private void FindColumnRebarIntersections(Document document, FamilyInstance column)
{
    // We will be computing the total length of the rebar inside the column
    double totalRebarLengthInColumn = 0;

    // Find rebar hosted by this column
    RebarHostData rebarHostData = RebarHostData.GetRebarHostData(column);
    if (rebarHostData == null)
    {
        return;
    }

    IList<Rebar> rebars = rebarHostData.GetRebarsInHost();
    if (rebars.Count == 0)
    {
        return;
    }

    // Retrieve geometry of the column
    Options geomOptions = new Options();
    geomOptions.ComputeReferences = true;
    geomOptions.DetailLevel = ViewDetailLevel.Fine;
    GeometryElement elemGeometry = column.get_Geometry(geomOptions);

    // Examine all geometry primitives of the column
    foreach (GeometryObject elemPrimitive in elemGeometry)
    {

        // Skip objects that are not geometry instances
        GeometryInstance gInstance = elemPrimitive as GeometryInstance;
        if (gInstance == null)
        {
            continue;
        }

        // Retrieve geometry of each found geometry instance
        GeometryElement instGeometry = gInstance.GetInstanceGeometry();
        foreach (GeometryObject instPrimitive in instGeometry)
        {

            // Skip non-solid sobject
            Solid solid = instPrimitive as Solid;
            if (solid == null)
            {
                continue;
            }

            SolidCurveIntersectionOptions intersectOptions = new SolidCurveIntersectionOptions();
            foreach (Rebar rebar in rebars)
            {
                // Get the centerlines for the rebar to find their intersection with the column
                bool selfIntersection = false;
                bool suppresHooks = false;
                bool suppresBends = false;
                IList<Curve> curves = rebar.GetCenterlineCurves(selfIntersection, suppresHooks, suppresBends, MultiplanarOption.IncludeOnlyPlanarCurves, 0);

                // Examine every segment of every curve of the centerline
                foreach (Curve curve in curves)
                {
                    SolidCurveIntersection intersection = solid.IntersectWithCurve(curve, intersectOptions);
                    for (int segment = 0; segment <= intersection.SegmentCount - 1; segment++)
                    {
                        // Calculate length of the rebar that is inside the column
                        Curve curveInside = intersection.GetCurveSegment(segment);
                        double rebarLengthInColumn = curveInside.Length;
                        totalRebarLengthInColumn = totalRebarLengthInColumn + rebarLengthInColumn;
                    }
                }

            }
        }
    }

}

Private Sub FindColumnRebarIntersections(document As Document, column As FamilyInstance)
    ' We will be computing the total length of the rebar inside the column
    Dim totalRebarLengthInColumn As Double = 0

    ' Find rebar hosted by this column
    Dim rebarHostData__1 As RebarHostData = RebarHostData.GetRebarHostData(column)
    If rebarHostData__1 Is Nothing Then
        Return
    End If

    Dim rebars As IList(Of Rebar) = rebarHostData__1.GetRebarsInHost()
    If rebars.Count = 0 Then
        Return
    End If

    ' Retrieve geometry of the column
    Dim geomOptions As New Options()
    geomOptions.ComputeReferences = True
    geomOptions.DetailLevel = ViewDetailLevel.Fine
    Dim elemGeometry As GeometryElement = column.Geometry(geomOptions)

    ' Examine all geometry primitives of the column
    For Each elemPrimitive As GeometryObject In elemGeometry

        ' Skip objects that are not geometry instances
        Dim gInstance As GeometryInstance = TryCast(elemPrimitive, GeometryInstance)
        If gInstance Is Nothing Then
            Continue For
        End If

        ' Retrieve geometry of each found geometry instance
        Dim instGeometry As GeometryElement = gInstance.GetInstanceGeometry()
        For Each instPrimitive As GeometryObject In instGeometry

            ' Skip non-solid sobject
            Dim solid As Solid = TryCast(instPrimitive, Solid)
            If solid Is Nothing Then
                Continue For
            End If

            Dim intersectOptions As New SolidCurveIntersectionOptions()
            For Each rebar As Rebar In rebars
                ' Get the centerlines for the rebar to find their intersection with the column
                Dim selfIntersection As Boolean = False
                Dim suppresHooks As Boolean = False
                Dim suppresBends As Boolean = False
                Dim curves As IList(Of Curve) = rebar.GetCenterlineCurves(selfIntersection, suppresHooks, suppresBends, MultiplanarOption.IncludeOnlyPlanarCurves, 0)

                ' Examine every segment of every curve of the centerline
                For Each curve As Curve In curves
                    Dim intersection As SolidCurveIntersection = solid.IntersectWithCurve(curve, intersectOptions)
                    For segment As Integer = 0 To intersection.SegmentCount - 1
                        ' Calculate length of the rebar that is inside the column
                        Dim curveInside As Curve = intersection.GetCurveSegment(segment)
                        Dim rebarLengthInColumn As Double = curveInside.Length
                        totalRebarLengthInColumn = totalRebarLengthInColumn + rebarLengthInColumn
                    Next

                Next
            Next
        Next
    Next

End Sub