Response Spectra Analysis
Response Spectra Analysis
(OP)
I have defined the response spectra in both direction
SPECX
U1 = UBC97FUNC = 9.81m/s^2
U2 = -------- = ---------
SPECY
U1 = -------- = ---------
U2 = UBC97FUNC = 9.81m/s^2
Then, Analyzed and view the story shears
I have noticed that static and dynamic values is the same for both direction
Story Load Loc P VX VY
STORY1 EQX Top 0 -291.16 0
STORY1 EQX Bottom 0 -291.16 0
STORY1 EQY Top 0 0 -291.16
STORY1 EQY Bottom 0 0 -291.16
STORY1 SPECX Top 0 1058.4 0
STORY1 SPECX Bottom 0 1058.4 0
STORY1 SPECY Top 0 0 1058.4
STORY1 SPECY Bottom 0 0 1058.4
Why is that?
Do I have to get the first direction first then move on to other direction to get the correct scaling factor?
I defined SPECCOMB in RS definition as a combination of both direction. Is this correct?
Pls. Advise
Thanks
SPECX
U1 = UBC97FUNC = 9.81m/s^2
U2 = -------- = ---------
SPECY
U1 = -------- = ---------
U2 = UBC97FUNC = 9.81m/s^2
Then, Analyzed and view the story shears
I have noticed that static and dynamic values is the same for both direction
Story Load Loc P VX VY
STORY1 EQX Top 0 -291.16 0
STORY1 EQX Bottom 0 -291.16 0
STORY1 EQY Top 0 0 -291.16
STORY1 EQY Bottom 0 0 -291.16
STORY1 SPECX Top 0 1058.4 0
STORY1 SPECX Bottom 0 1058.4 0
STORY1 SPECY Top 0 0 1058.4
STORY1 SPECY Bottom 0 0 1058.4
Why is that?
Do I have to get the first direction first then move on to other direction to get the correct scaling factor?
I defined SPECCOMB in RS definition as a combination of both direction. Is this correct?
Pls. Advise
Thanks





RE: Response Spectra Analysis
Check the following thread, hope it will help you.
http://www.eng-tips.com/viewthread.cfm?qid=233037
http://www.eng-tips.com/viewthread.cfm?qid=236265
RE: Response Spectra Analysis
Thank you for your quick response.
I have check that link you've given. As, expected We have the same values for scaling factors except for the Y-direction. You got 102.82, but in my solution I get 103.03. Please take a look at it so I can correct my self if I miss something.
I have the same problem with aqibusman. I am getting different results in dynamic base shear when getting it straight in story shears rather than in response spectrum base reaction which I think this two "should" be the same. Is there something wrong with these values?
I have attached an excel file for you to look at. Please correct me if you think I didnt make it right.
After scaling these factors, should I expect the value of Vy in EQSX to be 30% of Vx for orthogonal effect? Or it may happen that the value is significantly different?
Hoping for your response
AlphaXY
RE: Response Spectra Analysis
Forget the first question. I already got the same value of 102.9. I downloaded the original model provided by aqibusman and edited the model again and finally got the same value.
Newei, I hope you can help me with the other question.
Regards,
AlphaXY
RE: Response Spectra Analysis
Define 2 different cases one with Vx and other one is Vy and add them mathematically in load combination.
Best
Z
RE: Response Spectra Analysis
Got it. Thanks for the info. I will check it in my model as soon as I can and get back to you at once. However, just to make it clear, this is what you suggest:
Define SPECX and SPECY in response spectrum and combine it in load combination mathematically when you obtain scale factors for each direction (Say, 1.2DL + 1.6LL + 1.1SPECX + 1.1SPECY) "RATHER THAN" having SPECXY in response spectrum definition with scale factors of both direction to be used in load combination (1.2DL + 1.6LL + 1.1SPECXY).
Thanks
AlphaXY