Bridge Construction Project Jennifer Schofield, Kirsten Riggle, Justine Staniszewski 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

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 g  Bucket – 376 g  Total weights g  Final grams kg Mass of bridge (kg) Maximum Load mass (kg) Max Load/Bridge Mass Max Force held by bridge (N)

Results ΣFy= 0 =-w + F1y + F2y Cosθ= w/F1 F1= w/cosθ F1=.035/cos(30) F1= N w θ

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  m m  mom/force1.htm mom/force1.htm  ering/civil/bridge9.htm ering/civil/bridge9.htm  ary/physics-terms/torsion-info.htm ary/physics-terms/torsion-info.htm