08-10-2012, 01:23 PM
BRIDGES
BRIDGES.ppt (Size: 1.86 MB / Downloads: 181)
How Bridges Work?
Every passing vehicle shakes the bridge up and down, making waves that can travel at hundreds of kilometers per hour. Luckily the bridge is designed to damp them out, just as it is designed to ignore the efforts of the wind to turn it into a giant harp. A bridge is not a dead mass of metal and concrete: it has a life of its own, and understanding its movements is as important as understanding the static forces.
Basic Concepts
Span - the distance between two bridge supports, whether they are columns, towers or the wall of a canyon.
Force - any action that tends to maintain or alter the position of a structure
Compression - a force which acts to compress or shorten the thing it is acting on.
Tension - a force which acts to expand or lengthen the thing it is acting on.
Types of Bridges
The type of bridge used depends on various features of the obstacle. The main feature that controls the bridge type is the size of the obstacle. How far is it from one side to the other? This is a major factor in determining what type of bridge to use.
The biggest difference between the three is the distances they can each cross in a single span.
Tips for building a bridge
1. Commitment - Dedication and attention to details. Be sure you understand the event rules before designing your prototype.
Draw your preliminary design
ALL joints should have absolutely flush surfaces before applying glue.
Glue is not a "gap filler", it dooms the structure!
Structures are symmetric.
Most competitions require these structures to be weighed. Up to 20% of the structure's mass may be from over gluing.