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Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan

Concrete Subjected to High Temperatures  Compressive

Strength

of

Concrete

at

High

Temperatures

Prof. Dr. Qaisar Ali

CE 5115 Advance Design of Reinforced Concrete Structures

Fall 2011

41

Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan

Reinforcing Steels  Types 

Deformed Bar Reinforcement: ACI 3.5.3

Plain Reinforcement: ACI 3.5.4

Prestressing Steel: ACI 3.5.5

Structural Steel Shapes: ACI 3.5.6

Prof. Dr. Qaisar Ali

CE 5115 Advance Design of Reinforced Concrete Structures

Fall 2011

42

21


Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan

Deformed Bar Reinforcement  ASTM A 615, Specification for Deformed and Plain Carbon-Steel Bars for Concrete Reinforcement.  ASTM A 706, Specification for LowAlloy Steel Deformed and Plain Bars for Concrete Reinforcement.  ASTM A 996, Specification for RailSteel

and

Axle-Steel

Deformed

Bars for Concrete Reinforcement.

Prof. Dr. Qaisar Ali

CE 5115 Advance Design of Reinforced Concrete Structures

Fall 2011

43

Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan

Deformed Bar Reinforcement

Prof. Dr. Qaisar Ali

CE 5115 Advance Design of Reinforced Concrete Structures

Fall 2011

44

22


Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan

Deformed Bar Reinforcement Bar Designation

Area (in.2)

Weight (plf)

Diameter (in.)

No. 3

0.11

0.376

0.375

No. 4

0.20

0.668

0.500

No. 5

0.31

1.043

0.625

No. 6

0.44

1.502

0.750

No. 7

0.60

2.044

0.875

No. 8

0.79

2.670

1.000

No. 9

1.00

3.400

1.128

No. 10

1.27

4.303

1.270

No. 11

1.56

5.313

1.410

No. 14

2.25

7.650

1.693

No. 18

4.00

13.600

2.257

Prof. Dr. Qaisar Ali

CE 5115 Advance Design of Reinforced Concrete Structures

Fall 2011

45

Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan

Deformed Bar Reinforcement

fs = fy fs = Esď Ľs

Prof. Dr. Qaisar Ali

CE 5115 Advance Design of Reinforced Concrete Structures

Fall 2011

46

23


Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan

Deformed Bar Reinforcement Steel Minimum yield Ultimate Grade stress, f y (ksi) strength (ksi) 40

40

70

50

50

80

60

60

90

75

75

100

Prof. Dr. Qaisar Ali

Stress strain curves for reinforcement

CE 5115 Advance Design of Reinforced Concrete Structures

Fall 2011

47

Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan

Deformed Bar Reinforcement ď‚— Variation in Yield Strength ď‚— Distribution of mill test yield strength for grade 60 steel.

Prof. Dr. Qaisar Ali

CE 5115 Advance Design of Reinforced Concrete Structures

Fall 2011

48

24


Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan

Deformed Bar Reinforcement  Strength of Reinforcing Steel at High temperatures  Deformed reinforcement subjected to high temperatures in fires tends to lose its strength.

Prof. Dr. Qaisar Ali

CE 5115 Advance Design of Reinforced Concrete Structures

Fall 2011

49

Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan

ACI Chapter 3: Materials  Tests of Materials 

A complete record of tests of materials and of concrete shall be retained by the inspector for 2 years after completion of the project, and made available for inspection during the progress of the work.

 Water 

Water used in mixing concrete shall be clean and free from injurious amounts of oils, acids, alkalis, salts, organic materials, or other substances deleterious to concrete or reinforcement.

Prof. Dr. Qaisar Ali

CE 5115 Advance Design of Reinforced Concrete Structures

Fall 2011

50

25


Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan

ACI Chapter 3: Materials  Steel Reinforcement 

Reinforcement shall be deformed reinforcement, except that plain reinforcement shall be permitted for spirals or prestressing steel; and reinforcement consisting of structural steel, steel pipe, or steel tubing shall be permitted as specified in this code.

Visit of the Chapter

Prof. Dr. Qaisar Ali

CE 5115 Advance Design of Reinforced Concrete Structures

Fall 2011

51

Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan

ACI Chapter 4: Durability of Concrete  Sulfate exposures 

Concrete to be exposed to sulfate-containing solutions or soils shall conform to requirements of Table 4.3.1 or shall be concrete made with a cement that provides sulfate resistance and that has a maximum water-cementitious materials ratio and minimum compressive strength from Table 4.3.1.

Prof. Dr. Qaisar Ali

CE 5115 Advance Design of Reinforced Concrete Structures

Fall 2011

52

26


Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan

ACI Chapter 4: Durability of Concrete  Corrosion Protection 

For corrosion protection of reinforcement in concrete, maximum water soluble chloride ion concentrations in hardened concrete at ages from 28 to 42 days contributed from

the

ingredients

including

water,

aggregates,

cementitious materials, and admixtures shall not exceed the limits of Table 4.4.1. When testing is performed to determine

water

soluble

chloride

ion

content,

test

procedures shall conform to ASTM C 1218. 

Visit of the Chapter

Prof. Dr. Qaisar Ali

CE 5115 Advance Design of Reinforced Concrete Structures

Fall 2011

53

Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan

ACI Chapter 5: Concrete Quality, Mixing and Placing 

Average Strength of Concrete Produced in the Field 

It is emphasized in this chapter that the average strength of concrete produced in the filed should always exceed the specified value of fc′ used in the structural design calculations.

This is based on probabilistic concepts, and is intended to ensure that adequate concrete strength will be developed in the structure.

Prof. Dr. Qaisar Ali

CE 5115 Advance Design of Reinforced Concrete Structures

Fall 2011

54

27


Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan

ACI Chapter 5: Concrete Quality, Mixing and Placing  Average Strength of Concrete Produced in the Field 

Variation in Strength 

Variations in the properties or proportions of constituents of concrete, as well as variations in transporting, placing, and compaction of the concrete, lead to variations in the strength of the finished concrete. In addition, discrepancies in the tests will lead to apparent differences in strength.

Prof. Dr. Qaisar Ali

CE 5115 Advance Design of Reinforced Concrete Structures

Fall 2011

55

Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan

ACI Chapter 5: Concrete Quality, Mixing and Placing  Average Strength of Concrete Produced in the Field 

Variation in Strength 

Figure shows the distribution of strengths in a sample of 176 concrete cylinder tests for the concrete having nominal strength of 3000 psi

Results of tests

Strength less than nominal = 9

Strength more than nominal = 167

Prof. Dr. Qaisar Ali

CE 5115 Advance Design of Reinforced Concrete Structures

Fall 2011

56

28


Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan

ACI Chapter 5: Concrete Quality, Mixing and Placing  ACI recommendations for achieving specified strength in the field 

The ACI code recommends that selection of concrete proportions for achieving a specified concrete strength in the field shall be based on the required average compressive strength of concrete f cr′ and not on the specified strength. 

ACI table 5.2.2.

Prof. Dr. Qaisar Ali

CE 5115 Advance Design of Reinforced Concrete Structures

Fall 2011

57

Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan

ACI Chapter 5: Concrete Quality, Mixing and Placing  Selection of Concrete Proportions 

Proportions of materials for concrete shall be established to provide: 

Workability and consistency to permit concrete to be worked readily into forms and around reinforcement under conditions of placement to be employed, without segregation or excessive bleeding;

Resistance to special exposures as required by Chapter 4 of ACI;

Prof. Dr. Qaisar Ali

Conformance with strength test requirements of ACI 5.6. CE 5115 Advance Design of Reinforced Concrete Structures

Fall 2011

58

29


Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan

ACI Chapter 5: Concrete Quality, Mixing and Placing  Selection of Concrete Proportions 

Recommendations for selecting

proportions for concrete

are given in detail in “Standard Practice for Selecting Proportions for Normal, Heavyweight, and Mass Concrete” (ACI 211.1).

Prof. Dr. Qaisar Ali

CE 5115 Advance Design of Reinforced Concrete Structures

Fall 2011

59

Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan

ACI Chapter 5: Concrete Quality, Mixing and Placing  Sampling Frequency for Strength Tests 

ACI R5.6.2.1: As a measure of quality control, the code recommends following criteria for collecting samples of concrete cylinders from a given class of concrete: 

Once each day a given class is placed, nor less than

Once for each 150 yd3 of each class placed each day, nor less than

Once for each 5000 ft2 of slab or wall surface area placed each day. 

In calculating surface area, only one side of the slab or wall should be considered.

Prof. Dr. Qaisar Ali

CE 5115 Advance Design of Reinforced Concrete Structures

Fall 2011

60

30


Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan

ACI Chapter 5: Concrete Quality, Mixing and Placing  Strength Test 

A strength test shall be the average of the strengths of two cylinders made from the same sample of concrete and tested at 28 days or at test age designated for determination of fc′.

Prof. Dr. Qaisar Ali

CE 5115 Advance Design of Reinforced Concrete Structures

Fall 2011

61

Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan

ACI Chapter 5: Concrete Quality, Mixing and Placing  Criterion for Satisfactory Concrete Strength 

ACI 5.6.3.3: Strength level of an individual class of concrete shall be considered satisfactory if both of the following requirements are met: 

(a) Every arithmetic average of any three consecutive strength tests equals or exceeds fc′;

(b) No individual strength test (average of two cylinders) falls below fc′ by more than 500 psi when fc′ is 5000 psi or less; or by more than 0.10fc′ when fc′ is more than 5000 psi.

Prof. Dr. Qaisar Ali

CE 5115 Advance Design of Reinforced Concrete Structures

Fall 2011

62

31


Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan

ACI Chapter 5: Concrete Quality, Mixing and Placing  The steps taken to increase the average level of test results: 

It will depend on the particular circumstances, but could include one or more of the following: 

An increase in cementitious materials content

Changes in mixture proportions

Reductions in or better control of levels of slump supplied

Closer control of air content

An improvement in the quality of the testing, including strict compliance with standard test procedures

Prof. Dr. Qaisar Ali

CE 5115 Advance Design of Reinforced Concrete Structures

Fall 2011

63

Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan

ACI Chapter 5: Concrete Quality, Mixing and Placing  Investigation of Low Strength Test Results 

If any strength test of laboratory-cured cylinders falls below specified value of fc′ by more than the values given in 5.6.3.3(b), steps shall be taken to assure that load-carrying capacity of the structure is not jeopardized.

Prof. Dr. Qaisar Ali

CE 5115 Advance Design of Reinforced Concrete Structures

Fall 2011

64

32


Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan

ACI Chapter 5: Concrete Quality, Mixing and Placing  Investigation of Low Strength Test Results 

If the likelihood of low-strength concrete is confirmed and calculations

indicate

that

load-carrying

capacity

is

significantly reduced, tests of cores drilled from the area in question in accordance with “Method of Obtaining and Testing Drilled Cores and Sawed Beams of Concrete” (ASTM C 42) shall be permitted. 

In such cases, three cores shall be taken for each strength test that falls below the values given in 5.6.3.3(b).

Prof. Dr. Qaisar Ali

CE 5115 Advance Design of Reinforced Concrete Structures

Fall 2011

65

Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan

ACI Chapter 5: Concrete Quality, Mixing and Placing  Investigation of Low Strength Test Results 

According to ACI 5.6.5.4, concrete in an area represented by core tests shall be considered structurally adequate if the average of three cores is equal to at least 85 percent of fc′ and if no single core is less than 75 percent of fc′.

Prof. Dr. Qaisar Ali

CE 5115 Advance Design of Reinforced Concrete Structures

Fall 2011

66

33


Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan

ACI Chapter 5: Concrete Quality, Mixing and Placing  Investigation of Low Strength Test Results 

If criteria of ACI 5.6.5.4 are not met and if the structural adequacy remains in doubt, the responsible authority shall be permitted to order a strength evaluation in accordance with Chapter 20 for the questionable portion of the structure, or take other appropriate action.

Visit ACI Chapter 5.

Prof. Dr. Qaisar Ali

CE 5115 Advance Design of Reinforced Concrete Structures

Fall 2011

67

Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan

References  Reinforced Concrete - Mechanics and Design (4th Ed.) by James MacGregor.  ACI 318-02  PCA 2002

Prof. Dr. Qaisar Ali

CE 5115 Advance Design of Reinforced Concrete Structures

Fall 2011

68

34


Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan

The End

Prof. Dr. Qaisar Ali

CE 5115 Advance Design of Reinforced Concrete Structures

Fall 2011

69

35


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