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PCE 3 > PRELIM > Flashcards

PRELIM Flashcards

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1
Q

Is a stone-like material obtained by permitting a carefully proportioned mixture of cement, sand, and gravel or other aggregate and water to hardened in forms of shape and dimensions of the desired structure.

A

Concrete

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2
Q

Cement and water interact chemically to land the aggregate particles into a solid mass.

A

Concrete

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3
Q

What are the special aggregates

A

Lightweight Aggregate
Heavyweight Aggregate

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4
Q

What are the example of admixtures

A

Plasticizers
Airentraining Agents
Silica Pume
Fly Ash

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5
Q

The process of controlling conditions after placement of concrete

A

Curing

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6
Q

The resulting combination of two materials when reinforcement is completely surrounded by the hardened concrete mass, it forms an integral part of the member.

A

Reinforced Concrete

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7
Q

Concrete in which effective internal stress are induced artificially, usually by means of tensioned steel, prior to loading the structure

A

Prestressed Concrete

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8
Q

A technique for introducing stresses instructures during the process of construction, so that a more favorable state of stress will prevail under service loads

A

Prestressing

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9
Q

A stretched element in a concrete (usually made of steel) different from reinforcement which is without initial prestressing

A

Tendon

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10
Q

-This is a method of prestressing by which the tendons are tensioned before concrete is placed

A

Pre-Tensioning

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11
Q

-This is a method of prestressing by which tendons are tensioned after the concrete has harded.

A

Post-tensioning

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12
Q

-The tendons, usually wire or strands, are stretched between bulkheads or abutments and the concrete is poured around them

-When the concrete has hardened and reached the required strength, the tendons are released from the anchorages and the prestress is transferred to the concrete by bond

A

Pre-tensioning

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13
Q

-Concrete is cast, incorporating sheats for the tendons to pass

-When the concrete has gained the required strength, the tendons are tensioned against the steel bearing plate cast into the ends of the member

-The prestress is transfered to the concrete mechanical anchorage

-The space between the tendons and sheats is usually grouted on completion of the tensioning operation

A

Post-tensioning

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14
Q

Advantage of prestressed over reinforced concrete about cracks

A
  • Free from cracks under service loads and hence better appearance and durability
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15
Q

Materials for prestressed concrete steel

A
  1. High tensile steel wire or strand complying BS 5896:1980
  2. Allow steel bars complying BS 4486:1980
  3. Concrete
    - 30 to 60 MPa
    - Water with cement ratio 0:30 - 0.45 usually plasticizers is added to improve workability of concrete
    - 28 days curing
    - Strength transfer should not be less than 25 MPa in 7 days
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16
Q

The support of the beam

A

Bearing

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17
Q

Tendon bonded/not bonded throughout its length to the surrounding concrete

A

Bonded and Unbonded Tendon

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18
Q

A group of tendons

A

Cables

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19
Q

The upward deflection of a prestressed concrete beam when it is prestressed

A

Camber

20
Q

Circular prestressing refers to prestressing in round structures like tanks; prestressing in all other members is termed linear

A

Circular and Linear Prestressing

21
Q

The portion of the prestressed concrete beam surrounding the anchorage of post-tensioned tendons

A

End block

22
Q

Degree of prestress applied to concrete in which no tension (some tension and usually some flexural cracking) is permitted in the concrete under working loads

A

Full and partial prestressing

23
Q

The transferring of prestress to concrete

A

Transfer

24
Q

Classification of concrete structure where fully prestressed concrete structures in which there is no flexural tensile stress allowed under service conditions (working load) and very limited flexural tensile stress is allowed at transfer

A

Class 1

25
Q

Classification of concrete structure where prestressed concrete structures in which flexural tensile stress is allowed but not limited so that no visible cracking may occur under service conditions

A

Class 2

26
Q

Prestressed concrete structures are generally design with reference to the limit states of allowable stress and deflection of the service loads using elastic theory, and adequate ultimate strength theory

A

Limit States Requirements

26
Q

Classification of concrete structure where prestressed concrete structures in which cracking is allowed to occur under service conditions, but the width of cracks is limited to 0.1mm for members in very severe environments and not exceeding to 0.2mm for all members

A

Class 3

27
Q

The maximum stress that can be safely applied to a structure

A

Allowable Stress or Allowable Strength

28
Q

2 design considerations at transfer

A

a. Flexural Stresses
b. Upward deflection (camber)

29
Q

2 design considerations under service condition

A

a. flexural stresses
b. downward deflection

30
Q

2 design considerations under failure condition

A

a. Flexural strength
b. Shear strength

31
Q

Stress limitations in prestressed concrete in prestressing tendons

A
  1. The jacking force should not normally exceed 75% of the characteristic strength of the tendon
  2. The maximum initial prestress at transfer should not normally exceed 70% of the characteristic strength of the tendon
32
Q

Stress limitations in prestressed concrete at concrete for Allowable compressive stresses at transfer

A

At extreme fiber = 0.5fci
For near uniform distribution of prestress = 0.4fci

where fci is the concrete strength at transfer

33
Q

Stress limitations in prestressed concrete at concrete for Allowable tensile stress at transfer

A

Class 1 members - 1.0 N/mm² (solely due to prestressing force)
Class 2 & Class 3 members
-Pre-tensioned members 0.45√fci
-Post-tensioned memvers 0.36√fci

where fci is the concrete strength at transfer

34
Q

Stress limitations in prestressed concrete at concrete for allowable compressive stress under service conditions

A

In bending = 0.33fcu
In direct compression = 0.25fcu

where fcu is the characteristic strength of concrete

35
Q

Stress limitations in prestressed concrete at concrete for allowable tensile stress under service condition

A

Class 1 members
- no tensile stress

Class 2 members
-Pre tensioned: 0.45√fcu
-post tensioned 0.36√fcu

36
Q

Value of Grade 30,40,50,60 of pre tensioned

A

Pretensioned
Grade 30 = —-
Grade 40 = 2.9
Grade 50 = 3.2
Grade 60 = 3.5

37
Q

Value of Grade 30,40,50,60 of post-tensioned

A

Grade 30 = 2.1
Grade 40 = 2.3
Grade 50 = 2.6
Grade 60 = 2.8

38
Q

Advantage of prestressed over reinforced concrete about shear resistance

A

-Greater shear resistance and hence thinner web is possible, reduces dead weight, especially in long span structures

39
Q

Advantage of prestressed over reinforced concrete about rigidity

A

-Greater rigidity due to effectiveness of the whole uncracked section, hence smaller deflection

40
Q

Advantage of prestressed over reinforced concrete about load

A

-Lighter structure: hence saving headroom or smaller load on foundation, usually suitable for long span structures

41
Q

Advantage of prestressed over reinforced concrete about stress

A

-Test-proofing of materials for many structures, during prestressing, both the steel and the concrete are subjected to the highest stress that will exist in the structures during their life of service

42
Q

Material for prestressed concrete steel of high tensire wire or strand

A

High tensile steel wire or strand complying BS 5896:1980

43
Q

Material for prestressed concrete steel of alloy steel bars

A

Allow steel bars complying BS 4486:1980

44
Q

Material for prestressed concrete steel of concrete

A
  • 30 to 60 MPa
  • Water with cement ratio 0:30 - 0.45 usually plasticizers is added to improve workability of concrete
  • 28 days curing
  • Strength transfer should not be less than 25 MPa in 7 days

PCE 3 (3 decks)

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