EDSGN100 Truss Bridge Design
Final Design Report
Introduction to Engineering Design
EDGSN 100
Section 001
Don’t Truss Us LLC ®
Design Team #1
Daniel Alauzen, http://www.personal.psu.edu/dla5210, dla5210@psu.edu
Brian Sundberg, http://www.personal.psu.edu/bss5244, bss5244@psu.edu
Gaspar Lesznik, http://www.personal.psu.edu/gal5106, gal5106@psu.edu
Thadoe Swan Yi, http://www.personal.psu.edu/tis5323, tis5323@psu.edu
From left to right: Daniel Alauzen, Thadoe Swan Yi, Brian Sundberg, and Gaspar Lesznik
Submitted to: Prof. Berezniak
Date: 04/07/2013
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EDSGN100 Truss Bridge Design
Final Design Report
Table of Contents
Executive Summary
1.0 Introduction…………….……………………………………..……………….Page #4
2.0 General Factors for Design………………………………………………….Page #4
2.1 Structural Constraints.…….………….……………………….…….Page #4
2.2 Construction Constraints..……………………………….………….Page #5
2.3 Quality Control Testing.…………….………………………..…….Page #5
2.4 Aesthetics…………………………….……………………….…….Page #5
2.5 Economics ….………….…………………….……………….…….Page #5
3.0 Consideration of Design Alternatives……………………………………….Page #5
4.0 Selection of Bridge Design………..…………….…………………………….Page #6
5.0 Prototype Construction………..…………….……………………………….Page #6
6.0 Estimated Load Capacity………..…………….…………………………….Page #7
7.0 Prototype Load Testing….…………….…………………………….……….Page #7
8.0 Prototype Performance and Forensic Analysis….……………….….……….Page #7
9.0 Final Design Performance………….……………………………………..….Page #7
10.0 Refine the Design...…………….…………………………………….………Page #8
11.0 Conclusions and Recommendations………..…………….………………….Page #8
12.0 References.………..…………….…………………………………………….Page #8
Table #1
Table #2
Table #3
Table #4
Table #5
Table #6
Table #7
List of Tables
Load Test Results in West Point Bridge Designer…………………………Page #9
Cost Calculation using West Point Bridge Designer Software……….......Page #10
Material Specifications in West Point Bridge Designer……………..…...Page #10
Stick Weights Under Various Circumstances………………….…………Page #10
Bridge Aesthetics……………………………………………......………Page #11
Bridge Competition Overview………………………………......………Page #11
Design Team 1 Craft Sticks and Glue Used…………………......………Page #11
Figure #1
Figure #2
Figure #3
Figure #4
Figure #5
Figure #6
Figure #7
List of Figures
Concept Design Using West Point Bridge Designer Software………….Page #12
Strength versus Length Graph from West Point Bridge Designer………Page #12
Unglued Sticks: Weight Versus Number of Sticks…………..………….Page #13
Wet Glued Sticks: Weight Versus Number of Sticks…………...………Page #13
Dried Glued Sticks: Weight Versus Number of Sticks.………...………Page #13
Completed Bridge Design……………………………..………...………Page #14
Failure of the Bridge Deck.…………………………..……….....………Page #14
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EDSGN100 Truss Bridge Design
Final Design Report
Executive Summary
The purpose of the design project was to design a bridge that was structurally sound,
aesthetically pleasing, and cost efficient. The bridge design was limited by constraints that
limited the dimensions of the bridge to have a width from 4”-5” a height of at least 5”, and a
minimum span of 29”. Besides the size limitations, the bridge also had to weigh less than 400
total grams. There were also some other constraints that limited how the bridge could be
constructed by not allowing more than 50% of a stick to be glued, and no joint could have more
than a stack of 6 sticks.
Quality control was also performed on the sticks to help with the designing process. The
average stick, stick with wet glue on it, and stick with dry glue on it had its weight recorded, as
well as the number of “bad” sticks per every 20 sticks was recorded. This was to make it easier
to estimate the number of sticks needed to construct the bridge, and the maximum number of
sticks that could be used without the weight of the bridge going over 400 grams.
With quality control of the material and the bridge constraints in mind, different styles of
bridges were researched and a cumulative knowledge of truss bridges was formed between the
group members. With the information gathered about bridges the individuals of the group all
designed a bridge that met with the criteria listed above. A final design was created from the
individual designs and planning on the construction of that design began.
To construct the bridge, a design was drawn out to the actual scale the bridge would be
constructed. This design would act as the layout for the construction process, as the sticks were
laid out on top the design so that they could be measured and cut to the desired size. Following
the design the popsicle sticks were sanded to create an adhesive surface for the glue to stick to,
and then glued in place. The bridge was constructed by creating to the faces first, then the
roadbed. Once the three main components were completed, they were all glued together forming
the main portion of the bridge. From this main skeleton lateral bracing was added as seen fit in
order to increase strength making the bridge more rigid and less flimsy.
With the construction process completed an estimated load capacity was recorded and the
bridges were then tested until failure. The estimated load capacity was determined from the
simulation of the West Point bridge design software. The simulation showed stress along the top
portion of the bridge, but nowhere else so it was determined that the bridge could hold a good
amount of weight compared to its own weight. The value of 27.5 lbs. was decided upon due to
the construction of the bridge not being perfect to the design on the computer. The bridges were
also judged by a third party on how aesthetically pleasing their designs were. With the estimated
load capacity determined and the aesthetic value of the bridge judged, the bridge was tested until
failure. This was done by knocking a popsicle stick 10” from the left out of the roadbed. A
block with a bucket attached to the bottom of it was placed at the 10” mark. The bucket was
then slowly filled with sand until the bridge ultimately failed. The weight of the bucket filled
with sand was recorded as the load capacity of the bridge (see table 6 for all values).
After the bridge failed a forensic analysis was performed on the wreckage. It was determined
that the main component that failed on the bridge was the roadbed right beneath where the
weight was applied. This is because there was a major lack of bracing beneath the roadbed
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which was a design oversight that wasn’t anticipated. To improve upon this design the only
change that could be made would be to improve the bracing beneath the roadbed. That is the
only change that could be determined from the failure as it is the only component that failed on
the bridge. It is impossible to say if any other component like the bracing, or truss design had
any effect on the bridge failing so easily.
In conclusion the bridge did not perform as well as expected in the load bearing category, but
performed as expected in aesthetic value. The bridge was designed to look cool and have a
unique design so that is why the aesthetic ranking was no surprise. Unfortunately as stated
previously a minor design oversight with the roadbed ended up causing the bridge to fail far
sooner than anticipated. Overall many lessons can be taken away from this project and was very
funny to work with this group to see a project from start to finish.
1.0. Introduction.
Our task for this project was to create an optimal bridge design and then construct
our design using craft sticks and glue. An optimal bridge design is defined as “one that
satisfies all of the design objectives, specifications and constraints; passes a simulated load
test; visually pleasing, practical, and costs as little as possible.” Our project objectives
included designing a conceptual truss bridge, constructing physical prototype of our design,
and documenting the results.
2.0 General Factors for Design.
Many factors went into consideration for the design of our bridge including cost,
load capacity, aesthetics, ease of construction, and site requirements. It was important for our
team to carefully consider all of these factors so that our bridge was within the constraints
providing while also producing a quality bridge.
2.1 Structural Constraints.
Our bridge is going to be put to the test at a specific location, so it is important that all
of the requirements for our bridge are met. The requirements for our bridge were
provided by our instructor: “No part of the bridge may exceed 10-inches above the
end supports or 3-inches below the end supports. The bridge must have a roadway
that can accommodate a 4-inch high by 4-inch wide vehicle. The total outside width
of the bridge must be 5-inches or less. The length of the bridge must be greater or
equal to 30-inches in length, but may not exceed 34-inches in total overall length. The
total bridge must weigh 400 grams or less at the time of loading. The roadway (deck
or travel surface) must be constructed as if wheeled traffic were to cross over its span.
The roadway (deck) is the portion of bridge to be loaded. If you have bridge structure
over the roadway, an opening must be maintained above the loading area on the
roadway to allow the bridge to be loaded. (see figure 2 and 3 for picture reference of
dimensions)
2.2 Construction Constraints.
Our bridge was constructed using craft sticks and Elmer’s glue. Our roadway was
constructed to accommodate a 4-inch high, 4-inch wide vehicle. The roadway (deck)
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must be fully continuous along its width over the entire distance between the supports
(except for a gap exactly 10-inches from where the bridge end supports would be
located, assuming a 29-inch clear span.). No part of the roadway may be greater than
6-inces above or less than 2-inches above the top of the end supports. Craft sticks
used for the roadway (deck) must align normal to the long axis of the bridge. No gaps
shall exist in the roadway (deck) except where natural warping has occurred after
construction of the bridge. Overlapping of bridge deck sticks shall not be allowed.
2.3 Quality Control Testing.
When we had our craft sticks, we inspected each one for its structural integrity and
decided if it was fit to be used in the construction of our bridge. We had also previously
calculated specific information about the craft sticks under certain circumstances as follows: the
weight of popsicle sticks unglued, glued wet, and glued dry. (see table 4 for exact values, and
figure 3,4, and 5 for illustration)
2.4 Aesthetics.
Part of our design specifications was that our bridge must be constructed in a manner
so that it is pleasing to the eye. Our bridge was evaluated by our instructor and other
students for how it rates aesthetically. Part of our constraint is that we are not allowed
to paint or color the bridge, so the aesthetics must come from the design. Our bridge
was ranked the most aesthetically pleasing by the other students.
2.5 Economics.
Our design team was responsible for estimating the cost of our bridge based on how
many craft sticks and how much glue we were going to use and prices assigned to the
craft sticks and glue. The cost of each craft stick was $1,000 and the cost of each
gram of glue was $5,000. For our design, we estimated that we would need 320 craft
sticks and 60 grams of glue, totaling the estimated cost of construction to $620,000.
After the construction of out bridge, we had realized we had over bid because we only
used 20.8 grams of glue and had a significant amount of craft sticks remaining.
3.0 Consideration of Design Alternatives.
An important factor in the entire process was creating multiple designs and then choosing
which design would produce the best bridge. Our alternative design was quite basic overall.
It was a standard Warren Truss with a Pratt Deck. The design fared well in the West Point
Bridge Design software, but we decided as a group that our own twist on a K-Truss Bridge
would be much better.
4.0 Selection of Bridge Design.
The bridge design we chose to use is a slightly modified version of a K-Truss design
combined with own unique design for the bottom chord beneath the road bed. We chose this
design after several hours of thorough testing using the West Point Bridge Design software.
This design passed all of the tests in the software and had great ratings. The total weight of
our bridge was 400g. It cost us $620,000 to construct and the bridge was a simple design and
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was easy to construct. This design was the best choice because it was a simple design and
was the cheapest out of our options.
5.0 Prototype Construction.
The process of prototype construction consisted of the group building the bridge based
off of the design that looked to be not only the strongest, but also the most cost effective, and
aesthetically pleasing. The process started with each individual group member designing a
bridge using the West Point bridge designing software. Then different parts from each bridge
that added to the bridge design criteria listed before was used to create a hybrid of the groups
ideas. With the final design decided upon the amount of popsicle sticks required was estimated
(see table 7), and that amount of popsicle sticks was purchased so construction on the bridge
could start.
The construction process started out with a sketch of the design being drawn on a large
sheet of butcher paper. The sketch was made to scale so that it would be the same size as the
final bridge after construction. Using a sketch as a guide popsicle sticks were laid out on the
paper above the sketch so it was possible to tell which sticks had to be cut down, and where the
different glue joints should be. With the bridge all laid out the actual construction started. First
all pieces that had to be were cut down to the required size. To ensure a strong glue joints all the
popsicle sticks were sanded where the glue would be applied to make sure the contact between
the glue and the sticks was maximized.
The order of construction started with the left face of the bridge. After that side was
built, it was weighed to see if any changes had to be made to reduce weight and keep the bridge
within the guidelines of the project. After weighing the bridge it was determined that no changes
should be made and construction on the right face of the bridge began. Once both faces were
constructed it was time to construct the road bed. This was done by laying out popsicle sticks
flat, then gluing them together to create a large flat surface. Once the roadbed was the same
length as both faces of the bridge, the three individual parts were glued together. After the three
pieces were attached as the plan specified, lateral bracing was added along the top and bottom of
the bridge connecting the two faces. Since there was no actual design for the lateral bracing on
the design, the bracing was applied as found necessary to ensure stability and rigidity of the
bridge.
With the final prototype of the bridge completed, it was weighed on more time to see if it
still adhered to the guidelines. Unfortunately it did not so some last minute changes had to be
made to the bridge. Since there was no area in the design that seemed like it could be changed,
the only solution to the weight problem was to sand down different areas on the bridge to reduce
its total weight. This was troublesome because by sanding the bridge to reduce the weight, the
structural integrity of the bridge was also being compromised. For this reason one part of the
bridge wasn’t sanded more than the rest in an effort to make sure one part would cause all the
failure. Once the bridge was within the range as specified by the constraints, the design was
deemed complete and the bridge declared finished.
6.0 Estimated Load Capacity.
It was first estimated that the bridge could hold above 25 lbs. by meticulous examination
of the stresses and pressures on the parts of the bridge in West Point Bridge Design Software.
After construction of final design, it was decided that the model would not be able to hold more
than 30 lbs. because of difficulties in building a model that is perfectly identical with the design
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shown in West Point bridge design software. The two issues that two sides of the bridge (trusses)
are not exactly symmetrical and the top cord of bridge was warped a little bit in the final model
were what made it able to hold less load capacity than it actually could. Reasonably, a 27.5 lb.
load was picked which is the middle between the extremes of 25 and 30 lbs.
7.0 Prototype Load Testing.
The prototype load testing was a procedure of adding weight to the roadbed until the
entire bride failed. This was so that the total weight the bridge held before failure could be
recorded. The method for testing was to place a block with a bucket attached to it 10” from the
start of the roadbed. One of the group members would then pour sand into the bucket at a
constant rate increasing the load that was on the bridge. The sand was added slowly because
there was a fear that if sand was added too fast it would cause the bridge to collapse faster from
too much weight being dropped on it all at once. After the bridge collapsed the block and bucket
assembly was weighed on a scale and that amount was recorded as the bridges maximum load
capacity.
8.0 Prototype Performance and Forensic Analysis.
During the prototype testing the bridge performed not up to expectations. It failed much
more quickly than anticipated due to a minor oversight in construction. The bridge failed due to
a flaw in construction of the roadbed. The roadbed was not properly supported and eventually
lead to the bridge failing. That being said the failure was by no means catastrophic, nor did the
entire bridge collapse. The area of failure was very much limited to right where the weight was
applied. The point of failure is located along the roadbed right beneath where the weight was
being applied on the roadbed (see fig 7). Besides that area of failure it is hard to determine
where else the bridge may have failed due to the nature of how the bridge collapsed. Since no
other part of the bridge was damaged in failure it is assumed that the only “weak” point of the
bridge would be the roadbed.
9.0 Final Design Performance.
After looking at all the collected data, we determined that our bridge actually fared well
over-all. We came in third for BELC and our initial guess was accurate to what the actual weight
was that caused our bridge to fail. So maybe it was actually a good thing that our bridge failed at
such a low weight because then it wouldn’t have been nearly as accurate. Our load weight was
7th out of 8 teams so in that category we didn’t do too well. However, we did win in the
aesthetics category which is not surprising because we took great pride in our bridges
appearance. In cost we came in 6th which came as a big surprise to us. We used a lot of wood
and a lot of glue even though our bridge failed so quickly. A culmination of all these points
placed in 6th place over all for this particular design project. We have mixed feelings with this
placement. It is not terrible, but if it wasn’t for that roadbed failing we would have done so much
better. This was a fun project and we will take away a lot of useful pieces of information about
teamwork and bridge building.
10.0 Refine the Design.
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In an effort to redesign the bridge to fix the areas where failure took place no major
changes would take place. The only area where the bridge was affected from testing was the
road bed so all the changes would happen there. That being said the only change to the roadbed
that could remedy why the bridge failed would be supports along the bottom of the
roadbed. This is because the roadbed not being supported properly allowed it to fail so by better
supporting the bottom of the roadbed would ensure that that would happen if the bridge was
redesigned. Since no other area of the bridge failed during testing it is hard to determine what
other areas of the bridge could also be improved upon.
11.0 Conclusions and Recommendations.
Ultimately as a group we are all extremely pleased with the overall ascetic look of our
bridge. It is a real shame that several things went wrong. Our bridge was very heavy and
therefore we had to decrease the cross-bracing and couldn’t make it nearly as strong as we
wanted. This is where we thought it was going to initially fail because we couldn’t make it as
strong as we wanted. However, to our surprise it was actually the roadbed was the part of our
bridge that failed. It was a complete lapse of judgment and we almost completely forgot to brace
the bottom. In retrospect we were stupid to forget, but just like real life, mistakes do happen.
12.0 References.
12.1 ANGEL/Lessons/Design Project #1/EDSGN100_Bridge
Building_SOW_Sp2013.doc.
12.2 ANGEL/Lessons/Design Project #1/Final Design Report/EDSGN100_Bridge
Building_Specifications_Sp2013.doc.
12.3 ANGEL/Lessons/Design Project #1/Final Design Report/EDSGN100_Stick
Weights_Sp2013.xlsx.
12.4 ANGEL/Lessons/Design Project #1/Final Design Report/EDSGN100_Bridge
Competition_Sp2013.xlsx.
12.5 West Point Bridge Designer (2011). Developed by Colonel Stephen Ressler,
Department of Civil and Mechanical Engineering, U.S. Military Academy, West Point, NY
<http://bridgecontest.usma.edu/download2011.htm>.
12.6 Virtual Laboratory: Bridge Designer. Johns Hopkins University, Baltimore, MD
<http://www.jhu.edu/virtlab/bridge/bridge.htm>.
Reference of Tables
Table 1: Load Test Results in West Point Bridge Designer
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Table 2: Cost Calculation using West Point Bridge Designer Software
Table 3: Material Specifications in West Point Bridge Designer
Table 4: Stick Weights Under Various Circumstances
Table 5: Bridge
Aesthetics
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Table 6: Bridge Competition Overview
Table 7: Design Team 1 Craft Sticks and Glue Used
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Reference of Figures
Figure 1: Concept Design Using West Point Bridge Designer Software
Figure 2: Strength versus Length Graph from West Point Bridge Designer
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Figure 3: Unglued Sticks: Weight Versus Number of Sticks
Figure 4: Wet Glued Sticks: Weight Versus Number of Sticks
Figure 5: Dried Glued Sticks: Weight Versus Number of Sticks
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Figure 6: Completed Bridge Design
Figure 7: Failure of the Bridge Deck
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