Constructing Journal Week 2

This weeks tutorial in-volved making a balsa wood tower as high as possible. During the previous week my group met together and made a plan of what we were going to build to make the tallest tower possible. This can be seen to the left. As you will see later, we did not follow our initial design exactly but we definitely used it as the basic idea of what we were doing.

Here we have the forty strips of wood that we cut out prior to the tuto-rial, and they were ap-proximately 4mm wide

We started by creating the triangular (equilateral) base an then extending up five full strips stuck together in a line on each point. We then tapered each of the tree long strips of wood together and formed an elongated triangular based pyramid.

Secondly we began to fix triangles every two full length strips to help with stability. What we did change from the original drawing, was that we made the base smaller than a full strip per side of the triangle because we found it made the struc-ture a bit stronger and less subject to buckling.

Making the balsa wood tower

This image shows a close up on how we stuck together the triangles in the middle of the structure. We connected the flatter bits of the wood to the frame as we found the wood was less flexible when pressure was applied

Here you can see the full triangular structure with some of the triangles on the inside to help keep the shape and give the structure enough strength to stand on its own. As can be seen here the tower is not so tall.

Because the bottom vertical pieces of wood were carrying the most weight, we found that they were subject to buckling that would topple the tower over as the centre of gravity shifted. Because of this we connected a strip of wood diagonally between vertical pieces to strengthen the structure.

Once we had built the structure we had planned, we found that it wasn’t our desired height, so to increase its height we added two piece of wood on different sides of the triangle to keep building up.

This diagram shows how we connected the pieces of wood together and en-sured it was stable. We used little hori-zontal pieces of wood to hold together the new section because otherwise this section would have snapped.

This drawing shows a close up of how the old section of the structure and the new section connected. Rather than glue only a corner of a piece of wood to the other piece, we decided to cut the wood at an angle to increase the sur-face contact and make a stronger connection.

Things to be Improved

Figure 1

Figure 2

Figure 3

As can be seen in figure 1 we were able to reach up to the second story of the building by building in the stairwell. We managed to keep the tower upright for most of the time except eventually the weight of the tower became too much and the bottom of the tower began to buckle (figure 2) and severely distort the shape and centre of gravity, leading to its fall and the top of the tower snapping. There is always a point where the column (in this case the verti-cal parts) can no longer withstand its own weight and has no choice but to deflect outwards to relieve some of the stresses caused by the weight. Next time to improve the strength of the structure it would be better to add more wood diagonally across lining the vertical parts of the tower, as to provide strength and stability, and hopefully avoid a collapse. However this method will not allow for as tall a tower. Once the top of the tower snapped off, we tested the towers ability to hold a piece of paper, and it was successful.

Figure 3 shows another groups tower, they used a similar idea to us in that they used the same base shapes. They included little pieces of wood in the corners to help brace the structure and then proceeded to connect multiple pieces of wood together in a straight line and stick it on top. While their base may have been stronger, the long singular line of wood coming up from the top of the struc-ture proved to be too heavy and not stable enough, so snapped. To improve their tower they should have perhaps braced the long thin part on the top to counteract the compressive forces the weight of the top section was hav-ing on the tower.

Lectures and ReadingsWeek two’s lecture focused on structures that had gotten their design or inspiration from nature. For example the hanging flower pods. The guest speaker Peter C talked about animal architecture and plant architecture as well, for example; honeycomb or termite mounds. I found this informa-tion very interesting because now that I look around I can see so many structures that are structurally similar to those found in nature. The Lessons From Nature video also talked heavily on the idea of using structures in na-ture for non natural purposes, whether it be an exact replica or just taking one aspect or idea from something natural.

The reading by Ching talked about different types of construction, forces, and different structures. I found this section of the book particularly useful for my A01 assignment as many of the structures found in the book were also found in every day objects.

A ‘slab’ in terms of building is generally a large, flat, and generally thick piece of stone or concrete which is usually in a common geometric shape such as a square or rectangle.

Site Visit 1 A02 FullsizeFoundationThe foundation is just the earth

Footing

The two images above are of two different types of foot-ings. The first one is just a basic concrete footing around near the walls, and the second is a raft slab which is footing and flooring combined. Image 1 is of the basement, so the foot-ings are shallow as the ground has already been dug deep, the footings are about 400mm in depth and are resting on clay. The footing is founded into clay because it is strong and this site has lots of clay. The footing is reinforced concrete with the reinforcement being steel mesh.. The concrete has a pressure of 25MPa and this is the pressure it can take before crumbling. The function of the footing is to support the house.

1 2

The site I am visiting is a fairly modern family home that is in its early stages of construction. It has three stories including a basement, and will have a swimming pool outside as well as an eleva-tor. Because of these things, I am hoping to experience many different building techniques.

Image 2 is the raft slab and is the ground levels floor as well as the footings for the house. Before digging for the foot-ing the plumbing goes in first as can be seen above (the white tubes). There are ridges in the footings called internal and edge beams. The point of these steel reinforcing beams is to strengthen the footing. At the moment underneath the plastic there is packing sand which is used to help form the footings for the slab. The black plastic is polythene and is used to stop moisture from coming out of the ground and through the concrete. The last type of footing used here is a pad footing and it has steel columns in it.

Walls/Retaining Walls

The image above shows a waterproofing membrane and this serves the same purpose as the plastic on the footings, to stop moisture from getting through the concrete walls. This membrane is required as it is a basement so there is dirt on the outside of the walls.

The other two photos in the top right are of two types of retain-ing walls. The first one (closest to the top) is the shotcrete retaining wall and is the wall that is most used at this site, the second retaining wall is the sleeper retaining wall and it is just slid into the metal columns shown.

Other Photos

ReferencesLecture 2 Constructing Environments

Concrete Workz 2011, Middle Tennessee Concrete Finishers, Tennessee viewed 10 August 2013, <http://concreteworkz.com/concrete-slabs>.

Ching, F 2008, Building Construction Illustrated, 4 (edn), John Wiley & Sons, Inc, New Jersey.