Bridge Construction ProjectJennifer Schofield, Kirsten Riggle, Justine Staniszewski

http://randommization.com/2011/02/08/miniature-masterpieces-made-with-a-single-toothpick/

How are forces distributed on bridges?

Trusses are hinged connections that form a stable configuration

Nodes are joints in which trusses can be attached

The load is the weight applied at any specific point

Forces When loads are applied to

a truss only at the joints, forces are transmitted only in the direction of each of its members

A fixed node can provide support in both x and y direction

A rolling node can only provide support in the y direction

One or more nodes can be assigned per node

Types of Force Compression—Inwards force that

causes the object to compress when squished, opposite of tension

Tension—Outwards force exerted on an object, causes tension by forces exerted in opposite directions

Shear—Shear stress occurs when two fastened structures (or two parts of a single structure) are forced in opposite directions

Torsion—Stress produced in a body when it is twisted or when the two ends of a body are twisted in opposite directions

Bending—When a force is exerted downwards and causes the component to bend or to become warped

http://academic.uofs.edu/faculty/kosmahle1/courses/pt245/forces.htm

Hypothesis and Design Toothpicks were

doubled for extra support

The design on the back of the handout was used as a guide

Forces Distributed Throughout Bridge

A bending force is exerted on the bridge when the weight is added to the center

Forces Distributed Throughout Bridge

Compression forces are exerted on the bridge where the structure is supported by the cardboard which has a normal force, but the weight of the bridge is being forced downwards

Forces Distributed Throughout Bridge

Torsion or shear forces are exerted on the diagonal supporting beams of the bridge due to the angular forces upon them, as they are the major structural support components

Possible Weak Points The bridge will likely be

most vulnerable at the center of it where the weight is to be added. The outside elements will be the most supported because they will be located on a flat surface, whereas the middle area will be farthest from this location

Group Collaboration The bridge building

was partially completed by everyone in the group

The PowerPoint was primarily completed by Jen

The GoogleSketch images were primarily completed by Justine

The design of the bridge was composed primarily by Kirsten

Everyone in the group played a major role in the construction and completion of our bridge

Construction The construction of the bridge was a multiple-day process. This

can mostly be attributed to the fact that the glue had to have time to dry daily.

On the first day, the toothpicks were glued side-by-side in pairs. This was done so that the doubled up toothpicks could be used in the construction of the bridge in order to strengthen the design

On the second day, these components were used to be glued together in a group of four to complete the structural components that will hold the bridge on the surface it is placed on.

On the third day, the parts already created were added together to begin to form the bridge as a whole. We glued tooth picks together to form a “walk way.” This formation connected the trusses together, and helped to stabilize the bridge.

Procedure Trusses were formed “walk way” was created The three components were glued together The bridge was weighed The bridge was placed on the cardboard cut out Two strings were attached to the bucket The bucket was then weighed The pencil was weighed The pencil was placed on the bridge Bucket was attached using the strings to the pencil Weights were added until the structure of the bridge failed.

Testing Pencil-4.0 g Bridge- 35.0 g Bucket – 376 g Total weights-

5060 g Final grams- 5.440

kg

Mass of bridge (kg)

Maximum Load mass

(kg)

Max Load/Bridge

Mass

Max Force held by

bridge (N)

0.035 5.44 0.643382353 53.312

ResultsΣFy= 0 =-w + F1y + F2yCosθ= w/F1F1= w/cosθF1=.035/cos(30) F1= 0.2269 N

wθ

Conclusion All in all, since our bridge broke in so

many different locations, the pressures and forces were distributed fairly equally.

The truss that we believe broke first was the cause for the rest of the fractures.

The Elmer’s glue was not applied thickly enough to this location and it should have been supported more thoroughly.

References http://www.jhu.edu/virtlab/bridge/truss.h

tm http

://www.technologystudent.com/forcmom/force1.htm

http://science.howstuffworks.com/engineering/civil/bridge9.htm

http://science.howstuffworks.com/dictionary/physics-terms/torsion-info.htm