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March 29 , 2017

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 February 2, 2017.

Statement of Problem. A recent 100 year flood has destroyed a structurally deficient bridge located over Spring Creek, located near Puddintown Road in College Township, Centre County PA. This bridge provided vital access to the Mount Nittany Medical Center for residences, and hinders first responders as a 10 mile detour is required due to destruction of the bridge.

Objective. Pennsylvania Department of Transportation of (PennDOT) Engineering District 2-0 requires a new bridge design to replace the one destroyed by the flood.

Design Criteria. PennDOT District 2-0 requires that the bridge must include: standard abutments, no piers (one span), deck material shall be medium strength concrete (.23 meters thick), no cable anchorages and designed for the load of two AASHTO H20-44 trucks (225kN) with one in each traffic lane. The deck elevation of the bridge must be 20 meters and the deck span must be exactly 40 meters. There must be a design for both a Warren and Howe truss bridge.

Technical Approach.

Phase 1: Economic Efficiency. To ensure economic efficiency, design teams will use the Engineering Encounters Bridge Design 2016 (EEBD 2016) software to test the different bridge designs based on requirements, constraints, and performance criteria. The objective is to keep the cost as low as possible, far below $300,000 while still remaining structurally efficient.

Phase 2: Structural Efficiency. A prototype shall be designed for both a standard Warren and Howe truss bridge. Both bridges will be constructed of a maximum of sixty standard Popsicle sticks, Elmer’s white glue, and hot glue to attach the eight struts. Upon completion, the bridges will be tested by in the lab to catastrophic failure. The truss bridge that exhibits the best structural efficiency shall be determined by the amount of load it can carry. 1 | Page

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School of Engineering Design, Technology and Professional Programs

213 Hammond Building

Structural efficiency can be calculated by dividing the load the bridge supports at catastrophic failure by the weight of the prototype bridge. The designs of each were compared using tables and graph to display each bridge’s results.

Results.

Phase 1: Economic Efficiency. When designing both bridges, there was difficulty designing a bridge that was both inexpensive and structurally efficient. In order to do this, the Warren Bridge was constructed using carbon steel, which is cheaper than high tempered steel. In order to cut costs, bars were replaced by tubes which drastically decreased the overall price. Tubes can be used in places where there is not an overly large net force acting upon the member. It increases cost efficiency in relation to its structural efficiency. The Howe Bridge was constructed of carbon steel, which is cheaper but not as strong. Bars were also replaced in some parts by tubes. Overall, the results of the cost analysis of the bridge show that the Warren Bridge is cheaper to construct by approximately $37,000 than the Howe Bridge. More details of the results are discussed in attachment 1.

Phase 2: Structural Efficiency. There was a significant difference in the structural efficiency of the Howe and the Warren bridges. In testing, the Howe bridge performed much better than the Warren. The average structural efficiency was 316 for the Howe, versus an average structural efficiency of 266. This is largely a result of the fact that the Howe included verticals, which offered more support for the bridge. The Warren only had diagonals, and therefore the leftover popsicle sticks could be used as a reinforcement for the diagonals. However, this was not as effective as the additional support that came from having verticals and diagonals, as utilized in the Howe bridge design. Further details of the prototypes are discussed in attachment 2.

Best Solution. The best solution for this project is the Howe through truss bridge based on many factors including economic efficiency, structural efficiency, design efficiency, as well as constructability of the bridges.

The Economic Efficiency

The total cost of the Warren through truss bridge is $224,033 while the total cost of the Howe through truss bridge is $261,937.06. The Warren Bridge costs $37,904.06 less than the Howe Bridge.

The Structural Efficiency

The structural efficiency of the bridges is calculated by dividing the mass of the load at failure by the mass of the bridge. The Warren Bridge scored a 222 for structural efficiency compared to 393 for the Howe Bridge. There were a total of 6 design teams who submitted their bridge designs for both the Warren and Howe. This data was used to calculate the means (266 vs. 316), geometric means (258 vs. 305), minimums (174 vs. 233), maximums (378 vs. 467), and ranges (204 vs. 234) of the SE values for the Warren and Howe bridges, respectively. This data can also be found in Tables 7 and 8. This data

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shows that the Howe through truss bridge designs are overall much more structurally efficient than the Warren Bridge designs.

The Design Efficiency

The design efficiency of the Howe bridge was 666.50($/SE), whereas the design efficiency of the Warren bridge was 1,0009.16($/SE). The Howe bridge had a substantially better design efficiency than the Warren bridge.

Constructability

The constructability of the Warren truss bridge is overall $37,904.06 cheaper than the Howe truss bridge. The materials for the Warren Bridge cost $117,833 while the materials for the Howe Bridge cost $159,537.06. The connection cost of the Warren Bridge is $16,800 compared to $16,000 for the Howe Bridge. This cost is overall higher due to the connections of more joints in the bridge. The production cost depends of how many different type of materials used (size and types of bars) that need to be produced in order to successfully complete the construction of the bridge. The production cost for the Warren Bridge is $12,000 while the production cost for the Howe Bridge is $9,000. The total constructability of the Warren and Howe Bridges are $146,633 and $184,537, respectively.

Conclusions and Recommendations. As a result of the testing through both the Bridge Designer computer program and the popsicle stick prototypes, it is recommended that the bridge to replace the one destroyed by the 100-year-flood event should be a Howe truss bridge. Economically, the Howe was $37,904.06 more expensive than the Warren bridge, with the Warren also having a better constructability. However, the Howe was significantly lower in price than the $300,000 limit, coming in at a price of $261,937.06. The Howe was also much more structurally efficient than the Warren, and had a better design efficiency. Because the Howe is a safer, more stable, and structurally efficient bridge, it is the preferred design over the cheaper Warren bridge. Overall, the design team came to the conclusion that the structural efficiency of the bridge was a more important factor to consider than economic efficiency, due to the 100-year flood.

Respectfully,

Eric LopezEngineering StudentEDSGN100 Section 001Design Team 6This is Howe We Do ItCollege of EngineeringPenn State University

Eric JohnsEngineering StudentEDSGN100 Section 001Design Team 6This is Howe We Do ItCollege of EngineeringPenn State University

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Brianna BannisterEngineering StudentEDSGN100 Section 001Design Team 6This is Howe We Do ItCollege of EngineeringPenn State University

Tim HoganEngineering StudentEDSGN100 Section 001Design Team 6This is Howe we do itCollege of EngineeringPenn State University

Doug PisarekEngineering StudentEDSGN100 Section 001Design Team 6This is Howe we do itCollege of EngineeringPenn State University

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ATTACHMENT 1Phase 1: Economic Efficiency

Howe Truss. In order to design our Howe Truss bridge in the most economically sound way while ensuring to complete our objective, we used EEBD 2016 to conduct multiple trial and error load tests, reducing costs in all ways possible while avoiding catastrophic failure. The final minimum safe price that we reached can be viewed in Table 1 alongside the load test results of the purchased beams in Table 2.

The most significant expense was purchasing the materials for the bridge, specifically the carbon steel solid bar. The solid bar cost around $2 less per kilogram than the carbon steel hollow tube and could also bear more weight which led us to purchasing around 3,000 more kilograms of it, driving up the cost. Team 6 tended to use the less expensive tube bars to deal with the compression forces while spending more on the solid bars to counter the tension forces.

The group further lowered costs by reducing the diameter of the stronger solid bars making up the bottom chords and verticals while increasing the diameter of the hollow bars constructing the end posts, top chord, and compression bearing diagonals. The team found that the bridge would most likely fail somewhere within 4 beams of the bottom chord which may be observed in table 3. This failure can be predicted because these relatively smaller diameter carbon steel solid bars have the greatest force to strength ratio, experiencing massive tension while neither being reinforced with a thicker diameter nor higher quality steel.

Warren Truss. In order to design our Warren Truss bridge in the most economically sound way while ensuring to complete our objective, we used EEBD 2016 to conduct multiple trial and error load tests, reducing costs in all ways possible while avoiding catastrophic failure. The final minimum safe price that we reached can be viewed in Table 4 alongside the load test results of the purchased beams in Table 5.

The most significant expense was purchasing the materials for the bridge, specifically the carbon steel solid bar. The solid bar cost around $2 less per kilogram than the carbon steel hollow tube and could also bear more weight which led us to purchasing around 7,000 more kilograms of it, driving up the cost. Team 6 tended to use the less expensive carbon steel hollow tube bars in order to deal with areas experiencing both tension and compression forces at the same time but at smaller magnitudes(typically experiencing under 500 Newtons) while spending more money on the carbon steel solid bars to account for the larger magnitude forces(typically over 1,500 Newtons) that are specific to either tension or compression

The group further lowered costs by reducing the diameter of both the stronger solid bars making up the bottom chords, top chords, and end posts and of the hollow bars constructing the diagonals. The beam with the greatest force to strength ratio can be observed in table 6.

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ATTACHMENT 2Phase 2: Structural Efficiency

Howe Truss. The Howe Truss Prototype was designed and built using sixty popsicle sticks and white PVC glue. It is displayed pre and post test in figures 3 and 4 respectively. It had a mass of 0.168lbs. and the maximum load it held was 66 lbs. By dividing the maximum load and the mass, the structural efficiency can be found. In this case, the structural efficiency is 393 which was the second highest amongst the design teams (see table/figure 7).

Prototype Bridge. The Howe Truss Prototype Bridge was constructed using sixty wooden Popsicle sticks. 26 were used for each side of the truss bridge leaving 8 to be used as struts, 4 on the top and 4 on the bottom. The dimensions of the bridge were 4 inches in height, 4.5 inches in width, and 13.5 inches in length. The popsicle sticks were attached to one another using white PVC glue, and were given a multiple weeks to cure. The struts were connected to each side of the truss using hot glue that was applied the morning of the test. The truss prototype can be seen pre and post testing in figures 3 and 4 respectively.

Load Testing. The Howe Truss Prototype Bridges from all design teams were testeduntil failure. This test was administered by placing the truss over a gap and slowly adding weight until the bridge failed. The prototype failed when the load was 66.0 lbs. This resulted in a structural efficiency of 393. Table 7 shows the data used to calculate the structural efficiency including the mass of the truss prototype, the maximum load held, and the structural efficiency of every design team. The average structural efficiency was 316 with the maximum being 467 and the minimum being 233. Which results in a range of 234.

Forensic Analysis. The Howe Bridge prototype held a load of 66.0 lbs. before failing. The failure occurred when the hot glue joints connecting the top struts on the left side of the truss broke causing the truss to lean to its side (see Figure 4). It can be determined that the hot glue joints broke for two reasons. The first reason is that the bridge was not entirely symmetrical. This was discovered when the truss was placed on the testing block and did not sit entirely flat. This unevenness would have cause more torque on the joints, causing them to break in that fashion. The second reason is that our hot glue joints were just recently applied, and we did not let the hot glue fully cure before we had it tested.

Results. The results of the different design teams can be seen in both figure and table 7. The Howe Bridge prototype had a structural efficiency of 393 which was higher than the design team average of 316. This structural efficiency of 393 was greater than every other design team save design team 5, who had a prototype with a structural efficiency of 467.

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Warren Truss. The Warren Prototype was designed and built using sixty popsicle sticks and white PVC glue. It is displayed pre and post test in figures 5 and 6 respectively. It had a mass of 0.162lbs. and the maximum load it held was 36lbs. By dividing the maximum load and the mass, the structural efficiency can be found. In this case, the structural efficiency is 222 which was the second lowest amongst the design teams (see table/figure 8).

Prototype Bridge. The Warren Truss Prototype Bridge was constructed using sixty wooden Popsicle sticks. 26 were used for each side of the truss bridge leaving 8 to be used as struts, 4 on the top and 4 on the bottom. The dimensions of the bridge were 4 inches in height, 4.5 inches in width, and 13.5 inches in length. The popsicle sticks were attached to one another using white PVC glue, and were given a multiple weeks to cure. The struts were connected to each side of the truss using hot glue that was applied the morning of the test. The truss prototype can be seen pre and post testing in figures 5 and 6 respectively.

Load Testing. The Howe Truss Prototype Bridges from all design teams were testeduntil failure. This test was administered by placing the truss over a gap and slowly adding weight until the bridge failed. The prototype failed when the load was 36.0 lbs. This resulted in a structural efficiency of 222. Table 8 shows the data used to calculate the structural efficiency including the mass of the truss prototype, the maximum load held, and the structural efficiency of every design team. The average structural efficiency was 266 with the maximum being 376 and the minimum being 174. Which results in a range of 202.

Forensic Analysis. The Warren Bridge prototype held a load of 36.0 lbs. before failing. The failure occurred when the PVC glue joints connecting the diagonals on the left side of the Truss broke apart causing a catastrophic failure. (see Figure 6). It can be determined that the glue joints broke due to poor application of the glue because the glue was given over a week to cure.

Results. The results of the different design teams can be seen in both figure and table 8. The Howe Bridge prototype had a structural efficiency of 222 which was lower than the design team average of 266. This structural efficiency of 222 was lower than every other design team save design team 5, who had a prototype with a structural efficiency of 174.

Enclosures. Tables Nos. 1 through 8 and Figure Nos. 1 through 8 are attached.

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TABLES

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Table 1Howe Truss Bridge

Cost Calculation Report from Bridge Designer 2015

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Table 2 Howe Truss Bridge

Load Test Results Report from Bridge Designer 2015

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Table 3 Member Details Report from Bridge Designer 2015 for the Howe Truss Bridge Member with

the Highest Compression (or Tension) Force/Strength Ratio


Table 4 Cost Calculation Report from Bridge Designer 2015 for the Warren Truss Bridge


Table 5 Load Test Results Report from Bridge Designer 2015 for the Warren Truss Bridge


Table 6 Member Details Report from Bridge Designer 2015 for the Warren Truss Bridge Member

with the Highest Tension (or Compression) Force/Strength Ratio


Table 7 Load Testing Results for the Howe Truss Bridge

Design Team No. Actual Bridge Weight (gms)

Actual Bridge Weight (Lbs)

Load At Failure (Lbs)

Structural Efficiency

1. 83.4 0.184 58.5 318

2. 84.6 0.187 43.5 233

3. 65.3 0.144 36.0 250

4. 83.6 0.184 43.5 236

5. 69.0 0.152 71.0 467

6. 76.2 0.168 66.0 393

Min: 233

Max: 467

Range: 234

Average: 316

Geometric Mean: 305


Table 8 Load Testing Results for the Warren Truss Bridge

Design Team No. Actual Bridge Weight (gms)

Actual Bridge Weight (Lbs)

Load At Failure Structural Efficiency

1. 78.7 0.174 43.5 250

2. 91.2 0.201 76.0 378

3. 54.9 0.121 21.0 174

4. 86.7 0.191 58.5 306

5. 74.2 0.164 43.5 265

6. 73.5 0.162 36.0 222

Min: 174

Max: 378

Range: 204

Average: 266

Geometric Mean: 258


FIGURES


Figure 1. Howe Truss Bridge from Bridge Designer 2016


Figure 2. Warren Truss Bridge from Bridge Designer 2016


Figure 3. Howe Truss Bridge Prototype before Load Testing


Figure 4. Howe Truss Bridge Prototype Failure after Load Testing


Figure 5.Warren Truss Bridge Prototype before Load Test


Figure 6. Warren Truss Bridge Prototype after load Test


Figure 7. Howe Truss Bridge Structural Efficiencies


Figure 8. Warren Truss Bridge Structural Efficiencies


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