In RadHtmlChart the Column Chart is the vertical version of the Bar Chart. You can find more information and examples about it in our documentation as well as in the online demos. This means you simply need to rename your series from BarSeries to ColumnSeries and set the Stacked property of the first to true.
Regarding Shinu's answer I'd like to point out that it is related to the RadChart and not RadHtmlChart.
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