Guayabitos is a community of about 30 people straddling the Rio Pojo in a remote area of central Bolivia. On the south side of the river are the residents’ homes. On the north side are essential facilities: schools, stores, medical clinics, markets and roads. For much of the year, Rio Pojo is calm enough to be crossed on foot. But winter rains cause the river to flood and become dangerously impassable. Several residents have drowned in recent years attempting to cross it.
When Stevens Institute of Technology civil engineering students Nick Acquafredda ‘21, Peter Gallagher ‘21, Dan Mejlander ‘21 and Sam Quick ‘21 saw an opportunity to design a pedestrian bridge for Guayabitos as their senior design project at the Schaefer School of Engineering and Science, they jumped at it.
The idea for the Guayabitos footbridge came from the Bridge Program, an initiative of Engineers in Action (EIA), a nonprofit organization that works with local communities in third world areas in need to increase access to water and infrastructure. Launched in 2006 by Bridges to Prosperity and now operated by EIA, the Bridge Program offers university students the opportunity to design essential infrastructure for communities in need. Over the past 15 years, more than 700 students from 30 universities have designed and built 88 footbridges in 11 countries.
The senior design bridge project is sponsored by the international engineering firm Thornton Tomasetti and mentored by Leo Fernandez, PE, a civil/structural engineer at the company who has been mentoring Stevens engineering students for seven years. At the Schaefer School, Teaching Professor Leslie Brunell, PE, was the students’ faculty advisor.
Managing different aspects of the project
None of the students had any experience building essential infrastructure except for Gallagher, who had helped construct a six-kilometer water pipeline in northern Thailand with Engineers Without Borders. In September, the four took an introductory video course in the Bridge Program that included presentations by student chapters about completed projects. Each then focused on a different learning module of the Bridge Program. “These courses are very helpful,” Acquafredda said. “They were able to give us very good detailed guidance on where to begin.”
As a guide they also had the EIA Bridge Builder Manual, which provides technical specs based on those created by the American Association of State Highway Officials (AASHTO), which sets all transportation codes in the U.S., including for air, highways, rail and water.
Each managed a different aspect. Gallagher was the design lead and took responsibility for most of the structural design checks. “It's a suspended bridge, which means that it's using cables and tension to transfer the load, and that's transferring them to gravity anchors,” he said. “We had to find out what the maximum cable force is, and from that, we figured out how many cables we need. And then we completed a whole bunch of other checks, mainly making sure that these gravity anchors – which use their own weight to resist the forces that are being distributed across the bridge – were sufficiently safe.”
Acquafredda was the construction and safety manager. “I drew up a bill of quantities, made a construction schedule and then focused on some of the safety protocol – stuff that would have to be considered when on site.” That includes personal protective equipment (PPE), fall protection, safety boots and safety eyewear. “I also looked at risks that are involved with the project, and ways to mitigate these risks.” One such risk is bad weather, which can bring a construction project to a halt.
“Early on, I spearheaded the hydrology sections to understand the river’s behavior,” said Quick. HEC-RAS hydrologic engineering software was part of this process. “Towards the second semester, I started doing the community engagement plan. A huge part of this project is working alongside the community members – improving their skills and their local and technical capacity.”
In the first semester, Mejlander focused on project management and site assessment. “This semester, I gravitated more toward developing a 3D model for our bridge that can be used to showcase our design – to create cross-sections, 2D drawings of any part of the bridge, and to create a 3D model that we could structurally analyze.” To do so, he learned how to use Revit building information modeling (BIM) software.
Throughout the year, the team were advised by Fernandez and three of his Thornton Tomasetti engineering colleagues, and guided by their Stevens professors.
“I assisted the team with the layout, the hydrology to determine the required height of the structure, communications and the overall project deliverables,” said Brunell, with whom they met virtually every two weeks. “Professor Rita Sousa assisted with the erosion control and Professor Yi Bao with the Revit structural modeling.”
The biggest challenge
“Erosion mitigation is a very unique challenge to this area,” Quick said. “Not many of the previous EIA projects have had much erosion to navigate around. We had to come up with an erosion-mitigation design in order to try and make sure that the soil we were building upon was stable, and that we can ensure that this project would last for a long time and make a true impact on the community.”
Their approach to erosion mitigation uses rocks held in Gabion cages, jute netting and natural vegetation. The use of locally accessible building materials was a design requirement to make both construction and maintenance more cost effective and logistically manageable. The closest major city, Santa Cruz, is eight hours away.
“The team did an outstanding job and learned a great deal,” said Brunell, noting that their use of HEC-RAS and Revit software was innovative for the Bridge Program – and will now become part of it. “These packages were not used before by EIA student teams, and now modeling will become a new requirement for all EIA designs,” she said.
If you build it, Sam will come
The bridge at Guayabitos was supposed to be designed and built in 2020, but the Covid-19 pandemic brought the project to a halt. The goal is to revive the project this summer. The Stevens students’ design is one of a few that EIA is considering; whether their entire design or elements of it will appear in the final construction remains to be seen. Acquafredda, Gallagher and Mejlander all have internships lined up so will be unable to go to Guayabitos this summer, but Quick is determined to be there to participate in person alongside EIA student chapters from other universities. He’s brushing up on his Spanish and has created a GoFundMe to support his travel to Bolivia.
Either way, all four students will take this experience into their graduate studies at Stevens next year. Acquafredda and Quick will study construction engineering and management, while Gallagher and Mejlander will focus on civil structural engineering.
Dr. Brunell is hoping to establish a student chapter of EIA at Stevens. She said, “I plan to work with Leo [Fernandez] on another EIA bridge for the 2021-–22 academic year and hope that once we are past Covid-19, the design team will be able to travel for the build – and that a student chapter becomes a reality.”
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