Everything you need to build this bridge by hand: a full-size plan, the cut list, the joints and the glue order.

Paper

Build pack · ASCE Mid-South Student Symposium 2025

sandwich pratt-16 for ASCE Mid-South Student Symposium 2025

Mass: 11.5 g; no limit
Length: 48.9 in; 48 in gap
Sticks: 73; 15 in stock
Rule checks: All pass; 21 checked

Loads (simulated, not yet checked on real breaks)

First failure: 0.2 kg
Collapse: 0.2 kg
Efficiency (load ÷ mass): 20

Expected to break first: member crushing/buckling, at V8 (vertical).

The full-size plan

One truss seen from the side, 48.9 in long. Both trusses are built on this same plan. The plan prints full size across the pages outlined below: trim each page along its dashed line, lay it over the page to its left or above, line up the ⊕ marks and tape it. Print at 100% (“Actual size”) and check the scale bar on each page with a ruler.

Cut list

Every piece, labelled as on the plan. Lengths are the finished long edge, to the nearest 1/16 in. Angles are between the cut and the stick's edge (90° is square), left end first as drawn (bottom end first for verticals); where an end has two cuts, both are given. For the truss pieces, lay the stick on the full-size plan and mark the cuts from it.

Piece	What	Cut	Stick	Length, in	Ends
B1	bottom chord	4	1/16 × 1/16 in	3 13/16(3.79)	both square
B2	bottom chord	4	1/16 × 1/16 in	2 3/8(2.34)	both square
B3	bottom chord	4	1/16 × 1/16 in	2 13/16(2.81)	both square
B4	bottom chord	4	1/16 × 1/16 in	2 3/4(2.73)

The joints

Every kind of joint on the bridge, once, enlarged. Blue runs through; amber is cut to fit against it. Truss joints are seen from the side, like the plan; joints between the trusses are seen from above.

Side view · 13 like this on each trussOn each layer, two bottom chord pieces meet end to end here. The diagonals and verticals are cut against them.The chord is two sticks with the webs between them: each web runs to the chord's far face and is glued on both faces.Where webs meet each other at the joint, one runs through and the others are cut against it.

Glue order

Pieces that run through a joint go down first, because the others are cut to fit against them: the chords (and the end posts, where they run through the corner). Then the webs between them. Build the second truss the same way on the same plan. The pieces that join the two trusses go in last: the deck members first, then the bracing above them.

1
First truss: chords
B1, B2, B3, B4, B5, B6, B7, B8, B9, B10, B11, B12, B13, B14, B15, B16, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14
Pin them down on the plan over wax paper or plastic wrap.
2
First truss: webs
E1, E2, V1, V2, V3, V4, V5, V6, V7, V8, V9, V10, V11, V12, V13, V14, V15, D1, D2, D3, D4, D5, D6, D7, D8, D9, D10, D11, D12, D13, D14
Cut each end to the plan, then glue it against the chords.
3
Second truss: chords
B1, B2, B3, B4, B5, B6, B7, B8, B9, B10, B11, B12, B13, B14, B15, B16, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14
On the same plan, once the first truss is dry and lifted off.
4
Second truss: webs
E1, E2, V1, V2, V3, V4, V5, V6, V7, V8, V9, V10, V11, V12, V13, V14, V15, D1, D2, D3, D4, D5, D6, D7, D8, D9, D10, D11, D12, D13, D14
The same pieces again.

The rules, in short

Our summary of the ASCE Mid-South Student Symposium 2025 rules. If anything here disagrees with the rulebook or the organizer, they win.

Size and span

The bridge spans between two tables 48 in apart.
Overall length: 48 to 52 in.
Overall width: up to 7 in.
Height: up to 10 in.
No member thicker than 3/4 in.
The base may be at most 3/4 in deep.

The load test

1 in square steel tube on top; an all-thread rod from its middle runs down through the bridge to the bucket.

Materials

Allowed balsa sizes: 1/16 × 1/16 in, 1/8 × 1/8 in, 3/16 × 3/16 in, 1/4 × 1/4 in, 1/16 × 1/8 in, 1/16 × 1/4 in, 1/8 × 1/4 in, each up to 15 in long.
Members glued up from several sticks are allowed, up to 3/4 in.
Glue: super glue (CA) only.

Joints

The rules allow butt joints (a stick's end glued against another), lap joints (sticks overlapping side by side), sandwich joints (a stick glued between two others), gusset plates on one side, gusset plates on both sides, notches.
Gussets up to 2 × 2 in, 1/4 in thick.
Our designs will use only through-cuts you can make with a hobby knife: no notches or half-laps.

Mass and score

There is no mass limit.
Score: failure load ÷ bridge weight.

Plan pages (Letter)

These print one per page at full size. On screen they show at your display's scale.

Page A1 of 7 · sandwich pratt-16 for ASCE Mid-South Student Symposium 2025

Full size. Row A, column 1.

This bar is 2 in (50.8 mm) long.

The full-size plan

Cut list

The joints

Glue order

The rules, in short

Size and span

The load test

Materials

Joints

Mass and score

Plan pages (Letter)

The full-size plan

Cut list

The joints

Glue order

The rules, in short

Size and span

The load test

Materials

Joints

Mass and score

Plan pages (Letter)

From each stock stick