Frame. Now, consider a scenario where a structure, either partially open or fully open, is designed with a pitched roof, featuring beams connected to the column with pinned connections, in a Seismic Design Category E region. Would it be permissible under these circumstances to implement a horizontal truss configuration in an ordinary cantilevered column system where none of the branches attach to the column, but tie the gables beams together in a truss bracing fashion?

The objective here is to alleviate weak axis demand on the gable frames by orienting them in the strong axis direction. While the columns maintain single curvature, it's noteworthy that the introduction of a horizontal truss introduces increased demand, particularly due to the biaxial component from both seismic directions.

 

[erictlee]

Adding a comment and an image to refresh to the top of the list this morning to see if anyone has any thoughts.

 

[JLNJ]

A picture might be worth 1000 words here, but it seems to me that the design of the columns, the column anchorages, and the foundations are the critical part of a cantilevered column system and this will remain unchanged when you introduce the horizontal truss.

 

[erictlee]

@JLNJ I have been having issues with attaching files, but hopefully the file is attached and helps.

My concern is the grey area of increasing the energy dissipation elsewhere in the frame while increasing the redundancy and overstrength of the frame in general. There certainly is an increase in inelastic behavior at the column base which is what is intended by OCCS framing.

 

[lexpatrie]

Use the image function folks. Then we can see the picture without having to download it and open it separately.