Denver South High School Bench

Summary

This bench project was inspired by the special education teachers at Denver South High School who wanted a bench for their students to be able to use while they waited for the notoriously late bus. The special education teacher reached out to the engineering teacher who then approached me about taking on the project.

This project required starting the design process from the very beginning. I enlisted the help of one other classmate and together, we created design constraints and ideas with the special education class, secured funding and permits, designed the bench in Autodesk Inventor, found local suppliers, designed and built every component, installed the bench on-site, and are performing yearly maintenance and inspections.

Take Away / Skills Acquired:

1. Client engineer communication must be organized and regular, ensuring everyone involved in the project is getting the information
2. Save files to the cloud
3. Design with tolerances that reflect installation difficulties
4. Leverage and bounce ideas off of resources like experts in the field of engineering

Skills Acquired

1. MIG welding (introduction)
2. Concrete casting with rebar
3. Designing with tolerances
4. Creating project proposals for funding and support
5. Designing with durability and survivability in mind
6. Material and component research and purchasing

Project Walk-Through

Define the problem

The special education class at South Highschool has to wait up to 45 minutes for their notoriously late bus. This extended period of time standing can be challenging for students. To add on, the graduating class of 2021 needs to leave a lasting mark at the school and the retiring teachers deserve a memorial.

Generate Concepts

Working with the special education class, we worked on explaining the engineering process to the students and getting their design inputs. Design criteria was also thought out here. Every seat needed to have an armrest on either side, the bench needed to accommodate at least three people, the location had to be within 20 feet of the bus pickup location, and little to no maintenance should be needed for the bench. Other ideas that came out from this process was to develop sliding armrests that could lock to allow for varying seat sizes and ability for the students to personalize the bench.

Develop Solutions

My team and I used google images to draw inspiration and grasp an idea of how this bench could function. Through deliberations, we decided that rectangular prism concrete supports would be the easiest and cheapest to produce while not compromising on strength or weather ability. To create an ergonomic shape, we decided that creating an L shape steel support would allow us to place many 2x4’s in a flowing pattern. We eventually created this ergonomic shape by drawing a scale design of a very comfortable swinging bench. Finally, placing steel round bars between the concrete supports could support the entire seating section while looking minimal and clean.

The sliding armrests were going to be much trickerier. We thought about using linear bearings, a pin and hole design, or a metal round tube sliding over the steel round bar. The most cost effective and manufacturable solution seemed to be the round tube sliding over the round bar

Construct and Test Prototype

Due to our limited budget and lack of understanding of the value of building prototypes, all prototyping was done in Autodesk Inventor. I created 7 designs of the bench changing specific components as we researched material availability and worked through the construction plan.

Funding was secured through our school budget and Parent Teacher Student Association (PTSA) which enabled me to be reimbursed for purchases. This freedom allowed me to freely travel from supplier to supplier and find the best process and materials to fit the design. The only component of this entire bench that was outsourced was the water cut L support as we did not have the equipment to create such a defined shape.

Concrete Supports:

• A plastic pipe cut in half was glued to the top of our mold to create a curved armrest
• Rebar was placed inside the mold and since both sides were exposed, we tied string to the rebar and then to ceiling to ensure the rebar was in the middle of the supports
• Two holes were created to allow for the steel round bar to rest through

L-Supports::

• Original design had 1.5”x2.5” rectangles cut out (with appropriate tolerancing) to create ergonomic shape
• This design was poor however as we still needed to figure out a way to screw the 2x4’s into the metal plus this design would be difficult to put together in construction
• Final design involved cutting the experiment of the L support and then welding 1”x1” metal tabs above and below where the 2x4 would rest. Holes were drilled in every 1x1 tab and then welded to each support in a precise ergonomic shape

Armrests:

• Using Steel Flat Bar and round tube, we created incredibly sturdy armrests. The angle of the bend in armrests had to be very precise as it was to slide on bars and would just be slid onto the bench as it was being assembled.
• Wooden dowels were added to the top for a better hand grip and to reduce the heat where your arm would rest

The original plan was to dig a small foundation, fill with concrete and then slide the rebar sticking out of the supports into the holes made in the foundation. However, despite clear communication with the client, we learned on the day of breaking ground we were not allowed to dig. 4 weeks and many negotiations laters, we were told that the bench had to go in a completely new spot on top of concrete. Frustrated but determined to finish this project, we shortened the rebar poking out of the bottom of the concrete supports and began installation. The concrete padding was nowhere close to being level and since the concrete supports were two parts that were then connected through round bars, levelness and the holes being the same height was paramount to our success. In the end, we used a hammer drill and precisely drilled through marked locations. One section had to be drilled at a 3-degree angle to ensure components would line up. We then devised a new solution to attach the concrete supports to the concrete padding by using bolts that would go through the bench supports and then concrete anchors.

Despite the massive change in plans, the bench was constructed and is incredibly sturdy.

Evaluate Solutions

This bench was my first engineering project developing an idea from nothing to delivery to client. I am incredibly happy with the final product but many components could have been improved. This bench will last at the school for decades to come and is very visually appealing. I learned about nuances in engineering design you can not learn in class but only through projects. Our construction was completed on time and we ended slightly under budget. Most importantly, this bench allows the special education students to more comfortably wait for the bus, thanks to the retiring teachers of 2021, and shows how spectacular the class of 2021 was.

How project could have been improved

1. More documentation
• I never learned how and why to document a project. You may see in this write up there is a severe lack of pictures and designs. I also did not write enough about the process to tweak future designs; I simply kept them in my head. Thankfully I learned with this project though and now document every single step of an engineering project and ensure my ideas, problems, and suggestions are documented.
2. Redesign Armrests
• Increase Height of Armrests: This bench was designed for special education students to be able to easily stand up after sitting in. Therefore, the backrest forces you to sit more up-right while matching the curves of your body. The sloping design by the legs allows users to slide a little down and then push up. While our design was based on ergonomic standards and is great for pushing off or to stand up, the armrests are around an inch or two too low for optimal comfort while resting your arms.
• Improve Sliding Design: Because all of our prototyping was conducted through discussion and designing in Inventor, our sliding armrest idea was never able to be flushed out completely. Our design had bike seat post clamps to restrict the armrests from sliding once in position and then round tubes sliding over the round bar. After construction, our design worked, but was not perfect. There were a few pinching hazards and would sometimes get caught. My partner and I agreed that the poor functionality did not meet our standard and would be scrapped. We then permanently attached the armrests in place 20 inches apart. I have been haunted by this failure and have come up with many new, safer, and simpler ideas that could be applied on a new bench.
3. More defined timeline
• With COVID, school, applications to college, and my other projects, our timeline was not linear. Some weeks were full of work while others had none. I learned the importance of spreading out work in the beginning and sticking to the timeline. Even though we finished on time, stress could have been reduced had we made and stuck to a more realistic and thought out timeline.
4. Higher tolerances
• Since we had a massive change of plans after every component was built, we were very lucky that our tolerances in design still allowed for construction. However, we should have increased tolerances in the design for components like the holes for the round bar to pass through and the distance between L supports as these were critical components that should not be under any unnecessary stressors.
5. Better communication with the client
• The change in location could have been avoided had communication with the client been better. I learned the importance of weekly updates with the client and ensuring that most important details are agreed upon early and a full understanding is prevalent.
6. Backup files
• About a day after the final design phase, a pipe burst in my ceiling and ruined my computer. I lost most of my Autodesk Inventor files for this project because of the water damage. I did not have any backups of the design and had run out of cloud storage before the project began. I now know the importance of having backups and ensuring files are accessible in more than one place.