Week 02 journal

|W02| STUDIO FRAME

BUILD A STABLE STRUCTURE LONG ENOUGH TO BRIDGE (SPAN) ACROSS A 1500MM GAP

GLOSSARY

Structural Joint: is a junc4on where building elements meet without applying a sta4c load from one element to another1

Column: Columns are rigid, rela4vely slender structural members designed primarily to support axial compressive loads applied to the ends of the members2

Tension: When an external load pulls on a structured member, the par4cles composing the material move apart and undergo tension3

Frame: A rigid structure formed of rela4vely slender pieces, joined so as to surround sizable empty spaces or nonstructural panels, and generally used as a major support in building or engineering works, machinery, furniture, etc.4

Bracing: a system of braces used to strengthen or support5

Span: the distance between two supports of a structure 6

1 hOp://en.wikipedia.org/wiki/Joint_(building) 2(CHING, 2014, p. 2.13) 3(Elena Cox, 2003-­‐2014) 4hOp://dic4onary.reference.com/browse/frame 5hOp://www.thefreedic4onary.com/bracing 6hOp://dic4onary.reference.com/browse/span

In this ac4vity the main aim was to create a structure which span across a 1500mm gap with the tables as support bases. In this ac4vity the main material which was given to us was a 600mm*100mm*2mm Balsa wood. This was from the beginning a v e r y l i m i t e d t a s k w h i c h s e t constraints upon how we could design the bridge. Mainly because the given balsa wood length was too short for the span, and so the first significant elements which we had to complete was using the balsa wood to extend its length however s4ll managing to keep enough material to strengthen our bridge.

Construc4on System

The structure of the bases was achieved through trial and error un4l we seOled upon using the following design. S4cky tape and cra] knife was essen4al in the construc4on process to form the rigid joints between individual members.

The image below demonstrates posi4on 1.

The bridge is places along its thinner surface, this allows the construc4on to work as a truss system diver4ng the load distribu4on evenly. This posi4on has more of a capacity to resist strength.

The below image demonstrates the diagram which is drawn as posi4on 2.

The bridge is laying on its flat surface, we discovered that this posi4on is weak. This is mainly because the pressure on the diagonals aren't as sturdy, this caused bending.

hOp://www.ic.sunysb.edu/Class/phy141md/lib/exe/fetch.php? media=phy141:lectures:trussbridge.png

Compression and tension forces divert the force and pressure downwards.

The load path is shown below, demonstra4ng the strength of the bridge due to the truss system.

High compressive strength

We ini4ally used uhu-­‐glu to s4ck the pieces together however it was not holding, therefore we thought of using pins, however this would not work. We then chose to use s4cky tape to bind the thin pieces to the two long balsa pieces which would form as the horizontal distance along a 1500mm distance.

One of the main aspects which was a downfall with our bridge construc4on was the sloppy use of s4cky tape and the uncontrolled binding of the pieces together. This not only demonstrated the bridges construc4on faults, but also proved to be a factor which caused the instability and lack of strength in certain parts of the bridge, furthermore causing bending. Other teams used a more complex truss system, and did not have faults with material therefore was able to perform efficiently with their construc4on system of the bridge. Their load paths demonstrated the strength through design.

One of the main ideas explored in this ac4vity other then compression, tension, load paths and truss system was bending as a part of inflec4on and deflec4on. It is stated in Ching that “the nonconcurrent paOern of forces subjects a beam to bending and deflec4on, which must be resisted by the internal strength of the material” (CHING, 2014, p. 2.14). Even though this theory is directed towards beams and columns, it is suppor4ve for this bridge ac4vity. Hence, the bending moment tends to cause part of a structure to rotate or bend, evident within our structure, the weight causes the bridge to bend, depic4ng its faults within its construc4on system to withstand load.

(CHING, 2014, p. 2.14)

The material was also another factor which led to the construc4on being weak. Balsa wood is very thin and is easily bent. Due to this and the limited materials provided, the bridge structure which we created depended upon thin pieces of balsa wood, not just for the truss system, however to extend the length to fulfill the 1500mm requirement. Thus, the efficiency of the material was a significant factor which had a major impact on our bridge construc4on.