public ScaleBarStyleItem ScaleBarStyleItem {get; set;}

{
  //Create a scale bar using a style.

  //Search for a style project item by name
  StyleProjectItem arcgis_2dStyle = Project.Current.GetItems<StyleProjectItem>()
                              .First(si => si.Name == "ArcGIS 2D");

  //Note: Must be on QueuedTask.Run

  //Reference the specific scale bar by name 
  ScaleBarStyleItem scaleBarItem = arcgis_2dStyle.SearchScaleBars(
                      "Double Alternating Scale Bar").FirstOrDefault();

  //Reference the map frame and define the location
  MapFrame myMapFrame = layout.FindElement("Map Frame") as MapFrame;
  Coordinate2D coord2D = new Coordinate2D(10.0, 7.0);

  //Construct the scale bar
  var sbarInfo = new ScaleBarInfo()
  {
    MapFrameName = myMapFrame.Name,
    ScaleBarStyleItem = scaleBarItem
  };
  ElementFactory.Instance.CreateMapSurroundElement(
          layout, coord2D.ToMapPoint(), sbarInfo);
}

{
  //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;
}