In structural systems the floor and roof components support not only gravity loads, but also act as a diaphragm to transfer lateral loads (such as wind and seismic forces). These components also provide bracing to vertical elements and protect them against abnormal loading.
Precast concrete floor and roof systems can be designed and used as diaphragms. Hollow-core systems may utilize perimeter reinforcing and grouted joints or may use a reinforced concrete topping.
Double tee systems may include untopped or pre-topped tees, pre-topped tees with pour strips at the ends, or tees with cast in place topping.
More information on diaphragm design can be found in the PCI Design Handbook.