Hi,

I have a model which is subject to blast. The blast will effect the pipe and the structure which supports it, causing the structure and pipe to sway together.
I have modelled the blast as a UDL on the pipe and have treated it as a occasional case with an allowable stress set at 1.2 x yield stress. This allows the pipe to plastically deform without rupturing.
The structural Engineer informs me that the supporting structure sways by D1 during the blast.
My problem is I am not sure how to treat the structural deflection in my calculations, should it be coupled to the primary stresses or the secondary stresses?
If this deflection was due to wind it would normally be coupled to the secondary stress cases as the deflection is part of the cyclic stress range however common sense tells me that this is a single catastrophic event and as such, both the pipe and structure sway together and should not be treated as part of normal operation cyclic stress range considering the pipe will have to be replaced after the blast, therefore this deflection (D1) should be treated as a sustained condition and coupled to the occasional stress case, i.e W+P+UDL+D1...OCC stress case.
I look forward to your comments.