To my knowledge there are two approaches to designing structures for blast loading: you can take it on a member by member basis (modeling each beam with a Single Degree Of Freedom [i.e. SDOF] there are some good texts on that), or you can have a program analyze the structure as a whole and include the effects of plastic deformation and so forth.
But consider this for a moment: if you have a structure (say a frame made up of all welded tubes) and you were only interested in an elastic response.......what would you think of using the period calculated by the program [of the structure as a whole] and using that to get your DLF [i.e. Dynamic Load Factor]? There are a lot of charts that plot the DLF vs. duration time [of the ramp/triangle loading].
My first reaction to this approach [at the risk of answering my own question] is: it's sort of (inappropriately) mixing a solution for a SDOF and the results from a Multi Degree of Freedom analysis (as the FEA model clearly is). I'm not sure if the chart I mentioned previously would be applicable from this type of analysis.......or that this result would make it appropriate to apply this load [modified by that DLF] to members in the frame.
Thoughts?
But consider this for a moment: if you have a structure (say a frame made up of all welded tubes) and you were only interested in an elastic response.......what would you think of using the period calculated by the program [of the structure as a whole] and using that to get your DLF [i.e. Dynamic Load Factor]? There are a lot of charts that plot the DLF vs. duration time [of the ramp/triangle loading].
My first reaction to this approach [at the risk of answering my own question] is: it's sort of (inappropriately) mixing a solution for a SDOF and the results from a Multi Degree of Freedom analysis (as the FEA model clearly is). I'm not sure if the chart I mentioned previously would be applicable from this type of analysis.......or that this result would make it appropriate to apply this load [modified by that DLF] to members in the frame.
Thoughts?