Purpose and scope of this truss bridge resource and who it serves

What this truss bridge resource covers

A 12 m Warren truss loaded with 20 kN at its centre carries 20.0 kN of compression in the top chord, and it fails at 48.0 kN when that chord buckles. A learner who can explain why has understood most of the subject. This truss bridge resource is organised to get to that explanation by several routes.

The first route is the truss bridge designer, a two-dimensional pin-jointed truss that a student draws in the browser. It shows tension in warm colours and compression in cool ones, and it scales the load until the first member reaches its capacity. The second is a set of pages on truss bridge designs: the Warren, Pratt, Howe and K layouts, with the patents behind three of them, from Howe in 1840 to Warren in 1848. The third is a sequence of truss analysis lessons covering tension and compression, the method of joints, the method of sections and the factor of safety.

Beyond the screen, this truss bridge resource adds model bridge builds from craft sticks, toothpicks and file-folder card, a teachers corner with a unit plan, a short glossary of bridge terms, and a plain account of the classic desktop bridge-design software and its history. Each part stands alone, so a teacher can take only the analysis lessons or only the model builds.

What a learner can do afterwards

The goals are things a person can demonstrate, not topics to have heard of. After working through the lessons a learner can read a loaded truss and say which members are in tension and which in compression. They can predict which member fails first, and give the reason: in compression, the long slender one, because buckling load falls with the inverse square of its length. They can build a model, test it, and compare the result with what the calculation said.

That last step is the one that sticks. A calculation that says a card strip buckles at a few newtons feels abstract until a strip folds under a small hanging weight.

How the tools handle privacy

The designer has no accounts and no sign-in. It does not store what a user draws and it does not collect anything about them. When a student wants to show a design to a teacher, the design is encoded in the link, so sharing means copying an address. Closing the tab ends the session, and nothing remains on a server.

How the content is checked

Numbers on these pages come from a solver written for the purpose, and the solver was verified against hand calculations: a single triangle, a two-panel Warren truss, a bracket, a plain equilibrium check and a deflection found by virtual work. Every worked example is solved twice, by hand and by the solver, and the two results must agree before the page uses them.

The model is a simplification, and the pages say so where it matters. Members are ideal bars joined by frictionless pins, loads act at the joints, and the weight of the members is left out. Real bridges add self-weight, stiff joints and moving loads, and the results here are meant for learning how a truss works.