Precast parking garage questions 1

[Robbiee]

Working on my first parking garage. It is a hybrid structure of precast columns, beams, double T slabs and cast in place shear walls. Lateral loads to be transfered to shear walls by floors acting as rigid diaphragms. 3" cast-in-place topping will be provided.
Questions:
1-What are considered to be the diaphragm chords? The L-beams or some type of additional reinforcing?
2- Who designs these chords; the precast engineer or the engineer of record of the building?
3- Who designs the connections between different precast elements to resist lateral loads?
Thanks for the help

 

[JKStruct]

In my (brief) garage experience:

1) I've provided reinforcement in the topping slab to act as diaphragm chords.
2) The EOR is typically responsible for lateral analysis. Precasters will provide the design of the gravity system and all connections. The EOR is usually responsible for the foundation system and any CIP concrete pilasters, slab-on-grade, or retaining walls that may be required.
3) The precaster will provide connections between precast elements and shear walls based on the lateral forces you indicate. I've typically provided a shear wall schedule with forces in the walls at each floor.

One bit of advice -- talk to a local precaster. Or, if the contractor is on board early, talk to their proposed precasters. They are usually VERY helpful, and will assist you with many of your questions.

Details are important, esp. if this is your first project. Before the precaster is brought on board, you will need to make sure that the TT layouts are reasonable based on spans and bay dimensions (use the PCI manual). You'll also need to make sure the depth of your IT beam will allow enough clearance based on the floor/floor heights. Detail tooled joints between the TT's, give special attention to the drainage layout, make sure your shear walls can be attached to the diaphragm (i.e. they're on the correct side of stairwell/elevator openings, as precast drag connections are seldom practical).

That's a start -- again, talking to a precaster early is worth it's weight in gold... they'll usually look at a preliminary plan and details and offer great advice early in the process.

 

[Robbiee]

JKStruct,

Thanks for you input. What are the alternatives typically done to providing reinforcement in the topping slab to act as diaphragm chords?