Structural Mechanics and Concrete Technology
Structural Mechanics and Concrete Technology tests basic statics and strength of materials, then applies them to concrete: supports and reactions, shear force and bending moment, stress and strain, concrete grades, workability, cube testing, mix design and admixtures.
Mechanics essentials
- Equilibrium: sum of vertical forces and sum of moments about any point are zero.
- Simply supported beam: reactions are found by symmetry or moment take-off.
- Bending moment: for a simply supported beam with uniformly distributed load w over span L, maximum BM = wL²/8 at mid-span.
- Stress: direct stress = force / area; strain = change in length / original length; Young's modulus = stress / strain.
Concrete essentials
Concrete grades such as M20 and M25 denote characteristic cube strength in N/mm² at 28 days. Workability is checked by slump or compaction factor. Cube tests use 150 mm cubes cured and tested at 7 and 28 days. IS 10262 provides mix-design guidance; admixtures may modify setting, workability or durability.
Worked example
A simply supported beam spans 4 m and carries a UDL of 10 kN/m. Total load = 10 × 4 = 40 kN. By symmetry each reaction = 20 kN. Maximum bending moment = wL²/8 = 10 × 4² / 8 = 20 kNm. If the section modulus were 2 × 10⁶ mm³, bending stress = M/Z = 20 × 10⁶ Nmm / 2 × 10⁶ mm³ = 10 N/mm².
Traps
Do not mix kN and N or metres and millimetres; do not treat characteristic strength as the actual strength of every cube; do not confuse slump with strength; and remember that curing affects strength gain.