Name_________________________________ Class_______
Optimization: Building Bridges Scenario
The Problem
The National Bridge Inventory Database shows that there are about 600,000 bridges in the United States (Svirsky 2008). Most of these bridges were built before 1994 and maintenance of these aging bridges is a significant cost—oftentimes higher than the cost to construct the bridges themselves. The actual direct cost of corrosion for highway bridges is estimated to be about $8 billion (Yunovich et al. 2000). Because of these high maintenance costs, the government carefully scrutinizes the design, construction, and corrosion prevention of new bridges, including three slated to be constructed in Florida, Minnesota, and Arizona.
Your Task
In this activity, you will assume the role of scientist, engineer, construction worker, and so on, specializing in corrosion prevention. Using concepts learned from previous lab activities along with the supplemental data and information provided or your own research, you will decide upon the materials (rebar and coating) to be used in the construction of these three new bridges. As you select the materials, you will need to consider the rust-protecting ability, lifetime, and cost of the materials, along with the environment in which the bridge is built.
Procedure
1. Table 1 below contains important information about the locations where each of the bridges will be built. Review this information, considering how these details may influence the types of materials necessary for construction of a bridge in the area.
Table 1:
Environmental information concerning the location of future bridges.
Note: Values based
on yearly high and low temperatures for example cities (The Weather Channel Inc.
2008)
|
|
BRIDGE #1* |
BRIDGE #2 |
BRIDGE #3 |
|
Location |
Key Largo,
Florida |
Duluth,
Minnesota |
Tucson,
Arizona |
|
Average Temp Range |
11 – 36 deg C |
-36 – 27 deg
C |
4 – 47 deg C |
|
Humidity |
High
(60-100%) |
High
(60-100%) |
Very Low
(<20%) |
|
Winter Conditions |
No snow or
freezing temperatures |
Highest
snowfall of any U.S. city |
No snow or
freezing temperatures |
|
Required Lifespan |
40 years |
70 years |
100+ years |
*Processed (salt-free) sand will be used to mix the concrete.
2. Review the information in Table 2 below, which provides information about the possible types of corrosion-control rebar available for construction of the new bridges.
Table 2: Summary of
costs and life expectancy for steel-reinforced concrete.
|
Type of rebar/inhibitor |
Cost of bar ($/kg) |
Cost per deck area ($/m2) |
Increase in cost compared to
as-rolled rebar ($/m2) |
Estimated service life (years) |
|
As-rolled |
$0.44 |
$11.60 |
Baseline – 0 |
10 |
|
Epoxy-coated |
$0.66 |
$17.40 |
$5.80 |
40 |
|
Solid
stainless steel |
$3.85 |
$101.64 |
$90.04 |
75-120 |
|
Stainless
steel clad |
$1.54 |
$40.66 |
$29.00 |
50 |
|
Galvanized |
$1.00 |
$26.40 |
$14.80 |
40 |
|
Calcium
nitrate inhibitor |
N/A |
N/A |
$5.40 |
30 |
|
Silica fume
inhibitor |
N/A |
N/A |
$4.30 |
20 |
3. Using the information from Tables 1 and 2, along with your previous knowledge, determine what type of rebar and coating should be used in the construction of each of the three bridges. Be sure to consider the cost-effectiveness of the materials and what you already know about environmental effects on corrosion.
Assessment
Your group must write a three-paragraph statement to your supervisor summarizing your choice of building materials for each bridge (one paragraph per bridge). Be sure that your group includes the reasons for your choices. Your statement should convince your supervisor that each bridge will be safe, rust-protected, and economically reasonable given its location.