COURTHOUSE WASH PEDESTRIAN BRIDGE MOAB, UTAH
Team
- WYATT HANSEN
- L. KADE FLAKE
- JOSH KERKVLIET
- TRYGVE McCREA
PROPOSAL SUMMARY
Arches Engineering (AE) is a team of four civil engineering students at Utah State University (USU). The team has selected to work in conjunction with Jones and DeMille Engineering (JDE) to design a pedestrian bridge over Courthouse Wash in Moab, Utah. After analyzing the conditions, AE determined a prefabricated steel bridge with a modified bowstring truss style would best suit the 130-foot crossing.
A modified bowstring truss has a relatively low cost, is aesthetically pleasing, and is simple to construct. AE specifies to use a prefabricated bridge to reduce cost and simplify on-site construction. A drilled shaft foundation would best support the bridge over Courthouse Wash. This recommendation is due to the depth of the bedrock and the poor soil conditions. The design phase is anticipated to take 12 weeks and cost approximately $66,500.
ALTERNATIVES
The goal of AE is to implement a cost-effective option to shorten the pedestrian travel time between the Fairfield Inn and future businesses separated by Courthouse Wash. Currently, pedestrian traffic has no constructed option to cross the wash.
Pedestrians must walk farther to future businesses by crossing the bridge on Highway 191. AE considered four alternatives based on the following criteria: pedestrian walking time, overall cost, environmental impact, client’s need, property impact, and aesthetic appeal.
In addition to some alternate routes AE also evaluated other bridge types which included:
- Thrust Arch Bridge
- Beam Bridge
- Truss Bridge
- Suspension Bridge
- Cable-Stayed Bridge
- Timber Bridge
CRITERIA and DECISION MATRIX
Table 1 shows a Pugh Matrix comparing the design criteria to the four alternatives. Scores are assigned for how alternatives meet the design criteria. A score of 0, 1, or 2 represents an alternative poorly meets, somewhat meets, or best meets a design criterion, respectively. The bridge has a total score of 9. The do nothing, stair crossing, and highway crossing alternatives have scores of 3, 4, and 5, respectively. Therefore, the pedestrian bridge alternative best meets the design criteria.
| Decision Factors | Highway Crossing | Stair Crossing | Do Nothing | Bridge |
|---|---|---|---|---|
| Average Pedestrian Walking Time | 0 | 1 | 0 | 2 |
| Overall Cost | 1 | 1 | 2 | 0 |
| Environmental Impacts | 1 | 0 | 1 | 1 |
| Client’s Needs | 1 | 1 | 0 | 2 |
| Impacts to Property | 1 | 1 | 0 | 2 |
| Aesthetics | 1 | 0 | 0 | 2 |
SELECTED ALTERNATIVE
As shown in Table 1, the alternative that best fit the criteria was the pedestrian bridge. Building a bridge will best meet the design criteria for the site. The estimated total cost of construction and installation for Alternative 4 is $444,875, as shown in Table 2. The cost for building the pedestrian bridge is three times more than the next most expensive alternative; however, the other alternatives do not satisfy the design criteria. Therefore, constructing a pedestrian bridge spanning Courthouse Wash is the recommended alternative.
| Item No. | Description | Quantity | Unit | Unit Price | Total Amount | |
|---|---|---|---|---|---|---|
| 1 | Mobilization | 1 | LS | $20,000 | $20,000 | |
| Excavatikon | 2 | Clear and Grub | 55000 | SF | $0.25 | $13,750 |
| Dust Control | 1000 | kGal | $30 | $30,000 | ||
| Geotechnical Analysis | 1 | LS | $10,000 | $10,000 | ||
| Concrete | 12 | CY | $600 | $7,200 | ||
| Steel Reinforcement | 2400 | LB | $1.60 | $3,840 | ||
| Superstructure | 1 | LS | $177,950 | $177,950 | ||
| Install Superstructure | 1 | LS | $25,000 | $25,000 | ||
| Concrete Bridge Deck | 13 | CY | $800 | $10,400 | ||
| Reclamation Seeding | 0.6 | ACRE | $7,000 | $4,200 | ||
| Subtotal | $302,700 | |||||
| Contingency -25% | $75,675 | |||||
| Design Fees | $66,500 | |||||
| Total | $444,875 |
Design
- Superstructure
- A prefabricated steel bridge ensures reduced construction time and cost.
- Designed according to AASHTO LRFD Bridge Design Specifications, 2007.
- A modified bowstring style truss with a weathering finish compliments other pedestrian bridges in the area.
- A concrete deck provides a long service life with little to no maintenance.
- Substructure
- A drilled shaft foundation rests the weight of the bridge and traffic on the bedrock 30 feet below.
- The abutment, wing wall, and approach slab are designed to AASHTO LRFD Bridge Design Specifications, 2007.
TEAM
SPECIAL THANKS
- John Spendlove, PE Jones and DeMille Engineering
- Professor Austin Ball, SE Utah State University
- Professor Joe Caliendo, PhD, PE Utah State University