Kevin
To help you to begin to unpick the suggested technique, Consider only the 'dynamic time' part of the suggested technique for now.
There are 4 key work flow steps:
1. Carry out a modal analysis (guess the number of modes, start with 10,say)
2. Using the results from the modal analysis output (1. above), 'identify' the structure using a 'dynamic shock' analysis. We must ask for the mass participation factors [MPF's] as an output in the analysis definition and they appear in the .rpt file (I think). The MPF's must sum to 80% or more.
3. If the MPF's do not sum to >=80% repeat. goto 1. requesting more modes. repeat 2. to confirm we are now >=80% total MPF. Repeat as required. (care, brief comment on chasing irrelevant information below)
4. When sum of MPF's >=80%, the structure sufficiently 'identified', carry out the dynamic time study using the half sine F(t). Don't forget to ask for measures. 'Raw' output from a dynamic time analysis is minimal and you will be easily disappointed.
Practical pointer. When running shock/time studies the user has the choice of using results from a previously run modal study. It is clear that by doing this time can be saved as the steps 2 and 4 both require the results from the same modal analysis as an input. Running the modal study 'on the fly' means it is run twice taking longer. BUT if you want to reuse the modal study results to save time you must not change your model at all; not even by a datum point. If you do you will get a message saying something along the lines of 'the model has changed, can't use the modal study results'
Hope this helps
Regards
Charles
Aside:
'Pure shock' is an impulse; (Dirac function, http://web.mit.edu/2.14/www/Handouts/Convolution.pdf) a zero time length infinite amplitude event and exites all frequencies equally and is mathematically useful for 'system identification'. A structure has natural frequencies and it is only these that repsond to this shock. We get the impulse response 'PSD' graph as an output.
The half sine function you have is a short time based event, which we engineers tend to refer to as shock. This is why I proposed you consider dynamic time first.
More useful links ...
Alternative words describing use of mechnica for dynamic analysis here, just another presentation of the process ...
http://www3.eng.cam.ac.uk/DesignOffice/cad/proewild3/usascii/proe/pa_files/text/5d1_dynamic_guide.htm
Useful for understanding modal mass participation:
http://www.vibrationdata.com/tutorials/ModalMass.pdf
Ideally we want modal mpf >=80% in relevant directions. By relevant I mean lateral modes may not be of interest and therefore we need to be careful that we don't chase a 'global' MPF >=80% as a higher mode may be in an irrelevant direction (so mode shape is importannt). How the model is constrained influences this.
To go the frequency domain route by Industry standard spectra 'from a book', this is the sort of thing I was thinking of ...
http://shop.bsigroup.com/ProductDetail/?pid=000000000000218537
Some more learning resources
NAFEMS also have a code independent web-based dynamic analysis course that lends substantial (though more general) background.
http://www.nafems.org/e-learning/all_courses/el_dynamic/
Lots of useful backround here too
http://www.bksv.co.uk/Library/Search%20Resources
Why >=80% mpf? One could state authoritatively "It's an industry standard" ... Start here
http://www.eng-tips.com/viewthread.cfm?qid=126162
