Shear Wall on Beam (capacity design)? 2

[drile007]

Hi to all,

I am wondering how to design concrete beam which support shear wall loaded by earthquake. According to capacity design I have to protect the beam from collapse and avoid plastic hinges formed in the beam.

Okay, but which reduction factor should I use to calculate earthquake force. Can I consider small reductions or should I design a beam based on fully elastic earthquake forces?

Thank you for any toughts.

 

[HTURKAK]

Short answer ;

- This is at least Vertical Irregularity ( 12.3.3.3 Elements Supporting Discontinuous Walls or Frames.)
- The use of fully elastic earthquake forces may be overkill but at least you need to use overstrength factor .
- It is not a good idea to support shear wall on a beam .



Use it up, wear it out;
Make it do, or do without.

NEW ENGLAND MAXIM

 

[drile007]

Thank you @HTURKAK...ASCE-7 is something that I am unfamiliar with, so I am a bit confused.

When looking over Vertical Irregularity (12.3.3.3 Elements Supporting Discontinuous Walls or Frames) articles, I discovered that an overstrength factor should be applied. What does that mean? The elastic earthquake force should be divided or multiplied when designing a supporting beam?

 

[lexpatrie]

The connection is where the overstrength typically shows up. The connection needs to be stronger than the demand including the requirement for the overstrength factor, typically. If you have the AISC seismic design manual, it may be more clearly explained there....

 

[drile007]

Still confused about beam design...

1) Ok, connections should be design with elastic earthquake force multiplied with overstrength factor!?
2) But still don't know on which load should I design the beam under the shear wall? Elastic earthquake force should be divided or multiplied with overstrength factor?

 

[drile007]

BTW, I'm talking about reinforced concrete shear wall and beam.

 

[driftLimiter]

If your code allows ductility reduction (R factors), then you design the walls for the force corresponding with R Say this is Ve. The beam should be an amplified seismic force Ve x Overstrength.

Elastic earthquake forces are forces developed using no ductility reduction (R=1). If you use the elastic earthquake force, generally that would already include the effect of the Overstrength.

Ve = Cs*W
Cs = Sds/ R/I
Vomega = Ve*Omega


If there is still confusion, I recommend a through review of ASCE7 CH 11 and Ch12.
The answers to your questions are therein.