Chapter 14: Sitecast Concrete Framing Systems Flashcards
A level surface of concrete that lies directly on the ground. Used for roads, sidewalks, patios, airport runways, and basements or ground floors of buildings. Supported by the ground.
Slab on grade
Can slab on grade be suspended?
Yes
What is the usual thickness of slab on grade?
4-6 inches
What are the steps of subgrade preparation?
- Site cleared
- Organic topsoil is removed
- Subgrade is excavated
Protects the slab from moisture in the ground, such as a heavy plastic sheet. Must be durable and resistant to punctures.
Moisture barrier/vapor retarder
Where is the moisture barrier placed?
Under interior slabs, but not exterior
Drawing a stiff plank of wood or metal across the top edges of the formwork to achieve a level concrete surface
Strike off/screed
Flat-surfaced tools (bull floats/darbies: 4-10ft) are drawn across the concrete to flatten and consolidate its surface so the top of the slab is level but rough. Usually performed by hand.
Floating
Creates neatly formed edges and joints.
Edging and grooving
Done immediately after the second floating
Troweling
What is a trowel?
A thin, flat steel tool, pointed or rectangular, provided with a handle and held in the hand. It is used to manipulate mastic, mortar, plaster, or concrete. A machine whose rotating steel blades are used to finish concrete slabs.
Creates a slip resistant texture
Broom finish
Freshly-poured concrete must be kept _____ for at least the first week.
Damp
Reinforcing improves the cracking resistance of:
- Concrete shrinkage during curing
- Thermal expansion/contraction
- Concentrated stresses
- Differential settlement
Crushed rock/gravel 3/4” to 1-1/2” in diameter and 4-6 inches deep. Provides void space for draining and prevents moisture build up.
Drainage layer
Concrete walls are susceptible to cracking due to concrete shrinkage during _____, _____ _____, an other effects.
Curing; thermal stresses
Thin, lightly reinforced concrete slabs are prone to:
Cracking
Concrete wall panels are poured lying flat, much like a slab on grade. Once the panels have gained sufficient strength, they are lifted into their final positions. This eliminates the formwork, saves time and reduces cost.
Tilt-up construction
Concrete walls are most commonly cast over:
Concrete strip footings
Poor quality formwork construction leads to _____ in the concrete wall that become evident after the formwork is removed.
Defects
Poor consolidation leads to a _____ _____ in the wall. Unsound concrete will be removed and the area patched.
Rock pocket
Contain the concrete when the wall is poured, but becomes a permanent part of the wall. It acts as thermal insulation.
Insulating concrete forms (ICFs)
Spans across lines of support furnished by walls or beams
One-way solid slab
Vertical reinforcing bars _____ the column’s carrying capacity and gives it resistance to _____/_____ forces.
Increase; bending/buckling
How does a one-way concrete joist system/ribbed slab function?
The bottom steel in concentrated in spaced ribs or joists. The thin slab that spans across the top of the joists is reinforced only by shrinkage-temperature bars. This efficiently and economically spans considerably longer distances than a one-way solid slab.
Joists are placed 4-6 feet apart. The slab is 4-1/2 inches and can therefore span a greater distance than normal between joists.
Wide-module concrete joist system/skip-joist system
Rare system, used for heavily loaded industrial floors. The slab is supported by a grid of beams running in both directions over the columns. The slab is reinforced in such a way that the varying stresses in the different zones of the slab are accommodated within a uniform thickness of concrete.
Two-way solid slab
A system suited to heavily-loaded buildings such as storage and industrial buildings. The formwork is fat, except for a thickening of the concrete to resist the high shear forces around the top of each column.
Two-way flat slab
Used chiefly with two-way flat plate structures. Virtually eliminates formwork. Hydraulic jacks lift the slabs up the columns to their final elevations.
Lift-slab construction
Welded wire reinforcing may be partially discontinued at control joints in a concrete slab on grade.
True
Steel troweling of a concrete slab can begin as soon as the straightedging operation is concluded.
False - this occurs before straightedging.
The center portions of form ties remain permanently embedded in a concrete wall.
True
Wood dowels are used to bond a concrete column to its footing.
False - dowels in this case are vertical steel rebars installed in the footing.
Why are columns offset at the top?
To overlap the reinforcing for the column in the next story
A one-way concrete joist system can be thought of as a very thick one-way slab with the concrete between the joists left out because:
This concrete isn’t doing much work structurally
Flying formwork is:
A large piece of reusable floor formwork supported on trusses and moved with a crane
