SCHOOL OF ARCHITECTURE, BUILDING & DESIGN Bachelor of Science (Honours) (Architecture) Building Structures (ARC 2523) Project 1 Fettuccine Truss Bridge
Group Members
Student ID
Chan Jasmine
0308513
Charlene Chan
0308518
Kian Soon Jean
0314978
Lim Shu Yin
0307795
Nasreen Hajibeigy
0310538
Ye Min Aung
1006A79600
Content Page 1
Introduction
2
Methodology
3
Aims and Objectives
4
Precedent Study 4.1 History 4.2 Structure of the Bridge 4.3 Load Truss Analysis 4.4 Conclusion
5
Equipment and Materials 5.1 Equipment 5.1.1 Testing of Glues 5.2 Material 5.2.1 Properties of Fettucine 5.2.2 Quality Control
6
Experimenting Progress 6.1 Experimenting on Different Types of Trusses 6.1.1 Type of Truss 6.1.2 Load analysis 6.2 Design Features of trusses 6.3 Testing of beams 6.4 Full scale models testing 6.3.1 Mock-up (3) 6.3.2 Load Analysis 6.3.3 Improvements 6.5 Efficiency Calculations 6.6 Conclusion
7
Final Model Testing 7.1 Truss Design 7.1.1 Amendments and Modifications to Bridge Design 7.1.2 Fettuccine Bridge Construction 7.1.3 Joints 7.2 Load Analysis 7.3 Truss Bridge Testing 7.4 Efficiency Calculations
8
Conclusion
9
References
10 Appendix (Calculations cases)
1.0 Introduction Truss bridge is a structure composed of load bearing elements that form triangular units which are stressed in either tension or compression force on its joints. It is popular constructed due to its efficiency in load transfer and materials used. Few basic examples of truss are Pratt truss, Howe truss and Warren truss.
2.0 Methodology This project was divided into two tasks. In the first task, each of us had analysed one truss system out of six to determine which truss arrangement is the most effective. We had done calculations for each truss system based on moments, internal forces, reaction forces and component forces. In the second task, precedent study on truss bridges was done in order to understand the connections, arrangement of truss and orientation of truss. By using the info obtained from the precedent study, a fettuccine bridge was designed and constructed with 750mm clear span and maximum weight of 200g. The bridge was tested until it failed. As we aimed to reach a higher efficiency in our fettuccine bridge, aesthetic was not our priority. We determined the strength of the fettuccine and chose those truss designs that fully utilised its properties. Then, we tried out a few factors that could affect the efficiency of the truss bridge such as number of layerings of one member, the height between two beams and the ratio between the height and the width. Workmanship is one of the most important factors in the efficiency of the truss bridge. We distributed the job equally so that the outcome was even. We chose out the good quality fettuccine and omitted the bad one. Then, we came out with cad drawings and followed it to get the measurements so that human error and mistakes could be minimized. For load testing, we had used different methods for different bridges that we had made. We had tried to tie a recycle bag over the support of the bridge and put in random stuff into the bag. Later then we measured the weight of the bag. Eventually we decided to use packs of fettuccine and 500ml water bottle in the load testing to ease the calculation and enhance the accuracy. Lastly, the analysis report is produced based on the outcome of the final testing of the fettuccine bridge.
3.0 Aim and objectives The aim of our group is to get a high efficiency truss bridge. Therefore we set 4kg load and weight less than 200g as our target to reach during the load testing. The objectives of this project is to understand the tension and compression strength of the fettuccine and the force distribution in a truss. Besides, we have to design a perfect truss bridge which has high level of aesthetic value by using minimal amount of fettuccine. After the project, we were able to evaluate, explore and improve attributes of fettuccine and understand the load distribution in a truss. We could evaluate and identify tension and compression member and explore different arrangement of member in a truss structure.
4.0 Precedent Study Old North Park Street Bridge @ Concord, Massachusetts
Figure 4 (a): The old north park street bridge is now located at Riverside Park.
4.1 History After the first wooden bridge that was used to connect the Grand Rapids and the City of Walker was destroyed by flood, a new wrought iron Pratt truss bridge was built to replace it. The bridge provided access for both pedestrian and vehicles across the Grand River. After serving for almost 88 years, the bridge was determined to be deteriorated extremely which required expensive renovations. Hence, it was planned to be demolished and sold to scrap yet the local preservation managed to save one span of the bridge to be acknowledged as a historical significance.
4.2 Structure The Old North Park Street Bridge was one of the longest Pratt truss bridge in Michigan with its length of 589 feet. The bridge had five 116 foot spans set on piers in the river and each span was divided into 8 truss sections. The truss was characterised with outwards direction of diagonal members and additional cross bracing in the middle of the span. The outer vertical members and the diagonal members were thinner compared to the other members. The bridge was then reinforced with concrete pavement to withstand more load as the circulation gets busier.
Figure 4(b): The connections between the beams and the thinner vertical members.
4.3 Load Analysis As the bridge was paved with concrete to withstand heavier loads, the bridge deck was rested on the beams that were connected to the vertical members. A pair of eyebars were bolted to the vertical members to hold the diagonal members together. The outer two vertical members were much thinner compared to the others. This is because the bridge is supported by four concrete piers in the river and concrete abutments at each end. Figure 4 (c): View of the entrance of old north park street bridge.
The vertical members were reinforced with truss to withstand more compression force. They were connected to the beams through pin connection so that the force could be transmitted equally. Wrought iron is good under tension, hence the diagonal members could be thinner as they were in tension due to the strength of the material used.
Diagram 4(d): Compression and tension force in a Pratt truss bridge with cross bracings at the centre section.
The arrangement of the truss makes the bridge has more tension members compared to the compression members. The crossed ‘X’ braces in the centre section of the bridge reinforced the members in tension. As iron is good in tension, the Pratt truss design makes the bridge more efficient since most of its members are in tension.
4.4 Conclusion As fettuccine is good in tension but does not perform very well under compression, Pratt truss design which has most of its members in tension is a suitable design for the bridge design.
5.0 Equipment & Material 5.1 Equipment 1. Weights (car keys, phone, packets of fettuccine) A variety of items were used as weight to test on the fettuccine bridge such as car keys, phone and packets of Fettuccine Bridge.
2. 500ml water bottle This was used as a weight to the fettuccine bridge.
3. Bucket A big bucket was used to put all the 500ml bottles together to make the weight as one to test on the bridge.
4. Lanyard A lanyard was used to replace the S-hook in order to connect the weights and the bridge together.
5. Plastic bag Plastic bag was used to put the weights together
6. Tweezers It was used to carefully stick the fettuccines on each other as we used a very strong glue and we had to carefully place them in the correct position.
7. S- hook In order to connect the fettuccine bridge and weight together as well as making sure it was focusing on one point, a S-hook was used.
8. Three second super glue We have chosen this glue to use for our final bridge as we already tested a few other glues. This is due to its efficiency and speed of sticking the fettuccines together.
9. UHU glue UHU glue was tested to stick the fettuccines together. However, we have came to a conclusion that it is not suitable as it is not strong enough to hold them together for a long period of time.
10. Pen Knife A paper pen knife was used to cut the fettuccine. We used various sizes of pen knife with different strength to cut the fettuccine.
11. Metal ruler Metal ruler was not only used to mark the points of fettuccine that needs to be cut but also occasionally used to cut the fettuccine itself.
12. Digital SLR camera A camera was used to document the information and record it for further use.
5.1.1 Testing of Glues We have used two glues to test on the fettuccine bridge which are three second super glue and UHU glue. We have identified which one gives the best result to hold the fettuccines together in a sense of stability and effiency.
Types of Glue Three second super glue
UHU glue
Description Highest efficiency Fastest solidify time duration
Low effiency Slower solidify time duration
Figure 1: Types of glues and description
In conclusion, we have chosen the three second super glue as it is the most efficient glue to use. It also has the fastest solidify time duration.
5.2 Material 5.2.1 Properties of the chosen material The only material used in this project is fettuccine as it is the only material that is required in the brief. Hence, there were some analysis and research done on the fettuccine before making the final model.
Figure 2: Fettuccine used for bridge
Properties of Fettuccine
Thickness of 1mm Small yield point due to the brittleness Ultimate tensile strength ~2000psi Stiffness (Young's modulus) E~ 10,000,000 psi, (E=stress/strain)
We have tested the fettuccine strength by bending and breaking the both ends. In conclusion we have identified that handling it vertically is stronger than when it is horizontal. We have tested its strength of bending by taking a video which screenshots are as shown below.
5.2.2 Quality Control
Quality Control or QC for short, is a process by which entities review the quality of all factors involved in production. In this case, it is used to measure the perfect straight fettuccine that could be used in making the bridge and eliminate the twisted and bended fettuccine which will cause imperfection to the bridge if used.
Figure 3: Straight Fettuccine
Figure 4: Twisted Fettuccine
6.0 Experimenting Progress 6.1 Experimenting on different trusses 6.1.1 Different types of trusses -
Pratt truss A truss having vertical members between the upper and lower members and diagonal members sloping toward the centre.
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Howe truss Vertical members and diagonals that slope up towards the centre. In contrast to the Pratt truss, the diagonal web members are in compression and the vertical web members are in tension.
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Warren truss The Warren Truss uses equilateral triangles to spread out the loads on the bridge. It is a combination of Pratt truss and Howe truss. Interestingly, as a load moves across the bridge sometimes the forces for a member switch from compression to tension.
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K- truss A truss having in each panel two diagonals running from the ends ofone post to the cent er of the adjacent post, the arrangement being symmetrical about the centre of the truss.
6.1.2 Load Analysis (i)
Pratt Truss
Diagram 1.1.1 (i) The interior diagonal members are in tension while the vertical members are in compression when loaded. Fettuccine is good in tension but weak in compression, therefore the compression members have to be strengthen.
(ii)
Howe Truss
Diagram 1.1.1 (ii) The interior diagonal members are in compression while the vertical members are in tension when loaded. Fettuccine is good in tension but weak in compression, therefore the compression members have to be strengthen. (iii)
Warren Truss
Diagram 1.1.1 (iii) The equilateral triangles minimize the forces to only compression and tension. Interestingly, as a load moves across the bridge sometimes the forces for a member switch from compression to tension. Fettuccine is good in tension but weak in compression, therefore the compression members have to be strengthen.
(iv)
K – Truss
Diagram 1.1.1 (iv) The idea of the K truss is to break up the vertical members into smaller sections. This is because the vertical members are in compression. The shorter a member is, the more in can resist buckling from compression. However, the K-truss requires more members than the rest of the truss.
6.2 Testing of Beams The middle beams were tested, of which Beam 1 and Beam 2. The reason is to find out which could hold more load.
Conclusion: Beam 1 and Beam 2 broke at the same weight. However, beam 2 showed more elasticity from the compression struts in the beams. It held the weights longer than beam 1 did before breaking.
6.3 Design Features of each truss
6.4 Full scale Model Testing (750mm clear span) 6.4.1 Design Development of Bridges
6.4.2 Load testing of Full scale bridges (G,H,J) 6.4.3 Load Analysis & Improvision
6. 5 Efficiency Calculations After obtaining the weights from the full scale models (Model H, J & K), the efficiency for both the models were recorded and calculated.
Model H Efficiency
= (load)²/weight of bridge = 2.5²/0.19 = 32.89%
Model J Efficiency
= (load)²/weight of bridge = 1.5²/0.19 = 11.84%
Model K Efficiency
= (load)²/weight of bridge = 5²/0.187 = 133.69%
Based on the efficiency, we decided to improvise the reinforcements of Model K but sticking to the same design of it for our final design. Many minor adjustments were made from model H to J and finally to K to achieve the highest efficiency we could.
6.6 Conclusion From the efficiency of the full scale bridges tested, the simple Pratt truss with good workmanship, with the right ratio, height and proper reinforcements would be able to withstand heavy weights. The joints should be properly connected with appropriate adhesive, which in conclusion is the 3 second glue. Besides that, the selection of ‘A’ grade fettuccine to do our bridge would be vital in making a high performance and straight bridge. Each member has to be carefully selected before being stuck down with the adhesive glue. The weaker part of the bridge, especially the compression members are reinforced in order to achieve a higher efficiency. The utmost important factor for the efficiency of the bridge is the workmanship, to ensure every member is cut and paste perfectly and perpendicular to one another.
7.0 Final Model Testing 7.1 Truss Design The final truss design we chose was relatively similar to the previous test bridge’s truss due to the high efficiency we obtained from that test. Although the previous bridge was 10g overweight, we decided to use it and amended the number of fettuccine trusses in the final design. After determining the final results of the previous test bridge, improvisation to the final design was made through a series of analysis.
7.1.1 Amendments and Modifications to Bridge Design Our main concern was regarding the weight of the bridge as the brief requirement gave 200g whereas our previous bridge was about 210 g. Based on one of our earliest experiment of prioritizing the members, we understand that the vertical members require more reinforcement compared to the diagonal bracing members. This is because fettuccine is weaker when compressed. The layers of the diagonal bracings under tension were reduced from 2 to 1 layer.
Figure 7(a): The removal of a layer of fettuccine on tensile members.
Besides that, the dimensions of the bridge have been slightly modified. Firstly being the length which was reduced from 850mm to 820mm. This is to ensure a lower risk of the bridge failing due to the upward force of the table at the edge. The upward force may lift the edges of the fettuccine bridge and overthrow the equilibrium of the bridge. Furthermore, the spacing between vertical members was fixed so that they are similarly 75mm apart, leaving just 35mm rested on the tabletop.
820mm
80mm
750mm Figure 7(b): Dimensions of the final truss bridge.
Another change we applied was the center beams which are the points that the load will be latched on to. In our previous bridge, we used beam 1, a sandwiched 3-layer I beam. After the experiment to test the strength of the I-beam versus beam 2, a fettuccine simulation of a RC beam, the second choice was applied into the final design.
Figure 7(c): Section of beam 1 and beam 2
Figure 7(d): Beam type 1 & 2
7.1.2 Fettuccine Bridge Construction The construction steps can be divided into 4 main steps. It is important to follow a proper sequence so that the main frame is straight and stable, followed by other components.
First, the elevations for the final model are cad and printed out as a guideline. Based on the length of the 1:1 cad drawing, the strongest and longest 4 chords were made. Similar to previous tests, we used the concept of running bond so that no one part of the member is weaker due to more than one joint.
Figure 7(e): Top and bottom chords as main frame.
Second, the vertical members were attached using 3-second glue, using the printed drawing as guideline to ensure they are straight. They are attached on the inside of the top and bottom chords so that force of the load can be directly transferred across them.
Figure 7(f): Adding vertical members.
Next, the diagonal bracing members were attached. We trimmed the edges carefully in order for it to sit on top of the vertical members but within the 4 chords.
Figure 7(g): Adding diagonal members.
When the two side faces of the bridge were completed, we erected it and made sure that the vertical members are perpendicular to the tabletop using a MDF board and set squares. The two faces were stabilized by taping it to the drawing and the table. 50mm horizontal members were placed between the two faces to act as the connecting member of the two faces. The base is lined using plastic sheets to prevent the bridge from sticking to the table.
Figure 7(h): Joining the two faces.
Finally, when the bridge is able to stand upright, we cross-braced the open ends to ensure the bridge retain its shape. In the center, beam 2 is applied where 2 of it sits perpendicular to the bridge’s frame a on each side of the middle vertical member. They sit on top of the horizontal beam so the force of the load can move downwards onto the horizontal frames.
Figure 7(i): Diagonal bracing.
Figure 7(j): Beam 2 located in center.
7.1.3 Joints Joints are important in the way that they have to fit well with one another so that the transfer of loads can be even. Most of our joints were treated by trimming the stacked layers properly so they are flat and able to attach perpendicularly to the top and bottom chords.
The chords are created through many joints of 240mm fettuccines. We based the joint concept on running bonds, so that no one point of the member is weaker due to the presence of more than 1 joint. This is done by separating the 240mm fettuccine into 3 equal parts, the two marks being the points of jointing, where no 2 joints will be present at the same length of the member.
Figure 7(k): Running bond concept of jointing. The basic joint is to glue two flat surfaces together. This is used for the vertical or horizontal members that we glue in between the 4 chords. Putting them in between allows a better load transfer and also to prevent the bridge from collapsing inwards.
Figure 7(l): Flattened edges are glued together. The diagonal members were properly trimmed so that not only can their edges stick cleanly to the horizontal members; they still have space to attach to the vertical members. We believe that this method of jointing can help brace not only the vertical members and the horizontal members, but also to maintain the horizontal and vertical members in perpendicular to one another.
Figure 7(m): Trimming diagonal edges to fit.
7.2 Load analysis Based on the online software that helps us to analyze structure of bridges, we were able to identify the compressive and tensile members in our design. From there, we are able to reinforce the selected members that have a higher risk to be subjected to more forces.
Load
Figure 7(n): Identification of compressive and tensile members using online software. Fettuccine is stronger under tension and weaker under compression. Based on the experiments we conducted where most of our bridges fail as the compressed vertical members begin to bend and break whereas the tensile members remain intact for a longer period until the breakage of the vertical members overthrow the equilibrium of the forces. This prioritizes the vertical members for reinforcement; hence the final 3 layers of fettuccine used per vertical member.
The tension members, apart from the chords, which are the diagonal bracing members, were left as single layer fettuccines. With lesser needs to be reinforced, we chose to reduce the layers for the diagonal bracing members to prevent the weight of the bridge from exceeding the quota.
The 4 main chords and the 2 connecting beams in the center were properly reinforced. The 4 chords are important as they keep the other members in place as well as to spread the load horizontally to the tables. Since they endure both compressive and tensile forces, we used I beams to construct them, this makes them hard and sturdy. It also provides a flat surface for easier gluing of other members onto it.
The most crucial component will be the 2 beams in the center of the bridge. These are the points where the load will latch on to, making it a must for these beams to endure the load and not be the first to break. From the test conducted to identify the strongest beam, we concluded that beam 2; a fettuccine simulation of an RC beam is stronger than an I beam. They were attached to the top of the bottom chords, allowing load to be transferred from the beams onto the bottom chords. They will also brace the bottom chords so they do not cave inwards at the center.
Figure 7(o): Details of the center of the bridge.
Figure 7(p): Completed final truss bridge.
Truss Analysis Calculations Assumptions:
All members are perfectly straight All loads are applied at the joints All joints are pinned and frictionless Each member has no weight
Formula for perfect truss:
2J = M + 3
7.3 Truss Bridge Testing Our final bridge came up to a weight of 194 g. The test was carried out by masking taping the edge of the bridge between two chair desks with a clear span of 750mm. The load is a pail, attached via a lanyard tied around the two center beams. The pail is slowly filled with water, being the method of increasing the load.
Figure 7(q): Setting up for testing
Figure 7(r): First breaking point on bridge.
Figure 7(s): Collapsing of bridge.
During the bridge testing of our final fettuccine truss bridge, one of the bottom chords broke at 4.2kg of load, followed by the jointing of a lower horizontal member. The pull of the force continued and one of the top chords broke near the center of the bridge, followed by another point on both the top chords to snap, breaking the bridge into 2. Judging by the first breaking point, we believe it was a joint malfunction within the running bond stacked chord. It is most likely caused by the jointing of 2 edges that were not flat enough to click together. 3
2
1
7.4 Efficiency The formula use to determine the efficiency of the bridge is the square of maximum load applied divided by the weight of the bridge. A higher efficiency is obtained if the load carried is high and the weight of the bridge remains low. The final outcome from our test is recorded and input into the formula to obtain the efficiency of our bridge.
Efficiency = (Maximum load) ² / Weight of bridge = 4.2 ² / 0.194 = 90.93%
By the end of the bridge testing, the result we obtained is statically average, which was good compared to our first few attempts. The failure of the bridge is a result of human error and we believe that the efficiency could have been higher had all the jointing been more precise
As a conclusion to our final bridge testing, we find that it is important to ensure proper craftsmanship so that load transmission can occur smoothly and evenly.
8.0 Conclusion Upon the completion of this project, we are proud to say we have a deeper understanding on this topic of structural Analysis and we are able to identify tension and compression forces along with calculating the force acting on each member in particular. According to the efficiency equation, a high efficient bridge is defined as a bridge that can withstand high load with minimal weight. We have experimented numerous times just to get the best design of the bridge, which is to carry as many load as it can and also the numbers of fettuccine used should be lessen. Throughout the project, we have learned to identify important design elements and features (height, reinforcements, distance between members etc.) that could affect the structural integrity of the bridge to achieve a high efficiency. After analysing the load distribution in the bridge we did, we have strengthened the weaker part of the bridges. Besides that, we also came to realise that the crucial and determining factor in the efficiency of the bridge is the workmanship of the bridge. Any slight unevenness could transfer the load differently, causing the low efficiency of the bridge. In every model we did, we tried to keep our workmanship uniform by delegating certain task only to certain people to carry out. Proper way of adhesive and consistency of jointing the members are important to ensure the connections are strong. In conclusion, this project taught us how to think critically and apply our knowledge to our individual design when it comes to building construction details. This creates a high efficiency structure with minimal materials, which in return benefits the context and the users.
9.0 References Carr. J. (2002) Historical Details about the Old North Park Street Bridge. Tallahasse Community College. Retrieved from http://faculty.tcc.fl.edu/scma/carrj/Bridges/history.html on 5th October 2014. Garrett. B. (2008) Pratt truss Analysis. Retrieved from http://www.garrettsbridges.com/design/k-truss-analysis/ on 1st October Kenneth. M. (2005) Fundamentals of Structural Analysis. McGraw Hill publishers, New York. Taberrer. P. (2013) Local History: North Park Bridge. Creston Neighbourhood Associate News Bureau. Retrieved from http://therapidian.org/local-history-north-park-bridge on 5th October 2014.
10.0 Appendix 10.1 Photos during the process
(Left) How we bundle up the fettuccines to pick the best for the final bridge.
(Bottom) The process of gluing the fettuccines onto the bridge.
(Top) A few of us measuring the length of the middle support structure.
(Middle) The broken bridge after the testing of the final bridge
(Bottom) A group photo after a night of not sleeping!
10.2 Case study Calculations
Case 1 – Ye Min Aung 1006A79600
As for those four given cases above, an analysis was completed under consideration of weight of Fettuccine Bridge, amount of exerted force, arrangement of members and calculation. Each case was being discussed as the following:
Case One: Firstly, there are two diagonal members that are under compression, members AB and CF while member DE is zero force members. Other than that, all diagonal members left are under tension. Hence members that are under compression need to be strengthened with consideration of Fettuccine’s properties. Case Two: All the diagonal members are under tension, hence the load is considered well distributed. The vertical members are all in compression which is good in transferring the forces to the bottom chord. Yet the top and bottom chords of the truss are all under compression which make the truss to be easily crushed. Hence reinforcement in the top and bottom chords is necessary to enhance the strength of the truss design. Case Three: Horizontal members under compression are AB, HG and GF, while diagonal members under compression are JB, BG and CF. Most of the vertical members are under compression except for AJ. The remaining members are all under tension. The placement of trusses in this design causes many trusses to undergo compressive force. This can be overcome by reinforcing the vertical and diagonal members. Case Four: Horizontal members AB and BC are under compression. Diagonal members of DF and CG are under compression. The remaining of horizontal are all under tension. As for horizontal member AJ and diagonal BJ are zero. This design has alot of compression members that enhance the trusses. Thus, placing reinforcement in horizontal and vertical members can prevent from buckling.
Case Five: Members AJ, ED and DF hold little or no internal forces, thus they are redundant and should be removed if possible for higher overall bridge efficiency. A wider gap between two vertical members imposes a higher internal force within its diagonal and horizontal bracing. Most horizontal members are under compression. The bridge can be strengthened by closing the distance between vertical members and increasing their height at the cost of stability. Case Six: All the diagonal members are under compression while all the horizontal members are under tension. The vertical members CG and DF are under tension while only BH is under compression. Member AB is the highest tension member and member HC is the highest compression member. Member AB can be reinforced to ensure the minimum breakage of the member, ensuring a high efficiency of the bridge. Conclusion: The bridge truss with the least compression members would be able to withstand more weight. In case 6, it is the bridge with the lowest number of compression members. With this in mind, we assume case 6 has the highest efficiency among the rest.
