Nirmaanpro
Free to use

Beam, frame & truss analysis

Draw any 2D beam, frame or truss on the grid, give each member its own E, I and A, set supports and hinges, add point loads, UDLs, varying loads and moments, and get the bending moment, shear force and axial force diagrams with values, plus the deflected shape and reactions. Solved by the direct stiffness method, the same matrix method STAAD uses.

How to use this tool

  1. DrawPick a ready example from the list, or choose + Node and tap the grid, then + Member and tap two nodes. Member drawing continues from the last node; tap it again or press Esc to stop.
  2. SupportChoose Support and tap a node: 1st tap pin, 2nd roller, 3rd fixed, 4th none. For a roller with a horizontal reaction, select the node and pick it from the list.
  3. Section & EIChoose Select and tap a member. Pick the material and section, type E, I and A, or set EI as a multiple of the default (2 gives 2EI).
  4. HingesChoose Hinge and tap a node to make it an internal hinge, or tap a member to insert a hinge at that point. A circle marks every hinge.
  5. LoadsChoose Load and tap a member (point load, UDL, varying load, moment) or a node (force, moment). Distances are measured from the member’s start node.
  6. AnalysePress Analyse. Switch between bending moment, shear force, axial force, deflected shape and reactions. Tables with every value are below the drawing.
Full guide: units, sign conventions, supports, hinges, EI, messages

Units

Lengths in metres, forces in kN, moments in kN·m. E in N/mm², I in ×10⁶ mm⁴ (a 300 × 300 mm section is 675), A in mm². Deflections are shown in mm.

Sign conventions

  • Bending moment is drawn on the tension side of each member. On beams, + is sagging and − hogging; on columns and sloping members the number is the size of the moment.
  • Shear force: + when the part of the member to the left of a section is pushed up.
  • Axial force: + tension (red), − compression (blue).
  • Reactions: Rx + to the right, Ry + upward, M + anticlockwise.

Supports

  • Pin: stops movement in both directions, free to rotate.
  • Roller: one reaction only — vertical (the usual one) or horizontal.
  • Fixed: stops movement and rotation, so it also has a moment reaction.

Hinges

  • Internal hinge at a node (Hinge tool, or tick it when a node is selected): no moment passes through that joint. Used for Gerber beams and three-hinged frames.
  • Hinge at one end of a member (member panel): only that member is released, the others stay rigidly joined.
  • Truss member: pinned at both ends, carries axial force only.
  • Too many hinges make a mechanism; the tool then says which node can move.

About EI

For a statically determinate structure the moments and reactions do not depend on EI at all. For indeterminate beams and frames only the ratio of EI between members changes them, and the actual EI value sets the deflections. A truss uses A and E only.

Loads

“Down” is always vertical, even on a sloping member, as for self weight or roof load. “Perpendicular” acts at right angles to the member, as for wind on a slope. Distributed loads are per metre of member length.

Editing

  • Split member (member panel) adds nodes along a member and keeps its loads and section.
  • Type exact coordinates on the Grid tab, or change a selected node’s x and y.
  • Zoom with + and − or the mouse wheel; in Select mode drag empty space to move the view. Fit brings everything back into view.
  • Undo (Ctrl+Z) steps back. The model is kept in this browser; Save file and Open file move it between devices.

If you see a message

  • Unstable: the structure can move without bending a member. Add a support or a member, turn a roller into a pin, or remove a hinge.
  • Moment at a pinned joint: a moment load cannot sit on a node where every member is pinned. Put it on a member instead.
  • Equilibrium does not close: usually one member is far stiffer than the others; check its E, I and A.

Limits

Linear elastic, small deflections, plane structures. Shear deformation, P–delta and settlement are not included.