Draw joints and members, place supports and loads, and get the reactions and the axial force of every member, showing whether it is in tension or compression. The tool counts members and reactions (m + r against 2j, a necessary condition), also checks real stability from the geometry, solves statically indeterminate trusses too, and shows the equilibrium of each joint step by step.
It applies ΣFx = 0 and ΣFy = 0 at every joint, starting from one with at most two unknown forces.
If the force comes out positive when assumed to pull away from the joint, the member is in tension; negative means compression.
A truss is a structure of straight bars connected at their ends, like those in bridges, cranes or industrial roofs. Its strength is that each bar works only in tension or compression, which lets it span long distances with little material. This guide explains the assumptions and the two classic analysis methods, and works an example by hand.
With these assumptions each bar is a two-force member: only forces along its axis act at its ends. One number per bar is therefore enough, its axial force: positive if it is in tension (pulling on the joints) and negative if it is in compression (pushing on the joints).
In the plane, each joint gives two equations (ΣFx = 0 and ΣFy = 0). If j is the number of joints, m the number of bars and r the number of reactions:
Counting is not enough: a four-bar rectangle with no diagonal meets the count with certain supports and still deforms into a parallelogram. Stable trusses are built from triangles.
First the reactions are found from equilibrium of the whole truss. Then the joints are visited in an order where each has at most two unknown forces, and at each one ΣFx = 0 and ΣFy = 0 are written using each bar's direction cosines. It is convenient to assume every bar is in tension: if a force comes out negative, that bar is in compression.
If you only need the force in one particular bar, cut the truss with a line through that bar and at most two others, and write equilibrium of one of the two parts. Taking moments about the point where the other two cut bars meet, the force you want comes out of a single equation.
Spotting them first saves work:
A bar with zero force under one load case is not useless: it usually provides stability or works under other loads.
A triangular truss with joints A (0, 0), B (4, 0) and C (2, 1.5) in meters, bars AB, AC and BC, a pin at A, a roller at B and a 30 kN downward load at C.
If you draw this truss in the calculator you get the same forces: AB in blue (tension) and AC and BC in red (compression).
There are also space trusses (3D) and an advanced mode with loads along the bars, which are passed on to their joints.
These methods are in any statics textbook, for example R. C. Hibbeler, Engineering Mechanics: Statics (Pearson); F. P. Beer, E. R. Johnston et al., Vector Mechanics for Engineers: Statics (McGraw-Hill); J. L. Meriam and L. G. Kraige, Engineering Mechanics: Statics (Wiley). Simuveliq is not affiliated with these authors or publishers.
© 2026 Simuveliq. All rights reserved.