Oct 27, 2016

Kevin R. Kline, PE, District ExecutivePennDOT Engineering District 2-01924 Daisy Street - P.O. Box 342Clearfield County, PA 16830

Dear Mr. Kline:

Reference. PennDOT Engineering District 2-0, Statement of Work, subj: Concept Design for Vehicle Bridge over Spring Creek along Puddintown Road in College Township, Centre County, PA, dated September 2, 2016.

Statement of Problem.

A recent flood event has completely destroyed a vital bridge in Spring Creek along Puddintown Road in College Township in Pennsylvania Department of Transportation (PennDOT) Engineering District 2-0. The destruction causes problem for vehicle access to the Mount Nittany Medical Center. Since all traffic has been restricted around the destroyed bridge, no police or emergency vehicles will be available, which leads to safety concerns for the local residents.

Objective.

Penn-DOT has initiated an emergent project to design a new bridge to replace the destroyed one over Spring Creek.

Design Criteria.

The bridge should have standard abutments, no piers (one span); deck material shall be medium strength concrete (0.23meters thick). There should be no cable anchorages. The bridge is designed for the load of two AASHTO H20-44 trucks (225kN) with one in each traffic lane and the bridge deck elevation shall be set at 20 meters and the deck span shall be exactly 40 meters. Both a Warren through truss bridge and a Howe through truss bridge shall be analyzed; the specific design criteria, such as steel member type and size shall be determined during the design process.

Technical Approach.

Phase 1: Economic Efficiency.

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The cost of the bridge can be calculated by using the Engineering Encounters Bridge Design 2016 systematically depending on the requirements, constraints and performance of the bridge. While ensuring the bridge can hold its own weight and a standard truck loading, the cost needs to be kept as low as possible.

Phase 2: Structural Efficiency.

A prototype for both a standard Howe through truss bridge and a standard Warren through truss bridge shall be built and load tested to catastrophic load failure. Then the structural efficiency can be calculated by dividing the load the bridge supports at catastrophic failure by the weight of the prototype bridge. After the structural efficiency is determined, the bridge that has the best ability to safely dissipate live loads can be recorded and put into construction.

Results.

Phase 1: Economic Efficiency.

As stated in Attachment 1, both of the bridges have the ability to support the two AASHTO H2044 trucks; however, the Howe truss bridge causes $246,681.87 to be constructed while the Warren truss bridge only requires $229,448.15. As a result, the Warren truss bridge has greater economic efficiency.

Phase 2: Structural Efficiency.

As stated in Attachment 2, the range of structural efficiency tested in the load test for the Howe truss bridge goes from 176 to 332 with an average of 245 and a geomean of 238; the range of structural efficiency for the Warren truss varies from 183 to 643, with an average of 361 and a geomean of 365. Since the range, average, geomean of the warren bridge are all higher than those of the Howe Bridge, the Warren Bridge will have great structural efficiency when supporting the same amount of weight.

Best Solution.

The best solution to the problem should be building a new Warren truss through bridge over the Spring Creek. From table 7 and 8, it can be seen that the structural efficiency of warren bridge is greater than that of Howe bridge. The average value of warren bridge is 359.99(SE) while the average value of Howe bridge is 244.41(SE). The geomean value of Warren bridge is 333.99 and that of Howe bridge is 237.30. The design efficiency of Howe bridge is also greater than that of warren bridge as the value of Howe bridge is 1310.6 $/SE and the value of warren bridge is 1260.0 $/SE. Then from table 1 and 4, the total cost of Howe Bridge is $246,681.87; however, the total cost of Warren bridge is $229,448.15. As a result, Warren bridge has more economic efficiency. Additionally, the detailed cost for each part of the construction can also be compared. The material cost for Howe bridge is $142,281.9, which is slightly greater than $131,248.2 for Warren bridge. The connection cost for Howe bridge is $16,000 and $16,800 for the Warren

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truss. Nevertheless, the product cost for Howe bridge is $11,000 and warren bridge costs only $ 4,000. Overall, the constructability of warren bridge is greater than that of Howe bridge.

Conclusions and Recommendations.

When comparing the two bridge types together, a design of a Warren through truss bridge is recommended for a replacement of the destroyed bridge by a recent flood in Spring Creek since it is both more economic efficient and structural efficient. For the next step of advancing the design process, a thorough investigation and analysis of the Spring Creek area should be put into action. In order for the Warren truss bridge to be successfully constructed, numerous factors need to be considered, such as the soil condition, ground components and weather condition of the location where it needs to be built. After all the necessary information is gathered, the project can be finalized.

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Respectfully,

Miaoci ZhangChemical Engineering StudentEDSGN100 Section 001Design Team 8Design Team The Engineering QuartetCollege of EngineeringPenn State University

Haiwen GuanMechanical Engineering StudentEDSGN100 Section 001Design Team 8Design Team The Engineering QuartetCollege of EngineeringPenn State University

Jiao LiuMechanical Engineering StudentEDSGN100 Section 001Design Team 8Design Team The Engineering QuartetCollege of EngineeringPenn State University

Yiwen ShenMath StudentEDSGN100 Section 001Design Team 8Design Team The Engineering QuartetCollege of EngineeringPenn State University

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ATTACHMENT 1Phase 1: Economic Efficiency

Howe Truss.

Listed in attachment 1, the cost calculation of the Howe truss bridge is overall $246,681.87 (table 1). In table 2, the load test report details of the Howe truss bridge can be found. Then the tabulated member detail report is shown in table 3; the data shows that the member that the highest compressive or tension force / strength ratio is over 80% which means there is still some more potential to load more. Then the specific structure of the designed Howe truss bridge can be seen in Figure 1.

Warren Truss.

As it can be seen in attachment 1, the cost calculation of the Warren truss bridge can be found in table 4 which indicates the overall cost of this bridge is $229,448.15. In table 5, the specific load test report of the Warren truss bridge can be viewed and in table 6 the tabulated member detail report is also presented; the data shows that the member that has the highest compressive or tension force / strength ratio is nearly 94% which means the member is significantly close to its supporting limit value. Then the specific structure of the designed Warren truss bridge can be seen in Figure 2.

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ATTACHMENT 2Phase 2: Structural Efficiency

Howe Truss.

Prototype Bridge. The material used in the Howe bridge prototype is wooden popsicle sticks. The method used to build the bridge is to use glue to stick the connecting points and use hot glue to reinforce the structure. The number of Popsicle sticks used is 56. The height of the bridge prototype is 9.7cm, the length is 33.5cm, and the width is 11cm and the structure weighs 77.5 grams (Table 7).

Load Testing. The weight of the prototype is 77.5grams and the load at bridge failure is 32.2lbs (14,586.6grams). The structural efficiency of the Howe bridge prototype is: (Maximum mass supported)/ (Mass of structure) = 189. The minimum structural efficiency of Howe truss among all EDSGN100 design teams is 175, the maximum structural efficiency is 332, and the average structural efficiency is 245.

Forensic Analysis. The main reason of the failure of this Howe truss bridge is because of the unstable two side supports. The whole structure is inclined. When the load is put onto the bridge, the structure of the bridge is inclined to one side and the structure is folded and the connecting points on the bottom chord cannot stand that force, which leads to the failure. The minor reason is that the connecting points of the struts on the top chords were not strong enough to survive the inclination and were broken, which leads to the failure.

Results. The average of the structural efficiencies of the Howe truss bridge is 245; the geomean is 238. The maximum is 332 and the minimum is 176 so the range is 156. (Figure 7 and Table 7)

Warren Truss.

Prototype Bridge. The material used in the Howe bridge prototype is also wooden popsicle sticks. By applying the same method of using white glue to connect each joint together, and using hot glue to reinforce and stabilize the overall structure. The number of Popsicle sticks used is 60. The height of the bridge prototype is 10.3 cm, the length is 36.1 cm, and the width is 11cm and the structure weighs 80.6 grams (Table 8).

Load Testing. The weight of the prototype is 80.6 grams which is around 0.177lbs, and the load at bridge failure is 32.4 lbs. The structural efficiency of the Howe bridge prototype is: (Maximum mass supported)/ (Mass of structure) = 183. The minimum structural efficiency of Howe truss among all EDSGN100 design teams is 183, the maximum structural efficiency is 332, and the average structural efficiency is 643 (Table 8). The structural efficiency of our Warren truss bridge is at the low end comparing to the minimum and average value which indicates some evaluation and analysis have to be done to improve the rather inefficient structure.

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Forensic Analysis. The dominating reason for the Warren truss bridge to fail is the lack of support from the upper beams and the instability of the floor beam. The connecting joints were poorly glued and did not stick to each other, as a result, when the load is put on, the force hits those weak connecting points and split the entire structure apart. As it can be seen from Figure 6, two of the upper beams have completely broken from the structure and two of them were severely distorted from the original position since they were not strong enough to hold the load. Also, the left panel of the Warren truss structure is relatively weaker than the right one, since the right panel did not fall apart. The difference in stability causes the bridge to incline to the weaker side when the load is put one and eventually crushes the structure.

Results. The average of the structural efficiencies of the Warren truss bridge is 460; the geomean is 335. The maximum is 643 and the minimum is 183 so the range is 460. (Figure 8 and Table 8)

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TABLES

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Table 1Howe Truss Bridge

Cost Calculation Report from Bridge Designer 1026

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Table 2Howe Truss Bridge

Load Test Results Report from Bridge Designer 2016

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Table 3Howe Truss Bridge

Member Details Report from Bridge Designer 2016Member with the Highest Compression Force/Strength Ratio

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Table 4Warren Truss Bridge

Cost Calculation Report from Bridge Designer 1026

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Table 5Warren Truss Bridge

Load Test Results Report from Bridge Designer 2016

Table 6

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Howe Truss BridgeMember Details Report from Bridge Designer 2016

Member with the Highest Compression Force/Strength Ratio

Table 7

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Load Testing Results for the Howe Truss Bridge

Table 8Table 8

Load Testing Results for the Warren Truss Bridge

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FIGURES

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Figure 1. Howe Bridge Model from Bridge

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Figure 2. Warren Bridge Model from Bridge

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Figure 3. Howe Truss Bridge Prototype before Load Testing

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Figure 4. Howe Truss Bridge Prototype Failure after Load Testing

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Figure 5. Warren Truss Bridge Prototype before Load Testing

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Figure 6. Warren Truss Bridge Prototype Failure after Load Testing

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Figure 7. Howe Truss Bridge Structural Efficiencies

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Figure 8. Warren Truss Bridge Structural Efficiencies

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