Masonry Lintel Calculator

This calculator sizes a steel angle lintel over a masonry wall opening using triangular arching theory: the dead load is limited to the masonry within a 45-degree triangle above the opening (triangle height equals the smaller of half the Opening Span or the Wall Height Above Opening), plus any Live Load carried by a Tributary Floor/Roof Area above. Opening Span dominates Required Moment and Estimated Deflection by a wide margin -- span enters the moment formula squared and the deflection formula to a much higher power, outweighing Wall Thickness or Masonry Unit Weight even though all three move Total Load on Lintel by comparable amounts on their own. When Tributary Floor/Roof Area is set above zero, that area's Live Load contribution can dominate Total Load instead -- a large tributary area easily outweighs the masonry dead-load triangle. At the default 4 ft span, Estimated Deflection is a negligible 0.007 in; widening the opening to 10 ft (2.5x the span) pushes deflection to 0.699 in, roughly a hundredfold increase -- but only within a single Steel Angle Size bracket. Steel Angle Size and Min Bearing Length are looked up from stepped tables (four angle sizes by moment threshold; bearing length rounds up from span divided by 16, floored at a 4-inch code minimum) rather than computed continuously, so a small span change near a table boundary won't move them while a larger change can jump a full size -- and because each larger angle size is substantially stiffer (its moment of inertia jumps rather than scaling smoothly), Estimated Deflection is NOT globally monotonic in span: right at a Steel Angle Size boundary, a wider opening can deflect LESS than a narrower one, because it's carried by a meaningfully stiffer member.

At a heavier wall (24-inch thick, 150 pcf), for example, span 10.5 ft deflects 3.345 in on a size-1 angle, but span 11 ft crosses into size-2 territory and deflects only 2.575 in -- a real, physically correct drop from switching to a stiffer catalog angle, not a calculation error. Deflection does grow monotonically within any single bracket; it's only the bracket transitions that can dip. Tributary Floor/Roof Area defaults to zero for non-load-bearing walls -- Live Load has no effect on any output until Tributary Floor/Roof Area is set above zero. This is a preliminary sizing tool; have a structural engineer confirm the lintel for any load-bearing application.