	Applies To
	Product(s):	AutoPIPE
	Version(s):	V8i
	Area:	Modeling
	Original Author:	Bentley Technical Support Group
	Date Logged & Current Version	Sept. 2015 09.06.02.06

Question:

what I am really after is some assistance on dynamic modelling of the blast event.
I am applying a triangular blast profile over a very short time period which I am doing to each node of the affected pipe. To do this I am using a time force history and applying this to the nodes; some with a time delay.

I would like some more information on the best way of doing this and also, and most importantly, is it possible in AutoPipe to obtain a force time history of the reactions at the supports? At the moment, I seem to get just one force figure at each reaction which I assume is the maximum reaction force felt by that support.

Answer:

Internal Blast load:

By default, AutoPIPE reports only the maximum dynamic reaction force or response at supports. It does not directly provide full time-history reaction data in standard results output.

However, Time History Post Processor plots that are available in AutoPIPE version 09.06.xx.xx and later produces plot time-dependent behavior, where applicable.

When modeling short-duration (ex. impulsive, blast) loads, use the following best practices:

Increase the cut-off frequency to approximately 200 Hz
Enable automatic mass point generation up to 200 Hz
Consider, using the ZPA (Zero Period Acceleration) option to better capture high-frequency effects

For this type of load a static analysis can often be used as a simplified approach, however it may be conservative (up to ~2x response) compared to true dynamic results because of the dynamic amplification factor of 2.0. Of course, static response will ignore phasing.

Static analysis is a good way to checking the dynamic results since it bounds the response results.

External Blast load:

To simulate a blast load acting on the external surface of a pipe, a Wind load case can be used as a practical approximation. Define a Wind load case to represent the blast force. Since blast effects are often localized, it may be necessary to divide/split the pipe into multiple segments to accurately apply the load only where required by using the Split Segment(s) command (Home > Operations > Segments > Split Segment(s). Again, this allows selective application of the wind (blast-equivalent) load to only the exposed portions of the piping system.

03. How to dynamic model a blast event in AutoPIPE?

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Answer:

See Also