To Select by Cut Openings Option

Select the Cut Openings tool from the ribbon.
Select any one option from the four Cut Openings Option that are seen on placement tab

By Polygon Point

or
By Circle/Arc

or
By Boolean Subtraction

or
By Inverse Boolean Subtraction

By Circle/Arc option is selected.
Select the steel element.
Identify the axis. The vertical axis is selected for top view and the horizontal axis is selected for the front view for viewing the element.
Select the arc/circle.
Cut By Circle/Arc option

The selected part of steel element is cut according to the cut-openings-option used.