Constructing EnvironmentsWeek 2 Journal - Frame

Daniel Kellett 635876

Figure 1. Initial construction idea

When given the task of once again building the tallest tower, framework was set as the core to the problem needing solving. The initial idea was simply to build a vertical triangular prism, (Figure 1.), however with time constraints and the finite quantity of material it was determined that a tapered triangular prism would be more suitable to the amount of balsa wood provided. (Figure 2.) This design would ensure stability at the base with the capability to make a tall tower. The tapering also allows for the moment that occurs at the base to be less and therefore increase the overall integrity of the structure.

Figure 2. Idea vs. End Product

Tutorial Session 2 - Frame Analysis

Buckling and torsion is a common occurance in these structures without the integration of bracing and angled members within the structure itself. With limited resources we analysed two different bracing choices (Figure 1.). Idea 1 comprised of intermediate triangles placed within each section, however we soon realised that this would not solve the problem of torsion and buckling, but just reduce the visual effects when force was applied. We trialled Idea 2, seen above in Figure 1, which proved to be far more successful, however with pressing time constraints and the time limit on glue drying, we did not end up adding this additional bracing.

During the initial building phase it became evident that our planned tapered design, seen left of figure 2, would not reach fruition and so continuation of the triangular prisms followed, producing the final structure seen on the right hand side of figure 2.

Figure 3. Process

As time progressed we realised the glue would not dry quick enough and so we analysed various ways to continue the height of the tower. This led us the the finished product on the right hand image in figure 3. Tutorial Session 2 - Sequence of Process

Initial construction consisted of production of multiple triangles made from the thicker sections of balsa wood in order to provide greater support. With various thicknesses of wood, we used the thicker pieces at the bottom as they would eventually carry the greatest loads as height increased. As time progressed it became clear that numerous amounts of triangular prisms stacked to produce the tower would not be finished and so we decided to make each section comprise of two pieces of vertical balsa which can be seen in the central image of Figure 3.

Figure 4. Load Path Diagram - Tower

Tutorial Session 2 - Analysis

The framework structure allows for a stable system of construction with the addition of using limited amounts of materials. The only issue is that bracing is required to stabilise the overall structure. When using triangles, the best system to employ is a triangular pyramid that tapers as it progresses upwards. This maximises the width at the base for stability but also allows for greater heights to be reached. We planned to employ this system with our design and so, with the limits of time, we only had began to taper the first layers of the tower, as seen in the top section of the tower in Figure 4.

The activity employed the use of balsa wood as the material and on this scale the balsa wood reflected the characteristics that steel girders and other large scale materials show in framework. It also allowed for a visual representation of what force does to framework structures (discussed on next page). The use of super glue in this activity proved challenging as the glue did not dry at a rate that was required to produce a tower of substantial height.

At the completion of our tower, it was noted that one of the sides on the top section of our was bent inwards and did not show any signs of being rigid, but that of a floppy nature. It was tested by applying a small amount of vertical force to the top horizontal triangle layer and we discovered that it indeed was not carrying any of the structures weight down through it. This led to use determining the load path for the structure which can be observed in figure 4 on the left hand side.

Figure 5. Change in shape with force applied

The effects of force were tested on the towers produced by our groups at stages as the towers progressed in height. When the tower was at a height, as in the middle image of figure 3, there was little movement in the structure when lateral and vertical force was applied and this was due to the structure still being located relatively close to the ground and so the forces applied did not have a long way to travel in order to reach the ground.

As the structure approached completion it was noted that that structure moved a considerable amount when force was applied in the vertical and lateral directions and this can be seen in the diagram on the right (figure 5.)

Vertical force caused the structure to warp at each of the sections’ vertical columns and this could have been reduced by using columns that were thicker at their centre. The greatest warping was located at the initial point where the force was applied and this is located at the top of the structure.

Lateral force caused the structure to lean, progressively greater towards the top of the tower. With a great enough force this could cause the tower to bend, or even lean, eventually falling over. (caused if foundation systems are not substantial enough).

Tutorial Session 2 - Deformation

References: Aami Park Stadium 2009, Wikimedia Commons, United States, viewed 13 August 2013, <http://commons.wikimedia.org/wiki/ File:Melbourne_Rectangular_Stadium_construction_-_MCG_in_background.JPG>.

Ching, F. 2008, “The Building” in Building Constructed Illustrated, ed. F. Ching, 4th Edn, John Wiley and Sons Incorporated, Hoboken, New Jersey

Ching, F. 2008, “Wall Systems” in Building Constructed Illustrated, ed. F. Ching, 4th Edn, John Wiley and Sons Incorporated, Hoboken, New Jersey

Vassigh, Shahin, Interactive Structures Version 2.0, Wiley & Sons, Inc., 2008 DVD-ROM and Software Compilation