SCBF

[MOOK]

In the SCBF

1- Should we consider the whole seismic force on one side of the SCBF or should we divide the Seismic force and apply each half on each side of the SCBF?

2- If the SCBF is subjected to gravity loads (Dead + Live), should we consider the bracing to support part of this load or should we consider the bracing to resist seismic force only??

Is there anything in any code about that?

Thanks

 

[McEngr]

In the SCBF1- Should we consider the whole seismic force on one side of the SCBF or should we divide the Seismic force and apply each half on each side of the SCBF?

2- If the SCBF is subjected to gravity loads (Dead + Live), should we consider the bracing to support part of this load or should we consider the bracing to resist seismic force only??

Is there anything in any code about that?

Thanks

1- IF you apply it concentrically to the beam when you model it, it should distribute it proportionately. If it's giving you hangups because you chose a weak beam, then it's ok to apply to both sides as it collects the load from the diaphragm to the adjacent beams anyhow.

2- This is a loaded question. Have you ever designed a steel building in high seismic? You need to model it according to ASCE 7 load combinations. More specifically, section 12.4 (or in that realm - no codebook at home). Also note that the size of the brace per AISC 341 is controlled by the maximum force delivered to the system. You're essentially designing the brace to behave in its plastic zone to determine what the strength forces are to the rest of the braced frame (very tough to explain if you haven't done a real-life problem).

 

[MOOK]

In the SCBF1- Should we consider the whole seismic force on one side of the SCBF or should we divide the Seismic force and apply each half on each side of the SCBF?

2- If the SCBF is subjected to gravity loads (Dead + Live), should we consider the bracing to support part of this load or should we consider the bracing to resist seismic force only??

Is there anything in any code about that?

Thanks

1- IF you apply it concentrically to the beam when you model it, it should distribute it proportionately. If it's giving you hangups because you chose a weak beam, then it's ok to apply to both sides as it collects the load from the diaphragm to the adjacent beams anyhow.

2- This is a loaded question. Have you ever designed a steel building in high seismic? You need to model it according to ASCE 7 load combinations. More specifically, section 12.4 (or in that realm - no codebook at home). Also note that the size of the brace per AISC 341 is controlled by the maximum force delivered to the system. You're essentially designing the brace to behave in its plastic zone to determine what the strength forces are to the rest of the braced frame (very tough to explain if you haven't done a real-life problem).

Thanks McEngr for your answers

Unfortunately, I do not do buildings. All my experience is in oil and gas industry designing Non-building structures. However, my questions were regarding the exam more than real life.

Let me be more specific. If you got a problem of SCBF with Dead load, Live Load and Horizontal Seismic Force, would you use the bracing to resist part of the dead and live load or use the beam to resist the whole gravity loads??

 

[kevo_55]

Mook,

The short (ie: testbook) answer is no. The braces in BF systems are ment to resist lateral forces only.

I hope this helps.

 

[McEngr]

Mook,
The short (ie: testbook) answer is no. The braces in BF systems are ment to resist lateral forces only.

I hope this helps.

Also see the following attachment which comes from ASCE 7 section 12.7 which gives guidelines on how to model a structural system for seismic forces. I've argued with SE's that model a frame with a fixed base as I don't think it's a "true" model of what's happening unless it's actually fixed base columns, but that can be discussed in another thread as I don't think it answers your question.

 

[MOOK]

Thanks Guys for your answers

Kevo, is this common practice or something in the code?

 

[kevo_55]

It's in the code for inverted "V" braces, but I would think that it's more common sense.

Load always wants to get to the ground in the easiest way possible. For gravity, it will simply move via the columns.