Objective: Implement a non-zero margin of safety for Sizing.
A non-zero required margin of safety can be defined. This is useful in cases where a Failure Mode is defined as a percentage of limit load. For example, to model a post-buckling requirement at 50% limit load, the required MS at limit load is -0.5. Required margins can also be used to apply an analysis-specific knockdown or knock-up factor.
When a non-zero required margin is defined, the following equation is used to get the final margin of safety, MS.
\(MS=\frac{MS_{raw}+1}{MS_{required}+1}-1\)
This equation expresses a new margin of safety in terms of the distance between the required and the "raw" (compared to zero) margin of safety.
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Required margins are set in Failure Modes. See Create a Failure Mode.
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To be enforced on a selection of Zones or Joints, Failure Modes must be referenced by an Analysis Property. See Create an Analysis Property.
Open the failure mode that contains the method(s) to which you'd like to apply a required margin. This can be done from the Failure Mode Library or directly from the referencing Analysis Property.
Use the "Required MS" column to enter the desired required margin. Click "Apply" to save these values.
Size a selection of Zones/Joints to the applied required margins. Make sure all Zones have a Design Property, Load Property and an Analysis Property (which references the Failure Mode edited in Step #2).
There are several results visualization options that are particularly convenient when Sizing to required margins:
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Analysis Watch Window - Open the Analysis Watch Window for a selection of Zones to view both MS and raw MS, written in the form MS(\(MS_raw\))
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Legend - By default, when you plot the Minimum MS for each Zone, the MS with respect to required margins will be shown. But, for more specificity, plot the required margins input for each individual failure method using the Legend dropdown options