Designs ,Prototypes, and Testing of the Truss-Tie
PROOF OF CONCEPT: PROTOTYPES & ITERATIONS
Each of the three strap sections of the zip-tie is arranged to bind the corresponding structural member for building the truss. The diagonal strap of the zip-tie is positioned to form an angle of approximately 45 degrees with the horizontal member or the vertical member.
However, the lengths of the members for the frame of the emergency shelter could not be standardized because they were debris from the damaged buildings or trees. Therefore, the angle of the diagonal section of the truss for the frame also had to vary. For instance, sometimes the users needed to form a 30 to 60 degree angle for the diagonal section with respect to the horizontal.
The second concept was that the diagonal strap of the zip-tie could swivel so that it could support any angle of the diagonal section of truss.
The joint that connects the diagonal strap with body of the zip-tie was not sufficiently strong, and components separated even when users applied only moderate force. But, it did not influence the users’ control of tying, while they were building the diagonal section of the truss. This was because, even though the joint was broken, this always happened after the diagonal strap was locked by the ratchet inside of head of the zip-tie
The approach of the third concept was to reinforce the area (a) where the two zip tie heads intersected in order not to avoid failure. However, this proposal was considered inferior due to ergonomic reasons to the second proposal where users could tie the fastener more conveniently due to the direction of the sockets and straps. In addition, the third proposal incorporated the use of luminous additive to the plastic, anticipating that it would make it easier to construct shelters at night.
Typical zip ties are built by stamping or injection mold. This is an expensive process for a prototype. In order to test the second proposal at low cost, the two adapters which could fasten normal single cable ties were designed and fabricated by 3D printer.
The two adapters looked very similar to each other, but the directions of zip tie straps of the adapters were opposite, in order to accommodate left-handed and right handed users.
Due to the poor quality of the 3d printing material, the adapters fabricated were not sufficiently durable to withstand the pressure that each strap applied, so the test could not properly test.
Therefore, an adapter was made of aluminum by Computer Numeric Control (CNC) milling machine.
The result of the test for the second proposal using the aluminum adapter did not meet the anticipated expectation, because the frame created was easily distorted and looked like a confusing jumble.
In the way of ‘X-shaped tying type’, the users could bind the two members easily and securely because the force point was on the center of the intersecting point of the two members.
Therefore, a fourth proposal was formulated in order to tie the members more securely and without the prior distortions. The established regular zip-ties also can build up truss by the X-shaped tying. However, using this newly designed zip-tie, it was much more convenient for the user to control the members and the zip-tie straps, because it integrated the three normal zip-tie into one entity. This way, the user could hold the members and tie the zip-ties at the same time without the need of an assistant.
In addition, the most importantly, using the regular zip-tie could not be applicable to create the diagonal section of the truss, because it is structurally impossible to provide a fastener to connect from the strap for diagonal section of truss to opposite side.
In order to avoid interference of the straps, the body of the zip-tie consisted of three concentric layers—one for each strap. However, these modifications made the fastener too large axially, and weakened it structurally.
A sixth concept was generated in order to reduce the axial dimension of the fastener and increase its stability. If the two straps interfered and jammed, it seemed that there was sufficient space for the user to control the two straps of the zip-tie at the intersecting point inside of the fastener (A). However, the area at the bottom of the fastener was too thin and fragile (B). Making that thicker would cause excessive thickness (axially). Therefore, these conflicting issues were not fully resolved with this design iteration.
In addition to all the previous issues, a shortcoming involving all designs was observed. The shortcoming is as follows: The tail end of the zip-tie was inevitably unutilized and concern of material waste was raised.
A seventh concept was generated in the hope that it would resolve the prior ongoing issues of jamming, structural weakness, and excessive axial length, as well as the shortcoming of unutilized tail end of the zip tie. In this design iteration, the rotatable part of zip-tie could be detachable and the detached part could be used for extending the length of the straps (Right), while following figure explains how the other issues were addressed.
The jamming, excess axial length, and structural weakness issues were addressed as follows: In this prototype, the sockets were arranged upside down to slide without interference.
Each strap of the zip-tie was marked with embossed numbers and dots which indicated the binding order for the truss. The embossed numbers and dots were supposed to allow users who have a poor sight to assess the number of dots by touching.
Second Prototype and Test
The prototype adapter was too weak to withstand the forces necessary to support a structure. Therefore, it was redesigned to be stronger by increasing thicknesses of various locations, while the overall concepts remained unchanged.
For more precise testing, the adapter for the prototype was redesigned, and now, some of the components were clamped together by bolts and nuts. Additionally, the detachable part was not fabricated since single cable ties can be facilitated in case of expanding the ties. The test for the prototype showed that the seventh idea worked easily, simply , and securely.
Tests for building Emergency Shelters and a Transitional shelter for Truss-Tie (Trusty-shelter)
The shelter construction test was executed by using prototypes based on the eighth proposal. The time duration for constructing shelter elements was as follows for the emergency shelter 23 minutes, and for the transitional shelter 25 minutes. In the case of transitional shelter, the time required for the builders to apply the tarp cover on the frame was not included, because the design process is not completed yet. The response from the test building group was positive with respect to the transitional shelter type because using the Truss-Tie was simple, fast and effective. However, when builders construct the emergency shelter, Truss-ties on occasion slid down if the surface of members did not have sufficient surface roughness and if heavy roof covering material was used. This issue had to be resolved because the fastener needed to reliably bind using the broadest range of wood and structural members found on the natural disaster site.