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Balsa Wood Bridge

Balsa Wood Bridge Competition Rules

Team or Individual Event

Pre-Registration Required

 

Purpose

The objective of this event is to design and build the lightest bridge capable of supporting a given load over a given span. Students will design a device prior to the UL E&T Expo event.

Bridge Registration
  • Registration will begin at 8:30 AM, and end at 10 AM.
  • Sign in at the Games Registration Tent, located near the main registration tent. Competition location will be announced during registration.
  • Once the device is registered it will be turned over for impound and no further modifications will be allowed before the competition.
  • The bridge will be evaluated to determine if it meets the specifications provided.
  • Each school may bring two bridges (there is a maximum of two teams per school), and each team can have a maximum of four team members. Students may not be a member of both teams.
  • All teams are required to pre-register online to help facilitate planning. Click here to pre-register before the day of the event.
Bridge Construction
  • All construction must be completed prior to the event using balsa wood ONLY and white Elmer’s glue only. No other glue, screws, nails, wood, or other mechanical or chemical fasteners.
  • The bridge may not be coated with any material.
  • The bridge must allow the passage of one standard Hot Wheel’s Car along the entire length.
  • Bridge Span: Must span the 350mm opening. There is no maximum length.
  • The bridge must have a minimum width of 80mm throughout the entire cross-section of the bridge.
  • No portion of the unloaded bridge may extend more than 15 mm below the top surface of the test supports.
  • The road surface must be solid except for a ¼” hole in the center to accommodate the loading block (see below).
Bridge Loading
  • The load point will be at the center of the bridge.
  • The bridge must accommodate a 50mm long x 80mm wide x 20mm high loading block, ¼” eyebolt, washer, and wing-nut. The loading block is set up such that it will sit on the road surface with a sand bucket hanging from the eyebolt which passes through the surface. The bridge must have a pre-drilled ¼” diameter hole in the middle of the span for an eyebolt to pass through.
Testing
  • All bridges that met the specifications during registration will be tested.
  • Teams must be present for the loading and testing.
  • All safety equipment will be provided for the competition.
  • One end will be placed on a 50mm high wooden block to incline the bridge. The Hot Wheels Car will be placed on the elevated portion of the bridge and will be allowed to roll down its entire length. If the car gets stuck, the students are allowed two restarts. If the car still does not pass after two restarts, a penalty of 2 kg will be deducted from the sustained load until the car passes through (for example, if the bridge holds 20 kg and it takes the car 3 tries to get down the bridge, the bridge will be treated as if it only holds 18 kg).
  • The event supervisor will provide the Hot Wheels car.
  • The bridge will be centered on the testing apparatus, containing a 350mm opening between the bridge supports.
  • The loading block will be placed at the load point of the bridge. The eyebolt will be pushed up through the bridge and loading block from below and secured with a wing-nut and washer on top of the loading block. A standard 5-gallon plastic bucket (approx. 30cm diameter) will be suspended from the eyebolt.
  • The student will add sand to the bucket until failure occurs or the maximum load of 25 kg is reached. Two students will be allowed to test. One may scoop the sand into the bucket while the other steadies the bucket. The student who scoops sand into the bucket is required to wait 5 seconds between adding an additional scoop to be sure the bridge can sustain the load. The load must be applied in a reasonable amount of time. Hint: There is no advantage to build a bridge that will hold more than 25 kilograms.
  • The bridge must support a 5kg load for a minimum of 5 seconds to qualify for scoring.
  • The load used for scoring will be the weight of the bucket and sand only.

Scoring

The winner will be determined by the largest load/mass ratio with 25kg as the maximum load.