Steel T-Lintel

How it calculates

Section geometry and properties

The T-lintel is built up from two steel plates: a horizontal plate (flange, resisting the masonry) and a vertical plate (web). You specify each plate's width, thickness, and yield strength. The calculator then derives all section properties analytically:

• Neutral axis location from the bottom of the section (computed as the area-weighted centroid)
• Second moment of area Ixx about the major bending axis, accounting for parallel-axis theorem contributions from both plates
• Second moment of area Iyy about the minor axis
• Torsion constant J for St. Venant torsion
• Elastic section modulus Z_e = Ixx / y_extreme (top and bottom fibre)
• Plastic neutral axis location from the bottom, and the plastic section modulus Z_p
• Section slenderness and effective section modulus for slender sections

Section compactness and effective modulus

The flange and web element slenderness ratios are checked against AS 4100:1998 limits. If the section is compact, the plastic modulus Z_p is used. For non-compact or slender sections, the effective section modulus is reduced accordingly.

Load combinations and total design action

Permanent (G) and imposed (Q) actions are combined with wind (W) using AS 4100:1998 strength limit state combinations. The character of the imposed action (e.g. residential, office, storage) selects the appropriate combination factor. Wind loads are derived from either the wind class selection or directly entered wind pressure coefficients C_pt and C_pe/C_pi, together with the wind tributary width.

The total design action W* is computed from the governing combination, combining distributed and point loads.

Lateral torsional buckling capacity (Clause 5.3)

Because a T-section is a mono-symmetric member, the reference elastic buckling moment M_oa requires the mono-symmetry section constant beta_x:

beta_x = 2 * (integral of y(x^2 + y^2) dA) / I_11 - 2 * y_shear_centre

The slenderness reduction factor alpha_s and moment modification factor alpha_m (based on the moment values at the quarter-points and midpoint of the span) are then used to determine the nominal member moment capacity M_bx. The capacity factor phi is applied to give the design capacity phiM_bx.

Moment utilization = M* / phiM_bx ≤ 1.0

Deflection calculations

The calculator solves for deflections under short-term and long-term serviceability load cases using the beam boundary condition matrices. For a simply supported span with a combination of uniform distributed load and point loads, the deflection at any position x is derived by integrating the differential equation EI * y'' = M(x).

Separate solutions are computed for:

• Short-term deflection (dead + short-term imposed)
• Long-term deflection (dead + long-term imposed, including creep)
• Dead load only deflection and live load only deflection

Each is compared against the user-defined L/n span ratio limit and/or an absolute deflection limit.

Masonry bearing stress

The calculator also computes the applied stress due to the external masonry brick course (sigmaE) resting on the horizontal plate flange. This is a check on the bearing capacity of the T-lintel flange under the masonry tributary load, based on the plate yield stress and geometry.

Reactions and load linking

Pin support reactions at each end (R1 and R2) represent the vertical forces delivered to the supporting masonry piers or wall columns. These reactions are linked outputs - when connected to column or bearing calculations for the masonry piers, any change to the lintel loading updates the downstream calculations automatically.