Technical Approach. October 27, 2017

(1)

October 27, 2017 Kevin R. Kline, PE, District Executive

PennDOT Engineering District 2-0 1924 Daisy Street - P.O. Box 342 Clearfield 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 1, 2017.

Statement of Problem

. Severe flooding from a 100-year flood event has destroyed a

structurally deficient vehicle and pedestrian bridge over Spring Creek. The destroyed bridge is on a heavily traveled road and is a vital lifeline for vehicle access to the Mount Nittany Medical Center. All traffic has been redirected several miles around the bridge and puts the residents at risk since first responders do not have a direct route to the medical center.

Objective. Pennsylvania Department of Transportation of (Penn DOT) Engineering District

2-0 needs a design for a new vehicle bridge over Spring Creek to replace the bridge by the recent flood event.

Design Criteria

. Penn DOT District 2-0 has established the design criteria for the replacement bridge to include: standard abutments, no piers (one span), deck material shall be medium strength concrete (0.23 meters thick), no cable anchorages and designed for the load of two AASHTO H20-44 trucks (225kN) with one in each traffic lane. The bridge deck elevation shall be set at 20 meters and the deck span shall be exactly 40 meters. Concept designs for both a Warren through truss bridge and a Howe through truss bridge shall be performed by each Design Team. All other design criteria shall be selected by the design team.

Technical Approach

.

Phase 1: Economic Efficiency. Cost will be determined using EEBD 2016 to perform an analysis on the design of a stable warren and Howe truss bridge to keep the cost as low as possible. The cost range of the bridges should be between $150,000 and $300,000. The bridges should be able to safely support their own weight as well as the weight of a standard truck loading.

School of Engineering Design, Technology and Professional Programs 213 Hammond Building University Park, PA 16802-2701

(2)

Phase 2: Structural Efficiency. Prototype Warren and Howe truss bridges were constructed by each design team. These prototypes were built using a maximum of 60 Popsicle sticks, some of which were defective. To bond the members of the prototype brides, white Elmer’s glue was used. Hot glue was allowed to be used to bond the struts and floor beams to each of the trusses. The constructed prototypes had the following dimensions: 13.5 inches in length, 4.5 inches in width, and 4 inches in height.

Each of the prototype bridges were load tested using a bucket suspended from the center of the prototype. More mass was added to the bucket until the weight of the suspended mass resulted in too much stress at some location on the prototype. This would result in a failure of the bridge and the test was over. The ending amount of mass was recorded using a scale and the mass of the prototype bridges were also recorded before the test.

A detailed forensic analysis of the bridges was completed in order to determine why, how, and where each prototype failed. The designs of each were compared using tables and graphs to display each prototype’s results in comparison to one another.

Results

.

Phase 1: Economic Efficiency. While constructing the Warren and Howe bridges, there were difficulties to determine the correct relation of structural efficiency with the highest possible cost efficiency. The Howe Bridge was made of hollow tubes and bars of carbon steel carbon steel which had the greatest price of $314,168.81. While the Warren Bridge had a price of $237,523.48 and made of the same materials at varying sizes. The result of cost analysis of the bridges reveal that the Warren Bridge is $76,645.43 cheaper to construct when compared to the Howe Bridge. More details of the results are discussed in attachment 1.

Phase 2: Structural Efficiency. The structural efficiencies of the Warren and Howe prototype bridges are not the same. The Warren Bridge performed much greater in the testing. The average structural efficiency for the Warren Bridge was 250 in comparison to 278 for the Howe Bridge. This is due to the ability to have many reinforced member due to a smaller amount of bridge attributes needed to construct the Warren Bridge. The Warren Bridge could have multiple Popsicle sticks on each diagonal. This is because the Warren Bridge design does not include any verticals. In contrast, the Howe Bridge consists of many verticals and diagonals. This made it so that with a limited number of Popsicle sticks, the members could not be

reinforced. More details upon the results of the prototypes is discussed in attachment 2.

Best Solution

. The best solution for this project would be the Warren through truss bridge. This decision is based off of the economic, structural, and design efficiencies of the bridges, as well as their constructability.

The Economic Efficiency

The total cost of the Warren Bridge came to $237,523.38 while the Howe Bridge came to $314,168.81. The Warren Bridge cost $76,645.43 less than the Howe Bridge which is a considerable amount.

(3)

The structural efficiency (SE) 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 351 for the SE compared to 207 for the Howe Bridge. There were a total of 8 design teams who submitted data for each of their Warren and Howe through truss bridges. This data was used to calculate the means (250 vs. 278), minimums (175 vs. 176), maximums (409 vs. 546), and ranges (234 vs. 370) of the SE values for the Warren and Howe bridges, respectively. This data can also be found in Tables 7 and 8. The data shows that the Warren through truss bridge designs are more structurally efficient than the Howe bridge designs.

The Design Efficiency

The design efficiency of the bridges is calculated by dividing the total cost of bridge by the Structural Efficiency (SE) of the bridge. The more efficient bridge is determined by how low the number is. The design efficiency of the Warren Bridge is 676.70 while the Howe Bridge is 1,517.72. So, from this data we can conclude that the Warren Bridge is more design efficient.

The Constructability

The constructability of the Warren truss bridge is overall $76,645.33 cheaper than the Howe truss bridge. The materials for the Warren Bridge cost $135,123.48 while the materials for the Howe Bridge is $210,768.81. The connection cost of both bridges is $16,000. This cost is the same due to the number of joints being the same amount. The production cost depends on how many different types of materials (size, types of bars) need to be produced for the construction of the bridge. The production cost of the Warren Bridge is $9,000 which is lower than the production cost of the Howe Bridge at $10,000. The Warren Bridge has the lowest cost in each area of construction when compared to the Howe Bridge. The total constructability of the Warren and Howe bridges are $160,123.48 and $236,768.81, respectively.

Conclusions and Recommendations

. Based on the designs built by the Bridge Designer 2016 computer program and the Popsicle sticks, it is recommended that the replacement bridge be a Warren through truss bridge. The Warren Bridge is more economically efficient than the alternate Howe Bridge, having a total estimated cost of $237,523.48 and a savings of $76,645.33 compared to the Howe truss bridge. It is also structurally more efficient, as well as having a better design efficiency and constructability than the Howe truss bridge. To proceed please place contact SS&T INC for pricing and more details for the project.

Respectfully,

Natally Palma

Engineering Student EDSGN100 Section 002 Design Team 6

Design Team MANZ College of Engineering Penn State University

Alexandra Jung

(4)

Maxwell Lane

Zachary Lazur

(5)

ATTACHMENT 1

Phase 1: Economic Efficiency

Howe Truss

. The conclusion the group came to about the Howe Bridge Design after the cost efficacy and structural efficacy of the Howe Bridge was analyzed. The final design can be observed in figure 1. This was determined using EEBD 2016, and through the load test. The result of the load test of the bridges can be seen in table 2.

The problem related to compression forces affecting the Howe Bridge, was solved by making those areas solid bars of carbon steel. Hollow tubes on the Howe Bridge were found to be inefficient when supporting the bridge. I diameters of tubes were adjusted delicately to areas of bridge they were located at. Due to these differences in size the price of the bridge went up considerably.

When it came to the areas of tension our group had different solution than the

compression areas. Testing the different thicknesses of the bars and tubes, we discovered that we can use less thick bars or hollow tubes to reduce the price in the bridge. Unfortunately that increased the price of the bridge as a whole. If we used different, materials rather than carbon steel we could reduce the diameter of tubes and bars considerably but the cost efficacy would suffer as a result of this alteration.

The Howe Bridge design is completely made of carbon steel in both areas of tension and compression. This gave us optimal efficacy of the Structural and Cost for the bridge. A member detail report of one of these members can be viewed in table 3. If the bars near the center, at the top of the bridge were made any thinner, there would be structural failure near the center given that has to greatest forces acting on it. It goes the same for the bars below the bridge near the center except compression forces would cause them to fail and not tension. Making the tops and bottoms the same materials makes the bridge more economically efficient, as can be seen in table 1, by keeping the members consistent.

Warren Truss

. Once we were done experimenting with the Warren Truss Bridge, a final structural efficient and cost efficient bridge was designed. It can be observed in figure 2, which was done by reducing costs, while still keeping structural integrity in EEBD 2016.

As can be seen in table 5 in areas of compression we used hollow tubes and bars in many different sections of the bridge like the vertical bars were comprised solely of hollow carbon tubes. It required less solid bars for areas of compression but there still were some needed. The bottom chords near the center of the bridge required thick tubes for large compression forces.

While the areas where tension forces were applied many thick bars of carbon steel were required to support the weight of the bridge and the weight of the cargo on it. The top chords near the center and the hip verticals on both side of the Warren Bridge, especially required thicker bars of Carbon steel. This was all done by trial and error to see what the most cost efficient and structural efficient bridge possible. The highest load on a member of the bridge can be viewed in table 6.

(6)

ATTACHMENT 2

Phase 2: Structural Efficiency

Howe Truss

. The design of our Howe Truss consisted of Elmer’s glue and Popsicle sticks. It can be viewed in figures 3 and 4. It had a mass of 0.174 pounds and held a load of 36 pounds. The structural efficiency was calculated by dividing the maximum load by the mass of the bridge. The bridge had a structural efficiency of 207. This result was in the mid to low range of all the teams, but was slightly lower than the average of 278. These values can be seen in figure 7 and table 7.

Prototype Bridge. The Howe Truss Prototype Bridge was constructed using sixty wooden Popsicle sticks. The dimensions of the Howe Bridge were a height of 4, a width of 4.5 and a length of 14.5. All being in inches. The Popsicle sticks were bonded together using white Elmer’s Glue. The glue was given a minimum of a week to cure. Hot glue was used to connect the struts and floor beams. An image of the Howe Truss Prototype Bridge can be viewed in figure 3 and 4.

Load Testing. The Howe Truss Prototype Bridges from all design teams were tested until failure. This procedure was completed by suspending an increasing amount of mass from the center of the bridges. The prototype failed when the load was 36 pounds. This resulted in a structural efficiency of 207. Table 7 displays the mass of the bride, the maximum load, and the structural efficiency. The average structural efficiency for the design teams was 278. The minimum was 176 and the maximum was 546. These values give a range of 370. This displays that the prototypes from the various teams were not exactly consistent with each other. This is because they were all constructed with the same materials but not necessarily made in the same way with the same care.

Forensic Analysis. The prototype bridge broke when a mass of 36 pounds was applied. As seen in figure 4, the wooden Popsicle sticks did not snap. After the bridge was completed it could be seen that it was not symmetric. This caused uneven forces to be applied by the load to each of the trusses. This would have caused a torque to be present upon the bridge, which would apply a greater amount of stress to the glued bonds. After the load was applied, it could be seen that one side of the bridge had a greater force. The glued joints that broke and the bridge twisted in that direction as it fell. Another cause for this could be that the glue was not applied properly and given enough time to cure. Many of the design teams also had the same location of the failure at the glued bonds of the Popsicle sticks. This could be solved if given more time to cure or using another stronger type of glue.

Results. The results of the design teams can be viewed in figure 7 and table 7. The Howe Bridge prototype had a structural efficiency lower than the average for the design teams. Team 3 had the highest structural efficiency of 546 which is significantly higher the average of 278. The structural efficiency of the prototype performed better than three other teams, making this bridge to have results that were in the low to mid-range of all the design teams.

(7)

Warren Truss

. In figures 5 and 6 the Warren truss Bridge prototype made out of popsicles and Elmer’s glue can be observed. The weight of the bridge was 0.188 pounds which held a load 66 pounds. Using these values we calculated the structural efficiency of the bridge was 351 which was over the average of 250. These values can be seen in figure 8 and table 8.

Prototype Bridge. The dimensions of the Warren Bridge were a height of 4 inches, width of 4.5 inches, and length of 13.5 inches. The bridge as a whole was made of 60 Popsicle sticks which were bonded together with Elmer’s glue. After a week to let the glue cure we super glued the floor beams and struts to the trusses we constructed with Elmer’s glue. An image of the prototype can be viewed in figure 5.

Load Testing. The load test that was used on the Warren Bridge prototype was the same as the Howe Bridge prototype. After the test the load failure was 66 pounds with a structural efficiency of 351 and including ours table 8 shows the data from all the design teams. With the smallest structural efficiency value being 175 and the largest being 409 for the different groups. The average structural efficiency for the groups as a whole is 250. When compared with the others groups we did well when creating these prototypes and due to the variety of construction types the teams used the structural efficiencies varied.

Forensic Analysis. After the test on the Warren Bridge prototype was completed the results can be viewed in figure 6. The picture we took shows Bridge shifted and the front floor beam failed at the center as a result. The prototype did not fail immediately, but when more weight was added and stress was added to the joints. Due to the fact not enough time was allowed to pass, the glue was not allowed to set properly at the joints, which would have

resulted in the glue not being able to penetrate fully into the wood. This results in a weaker joint and caused the failure.

Results. The results of the design teams can be viewed in figure 8 and table 8. The Warren Bridge prototype had a structural efficiency lower than the average for the design teams.

(8)

(9)

Table 1 Howe Truss Bridge

Cost Calculation Report from Bridge Designer 2016

Type of Cost Item Cost Calculation Cost

Material Cost(M) Carbon Steel Solid

Bar (23096.2 kg)x($4.30 per kg)x(2 Trusses) = $198,627.41 Carbon Steel

Hollow Tube (963.6 kg)x($6.30 per kg)x(2 Trusses) = $12,141.40 Connection Cost (C) (20 Joints)x(400.0 per joint)x

(2 Trusses) = $16,000.00

Product Cost (P) 2 – 110 x 110 mm

Carbon Steel Bar ($1,000.00 per product) = $1,000.00 2 – 130x130 mm

Carbon Steel Bar ($1,000.00 per product) = $1,000.00 6 – 140x140 mm

Carbon Steel Bar ($1,000.00 per product) = $1,000.00 2 – 140x140x7 mm

Carbon Steel Tube ($1,000.00 per product) = $1,000.00 14 – 150x150 mm

Carbon Steel Tube ($1,000.00 per product) = $1,000.00 4 – 160x160 mm

Carbon Steel Tube ($1,000.00 per product) = $1,000.00 2 – 170x170 mm

Carbon Steel Tube ($1,000.00 per product) = $1,000.00 Site Cost (S) Deck Cost (10 4-meter panels)x($4,700

per panel) = $47,000.00

Excavation Cost (19,400 cubic meter)x($1.00

cubic meter) = $19,400.00

Abutment Cost (2 standard

abutments)x($5,500.00 per abutment) =

$11,000.00

Pier Cost No pier = $0.00

Cable Anchorage

Cost No anchorages = $0.00

Total Cost M + C + P + S $210,768.81 + $16,000.00 +

(10)

Table 2

Howe Truss Bridge

(11)

Table 3

Howe Truss Bridge

Member Details Report from Bridge Designer 2016

Member with the Highest Compression Force/Strength Ratio

(12)

Table 4

Warren Truss Bridge

Cost Calculation Report from Bridge Designer 2016

Type of Cost

Item

Cost Calculation

Cost

Material Cost(M)

Carbon Steel Solid

Bar

(10859.4 kg)x($4.30 per

kg)x(2 Trusses) =

$93,390.53

Carbon Steel Hollow

Tube

(3,312.1 kg)x($6.30 per

kg)x(2 Trusses) =

$41,732.95

Connection Cost (C)

(20 Joints)x(400.0 per joint)x

(2 Trusses) =

$16,000.00

Product Cost (P)

4 – 50x50x2 mm

Carbon Steel Tube

($1,000.00 per product) =

$1,000.00

5- 120x120x6 mm

Carbon Steel Tube

$1,000.00

6- 130x130 Carbon

Steel Bar

$1,000.00

4- 140x140 mm

Carbon Steel Bar

$1,000.00

2- 150x150 mm

Carbon Steel Bar

$1,000.00

4- 150x150x7 mm

Carbon Steel Tube

$1,000.00

4 – 160 x160 mm

Carbon Steel Bar

$1,000.00

4- 180x180x9 mm

Carbon Steel Tube

$1,000.00

4- 200x200x10 mm

Carbon Steel Tube

$1,000.00

Site Cost (S)

Deck Cost

(10 4-meter panels)x($4,700

per panel) =

$47,000.00

Excavation Cost

(19,400 cubic meter)x($1.00

cubic meter) =

$19,400.00

Abutment Cost

(2 standard

abutments)x($5,500.00 per

abutment) =

$11,000.00

Pier Cost

No pier =

$0.00

Cable Anchorage

Cost

No anchorages =

$0.00

Total Cost

M + C + P + S

$135,123.48 + $16,000.00

+$9,000.00+$77,400.00 =

$237,523.48

(13)

Table 5

Warren Truss Bridge

(14)

Table 6

Warren Truss Bridge

Member Details Report from Bridge Designer 2016

Member with the Highest Compression Force/Strength Ratio

(15)

Table 7

Load Testing Results for Howe Truss Bridge

Design

Team

No.

Actual

Bridge

Weight

(grams)

Actual

Bridge Weight

(lbs)

LOAD

At Failure

(lbs)

Structural

Efficiency

1

80.2

0.176

36.0

205

2

82.5

0.182

36.0

198

3

84.0

0.185

101

546

4

83.5

0.184

81.0

440

5

63.9

0.141

36.0

255

6

79.1

0.174

36.0

207

7

93.3

0.205

36.0

176

8

82.1

0.181

36.0

199

Minimum 176

Maximum 546

Range 370

Average 278

(16)

Table 8

Load Testing Results for Warren Truss Bridge

Design

Team

No.

Actual

Bridge

Weight

(grams)

Actual

Bridge Weight

(lbs)

LOAD

At Failure

(lbs)

Structural

Efficiency

1

90.2

0.198

81

409

2

87.8

0.193

51

264

3

78.5

0.173

36

208

4

93.6

0.206

36

175

5

80.6

0.177

36

203

6

85.4

0.188

66

351

7

93.0

0.205

36

176

8

77.4

0.170

36

212

Minimum 175

Maximum 409

Range 234

Average 250

(17)

(18)

(19)

(20)

(21)

(22)

(23)

(24)

(25)