Hi,

I am trying to apply the EN1998-1 seismic code to a system I have modeled. I have previously used the spectrum generator in the dynamic section to generate a spectrum according to the ASCE7 code. However, I would like to compare it to a model of the same system with the EN1998-1 Seismic code applied at the dynamic analysis stage.

My method, I thought, would be simple.. First I calculated the system according to ASCE7 using factors from the code to generate the curve. Then I thought I was able to copy the file (as the model is identical in static stage) and apply the EN1998-1 code. In Excel I generated a number of points to model the response curve described in the EN code. I thought I could simply open the copied file and go to the "edit spectra data" tab and just change the data points to suit the curve in EN1998-1. However, when I ran the model and went to my combined load cases for stresses I was getting the EXACT same values as the ASCE7 curve, despite the curves being slightly different.

Am i doing something wrong?

I didn't want to use the 'user defined time history wave form' option because my data was exactly laid out the same way as in ASCE7- i.e. Period vs g's.

Perhaps your system natural frequencies aligned with those points on the ASCE7 and EN1998 where the g's were identical anyway.

I doubt it - I have since changed several values drastically and no change.

I guess it's time you post your data.

This was the ASCE-7 data calculated by CaesarII,

Period(S) vs Acc.(g's) - Excell has rounded the numbers.

0.00 0.09
0.11 0.23
0.55 0.23
0.58 0.22
0.61 0.20
0.65 0.19
0.70 0.18
0.76 0.17
0.82 0.15
0.89 0.14
0.98 0.13
1.09 0.11
1.23 0.10
1.41 0.09
1.64 0.08
1.97 0.06
2.46 0.05
3.29 0.04
4.95 0.02
10.00 0.01

And then I fed in these data points, which were based on an excel file I made to calculate data points using EN1998-1.

0 0.1200
0.07 0.2000
0.15 0.3000
0.5 0.3000
0.51 0.3000
0.6 0.2500
0.66 0.2300
0.7 0.2100
0.74 0.2000
0.9 0.1700
1 0.1500
1.2 0.1300
1.23 0.1200
1.41 0.1100
1.64 0.0900
1.97 0.0800
2.46 0.0500
3.29 0.0300
4.95 0.0100
10 0.0100

Sorry - It's should be....

Period (ASCE-7)
0.00
0.11
0.55
0.58
0.61
0.65
0.70
0.76
0.82
0.89
0.98
1.09
1.23
1.41
1.64
1.97
2.46
3.29
4.95
10.00

Acc. (g's)
0.09
0.23
0.23
0.22
0.20
0.19
0.18
0.17
0.15
0.14
0.13
0.11
0.10
0.09
0.08
0.06
0.05
0.04
0.02
0.01

These were done inside CaesarII... I then replaced the generated values with...

Period(S).
0
0.07
0.15
0.5
0.51
0.6
0.66
0.7
0.74
0.9
1
1.2
1.23
1.41
1.64
1.97
2.46
3.29
4.95
10

with Acc. (g's)

0.1200
0.2000
0.3000
0.3000
0.3000
0.2500
0.2300
0.2100
0.2000
0.1700
0.1500
0.1300
0.1200
0.1100
0.0900
0.0800
0.0500
0.0300
0.0100
0.0100


Thanks in advance.

I meant your actual CAESAR II input data. These spectra, alone, do not indicate the system response. Specific accelerations are selected for each system natural frequency. There could be a (slim) chance that these spectra are identical in magnitude for the system's natural frequencies.

A more plausible answer is there is an input error.

If you do not want to post your model here, please send your (dot C 2) model to caesarii@intergraph.com.