Distributed (Uniform and Trapezoidal) forces and moments can be assigned along the length of piping and frame objects. The loads may be as simple or as complicated as required. Loads are specified in force-per-length or moment-per-length units.
Typical applications for distributed load assignments include snow load, buoyancy uplift, soil backfill load, live load, cable tray load, steam/heat tracing, and wind load. Although CSiPlant (and SAP2000) can automatically generate wind load as a function of height for piping and frame elements per ASCE 7, in some cases users may need to assign distributed loads if wind load needs to be applied using a different method.
A unique CSiPlant feature is that distributed loads can be assigned using Global or local axis of the selected piping or frame elements. There is also an option, which is the default, to assign distributed loads in the Gravity direction, which is the negative Global Z direction (-Z). If a user wants to assign distributed load in the -Z direction using the Gravity load direction, a positive value would be entered. However, if the user instead specifies Z load direction instead of Gravity, a negative value would need to be entered to assign a downward direction load.
In the “Distributed type” field you will find both Distributed and Point load option. The distributed point load option is largely a holdover from structural analysis in which engineers can assign point loads for internal analysis without having to divide the frame or piping into multiple pieces. For example, a 30 ft. long beam may have 3 or 4 point loads along the length which represent piping or equipment loads. For design reasons, the structural engineer doesn’t want to divide the beam into 4 or 5 segments, but he still wants to apply those concentrated point loads along the length. The distributed point load assignment accomplishes this.
Load assign options:
Add to Existing Loads: Adds the specified distributed load to the frame object. If one or more distributed load assignments have already been made, this option increases the existing load, assuming a positive load is being specified.
Replace Existing Loads: Replaces the currently specified distributed load, if any, with the new load. If no assignment exists, the new assignment is still made. This is the default option.
Delete Existing Loads: Deletes any and all distributed load assignments made to the selected object(s). When this option is selected, the items in the Load Type and Direction, Trapezoidal Loads, and Uniform Load areas of the form are ignored when the OK button is clicked.
If uniform and trapezoidal loads are specified at the same time, they are additive.
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To apply distributed load, select piping and/or frame elements to which you will assign distributed load, then Assign menu>Pipe Loads (or Frame Loads)>Distributed. In the example below we change the Load Pattern to WX, load direction X, and distance type to Absolute as shown. There is also the option to assign a distance type of "Relative", which enables users to assign distributed loads to percentage of length values along the element length. As you can see in the screenshot below, the distributed load for this wind load pattern varies as a function of height from 8 lbs/ft at the base to 19 lbs/ft at the top.
