Introduction to Reinforced Concrete

Vocabulary and key concepts from the Introduction to Reinforced Concrete lecture notes, covering material properties, prestressing methods, loading types, and design factors.

Concrete

An artificial stone-like composite material made by combining cement, water, fine aggregates (sand), and coarse aggregates (gravel or crushed stone), with or without admixtures.

8% to 15%

Concrete has relatively low tensile strength, typically ranging from about

quality pf constituents materials

water-cement ratio

mixing

transportation

placement

consolidation

finishing

curing

The quality and performance of concrete depend on several factors including (8)

150 mm x 300 mm (6in x 12 in) at 28 days

Compressive strength is determined by testing standard concrete cylinders measuring (specimen size)

20.7 Mpa to 48.3 Mpa — may exceed 70 Mpa

Typical structural concrete strengths range from

Hydration

The chemical reaction through which cement paste hardens and binds aggregates together to form a durable and solid mass.

Compressive strength, $f'_c$

The most important property of concrete, determined by testing standard cylinders measuring $150\,mm \times 300\,mm$ at 28 days after casting.

17 Mpa and None

Table 419.2.1.1 — Normal Weight & Light Weight Min. fc’ and Max fc’

21 Mpa and None

Table 419.2.1.1 — Normal Weight Min. fc’ and Max fc’

21 Mpa and 35^1 Mpa

Table 419.2.1.1 — lLight Weight Min. fc’ and Max fc’

Modification factor, $\lambda$

A multiplier used as a multiplier of $\sqrt{f'_c}$ in applicable code provisions to account for the properties of lightweight concrete.

Fine - ASTM C330M

Coarse - ASTM C330M

Modification Factor - 0.75

Table 419.2.4.2, What is the Fine & Coarse composition of aggregates and modification factor $\lambda$ of ALL-LIGHTWEIGHT

Fine - Combination of ASTM C330M & C33M

Coarse - ASTM C330M

Modification factor - 0.75 to 0.85^1

Table 419.2.4.2, What is the Fine & Coarse composition of aggregates and modification factor $\lambda$ of LIGHTWEIGHT, fine blen

Fine - ASTM C33M

Coarse - ASTM C330M

Modification Factor - 0.85

Table 419.2.4.2, What is the Fine & Coarse composition of aggregates and modification factor $\lambda$ of SAND-LIGHTWEIGHT

Fine - ASTM C33M

Coarse - Combination of ASTM C330 & C33M

Modification Factor - 0.85 to 1.00²

Table 419.2.4.2, What is the Fine & Coarse composition of aggregates and modification factor $\lambda$ of SAND-LIGHTWEIGHT, coarse blend

Fine or Coarse - ASTM C33M

Modification Factor - 1.00

Table 419.2.4.2, What is the Fine & Coarse composition of aggregates and modification factor $\lambda$ of NORMAL WEIGHT

0.75 to 0.85

Linear Interpolation from. to is permitted based on the absolute volume of normal weight FINE aggregate

0.85 to 1.00

Linear Interpolation from. to is permitted based on the absolute volume of normal weight COARSE aggregate

$$f_{ct}$$

The measured average splitting tensile strength of lightweight concrete, expressed in $MPa$.

Modulus of Elasticity of Concrete, $E_c$

A measure of the stiffness of concrete and its ability to resist deformation when subjected to applied loads, representing the stress-strain relationship within the elastic range.

Reinforced Concrete

A composite structural material consisting of concrete and embedded steel reinforcement that work together to resist applied loads, utilizing concrete for compression and steel for tension.

High Strength

Fire and Water Resistant

Rigid and Durable

Low Maintenance

Versatile

ADVANTAGES OF REINFORCE CONCRETE AS A CONSTRUCTION MATERIAL

Low Tensile Strength

Requires Formwork

Heavy Weight

Large Member Size

Long Construction Time

DISADVANTAGE OF REINFORCE CONCRETE AS A CONSTRUCTION MATERIAL

Prestressed Concrete

A type of reinforced concrete where internal compressive stresses are introduced using high-strength steel tendons before service loads are applied to counteract tensile stresses.

• Reduced tensile cracking and improved crack control.

• Increased load-carying capacity.

• Reduced member depth and self-weight.

• Improved stiffness and reduced deflection.

• Enhanced durability and service life.

• Greater economy for long-span structures such as bridges, parking structures, and large floor systems.

PRINCIPAL ADVANTAGES OF PRESTRESSED CONCRETE

Pre-tensioning

A method of prestressing where steel tendons are stretched and anchored against fixed abutments before the concrete is cast.

Post-tensioning

A method of prestressing where the concrete is cast and allowed to harden before the tendons are tensioned using hydraulic jacks and anchored.

Steel Reinforcement

is used in reinforced concrete structures to resist tensile stresses that concrete alone cannot effectively withstand

Reinforcing bars

are classified as either plain bars or deformed bars

Plain bars

bars that have a smooth surface and are generally used for speacial applications

Deformed bars

Reinforcing bars with ribs or projections rolled onto their surface to improve the bond between the steel and the surrounding concrete.

Young's Modulus of Elasticity, $E_s$

The ability of steel reinforcement to resist deformation; for nonprestressed bars and wire, it is permitted to be taken as $200,000\,MPa$(29,000,00 Psi).

Yield Strength, $F_y$

The stress level at which steel begins to deform plastically and undergo permanent deformation even after the load is removed.

Yield Strength

is one of the most important properties of reinforcing steel

420 Mpa (60,000 psi)

Grade 60 reinforcement indicates that the steel has a specified minimum yield strength of?

Grade 60 reinforcement

is the most widely used in building construction

Structural Loads

are forces and actions that a structure must safely support throughout its service life

Dead Loads (D)

Permanent loads that remain constant in magnitude and position throughout the life of a structure, consisting of the self-weight of structural elements and permanently attached materials.

Live Loads (L)

Movable or transient loads resulting from the occupancy and use of a structure, such as people, furniture, and stored materials.

Traffic Loads

are a special type of live load encountered in brodges and transportation structures

Impact Loads

Dynamic loads resulting from the sudden application of force, vibration, or collision, often accounted for through impact allowances in design codes.

Miscellaneous Loads

include other forces that may act on structures but do not fall under conventional dead or live load categories

• Lateral earth pressures on retaining and basement walls

• Hydrostatic pressures exerted by water on dams. tanks, and underground structures

• Uplift pressures on foundations and basements

• Blast loads resulting from explosions or sonic booms

• Centrifugal forces acting on curved bridges. railway tracks, and amusement rides

Examples of Miscellaneous

Environmental Loads

Forces produced by natural conditions such as wind, earthquake, snow, rain, and temperature effects.

Load factors

Numbers, almost always larger than $1.0$, used to increase estimated loads to account for uncertainties in estimating their magnitudes.

One fifth (1/5)

the narrowest dimension between sides of forms (aggregates)

one third (1/3)

the depth of slabs (aggregates)

three fourths (3/4)

the minimum clear spacing between individual reinforcing bars (aggregates)

Concrete Cover

A certain minimum thickness of concrete outside of the outermost steel to provide protection against fire and corrosion.

Strength Reduction Factor ($\phi$)

A design factor applied to nominal strength to account for uncertainties in material properties, construction quality, and analysis assumptions.