Beam-Column Joint Shear Failure

[yapitasarim]

Hi,

let's say you have to design a RC building in a highly seismic zone and your structure has highly ductile moment frames, aka Special Moment Frames. You have to design the beam-column connections of this structure, obviously. Let's say one of these connections has three beams of those special moment frames and one cantilever beam framing into this connection.

My question is: Would u neglect the cantilever beam while u design this connection? e.g. neglecting any kind of force transferred into the connection from this cantilever beam due to gravity and/or vertical component of the earthquake force etc.

U can refer to every code and/or explain technically why u would/not neglect the cantilever beam in such a connection. Thanks in advance.

 

[1503-44]

Alternatively, you could explain why you think it can be ignored.

Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[yapitasarim]

I don't think it can be ignored. But the Turkish engineers say that we can/should neglect the cantilever beam because:

1) It is not part of the Special Moment Frame or lateral load-resisting system

2) We will overdesign the joint if we take into account the ultimate moment capacity of the cantilever beams since the cantilever beam shouldn't go into the inelastic region. Because we don't design the cantilever beam to behave ductile.

 

[1503-44]

1) If you are only designing a frame for parallel forces, that might make some sense, but is that a realistic scenario? I don't think so. Even if you are designing for force in a direction 100% parallel to the frame, any load on the cantilever would tend to introduce lateral shear and torsion into the column, It is also not realistic to believe that earthquakes and wind loads always act parallel to the frame and probably tend to twist the column in one way or another. Torsion might be handled by floor framework, or lateral bracing and picked up by the perpendicular framework, which you have to confirm that is adequate to do so before anyone goes off ignoring cantilever contributions to Load.

2) True, it is not part of the resisting mechanism, but it is part of the mass supported by that structure, hence the potential loads that it will introduce.

Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[yapitasarim]

I agree with u.

 

[1503-44]

There is a structural eng forum.
Maybe others could comment if you reference this thread there.
Copy and paste the following there.

https://www.eng-tips.com/viewthread.cfm?qid=501208

Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."