Precast components in parking structures

Precast components in parking structures

27 Dec 2019

Introduction

This article describes the basic precast components which are being used in multilevel precast parking garages.

1. Advantages of precast building system for parking structures

Precast components are the most popular structural system for multilevel parking structures. Advantages of using a precast building system for parking structures are as follows:
  1.     Large spans with prestressed double tee slabs to create open and efficient layouts
  2.     Fire resistant precast concrete structure
  3.     Architectural design with different textures and colors in exterior precast panels
  4.     Durable and low maintenance building system
  5.     Fast, all weather erection with precast components
  6.     Cost advantage because of repetition in precast components

2. Precast components

Typical components of a precast parking garage:
  1.     Double tee
  2.     Spandrel beam
  3.     Column
  4.     Shear wall
  5.     Ramp wall
  6.     Inverted T beam
  7.     Stair / elevator walls
  8.     Solid slab
 
Picture 1. Typical components of a precast parking garage

3. Double tees

Precast double tees are structural slabs consisting of two vertical stems connected to each other by a horizontal deck (the flanges). Double tees are prestressed precast components made on pretensioning beds. The strands that are prestressed are placed inside the stems and the flanges are reinforced with a mild steel reinforcing mesh. Due to the optimized design precast double tees are used to create large clear spans in parking structures. Typical double tee flange width is 8 to 10 feet with size of up to 15 feet available. Stem depth can range between 12 to 34 inches (up to 5 ft). Typical double tee span length ranges from 25 to 55 feet and double tees with span of 80 feet or even more have been fabricated.
 
Picture 2. Precast double tee slabs

4. Precast spandrel beams

Precast spandrel beams are generally used at the perimeter of precast parking structures to support the double tees and transfer their loads to the load bearing columns or walls. Spandrel beams are prestressed precast components which are typically 76 inches deep with spans ranging from 48 ft to 60 ft having a web thickness of minimum 8 inches. Spandrel beams are supporting the double tees on either a continuous ledge, spot corbels or inside pockets. The exterior spandrels can be designed and fabricated with architectural finish in different colors and textures. Textures and finishes like acid etch, water wash, sandblast, exposed aggregates, polished surface, formliners, brick and stone veneers are possible.

Picture 3. Precast spandrel beams

5. Precast columns

Generally the precast columns are placed at the periphery of the car park where they support the spandrel beams and inverted T-beams. To support the spandrel beams the precast columns can be fabricated with ledges. Also columns can be fabricated with additional large corbels for the support of the precast IT-beams. The precast columns are reinforced with prestressing steel with additional mild steel reinforcing inside the corbels and ledges.
 
Picture 4. Precast columns in parking garage

6. Precast shear walls

Precast shear walls are provided in parking structures to resist the lateral loads like wind and seismic forces. Shear walls can be made as solid panels or with openings for lighting and ventilation purposes. Large corbels can be provided on the face of the shear walls to support the inverted T-beams.
 
Picture 5. Precast shear walls in parking garage

7. Precast ramp walls

Precast ramp walls are part of the lateral load resisting system and are placed inside the parking structure parallel to the ramps. Ramp walls are fabricated with spot corbels for the support of the double tees. In case ramps are situated at both sides then the spot corbels will be provided at both of the faces of the wall. Precast ramp walls can be made as horizontal panels or as multilevel vertical panels and are generally fabricated with openings for better visibility, ventilation and openness. 
 
Picture 6. Precast ramp walls in parking garage

8. Inverted T-beams

Inverted T-beams are supporting the double tee slabs and the beams are spanning between columns and walls. They are generally bearing on large corbels attached to the columns and walls or resting inside wall pockets. The precast IT-beams are prestressed components and are made on long line casting beds.
 
Picture 7. Precast inverted T-beams for parking garage

9. Precast stair and elevator walls

The staircase and elevator walls are made as precast solid walls that can be divided as horizontal panels or as multilevel vertical panels. For support of the precast stair landings the walls are fabricated with continuous ledges. 
 
Picture 8. Precast stair walls in parking garage

10. Precast solid slabs

Solid slabs can be used in parking garages at various locations such as the floor areas near the elevator lobby and staircases. Furthermore they will be used to cover the staircase and elevator shafts where the slabs are generally resting on ledges attached to the precast walls.
 
Picture 9. Precast solid slabs in parking garage

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