# bridge_documentation - WordPress.com

Urban and Civil

Nov 29, 2013 (4 years and 7 months ago)

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Vang
1

Casey Vang

Betsy Natter

Design and Society

March 4, 2013

Bridge Documentation

In this project, we learned how to build a bridge and all the little details that was
considered when designing the bridge. We learned about compression and tension forces,
different parts of the members, and how the bridge works. There were 4 activities t
hat we went
through. The first activity involved building a bridge that was already designed.
This helped us
learn how to assemble a bridge and which bars were compression or tension members.
The
second activity was testing the forces for compression and t
ension forces.
Once we obtained the
information for the members, we were able to calculate the forces and see which members were
more efficient.
The third activity was creating a bridge

of our own
.
This enables us

to use all the
information we
learned
to b
uild a bridge that is efficient and figure out if it will sustain ten
pounds

or more
.
Finally, the last activity involved getting into a group and determining whose
bridge was the best bridge
. After that, we built the bridge and tested it
.

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2

ACTIVITY 1
:

W
e built a bridge that wa
but when we tested our bridge, it failed at 17.5 lbs.
Our bridge failed in the center when one of
the tension members snapped (shown in the second picture).
The materials we used to build the
bridge were file folders, clay glue, and wood glue. The objective was to see how a bridge worked
and which parts were compressions or tension members.
Members are the bar of the bridge. As
shown
in
the photo below
, there
are members

that are hollow, the larger bars, and members that
were solid, the thinner bars. All the hollow members were compression members. The

hollow

shape of the member helped maintain compression forces because it didn’t bend as easily as a
solid bar.

Even though hollow tubes could be used as tension members, it was cheaper to just use
stripes
. T
he forces applied on the two different shapes are

also

the same when it comes to tension

force.

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3

ACTIVITY 2: We performed a test on different sized compress
ion and tension members. After
we gathered our results and calculated the forces, we pretended that we were writing a memo to a
town that needed a new bridge. In this memo, it explained all the details of the tests such as how
we did our calculations and t
he sizes of each member:

My team and I have constructed a test on paper files to see how strong the material is and
how much force can be used on it depending on the width and length of the paper files. Paper
files resemble steel a lot so this will be a s
caled down version. To test for the compression, we
built the files into a hollow tube for the members. For the tension, we used stripes of the paper
files. This will help figure out the lowest cost of material for a bridge that can with stand a
massive we
ight.

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4

Bridgetown needs a safe and sturdy bridge that will be built under a budget given from
the council and major. To figure out which member is the strongest, we made two different
cross
-
sectional area members; 7x7 mm and 10x10 mm. Also, we tested diffe
rent lengths ranging
from 5 cm to 20 cm for the members. To test the tension of the members, we tested the lengths at
10 and 20 cm and there was a range of cross
-
sectional area ranging from 2 mm to 8 mm. After
that, we used a lever to add force onto the me
mbers. We performed this by hanging a bucket to
the end of the lever and adding gravel into the bucket to determine the weight it is able to hold.
We did this to test the tension too but instead of putting the member in front of the fulcrum, it
was behind
so the lever can pull on it. This technique works because the force pushing down on
the lever will be the force needed to lift the object on the other side. To calculate the force used
on the members, we had to find the weight first, which is mass times gr
avity (W=MG). After
that, we found the torque because that’s the force used on a lever. To calculate the torque, we
multiplied the force we found with the length from the fulcrum to the bucket of gravel. Finally,
we divided the torque with the length from
the fulcrum to where the member is placed to
determine the force used on the members.

After collecting all the data, we found that the members with a cross
-
sectional area of
10x10 endured more force compared to the 7x7 members. As the length of the members

increased, the amount of force applied on the members decreased. This shows that the shorter
members with more cross
-
sectional area were more efficient because they didn’t buckle as much
as the longer members. Also, the member with a larger cross section
which is the 8 mm member.

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In conclusion, the members with a larger cross
-
sectional area and shorter length will be
the best shape when building the bridge. It will save material because we have to build shorter
members inste
ad of using more material for the longer ones.

0
20
40
60
80
100
120
140
0
5
10
15
20
25
Force

Length

Compression Test

Members with a width of 10x10

F1
0
20
40
60
80
100
0
5
10
15
20
25
Force

Length

Compresstion Test

Members with a width of 7x7

F1
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ACTIVITY 4:

Wendy Sorino’s Bridge

James Denson’s Bridge

0
20
40
60
80
100
120
0
2
4
6
8
10
Force

Width (mm)

Tension Test Width vs. Force

Series1
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Taylor Grover’s Bridge

My Bridge

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8

Pugh
Matrix

Cost

Strength

Aesthetics

Ease of
Construction

Total

Casey

2

3

2

3

10

James

3

1

4

1

9

Taylor

4

2

3

4

13

Wendy

1

4

1

2

8

After evaluating all the bridges, we choose Taylor’s bridge. His bridge scored the highest
on our pugh

matrix. The bridge he designed had fewer members so it would be easier to build.
This also made the cost cheaper than the rest of the bridge
, which was a total of about \$179,000
.
Even though it was not the strongest bridg
e, it was able to hold the amount

of force that was
required to pass. The design was simple and unique.

ACTIVITY 5:

This is the bridge we chose to create:

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Type of Cost

Item

Cost Calculation

Cost

Material Cost (M)

Carbon Steel Solid Bar

(1809.5 kg) x (\$3.78 per kg) x (2 Trusses) =

\$13,680.07

Carbon Steel Hollow Tube

(2570.3 kg) x (\$6.30 per kg) x (2 Trusses) =

\$32,385.72

Connection Cost (C)

(9 Joints) x (300.0 per joint) x (2 Trusses) =

\$5,400.00

Product Cost (P)

8
-

70x70 mm Carbon Steel Bar

(%s per Product) =

\$1,000.00

2
-

75x75 mm Carbon Steel Bar

(%s per Product) =

\$1,000.00

2
-

110x110x5 mm Carbon Steel
Tube

(%s per Product) =

\$1,000.00

3
-

240x240x12 mm Carbon
Steel Tube

(%s per Product) =

\$1,000.00

Site Cost (S)

Deck Cost

(6 4
-
meter panels) x (\$4,850.00 per
panel)
=

\$29,100.00

Excavation Cost

(85,000 cubic meters) x (\$1.00 per cubic
meter) =

\$85,000.00

Abutment Cost

\$9,000.00

Pier Cost

No pier =

\$0.00

Cable Anchorage Cost

No anchorages =

\$0.00

Total Cost

M + C + P + S

\$46,065.79 + \$5,400.00 +
\$4,000.00 +
\$123,100.00 =

\$178,565.79

The graph above displays the cost calculation of the bridge.

#

Cross
Section

Size
(mm)

Paper
Size

Length
(m)

Paper
Length
(cm)

Compression
Force

Scaled
Force

Tension
Force

Scaled
Force

1

Solid Bar

75

1.9

4.0

10.0

0

0.00

1258.8

40.87

2

Solid Bar

70

1.8

4.0

10.0

0

0.00

1024.51

33.26

3

Solid Bar

70

1.8

4.0

10.0

0

0.00

1146.07

37.21

4

Solid Bar

70

1.8

4.0

10.0

0

0.00

1132.41

36.77

5

Solid Bar

70

1.8

4.0

10.0

0

0.00

1010.85

32.82

6

Solid Bar

75

1.9

4.0

10.0

0

0.00

1184.39

38.46

7

Hollow Tube

240

6.0

8.6

21.5

1546.94

50.23

0

0.00

8

Hollow Tube

240

6.0

8.6

21.5

1455.51

47.26

0

0.00

9

Solid Bar

70

1.8

5.8

14.6

0

0.00

709.17

23.03

10

Solid Bar

70

1.8

5.8

14.6

0

0.00

709.17

23.03

11

Hollow Tube

110

2.8

7.1

17.7

15.53

0.50

478.21

15.53

12

Hollow Tube

110

2.8

7.1

17.7

90.68

2.94

403.05

13.09

13

Solid Bar

70

1.8

5.1

12.8

0

0.00

619.83

20.12

14

Solid Bar

70

1.8

5.1

12.8

0

0.00

619.83

20.12

15

Hollow Tube

240

6.0

10.0

25.0

1277.76

41.49

0

0.00

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To scale the lengths and widths of the
bridge members, we had to scale everything down
to 1/40 of the original size. For the lengths, since it was measured in meters, it had to be
converted into centimeters first. We multiplied the lengths by 100 since the
re are 100 cm in a
meter. Then, we divided the produ
ct by 40. The equation is:

Paper member l
ength = (Steel member length*100)/40

For the widths, since the measurements were already in mm, we just divided the widths
by 4
0
.

This equation is:

Paper member Wi
dth =
Steel member
Width/40

Before building the bridge, we had to determine if it would be able to sustain a certain
amount of force.

The forced
was measured in newton
. Our bridges

5
0

newton
s
, which is equivalent to 10 lbs. To scale
down the forces, we

divided 98 by the total
weight of the bridge’s truss mass. Trusses are the sides of the bridge. We also multiplied the sum
of the truss mass

by 9.8
, which is the force of gravity,

and 1.25.
Then we divided

the product

by
1000 newton

bef
ore we divided 98 by the quotient.

The equation is:

Force scaling factor = 98/(2911 kN + (truss mass in kg)*(9.8N/kg)*1.25*(1kN/1000N))

As shown in the table, all of our tension members were
only carrying 40 or less newtons

force

on them so it never excee
ded
10 pounds
. The compression
members were carrying 50 or
less

newtons
. Even though nothing exceeded 50 newtons, we still made changes to the bridge.
The size of the tension members seemed
too thin to be able to hold 10 lbs
, so we increased the
width to 4

mm
. We also rounded all the numbers up. After
that, we
increased
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11

the
width of

hollow members 7, 8, and
15 to 10 mm
. The tension members on the bottom of the
bridge

that he
ld the deck were too flimsy, so we added compression members on both

truss.

In the photo above, you can see the members on the bottom of the truss
. They were
tension members, but converted to

compression (hollow) members. We felt that it would be more
stable with the compression members

since there was nothing on the b
ottom to support the deck
.
These members were two 30 cm long and 10x10 mm wide bars.
Squared gusset plates (2cm by
2cm) were also made to hold the members together.

Gusset plates are small pieces of solid steel,
in our case we used paper files, which held
the members in place where each member joined.

For
the top, we created thre
e 10x10 mm wide members that was 9 cm long to connect the two trusses
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12

together at the top. At the bottom of the bridge where the deck is supposed to be, we made five
5x15 mm wide an
d 10 cm long members to connect the two truss
es

at the bottom. To complete
the bridge, we added plates to connect the corners of the
bridge
.

To add weights to this bridge, we put a piece of wood on top of the bottom of the bridge
,
where the deck is
supposed to be
. This piece of wood had two holes in the middle so we looped a
string through one hole then through a bucket and through the other hole. After that, we slipped
small pieces of wood into the rope at the top of the larger piece of wood to secu
re the rope and
there were knots tied right beneath the holes.
By using the piece of wood placed on the bridge, it
helped evenly distribute the weight.
We slowly added weights into the bucket and a
fter 12.5 lbs,
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13

our bridge failed.
When we put 10 lbs on the

bridge, the compression member on the bottom
bent downward. This was one of the extra members we added to the bottom of the bridge where
there were only supposed to be tension members. When we added 12.5 lbs, the diagonal member
on the right side buckled
and the whole bridge came down. This member was probably the one
that

50 newton
s

on it, which meant it was only able to hold 10 lbs.

Since the first part to fail was the bottom compression member, we should have designed
the bridge on the
program before making any changes. The compression member was too long
and that made it weaker. We could have increased the width of the bottom members to make it
stronger. The width of the diagonal compression members could had been increased too because
it wa
s too long, which made it more likely

to bend.

My team worked well together. We got everything done on time and when there was a
problem, we worked together to solve it. We also made decisions together and helped each other
out. Our te
amwork helped
me get through the project. There were times when I did not know
how to figure some things out and they would help me, such as my calculations for forces. We
also contributed ideas to make the bridge stronger. During the building phase, everyone had their
own share of work load. Taylor drew the layout of the bridge onto grid paper so we can build it.
James, Wendy , and I made the parts to the bridge. We all helped put the bridge together, but
James took it home to finish putting the two trusses together.

This project is related to the collapse of the I
-
35W Bridge because we were able to see
which part of different bridges failed.

When the I
-
35W Bridge failed, it was the gusset plate that
caused the bridge to collapse.

We noticed how when one part of the br
idge failed, the whole
bridge would come down too. This is called fracture critical.
Not only that, but we were able to
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14

measure forces just like how engineers would
before they built

bridges.
This project also helped
me focus on the university studies goals at Portland State University. For the writing goal, I
was
able

to
interpret

my ideas toward my group. We had great commu
nication with each other and
putting my data into a
table

helped me
explain

my information bett
er. The second goal is
quantitative literacy.
Throughout the beginning of the project we learned about all the factors
into building bridges and what would work. All the tests we performed helped me understand the
difference between compression and tension

members. It also helped me learn which member
was stronger. The third goal is inquiry and critical thinking. We faced a couple problems during
the process of building the
bridge. By determining what was wrong, it was easier to come up
with

solution
s for t
he problem. Some of the problems were

ing extra parts to the bridge and
making other parts

stronger. The fourth goal is ethics and social responsibility. All the team
members were compatible and we respected each other’s thoughts and ideas. That is how
we
came to the conclus
ion of our bridge. The last goal is diversity of human experience. After
learning about fracture critical, we learned the culture of America and how most of our
infrastructures are fracture critical. Bridges are part of this problem a
nd after building the
bridges,
we discovered how a bridge would collapse when one part of the b
ridge failed. After
this project, I have seen the perspectives of engineers and how they create
d

bridges. It is more
than just putting pieces together
. T
hey have

to measure every piece carefully and if the
measurements are

just slightly off, it will be a big impact on the bridge. This is something that
needs to be improved in our society today. I never cared for bridges and how safe they were until
after this unit
. Going through the building phases of a bridge has helped me learn not only about
bridges, but calculations, fracture critical, and how it affects the society.