Reinforced Concrete Design Lecture 2 Dr. Nader Okasha

Introduction Topics Reinforced concrete structures and concrete-producing materials Concrete mixing Mechanical properties of concrete Steel reinforcement sizes and mechanical properties

Reinforced Concrete Structures and Concrete-Producing Materials

Concrete Concrete is a mixture of cement, fine and coarse aggregates, and water. This mixture creates a formable paste that hardens into a rocklike mass.

Concrete Producing Materials Portland Cement Course Aggregates Fine Aggregates Water Admixtures

Portland Cement Types of Cement Type I: General Purpose Type II: Lower heat of hydration than Type I Type III: High Early Strength Higher heat of hydration quicker strength (7 days vs. 28 days for Type I)

Types of Cement Type IV: Low Heat of Hydration Gradually heats up, less distortion (massive structures). Type V: Sulfate Resisting For footings, basements, sewers, etc. exposed to soils with sulfates.

Aggregates Coarse Aggregates Fine Aggregates

Water

Admixtures Applications: Improve workability (superplasticizers) Accelerate or retard setting and hardening Aid in curing Improve durability

Concrete Mixing

Concrete Mixing In the design of concrete mixes, three principal requirements for concrete are of importance: Quality Workability Economy

Concrete Mixing Quality of concrete is measured by its strength and durability. The compressive strength of concrete is mainly affected by the water/cement ratio, degree of compaction, age, and temperature. Durability of concrete is the ability of the concrete to resist disintegration due to freezing and thawing and chemical attack.

Concrete Mixing Workability of concrete may be defined as a composite characteristic indicative of the ease with which the mass of plastic material may be deposited in its final place without segregation during placement, and its ability to conform to fine forming detail.

Concrete Mixing Workability Workability is measured by the slump test 1 2 3 4 12” slump Layer 1: Fill 1/3 full. 25 stokes Layer 2: Fill 2/3 full. 25 stokes Layer 3: Fill full. 25 stokes Lift cone and measure slump (typically 2-6 in.)

Concrete Mixing

Concrete Mixing Economical takes into account effective use of materials, effective operation, and ease of handling. The cost of producing good quality concrete is an important consideration in the overall cost of the construction project.

Mechanical Properties of Concrete

Mechanical Concrete Properties Compressive Strength, Modulus of Elasticity, Ec Maximum ‘Ultimate’ Strain Tensile, Splitting and Rupture Strength, ft , fct , fr

Mechanical Concrete Properties Compressive Strength, Normally use 28-day strength for design strength It is determined through testing standard cylinders 15 cm in diameter and 30 cm in length in uniaxial compression at 28 days (ASTM C470-93a)

Mechanical Concrete Properties

Mechanical Concrete Properties

Mechanical Concrete Properties Modulus of Elasticity, Ec Corresponds to secant modulus at 0.45 ACI 318-08 (Sec. 8.5.1) for normal concrete:

Mechanical Concrete Properties Maximum ‘ultimate’ strain ACI Code: = 0.003 Used for flexural and axial compression For normal strength concrete, ~ 0.002

Mechanical Concrete Properties Typical Concrete Stress-Strain Curves in Compression

Mechanical Concrete Properties Tensile Strength Tensile strength ~ 8% to 15% of Modulus of Rupture, fr For deflection calculations, use: Test: ACI Eq. 9-10 P fr unreinforced concrete beam

Mechanical Concrete Properties Tensile Strength Splitting Tensile Strength, fct Split Cylinder Test P Concrete Cylinder Poisson’s Effect

Creep Creep is defined as the long-term deformation caused by the application of loads for long periods of time, usually years. Creep strain occurs due to sustaining the same load with time.

Creep The total deformation is divided into two parts; the first is called elastic deformation occurring right after the application of loads, and the second which is time dependent, is called creep

Shrinkage Shrinkage of concrete is defined as the reduction in volume of concrete due to loss of moisture

Steel Reinforcement Sizes and Mechanical Properties

Steel Reinforcement Bars are deformed to increase bonding with concrete

Steel Reinforcement Stress-strain diagrams fu fy Yield stress, fy Ultimate stress, fy

Steel Reinforcement Steel grades MPa ksi 276 40 414 60 552 80

Steel Reinforcement Bar sizes