Inputs
Optional 4th value = per-member axial stiffness EA; if omitted, the global EA below is used.
Downward loads have negative Fy. Use any consistent units (kN, N, kip…).
EA = elastic modulus × cross-section area. Affects displacements; member forces in a determinate truss are EA-independent.
Method & assumptions
- Direct-stiffness method: each pin-jointed bar is a 2-node axial element, 2 DOF per node.
- Element stiffness k = EA/L assembled into the global stiffness matrix K; solves K·u = F for nodal displacements.
- Reactions recovered as K·u − F at restrained DOFs; member axial force N = (EA/L)·elongation.
- Sign convention: positive axial force = tension (T), negative = compression (C).
- Supports: pin restrains x & y, roller-y restrains y only, roller-x restrains x only.
- Linear-elastic, small-displacement theory. The deformed shape is drawn to an amplified visual scale.
Results
Nodes / Members
—
Free DOF / Total
—
m + r vs 2n
—
Max nodal displacement
—
Status
OK
Deformed-shape overlay
Tension
Compression
Undeformed
Joints / supports / loads
Support reactions
| Reaction | Value |
|---|
Member axial forces
| Member | Length | Axial force | T/C |
|---|