Workshop

Construc)on  workshop The task of the workshop is to build a beam that can bear most point load using materials provided. The load will be applied directly on top in the middle of our structure.

For our group, we were provided two 1200mm x 35mm x 35mm pine wood and two pieces of 3.5mm x 90mm x 1200mm plywood.

The plywood is strong vertically but because it only 3.5mm thick, it is easily broke horizontally. Pine wood on the other hand is much stronger than ply wood.

Both plywood and pine wood have many defaults which create weak points in the structure. Nails and sewers also create weak points because they compress timber, therefore change their original structure.

It can be seen later during the tests, most fractures happens at exactly where there is a nail or sewer.

The left picture show how we tried to avoid make the weak point weaker that we decided not to nail at defaulted area because we believe the nail will create a fracture along the texture of the default.

Construc)on  workshop Our design was using pine wood as beams and columns where plywood was used as reinforcement on both side. The idea that plywood is stronger putting it vertically and the thickness of the structure decide how strong it can be eventually form this structure. However in this case, we ignored the fact that by using columns to support the upper beam, the load was more concentrate under the columns, especially middle two columns, although the columns on each sides also take loads. As the second picture shows, the fracture happened exactly under the column. Also, as the structure bending, tension force is applied at the bottom column, so in most cases, bottom beam breaks ďŹ rst and followed by the lower part of the top column.

The sketches shows to main reasons why most structures we built started to fail from the bottom column and usually under the columns.

However, nail is also a reason if there is any.

Construc)on workshop Picture on the left shows how plywood react under the force, the bottom is under tension while the top part is under compression. Because of the nature of plywood (easy to bend when force is applied), we put more nails on top than bottom (which is under tension therefore is relatively stable).

We wanted it to be attached to the beam as strong as possible, so we chose the nails with bigger heads but have shorter body which will not go through the beams. As the load increase, plywood warped and detached from the main structure, along with miner fractures on bottom beam. And then the bottom of the plywood started to crack under tension. This is the beginning of total failure where the structure already started to have fractures in order to maintain its equilibrium.

Final test result of this structure was 315 kilo with deflec)on 73mm. The result shows this structure is not designed to bear load by bending.

Construc)on workshop

Group three:

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Structural system - Two beams with columns in between and one plywood is attached on one side of the structure. Connected by nails.

Analysis: - As point load is applied, most columns were only taking very few load while the column under the point load took most of the loads, which caused the fractures we can observe in picture 3.

- The bottom beam is under tension and cracked with the weakness created by nails.

- Compared to our design, the usage of vertically applied nails created bigger weak point because it crack the timber along its texture. Under tension, it is easier to crack further than apply the nails horizontally.

- however, because of the number of column used, it bear more loads than our design.

Load applied before total failure: 356 kilo Deflec)on: 66mm

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Construc)on workshop

Group two: Structural system: - Two beams connected by horizontally applied plywood and pine wood on top of plywood in order to hold the structure together and transfer load. No column in between.

Analysis: - As point load is applied, plywood detached from the beam due to lack of fix point along plywood. The bending force detached the nails from beam. However, this also decrease the number of weak point along the beam.

- The lower part of the beam started to crack under tension.

- Nails for attach top bracing created weak point at the beam and eventually cause the total failure.

Load applied before total failure: 358 kilo Deflec)on: 57mm

Construc)on workshop-­‐ reflec)on

All four structures are alike in terms of structural system that we all used pine wood as beams and plywood for load transferring. We all have considered the thickness of the structure influenced the strength of the structure, however, we all failed to put the influence of nails into consideration. As texted in other workshop group, I beam is ideal as it is highstrength and long-span. The flanges resist bending and tension while web transmitting forces.

Another ideal structure is simply put all materials one on top of another to avoid any nails or sewers which minimize weak points and avoid breaking consistent grain.

Also, the columns between beams increase the thickness of the structure, however, they also increase the tension force applied on the bottom pine wood and they decrease the load transmitted toward the end of this structure, putting more loads in the middle and eventually cause failure.