Deck 22: Concrete Construction-I Formwork, Reinforcement, and Slabs-On-Ground

Question 1

In a typical site- cast reinforced- concrete structure, the cost of formwork and shores is

A)approximately 50% of the combined cost of concrete and steel.
B)approximately 75% of the combined cost of concrete and steel.
C)approximately equal to the combined cost of concrete and steel.
D)approximately 25% of the combined cost of concrete and steel.
E)none of the above.

Answer 1

C

Question 2

According to building codes, plain concrete (concrete without steel reinforcement)is not permitted in new construction.

Answer 2

False

Question 3

Scaffold- type shores are generally made from

A)steel plates.
B)plywood.
C)dimension lumber.
D)steel pipes.
E)all of the above.

Answer 3

D

Question 4

The structural design of formwork design is the responsibility of the

A)structural engineer.
B)general contractor.
C)structural engineer, but the design must be approved by the building official.
D)general contractor, but the design must be approved by the structural engineer.
E)none of the above.

Question 5

The term flying form refers to

A)a large formwork assembly for roof slabs.
B)a large formwork assembly for floor and roof slabs.
C)a large formwork assembly for columns.
D)a large formwork assembly for concrete walls.
E)a large formwork assembly for floor slabs.

Question 6

Stirrups are used in a concrete beam

A)to increase the tensile strength of the beam beyond that provided by concrete.
B)to provide shear strength in the beam because concrete's shear strength is negligible.
C)to increase the beam's compressive strength.
D)to provide tensile strength in the beam since concrete's tensile strength is negligible.
E)to increase the shear strength of the beam beyond that provided by concrete.

Question 7

A doubly reinforced beam is one in which

A)reinforcing bars are provided in two layers at the bottom of the beam.
B)reinforcing bars are provided in two layers at the top of the beam.
C)reinforcing bars are provided in bundles of two bars.
D)reinforcing bars are provided at the top and bottom of the beam.
E)none of the above.

Question 8

In site- cast concrete construction, shores are used

A)as formwork for concrete columns.
B)as formwork for concrete walls.
C)in ground- supported concrete slabs.
D)in elevated concrete slabs.
E)none of the above.

Question 9

High- density overlay (HDO)on form plywood

A)improves the strippability of forms.
B)increases reusability of forms.
C)allows easier cleaning of forms.
D)all of the above.
E)none of the above.

Question 10

Which of the following statements is true?

A)Posttensioning is generally done at the construction site and yields a precast, posttensioned concrete member.
B)Pretensioning is generally done at the precaster's plant and yields a precast, prestressed concrete member.
C)Posttensioning is generally done at the precaster's plant and yields a precast, posttensioned concrete member.
D)Pretensioning is generally done at the construction site and yields a precast, prestressed concrete member.

Question 11

Stirrups are generally made of

A)No. 6 or No. 7 bars.
B)No. 3 or No. 4 bars.
C)No. 4, No. 5, or No. 6 bars.
D)bars of any diameter, as needed.

Question 12

The yield strength of prestressing steel is

A)60 ksi.
B)100 ksi.
C)50 ksi.
D)40 ksi.
E)none of the above.

Question 13

Height adjustability in shores made of dimension lumber

A)is provided through a screw- based metal assembly.
B)is provided through lapped members clamped together with specially made clamps.
C)is provided through A or B.
D)is not provided.

Question 14

Form liners are used to

A)allow acid etching of concrete form before placing concrete.
B)produce textured concrete surfaces.
C)allow acid etching of the concrete surface after stripping the forms.
D)ensure easy strippability of forms.
E)allow water washing of concrete after stripping the forms.

Question 15

Concrete shell roofs are not commonly used because

A)they require a relatively large amount of concrete per square foot of floor area.
B)they require prestressing, which substantially raises their cost.
C)they require a relatively large amount of steel reinforcement per square foot.
D)all of the above.
E)none of the above.

Question 16

The primary purpose of steel reinforcement is to increase the tensile strength of concrete elements. However, steel reinforcement is also used to increase the shear strength and compressive strength of concrete elements.

Question 17

Aluminum is commonly used as form and shore material because

A)its strength- to- weight ratio is high, which reduces the weight of forms and shores.
B)it is an easily nailable material.
C)it is chemically compatible with wet concrete.
D)its strength- to- weight ratio is low, which reduces the weight of forms and shores.
E)all of the above.

Question 18

The term prestressed concrete refers to both pretensioned and posttensioned concrete.

Question 19

Reshoring concrete structures are necessary where excessive deflection of floor slabs or foundation settlement is anticipated on removal of shores.

Question 20

Which of the following statements is true?

A)The term strands refers to reinforcing bars that have been bent to required shapes.
B)The term strands includes tendons.
C)The term tendons includes strands.
D)The term tendons refers to reinforcing bars that have been bent to required shapes.
E)None of the above.

Question 21

A PT concrete slab- on- ground may either be a ribbed slab or a constant- thickness slab.

Question 22

If a concrete member is not subjected to tensile stresses created by the loads, such as a slab on a firm base (ground), does it still need steel reinforcement?

Question 23

What is prestressing of concrete?

Question 24

Formwork for a concrete wall generally consists of

A)plywood, form ties, walers, and stiffbacks fastened together with clamps.
B)plywood, form ties, walers, and stiffbacks fastened together with duplex nails.
C)plywood, form ties, and walers fastened together with duplex nails.
D)plywood and stiffbacks fastened together with clamps.

Question 25

A vapor retarder is required under

A)all interior concrete slabs- on- ground.
B)all exterior concrete slabs- on- ground.
C)all concrete slabs- on- ground.
D)some interior concrete slabs- on- ground.

Question 26

Hooks are used

A)where the lap- splice length is excessive.
B)where lap splicing of bars will produce excessive congestion.
C)to lap splice reinforcing bars.
D)all of the above.
E)none of the above.

Question 27

In a PT concrete slab- on- ground, the tendons are stressed from the

A)live ends.
B)lower ends.
C)dead ends.
D)upper ends.
E)any one of the above.

Question 28

Mechanical couplers are used

A)where the lap- splice length of reinforcing bars is excessive.
B)to lap splice reinforcing bars.
C)as an economical alternative to lap splicing of reinforcing bars.
D)where lap splicing of reinforcing bars will produce excessive congestion.
E)none of the above.

Question 29

Why is steel reinforcement required in concrete?

Question 30

Concrete can be prestressed in two ways. Name them.

Question 31

The strength of concrete in a residential concrete slab- on- ground is generally

A)3,000 psi.
B)5,000 psi.
C)4,000 psi.
D)2,000 psi.
E)1,000 psi.

Question 32

Pocket formers in a PT concrete slab- on- ground are used at

A)live ends.
B)upper ends.
C)dead ends.
D)lower ends.
E)any one of the above.

Question 33

Hooks in bars are produced by turning the bars through

A)180° or 270°.
B)45° or 90°.
C)90° or 180°.
D)30° or 60°.

Question 34

The most important reason for providing ties in a concrete column is to

A)increase the shear strength of a column.
B)allow the formwork to be tied to the longitudinal bars in the column.
C)prevent the buckling of longitudinal column bars.
D)increase the compressive strength of a column.
E)Ties are generally not provided in a concrete column.

Question 35

A construction joint in a concrete slab- on- ground is required if the concrete in the slab cannot be placed in one continuous operation.

Question 36

The most important reason for providing ties in a concrete wall is to

A)prevent the buckling of longitudinal bars in the wall.
B)increase the compressive strength of the wall.
C)allow the formwork to be tied to the longitudinal bars in the wall.
D)increase the shear strength of the wall.
E)Ties are generally not provided in a concrete wall.

Question 37

Explain what the following terms mean: plain concrete, reinforced concrete, and prestressed concrete.

Question 38

Steel reinforcement in concrete elements that are permanently exposed to the earth, such as in footings, must have a minimum concrete cover of

A)3 in.
B)5 in.
C)4 in.
D)1 in.
E)2 in.

Question 39

The chairs used to support reinforcing steel bars are generally

A)steel chairs with plastic- coated feet.
B)steel- encased plastic chairs.
C)plastic chairs.
D)A and B.
E)A and C.

Question 40

The tendons used for prestressing a PT concrete slab- on- ground generally consist of

A)two- strand tendons, each strand made of seven wires.
B)a single 1/2- in.- diameter, nine- wire strand.
C)three- strand tendons, each strand made of seven wires.
D)a single 1/2- in.- diameter, seven- wire strand.
E)none of the above.

Question 41

What are the advantages of prestressing?

Question 42

Is concrete cover required in concrete foundations although a foundation is not exposed to the outside environment?

Question 43

Explain what a form- release agent is.

Question 44

What is the function of a vapor retarder under a concrete slab- on- ground?

Question 45

Explain what pretensioning of concrete is.

Question 46

What function do ties serve in a reinforced concrete column?

Question 47

A reinforced concrete column has vertical bars, referred to as longitudinal bars. Does a column need any other form of steel?

Question 48

Explain the difference between prestressing strands and prestressing tendons.

Question 49

Explain what stirrups in a reinforced concrete beam are and their function.

Question 50

What is concrete formwork? Which materials are commonly used for the formwork?

Question 51

Explain what reshoring is.

Question 52

What is a form liner and what is it made of?

Question 53

Apart from corrosion protection, what is the other function of concrete cover?

Question 54

Is the structural engineer of the project or someone else responsible for the structural design of the formwork for concrete elements? Give reasons for your answer.

Question 55

Explain what posttensioning of concrete is.

Question 56

What is a shore and which material is it made of?

Question 57

Explain what concrete cover is in reinforced concrete components and why it is necessary.

Question 58

If a concrete member is not a precast concrete member, can it prestressed? Explain.

Question 59

What is a lap splice in steel bars and why is it required?

Question 60

Which of the two methods of prestressing (pretensioning or posttensining)yields a precast, prestressed concrete member?

Question 61

Name the items of the equipment used to pull the prestressing strands.

Question 62

Explain what a control joint in a concrete slab- on- ground is and its purpose.

Question 63

Explain what a construction joint is.

Question 64

Explain what an isolation joint in concrete construction is.

Question 65

What is the function of a drainage layer under a concrete slab- on- ground?

Question 66

In which situations is a vapor retarder under a concrete slab- on- ground not needed?

Question 67

Which material is used for a drainage layer under a concrete slab- on- ground and why?

Question 68

What is the function of stirrups? Sketch commonly used open- loop and closed- loop stirrups.

Question 69

Describe the difference between (a)reinforcing steel and prestressing steel, (b)formwork and shores, (c)formwork and flying forms, and (d)shoring and reshoring.

Question 70

Concrete reinforcing bars come in limited lengths. Explain how we ensure their continuity in a long structural element, such as a column in a high- rise building or a long, continuous beam.

Question 71

Which material is used for vapor retarder under a concrete slab- on- ground?

Question 72

Explain what concrete cover is and the functions it serves.

Question 73

Explain how control joints in a concrete slab- on- ground are provided.

Question 74

How many wires are there in a typical prestressing monostrand?

Question 75

Why is a shear key required in a construction joint?

Question 76

What is a ribbed concrete slab- on- ground?

Question 77

Describe the differences between pretensioning and posttensioning of concrete. Is there any difference in the type of steel used in each case?

Question 78

Why should the control joints in a concrete slab- on- ground be provided as soon as possible?

Question 79

How does a vapor retarder under a concrete slab- on- ground affect the stresses caused by the shrinkage of the concrete slab?

Question 80

When a strand is tensioned (pulled), is it pulled from the dead end or live end?