Truss Analysis Wizard

How it calculates

The Truss Analysis Wizard uses a direct stiffness finite element analysis (FEA) engine to solve any planar 2D truss. You define the geometry - node coordinates, member connectivity, support fixities, and loads - and the solver assembles and inverts the global stiffness matrix to return forces and displacements simultaneously across every member.

Geometry and member modelling

Each member is modelled as a two-node axial bar element with user-specified cross-section area (A) and elastic modulus (E). The calculator supports a library of preset truss configurations - Flat Warren, Flat Pratt, Flat Howe, Flat Brown, King Post, Queen Post, Single Fan, Simple Fink, and Fink roof trusses - as well as fully custom node and element definitions. For non-custom configurations, straight chord regions are treated as continuous members rather than pin-jointed segments; this is more accurate but means results may differ slightly from a traditional hand analysis.

Stiffness assembly and solution

The solver assembles the global stiffness matrix from the individual element stiffness contributions, applies boundary conditions at pinned and roller supports, and solves the resulting system of linear equations for nodal displacements. Member end forces are back-calculated from the displacements using the element stiffness relation.

Sign conventions and outputs

• Positive bending moment indicates that the bottom or right side of the member is in tension.
• Positive axial load indicates a compressive load (compression-positive convention).

Results reported for each member and element include:

• Axial force - tension or compression demand in each member
• Shear force and bending moment envelopes along each element
• Nodal displacements and support reactions

Output tables include overall results by member type, maximum displacements by member, support reactions, results by element number, and results by node number.

Load application

Distributed loads can be applied to chord members. For preset configurations, loads are specified over the chord length; the FEA engine converts these to equivalent nodal contributions automatically. Advanced users can also apply loads directly by element number for non-standard cases. Multiple load cases are evaluated and an envelope of governing demands is reported.

Linking to design calculators

The Truss Analysis Wizard is an analysis-only calculator. After solving, member force demands (moment, shear, axial) can be linked directly to Design Only calculators - such as timber, steel, or cold-formed steel beam calculators - so each member is checked against the relevant code without re-entering geometry or loads.