Difference between revisions of "Mystery Architecture"
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Revision as of 01:22, 25 September 2019
Mystery Architecture is a Division B event that is set to return for the 2018 season. It was previously run as a trial event in New York during the 2013 season, and last run nationally in 2008. In this event, teams are given materials such as straws, cups, string, tape, wooden dowels, and other materials to build a structure. Structures that must be built have included cantilevers, arches, towers, and bridges. Most of the structures are judged on height/distance spanned and are required to hold a specified amount.
The key to this event is practice. One suggested way to practice is to compile a list of structures to build, and ask teammates or a coach to provide materials to construct these structures. If three or more students are involved with the event, they can build the same structure with the same materials separately, in order to observe the differences and see which strategies work better than others.
More keys to success in this event:
- Knowledge of building materials and how they can be used
- Experience in building and constructing structures out of those materials
- General knowledge of truss systems and how they work, etc.
- KISS: "Keep It Simple, Stupid". KISS is always a good thing to keep in mind for engineering events. The simplest ideas work the best and usually involve a combo of triangles and arches. Calculation of loads in the structures isn't necessary but can be useful. Knowledge of the limitations of your structures and how to fix them is key.
In short, the efficiency of a structure is equal to the weight supported divided by the weight of the structure. A large efficiency is desired, but the highest possible efficiency varies. At past national competitions, the top efficiency for towers was around 5500.
Truss Systems and Supporting Shapes
- Non-tied Arches are arches that exert pressure outward and downward. Examples include Roman arches in buildings and bridges which contain an arch in the substructure.
- Tied arches are a crescent shape with a tension member connecting each end of the arch to prevent outward pressure at the ends. This makes the arch self-contained and cancels horizontal stresses.
- Trussed Arch are tied arches with a network of trusses, usually triangular in nature. However, the arch can also only have vertical members to hold up a flat deck. Trussed arches are a very efficient way to build a bridge.
Triangles are very strong shapes since they spread weight evenly throughout the shape. However, like all truss systems, they are only useful when used in proper context. For the strongest trusses, equilateral triangles are ideal, but the trusses must be in harmony with the structure, meaning all the sides of the repeating triangles must be attached to the main structure. They must also be able to accommodate changes of distance between the beams. In general, the closer a triangle is to being equilateral, the stronger the structure will be.
X shapes can be found on many bridges and structures. Most of the time, they are used for tension purposes, to hold the corners of a box in so they stay square and do not collapse. While X shapes are great for metal structures, however, they are not always appropriate for wood or straw structures. They are good for keeping two parallel beams from separating, but it is important to have a beam that restricts the movement of these parallel beams. X shapes are not substitutes for structural members but are reinforcing members.
When building towers in Mystery Architecture, X shapes are very helpful, but only if they are needed (like for large mass supporting structures). The most important thing about X shapes is that they must, like almost all trusses, must be inside the beams or boxes they are trying to support to be most effective. Thus, they are much less useful in bridges than other structures.
When building towers in Mystery Architecture, it is imperative to have a larger base than peak, and the beams connecting corners must be straight and able to resist bending.
Tension and Compression
When building a structure, it is vital to consider tension and compression. This applies to all structures in this event, as well as other building events that involve similar structural members.
Tension members are beams which experience a "pulling apart" force. Tension member examples are the X shapes in a high school stadium, the wires holding up the road deck in a suspension bridge and the members at the bottom of a common truss. Metal is very strong in tension, but wood is much weaker.
Compression members are beams which experience a "pushing together" force. To help accomplish the task of supporting other members and prevent structural collapse, common designs for compression members include chair legs, straws, H beams in skyscrapers, and the "L shape" which is used in many balsa constructions. Wood is relatively strong in compression.
An easy way to think of these forces is by replacing the member with a piece of string. A tension member theoretically could be replaced with string as they are designed to keep members from separating. However, a compression member could not be replaced with string, as it would be completely unable to prevent the members from collapsing on themselves.