earthquake

[stamopoulos]

dear group,
i have an excel file containing a 5000 set of values of acceleration vs time.
i want to do a transient analysis applying that load to my model.
can i copy paste the values at once instead of manually inputing them?
also it asks for acceleration vs period, period meaning what? i want acceleration vs time

thanks for your help

 

[Drej]

>i have an excel file containing a 5000 set of values of acceleration vs time.
i want to do a transient analysis applying that load to my model.
can i copy paste the values at once instead of manually inputing them?

I suspect that your data is in the form of time vs "g" values. You don't have to manually input this. However, your approach depends on whether you want to do a "response spectrum" (ANTYP,SPECTR) seismic analysis or a full "time history" (ANTYPE,TRANS). You mention doing a "transient analysis", which implies that you want to use the time-history approach. However, you won't be able to use the accelerations in their current form. Instead, you'll need to obtain displacements (time vs displacement) from the accelerations - there are ANSYS functions available for you to do this (INT1, INT2 or *VOPER), or you can do it manually in excel using Simpson, Trapezoidal, etc. You can then put the displacements vs time into a table (*DIM,NAME,TABLE) and apply as a transient load using the D command (enclose the TABLE NAME in percent symbols e.g D,all,UX,%name%).

>also it asks for acceleration vs period, period meaning what? i want acceleration vs time
You haven't specified where you've got this information from, but I suspect you've been looking at both the response spectrum and transient methods. When you carry out a response spectrum analysis, your input is frequency (FREQ) vs spectral value (SV), since with this approach we are working in the frequency domain as opposed to the time domain. The spectral value is usually acceleration, but can be velocity, force, displacement...depending on the SVTYP you specify (and, of course, on the information you have). It is much more efficient to work within the frequency domain, but there are some restrictions on the level of modelling you can include. Response spectrum modelling is linear. Hence, for instance, you must ensure everything in your model is linear (no contact - except bonded - or EKILL/EALIV, no plasticity, no non-linear geometry). You must also obtain the response spectrum from your time vs accel data (see RESP command) and then peak broaden if necessary (especially if you're doing any analysis requiring the structure to be seismically qualified e.g nuclear installations, military, certain civil apps etc..). If your model contains non-linearities, you must use the transient approach (ANTYP,TRANS).

People have written books on this subject - VERY BIG books - and I could write all day about the pros and cons of each and on the theory. Hope the above helps as a start however.

Cheers,

-- drej --

 

[stamopoulos]

i do appreciate Drej for explaining
thanks
george