Precast Concrete Construction Flashcards
What is precast concrete?
concrete elements cast and cured in a manufacturing plant, then transported to the construction site
What advantages does precast concrete have over site-cast concrete? (4)
- high-quality forms can be reused hundreds of thousands of times, reducing formwork cost
- concrete mixing and pouring operations can be highly-mechanized
- work is performed in a climate-controlled environment at ground level
- use of Type III Portland cement and steam curing expedites the manufacturing process
How is precast concrete more efficient than site-cast concrete?
when compared to site-cast concrete, precast concrete assembly on site is faster and less affected by adverse weather conditions
How is the finish quality improved in precast concrete?
controlled casting conditions and high-quality forms allow for greater control of surface finishes
What is prestressing?
reinforcing with tightly stretched, high-strength, pretensioned steel strands produces greater structural efficiency
Which concrete members can be precast? (5)
- slabs
- beams/girders
- columns
- wall panels
- specialty items
What are precast concrete slabs used for, and what sizes do they include? (2)
- used for floors, roofs, bridge decks
- deeper elements span further than those that are shallower
When are solid flat slabs used?
used for short spans and locations where minimum slab depths are required
When are hollow core slabs used, and what makes them unique? (2)
- suitable for intermediate spans
- longitudinal voids replace much of the nonworking concrete
When are single tee slabs used, and what makes them unique? (2)
- used for longer spans
- most precast slabs have a rough top surface to accommodate a concrete topping later
When are double tee slabs used, and what makes them unique? (2)
- best suited for the longest spans
- double tee design allows for faster assembly at less cost
Describe the form and function of beams and girders. (2)
- provide support for slabs
- the projecting rebars will bond with concrete cast on site
Describe the form and function of precast columns. (3)
- usually square or rectangle
- provide support for beams and slabs
- typically reinforced without prestressing
Describe the form and function of precast wall panels. (2)
- precast wall panels may be solid, hollow, or sandwiched with an insulating core
- wall panels can be ribbed to increase their vertical span capacity while minimizing weight
What other concrete elements can be precast? (2)
- special concrete elements such as stairs can also be precast
- uniquely shaped structural elements
What sort of reinforcing do precast elements contain?
many precast elements contain both high-strength prestressing strands and conventional reinforcing
How are precast concrete elements assembled?
once on site, precast concrete elements are lifted into place and assembled
What determines the type of slab elements used in construction?
in all cases, choice of slab elements depends largely on span requirements
What framework can be used in conjunction with precast elements?
precast elements may also be mixed with site-cast concrete, steel, and masonry systems
What are the benefits of a site-cast concrete topping over precast slabs? (5)
- greater floor strength and stiffness
- greater fire resistance
- greater acoustic isolation
- easier integration of electrical services into floor system
- smoother, flatter floor surface
How are precast concrete members joined together? (4)
- bolted, welded, or grouted connections are commonly used
- connections can also be post-tensioned to produce continuous beam action at points of support
- the simplest connections rely on gravity
- with spanning members, bearing pads are usually inserted at points of contact to prevent grinding and allow for limited movement
How are precast column-to-column connections established? (2)
- metal-bearing plates and embedded anchor bolts are cast into the ends of the columns
- connections are dry-packed with grout to provide full-bearing and protect the metal connectors
How are precast beam-to-column connections established? (2)
- beams are set on bearing pads at the column corbels
- steel angles are welded to metal plates cast into the beams and columns
How are precast slab-to-beam connections established? (3)
- hollow core slabs are set on bearing pads on precast beams
- steel reinforcing bars inserted into the slab keyways span the joint
- good example of a gravity connection
