CONSTRUCTION WORKSHOP ! MATERIALS! !
! This material is plywood which is thin sheets of timber glued together to create a sheet. Plywood is know to be weak in compression and stronger in tension. This material is also flimsy in deflection, meaning it twists and turns easily. When using this material, it is only really useful when pressed between of materials so that it is bound in its position.! !
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This material is a dressed timber which is strong in tension and compression, however has a weakness in bending due to its fibrous makeup. The grain runs horizontally down the material and weakness are evident where the grain runs off the piece of timber.! !
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Here is a pine that isn't dressed or finished. This type of material is commonly used for things like studs or noggins. You can tell it isn’t dressed by feeling the roughness of the material and noticing the knots in the wood. When using this timber you have to consider where to place the knots as they are the obvious imperfections in the material.!
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! THE OBJECTIVE!
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To create a structure out of the given material, no more than 400mm high, that spans a minimum of 1m and has to structural capacity to carry the greatest point load at the centre of the structure.!
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OUR DESIGN!
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My group was given two pieces of plywood and two pieces of the dressed wood. After much deliberation and uncertainty, we decided to create a design which sandwiched two pieces of the plywood which we had cut length ways between the other 2 pieces of timber. We had left over wood which was nailed on the top and bottom of the structure. Everything was nailed together with nails in pre drilled holes.!
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THE OUTCOME
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As can be seem above, our design was a bust. It took just under 300 kilograms of weight, around half that of the group with the strongest design which managed to withstand slightly under 600 kilograms. When doing the destruction test we were able to noticed a few things that were wrong with out design that we could have fixed had we known about them earlier. One thing was the extra pieces of plywood that we attached. They provided absolutely no structural value and the top piece began to warp in compression as soon as the structure began to bend under the weight. Another flaw, and ultimately the one that made us come unstuck, was the massive nails in the centre of the structure all place incrementally. It was here that the structure buckled and cracked under pressure.
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COMPARISON TO OTHER STRUCTURES
! The structure pictured in the middle is the one that was able to take almost 600 kilograms of weight which is close to 7 average adults! Their failure ended up being an imperfection in one of their supports, a knot that just gave way under the pressure. The principle behind their design was that like a basic truss, which looking back now would have been a smart decision to make because this design has been proven to be able to span long enough distances and take heavy loads. They were also able to take a deflection of 57.
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! CONCLUSION A few things that I have taken out of this construction workshop are:
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Take a few more minutes to think about the design and its capacity to bear a load first.
! Plywood is weak unless stuck between other materials. ! -
Knots and other flaws in the wood are where the pressure is going to explode through, so selection of material is very important. Also, the placement of these flaws are also important.
! A truss is a very sturdy and strong design. ! Adding nails while weaken the structural integrity of the timber. ! These are some things that I would think about before doing this kind of workshop again. ! ! ! ! -
A FEW GLOSSARY TERMS‌. Eastern Saw- is skinnier and cuts the timber more on the pull Western Saw- has a thicker top and cuts the timber more on the push Pistol Grip- a grip where you're index finger points down the saw so that the bones in your wrist are loosened up which makes sawing easier.
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