Running a classroom bridge design contest: rules and a fair test

Two formats for a bridge design contest

A classroom bridge design contest takes one of two shapes. In the software format, every student gets the same span, the same supports and the same load, designs a truss on a computer and is ranked by cost: the cheapest bridge that carries the load wins. That is the original format of the national contest, which ran annually from the early 2000s. The national contest ended in 2016; class and school contests continue on the same format.

In the model format, students build a bridge from a fixed materials list and it is loaded to failure; the winner is the bridge with the highest load carried divided by its own mass. Rank by that ratio, not by load alone, since raw load goes to whoever uses the most wood.

For a first contest, choose one format and stick to it. The software format needs a computer lab for a lesson and no consumables. The model format needs sticks, glue, a scale and a test frame, and takes longer, but students remember it. The sheet on model bridge building covers the build and test side, and the truss bridge designer can serve as the software side if the ranking rule is stated in the rules, for example by failure load at a fixed member count.

A rules template for a bridge design contest

Write the rules down and hand them out before building starts. A short table is enough.

Item	Rule to fill in
Span	One value, the same for every entry
Supports	Where the bridge rests, and how far apart
Load	Where it is applied (centre of the span, at a joint) and how it is added
Materials	Identical list for all, with quantities
Size limits	Maximum length, width and height of the bridge
Mass	Weighed dry on one scale before testing
Score	Cost, or load divided by mass
Tie-break	Order of tests applied if scores match
Inspection	Who checks compliance, and when
Disqualification	What makes an entry invalid

Keep the list short. Rules that need a page of explanation produce arguments, so print the table on one sheet, read it aloud once before building starts, and keep one signed copy by the test frame for reference on the day.

Running the software contest step by step

Give everyone the same brief on one card: the span, the support type, the load and the ranking rule. Students open the designer, load the same preset and work alone or in pairs for one lesson. Each submits their final design as a link, since the designer stores nothing and a design lives in its address, and the organiser opens every link in turn. In the designer, test each design to failure and write down the failure load and the number of members.

The designer on this site does not price a bridge, so a contest run on it needs a ranking rule you state yourself: highest failure load for a fixed number of members, or fewest members that still carry the 20 kN preset load. A cost-scored contest, in which students watch a simulated truck test their steel truss, is available in the ASCE browser edition described on the teachers page.

Set a time limit and a limit on the number of test runs per student. Without one, the contest becomes a search for the last percent, and the lesson on why a design fails gets lost.

Run one practice round before the real bridge design contest. Students who have already broken a bridge once understand the scoring rule, and the organiser finds out which rule in the template is unclear. Announce the contest a lesson ahead, and let students see the record sheet so that nothing about the scoring is a surprise.

Registration and schedule for a class contest

Registration for a class contest is a list, not a form. Before the brief goes out, register each team on one sheet: the names, the team size, the grade band and the format it enters. Closing registration a lesson before the design window opens tells the organiser how many test slots to book. Grade bands are worth fixing early. The national contest admitted middle school students in grades 6 to 8 from 2014, on the same schedule and with the same software as its high school contest, and a class contest can keep the two bands in separate rankings in the same way. That middle school contest was sponsored in part by the West Point Center for STEM Education and the United States Naval Academy’s STEM program.

A schedule of three dates is enough for one class:

Date	What happens
Lesson 1	Brief handed out, rules read aloud, practice round
Lesson 2	Design window; each team submits one final design before the bell
Lesson 3	Inspection, weighing, test day and results

Put the schedule on the same sheet as the rules, and announce any change to every team at once, so no team works to an older version of it.

Scoring and tie-breaks

Decide the score before anyone starts. For the model format it is the ratio of the failure load to the bridge’s mass, with both numbers written on the record sheet. Suppose one bridge carries 4200 g and weighs 140 g, and another carries 5400 g and weighs 270 g: the first scores 30 and the second 20, so the lighter bridge wins even though it held less.

Ties are rare with measured scores but not impossible, so give an order in the rules: first the lighter bridge, then the one with fewer members, then a retest of both on the same frame. Agree it in advance, not on the day.

Run every test the same way, in the same place, with the same frame. Weigh the bridge, inspect it against the rules, then rest it on the supports at the fixed span. Hang a bucket from the centre and add weight in small steps, pausing after each. Record the load at failure including the bucket, and note which member failed first.

Eye protection is required for anyone near the frame, and a padded catch box goes under the bridge; the full safety routine is on the model bridge building sheet.

Fairness and awards

Fairness comes from sameness: one materials list, one scale, one test frame, one inspector. Inspect each bridge before it is loaded and reject an entry that breaks a size rule, not one that merely looks fragile. Let entrants watch every test.

Awards can follow the data: best ratio, lightest bridge that carried the full test load, and the best account of a failure in the student’s own words. The teachers page has a rubric that fits these awards, and the contest history traces where the cost-scored format came from.

Entry	Student or group	Bridge mass (g)	Failure load (g)	Load divided by mass	First member to fail	Inspection passed
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