Constructing Journal Week 6Structural Concepts Part 2

We initially used tracing paper to draw over the map the main structural concepts we were going to include so that we did not confuse ourselves when we were building as we only had a little amount of time.

This balsa wood represents the concrete columns which were poured in situ that both support a section of the root and are there for aesthetic design. The horizontal pieces of wood represent the steel ‘grate’ like pieces that are there for aesthetic purposes.

We used thin card to build our model (Theology building) and balsa wood, with sticky tape to stick it together due to the lack of time. Initially we had trouble reading the plans and figuring out what the sizes of each wall was, but we managed after a little while of thinking through what we were doing. As can be seen in the image above, there are columns which help hold the structure up, and also transfer the compressive forces of the roof down into the concrete footings. Some walls are not shown as we did not have enough time to complete them.

The circled section on the im-age above shows the partially cantilevered roof of the Theolo-gy Building. A cantilever means it is only fixed on one side of the roof and is overhanging the ceiling with no structural supports underneath it. Things that are cantilevered generally need to have reinforcement in them in the top because that is where the structure is in tension as the force of gravity acts on the unfixed end of the cantile-ver.

Timber Workshop

Beam Making

In the timber workshop my group was given four pieces of wood, two of which were thin plywood and the others which were a simple piece of wood.

We learnt that plywood was very week when laid out horizontally with weight on it but quite strong when placed on its thin edge. We also learnt not to push in the nail too hard into the wood as it would puncture the wood and create a weak point.

After learning these things we tried to use them to our advantage in creating a beam.

Our beam when put in the system that put weight onto the beam could only old hold 195kg in the end, how-ever started out at 330kg before decreasing as the beam broke and the nails popped out due to them being pushed into the end grain which was softer than nailing across the grain. As can be seen above the beam twisted as one side of the plywood be-came detached from the wooden blocks

As can be seen above our beam had a box like shape in the center as we at the time believed it would make the beam stronger. If we were to do it again, it would be better if we used the other stron-ger wood as the basic frame of the beam rather than the plywood, as it was much stronger and would have been able to withstand more weight. In the end our beam had around 35mm of deflec-tion.

This exercise was a good learning experience be-cause we now know what not to do and have also learnt - through watching others - of ways in which we could have improved our design.

Timber Workshop

Others Beams

This groups beam (as seen above) was able to withstand 250kg of weight before breaking and had a deflection of approximately 50mm which was larger than our deflection.

They placed the plywood diagonally across the beam however this did little help in keep-ing the beam strong as at the first chance it began to buckle and pop off. The beam failed at the knot in the wood because it was in an area of tension, and also at one of the screws as that was an area of weakness.

This group used the idea of an I-beam to create their beam, using the plywood in the centre to almost reinforce it in its weakest point (the mid-dle). It was able to withstand a weight of 330kg with a deflection of 15mm which was very little compared to the previous beams.

The change in the way the wood was fixed together (I - Beam shape) meant that it could withstand more weight due to its greater ability to deal with tension. This beam was very good in that it didn’t deflect much, however couldn’t hold the most weight.

This beam was by far the strongest as it was able to withstand a grand amount of 590kg before it gave in and broke.

The issue with this beam was that the ply-wood was not connected to the core sec-tion of the beam well, so when weight was applied (as can be seen below) the plywood tended to buckle and therefore weakened the beam. During this particular ‘beam crush-ing’ we learnt that unlike steel, wood does return to its original shape where as steel stretches as it is malleable.

Lecture/Readings

This week while I was walking to class I noticed something on the concrete which I had just learnt from the reading (Ching). What I saw was an impres-sion that was left by the wooden formwork and in this case it would seem that the wood used in the formwork was similar to that of sandblasted plywood. This just made me realise how much I am learning from the readings as I can now pick up on many things to do with buildings and it makes everything so much more interesting.

Height to width ratio is used in building when designing support structures such as a retaining wall. For example the width of the footings in retaining walls are typically proportionate to the height of the wall. So if the height was going to be increased in the wall then the width would have to be changed as well, also depending on the lateral forces the ratio may have to change.