A hybrid concrete structural system combines precast and cast-in-place concrete in the same parking structure, using each where it works best.
Common combinations include precast double tees or slabs on cast-in-place columns and beams, precast elements with a cast-in-place topping, or cast-in-place post-tensioned floors with precast facades, stairs or walls. The goal is to gain precast’s speed and plant quality while keeping cast-in-place’s continuity and flexibility where the site or design needs it. See structural systems of parking.
Why designers use it
- Faster erection than an all cast-in-place structure.
- Fewer joints than an all-precast structure where a cast-in-place element ties pieces together.
- Flexibility for irregular sites, ramps and transitions.
- Precast architectural facades on any structural frame.
What to watch
- Connections and interfaces between precast and cast-in-place parts, where water and movement concentrate.
- Coordination between two trades and sometimes two engineers.
- Different durability details for each system. See chloride-ion contamination.
The Parkonomics view
Hybrid systems are a way of choosing the right tool for each part of a structure. The interfaces are where the savings, and the leaks, are found.
Related terms: Precast Pretensioned Concrete, Post-Tensioned Concrete, Structural Systems of Parking, Conventionally Reinforced Concrete, Expansion Joint, Hybrid Steel System