IM Pei designed an (unbuilt) expansion for Dallas City Hall. The building would run parallel to the main building and be connected by bridges at those grooves... using similar materials and scale. The rest of the block would be filled in with a low-rise building surrounding a courtyard.
Unfortunately the plans for the expansion have gone missing. Read the full story with details: https://www.aiadallas.org/v/columns-det ... s-Back/ol/