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The Challenge:
Design and construct a bridge using only the provided 1/4" x 1/4" lumber and wood glue that can safely span a 12-inch gap. The bridge must adhere to specific size constraints and will be tested for its structural efficiency. The efficiency will be a ration of bridge weight in ounces/how many lbs the bridge holds.
Constraints:
Bridge must be a SUSPENSION Bridge or a TRUSS Bridge!
No PIERS!
Center of the bridge must accommodate the load, a 3"x 6" block of wood with hook.
Bridge must span gap that is 12 inches wide.
Bridge must be no longer than 18 inches long.
The bridge cannot be taller than 5 inches.
Bridge cannot be wider than 4 inches.
Each group will be allotted 20 linear feet of 1/4"x 1/4" lumber to build. Any material used beyond their allotted amount will result in a loss of points.
Various joint types are allowed and encouraged.
Paper gussets should be used. (no wood gussets)
Groups of 3 max! Pairs encouraged. Singletons allowed of course!
Tools:
Hot glue Gun
Wood Glue
Tape
Building board (use it appropriately)
Utility Knife
Cutting Board
Miter Scissors
Materials:
Metered Hot glue sticks
20 Linear Feet of 1/4" beams (keep in baggies in the bin!)
1 sheet of graph paper (use it carefully)
Efficiency Ratio = (Maximum Load Held) / (Weight of the Bridge) :
This means a higher number is better, indicating the bridge held many times its own weight.
Here's the calculation:
Step 1: Convert to similar Units!
Remember 1 pound = 16 ounces!
Step 2: Calculate the Efficiency Ratio
Efficiency Ratio = Maximum Load Held (POUNDS)/ Weight of the Bridge (POUNDS)
Example: Let's say a bridge weighs 5 ounces and held 30 pounds.
Vocabulary:
beam – a horizontal supporting member
bridge – a structure that spans a gap
buckle – to bend under compression
column – a major vertical support of a structure
compression – the tendency to push, squash, or squeeze a material
constraint - limit
efficiency – the strength-to-weight ratio
force – the capacity to do work or cause physical change; energy, strength, or active power
joint – a place where two or more things come together and are united
lamination – the act of layering a structure
load – the overall force to which a structure is subjected in supporting a weight or mass or in resisting externally applied forces; the amount of weight or mass supported by the lift of an airplane or airplane wing
mass – the amount of matter within an object
model – a small object, usually built to scale, that represents in detail another, often larger, object
modification – a change in design, hypothesis, or prototype
racking – a type of stress that distorts a square or rectangle, causing it to become a parallelogram
rigid – stiff or not easily bent
roadbed – the foundation of a road
scale – a system of proportion
side grain – the grain of wood as seen from the side of the wooden strip
side view – a view from the side of something
sketch – a drawing, usually freehand, that provides a quick illustration of an object or process
span – the measure of the distance between supports
substructure – the structure of a bridge that extends below the roadbed
superstructure – the structure of a bridge that extends above the roadbed
tension – the force pulling a material apart
timber – the wood used as a building material
tower – a tall structure that acts like a cantilever beam
truss – a rigid framework, as of wooden beams or metal bars, designed to support a structure such as a bridge
Bridge Design Deep Dive (Alternate Assignment)
This assignment attached is a research and design task for students who need an alternate learning activity during the hands-on bridge building project. It focuses on the science and engineering behind the two types of bridges you are building.
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