AffanLTB

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SECTION & GEOMETRY

Section source

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Section (type to search)

Material constants (elastic)

Young’s modulus E (GPa)

Poisson’s ratio ν

Shear modulus G (GPa)

Defaults to EN 1993-1-1 (E = 210 GPa, G = 80.77 GPa, ν = 0.3). Change E or ν and G follows (G = E / 2(1+ν)); change G and ν follows. Mcr is proportional to E and G, so use E = 205 GPa to reproduce a STAAD.Pro default run.

Span type

Span, L (m)

SUPPORTS — in-plane bending condition

Pinned or fixed ends determine the member end moments (slope-deflection solution for the UDLs and point loads, including continuity over interior supports). Out-of-plane lateral/warping restraint is separate — see Constraints. A free (cantilever) end is not supported yet.

LEFT END

Support type

RIGHT END

Support type

Configuration: —

CONSTRAINTS — lateral & warping restraint

At each true end the section is held against lateral displacement and twist (fork support); choose the lateral-slope (v′) and warping (θ′) restraint. The 0.7 preset has no exact physical spring: it is calibrated per member so the uniform-moment Mcr matches the k = kw = 0.7 formula (exact at 0.5 and 1.0).

LEFT END

Preset

RIGHT END

Preset

INTERMEDIATE RESTRAINTS

Each row restrains any of the four buckling DOFs at an ordinate (height above the shear centre): lateral displacement v, lateral slope v′, twist θ, warping θ′. A lateral brace on the top flange is “v fixed” at the top flange. Spring units: v kN/m · v′, θ kNm/rad · θ′ kNm³.

x (m)	Ordinate	v	v′	θ	θ′

LOADING

Downward loads positive; heights are measured above the shear centre (negative = below). Sagging moment is positive.

UDL, w (kN/m)

UDL height above shear centre (mm)

Quick set height

Applied end moment, left (kNm)

Applied end moment, right (kNm)

Acts on pinned ends. At a fixed end the support reacts it, so the field is disabled.

POINT LOADS

x (m)	P (kN)	Height above SC (mm)

Load height convention. Heights are geometric: positive is above the shear centre, negative below, and the load direction is taken from the sign of the load. A downward load above the shear centre, or an upward load below it, is destabilising. STAAD.Pro uses a different convention: its ZG is positive for a destabilising load and negative for a stabilising one, whichever way the load acts. When comparing with STAAD, set ZG from the effect, not from the position.

LOADED BEAM

BENDING MOMENT DIAGRAM

—

Mcr, elastic critical moment (peak moment at buckling)

Buckling factor, λ = Mcr / M_max—

C1—

C2—

Peak applied moment—

EUROCODE 3 CHECK — EN 1993-1-1, 6.3.2 (second check, bending only)

Yield strength fy (MPa)

Partial factor γM1

Method

Buckling curve

Section class

kc (Table 6.6) for the f modification, optional

Design parameters

National Annex name (printed in the report)

Cross-section class—

Section modulus Wy—

Slenderness λ̄LT—

Buckling curve—

Reduction factor χLT—

Buckling resistance Mb,Rd—

Peak applied moment MEd (loads taken as design loads)—

Utilisation MEd / Mb,Rd—

Bending only: no axial force, shear or torsion interaction. Class 4 sections are not treated. γM1 = 1.0 follows EN 1993-1-1 6.1 for EN 10025 steel; use the National Annex value where it differs, and make the local checks required by the National Annex. The loads entered are treated as design (factored) values. For a continuous beam, Mcr belongs to the whole beam as analysed and MEd is the peak moment; with the per-span method each span has its own Mcr and MEd and the governing span is shown.

Mcr comes from the AffanLTB eigenvalue solver (segmented Hermite + bubble basis, runs entirely in your browser) 24 regression checks + differential tests vs reference solver. C1/C2 are back-calculated from two solver runs (load at the shear centre and at its true height) through STAAD’s own Mcr formula.

BUCKLED MODE SHAPE (ideal beam, from the critical eigenvector)

MOMENT DIAGRAM

AffanLTB — Lateral Torsional Buckling

AffanLTB: disclaimer and terms of use

AffanLTB licence