US (TSA national) · Balsa: 1/8 × 1/8 in sticks
9 in gap · a loading block on top at mid-span · no mass limit
Official rules (PDF)(opens in a new tab)This contest limits outside help to guidance: the students design and build the entry. Design your own bridge. The designs here are worked examples to learn from, not entries to copy. The advisor certifies that only the two team members worked on the entry (the form quoted is the 2025-26 edition); the rules don't mention AI tools.
Help from adults: The advisor certifies that only the two team members worked on the entry.
“I also certify that only the two (2) team members noted have worked on the entry they are submitting for testing and evaluation.”
Your entry must include:
This contest limits outside help to guidance. Use the explorer to see what makes a bridge strong for these rules; design and build your own entry.
Our summary of the official rules. If anything here disagrees with the rulebook or the organizer, they win.
Where a rule can be read two ways we use the reading the organizer most likely meant and show the other. Where ours is the looser one, ask your organizer before you rely on it.
the advisor certifies that only the two named team members worked on the entry, so outside help is limited to guidance: the students design and build, and the site's designs are worked examples. The form quoted is the 2025-26 edition; the 2027 brief requires a Team Verification Form
The other reading: the form is only about who built the entry, and the rules don't mention AI tools, so 'silent'
the +/- 1/8 in tolerance widens every range: length 9.875-11.125 in, width 1.875-3.125 in, height 5.875-7.125 in (a solution measuring inside the widened range passes)
The other reading: the tolerance is the judges' measuring allowance and designs should hit the nominal ranges (length 10-11, width 2-3, height 6-7 in)
“The problem statement for 2027 is to design a balsa structure that will support the greatest load possible (on the top and in the center) using the least number of materials.”
“A substructure element is not permitted.”
“The solution must transfer the load from the test block to the top of the abutments as efficiently as possible.”
“The span of the abutments will be 9".”
“Length Minimum 10" Maximum 11"”
“Width Minimum 2" Maximum 3"”
“Height Minimum 6" Maximum 7"”
“A tolerance of +/- 1/8" will be applied for the length, width, and height of the solution.”
“Test Block 6" long x 2" wide x 3/4" tall”
“The test block will be placed on the top of the solution in the center.”
“The test block will cross the solution – not be placed parallel to the length.”
“The minimum 6" height must be maintained under the test block for the duration of the test block.”
“No part of the constructed solution may extend above the bottom of the test block.”
“The 1/2" test rod opening must pass vertically through the center of the solution.”
“The solution may not contact any surface of the abutments at any time other than the top surface.”
“Balsa strips (1/8"x1/8") are the only building material permitted.”
“A maximum of 14 linear feet of balsa is allowed to construct the solution.”
“The participants may choose glue type; however, hot-melt glue is not allowed for the pre-built or on-site semifinal structures.”
the block lies across the solution (6 in across, 2 in along the span), as the p4 drawing and its Special Note say
The other reading: Specification 3 ('perpendicular to the solution's width') puts the 6 in length along the span
height is measured from the abutment top (the solution's underside, since nothing may go below it) to the top of the solution, excluding the block (p1 dimension diagram)
The other reading: height includes the block resting on top
spec 4 ('the minimum 6" height must be maintained under the test block for the duration of the test block', the last word a slip for 'test') ends the test once the top under the block sags below the minimum height (5.875 in with the tolerance), so a solution may sag only by its built height minus that
The other reading: a requirement on the unloaded solution only, with the test running to breakage
'substructure is not permitted' and 'top surface only': no part of the solution goes below the abutment tops (hang_max 0)
The other reading: a substructure means piers or abutment-like members only, and a truss may still hang into the gap without touching the abutment faces
the 1/2 in rod column at the centre of length and width is clear for the full height, top to bottom (Special Note: 'from the bottom to the top')
The other reading: only a hole in the members the rod actually meets
TSA's 'lap joint' (two pieces glued with the grain at right angles) is the schema's 'lap' (a member on the receiver's face); the p4 rabbet and half-lap sketches are 'notch'; mitre is 'butt'. The generator does not build notches. A lap closer to collinear than 15 degrees counts as lamination (not checked)
The other reading: none
strip length is not stated; 36 in (the usual balsa strip) so it never binds on an 11 in solution
The other reading: none
efficiency = load held / bridge mass; the brief says only 'greatest load ... least number of materials'
The other reading: a TSA rating sheet (not in this file) weights load, efficiency and documentation differently
“Laminations of any kind are NOT allowed in the construction of the solution.”
“Lap joints are allowed and involve the gluing of two pieces of balsa material with the grain pattern normally at right angles”
“Gussets are not allowed to be used in the construction of the solution.”
“Excess glue on joints is considered a gusset and will result in disqualification.”