[go go white sox]

Originally Posted by Swicago Swi Sox

Some Further explanation, if interested...

Office tower floor structure in Chicago tend to be Composite Steel Framed floors (steel beams holding up concrete slab on a metal deck). This allows for for more open floor plans and more flexibility for future tenants to re-configure the entire floor plates. It is much easier move walls around, cut new stair openings...etc...in a steel construction than a concrete structure. The "drawback" from a developer side, is that the structural sandwich (from ceiling up through the slab of the floor above) is much thicker with steel beams, since you need a Slab (~6") and steel beams and girders (24" to 36") plus some space between the beams and the ceiling for MEP. This leads to maybe an extra 4 to 5 feet per floor, which adds height that leads to more curtain wall cost, more cost in the vertically running MEP (pipes an wire) and more cost in the building lateral system due to the extra height. This extra cost is worth it to get the open and flexible floor plans for office tenants.

Residential towers are usually flat plate concrete with or without post-tensioning. Long open spans are less important in residential floor plans, and residential towers, especially rentals, are designed to have the same floor plan for most of the life of the building. This means it is less likely that new holes will be cut or that there are needs to move lots of walls...etc. The flat plate can be 8" to 12" thick and that's it, especially if the developer goes for the "loft look" so they don't need a ceiling to hide ducts and other MEP. However the spans are less, and while you can kinda cut through regular flat plate concrete, its really tough to cut through post tensioned concrete. Obviously, with a smaller structural sandwich the towers are shorter and you save of everything else at the detriment of being locked into the designed use/configuration.

Thank you for the thorough explanation! Good stuff looking forward to see new renders