Analysis Summary
To design this bridge, statics and mechanics where taken in consideration to make this bridge rigid and that this bridge will handle the 20kg. One of the main reasons is to find the internal stresses locate in the bottom beam, the maximum shear and bending moments are located at Appendix A-2. For the distributed load of the 38mm X 38mm plate that will be place at the time of the test is in Appendix A-3. For the lift mechanism statics also where taken in consideration because this bridge will be like a bascule bridge, were “is a moveable bridge with a counterweight that continuously balance a span” (Wikipedia.com).
Requirements
This bridge has not to exceed 85 grams in weight.
The material will be only consisting of balsa wood and any type of glue.
Must have a span clear opening of 400 mm.
Road deck must be within 12 mm of the abutment level at the outside edge.
A 38 mm wide solid balsa wood road deck.
8 mm diameter hole in the center of the deck for testing.
The deck must be bigger than 32 mm X 25 mm.
The lifting can be done by manual or automated.
The bridge should be fully support by both abutments.
Design & Analysis
Design Ideas
Types of bridges
Lifting Mechanism Systems
Dimensions
Stresses on each beam
Stress analysis for distributed load
Dimensions
Lifting Mechanism system analysis
Forces acting on the lifting mechanism
Minimum shaft diameter
Stress analysis for the shaft
Beams dimensions for the lifting base
Beams dimensions for the width of the bridge
Bridge deck; beams dimensions and number of beams
Bridge deck; stringers dimensions and number of stringers
Top section of the bridge; beams and lateral bracing
Lifting mechanism; gears, gear rack, and shaft
Counterweight links; dimensions and locations
Gears ratio
Technical Risk Analysis
Weight of the bridge
Holding the 20 kg requirements
Lifting mechanism system
Failure Mode Analysis
Ductile failure
Fatigue failure if the load stay for longer time
Operation Limits and Safety
Support 20kg no more
No cars on top of bridge when is raising