For a blast over pressure of 1 bar and when we fill in and run the analysis, only see the moment / diagram only vertical direction and not horizontal direction, why?
Some warnings may appear while modeling this load case: No. 593 Saddel effective angle < 30Deg (blast int Max P (Corroded inertias) (Corrded Weight), revise design of vessel.
why and how to avoid.
This is obvious an input of wind drag is necessary for the horizontal blast forces. The blast effect consists of 2 effects - the
1. Overpressure
2. Blast drag.
Please refer to the Videos
1. YOUtube techtalk here
Understand how exactly the forces are computed and applied to obtain the shear forces and bending moments.
2. Consider motion, seismic, and wind loadings with ease for optimized pressure vessel supports design
Review and analyze design report for supports and for motion, wind and seismic load cases
3. Efficient Load Case Definition for Pressure Vessel Design
run analysis using the brand new user-friendly Motion and Blast Loading conditions feature
In the report the shear loads and moment are calculated in vertical and horizontal transverse directions and vectorially combined to obtain the resultant. See image below for diagrammatic representation for both vertical and horizontal directions:
The input of the blast drag and overpressure is performed by the user. The dynamic wind pressure is significantly higher than the usual value for a simple wind load analysis. This is a user input and we cannot guide you how to obtain it. Sometimes users perform CFD analysis or hand calculations.
Question:
What is the basis for considering the allowable stresses?
Answer:
Please see the webinar on this topic.
The design code does not mention allowable stress for blast specifically. But AutoPIPE Vessel considers for blast exceptional allowable stress = 90% yield.
Under Design Conditions tab click "View"
Observe that there is a factor C4 which is 90% allowable stress for test/abnormal conditions. Also, user can select User Defined and change this factor.Below shown to the right the materials tab under shell in the blast tab where the 90% yield is applied for Exceptional Allowable Stress for blast load case:
Users are able to change the value of allowable stress for any specific load case.
Go to "Load Conditions" and select "Blast" under load case, uncheck "Use Default" under safety factor, instead select "User Defined" and click Edit
The value of C4 to 80% as an example:
Click OK and go to the blast tab under "Material" tab in any shell component like explained above, observe that the exceptional allowable has changed to 80% of yield:
How to adjust the B stress factor for calculations subjected to external pressure which is needed for blast load case analysis?
B factor is calculated from ASME IID rules unless specified by user:
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