3D-Printed Railway Bridge Competition

• Only polylactic acid (PLA) filament may be used to make the bridge pieces, and all of the bridge pieces must be comprised of 100% extruded PLA.
• The span (face-to-face of supports) will be 22.0 inches. The face of the support will be undercut at an undisclosed angle to prevent designs from utilizing wedging action between support faces (see figure below).

^{Figure 1. The bridge piers have a 22 inch clear span.}

• The overall size of the fully assembled bridge must fit within a space that is 10 inches x 10 inches x 26 inches long.
• Up to 24 individual 3D-printed pieces may be used to construct the bridge.
• The total bridge weight (sum of all individual pieces) must be less than or equal to 500 grams.
• All pieces must collectively (at the same time) fit into a specially made box that is 220 mm x 220 mm x 165 mm tall (8.66 inches x 8.66 inches x 6.50 inches). The box will have a lid that must fully close with all pieces inside.
• No adhesives or non-printed hardware (screws, bolts, pins, etc.) may be used to join the bridge pieces together. Connections of the individual pieces will be made by designing and printing pieces that have interlocking joints and/or connection components. Note, 3D-printed pins, dowels, etc. are allowed but they each count towards the 24-piece limit. Un-extruded filament may not be used to reinforce joints or for any other purpose.
• The bridge must allow for the passage of a train that is 3.5 inches wide x 3.5 inches tall across the bridge. The trail will pass along a route that is centered on the 12 inch-wide piers and the bottom of the train is located 1.5 inches above the piers (refer to figure 2 below). Please watch the video to see how this will be verified.

^{Figure 2. No members may occupy the train passage area}

• The load will be applied to the bridge through a loading block at mid-span with “wheels” that are spaced at 2 inches on center (refer to figure below). There will be a ¼”-diameter threaded steel rod that will be attached to the loading block from the bottom side. Therefore, there must be at least a 3/8 inch clearance at the center of the bridge from the bottom side to allow for the attachment of the .25-inch rod (refer to figure of loading block below and watch the video for clarification). The load will be applied to the bridge by pulling downward on the loading block at a displacement rate of 0.5 inches per minute until failure of the bridge occurs.

^{Figure 3. The loading block that will be used to apply loading to the bridge at mid-span}

On the day of the competition, students will check in their bridge pieces where they will be inspected for compliance with the bridge rules. Compliance will be verified in the following manner.

1. The student will present the actual 3D filament spool(s) with label or a photo of the spool(s) used to prove that PLA filament was used.
2. The pieces will be counted (to make sure that no more than 24 pieces are used).
3. The pieces will be weighed (to make sure that the total weight is 500 grams or less).
4. The student will then place the pieces in the box to verify that they all fit within the 220 mm x 220 mm x 165 mm tall (8.66 in x 8.66 in x 6.50 in) size restriction.
5. If the bridge pieces meet the three criteria above, the student will then have 5 minutes to assemble the pieces into the final bridge. No more than 5 minutes may be used to assemble the bridge.
6. The bridge will then be checked for overall size (it must fit within a space that is 10” x 10” x 26” long).
7. The bridge will then be placed on representative piers and checked to make sure that a 3 ½” x 3 ½” train may pass across the bridge at a height that begins at 1.5 inches above the piers.

Qualifying bridges will be judged for overall design and aesthetic categories.

Qualifying bridges will be placed on display until load testing to failure.

The load will be applied to the bridge through a loading block at mid-span with “wheels” that are spaced at 2 inches on center (refer to figure below). There will be a .25-inch-diameter threaded steel rod that will be attached to the loading block from the bottom side. Therefore, there must be at least a 3/8 inch clearance at the center of the bridge from the bottom side to allow for the attachment of the .25-inch rod (refer to figure of loading block below and watch the video for clarification). The load will be applied to the bridge by pulling downward on the loading block at a displacement rate of 0.5 inches per minute until failure of the bridge occurs.

Maximum load-carrying capacity of the bridge

1^st place – Ender 3 3D printer

2^nd place – Beats Solo 3 wireless headphones

3^rd place – JBL Charge 4 bluetooth speaker

Overall design aspects and joint details

1^st place – $75 Amazon gift card

2^nd place – $50 Amazon gift card

3^rd place –$25 Amazon gift card

Bridge aesthetics

1^st place – $75 Amazon gift card

2^nd place – $50 Amazon gift card

3^rd place –$25 Amazon gift card

Prizes sponsored by GFT