STRUCT MIDTERMS

REINFORCED CONCRETE

• It is a composite material made of CONCRETE and STEEL REINFORCEMENT

• A reinforced concrete with at least minimum amounts of non-prestressed or prestressed reinforcement required by this code

CONCRETE

High compressive strength, but week in tension

STEEL REINFORCEMENT

High tensile strength, placed strategically to resist tension force

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).

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

Modulus of Elasticity (NSCP 2015 Section 419.2.2)

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

National Structure Code of the Philippines 2015

Establishes minimum requirements for structural systems through prescriptive and performance-based provisions, enabling new materials and designs, and reflecting the latest seismic practices for earthquake-resistant structures

Reinforced concrete

A reinforced concrete with at least minimum amounts of non-prestressed or prestressed reinforcement required by this code

D in loads

Dead load

L in loads

Live Load

W in loads

Wind Load

E in loads

Earthquake Load

R in loads

Roof Live Load

F in loads

Fluid

DESIGN STRENGTH

• provided by a member, its connections to other members, and its cross sections in terms of flexure, axial load, shear, and torsion.

• shall be taken as the NOMINAL STRENGTH

Low Tensile Strength

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.

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 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.

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.

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.

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 (slow deformation under sustained load) and shrinkage, which can affect long-term stability and serviceability if not properly accounted for