final bridge report
DESCRIPTION
Civil Engineering 2015TRANSCRIPT
2016 NJIT Steel Bridge
Report
Top 10: Take IICE 490 – 203
Written by:Devin Berniz
Introduction
We all know what bridges are and what they look like, but what makes a bridge
successful? A successful bridge will not only get you from point A to point B, but it will also
meet code requirements along with budget requirements and side goals which will vary from
client to client such as aesthetics. In order to design a successful bridge, the first step is to come
up with goals. A bridge can only be as successful as what is trying to be achieved.
Competition
I. Background
The student steel bridge competition is designed to provide a project experience that
replicates issues, concerns and challenges that civil engineers face on a day by day basis in
practice. In order to approach these challenges successfully, students must apply engineering
principles and theory acquired from class and work together as a team effectively. In doing so,
each student will ultimately gain the vital experience of what it is like to complete a project
from start to finish. Steps taken to achieve these goals will consist of designing conceptually
before coming up with a final bridge design that will reach its goal expectations, running several
tests, and then finally bringing the bridge to life through fabrication, erection and running more
tests. As a result, this project experience should give students great insight of the common
issues that engineers face in practice such as spatial restrictions, material properties
(compressive and tensile strength, etc.), management and cost.
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II. Categories
Overall, there are 7 separate categories in which we get scored on. There’s construction
speed, lightness, stiffness, construction economy, structural efficiency, display, and overall
performance. Construction Speed is solely how long it takes to construct the bridge. Number of
builders is irrelevant and the team with the shortest time would place first in this category. The
winner of the lightness category will be the team that designs the lightest bridge without
failing. The next category coincides with lightness, which is stiffness. Stiffness is judged by how
much the bridge deflects or in simpler terms, how much it bends. For this category, it is
imperative to stay as far away as possible from a smiling bridge. The reason why this category is
so tricky is because it clashes with lightness as well. In some cases, a lighter bridge will have
more deflection than a heavier bridge depending on how it is designed. By combining these two
categories, the goal would be to design the lightest bridge with the least amount of deflection,
which is what many schools will end up trying to achieve. The next category on the list is
construction economy. This is one of the two most important categories when it comes to
which school will design the winning bridge. It is determined by who can build a bridge with the
lowest construction cost (Cc) based on an empirical equation. The other equally as important
category is structural efficiency. This particular category is based on who can design a bridge
with the lowest structural cost (Cs). These two categories combined make up the overall
performance category (Cc + Cs), which determines who designs the winning bridge. The bridge
achieving the lowest value of the two categories combined wins the overall competition.
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III. Changes
There are some pretty big alterations to this year’s competition that will influence how
we design our bridge. Although there are a few minor changes, the major changes that will
impact our design the most are the fact that there are six load cases that are asymmetrical
including a constant point load that is slightly offset from the center (Table 7.1). The rules also
indicate that no one will know from which side of the bridge the loads will be measured from,
therefore it’s not as simple as supporting the bridge from where the determination of D is
because we won’t know. However, we were left with the choice of taking a chance and
guessing from which side they will take the measurements and designing a bridge with best
results, or taking the safe route and making a symmetrical bridge that will give the same results
no matter what side is chosen for the measurements of the determination of D.
Another major change that made an impact our design is the fact that the weight of the
bridge has a lesser effect on the final cost of the bridge compared to last year. For this year’s
competition, the structural Efficiency “Cs” = Total weight (pounds) x 10,000 ($/pound) +
Aggregate deflection (inches) x 1,000,000 ($/inch) + Load test penalties (6.2.6), whereas last
year was 20,000 ($/pound). This makes it possible to play with all sorts of tube diameters and
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thicknesses without making too much of an impact on final cost. Many if not all schools will
take advantage of this.
As for the construction side of the competition, there are a few changes that will
strongly impact the speed of construction and we all know that construction speed is always
king and queen of the competition. Therefore we need to come up with a strategy that will
ultimately give us the best results. The changes from last year include the fact that the river
now extended using the whole width of the construction site boundary lines (Figure 1 drawn by
ASCE-AISC). It is because of this reason that there are now two separate starting locations for
the builders as show in the site plan below. This makes it a bit complicated as to how many
builders should be used to give us the best results. As of now, we are thinking two builders on
each side for a total of four builders, but we won’t know what will give us the results we’re
hoping for until practice starts.
Another reason why were are strongly considering 4 builders is because of the fact that
now two members can be preassembled as long as the assembled pieces get carried by two
builders. There is a lot of trial and error to be done with this in order to figure out what the best
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(Figure 1)
approach is. Lastly, they brought the idea of using a pier back into the competition, which will
greatly impact how we construct our bridge, but again, this is all something to be figured out
with trial and error.
NJIT History
NJIT has come a long way since competing in the ASCE-AISC Steel Bridge competition for
roughly 20 years now. It wasn’t always as easy as it has been to earn a spot at the national level
of competing. The Metropolitan Regional Competition was more than enough struggle to make
it a goal just to reach the national level. Throughout the years we have progressed through
setting higher standards, expectations and goals, but most importantly we have learned to
grow as a team.
It has been a decade now that we have been winning 1st place in the Metropolitan
Regional Competition without a sweat. Not only that, but previously our best ranking nationally
was 12th place overall and now we have improved earning ourselves a spot in the top ten
finishing 6th place overall.
Goals & Schedule
Considering that we have won regionals for a decade straight, we definitely want to
continue that tradition. As for competing at the national level, we would like to continue the
path of reaching the very top. The goal is always to progress. We placed 12th place overall
nationally 2 years ago and 6th place last year. Although the ultimate goal is always to get first, it
is our expectation and one of our goals to at least reach a spot in top 5.
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In order to achieve our goals, we must be determined and follow a strict schedule as
follows:
SCHEDULEHave top designs ready to show Schiavone by October
Choose the final design by November
Start working in SolidWorks by November
Get orders for materials sent out before January
Complete Jig and Fabrication Drawings by February
Start of fabrication of the bridge by early February
Finish fabrication by the end of February
Begin Practicing by early March
Design Process
I. Training
There is no time to waste when it comes to designing a winning bridge; and being
determined as we are, we went straight to the lab as soon as we got back from the 2015
national steel bridge competition. Although the rules for the upcoming year’s competition
didn’t come out until August, there was still a lot of work to catch up on in order to get ahead of
the game. Our first step as captains was to familiarize ourselves with drawing in 3D Wireframe
in AutoCAD and designing our own bridges using the previous competition’s rules. Then in
order to analyze the bridges that we designed in AutoCAD, we had to import our CAD drawings
into a program called SAP2000. SAP2000 makes it easier for us to input all load cases and
desired tube sizes for our wireframe drawing of our bridge. We then took all data from the
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tables that SAP2000 provided and imported it into a formulated excel file that converts all of
the data into a final cost of our bridge design. We were able to create this excel file using
formulas listed in the rules for construction cost and structural cost, and then we created our
own empirical formula for building time to be included in the cost to give us an accurate overall
cost of our bridge the way it would be judged at the competition.
II. New Rules
As soon as the rules came out for the upcoming year’s competition, the first thing we
did was point out all of the obvious big changes from the previous year’s competition that
would influence the way we design for this year’s competition. We then took a solid week of
clarifying each word precisely so that we knew exactly the kinds of things that we can get away
to use to our advantage that would either improve our bridge structurally, economically, or
building time. If there were any difficulties interpreting the rules for any reason, we are to
report them, which is why it is vital to check for clarifications of the rules on the “website” on a
day by day basis since it can potentially influence change to our design.
III. Final Bridge Design Process
Once we had a good understanding of the rules and all of our constraints, it was time to
design. Our first approach was to analyze the moment diagram for each load case (Figure 2),
and to overlap them to see what kind of overall shape it would provide.
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0 50 100 150 200 250 3000
10000
20000
30000
40000
50000
60000
70000
Load Case 1Load Case 2Load Case 3Load Case 4Load Case 5Load Case 6
We then took the outermost line of each moment diagram and extended each line so that they
would intersect and provide an overall shape for minimal material use without failure (Figure
2). The next step was to scale the provided shape to the necessary dimensions that would
satisfy our span and height restrictions of our bridge. Since all of the values that we got in the
process of designing our bridge only occur in a perfect world, the only way to take that in
consideration is to manipulate certain values by a fraction of on an inch where necessary, which
serves as a minor factor of safety. These precautions need to be taken so that we don’t get a
failing bridge when competition day comes. After obtaining the overall shape that we would
analyze with further investigations, we came up with various versions of a simple suspension,
Howe, Pratt and Warren truss to see what kind of structure would provide the best results.
After observing that the Pratt and Warren truss provided the best result, we then came up with
preliminary truss designs to do further investigating on (Figure 3).
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(Figure 2)
From our preliminary ideas, design (c) of a warren truss kept providing the kind of results that
we were looking for, but we still knew that there was room for improvement. Since there is a
lot more wiggle room to play with the weight of the bridge compared to last year’s rules, that
left us with a lot for options to play with bigger tubes and the boundaries of our shape, while
still keeping in mind not to add to many more members since construction speed is king and
queen of the overall competition. Our first thoughts to adding weight in a beneficial way were
to extend the outermost diagonal members to a flat top, thus creating a trapezoidal shape
(Figure 4). On top of that, we also toggled with the angles of the outermost diagonals. We
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(Figure 3)
(a)
(b)
(c)
(d)
analyzed results using a 30, 35, 40 and 45 degree angle from the connection at the abutment. A
45 degree angle ultimately gave us our best results while only adding an additional 4 members.
IV. Deck Truss
After being satisfied with the design of our bridge in 2-D, it was time to give it some
volume and add 3 dimensional components such as the deck truss and abutments. Although
the main components of the bridge that influences how much weight a bridge can uphold is the
truss design of the top chord, it wouldn’t be practical to use single tubes for the deck and
abutments. Not only that, but we also had to meet certain template restrictions drawn by
ASCE-AISC (Vehicle Clearance Template/A Section provided on the next page), which gave us no
choice but to make our decking three dimensional. The trick isn’t just to abide by the
restrictions given to us but how to optimize our design in the best ways possible given our
restrictions. For example, we could have made our decking consist of completely horizontal
double tubed members, but why would we do that when we know that the more vertical we
make it, the better. Provided in Figures 5.1 and 5.2 below is the decking design that we feel
comfortable with providing numbers that we are happy with.
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(Figure 4)
(Figure 5.1) (Figure 5.2)
VI. Tubing
Once we were confident with our overall shape and design of our bridge that would give
us the results we were looking for, the next step was to come up with tube sizes that would
optimize our bridge. It isn’t always a guarantee that our supplier has all the sized tubes that we
need in stock, therefore we had to first come up with a list of tube sizes and total lengths
needed to create our bridge and from there we are given a response of which tubes cannot be
provided. In this case we simply just bumped up the diameter and thickness values to a tube
sizing that they can provide just because of the fact that weight doesn’t make as big as an
impact on final cost as it did last year. Although there were cases where we knew we could go
down in size, which we did in order to compensate for all of the other tubes that went up in
diameter and thickness. The thing about going down in size however is followed by more tests
to make sure we don’t go to the point of failure.
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V. Abutments
Once we had a full understanding of our entire bridge in 3-D from the deck up, it was
time to come up with a design for the abutments. Most of the design was influenced by how
the rest of the bridge was designed since the decking and top chord both need to connect to
the abutment. Where we were able to be more so creative instead of depending on the decking
or top chord was the design of the lacing as shown below in Figures 6.1, 6.2 and 6.3.
VII. Fittings
The style of fittings for the bridge we used for last year’s competition seemed to work
really well. We plan on using the same style of fittings for the decking, diagonal, and lateral
members, while also incorporating a different style of fittings that has been used in previous
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(Figure 6.1) (Figure 6.2) (Figure 6.3)
years for the thicker tubing of the top chord (all styles of fittings provided below and on the
following page).
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Top Chord Female
Top Chord Male
Decking Male
VIII. Final Drawings
As soon as our bridge was complete in design form, the only thing left before fabrication
was to come up with a shop drawing of every different member and to define it in a way that
its’ almost like giving instructions on how to create the member. Important information to
provide in these drawing are things such as specific angles, lengths, diameters, thicknesses, etc.
of every component of that member as provided below and on the following page.
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Decking Female
Conclusion
If there is one thing I have learned about the designing aspect of making a bridge is that
there is always room for improvement, but the challenge is to do the best that you can with the
time given to you, while simultaneously making sure to abide by rules/code requirements.
Lucky enough we have three co-captains this year to share all of the responsibilities and tasks
needed to reach our goals, which brings me to another valuable lesson. I have learned and
lived through understanding the difference between having slackers for lab partners in class
and what true teamwork is. I am so fortunate to have the same co-captains that I was a builder
with last year. They understand the kind of hard work that it takes to reach the very top and
what it takes to design a successful bridge. We can proudly say that we have given our design
our best efforts with the time given to us and the only thing left to do is to bring our design to
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life. We understand that many schools will design successful bridges, but who will design the
most successful bridge?
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