JavaScript must be enabled in order to use this site.Please enable JavaScript in your browser and refresh the page. Drawing slab openings The Slab Opening tool () defines an opening in the slab. To draw a slab opening Choose the Slab Opening tool (). Click at each slab-opening vertex consecutively. Snap to the first vertex and click to close the polygon (or type "c" and press <Return>). Note: You approximate curves with a series of straight edges. Parent topic: Defining the Structure