Week two logbook

Structural joint:

Fixed joint

Pin joint

Roller joints

Week two in tute ac8vity was using a 10*60 cm long balsa board. This material is soE (easy to cut) and fragile.

Our first idea was built a bridge that has two layers. The ini8al thought was the beam under the main bridge will provide extra strength to the bridge therefore the bridge can bear more load. However, aEer calcula8on, the result shows there’s not enough material. And also because of the 8me limit, we give up our first idea.

The board was cut into 5cm wide s8cks, and connec8ng them together. These s8cks were then proven to be to thin to even hold their own weight. Tap was using for enhancing the strength of s8cks.

The second idea was to get rid of the extra layer and lengthening the bridge for aPach on the table. The thickness of the frame also reduced. At this point, group members thought there will be alterna8ve way to enhance the strength of the frame and the material saved can be used for reinforcement in the middle.

Pins were also used to enhance the strength of the frame, like reinforced bar in concrete beam. In this case, pins were put on four sides and tap were used to fix pins. Unfortunately, pins are too heavy compared to the balsa frame. therefore, the structure bended without any load.

Also, the group member believed the bending is also because of the length of the structure as well as the mu8-­‐ connec8ng points along the structure.

Therefore, the structure was aPached to table by pins, tap and a founda8on. The original idea was directly aPach the structure to table, which believed to be more stable since more connec8ng points means easier to get loose. But the structure itself can hardly be aPached to table without damage it. Experiments shows under our circumstances, the way this structure aPached has very small effect.

The bending is because of the self weight of this structure.

Also because of flexibility of connec8ng points.

This is the first bridge being examined during the workshop. The structure of this bridge is rela8vely strong because the frame is thick and by puYng is ver8cally, it can bear more loads. The way they connected the frame is good for transferring the load from the structure to the table.

The reason they aPached the bridge to the table is illustrated in the sketch leE. There has to have forces at two end holding the structure from bending so that load can be bePer transferred to the table.

However, there is one designing fail in this case. As the loads increasing, the bridge started to turn on leE side and eventually rollover.

It can be deducted that this might because of the uneven thickness of the bridge, as they bended at different level. However, there may have other reasons.

There are two ways connec8ng two beams of the bridge. However the differences is hard to compare since the two bridges are different in many ways including bonding materials, thickness of the frame and even length.

This picture clearly shows the difference of beam thickness. Thin beam bend when the load is apply but thick one remain straight.

Like beam in buildings, if the former has a reinforced bar at the boPom of the beam, it will be stronger.

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As the beam in this bridge is very thick, it can bear more load. However, there’s a designing problem that it is very hard to put load on it as it has only one beam. Also when the load is applied, the bridge bend horizontally to one side.

For all these structures, the kind of force applied on balsa s8cks within two parallel beams is tension as they are holding two beams from going apart. Similarly, tension is also applied on the beam.

When there is no reinforcement in between, the two beams naturally going away from each other when there is a load applied.

It becomes unstable.

This might because the load cannot be transferred to the end of the beam very well, so it bend to the side which the middle connec8ng beam is.

glossary Structural joint: the way structural elements connected to each other.

Three ways: BuP joints, overlapping joints and molded or shaped joints.

Also can be categorized into: fixed, roller and pin joints (Ching, 2008, p.2.30).

Column: rigid, rela8vely slender structural members designed primarily to support axial compressive loads applied to the ends of the members (Ching, 2008, p.2.13).

Bracing: the reinforcement in the picture on the right.

Span: the extent of space between wo supports of a structure. Also, the structure is supported (Ching, 2008, p.2.07). A bridge is a span.

Frame: in a physical construc8on, frame is the structural system which support other components in the system. The bridge we built in the workshop is a frame.

A frame of a building (Timber Frame Homes & More, 2014).

Reference list:

Ching, F. D. (2014). Building construc.on illustrated. John Wiley & Sons.

Timber Frame Homes & More. (August,2014). Retrieved from: hPps://8mberframehome.wordpress.com/tag/hammer-­‐beam/