It is important to understand the different objects used to define design strips.

Span segment A line segment-line entity that is intended to indicate a portion of a structural span or a whole structural span. The "at support" properties of the Span Segment indicate where the span starts and stops.

Span One or more connected Span Segments that together make up a single structural span. Nearly all spans require only one Span Segment.

Frame One or more Spans that are connected together to form a continuous line of spans.

Span Segment Strip A set of cross sections associated with a Span Segment. The Span Segment can have up to three Span Segment Strips (left, center and right). These are known as design strips.

See the following image for further explanation.