Bridge Designer
Pick a bridge style — truss, arch, girder, cantilever, cable-stayed or suspension — tune it, load it, and find out exactly how much it can carry before the first member yields or buckles.
- Twelve parametric build styles — girders, every common truss, arches, cantilevers, cable-stayed and suspension
- One unified 2D frame solver handles axial, bending and tension-only cables
- Combined axial + bending stress, Euler buckling and cable-slack capacity checks
- See exactly how many times the load your bridge survives and which member fails first
- Live curved deflected shape, bending overlay, colour-coded forces and a synced editable model
The Bridge Designer is an interactive 2D structural analyser built on a unified frame/beam-column finite element solver. It models every major bridge build style — beam and girder decks, Pratt/Warren/Howe/K and bowstring trusses, deck and tied arches, cantilever (Gerber) spans, cable-stayed decks and suspension bridges — then checks each member for combined axial + bending yield, Euler buckling and cable slack to find the maximum load the structure can carry and which member governs.
It is available on the Pro plan. For free beam bending, shear, moment and deflection analysis, use the Beam Stress & Deflection Calculator.
Worked example: Horizontal thrust of a 3-hinged arch, span 40 m, rise 8 m, 200 kN apex load
- By symmetry each support carries a vertical reaction V = P/2 = 100 kN
- Take the left half and sum moments about the crown hinge: V·(L/2) − H·h = 0
- Horizontal thrust H = P·L / (4·h) = 200 × 40 / (4 × 8)
H = 250 kN inward at each abutment (the deck or foundations must resist this thrust)
Which bridge types can the Bridge Designer model?
Twelve parametric build styles: simple and continuous girders; Pratt, Warren, Howe, K and bowstring trusses; deck and tied (bowstring) arches with 2-hinged, 3-hinged or fixed supports; cantilever (Gerber) spans with internal hinges; cable-stayed decks in fan or harp layouts; and suspension bridges with a parabolic main cable and hangers. Pick a style from the gallery, tune its parameters, then refine it freehand on the canvas.
How can one tool analyse trusses, arches and cables together?
It uses a unified 2D frame (beam-column) finite element solver with three degrees of freedom per joint (horizontal, vertical and rotation). Frame members carry axial force and bending; truss members are pin-ended bars carrying only axial force; cables are tension-only and are solved iteratively, going slack (zero force) if a load would put them in compression. This single engine reproduces a pin-jointed truss exactly while also handling rigid arches, girders, towers and cable systems.
How does it work out how much load the bridge can take?
Because a linear-elastic structure scales proportionally with load, the tool divides each member's capacity by its demand to get a load factor. Capacity combines axial and bending stress against yield (σ = |N|/A + |M|·c/I), adds Euler buckling for compression members (P_cr = π²EI/(KL)²), and treats slack cables as carrying nothing. The smallest load factor across all members is how many times the applied load the bridge survives before first failure.
What are hinges and why do arches and cantilevers use them?
A hinge (moment release) lets members rotate freely relative to each other while still transferring axial and shear force. A 3-hinged arch has hinges at both springings and the crown, making it statically determinate and insensitive to support settlement. Cantilever (Gerber) bridges use internal hinges to drop a simply-supported suspended span between two cantilever arms. You can toggle hinges per member end in the model table.
Why do long girder spans 'fail' while trusses and arches survive?
A straight girder carries load purely in bending, so its stress depends on section depth — a shallow section over a long span reaches yield quickly. Trusses and arches convert the same load into mostly axial forces, which a given cross-section resists far more efficiently. If a girder shows a low load factor, increase the section depth, shorten the span, or switch to a truss or arch.
Why is the Bridge Designer a Pro feature?
It is a full interactive structural design environment with a parametric style gallery, a live frame solver and combined-stress capacity checking. It is included with the Pro plan. The Beam Stress & Deflection Calculator offers free single-span beam analysis if you do not need full bridge design.