Chapter 14: Sitecast Concrete Framing Systems

Question 1

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.

Answer 1

Slab on grade

Question 2

Can slab on grade be suspended?

Answer 2

Yes

Question 3

What is the usual thickness of slab on grade?

Answer 3

4-6 inches

Question 4

What are the steps of subgrade preparation?

Answer 4

• Site cleared
• Organic topsoil is removed
• Subgrade is excavated

Question 5

Protects the slab from moisture in the ground, such as a heavy plastic sheet. Must be durable and resistant to punctures.

Answer 5

Moisture barrier/vapor retarder

Question 6

Where is the moisture barrier placed?

Answer 6

Under interior slabs, but not exterior

Question 7

Drawing a stiff plank of wood or metal across the top edges of the formwork to achieve a level concrete surface

Answer 7

Strike off/screed

Question 8

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.

Answer 8

Floating

Question 9

Creates neatly formed edges and joints.

Answer 9

Edging and grooving

Question 10

Done immediately after the second floating

Answer 10

Troweling

Question 11

What is a trowel?

Answer 11

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.

Question 12

Creates a slip resistant texture

Answer 12

Broom finish

Question 13

Freshly-poured concrete must be kept _____ for at least the first week.

Answer 13

Damp

Question 14

Reinforcing improves the cracking resistance of:

Answer 14

• Concrete shrinkage during curing
• Thermal expansion/contraction
• Concentrated stresses
• Differential settlement

Question 15

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.

Answer 15

Drainage layer

Question 16

Concrete walls are susceptible to cracking due to concrete shrinkage during _____, _____ _____, an other effects.

Answer 16

Curing; thermal stresses

Question 17

Thin, lightly reinforced concrete slabs are prone to:

Answer 17

Cracking

Question 18

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.

Answer 18

Tilt-up construction

Question 19

Concrete walls are most commonly cast over:

Answer 19

Concrete strip footings

Question 20

Poor quality formwork construction leads to _____ in the concrete wall that become evident after the formwork is removed.

Answer 20

Defects

Question 21

Poor consolidation leads to a _____ _____ in the wall. Unsound concrete will be removed and the area patched.

Answer 21

Rock pocket

Question 22

Contain the concrete when the wall is poured, but becomes a permanent part of the wall. It acts as thermal insulation.

Answer 22

Insulating concrete forms (ICFs)

Question 23

Spans across lines of support furnished by walls or beams

Answer 23

One-way solid slab

Question 24

Vertical reinforcing bars _____ the column’s carrying capacity and gives it resistance to _____/_____ forces.

Answer 24

Increase; bending/buckling

Question 25

How does a one-way concrete joist system/ribbed slab function?

Answer 25

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.

Question 26

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.

Answer 26

Wide-module concrete joist system/skip-joist system

Question 27

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.

Answer 27

Two-way solid slab

Question 28

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.

Answer 28

Two-way flat slab

Question 29

Used chiefly with two-way flat plate structures. Virtually eliminates formwork. Hydraulic jacks lift the slabs up the columns to their final elevations.

Answer 29

Lift-slab construction

Question 30

Welded wire reinforcing may be partially discontinued at control joints in a concrete slab on grade.

Answer 30

True

Question 31

Steel troweling of a concrete slab can begin as soon as the straightedging operation is concluded.

Answer 31

False - this occurs before straightedging.

Question 32

The center portions of form ties remain permanently embedded in a concrete wall.

Answer 32

True

Question 33

Wood dowels are used to bond a concrete column to its footing.

Answer 33

False - dowels in this case are vertical steel rebars installed in the footing.

Question 34

Why are columns offset at the top?

Answer 34

To overlap the reinforcing for the column in the next story

Question 35

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:

Answer 35

This concrete isn’t doing much work structurally

Question 36

Flying formwork is:

Answer 36

A large piece of reusable floor formwork supported on trusses and moved with a crane