Lintel

A lintel is a horizontal structural beam spanning a door or window opening in a wall. Its purpose is to transfer the wall load above the opening to the side walls, allowing the opening to remain unobstructed. In modern Indian construction, RCC lintels (precast or cast-in-situ) have replaced traditional stone, timber, and brick-arch lintels in nearly all new construction. The Indian standard IS 456:2000 governs RCC lintel design; IS 1905:1987 (masonry walls) covers the bearing on masonry; NBC 2016 Part 6 specifies minimum lintel widths and depths.

Design loads: (a) self-weight of the lintel, (b) the wall load directly above the opening (called 'arching action' load for masonry — only the triangular zone above the opening is carried by the lintel; rest is arching to side walls), (c) any beam reaction landing within the triangular load zone, (d) concentrated load if a column lands above the opening. The triangular zone has equilateral geometry — base = clear span of opening; height = 0.866 × span. For a 1.0 m wide door: triangular wall load over 0.866 m height. Above this height, the wall load arches to the side walls and bypasses the lintel.

Minimum bearing on side walls per IS 1905 Cl. 4.2: 150 mm each side. Minimum depth: 100 mm (small openings ≤ 1.0 m); 150 mm (standard openings 1.0-1.5 m); 200-300 mm (large openings >1.5 m). RCC lintels typically have 2-T10 bottom + 2-T8 top with stirrups at 150-200 mm c/c. For openings >1.8 m wide, the lintel is engineered explicitly by the structural engineer, not just from a standard schedule. The most-violated clause is concentrated load arrangement — many residential projects place a column directly above a window opening without redesigning the lintel for the heavy point load; this causes lintel failure under cyclic loading.