week 2 Constructing Environments India McKenzie 639 234
Construction Method
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As opposed to the mass construction used in last weeks studio task, the materials we were given this week required us to create a post and beam style structure using the thin balsa wood beams and super glue. We began by sketching geometries for the base, deciding on a square base due to its symettry and stability. In retrospect, the use of a triangle base would have been a more effecient use of materials by removing the fourth component as well as being a more rigid structure against lateral forces. After we established the base formation, we then wish to confront our construction method. Learning from the failures of last weeks’ haphazard formation, it was imperative that we plan the stages of construction to be effective with our time and our materials both of which acted as constraints to the brief. We opted for a modular sectioned method whereby each group member was given a task in creating a number of individual modules that could simply be connected together to form the vertical structure. This division of labour mimiced the specialised members of a construction team as we assigned responsibilities to each member. It also made efficient use of limited time and operated on sound principles that if executed correctly, have been found to yield effective results in large scale building constructions. The difficulty we had was with the imprecise nature of the materials and the error or margin being small. The use of superglue also complicated the matter as it required compression and time in order to set properly. Slight differences between each module became apparent when we began to construct the model and the posts didn’t align as they should theoretically have done.
Joints + Structure
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As we experimented with the properties of the materials, we experimented with a couple of different joint styles in order to evaluate the rigidity and appropriateness of the different types. One suggestion was the ‘Moulded or Shaped’ joint that would have been structurally sound with the balsa connections yet the time constraint ruled this option out as it was labour and time intensive. Instead we opted for a stacked ‘butt joint’. This can be seen in the sketch design below. The decision to inset the posts within the horizontal beam structure was discounted due to the potential for vertical slippage once the dead load above became too much. We were unsure if the adhesive could cope with the downward pressure and thus opted to create a point & load system by aligning the posts directly above one another.
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“lateral and torsonial instability” The post and beam system is effective in acheiving height however the balsa wood proved to be a particularly flexible post option thus creating this “lateral and torsonial instability” throughout the structure. In order to counteract this instability we sought an element that would add rigidity to our design. Our first attempt to stabilise the structure came from our readings of Chapter 2 of Ching. At first, we consulted the chapter to assess the most suitable spanning and bracing options. Given the square formation of the base, Ching suggested that we use a two-way span rather than a one-way which is better suited to rectangular objects. Yet we quickly establish that cross spans would be relatively ineffectual and an ineffective use of materials. We then explored the concepts of bracing which proved a more efficient use of materials. Whilst the cross-bracing was noted to be more stable, the regular length of the rods meant this option was impossible without reducing the width of the structure. It also would have consumed a significant amount of our finite supply of balsa. We opted for the simple knee joint to counteract these restrictions and provide extra support to “resist lateral forces”.
Rigidity
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As we began to put our modular sections together we began to have issues with the adhesive in that the glue required compression and time to set in place. This meant thtat our point and beam system was placed under extensive stress as the downward pressure required for the glue drying process, meant that the weaknesses in the structure were exaggerated. As illustrated in the diagram below, the concentrated load ran directly through the vertical posts and caused a deformation of alignment particularly at the bottom. This can be seen in the image as the posts on the base are seen to buckle inwards despite the knee bracing. The sketch identifies the weaknesses and illustrates how the imprecise construction process resulted in the development and exacerbation of weak points as the tower grew in height.
Weaknesses
Reflection
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Once we had exhausted our supply of materials, and acknowledged our structure was neither the tallest, nor the most rigid in the group, we decide to first analyse and detect the elements that made the other groups’ structures more successful. We identified the geometry of the triangle to be a much more logical form for the base which lends well to the structural rigidity of the truss system which draws upon the linear members and a webing system to create rigidity between the chords. Our next step was to analyse the destruction of our structure and thus we then applied a force to one corner. This highlighted the weakness of the point and beam system as the concentration of load on a single point lead to the buckling of the ‘long slender’ columns and the structure folded in on itself. This was partly due to the incompetency of the the adhesive to perform its function and the innaccurate construction methods.