public sealed class ScaleBar : MapSurround, ArcGIS.Desktop.Mapping.IElement, System.ComponentModel.INotifyPropertyChanged, System.IComparable, System.IDisposable, System.IEquatable<Element>  

{
  //Note: Must be on QueuedTask.Run

  //Build geometry
  Coordinate2D ll = new Coordinate2D(5.0, 6);
  Coordinate2D ur = new Coordinate2D(6.0, 7);
  Envelope sbEnv = EnvelopeBuilderEx.CreateEnvelope(ll, ur);

  //Reference a Scale Bar in a style
  StyleProjectItem stylePrjItm = Project.Current.GetItems<StyleProjectItem>()
                .FirstOrDefault(item => item.Name == "ArcGIS 2D");
  ScaleBarStyleItem sbStyleItm = stylePrjItm.SearchScaleBars(
               "Alternating Scale Bar 1")[0];
  //ScaleBarStyleItem sbStyleItm = stylePrjItm.SearchScaleBars(
  //                                   "Double Alternating Scale Bar 1")[0];
  //ScaleBarStyleItem sbStyleItm = stylePrjItm.SearchScaleBars(
  //                                    "Hollow Scale Bar 1")[0];

  //Create Scale Bar
  ScaleBarInfo sbInfo = new ScaleBarInfo()
  {
    MapFrameName = mapFrame.Name,
  };

  var sbElm = ElementFactory.Instance.CreateMapSurroundElement(
                                     layout, sbEnv, sbInfo) as ScaleBar;
}

{
  //Note: Must be on QueuedTask.Run
  //Build geometry
  Coordinate2D ll = new Coordinate2D(5.0, 8);
  Coordinate2D ur = new Coordinate2D(6.0, 9);
  Envelope sbEnv = EnvelopeBuilderEx.CreateEnvelope(ll, ur);

  //Reference a Scale Bar in a style
  StyleProjectItem stylePrjItm = Project.Current.GetItems<StyleProjectItem>()
                               .FirstOrDefault(item => item.Name == "ArcGIS 2D");
  ScaleBarStyleItem sbStyleItm = stylePrjItm.SearchScaleBars(
                                "Scale Line 1")[0];
  //ScaleBarStyleItem sbStyleItm = stylePrjItm.SearchScaleBars(
  //                                           "Stepped Scale Line")[0];
  //ScaleBarStyleItem sbStyleItm = stylePrjItm.SearchScaleBars(
  //                                            "Scale Line 2")[0];

  //Create Scale Bar
  ScaleBarInfo sbInfo = new ScaleBarInfo()
  {
    MapFrameName = mapFrame.Name,
    ScaleBarStyleItem = sbStyleItm
  };

  var sbElm = ElementFactory.Instance.CreateMapSurroundElement(
                    layout, sbEnv, sbInfo, "ScaleBar Line") as ScaleBar;
}

{
  //Update a map surround.
  //Note: Must be on QueuedTask.Run
  // Reference and load the layout associated with the layout item

  // Reference a scale bar element by name
  MapSurround scaleBar = layout.FindElement("MyScaleBar") as MapSurround;

  // Reference a map frame element by name
  MapFrame mf = layout.FindElement("MyMapFrame") as MapFrame;

  if ((scaleBar != null) && (mf != null))
    //Set the scale bar to the newly referenced map frame
    scaleBar.SetMapFrame(mf);
}