Topic 3 of 6 · Form 5
Structural elements: walls, lintels, beams and frames
Load-bearing and non-load-bearing; solid and cavity walls; bonding; wall ties; damp-proof courses; slenderness (height to thickness ratio); openings and lintels; movement joints.
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Walls
Load-bearing and non-load-bearing; solid and cavity walls; bonding; wall ties; damp-proof courses; slenderness (height to thickness ratio); openings and lintels; movement joints.
Lintels and beams
Reinforced concrete lintels carry the wall above openings, with steel bars in the tension zone (bottom of a simply supported beam) and adequate cover (about 25 mm) to prevent corrosion. Bearings of at least 150 mm on each side.
Reinforced concrete
Concrete is strong in compression but weak in tension; steel reinforcement resists tension. Mix design (e.g. 1 : 2 : 4 for general work, richer mixes for structural work), water–cement ratio, compaction (vibration) and curing (about 7 days moist).
Frames
Reinforced concrete and steel portal frames for large spans (factories, warehouses); columns, beams and slabs; connections.
Loads and moments
Bending moment for a simply supported beam with a uniformly distributed load: M = wL²/8.
Worked example: A beam of span 4 m carries a uniformly distributed load of 10 kN/m. Find the maximum bending moment.
M = 10 × 4² ÷ 8 = 20 kN m
Fire resistance
Concrete cover, fire-resistant materials and compartments.
Check yourself
- Why is steel placed near the bottom of a simply supported lintel?
- What is the purpose of concrete cover to reinforcement?
- Find the maximum bending moment for a 6 m span carrying 5 kN/m UDL.
Show answers
- The bottom of the beam is in tension, which concrete cannot resist.
- To protect the steel from corrosion and fire and ensure bond.
- 5 × 36 ÷ 8 = 22.5 kN m
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