ARCHITECTURAL STRUCTURES- REINFORCED CONCRETE DESIGN

REINFORCED CONCRETE

a composite material made of

CONCRETE and STEEL REINFORCEMENT

CONCRETE

High compressive strength, but weak in tension

STEEL REINFORCEMENT

High tensile strength, placed strategically to resist the tension force

Buildings

Bridges

Dams

Pavements

Foundations

Where is reinforced concrete used? (5-BBDPF)

•High Strength

•Durability

•Versatility

•Economy

•Fire Resistance

•Low Maintenance

•Good Bonding with Reinforcement

•Monolithic Construction

•Availability

•Sound and Vibration Insulation

advantages of reinforced concrete as a structural material (HDVEF- LGMAS)

Compression

Concrete is excellent in _______________________

tensile strength

Steel reinforcement compensates for concrete's weak __________, making the composite material strong in both tension and compression.

durability

Resistant to weathering, corrosion (when properly designed), fire, and pests. Long service life with minimal maintenance if designed and constructed correctly.

versatility

Can be molded into virtually any shape, making it suitable for various architectural and structural forms (e.g., beams, slabs, columns, domes, shells).

Useful in a wide range of structures, including buildings, bridges, dams, and highways.

economy

Relatively low material cost, especially where local materials (cement, aggregates) are available. Minimal formwork labor for repetitive structures (e.g., precast components).

Fire Resistance

Concrete is non-combustible and provides good fire protection for steel reinforcement inside, maintaining structural integrity during fires.

Low Maintenance

Compared to other materials (e.g., steel or timber), reinforced concrete structures generally require less maintenance over time.

Good Bonding with Reinforcement

Steel and concrete bond well due to similar thermal expansion properties, which ensures that the materials act together under loads.

Monolithic Construction

Cast-in-place concrete can create seamless, joint-free structures that reduce weak points and improve structural integrity.

Availability

Materials used (cement, aggregates, water, steel) are widely available, making reinforced concrete accessible worldwide.

Sound and Vibration Insulation

Dense concrete mass provides good sound insulation and damping of vibrations, beneficial for buildings and infrastructure.

•Low Tensile Strength (in Concrete Alone)

•Heavy Weight

•Cracking

•Corrosion of Steel Reinforcement

•Construction Time

•Environmental Impact

•Formwork Cost and Labor

•Difficult Modifications

•Quality Control Issues

•Time-Dependent Deformations

Disadvantages of reinforced concrete as a structural material

(LHCCC-EFDQI)

Low Tensile Strength (in Concrete Alone)

Concrete is weak in tension, so it must always be combined with steel reinforcement, which adds to cost and complexity.

Heavy Weight

High self-weight due to the density of concrete (~2400 kg/m³) increases dead loads on foundations and supporting structures. Not ideal for lightweight construction or structures requiring mobility.

Cracking

Concrete is prone to shrinkage and cracking due to drying, thermal changes, or overload.

Even small cracks can allow moisture and chemicals to reach the reinforcement, leading to corrosion.

Corrosion of Steel Reinforceme

Corrosion of Steel Reinforcement

Steel can corrode if the concrete is permeable or poorly designed/mixed (e.g., low cover, poor compaction), leading to spalling and structural damage.

Requires proper design, materials, and maintenance to prevent durability issues.

Construction Time

Curing time is required (typically 7–28 days), slowing down construction compared to materials like steel or precast systems.

Environmental Impact

Cement production contributes significantly to CO₂ emissions, making reinforced concrete less sustainable unless low-carbon materials or techniques are used.

Extraction of aggregates also affects ecosystems.

Formwork Cost and Labor

Formwork is often complex, especially for custom shapes, and can account for a large portion of the total cost in cast-in-place construction. Requires skilled labor and proper sequencing.

Difficult Modifications

Post-construction changes (e.g., cutting openings, strengthening, or remodeling) are harder and more costly compared to steel or timber structures.

Quality Control Issues

On-site concrete work depends on mix design, workmanship, weather, and curing, leading to variable quality. Poor practices can result in lower strength, durability, or even structural failure.

Time-Dependent Deformations

Prone to creep and shrinkage, which can affect long-term stability and serviceability if not properly accounted for.

creep

slow deformation under sustained load

Modulus of Elasticity

The ratio of the nominal stress to the corresponding strain for tensile or compressive stresses below the proportional limit of the material.

Concrete

has a modulus of elasticity which varies with the different concrete strength, concrete age, type of loading and the proportions of the cement and the aggregates.

25 mm diameter of bar and

(4/3) diameter of aggregates.

For parallel non-prestressed reinforcement in a horizontal layer, clear spacing shall be at least the greatest of ___________ diameter of bar and _________ diameter of aggregates.

at least 25mm

For parallel non-prestressed reinforcement placed in two or more horizontal layers shall be placed directly above reinforcement in the bottom layer with a clear spacing between layers of _______________

at least the greatest of 40mm,

1.5 diameter of bars, and

4/3 diameter of aggregates

For longitudinal reinforcements in columns, pedestals, struts, and boundary elements of walls, clear spacing between bars shall be __________________________________________________

maximum

For rectangular beams to be the most efficient, reinforcing bars should be arranged in such a way that the effective depth of the reinforcement is the __________________________. Minimum cover, which for beams not exposed to weather or in contact with the ground is 40mm, and minimum spacing between parallel bars, which is the greater between 25mm or the diameter of the bar, must be followed.

40mm

Minimum cover, which for beams not exposed to weather or in contact with the ground is _____________, and minimum spacing between parallel bars, which is the greater between 25mm or the diameter of the bar, must be followed.

~2400 kg/m³

density of concrete

cement,

aggregates,

water,

steel

Materials used for reinforced concrete (CAWS)