“Shelter Cots”Energy and Sustainable Systems
Project No. 13431Multidisciplinary Senior Design Technical Paper
Friday February 15th, 2013Libbi Cook, Industrial and Systems Engineering/Engineering Management
Kevin Encarnacion, Industrial and Systems Engineering/Industrial EngineeringDerek Kirsch, Mechanical Engineering
Jennifer Patterson, Mechanical Engineering
Abstract
There are homeless people all over the world, and Rochester, New York is one of those places. The purpose of this project was to provide a local homeless shelter, St. Joseph’s, with cots that save storage space and provide bed bug resistance and durability. Twelve cots were designed, tested and provided to the shelter with a replacement plan.
Introduction
St. Joseph's House is a homeless shelter and soup kitchen located in downtown Rochester. They operate a bed shelter in the winter months, starting in October and running until April. In the year 2011, the shelter experienced a bedbug infestation in which their wooden benches and cots had to be disposed of. As a result, the shelter purchased army cots to replace the former cots. However, due to the fact that many of the tenants tend to bring bed bugs from their current living conditions, the shelter takes extra precautions and places the current cots in the freezer to kill any living bacteria or bugs. They also wash the linens on sanitary settings. This has reduced the cradle-to-graveness of the current cots, which are not expected to last more than one more season because the cots are intended for temporary use, not daily sleeping arrangements. A group of RIT students worked together to come up with a preliminary design in which cots are able to be stacked when not in use and double as a bench. However, they were not able to analyze the design or create a prototype.
The preliminary design was then given to our multidisciplinary senior design group as their project. A new design was created to provide the shelter with a stackable design; however, towards the end of the first quarter of the project, a new specification was introduced to the team: the cots were to be stackable.
This was discovered when the team went to a budget meeting at St. Joseph's so the customer would be able to review our design, approve, and give us a set budget. It was noticed that the home had recently set up a series of pulleys, which were used to suspend the cots into the air. The team then discovered that this was a temporary solution to the space issue that was hoped to become a long-term solution. We were then given a series of new requirements:
• Cots must be suspended/hung on pulleys both vertically and horizontally through use of hooks, loops, etc.
• Due to (1), weight of cot must be kept at a minimum.• Due to (1), cots will not be used as benches.• Mattress is not preferred due to storage concerns as well as to ensure the
elimination of bedbug infestation.• Due to (4), guest must be able to sleep comfortably; the current cots have a
canvass, which is deemed comfortable.There are several issues with the cots that are already on the market. The
most obvious issue was that the frames are collapsible and contain small spaces
where bed bugs can hide. The cots that were at St. Joes at the beginning of the project were of this type and the taking down/putting up process was causing damage to the cots. The second issue that arose was that the canvas part of the cot was not removable/washable. This is a necessity due to the bed beg prone environment.
A previous design was developed by a Design for a Sustainable World team. This design followed the original intent of stackable cots, but was not tested. This project used this design as a starting point, but the customer’s needs differed from the previous project’s goals.
Design Process / Methodology
In order to fully obtain an understanding for what the needs are, a functional decomposition was created. The functional decomposition goes through all of the steps that are needed in order to effectively deal with the shelter issues. This specific functional decomposition states our three main needs: provide sleeping surface for the guests, reduce the storage space of the sleeping surfaces, and reduce the amount of bedbug rates. These main needs were then broken down even further into categories of what these need’s needs are. Overall, these needs are broken down in such a way so that all of the needs that are needed to alleviate these shelter issues are addressed.
After the functional decomposition was developed, the next step was to take these specific issues and begin researching. The team broke down these issues into the main categories: storage possibilities, bedbugs, and ergonomics. Originally the team thought the way to approach the storage issue was to allow these cots to stack. When these cots were stacked they would double as a bench. The bedbugs were approached through various questions about how these cots were to be cleaned, since bedbugs are difficult to get rid of. The ergonomic research was done in order to create a cot that would be able to withstand a male in the 95 th percentile. Through this research, various concepts were then developed that met all of these needs.
With this list of needs, the team got together and began to discuss a variety of ideas. These lists of ideas were then broken down even further into four main categories: stackable frame, folding frame, transforming frame, and air mattress. Each of these bed types were then scored against a set of criteria which were all determined by the customer. Through a weighted calculation it was found that the stackable frame was the best solution for the needs of the shelter, second to the air mattress. However, about a month into the development of this process, it was discovered that the cots were no longer required to stack but rather hang from the ceiling via pulleys. As a result, the team was set back by approximately two weeks in which new designs had to be thought of to adhere to these changes.
Two specific designs were then developed that were made to be stackable: “The W” and “The Sled”. A Finite Element Analysis was then performed on these sleds via SolidWorks and setting the material to be galvanized steel. The cots were modeled as square members due to simplicity and were tested having a distributed load of 250 lbs across the members. It was found that “The W” was not as structurally sound as that of “The Sled” due to the lack of reinforcing members. “The
Sled” was found to have yield strength of approximately 30,000 psi with the highest amount of stress the cot being able to withstand about 900 psi. These numbers confirmed that the cot was definitely able to withstand a person in the 95 th
percentile and that these cots are actually overdesigned for their purpose. The building process was simple, conduit was cut and welded together. Then
the polyester material was chosen as the fabric to be slept on. A steel bar was placed along the edges of the fabric and a spray adhesive was applied. Copper reinforcer grommet rings were then added as the attachment points for the straps.
The cot was tested under a break test in which a certain amount of weight was placed upon the frames and then was to be analyzed. This was testing using pallets to distribute the load - 50lb bags were added until an anticipated break. When the weight exceeded 1600lbs it was deemed safe and strong enough for the constraints. Also, with the weight on it an individual climbed on the stacked bags and shifted their weight back and forth. Although the frame gave a little it showed no signs of permanent stress or break.
When the 1600lb weight was placed on the frame in a point load fashion, the frame did bend until the pallet reached the middle leg but still there was no fatal damage. The equivalence of this scenario would be four 400lb point loads on the weak points of the frame, there is virtually no case of this happening- even if four 400lb individuals sat on the sides of the frame the load would be more distributed.
Results & Discussion
Final ProductThe final product successfully met most of the specifications. All of the
testing was successful. The cot is able to support a large-sized adult and provide a reasonably comfortable sleeping surface. The cot is easy to clean and does a good job of remaining bed bug free. It is more than durable enough to last through regular use.
The cots were delivered to St. Joseph’s House, where they were put into use immediately. Feedback was received from actual use, and a few small design revisions were implemented.
Many issues arose due to the group dynamics. Like mentioned below, communication added to that. Many of the ideas that were presented were highly disagreed upon and actions were taken without group consent. This caused immediate frustrations within the group; however, with the help from our guide and some communication with the customer, the issues were resolved.
Midway through the project, we were tasked with changing the specification of a stackable cot to one that could be hung. This put behind by two to three weeks of work. Although we would have preferred to know this earlier on, due to the nature of the project and its simplicity, we were still able to pull through and bring the customer what they wanted.
In the two-quarter time period that the group had to work on this project, we faced many difficulties. The positive outcome is that we have learned that communication is key. Many of the issues that we had were related to poor communication. In working with other disciplines, we also recognized that not
everyone thinks the same. It takes time and patience to relay information to those who do not think like you.
Conclusions & Recommendations
The design project can overall be considered a success. All needs were met and the client was satisfied. This project had a few unique turns both despite, and in spite of, being so simple and straightforward. Due to its simplicity, a working design and prototype was created very early in the project, much sooner than usual. This in turn made everything else happen much sooner, such as testing. This enabled the team to receive feedback from the products actual use, and make design alterations as needed. Unfortunately, this also created a vacuum of work needed, which is part of what to the group tensions discussed above.
The main recommendation for future work, for a project like this, is to either increase its complexity or decrease the number of engineers assigned to it. This should alleviate most of the issues face during this project.
Acknowledgements
The design team would like to thank Sarah Brownell, Adam Uzelac and John Kaemmerlen for their support and guidance in this project.
