Reinforced Concrete Basics

Reinforced Concrete

• Concrete with embedded steel reinforcement
• Materials act together to resist forces
• Plain concrete lacks reinforcement
• Ferrocement uses cement mortar over wire mesh
• Cast-in-place concrete is deposited and hardened in place
• Reinforcement absorbs tensile, shear, and compressive stresses
• Deformed bars have surface deformations for better bond with concrete
• Tension reinforcement absorbs tensile stresses
• Compression reinforcement absorbs compressive stresses
• Balanced section: tension and compression reinforcement reach yield strength simultaneously
• Over-reinforced section: concrete reaches ultimate strain before the tension reinforcement, which is a dangerous design
• Under-reinforced section: tension reinforcement reaches yield strength before the concrete, a desirable design
• Assumptions in Elastic Theory: plane sections remain plane, concrete is elastic, and stress varies from zero at the neutral axis to a maximum at the extreme fibers

Beam

• A rigid structural member that transfers transverse loads
• Simple beam: single span supported at ends
• Semi-continuous beam: two spans (with or without restraints at ends)
• Cantilever beam: supported at one end, the other end extending beyond the support
• Continuous beam: supported on more than two supports
• T-beam: part of floor and beam unit (poured simultaneously)
• Reinforced concrete beam: designed to act together with longitudinal and web reinforcement

Beam Nomenclature

• Effective Depth of Section: Measured from the compression face to the centroid of the tension reinforcement
• Bar Spacing: Center-to-center spacing of parallel bars, regulated by bar diameter, maximum aggregate size, and section thickness
• Span of Supports: Distances between posts, columns, or supporting walls
• Concrete Layer/Cover: Concrete protecting steel reinforcement from fire and corrosion (measured from reinforcement surface to outer concrete surface)
• Bond: Adhesion between concrete and reinforcing bar
• Bond Stress: Adhesive force per unit area of contact between a reinforcing bar and surrounding concrete
• Developmental Length: Reinforcement length required to develop design strength at a critical section

Concrete Column

• A structural member that resists applied forces (vertical and lateral)
• Short column length <= shortest lateral dimension x 10
• Long column length > shortest lateral dimension x 10
• Tied column: vertical bars and individual ties
• Spiral reinforcement: continuous, evenly spaced spiral (held firmly by spacers)
• Balanced section: tension and compression reinforcement reach yield strength simultaneously
• Over-reinforced section: concrete reaches ultimate strain before the tension reinforcement, which is a dangerous design
• Under-reinforced section: tension reinforcement reaches yield strength before the concrete, a desirable design
• Bundled reinforcement: two to four bars tied together to form a single unit reinforcement

Composite Column

• A column with structural steel embedded into its concrete core (spiral column)
• Combined column: steel encased in concrete

Minimum Bend Diameters

• Minimum diameter for bends (for different bar sizes)
• Internal bend diameter related to reinforcement size

Concrete Protection for Reinforcement

• Minimum cover (in mm) for different locations/exposure conditions

Concrete Slab

• Principal reinforcement: reinforcement absorbing loads and moments
• Shrinkage reinforcement, temperature reinforcement: perpendicular to principal reinforcement, absorbing shrinkage and temperature changes
• Concrete topping: thin layer of high-quality concrete placed on existing concrete to form a floor surface
• Bonding layer: thin mortar layer on existing concrete before new concrete slab
• Construction joint: where two successive concrete placements meet
• Isolation joint: gap between concrete slab and adjoining columns/walls (for movement due to temperature)
• Control joint: line of weakness where cracking may occur during tensile stress

Foundations

• Types of foundations, including shallow and deep
• Isolated footing, spread footing, square block footing, mid-footing, corner footing, edge footing, square sloped footing, stepped footing, rectangular footing, combined footing
• Rectangular combined footing, trapezoidal combined footing, continuous footing, strip footing, strap footing
• Mat foundation, ribbed mat, cellular mat, floating foundation, grillage/grid foundation, wall footing

Pile Foundation

• Types of piles (timber, H-pile, pipe, precast concrete, cased, uncased)
• Bearing pile, friction pile
• Types of pile drivers (drop hammer, steam hammer, single acting, double acting)
• Pile cap
• Types of piles include cased, uncased, cast-in-place, steel, composite, and timber
• Pile eccentricity, pile tolerance
• Negative friction
• Batter pile

Caissons

• Types of caissons (box, open, pneumatic)
• Parts of pneumatic caisson (air lock, compressed air-line, blow-out line, working chamber, cutting edge, bell bucket, casing)

Formworks

• Temporary structures that contain and support concrete during placement
• Types of formworks
• Scaffolding, falsework, staging, shore, wale, breast timber, ranger, waler, wedge, strongback, stiffback, spreader, spacer, grade strip, bulkhead, yoke