Mystery Architecture

Mystery Architecture is a trial event being run in New York's Division B competition for the 2013 season. In this event, teams are given a building task and materials such as straws, cups, string, tape, wooden dowels and other materials to build their structure. Structures that must be built have included cantilevers, towers, bridges, and sometimes others. Most of the structures are judged on height/distance spanned and/or required the structure to hold a specified amount.

Strategy
The key to this event is practicing a lot. Ask people on your team to make a list of structures to build and then give you materials similar to the list above and then construct it. It might even be best if you have three or some other engineering inclined students to build the same structure with the same materials separately. This is so you can observe the differences and what works and what doesn't.

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 that is a combo of triangles and arches. Remember, you don't have an engineering degree. Calculation of various aspects of your structures isn't necessarily needed but is useful. Knowledge of the limitations of your structures and how to fix them is key.

Arches
Tied-arches are in a crescent shape. There is a tension member that goes inside the arch connecting each end of the arch to prevent outward pressure at the ends. This can make the arch self contained and cancels horizontal stresses.

Non-tied Arches are arches that exert pressure outward and downward. Examples, Roman arches in buildings, bridges with the arch in the substructure.

Trussed Arch are tied arches with a network of trusses, usually triangular in nature. However it can have just vertical members that hold up a road deck. Very efficient way to build a bridge.

Triangles
Triangles Triangles are very strong shapes, since they spread weight in a even way (they are not always the strongest shapes!). However, like all truss systems the are only useful when used in proper context. They are the most important part of truss but when used for other purposes are almost worthless. For the strongest truss, you want to use an equilateral triangle. However, the trusses must be in harmony with the structure, meaning all the sides of the repeating triangles must be glued to the main structure (beams that the trusses are holding together). They must also be able to accommodate changes of distance between the beams. If you can't use an equilateral, the closer you can get your triangle to be one, the closer the strength will be compared to the equilateral.

X's
X's can be found on many bridges and structures. Your high school stadium probably has them between posts that hold up the seats, they are in skyscrapers, etc. Most of the time they are used for tension purposes, to hold the corners of a box in so they stay square and don't go out. X's are great for metal structures and are practically a staple. However, they are not always appropriate for wood, straw, or whatever structures. They are good for keeping two parallel beams from separating but it is important to have a beam also connect the parallel beams in a square pattern or at least at both ends. X's are not substitutes but are reinforcement for what is there.

They are not great for bridges because they are heavy and not as efficient as triangles, however are good for towers unless you are trying to go super-light (below 8 grams). When building towers in Mystery Arch, they are very helpful, but only if they are needed (like for large mass supporting structures). The most important thing about Xes is that they must, like almost all trusses, must be inside the beams or boxes they are trying to support to be most effective.

Pyramid Method
When building towers, in M. Arch (and Towers), it is imperative to have a bigger base than you have top, and the beams connecting corners to corners must be straight and resist bending.

Difference Between a Tension Truss Beam and a Compression Truss Beam
It is important to think about tension and compression when building a structure. In Boomilever, Bridge and some similar projects in mystery arch, this is more important. In tower, it isn't really because the simple tower is almost all compression, the only thing to think about is the compression/tension ratios your tower and its trusses have as the near vertical members (poles) linking the top corners with the bottom corners spread out as you get lower in the tower. In this case, the structure gains stability at the expense of more wood needed to span the gaps between the poles as they get further and further apart.

Tension members are beams that theoretically could be replaced with string as they are designed to keep members from separating. Tension member examples are the X's in your high school's stadium, the wires holding up the road deck in a suspension bridge, and most importantly, trusses that start from the middle of a bridge and go up and out

Compression members are beams you would rather replace with steel if you had the opportunity as they are basically similar to chair legs. Compression members resist against the Gravity that pulls you toward the ground. To help accomplish the task of supporting something, common designs for compression members (which are the legs of your chair) include chair legs, straws, H beams (in skyscrapers) as well as the "L" which is used in lost of balsa constructions. When you think about it, compression members are some of the most simple things to make, for instance, if you want to sit on something, just pull up a log and sit on it and it is a compression member. However, you can't use logs for your M. Arch projects and for your towers, bridges, and boomilevers.

Unfortunately, this is where it gets hairy. Efficiency = Weight Supported / Weight of the structure. You want to have the largest number possible. So... what is possible? That is why these events were made, the top ratio of eff for towers at national competition was around 5500:1 or about 550000%. The following are tips to increase efficiency in the three balsa events and can be applied to M. Arch.