Reinforced Concrete Design / module 1
How reinforced concrete works
Why two materials that behave nothing alike make the most used structural material on earth — and what happens at the moment the concrete cracks.
What you will understand
- Explain why concrete alone cannot span
- Describe how bond makes two materials act as one
- State what changes at the instant a section cracks, and what does not
- Trace a load path from slab to ground
- Distinguish material strength, member resistance, stiffness, ductility and durability
Lessons
Why concrete needs reinforcement
The one property that decides everything about how concrete is used.
Bond, cracking and what changes at first crack
The moment a reinforced section stops behaving like a lump of concrete.
Load paths, member types and how a concrete frame works
From a footprint on a floor to a pressure on the ground.
Four properties that get confused
Why a stronger concrete does not fix a deflection problem.
Module summary
- Concrete is strong in compression and unreliably weak in tension
- Reinforcement is placed where the concrete would otherwise be in tension
- Bond makes steel and adjacent concrete share the same strain
- Flexural cracking can be expected in service; its width, cause and effect still need assessment
- After cracking the compression zone shrinks and the lever arm settles
- Strength, stiffness, ductility and durability are four different properties
Teaching basis and review status
These are educational models and exercises. Check their assumptions before using the results. The full technical content and every diagram have not yet been independently verified.
Concrete and steel calculations retain their stated first-generation Eurocode teaching basis. Use the standards and amendments specified for your project; do not mix generations without an appropriate design basis.
Read the lesson register and outstanding review notesCheck your understanding
Check yourself
Why does reinforced-concrete design assume the concrete carries no tension at the ultimate limit state?
Practice
A plain rectangular concrete section is 250 mm wide and 500 mm deep, with a mean tensile strength of 2.60 N/mm². At what moment does it crack, in kNm?
Check yourself
What does bond between steel and concrete allow the designer to assume?
Practice
An internal column on a 7.0 m × 8.0 m grid supports five floors at an ultimate design load of 14.0 kN/m² per floor. Ignoring the column's own weight, what is the axial load at the base, in kN?
Check yourself
A beam satisfies its strength checks but deflects excessively. What is the most effective change?