Design Response Spectrum

[ben3929]

Can someone explain to me on how to use the design response spectrum curve? I developed the curve base on acceleration values that I determined for T0, Ts, 1, and TL periods. I also calculated approximate fundamental period of 2 story building frame. I am not sure what I need to compare next.

 

[mike20793]

I assume you are doing this by hand and not having a computer program do the design for you. Here is a brief overview. Once you have the building frequency, you need to find displacements using the equation of motion so you can plot the mode shapes. Once you have the mode shapes, you need to calculate participation factors and effective modal mass for each mode to substitute as m into F=ma. When you have that, you take the design spectral acceleration from the design response spectrum you generated (a in F=ma) and you can find the base shear by combining the nodal forces (F in F=ma) for each mode shape. There are various ways to combine the nodal forces such as square root of the sum of squares (SRSS, most frequently used), algebraic summation, cubic formulations, etc.

 

[KootK]

I am not sure what I need to compare next.

I`ve interpreted your question a bit differently from Mike. It sounds to me as though your next steps would be:

1) Enter your response spectrum graph with your building period and exit with a design acceleration.

2) Plug your design acceleration into the ASCE 7 to work out the base shear.

3) Distribute your forces to the various masses using ASCE 7 equations.

4) Start designing stuff.

Let us know if you need more detail.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[ben3929]

I think KootK answered my question. building period is between T0 and Ts therefore design acceleration will be same as SDS valve. Now how do I avoid resonance occurrence. building period is appx 0.2s and T0 and Ts are 0.09 and 0.452s respectively.

 

[JoshPlumSE]

Huh?

If there is something about the site that causes large accelerations at a particular natural period (think Mexico City) then the response spectrum plot would have that "resonance" built into it.

 

[KootK]

Now how do I avoid resonance occurrence.

Like Josh says, it`s baked in the cake. The fact that your acceleration will be higher (or sometimes lower) than the ground acceleration accounts for resonance.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[KootK]

Really, being on the constant acceleration plateau (SDS) implies that your building will be about a resonant at it would be possible to be given the amount of damping assumed.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[mike20793]

Sorry, it looks like I did misinterpret your question. I agree with the other posts above for the next steps. Good stuff.