Materials and Structures
What the domain tests
Materials and Structures tests material selection, concrete and steel behavior, load paths, simple structural analysis and seismic detailing. You should be able to check whether a member is safe and serviceable, not merely draw it.
Core rules
- Cement: ordinary Portland cement is general purpose; sulfate-resisting cement suits sulfate soils and sewage exposure. Store cement dry and use it in rotation.
- Steel: Grade 40 has a yield strength of about 280 MPa; Grade 60 about 420 MPa. Ductility, lap length and anchorage matter more than nominal diameter alone.
- Concrete: characteristic strength is measured on 150 mm cubes at 28 days. Elastic modulus is roughly 4700 x square root of f'c in MPa. Creep and shrinkage affect long-term deflection.
- Structural behavior: loads include dead, live, wind and seismic. Use load combinations, shear and moment diagrams, and check deflection, usually L/250 or L/360. Indeterminate frames redistribute moments; determinate beams do not.
- Seismic: use ductile detailing, confined ties, strong-column weak-beam hierarchy, shear walls and avoidance of soft storeys.
Worked example
A simply supported beam spans 6 m under a 20 kN/m uniform load including self-weight. Maximum moment = wL2/8 = 20 x 36/8 = 90 kNm. Maximum shear = wL/2 = 20 x 6/2 = 60 kN. For a lever arm of 0.45 m and fy = 420 MPa, As is about M/(0.87 fy d) = 90 x 10^6/(0.87 x 420 x 450) = 547 sq mm. Show units and self-weight; omitting either is a common error.
Traps that cost marks
Mixing service loads with ultimate loads. Ignoring self-weight. Using the clear span instead of the effective span. Specifying Grade 60 steel but designing with Grade 40 strength. Checking strength but not deflection or seismic detailing.