Structural element beam has got the following definition:

 beam {b1} type Frame curve {c1} xsection {cCss} alignment (Alignment) eccentricity {Eccentricity.X,Eccentricity.Y,Eccentricity.Z} alpha (CssAlpha) lcsRx (CssLcsRx) lcsMirrorZ (LcsMirrorZ) lcsMirrorY (LcsMirrorY) cssMirrorY (CssMirrorY) cssMirrorZ (CssMirrorZ) layer (Layer) styles [ ViewStyle ] metadata ( Metadata )

beamWeight := b1.GetBasicMassKg()
beamVolume := b1.GetBasicVolume()

Note: Volume and weight are negative for wrongly oriented section or curve.

A beam is basically a line where a certain cross-section is assigned to (in terms of structural engineering). Cross-section is a particular area, that can be defined in separate class. And has got therefore its independent coordinate system. Line can also have its own independet coordinate system (i.e. edge Lcs). And how to allocate the cross-section according to our needs?

Each beam can have specific alignment:

CssAlignment.None   (origin of the cross-section class is put on the beam line)
CssAlignment.Centre (centroid of the cross-section bounding box is put on the line)
CssAlignment.Top    (middle point of the X edge and  of the bounding box is used)
CssAlignment.Bottom
CssAlignment.Lef
CssAlignment.Right
CssAlignment.TopLeft + variants /TopRight/BottomLeft/BottomRight

Original area definition

Beam with above area as a cross-section and various alignments