The Paper River Chasm Project Team Canada ME104Q University of Rochester The Paper River Chasm is an opening that extends 8.5” over the Paper River. Several years ago, a bridge was built across the chasm which collapsed soon after, due to insufficient engineering. Many years have passed, leaving the cities on either side with no access to their nearby neighbors. It has now been put to several people to engineer a design for the building of a new bridge. This design attempts to take a step toward the actualization of a new bridge. Although it is only a rough model, it will provide insight into the structural needs required to build a new, successful, Paper River Chasm Bridge. The model is built of 1/16 inch thick 6061-T651 aluminum. This temper of aluminum artificially rolled and straightened, and has a yield strength of 37 ksi. Ansys Workbench was used to assist in the initial design and testing of the model. The current bridge is the product of this design work. Executive Summary According to Ansys, the figure of merit for our bridge is roughly 940. The safety factor with the given weight of two members of the team is approximately 2 at the high stress points. The entire bridge is made out of 6061-T651 aluminum and the pieces are attached with aluminum rivets. Summary Team Canada at the University of Rochester: Joe Subjeck ME104Q Student Julia Cossé ME104Q Student Mike Russell ME104Q Student Andrew Hilmer ME104Q Student Working in collaboration with: Dr. Quesnel ME104Q Professor Shop Crew The People Reasons for Design This design was chosen in an attempt to minimize material, and maximize efficiency. Instead of using a square design with one horizontal load beam and four vertical support legs, the corners of the top load beam were angled to reduce both the amount of material and the overall weight of the design. Since the typical range of safety factors for mechanical engineering design work is 2-3, this bridge was designed with a safety factor of slightly above 2 in critical locations. Brackets were added to connect the two legs on either side of the bridge in order to prevent them from sliding out when a load is applied. Finally, extensions were added to each of the bridge’s legs and folded out, providing stability in order to prevent the bridge from tipping over. Image is courtesy of Dr. Quesnel Procedure The bridge will be tested by applying a load, to the top beam. The load will be the combined weight of two team members. The weight of the two team members will be recorded along with the weight of the bridge. The merit of the bridge will be determined by calculating the ratio of the magnitude of the load applied to the weight of the bridge. The two team members will stand on an 11.8 pound plank of wood that will be connected by a chain to the device created by Dr.Quesnel shown in the diagram below. This device will then be placed on the actual bridge with the wood and the two team members hanging from it, thus placing the total load on the bridge. The board will hover very close to the ground (to reduce the risk of injury) and a paper river will be placed beneath it. The paper river will the be pulled from beneath the board while the two team members are standing on it with the full load applied on the bridge. The bridge must be strong enough to support the full load while the paper river is removed from beneath it. If the paper river is removed successfully, then the bridge will have been successfully built. Ansys-produced model of bridge design. Ansys Produced Geometry Image portraying the safety factor of the bridge. Stresses that result from a load of 320 lbs. Ansys Produced Simulations Properties of 6061-T T651 aluminum has a yield strength of 37 ksi. Also, when the material is bent against the grain of the metal, the alloy tends to crack when an angle of approximately 90 degrees is reached. Even when the alloy is bent in a direction that follows the grain of the metal, some cracking can occur in angles of 90 degrees or greater. Although all of the bends in this model follow the grain of the metal, some cracking resulted in the 90 degree bend that connects the top surface of the load beam to the sides of the beam. These cracks caused some worry as to how well the bridge would support the weight of two team members. However, since the stress model of Ansys Workbench portrays that little stress is present in these areas, it is likely that the bridge will still perform as expected. Some other evidence of how grain direction can effect the building of the bridge can be seen in the areas of the bridge that were cut at different angles. Most noticeably, the underside of the bridge at the diagonal cuts are cut much more roughly that the cuts that were made in line with the grain, along the folds. This roughness would create different stress levels along the diagonal cuts from what they would be expected to regularly be.