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General assumptions

Below are some general assumptions for handling distributed ground displacement loads:

(1) Distributed ground displacements can be assigned to any pipe or frame object, but they will only have an effect when distributed supports are also assigned to the same object.

(2) Distributed ground displacement loads assigned to a pipe will not impose any load on the pipe's discrete supports. If the user wishes to apply a matching point displacement load to a discrete support, such a load would need to be applied separately.

(3) When distributed supports are assigned to two adjacent pipes that share a common joint, distributed supports internally generate two sets of springs at a common joint. The first set represents the last discrete support for the first pipe, and the second set represents the first discrete support for the second pipe. Distributed ground displacement loads are applied independently to each pipe, potentially resulting in a displacement discontinuity at the common joint. Such a displacement discontinuity is acceptable and will be reflected in the analysis results.

Applying distributed ground displacements

Distributed ground displacement can be applied to pipes and frames via the following two menu commands (see Figure 1):

• Assign > Pipe Loads > Distributed...
• Assign > Frame Loads > Distributed...

Figure 1: Form for applying distributed ground displacements

Internal modeling

When distributed supports are assigned to a pipe or frame element, analysis model for the ground displacement loads is created as follows (see Figure 2):

(1) Identify location of discrete supports representing the distributed support.

(2) Use interpolation of the ground displacement load to calculate its values at the locations of discrete supports.

(3) Apply the ground displacement load to the fixed end of links that internally represent each discrete support.

Figure 2: Internal modeling of distributed ground displacements

Examples

Figures 3 and 4 show graphical representation of distributed ground displacements assigned to a single pipe and to two adjacent pipes.

Figure 3: Distributed ground displacements applied to single pipe

Figure 4: Distributed ground displacements applied to two adjacent pipes