Name: Holly Saunders
Student No: 583535
Fig 1. (Above) Our completed model
Tutorial: 18
Our group model was put together in answer to a required truss roof for the Victorian markets. It spanned the entire length of the target area. It focused a lot of weight in the center that did not have support and I feel that for this reason it was largely unsuccessful. It failed to maintain support of its own weight let alone added pressures. When pressure tests were applied beams continually popped out of place. The true strength in this design lay at the top of the structure. If we had made a system that incorporated a cage-like truss system it would have supported a lot more weight, more efficiently. The overall design of this project started with a corner-piece which supported itself. (See Fig. 2 & 3). We then applied extra support to the structure (See Fig. 4 & 5) to place the pressure on 5 central points, being the center and four corners and communicated through beams across the structure. Fig 6 is the basic frame of our overall structure, I believe this is the part that is mostly unsuccessful in its design.
Fig 2. (Above Left) stabilizing the main beam Fig 3. (Above Right) developing the angular beams
Starting with a single length of spaghetti we decided to support the strand by using a smaller truss support at the base. An image showing the support for the main pillars is in Fig. 2 . Next we decided to reinforce the main pillars using a small addition which sat underneath and spanned the diagonal support along the base of the roof and the extended main beam which would later serve to additionally support the centerpiece.
Fig 4. (Above Left) constructing the central support base. Fig 5. (Above Center) reinforcing the central beams. Fig 6. (Above Right) the basic frame of our structure.
Also, if we had used this concept entirely the structure would have supported itself over vast distances as the forces would have cancelled each other out. Instead what we ended up with was a weak base that bucked when the cage was subjected to pressure tests.
Fig 7. (Above) The implementation of the truss cage.
The centerpiece was based around a twisted quadrilateral form that tied in towards the center then back out again to form the base of the final portion of the roofing. This is seen in Fig. 7. If it had been measured correctly, our roof would have withstood a decent amount of pressure. A horizontal cage of triangular beams sat high and low to meet at a central point.
down the length of the supporting beams. Where this compares between our triangular base system and theirs is the dynamic interrelationship they have incorporated with all points in their structure.
Fig 9. (Above) Project by an alternate group. Photo taken by Holly Saunders. Fig 8. (Above) Project by Michael Mack + Group. Photo also taken by Michael.
Where this compares with other groups is that in Fig 8, taken by Michael Mack, we see triangular support throughout the model which relies heavily on its own structure to carry its length and weight. It could also easily incorporate the weight of a roof which would transfer
Alternatively in Fig. 9 above, a hexagonal base support distributes the load of a point to several evenly placed ones. This minimalizes the downward impact on set points. This is successful in its ability to manage more downward force. It didn’t make use of the structural supports as well as it might have though. The bulk of the hexagonal bases sits in the open air without support.
It is not as easy to implement a cantilever or columns or brickwork around a truss that is not designed to hold them up. The materials differed in the way that the elephant enclosure relied on compression and wasn’t nearly as susceptible to tensile forces. If I had been trying to support an elephant enclosure with a truss system I would not use a material so inclined to buckle. Building a ceiling or roof means that you have to support the weight of the overlaying materials and any potential weight on top of those. Our cantilever sheltering for the elephant withstood an enormous amount of downward force; however a truss system underneath it to support extensions would have enabled the elephant to be housed more comfortably. Truss systems are designed to extend further and rely on the weight of the materials in a consistent tensile and compressive unity. The bricks were simply compressed and their weight along with their inability to form complex shapes meant severe limitations to the overhanging shelter which was deemed insufficient. Our truss system is much the same. It incorporates height over width and length which are the key strengths in a truss system. Fig 10. (Left) Stress and Strain on a cross section of our design. Fig 11. (Right) Steel light-weight trusses by Kecuk.com
Ultimately, our design did not answer the need for an open space. What would have been better is using the base for the truss in shorter lengths measured out equally and spanned across the entire length of the (paper) room without requiring additional support. We also could have measured our pieces and been more efficient with our resources. Over all there was a good concept in our design. Supporting the beams and allowing the weight to be distributed not just on one pressure point but across several meant that the structure was able to convert a decent amount of stress and strain before buckling. There were a few reasons for the failure of this design, the first being that we did not measure out our beams to maintain the integrity of their length. The second is that we put little planning and instead considered propping to support. Another reason that this structure failed is that we were using long pieces to carry more weight than what they were designed for and so a buckling effect occurred whenever pressure was applied. This meant that the structure would snap and break when it came to placing any load or force on it. This implies that it would not have supported further weight such as roofing or insulation. The image in Fig 11. is a more successful way of implementing the truss system I was trying to construct in my model. It is purely functional and efficient. This will most likely be implemented in future designs.
o Photos from figures 1-7 & 10 were all taken of my group work on my camera. o Photo in Figure 8 was taken by Michael Mack of his own project. o Photo in Figure 9 was taken my me of an alternate group’s work who has not been made known to me. o Picture in Figure 11 is from kecuk.com 2011; http://kecuk.com/2011/06/19/designlightweight-steel-roof-truss.html; retrieved 04/04/2012