Building Structures (ARC 2523) Project 1 Fettuccine Truss Bridge
Ch’ng Xing Yue 0310425 Fam Li Kian 0310639 Goh Chin Zhi 0314562 Wesley Hew Xin Han 0307585 Sharifah Diyana Syed Hussain 1006AH78373 Lim Wei Ze
Tutor: Ms. Ann See Peng
Table of Content Introduction Methodology Precedent study Analysis i) strength of materials ii) truss analysis -
Mock up 1
-
Mock up 2
Final model testing Conclusion Appendix – exercise References
Introduction 1.1 Study Objective The objective of this particular study is to explore and thus evaluate and improve on knowledge of skeletal construction. In the event of constructing a truss bridge with fettuccine, exploration on truss members in different arrangement was carried out while applying the understanding of load distribution in truss systems. Besides that, understanding and the application of the knowledge on calculating the reaction force and internal force within the truss design. Lastly, gaining the ability to identify the tension and compression members in a truss structure to fully utilize the potential of the material Fettuccine.
1.2 Project Overview In a group of 6, a truss bridge was produced by using fettuccine as the construction material. Before starting with the model making, students were required to carry out precedent study of a truss bridge. With a clear span of 750 mm and a maximum weight of 200 g, the truss bridge is then subjected to a point load which determines the efficiency of the structure. The efficiency of the bridge is calculated with the formula: (đ?‘€đ?‘Žđ?‘Ľđ?‘–đ?‘šđ?‘˘đ?‘š đ??żđ?‘œđ?‘Žđ?‘‘)2 đ??¸đ?‘“đ?‘“đ?‘–đ?‘?đ?‘–đ?‘’đ?‘›đ?‘?đ?‘Ś, đ??¸ = đ?‘Šđ?‘’đ?‘–đ?‘”â„Žđ?‘Ą đ?‘œđ?‘“ đ??ľđ?‘&#x;đ?‘–đ?‘‘đ?‘”đ?‘’ For this project, only glue is allowed for the connection of the bridge members.
1.3 Report Overview
This report includes the precedent study of the bridge our group referred to while designing the truss systems of the fettuccine bridge. Besides that, the report also includes the development process of the fettuccine truss bridge including the analysis and calculation of the particular design.
Methodology DESCRIPTION Precedent Study
A study on different types of bridge trusses will be conducted. We will study the connections and arrangements of members. This will be then applied to our model bridge.
Material Testing
The strength of different types of fettuccine and glue will be tested out.
Model Making
Based on the AutoCAD drawings done, the sides of the bridge will be constructed before joining them together using members.
Structural Analysis
The analysis of both mockup and final model will be carried out after each testing.
Working Schedule: DATE
TASKS
21 September 2014
Material strength testing of different fettuccine.
24 September 2014
1st Mockup model making and testing.
28 September 2014
2nd Mockup model making and testing.
30 September 2014
Final model making.
1 October 2014
Final model submission and testing.
3 October 2014
Final report submission.
MATERIALS
DESCRIPTION
Butter Paper
Design of chosen truss bridge is drawn on the butter paper as a reference for placement of each member.
Fettuccine
Fettuccine is used to construct the entire truss bridge.
Masking Tape
Masking tape is used to keep the alignment of each member in place before gluing.
Super Glue
This glue instantly holds the fettuccine together due to the strong bonding.
Plastic Bag
Tied around center point of bottom chord of the bridge for testing purposes.
Water Bottle
Used to measure the amount of water as weight during testing process.
Camera
Recording of all work progress.
Electronic weighing scale
To obtain accurate weight measurement of the Fettuccine bridge. For the final bridge model, we weighed the members before assembling it together to ensure it’s within 200g.
Precedent Study -Railway Bridge Tulle
Image 1 : Railway Bridge Tulle
Railway Bridge Tulle is a railway bridge which built at 104 years ago. The railway bridge across the Danube at Tulle has been completely reconstructed. The new bridge is based on warren truss construction. The construction period only took 15 months. The total length of the bridge is approximately 440m, each span width around 13m.
Load In order to have a stable and strong truss bridge, the concept of force equilibrium should be apply. Assuming the point load is at the centre of the bridge, and both side of truss bridge are fixed points. Joint connection
Image 2 & 3 : Rigid Joints. Gusset Plate and Bolts Joint Connection
Arrangement of Members
Points of Horizontal Members at lower chord connected to the truss Image 4 : Bottom view of Tulle Bridge
The base of Tulle Bridge is connected by horizontal members.
Pin Joints
Point of Horizontal Member Connect to Truss Image 5 : Tulle Bridge side view
Top view of Tulle Bridge
For the upper chords, horizontal members are welded to the intersection point of the truss to hold both sides of the truss members in shape and ensure the distance is the same along the bridge. The bracings hold the horizontal in position to prevent deformation of the bridge when load is applied. As the report mentioned previously, the top chord of warren truss are greatly affected by compression while the bottom chord of warren truss is experiencing tension force. The bracings as shown on diagram above act as a member to distribute the compression force and hold the members in position. The bottom chord of Tullen Bridge does not required as much bracings as the members (steel beams) are great in tension force. .
Analysis Materials analysis Types of glue
Time taken to dry out
Strength
Weakness
UHU glue
Takes relative long time to dry.
• Large surface • Flexible when contact area with force is applied material
Superglue (Dolphin)
Solidifies fast.
Could bear relative heavy load.
•
•
Becomes fragile after it dried off a few days later. Low surface contact area with materials
Hot glue gun
Solidifies very fast.
• Large surface contact area with material
• The glue peels off easily. • Messy and bulky in size.
Rubber glue (Dunlop)
Takes relative long time to dry.
• Large surface contact area with material • Stronger than UHU
• Needs 24 hours to gain maximum strength • Flexible when force is applied
Load Analysis of Fettuccine
The diagram above shows different orientations of fettuccine and the load being applied from the top. When the fettuccine is placed horizontally, the thickness of the fettuccine is thinner, therefore the load it can withstand is small. The area of breaking point of the fettuccine also increases with the horizontal placement. The vertical fettuccine is stronger in this case as it has a smaller breaking point surface. But when the fettuccine is 4 members thick, the length of the fettuccine for both sides are the same (5mm).
Types of Fettuccine
Shape
Strength
Standard San Remo
Flat (Easier to glue)
Weak
San Remo Spinach
Slightly rounded (smaller surface area in contact with the glue)
Stronger than standard San Remo Fettuccine
Standard Divella
Relative rounded and larger in size
Strongest
Standard San Remo
San Remo Spinach
Standard Divella
Types of designs for middle support of the bridge Types of design
2
1
3
Number of members
3
6
6
Load withstand (kg)
2.5
6.1
5.4
We decided to use the 2nd design instead of triangles after the test due to the realization that we could not create a perfect triangle to efficiently transfer the load.
Truss analysis
Truss Analysis
Pratt truss has been chosen as the mock up bridge to test the load bearing of the truss. The load will be hang at the center of the bridge to act as point load. There are several factor to be considered to ensure that it can withstand 50N. Factors affecting strength of bridge: 1. Types of bracing used 2. Span to depth ratio 3. Joint connection and displacement of fettuccine 4. Design of middle member supporting load 5. Number of fettuccine used in one member Mock Up Fettuccine Bridge 1
Side Elevation of Mock up Fettuccine Bridge
Top elevation of Fettuccine Bridge
Total weight :236g Height : 10cm Length : 90cm Load : 4.1kg Pratt truss has high efficiency due to the vertical member and horizontal member. The diagonal member act as tension member and vertical member act as compression member. The purpose of this orientation of the members is to achieve force of equilibrium. Imagine it as a simple triangle, 3 forces acting at a point can be represented in size or direction by the sides of a closed triangle, then the forces are in equilibrium, provided their directions can form a closed triangle.
As to prove the assumption is correct, calculations has been done to determine the efficiency of fettuccine bridge.
+↑
Clockwise = positive
đ??šđ?‘Ś = 0
đ?‘€đ??´ = 0
đ??´đ?‘Ś + đ??ľđ?‘Ś − 50 = 0 đ??´đ?‘Ś + đ??ľđ?‘Ś = 50 đ?‘†đ?‘˘đ?‘?đ?‘ đ?‘Ąđ?‘–đ?‘Ąđ?‘˘đ?‘Ąđ?‘’ đ??ľđ?‘Ś đ??´đ?‘Ś + 25 = 50 ∴ đ??´đ?‘Ś = 25N
50 9 Ă— 5 − đ??ľđ?‘Ś 90 = 0 2250 - 90đ??ľđ?‘Ś = 0 2250 = 90đ??ľđ?‘Ś ∴ đ??ľđ?‘Ś = 25đ?‘ → 1
25N 25N Section equation is used to interpret the internal tension force or compression force.
5 đ?œƒ
10
đ??šđ?‘Žđ?‘? đ??ľ
đ??´
đ??šđ?‘Žđ?‘? đ??šđ?‘‘đ?‘?
tan đ?œƒ = cos đ?œƒ = sin đ?œƒ =
10 5 5 125 10 125
đ??ś
đ??ˇ 25N
𝑀𝑏 = 0 − 𝐹𝑎𝑏 (10) − (𝐹𝑎𝑐 cos 𝜃)(10) − (𝐹𝑎𝑐 sin 𝜃)(40) = 0 5 10 − 10 𝐹𝑎𝑏 − 10 − 40 = 0 125 125 4.472 − 35.777 𝐹𝑎𝑏 = −10 ∴ 𝐹𝑎𝑏 = 3.13𝑁 → 1 +↑
𝐹𝑦 = 0
− 𝐹𝑎𝑐 sin 𝜃 + 25 = 0 𝐹𝑎𝑐 sin 𝜃 = 25 25 𝐹𝑎𝑐 = sin 𝜃 25 𝐹𝑎𝑐 = 10 ( ) 125 ∴ 𝐹𝑎𝑐 = 27.95 (𝑇𝑒𝑛𝑠𝑖𝑜𝑛) → 2
𝐹𝑥 = 0
− 𝐹𝑎𝑏 − 𝐹𝑑𝑐 − 𝐹𝑎𝑐 cos 𝜃 = 0 𝑆𝑢𝑏𝑠𝑡𝑖𝑡𝑢𝑡𝑒 𝐹𝑎𝑏 𝑎𝑛𝑑 𝐹𝑎𝑐 (𝐶𝑜𝑛𝑡𝑖𝑛𝑢𝑒)
Joint Connection
Joint with gusset plate
Joint without gusset plate
A gusset plate like fettuccine is used to improve the load distribution. It acts as a connection to increase the contact surface area between horizontal member and the diagonal member. At the other side, the horizontal member and diagonal member does not connected by gusset plate. These arrangements are to test the difference of having gusset plate, hence to reduce the unnecessary weight.
Number of fettuccine for one member Position
Number of fettuccine
Top horizontal
4
Top diagonal
1
Top vertical
2
The number of fettuccines for each members has been done according to our truss analysis. The compression members should use the most fettuccine to reduce the compression force. As fettuccine is good in tension force, the tension member required 2 fettuccine to stack together to support the fettuccine bridge. The diagonal member act as a member to distribute the force and to avoid torsion force act on the bridge, hence it requires 1 fettuccine only.
Position
Number of fettuccine
Bottom horizontal
4
Bottom diagonal
1
Bottom vertical
2
Bottom vertical (triangular column)
3
The number of fettuccine stacking for one member is similar to top of the fettuccine. There are only one changes as to allow the member withstand the point load. A triangular column-liked fettuccine is used for the bridge. The strength of triangular column has been tested and shown in fettuccine-testing (methodology).
Position
Number of fettuccine
Side Vertical
2
Side Diagonal
2
As the weight of top structure is heavier than the bottom structures, we worried that the side structures cannot withstand the weight itself, causes bending and reduce the strength of fettuccine bridge. Hence, we decided to stack 2 fettuccine for each member to reduce possibility of bending. After testing
The bridge breaks when the total point load weight 4.1kg. The triangular column itself does not broke, but the horizontal members. We concludes that it is possibility of 3 second glue affects the strength of fettuccine bridge as the horizontal has been done before 2 days we test the bridge. The placement of broken member should be changed to improve efficiency of fettuccine bridge. The whole structures are still rigid after testing. Hence, we decided to change the number of fettuccine stacks for each members to reduce the total weight.
Final Model Testing
1st bottle
4th bottle
7th bottle
11th bottle
Mock Up Fettuccine Bridge 3
â–˛ Top Elevation of Mock up Fettuccine Bridge
â–˛ Side Elevation of Mock up Fettuccine Bridge
Total weight :196g Height : 100mm Length : 850mm Load : 5.744kg A Pratt truss similar to the previous test models was used due to the high efficiency of the vertical and horizontal member. The diagonal member act as tension member and vertical member act as compression member. The purpose of orientation of the members is to achieve force of equilibrium. Although the spinach fettuccine has smaller contact surface, but it is stronger than the normal fettuccine. Hence, we have chosen the spinach fettuccine in building our final bridge model.
The efficiency for the final bridge is:
E=
(5.744đ?‘˜đ?‘”)2 196đ?‘”
0.1683
Joint Connection At both sides, the vertical and diagonal members are laid on the outer surface of the horizontal members by using super glue. After tested the first and second bridge, we decided to use the first joint connection by removing the gussets. This is to maximize the surface area in contact so that every members can hold still in place and perform well in acting with the forces applied.
At the top and bottom part, the vertical members was stacked on the horizontal member and following by the diagonal bracing on top of the vertical members. While force is applied, the vertical members can transfer load down directly since they are sitting on top of the horizontal member.
Number of fettuccine for one member Position
Number of fettuccine
Top horizontal
4
Top diagonal
1
Top vertical
1
Through the first and second model testing, we realized that the top vertical members could be reduce to just one layer since it is not in direct contact with load applied. This is also one of the approaches taken in order to reduce the total weight of the bridge. Besides, there are only one layer of diagonal members because they act as bracing to prevent torsion force. Hence, one layer will be sufficient to support the trusses.
Position
Number of fettuccine
Bottom chord
4
Bottom diagonal bracing
1
Bottom bracing
1
Bottom bracing (middle)
8 (divided into two, four on each side)
The number of fettuccine supporting the horizontal chord for both top and bottom have been reduced to one as it didn’t require to withstand much force but rather to prevent torsion of the bridge. The middle bottom bracing which holds the load applied are required to be stronger since it has direct contact with the load. Hence 8 fettuccines are used to strengthen the member. The fettuccines are divided into half, where four layers of fettuccine are stacked together to form a member. The two members were placed side by side to provide a wider surface area for the hook to hold the load and to prevent it from breaking easily.
The middle bottom bracing Position
Number of fettuccine
Side Vertical
2
Side Diagonal
1
In order to withstand the force of the weight, the number of fettuccine in the side bracings remain unchanged. The amount of fettuccine in the diagonal bracing was reduced to one as it helps prevent sliding of the vertical and horizontal members under pressure.
After testing The final bridge managed to support a maximum of 5.744kg before breaking. The middle bottom bracing remains unbroken as the bottom chord had snapped first causing the entire bridge to cave in downwards. This is partly due to the difference in height of tables used during the testing of the bridge, the improper transfer of force causes the chord to split on both sides.
Middle beam didn’t break during testing
The bottom chord after splitting
The bridge had broken on opposite ends at the moment of breakage. The torsion caused all the horizontal bracings to twist and snap although several portions of the side bracings remains in one piece a side from point breaks.
Conclusion The final bridge has the highest efficiency out of all the model testing we did and was considered a success to us. Throughout the whole project, different materials, arrangement of members and joint connections are used to explore and improve the bridges. We came out with systematic ways to do the model in order to reduce the time taken for the construction and to increase the precision of the Fettuccine bridge. We also realized the importance of workmanship during the model making. Inaccurate or twisted fettuccine will contribute to the deformation of the bridge and thus causing lower efficiency. We did identify the tension, compression members and weak points as to determine on which parts to strengthen and which to reduce the layers of Fettuccine used. This method allows us to reduce the weight of the bridge to meet the requirement of the brief. Lastly, this project allows us to understand the importance of structure and construction method in design and the load distribution in truss to enable us to create a better structure for our designs in the future.
Reference
Reference List : Analysis of Structures. (n.d.). Retrieved from http://ocw.nthu.edu.tw/ocw/upload/43/733/static_ch6.pdf Calvert, J. (2000, January 1). Truss Design. Retrieved from https://mysite.du.edu/~jcalvert/tech/machines/bridges.htm Trusses Introduction. (n.d.). Retrieved from http://www.ce.memphis.edu/3121/notes/notes_03a.pdf
Image Reference : Image 1 : Retrieved by http://structurae.net/photos/144783-tulln-danube-river-railroadbridge Image 2 : Retrieved by http://structurae.net/photos/144765-tulln-danube-river-railroadbridge Image 3 : Retrieved by http://structurae.net/photos/144763-tulln-danube-river-railroadbridge Image 4 : Retrieved by http://structurae.net/photos/144760-tulln-danube-river-railroadbridge Image 5 : Retrieved by http://structurae.net/photos/144783-tulln-danube-river-railroadbridge