Specifies the applied direction of the spectrum/DLF shock load. Select X, Y, or Z. You can also enter direction cosines, such as (.707, 0, .707), or direction vectors, such as (1,0,1).
This value is used as follows, depending on the analysis type:
For earthquake analysis:
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Direction specifies the loading direction.
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Direction indicates the dependence or independence of the loads. When modal combinations precede spatial combinations, loads with the same direction are summed at the modal level before any spatial combination.
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Direction acts as an output label for the maximum contributor, such as 3X(1), where the first profile in direction X is reported as X(1). 3X(1) indicates that the largest contributor to the total response is from the third mode of vibration and due to the first spectrum/shock defined as X.
For force spectrum analysis, the force vector (direction) is already established:
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Direction indicates the dependence or independence of the loads as discussed above.
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Direction acts as an output label for the maximum contributor, as discussed above for earthquake analysis.
For time history analysis, time history combinations are algebraic (in-phase):
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Direction acts only as an output label for the maximum contributor, such as 3X(1).
To define an earthquake type of loading, CAESAR II must know what how the earthquake shock acts from the shock spectrum table. CAESAR II must also know the direction of the shock. A shock load case is typically comprised of three shock components in the X, Y, and Z directions. The combination of each of these components shock loads defines the earthquakes dynamic loading of the piping system.
Skewed directions can be entered by giving a direction cosine or direction vector. Skewed shock contributions are entered when the piping or structural system appears particularly sensitive to a shock along a skewed line. This most often occurs when most of the piping system does not lay along the X and Z axes.
Any number of shock components can act in the same direction. For example, there can be two X direction components. This usually occurs with independent support shock contributions where one X direction component applies to one support group and another X direction component applies to a different support group. There can also be two shock components in the same direction without having independent support contributions, by defining two shock contributions in the same direction without start, stop, or increment node entries.
In the simplest form of force spectrum loading, there is only a single shock component in the load case. For that situation, there is only a single line of input on the Load Cases tab. When there are multiple lines of input on the load case screen, such as in analyzing a traveling pressure wave that impacts different elbow-elbow pairs, there can be many components to the shock load case. The combination of responses from each of these shock loading components can be established in one of two ways. If the value of Direction is the same for each load component, then the directional combination method is used to combine the responses from each load component. If the value of Direction is different for each load component, then the spatial combination method is used to combine the responses from each load component. Directional combinations are always made before modal combinations, while spatial combinations can be made before or after modal combinations. The default is to perform the modal combinations before spatial combinations. Either spatial or directional combinations can be made using the ABS or SRSS method.