Spectrum match

[eero-matti offline]

It seems that SeismoArtif constantly produces acceleration histories which doesn't fit into +-10 % allowable range when compared to target spectrum, but still states that convergence has been archived. In practice this is probably not an issue, but for example ASCE 4-98 states that any point of the spectrum should not lie below 10 % of the target spectrum. That makes the acceleration histories not usable in the analysis where strict following of the codes is required. Of course this could be managed by increasing the acceleration using spectrum factor. Another problem is that we have been using quite accurate acceleration histories for long time and now down grading is probably not an option. I'm not an expert to say what causes the acceleration histories to be inaccurate, but the software limit for 3 iterations seems a bit small for me (our old software did something like 5 to 20 iterations, described in the: http://www.kolumbus.fi/pentti.varpasuo/ ... ra_v02.htm).

It would be highly appreciated if you could slightly improve the accuracy of the acceleration histories in the next version. Thank you!

[seismosoft offline]

Hi eero-matti,

We suggest that you use the third method, Artificial Accelerogram Generation & Adjustment, which can be considered as a n evolved method of Artificial Accelerogram Generation. It can accept more the 3 iterations, and it allows for better convergence with smaller tolerance (you can try a 5% value).

Seismosoft Support

[huffte offline]

I might also add that, at least for most specifications, the 10% rule is applied to the average of all artificial accelerogram spectra, not to any individual spectrum. I cannot claim to know the intimite details of ASCE 7-98, but have typically seen the rule applied to the average of the suite, not to individual records. Maybe 7-98 requires this for all records (which seems a bit unusual since the more closely each individual record if forced to match the target, the greater the chances for unrealistic motions), but I just thought I would mention it.

[eero-matti offline]

Thank you! I'l give a try now.

[eero-matti offline]

Thank you Hufte. You are absolutely right. In the KTA 2201.1 standard chapter 4.3.3 (2) the same idea has been stated more clearly and it's easy to adapt for the individual spectrum: "Time histories shall be considered as compatible with the ground acceleration response spectrum detailed in Section 3.5 if the amplitudes of no more than 10 % of the control frequencies of the response spectrum calculated for a damping ratio of D = 0.05 are lower than 10 % of the amplitudes of the goal spectrum."

Changing of the calculation method to the Artificial Accelerogram Generation % Adjustment helped my problem. Now the accelertion histories are much more precise if I set the tolerance lower. Thank you for your help!