bridge specs

Bridge Specification and Instruction Guide
Preparation:
You will need:
248 x Pop sticks
1 x Industrial Glue (Provided)
1 x Wood Glue (Provided)
1 x Scissors
1 x Cardboard Card Piece (1200mm x 210mm)

Bridge Specifications:
Height = 80mm
Length = 1190mm
Width = 220mm at the top & 210mm at the bottom
Weight ≈ 300g (without glue)
Pop sticks used ≈ 250

Preparation:
1. You will need to cut 141 pop sticks and cut them down to a size of 91mm from the original
length of 110mm.
2. Other lengths will be cut to length relative to the bridge constructed.

DO NOT THROW AWAY THE CUT OFFS! These will be used for reinforcement.
This preparation will be essential when coming to constructing the end supports of the
bridge, as it will save you/your team time.

Design Instructions:
**Note to constructors, it is preferred if the industrial glue is used for the triangular trusses
and diagonal beams whilst using the wood glue for the end supports and top and bottom
beams. This will maximise the strength of the bridge as the industrial glue is very strong but
does allow for movements of the joint whilst still keeping the structure up.
1. The main design on the bridge consists of many equilateral triangles interconnected with
one another to form the main structure of the bridge. So to construct this simple triangular
structure, start of with 3 pop sticks, with lengths of 91mm. Place the first pop stick
horizontally then place the 2 other pop sticks on one
side of the horizontal one. This should form the
equilateral structure with the pop sticks being at an
angle of 60o. When the structure looks like the
diagram 1.1(right), proceed by using wood glue to
connect each joint of the pop stick and apply pressure
until the glue has set by placing bricks on the joints.
Vv Figure 1.1

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2. Once you have this main triangle, construct others which are as closely identilce to
eachother as possible. When you have two triangles constructed and glued, it is time to
connect them forming the main structure of the bridge. When the two triangles are
connected at the bottom, one triangle must be
placed ontop of the other. In this diagram the
triangle on the left is ontop of the one on the
right. The pink member on the top is glued to the
top traingle from the bottom and connects to the
bottom triangle at the front. The glued structure
is shown on the right in figure 1.2.
asn Figure 1.2

3. To continue this pattern, when connecting the next triangle, remember that if the triangle
you are connect to is already on top of one triangle, then the next bonding triangle must be
glued to the bottom. In the example below. Triangle 1 is glued on top of triangle 2.
Therefore triangle 3 must be glued under triangle 1. This change from top to bottom will
keep the structure straight where as constantly gluing one triangle on top of the next will
make the truss bend to one side. Figure 1.3 visually depicts the joint structure of the truss
used in the bridge.
Figure 1.3



4. When the desired number of the triangles are created, it is time to reinforce the ends and
create the ends of the bridge which the whole weight of the bridge will be supported by.
Firstly measure the bottom of the triangular structure created. The length should be roughly
1092mm long. Therefore 2 pop sticks of 49mm are to be cut and placed on the bottom of
the triangles. If the length is shorter or longer, cut the appropriate lengths needed and
attach (red line) it to the end triangle like shown in the diagram below. Therefore the total
length of the bridge should be 1190mm. Figure 1.4 displays this.





Figure 1.4
49

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5. Next when the bottom member is attached, measure 4 pop sticks which have a length of
78mm and attach them to the bottom member which was attached in the previous step.
When finished the ends will look like figure 1.5 below. The gap in between each vertical pop
stick isn’t overly important but make sure that 4 pop sticks fit on that member and are
glued.

78
Figure 1.5

49

6. Now for the other horizontal members, the best thing to do it to actually place full length
pop sticks at the last horizontal pop stick and measure how much needs to be cut off the
end so the horizontal pop meets the end vertical member and the end of the triangle which
is shown in figure 1.6. When the members are cut, glue them to the structure. Repeat this
procedure for the other side of the bridge truss.
94.5


78
Figure 1.6

49

7. When one truss is fully complete, repeat steps 1-6 for the other two trusses.



8. To connect the trusses made, firstly take two trusses and line them up so they are 105mm
apart. Then on every top triangle joint, place a single pop stick on top of the joins and make
sure the trusses are roughly 105mm apart. Then place the glue on the joins and hold it in
place until it dries making sure that there is around 5mm overhang from the outside truss.
Figure 1.8 shows this.
110

Figure 1.8
80

105

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9. Then diagonally you will need to cut two pop sticks which have a length of 75mm and glue
these members together to have a total length of 132mm. Therefore there will be overlap of
the pop sticks which needs to be glued together. This will strengthen the joint as it is
diagonal when it is glued together. When this member is complete glue it to the two trusses
on diagonally and glue both ends to both trusses shown in figure 1.9a below. Make sure that
the thin side of the pop stick is vertical. This allows for more force to be taken by the
member. Figure 1.9b shows this

110

1
Figure 1.9a) 3
80
2
Figure 1.9b)

105

10. For this step repeat step 9. But this time make the member diagonal in the other direction.
Therefore when this is done to the full truss and connected the 3rd truss, there will be visible
V’s and /\’s. This helps distribute the load of the forces acting on the bridge. When it is
complete figure 1.10 shows the dimensions that should be obtained.
220

110
110


80

105

210

Below are the Design drawings and the measurements that are ideal due to the instructions given
above.

Side view:
1190

94.5

78
49

91
Top/ bottom View:
1190


220
94.5
91

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**The gray dotted lines are to show members which are not on the actual side of the bridge but can
be seen through this view. ie on the side view and top/bottom view, the dotted gray lines represent
the diagonal members that are installed in step 9 &10.
220
Front on View:

80

105

210


When the bridge is complete and weighed, if the weight is below 450g, reinforcement may be placed
if desired. This may be done by using the off cuts and gluing them to the diagonal members, or
adding extra glue (industrial) to the joints in the middle to strengthen the joints.



Cost:
Material
Cost per Unit
Number of Units
Total Cost
Pop Sticks
$8/1000
248
$1.98
Glue (industrial)
$20/5000cm3
75cm3
$0.30
Glue (wooden)
$5/500cm3
40cm3
$0.40
Total=

$2.68

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