The Friendly Bridge

Hello! I am Victoria Rodriguez, a 17-year-old and an upcoming 12th grader from Anaheim, CA. I found the "Make It Bridge" contest in early April and decided to contribute my own piece based on my local park. Although I have played around with 3D modeling in the past, this is my first time starting a passion project completely from scratch. I made the bridge design in Fusion 360 and physically built it on a 1:20 scale.

For the design of this project, I made it my goal to create something efficient, practical, and non-destructive to the environment. I wanted to make a bridge that would not require the waste of lots of natural resources in its production. Playing with materials and watching construction zones over the years has made me realize that wood waste is abundant in any projects that require it. I would like to imagine that this design can be made entirely out of recycled wood and recycled steel.

For the CAD design:

• Fusion 360
• Measuring tape

For Physical design:

• A 3D printer
• Wood (foundation, main beam flange, main beam web + underbelly beams, beam add-ons)
• Wood Cutting Tools (electric saw, carving tools)
• Screws & wood glue
• Paper mache
• Caliper
• Paint

A great design needs a great concept so I looked around my local area to seek inspiration! I found a lovely river at Eisenhower Park and there was a spot where I believed a bridge would fit perfectly. The location was inspired by the fact that I was too scared to cross the river by stepping on the few loose stones (although I did see brave younger kids cross the stones with ease). I believed a bridge on this spot would bring some security to the community, parents of curious children, and fearful people like me.

With the help of my mom, I measured the distance of the river banks with a measuring tape. This helped me imagine the scale of my bridge and what design would be suitable for this area. I already knew I wanted to make a bridge with sustainable materials but I needed to ensure that the design was additionally well-supported and safe.

Ideas I knew I for sure wanted on my bridge:

• Of course, I wanted the design to pair well with sustainable materials like recycled wood and metal.
• I envisioned a bridge with a slight but comfortable arch as I know a curved design would help distribute weight more easily.
• The design must not be too complex so it can be reused in other locations that may need to quickly implement a bridge for safety.
• I want to make it 20 feet long as that seemed like the average distance between riverbanks at multiple areas of the river.
• I wanted it to be able to support a vehicle if need be.

Opening my first big Fusion 360 project is a landmark in my 3D designing journey and so I wanted to show it here as an important step.

I organized my components into 5 parts (although only 3 were used by the end, better safe than sorry). The important components designed were:

• The Wooden Arch Base: the visible floor of the bridge.
• The Metal Arch Base: the support beams!
• The Wooden Sides: The railing and safety net of the bridge.

To start designing the base, I sketched a 3-point arch on a vertical plane. The arch had a consistent height of 7 inches and spanned 20 feet. I then extruded the arch sketch to make a width of 12 feet. I wanted it to be wide enough for a vehicle to comfortably go through it. According to the CA Highway Design Manual, the preferred lane width is 12 feet so I wanted to go along with that for extra security. All in all, the design can definitely and securely hold the weight of several pedestrians. I added indents on the arch to indicate where each wooden slab part needed to be cut to make the arch.

(PLEASE SEE ALL PICTURES FOR THE WHOLE PROCESS)

I designed the wooden railing and supports simultaneously to ensure they pair well together, so I apologize for the confusion on this step. I did not skip steps; the metal beam supports will be addressed in Step 5.

To design the railing, I made a 5x5 inch sketch on the horizontal plane just along the edge of the wooden base and metal beam. I extruded the sketch 4.5 ft up and 0.5 ft down to make the pillar a total of 5 ft tall in total. With the size of one pillar established, I duplicated the pillar 5 times with a path pattern that followed the arch of the metal beam. To make the top of the railing, I made a midplane between pillars and drew up a sketch to match the arch. It was extruded to make a 20'x8"x4" arch. The bottom of the railing was made in the same way but the dimensions were scaled to inside the pillars. The cross beams on the railings are designed to not intersect but support the railing well at its angle. Each cross-beam slab is 4'8"x5"x2" and the edges are meant to be cut to fit each corner between the pillars and the top bar. 10 slabs will be needed to complete one side. With that, the design is reflected on the other side of the bridge and the railings are complete!

(PLEASE SEE ALL PICTURES FOR THE WHOLE PROCESS)

The beams and supports were designed simultaneously with the railings but this section is only meant to highlight how I made the supports.

To make the curved beam, I made a sketch along the side of the bridge and extruded it. The final dimensions for the beam: beam height: 8", flange width: 2', flange thickness: 2", web thickness: 5", and beam length: 18'. Besides these dimensions, the beam has some welded add-ons. Between the railing and base, there is a thin 1"x6" steel add-on (curved according to the arch) that is meant to be welded right on the corner of the beam. This edge is meant to act as a place for the arch base to rest and for bolt placements. After that, there are add-ons within the insides of the beam. Along the positions of the railing pillars, there are 0.5" thick steel sheets for additional bolt placements. In the middle of each of these segments, there are 2" thick steel supports. I believed these supports would help the beam stability and in keeping its shape.

Although the base beam is custom-made for the bridge, it can be replaced with one of similar dimensions as long as the metal add-ons are welded together well.

To create the underbelly of the bridge, I first designed the steel parts that would complete the steel foundation. I created a sketch on all of the steel sheets on one side of the underbelly (parallel to the railing pillars) and extruded the sketch to meet the paired sheet on the other side. These beams were 5"x5"x8'. This may be difficult to visualize but please reference the photos attached above. Once the 6 steel beams were aligned evenly along the bottom of the bridge, I designed the wooden cross beams that would go in between each segment. These were designed with the use of midplanes and path patterns to get the exact angles correct for each part. An individual crossbeam's dimension is 5"x4"x9.5', not including the edges and centers that would have to be cut in order for the panels to fit together. Ideally, for the center of the intersecting beams, one of the beams can be cut to match the other. However, I displayed another method of intersecting the beams in my physical 1:20 scale model.

After designing the full-scale bridge in CAD, I wanted to bring it to life through a 1:20 scale model! Using the Inspect tool in Fusion 360, I accurately scaled every part of the bridge. The final bridge would be 12 inches long and 7.2 inches wide.

First I 3D printed the wooden base and railings. Ironically, almost all of the wooden parts will be 3D printed while the metal parts are wooden, but I've determined that was the best way to get the most accurate model. For the other parts of the bridge, I used a small mechanical saw to cut dimensionally accurate wooden pieces and then attached everything together with screws and wood glue.

To make the beams: For the flange parts, I cut 4 flexible bamboo pieces (14x7.64x1.8in) to the length of the arch base and then I screwed (M2*8mm screws) the 2 cuts onto the bottom sides of the base to make the top flange curved. The next 2 cuts were used to sandwich the webs. For the webs of the beams, I cut 2 wood pieces (0.25x0.25x11.8in) to fit along the curve. I used M2.6*12mm screws to connect the web cuts to the top flanges and then M2*8mm screws to connect the bottom flanges to the webs. For the beam add-ons, I thinly cut 0.25x0.25x11.8in and 0.078x0.375x15in square wooden dowels to fit inside the beams. Attach the add-ons with wood glue and Ta-Da! The beams are complete.

To make the underbelly: I used 0.25x0.25x11.8in square wooden dowels. The metal beam parts of the underbelly would be cut to exactly 4.8 inches (for a 1:20 scale). The crossbeams, however, were cut not exact cuts every time. I used angled cuts on the corners to make them diagonally fit inside. But how would they intersect? There are many answers to this question but for this physical model, I went with half-lap joints! I carved out half the intersecting parts for each crossbeam, paired them, then stuck the crossing pairs in between each metal support beam with wood glue. Took a bit of trial and error, but I'm pretty proud of the results.

(PLEASE SEE ALL PICTURES FOR THE WHOLE PROCESS)

For the model base, I got a piece of wood 0.5x0.5x12in.

The first thing that needed to be done to start with the terrain building was marking where the bridge would sit. I used thick (0.5x0.5x12in) square dowels and screws to build the foundation of the bridge and mark where the bridge would sit.

To create the land and water parts of the model, I had my mom help me make paper mache using old newspapers. This material would be used to make a subtle but pleasant texture. It took several days for the paper mache to harden completely and I could proceed with painting. I painted in dark shades for the first few coats and then dry-brushed light colors after the coats underneath dried. For the water, the pattern of the light colors is more separated to give the illusion of waves while the pattern in the grass is tight to show strands.

Everything is done. Finally, everything can be put together and the work can be admired. I'm so thankful I stumbled upon this contest; otherwise, I would have never tried doing a large-scale project on Fusion 360. I learned so many new techniques because of this project and it has pushed me to test my limits and create something I never imagined I could. Thank you for this opportunity!