// Cut a beam with 3 instances of a void-cutting family
// The Family Parameter "Cut with Voids When Loaded" must be true for the cutting family
void CutBeamWithFamilyVoid(Autodesk.Revit.DB.Document doc, FamilyInstance beam, FamilySymbol cuttingSymbol)
{
    LocationCurve lc = beam.Location as LocationCurve;
    Curve beamCurve = lc.Curve;

    for (int i = 1; i <= 3; i++)
    {
        XYZ beamLocation = beamCurve.Evaluate(i * 0.25, true); // position on the beam for this cutting instance
        beamLocation = beamLocation - XYZ.BasisZ; // adjust for top-aligned curve

        Level level = doc.GetElement(beam.LevelId) as Level;
        FamilyInstance cuttingInstance = doc.Create.NewFamilyInstance(beamLocation, cuttingSymbol, level, StructuralType.NonStructural);
        InstanceVoidCutUtils.AddInstanceVoidCut(doc, beam, cuttingInstance);
    }
}

' Cut a beam with 3 instances of a void-cutting family
' The Family Parameter "Cut with Voids When Loaded" must be true for the cutting family
Private Sub CutBeamWithFamilyVoid(doc As Autodesk.Revit.DB.Document, beam As FamilyInstance, cuttingSymbol As FamilySymbol)
    Dim lc As LocationCurve = TryCast(beam.Location, LocationCurve)
    Dim beamCurve As Curve = lc.Curve

    For i As Integer = 1 To 3
        Dim beamLocation As XYZ = beamCurve.Evaluate(i * 0.25, True)
        ' position on the beam for this cutting instance
        beamLocation = beamLocation - XYZ.BasisZ
        ' adjust for top-aligned curve
        Dim level As Level = TryCast(doc.GetElement(beam.LevelId), Level)
        Dim cuttingInstance As FamilyInstance = doc.Create.NewFamilyInstance(beamLocation, cuttingSymbol, level, StructuralType.NonStructural)
        InstanceVoidCutUtils.AddInstanceVoidCut(doc, beam, cuttingInstance)
    Next
End Sub