1. Design and Control of Concrete Mixtures CHAPTER 11
Steel Reinforcement
Design and Control of Concrete Mixtures
CHAPTER 11
Design and Control of Concrete Mixtures, 16th edition, Chapter 11 – Steel Reinforcement

2. Overview Why Use Reinforcement Reinforcing Support Reinforcing Bars
Welded Wire Reinforcement
Prestressing Steel
This module discusses the use of steel reinforcement in concrete, including steel reinforcement and types of reinforcement.

3. Why Use Reinforcement in Concrete?
Concrete is very strong in compression, but relatively weak in tension. The tensile capacity of concrete is only about one tenth of its compressive strength. Consider the beam shown here. Load applied at the center of the beam produces compression in the top of the beam, and tension in the bottom at midspan. Unreinforced, plain concrete, beams can fail suddenly upon cracking, with little warning.

4. Why Use Reinforcement in Concrete?
The addition of steel reinforcement significantly increases the load capacity of that same beam as shown in this figure. Placing reinforcement in the tension zone of concrete, as shown, also provides crack control in addition to strength and ductility to concrete structures.

5. Why Use Reinforcement in Concrete?
Also used for:
Some portion of compression loading
Diagonal tension or shear
Internal pressures in circular structures
Reducing crack sizes
Limit crack widths
In addition to resisting tensile forces in structural members, reinforcement is also used in concrete construction for the following reasons:
• To resist a portion of compression loading.
• To resist diagonal tension or shear in beams, walls, and columns.
• To resist internal pressures in circular structures such as tanks, pipes, bins, and silos.
• To reduce the size of cracks in concrete by distributing stresses resulting in numerous small cracks in place of a few large cracks.
• To limit crack widths and control spacing of cracks due to stresses induced by temperature changes and shrinkage.

6. Reinforcing Bars (Rebar)
High tensile strength, strain compatibility
Bond between steel and concrete
Steel reinforcing bars (also referred to as rebar) are remarkably well-suited for concrete reinforcement because they have high tensile strength and strain compatibility. The bond between concrete and steel allows for an effective transfer of stress or load between the steel and concrete so that both materials act together in a composite action.

7. Grades
ASTM A615- Standard Specification for Deformed and Plain Carbon-Steel Bars for Concrete Reinforcement
Grade 40
Grade 60
Grade 75
Grade 80
Reinforcing bar is specified by ASTM A615. The most common form is grade 60. If weldablity is important for construction purposes, ASTM A706, Grade 60, provides provisions for rebar that allows for reliable welding.
ASTM A706- Standard Specification for Deformed and Plain Low-Alloy Steel Bars for Concrete Reinforcement

8. Reinforcing Bars Darwin and others 2015
Reinforcing bars have distinct stress-strain curves with a definable yield plateau for the lower strength low-carbon steels. The observed strain hardening of reinforcing bars is not considered in the design of structural reinforced concrete. Some reinforcing bars, particularly those steels with a grade of 75 and higher, do not always exhibit a well-defined yield point.
Darwin and others 2015

9. Reinforcing Bars Courtesy of CRSI
In order to enhance bond, reinforcing bars are produced with deformations, as shown here, to provide mechanical bond between the bars and the concrete. To uniquely identify the reinforcement, reinforcing bars are marked during production with a letter and number signifying the type and grade of steel. The bar mark also contains a letter or symbol identifying the mill in which the bar was produced. Additionally, the bars are marked with their bar size, such as the number ‘4’ indicating a No. 4 bar.
Courtesy of CRSI

10. Summary of ASTM Strength Requirements for Reinforcement
This table lists the minimum yield and tensile strengths for the most common ASTM types of steel reinforcement.

11. Summary of ASTM Strength Requirements for Reinforcement

12. Reinforcing Bars
The bar size number is approximately the bar nominal diameter in eighths of an inch (that is, a No. 4 bar has approximately a 4/8-in., or 1⁄2-in., diameter). Alternately, rebar may be produced and marked to true metric sizes. These tables list typical bar sizes for standard ASTM reinforcing bars.

13. Corrosion Protection
In exterior environments exposed steel corrodes. Fortunately, when concrete surrounds the steel, it can provide some level of corrosion resistance as cover. In extreme cases, the corrosion can result in a reduction in the strength of the element.

14. Epoxy Coated Reinforcement
To improve the corrosion resistance of reinforcing bars under severe conditions, the bars may be epoxy coated or zinc coated (galvanized), both (dual coated), or under special circumstances, stainless steel bars may be used. Epoxy-coated reinforcement is generally recognized in the field by a green or purple coating. ASTM A775 and ASTM A934 cover the requirements for bars coated before or after fabrication (respectively) including surface preparation. Zinc and epoxy dual coated bar requirements are covered in ASTM A1055.
ASTM A775- Standard Specification for Epoxy-Coated Reinforcing Steel Bars
ASTM A934- Standard Specification for Epoxy-Coated Prefabricated Steel Reinforcing Bars

15. Epoxy Coating
Care must be taken to minimize damage to the epoxy coating during shipping and placement. Damage to the epoxy coating may result in localized corrosion and reduced performance.

16. Zinc Sacrificial physical barrier Cathodic protection
ASTM A767-Standard Specification for Zinc-Coated (Galvanized) Steel Bars for Concrete Reinforcement
Sacrificial physical barrier
Cathodic protection
Bars are typically galvanized after cutting and bending to the project requirements. Design using galvanized bars is the same as that for uncoated bars, except that bend diameters may be greater than those for the uncoated bars. Galvanized bars are covered by ASTM A767-
Standard Specification for Zinc-Coated (Galvanized) Steel Bars for Concrete Reinforcement

17. Stainless Steel Reinforcement
ASTM A955- Standard Specification for Deformed and Plain Stainless-Steel Bars for Concrete Reinforcement
Stainless-steel reinforcement may be selected where very long life is required or properties other than simple corrosion resistance is required. Stainless-steel reinforcement shall comply with ASTM A955- Standard Specification for Deformed and Plain Stainless-Steel Bars for Concrete Reinforcement

18. Welded Wire Reinforcement (WWR)
ASTM A1064
ASTM A1022
ASTM A884
ASTM A1060
For reinforcing thin slabs and other structural elements, an alternative to reinforcing bars is welded wire reinforcement (WWR), also known as welded wire mesh or fabric. A grid of orthogonal longitudinal and transverse cold-drawn steel wires is welded together at every wire intersection. The size and spacing of the wires can vary in each direction, based on the requirements of the project. Plain (smooth) wires are designated with an “MW” (“W”) and deformed wires are designated with an “MD” (“D”). Plain and deformed welded wire reinforcement is covered in a combined standard, ASTM A1064, Standard Specification for Steel Wire and Welded Wire Reinforcement, Plain and Deformed, for Concrete. Stainless steel wires are specified according to ASTM A1022, Standard Specification for Deformed and Plain Stainless Steel Wire and Welded Wire for Concrete. Epoxy-coated WWR is available in accordance with ASTM A884, Standard Specification for Epoxy-Coated Steel Wire and Welded Reinforcement. Galvanized WWR is available in accordance with ASTM A1060, Standard Specification for Zinc-Coated (Galvanized) Steel Welded Wire Reinforced, Plain and Deformed for Concrete.

19. Welded Wire Reinforcement
As per the table here, a 152 x 152-MW26xMW26 (6 x 6-W4xW4) would provide 170 mm2 per meter (0.08 in.2 per foot) of width of welded wire reinforcement.

20. Welded Wire Reinforcement

21. Prestressing Steel (Pretensioning)
In prestressed members, compressive stresses are purposefully introduced into the concrete to reduce tensile stresses resulting from applied loads, including the self weight of the member (dead load). Pretensioning, as shown, consists of tensioning a steel tendon in the forms prior to placing the concrete and cutting the stressed wires after the concrete hardens. Pretensioning then adds a precompression to the concrete to offset tension stresses induced later during loading.

22. Prestressing Steel (Post-Tensioning)
Post-tensioning, as shown, consists of casting the concrete around tendons placed are in tubes or ducts. After the concrete hardens, the tendons are stressed. After stressing, the tubes or ducts maybe grouted (bonded tendons) or left ungrouted (unbounded tendons).

23. Prestressing Steel
Prestressing steel comes in three standard types: wires, tendons composed of wires, and high strength alloy steel bars. Prestressing steel, such as strands, bars, and wires, transfer the compressive stresses to the concrete. Tendons must be properly placed and stressed only after concrete has developed enough strength to withstand the load. If the tendon is improperly placed, there is inadequate concrete cover, the concrete is not strong enough, or the tendon is over stressed, a blow-out can occur

24. Prestressed and Post-Tensioned Concrete
Precast/Prestressed Concrete Institute:
Post-tensioned Concrete Institute:
Links to more information

25. Standard Prestressing Tendons
The requirements for prestressing steels are covered by ASTM A421, and ASTM A722. The most common form of tendon consists of low-relaxation seven-wire strand ASTM A421, Grade 270.

26. Summary Why Use Reinforcement Reinforcing Support Reinforcing Bars
Welded Wire Reinforcement
Prestressing Steel

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