Show Interaction Surface

Form:  Interaction Surface, Interaction Surface (Caltrans)

Use the Display menu > Show Interaction Surface command or   button to access the Interaction Surface form for concrete sections that have reinforcing specified. If the section is not concrete and reinforcing is not specified, this command will not be available. In Section Designer the interaction surface is defined by a series of PM curves that are equally spaced around a 360 degree circle. For example, if 24 curves are specified (the default), there is one curve every 15 degrees (360/24 curves) .

Use the Edit menu > Copy All command to copy the data in the table to the Windows clipboard for pasting into another program such as Excel for further review.

Figure a below shows a three dimensional view of an interaction surface using the default view direction of plan angle = 315 degrees and elevation angle = 35 degrees. Figures b and c below illustrate how the plan and elevation angles are defined. Following the figure are explanations of the terms used in the figure.


The 3D View form has four fast view buttons labeled 3d, MM, PM3 and PM2. The fast view buttons automatically set the plan and elevation angle to display the specified 3D view. The fast view 3d view is as shown in the figure above. The other fast views display 3D perspective views of the specified planes.

Note:  When the Display menu > Show Caltrans Interaction Surface command is used to display this form, Options for controlling strength reduction (phi factor) and the reinforcing steel yield stress are not available.