Steel Angle Lintel (old AS 4100:1998)

How it calculates

The Steel Angle Lintel calculator designs angle, T-lintel, and PFC+plate steel lintels to AS 4100:1998 using limit state (LRFD) design. It models the lintel as a beam with multiple supports and loads, then checks section capacity, member capacity, shear, combined shear-moment interaction, flange loading, and deflection.

Section types and properties

Three lintel types are supported, each with its own section property calculation:

• Single angle - properties are calculated for bending about the geometric axis, assuming the angle is restrained from lateral deflection and rotation at its supports. Equal and unequal angles can be oriented for the loading direction.
• T-lintel - treated as a T-section loaded on its two flanges, with capacities derived from the combined geometry.
• PFC+plate - a parallel flange channel with a welded flat plate; composite section properties are computed from the combined geometry.

Moments are resolved about the principal axes per AS 4100:1998 Cl 5.7 (axes labelled '11' and '22'). Net areas equal the gross area with the maximum allowed holes.

Moment capacity checks (AS 4100:1998 Cl 5.1, 5.3, 5.6, 8.4)

The bending demand M* is compared to the governing effective moment capacity. Section moment capacity M_s is calculated from the reduced section modulus, accounting for yielding and local buckling per Cl 5.2 and Cl 5.3. Member moment capacity M_b incorporates lateral-torsional buckling over the unbraced length between lateral restraints per Cl 5.6. For biaxial bending, the combined interaction check follows Cl 5.1 and Cl 8.4. About the minor principal axis, member moment capacity is taken equal to the section moment capacity.

utilization = M / (phi × M_gov) ≤ 1.0*

Shear capacity (Cl 5.11) and interaction (Cl 5.12)

Web shear capacity phi × V_v is based on web yield and shear buckling per Cl 5.11. Where bending moment and shear are both significant at the same location, a shear-moment interaction check is applied per Cl 5.12.

Flange loading checks

For distributed and point loads applied at an eccentricity from the web, separate flange shear capacity (Cl 5.11) and flange moment capacity (Cl 5.3, 5.1, and 5.6) checks are performed at the load locations. T-lintels carrying masonry loads typically require these checks.

Deflection analysis

Short-term, long-term, and imposed-load deflections are each compared to their respective span or absolute limits. The governing load case for each deflection type is identified and reported.

Assumptions

The beam is of uniform cross-section along its full length, net areas equal the gross area with maximum allowed holes, and bearing limit states are not checked. All distributed loads are applied at one eccentricity and all point loads at one eccentricity. Detailing requirements are checked separately.