How to get the span name of deck by using expression in OpenBridge?

Hello there.I would like to get “span name” of Deck by using expression and show it in properties ,just like  showing “Span name” of BeamSegment in Fig.1.

                            Figure.1

For this purpose，I tried to use an expression which is "this.GetElement().Deck_SpanName" in Fig.2.But it failed finally.

                          Figure.2

So I'm here for help.Thanks!