APSC 200: P2 Final REport

Dr. B.H. Keuper, Ph.D., P.EngDepartment of Civil Engineering  Ellis Hall  Queen’s University  Kingston, ON  Dear Dr. Keuper,

Bridge Street & Co would like to extend our gratitude to your company for awarding our firm the contract of designing a bridge for the dog park. Our firm is proud to present to you a design for a safe and functional bridge for the park.

Bridge Street & Co had 4 specialists working on this design for your company. Alexander Toulany was the technical specialist, and is experienced in using Solid Edge software which was used to model and evaluate the preliminary designs, and the final product. Josh Riseling was the construction and finance manager. Josh has extensive experience working with engineering firms and is knowledgeable about the economic costs associated with projects such as these, and will be an asset in this design process. Marcos Rohr was the design and materials specialist. Having attended St. Lawrence College he has an extensive knowledge base on AutoCad and has hands on experience designing and evaluating Civil Engineering projects. Victoria Blake was the resource manager and environmental specialist whom has experience in the environmental sector which is important in evaluating the long term effects of this project.

In the following report, you will find details outlining the design process, and the total cost of the proposed bridge for your park. There is also a detailed model of the prototype enclosed.

Again, the firm would like to thank you for the opportunity to work with you, and we encourage you to contact us regarding any questions you may have about our final design.

Bridge Street & Co.

125 Main Street, King City, OntarioR4Y 6A7

Honesty Statement

Our signatures below attest that this submission is our original work.

Following professional engineering practice, we bear the burden of proof for original work. We have read the Policy on Academic Integrity posted on the Faculty of Engineering and Applied Science web site (http://engineering.queensu.ca/policy/Honesty.html) and confirm that this work is in accordance with the Policy.

Individual 1:

Signature: ______________________________ Date: December 6th, 2015

Name : Alexander Toulany ID # :10129734

Individual 2:

Signature: ______________________________ Date: December 6th, 2015

Name : Josh Riseling ID # :10148643

Individual 3:

Signature: ______________________________ Date:December 6th, 2015

Name : Marcos Rohr ID # : 10175849

Individual 4:

Signature: ______________________________ Date: December 6th, 2015

Name :Victoria Blake ID # :10090138

Space below is for a table showing which portions of this report each individual made a significant contribution toward.

Content

Identify here the sections of the report for which you personally contributed content.

Write-up

Identify the sections of the report that you personally wrote or edited.

EditingIdentify the sections of the report that you personally edited.

Individual 1

Background information, model drawings, internal force calculations, final design assessment

Background information, model drawings, internal force calculations, final design assessment

General editing

Individual 2

Problem Definition, Project Scope Design Criteria, Project Economics, Social and Environmental Considerations, Final Design

Problem Definition, Project Scope Design Criteria, Project Economics, Social and Environmental Considerations

General editing

Individual 3

Design Selection, Conclusions and Recommendations

Design Selection, Conclusions and Recommendations

General editing

Individual 4

Stakeholder needs, Cover letter, executive summary, background information, safety, creative thinking, Design Criteria

Stakeholder needs, Cover letter, executive summary, background information, safety, creative thinking, Design Criteria

General editing

Executive Summary

Bridge Street & Co was tasked with designing, building and testing a timber bridge to allow pets to cross a narrow stream in a park. The firm created a preliminary design and proposed a cost structure for the project. The team then improved on the preliminary design in many ways and compiled a comprehensive plan to build the prototype. The bridge was required to be at least 8 feet long, and have a width between 8 inches and 1 foot. The maximum height of the structure was permitted to be 1.5 feet. It was assumed that the bridge would be standing on strong ground supports on each end when implemented in the park. During the testing process of the bridge, it was evaluated based upon the deflection at the midpoint, the weight of the bridge before loading, and the cost of materials used in building the bridge.

Because the bridge will be used by pets, it is important to the owners of the pets, and the pets themselves that the bridge is safe. The owner of the dog park is also a major stakeholder of the project, as the performance of the bridge will directly impact the customer satisfaction. Bridge Street & Co, along with the Civil Engineering department of Queen’s University are also stakeholders, as their reputation is at stake.

Bridge Street & Co. conducted thorough research on typical timber bridge structures, qualities of wood and jointing methods of timber members to create a preliminary design using a warren truss and gusset joints. This design consists of two truss members on each side, connected by horizontal bars and covered in thin plywood to create a smooth surface for patrons to walk on. An internal force analysis was conducted for the preliminary design, identifying the members in tension or compression. Based on this model, vertical supporting members were added to the trusses and gusset plates were added to the joints.

An economic analysis was compiled for the project, and included the cost of materials, cost of labour and any other ancillary costs that the team required during the design process. The preliminary estimate was quoted at $8072.20, but the final cost of the project was slightly under budget at $7460.50.

The firm spent approximately 6 hours per week on this project during the prototyping weeks, and spent additional time in the workshop in the last days leading up to testing. Each member of the firm contributed equally to each of the reports, based on their self-identified strengths.

ContentsExecutive SummaryiList of FiguresivList of Tablesv1Introduction11.1Problem Definition11.2Project Scope12Stakeholder Needs12.1Pet Owners and Pets12.2Park Owner and Employees12.3Civil Engineering Department22.4Local Environment22.5Bridge Street & Co. Engineering Firms23Background Research23.1Truss Design23.1.1Warren Truss33.1.2Pratt Truss33.1.3Howe Truss33.2Types of joints43.2.1Lap Joints43.2.2Gussets43.2.3Notched Joint53.3Properties of wood54Design Criteria64.1Size and Strength64.2Materials64.3Cost64.4Environmental Impact64.5Aesthetics64.6Safety75Design Drafting75.1Creative Thinking75.2Concept Selection76Social and Environmental Considerations96.1Environment96.2Society97Safety Considerations108Project Economics109Final Design129.1Testing and Results149.2Assessment of Design to Project Metrics159.2.1Materials159.2.2Dimensions159.2.3Safety159.2.4Time159.2.5Weather Resistant169.2.6Pet Friendly169.2.7Aesthetically Pleasing1610Recommendations and Conclusions1611Works Cited1812Appendix A – Gantt Chart1913Appendix B – Calculations for Internal Forces20

List of Figures

Figure 1: Components of a Truss Bridge [3]3

Figure 2: A Warren Truss Pattern [5]3

Figure 3: A Pratt Truss Pattern [6]3

Figure 4: A Howe Truss Pattern [7]4

Figure 5: Examples of lap joints used in timber bridges. [8] [11]4

Figure 6: An example of gussets on a roofing truss. [9]4

Figure 7: A notched joint for T shaped members [8].5

Figure 8: Compression forces acting parallel and perpendicular to grain5

Figure 9: Orthographic and Isometric View of the Initial Proposed Design8

Figure 10: Typical joint connections using I-beams and gusset plates.8

Figure 11: End of truss showing the additionally wooden piece on the bottom of the truss9

Figure 12: Isometric and Orthographic View of Final Design13

Figure 13: Internal Forces Represented in Each Truss Member14

Figure 14: The prototype bridge during testing14

List of Tables

Table 1: Materials Cost Breakdown11

Table 2: Design and Labour Cost Breakdown12

APSC 200: P2 Final Team 4 | i

IntroductionProblem Definition

For some pets crossing a small stream can be difficult and unsafe. In order for the pets to cross this stream, the safest solution is to build a bridge. The Department of Civil Engineering at Queen’s University has requested that a timber bridge for pets be designed and constructed to cross a small stream in a park for pets. The design of the bridge should provide a new path for pets up to and including 55 kg in weight to cross the small stream safely, however to maintain a safe design the bridge should be able to withstand more massive loading. The societal goal of this project is to provide a new path to cross the small stream in the pet park, while the environmental goal is to have as little negative impact as possible.

Project Scope

The firm has been tasked with designing and constructing a small bridge for animals. The team will estimate and keep track of the economic costs of the construction of the bridge, which includes the labour to build the bridge and the time that it takes to design and test it. The materials to construct the bridge were financed and provided by the Queen’s University Civil Engineering Department. The entire bridge must occupy a minimum of 8 feet in length, and no more than 1 foot in width and 1.5 feet in height. The team has made the assumption that the bridge is to be built in a park for pets only, and is not required to be able to support the full body weight of a person. The team has also made the assumption that maintenance and upkeep of the bridge will be handled by an external body.

Stakeholder NeedsPet Owners and Pets

Assuming that this bridge is intended to be installed in a dog park, the pets and their owners are a major stakeholder in this project. The pets will be using the bridge directly so the bridge should be safe and be able to carry the expected loading of pets on the deck of the bridge. Since the pet owners are directly responsible for their pets at the park, the bridge should not harm the pets in any way and should enhance their experience at the park.

Park Owner and Employees

The park owner and any maintenance workers of the park will be held accountable for any damages caused to the bridge. The design should be sturdy and be protected from the elements so it will be able to last outdoors and require as little maintenance as possible. All pieces should be securely attached so that nothing will fall off and jeopardize the safety of the patrons, or negatively influence the pets’ or owners’ experience at the park.

Civil Engineering Department

The Civil Engineering Department has awarded the firm with the task of designing the bridge, which also adds them as a primary stakeholder. Although the firm is ultimately be held accountable for the design, the Department’s reputation may be at stake if it is dysfunctional. The bridge should be made with care to ensure a quality product for the client.

Local Environment

The local environment will also be directly influenced by this project. It’s possible that the bridge may alter the flow of the natural environment surrounding the bridge. If any parts of the bridge are toxic or will dissolve in water it has the potential to affect the aquatic life in the river beneath the bridge. Every effort should be made to ensure that the natural environment is not negatively influenced by this bridge.

Bridge Street & Co. Engineering Firms

Lastly, an important stakeholder in this project is the firm itself. Since the firm is very young and has only formally completed one design project together, the reputation of the company is at stake. If the project is designed poorly, the Civil Department may not award the team another contract in the future. The firm will create a cost effective, sustainable bridge to uphold our reputation.

Background ResearchTruss Design

As defined by Michael A. Ritter, “Trusses are structural frames consisting of straight members connected to form a series of triangles,” [1]. Trusses contain no external loading; they are only connected and loaded on the supports at the end of each truss. As a result, these members only contain axial forces in tension or compression [2].

Figure 1 shows the various components involved in designing a truss bridge. Some of these components include struts connecting the upper vertices of each truss member, lateral bracing diagonally connecting the struts, and stringers and floor beams to support the deck [3].

Figure 1: Components of a Truss Bridge [3]

Warren Truss

Warren Trusses are characterized by a series of equilateral triangles spanning the length of the bridge, shown in Figure 2. Sometimes, vertical trusses are added within the triangles to increase the span of the bridge [4]. Diagonal loads are subject to both compressive and tensile internal forces. The direction of these internal forces alternates between diagonal members.

Figure 2: A Warren Truss Pattern [5]

Pratt Truss

A Pratt Truss is classified by, “…having its diagonal members (except the end diagonals) slanted down towards the middle of the bridge span,” [4] as shown in Figure 3. Tension is experienced in diagonal members while compression is experienced in vertical members [4].

Figure 3: A Pratt Truss Pattern [6]

Howe Truss

Similar to the Pratt Truss, the Howe Truss is defined as having its diagonal members slanted up towards the middle of the bridge, as seen in Figure 4 [4]. Compression is experienced in the diagonal members while tension is experienced in vertical members [4].

Figure 4: A Howe Truss Pattern [7]

Types of jointsLap Joints

Lap joints are typically used in conjunction with adhesives to provide support at joints, however it can be modified to be used with bolts or screws. This is a good choice when the two connecting members are in compression since it can be easily torn apart in tension. To add strength to these joints, a common modification is notching out squares from each member so that the two pieces interlock [8] [9].

Figure 5: Examples of lap joints used in timber bridges. [8] [11]

A B

Gussets

Gussets can be very strong in bridge design, especially when bolts are also being utilized. In truss construction, these are often used but in the form of metal plates which join the many members together. Gussets can go either on just the outside of the truss, or on both the inside and outside depending on how much extra strength is needed in the joints.

Figure 6: An example of gussets on a roofing truss. [9]

Notched Joint

Although not as strong, notch joints may be useful on outside members where the force on the joint is not large. The notch joint requires only one screw to hold it in place so may add less weight to the bridge than the other joint methods. Notched joints are similar to lap joints but are used to connect beams into a T shape. By cutting out part of the supporting beam, the strength in that member is significantly reduced and cannot be treated as a truss in calculations since it has loading along its length [8].

Figure 7: A notched joint for T shaped members [8].

Properties of wood

Wood is a strong and relatively renewable building material used in all sorts of construction projects. The structural properties of wood vary by the type of wood, how it was cut, and type of growth. Generally, wood materials can withstand greater forces when these forces are applied parallel to the grain, and it also performs better under compression than under tension. Figure 8 below represents compression forces acting parallel and perpendicular to the wood grain.

Figure 8: Compression forces acting parallel and perpendicular to grain

Design Criteria Size and Strength

As specified by the department, the bridge must be at least 8 feet long, at most 1.5 feet tall and 1 foot wide. The bridge should be designed to carry animals weighing up to 55kg, however a safety factor of 4 was used in the design process to ensure that even in the winter with snow or moisture build-up that the bridge remains sturdy. The bridge should deflect as little as possible when subjected to the maximum loading.

Materials

The department provided all materials for the prototype of the bridge. At most, the bridge could be made of twenty 4 foot lengths of 1’ x ¾’ thick pine lumber. Unlimited bolts, screws and small to medium sized nails were provided, however each unit used will be accounted for in the cost of the bridge. Every effort should be made to conserve materials, as it will ultimately reduce both the cost and the weight of the bridge.

Cost

As stated above the materials were provided for the team by the department; however, the team was not required to use all given materials in building the bridge. Although safety was the biggest concern, the total cost of the bridge was also very important, as it was a criteria in testing along with weight, and deflection. During the design process and during construction, the team optimized materials and always looked for ways to reduce cost while still maintaining the safety factor incorporated into the design.

Environmental Impact

One of the most prominent criteria for the bridge was its environmental impact. The bridge should not negatively alter the condition of the local environment. For example, all pieces of the unit must be securely attached, so that they don’t fall off and impact the flow of the stream below. Any paints, or protective coatings on the wood must be environmentally friendly and not leech into the surrounding soils and wetlands. If the bridge somehow harms the ecology surrounding it, it cannot be considered successful.

Aesthetics

This bridge will be for use in a recreational dog park. Because of this, the structure should add beauty to its surroundings and enhance the experience of the patrons. It should not only be safe for the pets to use, but also compel the pets to use it to maximize the return of the project.

Safety

The most important criteria for this bridge is to uphold any municipal safety bylaws and ensure that the pets may cross the stream safely. The patrons of the park would be unhappy if anything were to happen to their pet and would not want to visit the park again. To avoid issues such as this, the bridge should be able to support more than its maximum load, and all pieces should be securely fastened. All materials used should be non-toxic to pets, all rough timber edges should be properly sanded and all screws and bolts should be sunken to avoid hurting the animals and maintenance workers.

Design Drafting Creative Thinking

The team employed similar methods used in past projects to generate a wide array of ideas for the design. The most useful method was the sticky note method, where team members would individually write down as many ideas individually as possible. The team then categorized the ideas into truss designs, safety considerations, environmental considerations, jointing methods, possible roadblocks, and overall designs. From this idea generation process, the team was able to think critically about what was required of the bridge and different ways the firm could construct a successful bridge. From this process, the initial bridge design was conceptualized, shown in Figure 9.

Concept Selection

Following the creative thinking process, the SCAMPER method was used in order to select and improve the most popular ideas. The Warren truss pattern was chosen to be the initial frame due to its load transferring characteristics (as previously described in 3.1.1), aiming for an optimally balanced structure. Given Bridge Street & Co.’s past experiences with similar projects, the possibility of reinforcing and adding to the frame was always considered. Some ideas were kept in mind but not implemented. For example, gusset plates were chosen as an alternative for complicated and crowded joints but were not part of the initial design. Building costs were tentatively minimized by reducing the height and width to the minimum dimension requirements. Figure 9 below was taken from the project proposal and represents the preliminary design.

Figure 9: Orthographic and Isometric View of the Initial Proposed Design

As expected, during the bridge construction, some joints were too crowded and not all beams were able to be properly secured. These joints had to be modified in order to improve the bridge stability and strength, and also to pass the company’s quality check. A combination of wooden I-beams and plywood gusset plates were implemented on these crowded joints. The wooden I-beams added strength to the truss joints, enabled the connection between horizontal members, improved the load distribution of the bridge and acted as a support for the floor joists. The gusset plates enabled the connection of the diagonal members without crowding and also added strength to the bridge joints by connecting all pieces together. Figure 10 below shows a typical connection of the bridge.

Figure 10: Typical joint connections using I-beams and gusset plates.

The bridge height had to be increased from 8 inches to 11.5 inches to accommodate such changes. The bridge length was reduced from 108 inches to 102 inches in order to reduce material usage. Originally, screws were used to connect the bottom horizontal members. Although, given the nature of forces acting on the truss, the screws had to be replaced by bolts. Finally, the last design change was adding a small piece of wood at one of the bridge’s support to improve stability, shown in Figure 11. The lack of stability was due to the use of warped wood of a horizontal member, which resulted in an elevation difference of ½ of an inch between the bottoms of each truss.

Figure 11: End of truss showing the additionally wooden piece on the bottom of the truss

Social and Environmental ConsiderationsEnvironment

Since the bridge is being made out of wood, it was important to reduce the amount of materials that were required to build the bridge so that the environment is not negatively affected. The bridge was designed to the minimum width requirement and the height was designed to be only a foot. Another aspect that was important to consider was how the bridge would affect the natural environment surrounding it. It was important that the bridge does not have a negative effect on the flow of the stream and any wildlife that may inhabit the area. The bridge was designed so that it would be longer than the required 8 meters in length. This was so that the bridge could be set up higher on the banks of the stream in an effort to reduce the effect on the flow of the stream and the wildlife that may use the stream. Some other considerations that were made included the future weather proofing of the bridge. Since the bridge will constantly be subject to natural weathering conditions, some form of protection and/or maintenance of the bridge will need to be performed on the bridge before it is implemented. The bridge was put together securely so that it would not break apart and clog the stream. Bolts were used instead of nails to secure the bridge to increase safety and decrease the likelihood of failure.

Society

The bridge also needed to take into account the impact it would have on society. In order to achieve pet owner satisfaction, the bridge needs to provide a path that allows pets to cross the stream. The bridge was designed with strength and stability in mind so that the pets would be able to cross safely and the pet owners would not need to worry about their pets. One other aspect that was important for the safety of the pets was the decision to create flooring on the bridge that was continuous; thus the firm used as much material as needed to make the deck safe. If there were any slots in the flooring or gaps in the flooring, then the safety of pets that cross the bridge would be at risk. Railings and walls were taken into consideration early in the design phase, but were ultimately not added to the bridge model since they were not crucial to the structure. It was later recommended after testing that they be implemented to improve user safety.

Safety Considerations

Since the bridge is not used by motor vehicles, or over 3 meters in length it is not subjected to any strict municipal, provincial or federal regulations [10]. The bridge was designed with a safety factor of 4, but after several additions to the design during construction the safety factor was much higher.

As outlined in the Ontario Structure Inspection Manual, timber bridges exceeding 3 m in length should be examined every two years for rot or decay, splits or shakes, weathering, insect damage, abrasion and wear, cracking and fire or chemical damage [10]. Although this project does not legally fall under these guidelines the firm recommends that the bridge be checked once after the first year, and every two years after that. All records of the bridge’s condition should be kept in a log book and reviewed by the owner whom should arrange proper maintenance.

Signs should be posted around the structure explaining that the bridge should only be used by pets not exceeding 55 kg. The signs should also outline any other safety precautions, for example if the bridge ices before the natural ground, so that pets and their owners are not harmed through negligence.

Project Economics

All amounts of materials used have been calculated based on the final design. Careful measurements were made of the wood and counts of the nails, screws, and bolts were conducted. The final cost of materials was more than the projected cost in the proposal. In large part, the additional costs incurred were spent in order to uphold the high standard of safety in the design. Initially nails were planned to be used because they were the least expensive fastener. However, as the building process began, more bolts were used than nails, since nails did not offer much strength in tension. The bolts provided a greater amount of stability to the joints, which were the most vulnerable part of the bridge design. Also, the amount of lumber used was slightly higher due to adjustments that were made in the initial design as the building progressed. Extra supports were added to the initial design so that the bridge would be stronger and more stable. Additional gusset plates were added to the bridge, as discussed in Section 5.2, which increased the amount of bolts used as they were able to secure the gussets on either sides of the jointed beams.

The actual costs for the materials that were used to construct the bridge can be seen in Table 1.

Table 1: Materials Cost Breakdown

Material

Amount Used

Material Cost

Total Cost

1” by 1” lumber

64

$1.00 per foot

$64.00

1/8” plywood

8.5 square feet

$1.00 per square foot

$8.50

Nails

8

$0.10 each

$0.80

Screws

26

$0.20 each

$5.20

Bolts

64

$0.50 each

$32.00

The cost of the materials for the bridge is $110.50.

All times spent in the workshop, creating the design, and construction of the bridge were calculated based on time spent in meetings that were used to design the bridge and time spent building the bridge in the workshop. A Gantt chart, as seen in Appendix A – Gantt Chart, was created during the initial phases of the bridge designing. The Gantt chart provided a schedule that was useful for time management. The chart helped schedule workshop hours and labour hours for the team. Time was spent effectively and efficiently as the group used the time to carefully plan out how the bridge would be put together. For example, deliberate thought was given to how the beams would be jointed together. As well, lengths were calculated beforehand, in order to reduce time spent in the workshop. The group also spread out tasks as there were a lot of pieces that needed to be cut and assembled. The distribution of tasks made the building of the bridge progress more smoothly and efficiently.

The actual costs for the time spent designing and constructing the bridge can be seen in Table 2.

Table 2: Design and Labour Cost Breakdown

Group Member

Time Spent in Workshop

Cost Charged per Member in workshop

Time Spent on Labour

Cost Charged per Member for Labour

Total Cost for Group Member

Group Member 1

8 hours

$800.00

10.5 hours

$1050.00

$1850.00

Group Member 2

8 hours

$800.00

11 hours

$1100.00

$1900.00

Group Member 3

8 hours

$800.00

10 hours

$1000.00

$1800.00

Group Member 4

8 hours

$800.00

10 hours

$1000.00

$1800.00

The total cost for the labour was $7350.00, adding up to a total cost of $7460.50 for the project.

Final Design

Shown Figure 12 are the orthographic and isometric views of the final design. The dimensioned length and angle units are in inches and degrees respectively. Imperial units, instead of metric units, were used because dimensions of the lumber were provided in imperial figures and because it proved to make working in the workshop simpler. Figure 13 depicts the internal forces in each two dimensional truss. Calculations for these internal forces are shown in ‘Appendix B – Calculations for Internal Forces’. It was assumed that the loading, 539N, would be evenly distributed between the two trusses on each side of the bridge; thus, a force of 269.5N was used to calculate the internal forces in each truss.

Figure 12: Isometric and Orthographic View of Final Design

Figure 13: Internal Forces Represented in Each Truss Member

A modified Warren Truss pattern was used for the final design; vertical truss members were added to each joint. Cross beams, spanning the width of the bridge, connect the two trusses at each joint. I-beam joints were used at each feasible joint. The overall length was modified to 8.5’. Gusset plates were used at joints involving diagonal truss members. Some screws, initially planned to connect truss members, were replaced with bolts. A stint was added to the underside of one truss member to help correct its deformed shape. Justification for these changes is explained in 5.2 Concept Selection.

Testing and Results

Figure 14 shows the bridge during testing day.

Figure 14: The prototype bridge during testing

The team ranked 17th overall out of 27 teams. With regards to cost of materials and weight, a ranking of 15th was achieved while for deflection at midpoint, a rank of 16th was obtained.

Assessment of Design to Project Metrics

The final design meets or exceeds expectations when considering the design criteria and constraints involved in this project.

Materials

There was a limited amount of materials that could be used to construct the bridge. The given lumber materials were precut and included twenty 4’ lengths of 1” by ¾” lumber, two 1’ x 4’ sheets and one 2’ by 4’ sheet of 1/8” thick plywood. In excess, after the completion of the bridge, were four 4’ pieces and a 1’ by 4’ sheet of plywood. The final design weighed 5.05 kg.

Dimensions

The restrictions regarding dimensions of the bridge were a width between 8” and 1’, a maximum height of 1.5’, and a minimum length of 8’. The final design was 8’ 6” in length, 11” high, and just over 8” wide. The extra length was provided to help account for the thickness of the sawhorses; the team wanted maximum contact with the bridge and the sawhorses to better distribute the load.

Safety

55kg was applied to the midpoint of the bridge to help determine its safety under a loading stress. The bridge was actually able to carry over 90kg during testing. Therefore, the bridge was able to successfully hold over 60% of the required load.

Deflection of the bridge was minimal. Testing showed approximately 7.38mm of deflection at the midpoint. However, the deflection meter was placed on the truss which had a deformed piece of wood. This piece may have caused much of the observed deflection; during testing, the deflection of the other side of the bridge was unobservable. In conclusion, this low deflection contributes to the safety and stability of the bridge by keeping material strain minimal.

There were no railings present on the prototype to prevent pets from falling off of the bridge. Installing guard rails would be a simple way to significantly increase user safety.

Time

Approximately four weeks were given to design, build, and test the bridge. The design was relatively simple to construct and usually only two team members at a time were needed to construct the bridge. This increased our efficiency and decreased the total time needed to complete the project thus reducing the total cost of the project.

Weather Resistant

The bridge was constructed with materials that can withstand some stresses due to weathering. Components will not become easily destroyed in wind, rain, or sunshine. Depending on the climate in which the bridge is used, further weather protection may be needed.

Pet Friendly

The needs of the pets were kept in mind throughout the design processes. Because the deck of the bridge is located on top of the trusses, a gentle incline was proposed to ensure pets can easily climb across. Rough edges were sanded to ensure no sharp splinters that could hurt pets were present. It is recommended that guard rails be installed along the length of the deck to increase safety for users.

Aesthetically Pleasing

While not much thought was dedicated to making the bridge aesthetically pleasing, the beauty of the design could be seen. Edges were sanded and cleaned to improve pet friendliness, gusset plates were uniform and constructed to the edges of the trusses to minimize materials, and joints were made flush with each other to increase strength. By keeping the bridge safe and clean, the beauty of the engineering was apparent.

Recommendations and Conclusions

The final design of the timber bridge was successful; it met, if not, exceeded all of the requirements. The bridge was able to hold the minimum 55kg (6 sand bags) required whilst presenting a 7mm deflection, and more impressively, hold all of the 10 sand bags (estimated 90kg) available during the testing. Its overall dimensions met the design specifications which were a minimum of 8 feet in length, a maximum of 1 foot in width and a maximum of 1.5 feet in height. The cost of the bridge was competitive to the costs from the other companies, ranking 16th out of 27 companies.

Although the prototype was successful, the design can be further improved with the following recommendations: using screws instead of the bolts used to hold the gusset plates, using better quality wood, reducing the bridge’s length, and adding guard rails.

Using screws to hold the gusset plates and the other structural members together would not have had a significant impact of the bridge stability, since there are minimal lateral forces acting on the bridge. This measure would reduce the costs by an approximated $15.60 (14%) and also reduce the weight of the bridge. Using better quality wood would improve the bridge’s strength and stability. It would also reduce the deflection, since most of it was noticed to be due to the wrongful use of a warped piece as a horizontal member. Also, the bridge was designed to extend over an 8.5 feet span but can now be reduced to an 8 feet length. This measure would also save in material usage, weight and cost. Finally, guard rails can be added at an extra cost of $5.00 to improve pet safety and aesthetics.

Bridge Street & Co. also recommends that the bridge is checked for maintenance after the first year of use, and every two years after that.

Works Cited

[1] M. A. Ritter, "Timber Bridges: Design, Construction, Inspection, and Maintenance," United States Department of Agriculture, Washington, DC, 1990.[2] D. C. MacDougall, CIVL 230 Course Notes, Kingston: The Campus Bookstore at Queen's University, 2015. [3] Wikipedia, "Parts of a Truss Photo," 2015. [Online]. Available: https://en.wikipedia.org/wiki/Truss_bridge#/media/File:Parts_of_a_truss_bridge.svg. [Accessed November 2015].[4] V. T. H. CHU, "What are the differences among Warren Truss, Howe Truss and Pratt Truss?," 2015. [Online]. Available: http://www.engineeringcivil.com/what-are-the-differences-among-warren-truss-howe-truss-and-pratt-truss.html. [Accessed November 2015].[5] Wikipedia, "Warren Truss Photo," 2015. [Online]. Available: https://en.wikipedia.org/wiki/Truss_bridge#/media/File:Warren_truss.svg. [Accessed November 2015].[6] Wikipedia, "Pratt Truss Photo," 2015. [Online]. Available: https://en.wikipedia.org/wiki/Truss_bridge#/media/File:Pratt_truss.svg. [Accessed November 2015].[7] Wikipedia, "Howe Truss Photo," 2015. [Online]. Available: https://en.wikipedia.org/wiki/Truss_bridge#/media/File:Howe_truss.PNG. [Accessed November 2015].[8] G. Boon, "Bridge Joints," 2005. [Online]. Available: http://www.garrettsbridges.com/building/bridge-joints/. [Accessed 2015].[9] Wood University, "Glossary," [Online]. Available: http://www.wooduniversity.org/Data/Sites/5/media/images/glossary/X505%20Figures/png/gusset.png. [Accessed 2015].[10] Ministry of Transportation, Ontario Structure Inspection Manual, The Queen's Printer for Ontario, 2008. [11] "Craftsmanspace," [Online]. Available: http://www.craftsmanspace.com/sites/default/files/free-knowledge-articles/t_half_lap_joint.gif. [Accessed 2015].

Appendix A – Gantt Chart

Appendix B – Calculations for Internal Forces