The simplest way is to add the SQL record to the `sys_pages_layouts` table and the HTML template file with the proper content.See example with 3 columns layout:

INSERT INTO `sys_pages_layouts` (`id`, `name`, `icon`, `title`, `template`, `cells_number`) VALUES 

(14, 'bar_content_bar', 'layout_bar_content_bar.png', '_sys_layout_bar_content_bar', 'layout_bar_content_bar.html', 3);

And the content of the template/layout_bar_content_bar.html:

<!-- layout bar content bar (bcb) [ start ] -->

<div id="__page_id__" class="bx-layout-wrapper bx-layout-bcb">

    <div class="bx-layout-row bx-clearfix">

        <div class="bx-layout-col bx-layout-bcb-bar1 bx-layout-column-thin">

            <div class="bx-layout-cell bx-def-padding-sec-right" id="bx-layout-cell-1">

                __cell_1__

            </div>

        </div>

        <div class="bx-layout-col bx-layout-bcb-content bx-layout-column-half">

            <div class="bx-layout-cell bx-def-padding-sec-leftright" id="bx-layout-cell-2">

                __cell_2__

            </div>

        </div>

        <div class="bx-layout-col bx-layout-bcb-bar2 bx-layout-column-thin">

            <div class="bx-layout-cell bx-def-padding-sec-left" id="bx-layout-cell-3">

                __cell_3__

            </div>

        </div>

    </div>

    <bx_include_auto:_row_1_column_dump.html />

</div>

<!-- layout bar content bar (bcb) [  end  ] -->