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For
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moment
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shear
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diagrams,
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CSI Software calculates exact response values only at output-station locations. Linear interpolation is then used to plot response between output stations. Users who wish to obtain exact numerical values for the response at points other than output stations may do so using the Diagrams for Frame Objects menu.
Consider the example of 9m-long simply supported girder loaded with a 1kN/m uniformly-distributed load. When moment diagrams are plotted for the same object and loading conditions, except with variable output-station spacing (4.5m, 3m, and 0.9m), results are as shown in Figure 1:
Figure 1 - Girder moment diagrams with variable output-station spacing
A parabola represents the true moment diagram which results from a uniformly distributed load. Depending on the number of output stations, CSI Software approximates this shape with a series of linear segments. It is most accurate and practical to use a sufficient number of output stations. Ten output stations per span should suffice.