Post on 08-Mar-2016
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Knowledge map of week 1
Our team chose an approximate rectangular shape which we
thought can best fit the shape of the object given by tutor, has
the least space wasted and costs the least amount of materials
(MDF). Plus, as our base was the smallest among three groups, it
actually saved our time so that more time could be spent on wall
rising.
Studio 1 – Compression (hollow tower constructing)
When building the walls of the tower, we chose stretcher bond, which is most
frequently used in real building constructing because it has the longest load
path – with a longer pathway, the load is more separated (the shadow shows
the areas in which loads are separated) and therefore the structure becomes
more stable and can hold more load (ref: studio 1).
A technical problem showed up when we created the opening – in
order to make it wide enough to let the object get through, we
need to tie up at least three bricks horizontally with rubber band,
but it would become very unstable when more bricks are loaded
onto it because the three bricks are not strongly compressed
together and they would break up easily from the crevices
between them. Thus we did not build an enclosed structure but
left it semi-closed.
The final collapse happened when we tried to remove some of the
bricks from the middle part, which eventually caused a shift of the
gravity center and thus the whole body biased to one side and fell
down.
During the deconstruction
process, we found that the most
easily-removed bricks are either
on the open edges of the walls,
or at the turning corners where
the walls change direction. The
latter is because the plane walls
are the main support of the
whole structure and thus the
corner bricks are the weakest
parts which do not bear much
load as the plane walls do. The
marginal bricks are even easier
to remove because they are only
compressed at one end.
At first we were just making holes within the structure, but after an
accidental crush, the structure then became shuttle-shaped with a wide
body and a relatively narrow base. This is probably due to the strong
bending stress (ref: 2.14 Ching, ‘Beams’) created by the stretcher bond,
and also because the base is wide and firm enough to hold up the entire
structure.
Comparison with the other teams:
This team’s structure is not very high but must be the strongest among the three
groups. It has a base shape between circle and square, which behaves as a
two-way system (ref: 2.19 Ching, ‘Structural Units’) that spread the load equally
in four directions. Additionally, they thickened the base by adding several more
layers of bricks both vertically and horizontally, thus the load path is even longer
and the base is even stronger.
This team made a circular base for their tower, which uniformly
spreads the load in all directions to make the foundation stable.
It is also a large base which can bear more loads and thus
theoretically the tower can be built higher. However, the
grandness of the base also causes some problems, including a
waste of space and materials, and a much longer constructing
period, which actually limited the final height of their tower.
Their walls are also based on stretcher bond. And they created
an opening which we did not have. Yet they did not upload
many bricks onto the opening either, probably because they
met the similar problem as we did.
Their walls are also built in a
different way, laying bricks facing
two directions alternately, to
make it more efficient to build the
tower higher. However, as the
contact area between two brick
layers becomes smaller, the
stability of the whole structure is
also declined.
Knowledge map of week 2
This time the three groups coincidently chose the same
equilateral-triangle instead of square base, because triangle is
relatively rigid and stable. Also, among all polygons, triangle has the
least sides so it can help reduce material usage (ref: 2.17 Ching,
‘Frames & Walls’).
Studio 2 – Frame (balsa wood tower constructing)
Our team decided to build a triangular prism. To increase its stability,
in each storey, we joined every top vertex with the mid-points of its
corresponding side, so that three truss frames (ref: 2.16 Ching, ‘Truss’)
can be created within one single storey.
In this case, the load pressed on each vertex (except for the ones on the ground or at the top-end of the tower) can
be separated into four different pathways. In addition, we joined the three spatial sticks together to further
separate the load, and in the meantime, when one of the three sticks is overloading and tends to bend, the tension
provided by the other two can help prevent it from deforming.
To prevent the three vertical legs from
moving and strengthen the base, we
added a small piece to each base corner,
perpendicular to the bisector of that
angle, and then glue the four pieces all
together to create a strong joint.
Due to the lack of super glue, we had to try another two ways to join the sticks, using pins and tape
respectively.
Pin connection is not suitable in this case because the materials are thin balsa wood sticks, which are very
crisp and can be easily broken when drilling holes on them.
Super glue is the best choice as it can realize butt joint which is ideal for light materials like balsa wood (ref:
2.30 Ching, ‘Joints & Connections’).
Tape doesn’t fit this structure either because we were building a three-dimensional structure but tape can
only work well on a plane.
Yet tape can be very useful for two-dimensional joining, especially
when joining three sticks together to make a right angle, because it
actually creates a triangular shape at the corner to make it a rigid
frame. The following shows how to make the best use of tape joint
(based on experiments in studio 2):
Turn over Repeat
Comparison with the other teams (1):
This team made a complex structure with four
different bracing patterns to reinforce the tower,
namely K-brace, cross bracing, Knee bracing and the
simplest one-member brace (ref: 2.22 Ching, ‘Lateral
Stability’). All of them are based on triangular frames
to spread out loads and make them rigid.
They cut the materials into very thin pieces, which
actually lightened the dead loads provided by the
self-weight of the structure (ref: 2.08 Ching, ‘Loads on
Buildings’). The final structure is bamboo-shoot-shaped, with the
storeys becoming narrower as the tower grows up.
Unlike prism ones, this structure has bevel sides in some
storeys. Because those bevels have the same length,
they need to have very similar inclination angles to make
the top plane even. Obviously this requirement is hard
to achieve manually, and that’s why their tower biased
to one side for several times. However, since the
materials are very light, the slight shift of the gravity
center didn’t matter a lot. Thus their tower finally grew
very high and reached the ceiling.
This team’s structure is a combination of a few separate triangular
prisms, and each of them is a completed frame without any shared
side with others. This means those sections can be built separately
at the same time and thus the constructing process can be much
more efficient.
Comparison with the other teams (2):
Similarly, they also chose a K-brace-like
frame to strengthen the tower walls. But
they made a difference by inserting a
right-trapezoid-shaped frame to each side
plane, which meant there were three
triangular frames within one side plane and
this structure should be the most stable one
among the three groups (ref: 2.22 Ching,
‘Lateral Stability’).
The challenge is to make
sure the base and top of
two adjacent storeys have
the common mid-point or
center of gravity, so that the
whole structure can stay
steady with a gravity center
right in the middle as it
grows up.