Lake Perris Renewable Energy Bridge

My name is Shutian Xiang, and I am 18 years old and a rising senior in high school. In my community, one of the favorite places of my family and I is Lake Perris. The last two images attached above are take during our most recent trip there. The lake is a reservoir and a part of the California State Water Project completed in 1973. The diamond blue lake is surrounded by rolling hills on three sides, and the idyllic Alessandro Island draws visitors to it with its unique geography. However, the island is only accessible by boat, as shown in the photo. Thus, it can be made more easily reachable by visitors if there were a bridge connecting the island and land. The bridge would be around 0.5 mile.

In the research and brainstorming phase, I had several objectives in mind. Specifically, I would like to utilize the natural resources (wind, solar, or hydro power) around it and allow it to aesthetically blend in with the natural environment.

To accomplish these objectives, the bridge has an open air top design consisting of beams and rafters. This would allow vine plants, such as star jasmine, to grow along the structure until it covers the top and provides a natural shade. But how to water these plants? Solar energy could be harnessed through sets of solar panels mounted above the top structure along the bridge and used to power irrigation pumps that draw water from the lake. The remaining electricity from the solar panels can also light the bridge at night with outdoor solar powered lights.

The bridge adds a shaded region located above water for visitors to rest during the blazing-hot summers of California and is an eco-friendly addition to the Lake Perris Recreational Area. Furthermore, the bridge is designed to be a safe and cost-effective due to the bridge's inner structure and open top design.

"Lake Perris." https://photos.wikimapia.org/p/00/00/61/24/75_big.jpg. Accessed 20 July 2023.

Supplies

• Fusion 360
• Adobe Illustrator (for illustrating idea on green plants)
• Photoshop (for editing final image presentation)
• Notebook and Pen

Step 1: Research on the Inner Structure of a Bridge

Why are Many Bridges Arched?

I first began this project by researching the physics behind the arch of a bridge. As shown in Figure 1, there is compression on the surface of the single beam, and tension results on the bottom. As tension stretches the lower portion, the bridge may eventually fail to resist compression and buckle. Thus, the support assumes the role of dissipating the forces so that not a single area is weak and prone to concentrated force.

Thus, the arch can help dissipate the force along to the bottom where is it transferred into the abutments. By Newton's Third Law, the reaction force from the ground is equally exerted onto the abutments to hold the bridge up (Figure 2).

What is Da Vinci's Bridge Structure?

After some research, I stumbled upon an image of the Da Vinci's self-supporting bridge structure. Though it is only built from a few wooden beams without any screws, it can self-support and hold up the weight of a person (Figure 3). Like the arch, da Vinci's bridge relies on the dissipation of forces as shown in Figure 4. The center beam is acted upon by a force pointing down (blue arrow), while the two beams beneath it supports the center beam and is acted upon by a force pointing up on the two ends (red arrow). Thus, it is able to be self-supporting.

I found the physics behind the bridge's inner structure very fascinating and decided to model the inside structure for my bridge design similar to Da Vinci's bridge, with some modifications.

Kwong, Norman. "Physics of Bridges." University of British Columbia, https://phys420.phas.ubc.ca/p420_04/norman/physics_of_bridges.ppt. Accessed 20 June 2023.

"Leonardo Da Vinci's Self-Supporting Bridge." Enredando No Garaxe, https://enredandonogaraxe.club/en/leonardo-da-vinci-bridge-self-supporting/. Accessed 22 July 2023.

Step 2: Identify the Problem & Brainstorm

The Alessandro Island is around 0.5 miles from the shore of Moreno Beach. Using materials such as steel and concrete, a modern single arch bridge can span between 200 to 800 feet. I referenced these dimensions as I would model a single unit of my bridge design to be of similar length. Thus, for the bridge to last this distance and be structurally stable, it could have 12 connected units with each individual section spanning 220 feet in real life.

Step 3: Model Substructure of Bridge

• (Images 1-2) The first photo is a layout of the foundation for one individual unit of the bridge, and the second photo the interweaving of the bars to reinforce the structure. Similar to Da Vinci's bridge structure, it has the ability to "self-support".
• (Image 3) The bridge has a height-to-span ratio of 1:5.
• (Images 4-6) I made the structure different by making layers of bars interweave upon one another. I also made a trapezoid-shaped support by the abutment to support the top bars which are directly below the deck of the bridge. In the process of creating this model, I primarily used the mirror function to increase efficiency. I would create an Offset Plane that divides the middle of the structure, and mirror the bars and beams to the other side.
• (Image 7) I finally covered the top section, which would likely be paved with concrete and in part, asphalt.
• (Image 8) I then linked the individual units together as such, finally extending it to 12 units long.

Step 4: Model Superstructure of Bridge

• (Images 1-2) For inspiration, I searched up various types of roofs on bridges and for pergolas. These two images in particular gave me inspiration for my design. This design would be cost-effective as the roof saves material, and provides a support for vines to cover. In addition to shade, these vine plants would help the bridge blend into its natural surroundings and habitat.

Modeling the Beams and Rafters in Fusion 360:

• (Images 3-5) I finally finished modeling the beam and rafters for half of one unit. The curved section of the beam is created using the Loft feature, in which I connected the sketches of rectangles across three different planes. I also modified the look of the beam with the Fillet feature. I then created multiple Offset Planes and used the Mirror function to mirror these components onto the other half of the bridge unit. The Mirror function was repeated with each unit of the bridge until the entire 12-unit long bridge is completed.

Step 5: Add Solar Panels

• I created a solar panel model in another file, then inserted it into the bridge model. The solar panels only required a few extrusions, with the goal of making them look similar to solar panels in real life. Then, I combined two panels in one file with a simple mount.
• These sets of solar panels could line the entire length of the bridge, on both sides. Therefore, there will be a total of 50 sets of solar panels.
• These solar panels would power the water pump(s) that draws water for the vine plants and solar-powered lights along the bridge after dark.

Brief/Approximate Calculations for Electricity Generated by Solar Panels:

• According to ElectroRate, an average water pump uses around 1,200 kWh of electricity per month.
• To simplify the calculations, assume each set of solar panels together form an equivalent of a 60-cell standard solar panel (3.25" by 5.5"). A 60-cell can generate around 270-330 Watts per hour. If it gets direct sunlight for 5 hours each day and generates an average of 300 Watts per hour, it comes out to 1500 Watts-hours or 1.5 kWh.
• Each month, one set of solar panels (60-cell) can generate 45 kWh. Together, the 50 sets can generate 2,250 kWh, which would be enough for the water pump to draw up water from the lake.
• The remaining electricity can be used to power some outdoor solar-powered hanging light such as the one shown in Image 5.

"How Many Watts Does a Well Pump Use?" ElectricRate, https://www.electricrate.com/well-pump-energy-usage/. Accessed 23 July 2023.

Step 6: Add Railings

• The final step was to add railings to ensure the safety of visitors.
• The railings were created in a similar way to beams and rafters for the roof. The posts were created with the Loft function. The baluster was only created once, and then copied along the entire unit with the Rectangular Pattern function. Again, the Mirror function was used so that the railings extended to the entire bridge.

Step 7: Visualize the Completed Bridge With Vines

To model the finished visual image of this bridge, I used Adobe Illustrator to draw on some green vines. I also inserted an image of what the bridge may look like in real life from a bird's eye view with screenshots taken from Google Earth, finally using Photoshop to combine these images together.

Lastly, I have attached two pictures that I took on my visit there (last two images).

Thank you for reading my Instructable!