SCHOOL OF ARCHITECTURE . BUILDING & DESIGN Research Unit for Modern Architecture Studies in Southeast Asia (MASSA) Bachelor of Science (Hons) (Architecture)
BUILDING STRUCTURES (ARC 2523) Project 1: Fettuccine Truss Bridge Tutor: Ms. Norita Johar
Group Members: KONG REN HENG
(0316416)
LIM WAI MING
(0317068)
MICHAEL KON KEEN YIH
(0300478)
PUA KEE HUI
(0316672)
TAN MING LONG
(0311069)
STANLEY WONG KHUNG YOU
(0317236)
Table of Contents 1. Introduction 2. Methodology 3. Precedent Studies 3.1 Introduction 3.2 Structure Design 3.3 Truss & Joint 4. Analysis & Design Development 4.1 Adhesive Analysis 4.2 Material Strength Analysis 4.2.1 Properties 4.2.2 Horizontal Alignment 4.2.3 Vertical Alignment 4.3.4 I-beam Alignment 4.3 Design Development 4.3.1 Initial Design 4.3.1.1 Design Idea 4.3.1.2 Truss Analysis 4.3.1.3 Model Making Process 4.3.1.4 Model Testing 4.3.1.5 Efficiency & Improvement 4.3.2 Second Design 4.3.2.1 Truss Analysis & Enhancement 4.3.2.2 Model Testing 4.3.2.3 Efficiency & Improvement 4.3.3 Third Design 4.3.3.1 Truss Analysis & Enhancement 4.3.3.2 Model Testing 4.3.3.3 Efficiency & Improvement 4.3.4 Fourth Design 4.3.4.1 Truss Analysis & Enhancement 4.3.4.2 Model Testing 4.3.4.3 Efficiency & Improvement 5. Final Design 5.1 Design Finalization 5.2 Amendment of Layers and Components 5.3 Layering & Joining Method 5.4 Model Making Process 5.5 Load Test & Forces Calculation 5.6 Efficiency & Improvement 6. 7. 8.
Conclusion Case Study Reference
1.0 Introduction In a group of 5 – 6 people, we are required to design & construct a bridge solely with Fettuccine. The bridge must be design to maximize its load bearing capacity meanwhile comply with the requirement of having a clear span 750mm and weigh not exceeding 200g. The efficiency of the bridge will be calculated based on the load it withstand. This objective of this particular project is to develop students’ understanding on forces distribution in a truss and also helps student to understand tension & compression forces in bridge construction. Meanwhile, it trains student to tackle the challenges through constructing the bridge which comply with the requirement while not losing its aesthetic values.
2.0 Methodology Students in a group of 5-6 were given a task to construct a truss bridge using the only specific material – fettuccine pasta. Before the construction started, a research on Calhoun Street Bridge in New Jersey, U.S. was conducted to provide the student a brief idea about the construction & design of the truss bridge. Base on the precedent study, students required to do further analysis about the joints and structure component of the bridge to understand how the forces was transferred between the members. Before the constructing the bridge, a series of test is conducted to examine the strength of the fettuccine. Besides that, various type of adhesive were tested to identify the performance that is suitable to be use with fettuccine. Pennsylvania truss have been selected as the construction method after analysing its pros and cons. Details of the joints and the amount of fettuccine used for each member was figure out based on the research & analysis. Next, the drawings and the calculation of the bridge is produced to minimize the mistakes during model making session. The main structural component of the bridge is first erected then followed by the sub component. The bracing will be installed to connect between components to enhance its stability. In addition, the load testing will be carried out upon completion of each fettuccine bridge. A bucket is hold by a hook is connected to a string that tied in the middle of the bridge to serve as a point load. Then, water was added continuously into the bucket until the bridge break apart. Last but not least, a thorough analysis will be executed to examine the reason of failure of each fettuccine bridge. Various way of improvement will be suggested and developed into the next model in order to achieve efficiency.
3.0 PRECEDENT STUDIES 3.1 Introduction The Calhoun Street Toll-Supported Bridge is the oldest of the 28 bridges (motor vehicle and pedestrian) that currently span the Delaware River between Pennsylvania and New Jersey. It is a Phoenix Pratt Truss with a total length of 1,274 feet, it also holds the distinction as the Commission's longest through-truss bridge and the Commission's only seven-span truss bridge.
Calhoun Street Toll Supported Bridge, Source Google Maps
2D - Diagram of Pin Connected Prat Truss Bridge.
3.2 Structure Design (Function)
The Calhoun Street Bridge is a seven-span wrought iron pin connected truss bridge containing 730 tons of iron and steel. A timber-plank pedestrian sidewalk is supported by the upriver truss on steel cantilever brackets. It was posted for a three-ton weight limit, eight-foot vertical clearance. On May 24, 2010, the bridge completely closed to vehicular and pedestrian traffic to undergo much-needed renovations including truss repair and repainting, deck replacement, and repair of approaches.
.
The Calhoun Street Toll-Supported Bridge is the oldest of the 28 bridges (motor vehicle and pedestrian) that currently span the Delaware River between Pennsylvania and New Jersey.
The bridge is the most heavily used vehicular two-lane truss structure in the Commission's system. It carried an average of 18,400 vehicles per day in 2009.
The bridge is currently posted for a 3-ton weight limit, an 8-foot vertical clearance and a 15-mph speed limit. In 2008, an average 18,400 trips were made across the bridge per day.
3.3 Truss & Joint There are many types of truss bridges. We studied few types of truss system and selected Calhoun Street Toll Supported Bridge as our precedent studies to analyze the tension and compressive the strength of the construction materials used and the force distribution in the truss.
Pratt truss The truss has diagonal web members which form a V-shape. It is designed by Thomas and Caleb Pratt in 1844 and became popular for railway bridges because it made good use of iron. The bridge has many variations, most with their own unique name. E.g. the Baltimore, Pennsylvania, and the Parker are all based off the Pratt. Having its diagonal members (except the end diagonals) slanted down towards the middle of the bridge span. Under such structural arrangement, when subject to external loads tension is induced in diagonal members while the vertical members tackle compressive forces. Thinner and lighter steel or iron can be used as materials for diagonal members so that a more efficient structure can be enhanced.
The chords and members of a truss bridge experience strain in the form of tension and compression.
Joints
Detail 1
Detail 3
Detail 2
Detail 4
The use of details such as pinned joints, rocker joints and pinned eye hooks allow the bridge to transfer loads so that the steel does not reach its yield point. These joints help the bridge to move and adjust as loads are applied and removed. Allowing the bridge to move in this manner places the steel and tension which places the steel at its highest strength.
4.0 Analysis & Design Development 4.1 Adhesive Analysis Since the components of a bridge is not manufacture in one-whole piece, it requires bolts & nuts in order to join the component on site. Same goes to Fettuccine Bridge, members need to be connected together using adhesive in order to form a structure ensuring the forces applied can be transferred equally to each member. Various adhesive with different properties were used to test with fettuccini to get the best result on achieving maximum stability of connection. Types 3(s) Glue (V-Tech)
Observations 1. Took shortest time to solidify. 2. Members are rigidly join together when applied
Conclusion Highest Efficiency Can be apply on main structural member.
UHU Glue
1. Took quite amount of time to solidify. 2. Members are movable, having chances to glide in the early stage. 3. Components are bendable after dried up.
Medium Efficiency Can be apply on members which are pre-stressed / prone to bending
Hot Glue Gun
1. Took longest time to solidify. 2. Creating bulky finishing when dried up.
Low Efficiency Same Effect as UHU glue but it increase the weight of the bridge.
From left: UHU Glue, 3 Sec Glue, Hot Glue Gun
4.2 Material Strength Analysis 4.2.1 Properties
Fettuccine is the only designated material for this particular bridge construction. Series of analysis were done to identify the properties and the strength of the material before the construction of the truss bridge. Fettuccine is a type of pasta which is flat and measuring about 1mm thick & 4mm wide (it differs between brands). It possess high tensile strength while relatively low in compression strength which makes itself easily to snap due to low elasticity value.
According to the research, Fettuccine’s maximum tensile strength is about 2000 PSI which equivalent to 137.9 Bar and the stiffness which according to Young’s modules is around 10,000,000 PSI. From the research, we can conclude that the compression strength of Fettuccine need to be enhance in order to withstand the applied forces and transfer it to the other member to achieve equilibrium state.
To identify the optimum stacking method, we have tested the Fettucine in three types of configuration: (A) Horizontal Alignment (B) Vertical Alignment (C) I Beam Alignment
4.2.2 Horizontal Alignment
Three layers of horizontal fettuccine stack
Before the test, we have chosen the fettuccine without any defects and set the clear span to 200mm as the fixed variable. By manipulating the layers, the maximum bearing load of the fettucine were recorded. Length of Fettuccine (mm)
Clear Span (mm)
Layers
250 250 250 250 250
200 200 200 200 200
1 2 3 4 5
Max Bearing Load (Approx.) (g) Horizontal Align 200 300 410 550 700
Observation: The horizontally aligned fettuccine able to withstand up to 700g of water when it is stacked into 5 layers. From the picture, we can notice that the fettuccine was bended to counter against the shear forces applied to it. This has shown that the Fettuccine is good in resisting tensile forces. Conclusion: As this configuration of fettuccine tend to be bent easily when a point load is applied at the centre, we decide to avoid applying this type of configuration in the design.
4.2.3 Vertical Alignment
Three layers of vertical fettuccine stack
Same as previous, the fettuccine without defects were chosen for the test and the clear span is set to 200mm. By manipulating the layers, the maximum bearing load of the fettucine were recorded. Length of Fettuccine (mm)
Clear Span (mm)
Layers
250 250 250 250 250
200 200 200 200 200
1 2 3 4 5
Max Bearing Load (Approx.) (g) Vertical Align 300 410 600 750
Observation: The vertically aligned fettuccine is able to withstand more loads than the horizontally aligned with the same 5 layers before it broke apart. From the picture can clearly see that the extent of bending of this particular arrangement is not as much as the previous arrangement. Conclusion: The vertically aligned fettuccine could resist the shear forces better but eventually it broke as the load increases. Hence, we decide to use this configuration as the non-structural members or bracing in the design.
4.2.4 I-beam Alignment
I-Beam configuration
After the previous testing, we started to construct the fettuccine to mimic the style of the I-beam. The web (vertical member) is created by stacking more than one layers of fettuccine, and then was covered by a layer of flanges (horizontal members) on the upper & lower side. Length of Fettuccine (mm)
Clear Span (mm)
250 250
200 200
Layers of Vertical Member 3 4
Max Bearing Load (Approx.) (g) 850 900
Observation: The vertically arranged fettuccine managed to withstand a larger amount of load until the point where the centre bends and the load shears through the strip. This further confirmed the assumption that fettuccine is good in resisting tensile forces. Conclusion: The added layers on top & bottom enhance the shear force resistance thus maintaining the stability and stiffness. Hence, it is been chosen to act as the main structural members in the design.
4.3 Design Development 4.3.1 Initial Design 4.3.1.1 Design Idea First Fettuccine Bridge is designed and modified based on Pratt Truss. This bridge is made to test the maximum load carried with the absent of consideration for the weight of bridge. Then, the weight of the bridge will decrease radically for the subsequence bridge to meet maximum weight of 200g as per requirement.
Based on the precedent study, we found that the highlighted points of Pratt truss are the weakness to achieve even force distribution of the whole bridge for point load. Therefore, we decided to modify the top chord into a curve instead of straight line to achieve better force distribution.
Load ‘X’ diagonal bracing is added in the middle segment as support member to resist point load in the middle segment. Other long diagional bracing is also added in order to distribute the force from the ‘X’ to the side. Besides, short diagonal bracing is added help to distribute the force evenly.
3 layers of fettucine I – Beam Layers of Fettucine of the bridge truss The base is formed with I – beam as one of the important member in order to withstand the forces from the point load and the members of the bridge. The other members of bridge are formed by 3 layers of fettucine. The size of the bridge is 150mm height, 825mm length and 80mm width.
First Bridge Model
4.3.1.2 Truss Analysis
Load
Tension Force Compression Force Assumption analysis of tension and compression forces exert on each member of the truss for point load testing.
4.3.1.3 Model Making Process
I - beam was made with length 825mm as the base of the bridge.
Vertical components were erected on the base. The height of vertical components were 150mm, 145mm, 135mm, 120mm, 100mm, 75mm and 45mm.
Curved chord was added on top of the vertical components.
Diagonal bracing were added in between the segments.
Horizontal components with width 80mm were added to join two trusses. Lower horizontal components were sat on the base, while upper horizontal components were joined under the curved chord. ‘X’ bracing was added horizontally between the base components in the middle segment. Then, two horizontal components which formed with 5 layers of fettucine were added on the ‘X’ bracing as load hanging component. ‘X’ bracing was used help to distribute the force from the load hanging component.
4.3.1.4 Model Testing
Load testing for First Bridge ‘S’ hook was hanging over the load hanging component of the bridge used to hang a pail as shown in figure above. 500ml of water was added constantly into the pail during the testing.
Snapped off load hanging component The bridge with 0.269kg of weight was able to withstand 3.9KG of load. The failure occurred at the load hanging component. It snapped off when the load was added up to 3.9KG. The other part of the bridge remains fine. The reason of the failure is the ‘X’ bracing under the load hanging component is not effective as it is not distributing the force well to the base.
4.3.1.5 Efficiency and Improvement
3.9KG
EFFICIENCY = =
(đ?‘€đ??´đ?‘‹đ??źđ?‘€đ?‘ˆđ?‘€ đ??żđ?‘‚đ??´đ??ˇ)^2 đ?‘Šđ??¸đ??źđ??şđ??ťđ?‘‡ (3.9 )2 0.269
EFFICIENCY = 56.5 Suggested improvement: 1) ‘X’ bracing under load hanging component should be place on the base, so that the force will transfer effectively from the ‘X’ bracing to the base. 2) Vertical diagonal bracing is joined by the side of the segments. 3) Decrease the number of layer of fettucine for the vertical diagonal bracing and curved chord from 3 layers to 2 layers in order to decrease the weight of bridge.
4.3.2 Second Design 4.3.2.1 Truss Analysis & Enhancement
Second Test Bridge For the second bridge, we decreased the layer of fettuccine in order to reduce the weight to around 200g. The vertical length of the fettuccine bridge remained the same and the middle load distribution part is highly reinforced. The span of the bridge and its width are maintained at 840mm and 80mm respectively, the height is also maintained at 150mm.
Reinforced Load Hanging Member
The main load hanging member (red square box) is situated on top of both of the bases. After that, both ends of the main load hanging member are joined with the vertical member. This is to ensure that the load hanging member is well connected to the whole bridge structure so that the load can be distributed effectively. An Xtruss is used to support the main load hanging member. Two additional load hanging members (blue square box) are added to both sides of the main load hanging member so that they can divert the load exerted separately.
4.3.2.2 Model Testing
Around 1kg loading, the bridge showed a significant bend at the top of the bridge.
Around 1.5kg, the top part of the bridge showed sign of collapse as it could not support the load distributed any longer.
When the load reached 1.7 kg, the top of the bridge collapsed. After that, the middle part of the main base collapsed as well. This is due to the fact that when the top part of the bridge collapsed, all the loads are distributed throughout the base only.
4.3.2.3 Efficiency and Improvement Based on the load test, the second bridge is far from reaching our goal which is supporting a load of 5 kg because the curved top part of the bridge is too thin. It could not support the load distributed to it. Besides that, the bridge is too tall and it is not in proportion, therefore unnecessary weight is increased for the bridge and its efficiency is decreased.
Besides that, the edge of the curved part of the bridge does not touch the end of the base, causing the load to be distributed unevenly at the edge.
Beam Chord
Column
Moreover, the curved part of the bridge is joined to the members at both sides by being attached beneath the top vertical beam. This reduces the strength of the chord as the joint is not as strong as if the chord is attached to the top of the beam.
EFFICIENCY = =
(đ?‘€đ??´đ?‘‹đ??źđ?‘€đ?‘ˆđ?‘€ đ??żđ?‘‚đ??´đ??ˇ)2 đ?‘Šđ??¸đ??źđ??şđ??ťđ?‘‡ (3.5)2 0.2
EFFICIENCY = 61.25 Suggested Improvement: 1) Increase the layer of the curved chord of the bridge. 2) Ensure the edge of the curved chord touches the end of the base. 3) Decrease the length of the vertical components.
4.3.3 Third Design 4.3.3.1 Truss Analysis & Enhancement From the second design, the study about the failure have learned that the curved top chord must be sitting on top of the vertical component in order to spread the forces to the lateral member. The middle part of the bridge where the load will be hang is further strengthen by doubling the vertical component which connects the base and the curved chord. The snapping of the previous test bridge inform us about the weakness of the curved chord. Hence, the layers of fettuccine were increased from 2 to 3 with the support of lateral bracings added on the middle. The span of the bridge and its width are maintained at 840mm and 80mm respectively, but the height is decreased to 105mm.
Improvised Diagram of Third Bridge (Red: Top Chord w/ 3 layers, Blue: Doubled Vertical Component)
The lateral bracing provide support for the curved arc as well as distributing the forces among the members.
4.3.3.2 Model Testing
(A)
(B)
(C)
(D)
(A) The curved chord started to bent. (B) The force exerted ripped off the arc from the vertical component (C) Snapped arc (D) The load hanging component also broke due to arc failure.
Before the load test, we have found that the curved arc member already bended due to craftsmanship. The water is continuously added during the process. Around 2kg, the bended curved member started to deform. Eventually the curved arc snapped causing the bridge to collapse when the water is added until 3kg.
4.3.3.3 Efficiency & Improvement The load that the bridge can withstand has increased from the 1.7kg of the previous bridge to 3.5kg. The middle load distribution part is very effective as it doesn’t buckle. However, the fettucine at the upper curve part breaks and the whole bridge collapsed. This is due to the curve part. Moreover, the spot on the curve which broke first is not reinforced by bracings. Suggested Improvement: 1) Increase the number of layers. 2) Support the bridge with overhead bracings that further reinforced the bridge.
EFFICIENCY = =
(đ?‘€đ??´đ?‘‹đ??źđ?‘€đ?‘ˆđ?‘€ đ??żđ?‘‚đ??´đ??ˇ)^2 đ?‘Šđ??¸đ??źđ??şđ??ťđ?‘‡ (3.5 )2 0.191
EFFICIENCY = 64.14
4.3.4 Fourth Design 4.3.4.1 Truss Analysis & Enhancement Due to the previous failure, using the same design, we decide to use the remaining available weight around (10g) to add two more lateral bracing in the middle (total four)and “V� bracing on the side to increase the arc stability.
The additional 10g is added with the addition of lateral bracing.
4.3.4.2 Model Testing
(A)
(B)
(C)
(D)
(A) The curved arc starts to snap at the end of the support of the lateral “X” bracing. (B) The Bridge starts to fail due to the loss of the arc support (C) & (D) The failure component after testing.
When the water added reached 3kg, the arc started to bend at the end of the “X” bracing. After a few moments, the deformation become worse. The arc ultimately snapped but the bridge did not break immediately. It sustained the weight for almost 5 second before it broke apart. It recorded the weight of 3.5kg.
4.3.4.3 Efficiency & Improvement The “X� bracing indeed play an important role in distributing the loads. But reason that causing the bridge to fail is the incomplete braces. The “X� in the middle distribute the loads to the side so does the “V� bracing. But, when the load reach the end of the “X�, only one side of the forces transferred to the “V� bracing, the other side remains on the arc which cause an imbalance situation. This eventually turns the bridge to break apart.
EFFICIENCY =
(đ?‘€đ??´đ?‘‹đ??źđ?‘€đ?‘ˆđ?‘€ đ??żđ?‘‚đ??´đ??ˇ)^2
=
đ?‘Šđ??¸đ??źđ??şđ??ťđ?‘‡ (3.5 )2 0.198
EFFICIENCY = 61.86 Suggested Improvement: 1) Uses “X� bracing instead of “V� for the top of the structure. 2) Improve craftsmanship in terms of cutting.
5.0 Final Design 5.1 Design Finalization
Final bridge design After having 4 test bridges, we finalized our bridge design, overcoming its flaws and optimizing the bridge’s load distribution efficiency. 1) The middle of the bridge is highly reinforced due to the fact that we decided to use a single point load in the middle. We doubled the vertical components in the middle of the bridge to increase its compressive strength. 2) The horizontal components remain the same from the start. It acts as a connecting member between the two bridge trusses. 3) For the load hanging part, we decided to use back the design of test bridge 1, which is an I-beam supported by a 4 layers x truss. Since the previous positioning of the load hanging components appeared to be a failure, we decided to place all load hanging components on top of each other on the base so that the load can be distributed to the base and to the other part of the bridge. If we place the x- truss between the two base I-beams, the x-truss is only supported by the adhesive, thus minimizing the load distribution efficiency. 4) The top chord of the bridge remains curved to increase its tension strength. The flexibility of the curved chord enable load to distribute smoothly without any obstruction. The end of the curved chords are connected to the base so that the loads can be distributed to it and supported by the reaction force. 5) Diagonal bracings are used to divert the load from the base to the curved chord or vice versa. For the diagonal bracing, we used only the full slanted components because they turn out to be more than enough to distribute the load effectively. Therefore, we removed the smaller components and used the additional weight to further reinforce the bridge. 6) In order to maximize the strength of the curved chord, we added lateral bracing throughout the whole curved chord. The lateral bracings were able to support the curved chord while receiving loads from the vertical components.
(A)
(B)
(C)
(D)
(E)
(F)
(A & B) Load hanging component at the middle of the bridge (C) Top view (D) Lateral bracing (E) Elevation (F) End part of the bridge
5.2 Amendment of Layers and Components For the base, we stick to our initial idea which is to make it an I-beam as I-beam had the strongest compressive strength among the other beam design. Since the base is the most important structure of the whole design, we wanted to make it as strong as possible, but not too heavy until it contributes to the compressive strength of the load itself.
3 layers of fettucine I - Beam Layers of Fettucine of the bridge truss The vertical components remain as 3 layers because it is the ideal number of layers in terms of support and weight. If we use 2 layers, the vertical components will be too weak to support the structure and will end up like test bridge 2, breaking due to the lack of reinforcing. However, a layer of 4 fettuccine is used for some bridge component only because the extra layer of fettuccine increases the overall weight of the bridge drastically, thus decreases the efficiency of the bridge. For the curved chord, we decided to make it 3 layers as it provided the ideal strength and flexibility. 2 layers are not recommended because although it had a better flexibility, the components appeared to be too weak to support the structure. 4 layers are not used as well because the curved chord will lose its flexibility, making it unable to bend according to the shape of the vertical components. The diagonal bracing also remain as 3 layers to provide support to the entire bridge. It holds the base and the curved chord together, preventing them from collapsing. If a thinner member is used, the bridge will collapse immediately, while if a thicker member is used, the bridge will appear to be overweight.
2 layers of fettucine
4 layers of fettucine
3 layers of fettucine
I - Beam
Layers of Fettucine of the bridge components The horizontal components consist of 2 layers so that it can support the two truss bridges, preventing them from crushing each other. If a single layer of fettuccine is used, the support is too weak but if more than 2 layers of fettuccine are used, it will appear to be wasteful as the components do not contribute to any load distribution. Lastly, the lateral bracing used for the 6 segments in the middle of the curved chord are composed of 3 layers, while the lateral bracing used for other segments are composed of 2 layers. This is due to the fact that the middle part of the bridge experiences the biggest load, therefore 3 layers of fettuccine is used. As the forces decreases while approaching the edge, lateral bracing of 2 layers are used so that the bridge would not overweight.
5.3 Layering & Joining Method Layering Method Running bond pattern
Cross section of I - Beam Running Bond Pattern: Brickwork running bond pattern construction method was adopted in the making of the curved chord and base components. Running bond allow us to lengthen the fettuccine to the span we preferred in a way of intersection when laying each other. Beam: 4 layers of fettuccine were neatly overlapped on each other to create the requirement thickness. After that, 2 fettuccine with the same length were pasted on the rough surface of the overlapped fettuccine to provide compression force. Therefore, the I-beam created is strong and durable enough to withstand heavy loads. Overlapping: Bracing and trusses were made of 2 to 4 layers of Fettuccine staking together. Joining Method The Components are joined to each other in a way that each component is connected to each other, so that the load can be distributed with maximum efficiency. The diagonal bracings are fit perfectly into each segment so that no additional force is created. Before the curved chord is joined to the vertical components, the tip of each component is smoothening until a certain degree with sandpaper. This is to ensure that the curved chord can lay perfectly on the vertical components and the load can distribute evenly to the curved chord. If the curved chord is joined onto a rough surface, an uneven load distribution from the vertical components will cause the curved chord to collapse. Lateral bracing is jointed perfectly between the two curved chords so that the two curved chords are well supported. The lateral bracings also act as load distribution members.
The reason we fit all the members perfectly to each other is because we wanted to make the bridge a whole, so that all members are dependent to each other, one member snaps and the others will snap as well. The model testing session was carried out 3 hours after the bridge completion. In order to ensure the bridge reached its strongest state, we used a hairdryer to blow the bridge with cool air for a few hours, so that the superglue can reach their maximum bonding strength.
Condition of the bridge after the test During the test session, the bridge appears to be very strong even the load reached 2.5kg. After the load surpasses 2.5 kg, the curved chord of the bridge appeared to budge a little, but there were no visible deformation on the bridge. The curved chord started to show visible deformation as the load increases. When the load reached 3.9kg, one of the base member snaps, after that the load hanging part of the bridge instantly breaks while the other parts of bridge remained intact.
5.5 Load Test & Forces Calculation
During the load test, the final bridge managed to perform well which bending did not occurs on any members especially on the arc chord. But, out of our expectation, the base cracks when the weight is added until 4 kg and eventually broke apart. The other members were remain on position when the base failed to withstand the forces.
5.6 Efficiency & Improvement
4.009KG
EFFICIENCY = =
(đ?‘€đ??´đ?‘‹đ??źđ?‘€đ?‘ˆđ?‘€ đ??żđ?‘‚đ??´đ??ˇ)^2 đ?‘Šđ??¸đ??źđ??şđ??ťđ?‘‡ (4.009 )2 0.191
EFFICIENCY = 84.15
The efficiency is lower than what we expected, but we still seek for more improvement. After some analysis, we realize that our bridge faces member failure rather than structural failure. One of the base members is not glued properly, therefore influencing the other members. Suggested Improvement: 1) Workmanship needs to be improved.
6.0 Conclusion Upon the completion of this project, we successfully produce a very strong bridge. Throughout the process, first and for most, precedent studies were done to give us a clear direction for our bridge design. It also helped us to develop a better understanding on how truss bridge works. This shows the importance of doing a detailed precedent study for a specific project. Although the bridge does not meet our expectation, we are still very satisfied with the outcome. After spending days and nights making test models and doing research, it was worth it as our bridge improved significantly in terms of aesthetic and functional purpose. The experience is priceless as we managed to explore more than what we learn in class. We also managed to sharpen our skills such as critical thinking, problem solving, idea generating, workmanship, communication, negotiation and most important, teamwork. After this project, we fully understand the principles of tensile and compression strength, distribution of force in a truss, jointing method and other else. Of course, we would never improve so much without the guidance of our tutor. Since our bridge faces member failure rather than structural failure, we believed that our bridge can reach an even higher efficiency if we provide a better workmanship to it. Leaning is a lifetime process, it is up to us to learn from our mistakes to continue developing towards better understandings and beyond better in future performance.
7.0 Case Study Case 1 Member(s) with zero internal force Highest tension in members Highest compression in members
DE 414.61kN, member AH 360kN, member AJ
Case 2 Member(s) with zero internal force Highest tension in members Highest compression in members
DE 414.61kN, member AH 360kN, member AJ
Case 3 Member(s) with zero internal force Highest tension in members Highest compression in members
AJ, DE 345.71kN, member AB 414.61kN, member BJ
Case 4 Member(s) with zero internal force Highest tension in members Highest compression in members
AJ, DE, DF 345.71kN, member AB 414.65kN, member BJ
Case 5 Member(s) with zero internal force Highest tension in members Highest compression in members
AJ, DE, DF 345.71kN, member AB 414.628kN, member BJ
Case 6
Member(s) with zero internal force Highest tension in members Highest compression in members
AJ 544.8kN, member HJ 511.4kN, member GH
From the analysis we can see that: 1) The highest tension and compression forces in each cases are about the same, with the exception of case 6. 2) Case 1, case 2 and case 6 have the least number of members with zero internal force. 3) Case 4 and case 5 have the most number of members with zero internal force. Therefore we can conclude that the truss from case 1 and case 2 are the most effective, while the truss from case 4 and case 5 are the least effective.
8.0 Reference -
Delaware River Joint Toll Bridge Commission. (2014). Calhoun Street Toll Supported Bridge. Retrieved May 4, 2015 from website https://www.drjtbc.org/default.aspx?pageid=78
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