Bachelor of Science (Honours) (Architecture)Building Structures (ARC 2523)

Project 1: Fettuccine Truss Bridge

Names and ID:

Ahmad Farhan Shah Bin Syed Amanullah 0303012Chan Kah Leong, Leon 0310587Ng Sueh Yi 0310700Nur Fazlin Binti Zulkifli 0303613Tan Hui Xian 0311719Yasaanth Kirishnamoorthy 0304863

Contents

IntroductionPrecedent Study Forth Bridge

Material Analysis:Material StrengthTesting of Material Strength

Truss AnalysisDesign RationaleBridge Design

Bridge Testing and Analysis:Fettuccini Bridge PrototypeFettuccini Bridge Final Model

ConclusionAppendixReferences

Introduction

The aim of this project is to develop the understanding of tension and compressive strength of construction materials as well as the force distribution in a truss. This project requires designing a perfect truss bridge which is of high aesthetic value and minimal construction material. The bridge has to be of 600mm clear span and maximum weight of 150g. This report is a compilation of our understanding and analysis on the precedent study, construction materials and the design of our truss bridge.

Precedent StudiesIntroduction

An analysis on precedent studies is conducted to aid in the design and construction of the fettuccine bridge, as it provides the knowledge and understanding required to construct a bridge that is efficient in carrying load and withstanding stress and forces. The precedent study of our analysis is the Forth Bridge in Scotland. The analysis of this precedent study includes a brief introduction of the bridge, the elements of the bridge and how the bridge works in tension and compression.

Forth Bridge AnalysisIntroduction:The Forth Bridge is one of the most famous cantilever bridges in the world. The bridge was officially opened in 1890, and it is the first cantilever-type bridge to be built of steel. It carries over 200 trains a day over the Firth of Forth between North and South Queensferry. Techniques used in the construction of this bridge is seldom seen in modern day bridges, having been replaced by faster and cheaper methods, due to the cost and complexity of the construction and design of this bridge. Possible design improvements and construction techniques can be implemented due to advances in design and construction, the development of materials and reduction of cost in what is considered a necessity in a modern day bridge.

Figure 1: Elevation of the Forth Bridge

Elements of the Bridge (Arrangement of Members and Orientation):The total length of the bridge is 2460 meters. It is made up of two approach viaducts, six cantilever arms supported by three towers, with two central connecting spans. There is an abutment at the end of each of the two outer-most cantilevers, and the distance between the centre lines of these two towers is 1630 meters. Two railway lines linking much of Northern Scotland with Edinburgh and England to the South cross the Forth Bridge, supported 47.8 meters above high water. The lines of the track sit on an internal viaduct supported within the enormous cantilever towers and arms which is often overlooked.The centre-most section of the bridge consists of three main piers, with two cantilever arms built out from each pier. Two approach viaducts consisting of a pair of lattice girders each spanning over fifty-one meters lead up to this central section, supported over forty meters above high-water level on masonry piers.Of the six cantilever arms, four are free cantilevers and two are fixed. The fixed cantilever arms are held rigidly in position by the two granite abutments at the ends of each approach viaduct. Two suspended spans, over one hundred and five meters long link the two outer cantilever towers with the central one. The superstructure for this bridge works as a standard truss, with some members always in tension and others always carrying compressive forces.

Figure 2: Living model showing principle of the Forth Bridge structure

How the Bridge experience Stress and Forces:

Two men sitting on chairs with outstretched arms represent the main cantilever towers, in between them is a central span connecting the two. Bricks at either side provide anchorage for the cantilevers. When load is applied to the central span, represented by a third man, the outside mens arms come into tension, whereas the sticks they are holding and the mens bodies experience compressive forces. This principle is applied to all three cantilever towers of the bridge.

All compression members (struts) in this bridge are tubular sections made up of many small steel plates riveted together, whereas tension is carried in lattice truss members. Lattice trusses spanning between the main superstructure members provide wind bracing.

Four separate masonry piers support the base of each of the three cantilever towers five and a half meters above high-water. Each pier varies in depth depending on the ground below, with each being almost fifteen meters in diameter at the top and larger beneath the water. The great cantilever towers rise from these piers, and the cantilevers themselves spring towards either shore.

Figure 3: Sketch of the central Inchgarvie tower showing the simplified positions of applied loads for analysis purposes.Material AnalysisMaterial StrengthFettuccine

As fettuccine is used as the only material for the model, its attribute is required to be studied and tested before jumping straight to designing our bridge. We thought it imperative to study the strength of a single fettuccine, as tensile and compressive strength in particular plays a big role in determining the success or failure of structure.

Adhesives

&

Hot glue to "weld" the joints together and further strengthens themExtremely strong, spot-accurate gluing, will flow into smallest corners and joints

Testing of Material StrengthAim of the experiment: To investigate the relationship between the length of the fettuccini and the maximum load said fettuccini can carry.

Inference: The maximum load a fettuccini can carry before it breaks depends on the length of the fettuccini.

Hypothesis: The maximum load a fettuccini can carry before it breaks decreases as the length of the fettuccini increases.

Variables in the experiment:Manipulated variable: The length of the fettuccini in cm.Responding variable: The maximum load the fettuccini can carry.Fixed variable: The type and width of the fettuccini used. The weight of the weight balance.

List of apparatus and materials: Fettuccini, clamp, weight balance, load.

Arrangement of the apparatus:

Figure 1.1

Process:1. The apparatus and materials are arranged as shown in (fig 1.1)1. The same type of fettuccini with a width of 5 mm is used.1. The length of the fettuccini, L = 2 cm.1. The fettuccini is loaded with weights until it breaks. 1. The maximum load the fettuccini can carry before it breaks is recorded.1. Step 4 and 5 are repeated three times with the same type of fettuccini of the same length and the mean value is calculated. 1. The experiment is repeated with L = 4, 6, 8, 10, 12, 14, 16, 18 and 20 cm.1. Once the data is collected, a table and a graph are plotted.

Tabulating Data:Length, L (cm)Load, w (g)Mean Load, g(w1+w2+w3)/3

W1W2W3

2400420390403

4175180165173

6115115115115

810090110113

10859595106

12120115105100

14959011596

161009010092

1885858083

2075707573

Analyzing the data:

Figure 1.2According to the above graph, the fettuccini carries the highest mean load of 403 grams when its length is L = 2 cm. There is then a drastic drop in the mean load it can carry when the length is changed to L = 4 cm and L = 6 cm. However, the deviation in the mean value of the load is not as apparent when the length of the fettuccini is between L = 6 cm and L = 10 cm. The graph in Figure 1.2 clearly shows how there is a decreasing trend in the mean value of the load it can carry with the lowest mean load of 73 grams being recorded when the longest fettuccini of L = 20 is used. Conclusion:The data verifies that our hypothesis, the maximum load a fettuccini can carry before it breaks decreases as the length of the fettuccini increases is correct.

Truss AnalysisPRATT TRUSS This truss was patented in 1844 by two Boston railway engineers; Caleb Pratt and his son Thomas Willis Pratt. It became popular for railway bridges because it was able to have long spans.

ARRANGEMENT OF MEMBERS AND ORIENTATIONYou can identify a Pratt truss by its diagonal members, which (except the very end ones) all slants down and in toward the centre of the span. All the diagonal members are subject to tension forces only, while the shorter vertical members handle the compressive forces. Since the tension removes the buckling risk, this allows for thinner diagonal members resulting in a more economic design.

What is remarkable about this style is that it remained popular even as wood gave way to iron, and even still as iron gave way to steel.

PARKER TRUSS

The Parker truss is named after Charles H. Parker who patented the design on February 22, 1870.

ARRANGEMENT OF MEMBERS AND ORIENTATIONIt is a variation of a Pratt truss but differs from the Pratt in that the top and bottom chord are not parallel. It seems initially Parker used a curved top chord, but later it was simplified to use a polygonal, or series of straight sections not in a line forming an approximate curve. The Parker uses less material than an equivalent Pratt, but is a bit more complex to build.

Design Rationale

For this project, we are required to carry out a precedent study of a truss bridge, and using the information obtained from the precedent study, we are required to design and construct a fettuccini bridge of 600mm clear span and maximum weight of 150g. The bridge must be of high efficiency, which means using the least amount of materials to sustain a higher amount of load. This bridge is tested to fail, therefore, its strengths has to be determined in terms of tension and compression strength as well as the material strength.Through a series of experiments with the formation of bridge members and chords, including the testing of the strength of the material used, which are the fettuccini and the adhesives, we have designed and constructed a final bridge model of high efficiency and high aesthetic value.

Bridge Design

The bridge is designed with all aspects of the criteria brought into consideration, including the aesthetic value of the design, the minimal use of construction materials as well as the high level of efficiency. The bridge is well balanced in terms of the number of members on each side, with a curve member at the top and the bottom to provide smoothness to the visual aesthetic of the design. The use of the amount of construction materials is just enough to provide high efficiency in withstanding the load applied.

Details of the Bridge:Height and width = 11.3 mm (at the middle), 60cm clear span, 66cm in totalLength (top chord) = approx 660 mmLength (bottom chord) = approx 600 mmWeight of this bridge = 138 gMaximum load = 11kg

Effiency: [(11)2]/138 = 0.88

Force Distribution in the TrussThese are the critical members within the bridge that undergoes tension and compression when force is applied to it.

Figure: Diagram of the bridge indicating the tension and compression members

Members in Tension

Figure: Diagram of the bridge indicating the direction of forces in tension members

The members in tension are the diagonal members which all points towards the centre of the bridge, where the load is applied. When forces are pulling the bridge and its members downwards from the centre, these members help to balance the load by pulling in two opposite directions, half to the right and half to the left. The members at the top are longer compared to the ones at the bottom, because the force is pulling from the bottom, therefore the members at the top has to be longer in order to withstand the pulling force from the bottom.

Members in Compression

Figure: Diagram of the bridge indicating the direction of forces in compression members

The members in compression are the vertical and horizontal members that hold and support the bridge. The vertical members function to support the diagonal members and the horizontal members function to hold the vertical members. The force pulling from the bottom is distributed along the bridge according to the length of the vertical members, with the centre vertical member being the longest to withstand the direct pull from the centre of the bridge. The horizontal members are set in a concave shape with the ends curving downwards in opposition to the direct pull of the force from the bottom, to withstand the downwards pulling force more effectively.

Bridge Testing and Analysis:Fettuccini Bridge PrototypeThe prototype model was built to test the efficiency of the bridge before the final testing. The model was done using the reference of the cad drawing. The entire vertical members were fixed first for making the work easier and faster. The entire vertical members were strengthened with two layers of fettuccini to face the compression force. Then the arch was neatly glued together with the vertical members to form a frame in which the tension members were fixed. The truss frames were made twice to build the complete bridge.

The trusses were joined together with intermediate horizontal members. This part was done with fixing the fettuccini in between the trusses. After the completion of model it was put for testing to check its efficiency.

The testing was done with wrapping the intermediate members with cling wrap. The cling wrap was wrapped strongly at the centre and tied to a bag. It was made sure the bag was light for adding the weight. Then the edged of the bridges were placed to the tables. The weights were added slowly to the bag. The weight of the bridge was 117 grams.The testing was done slowly until the bridge fails. When the weight was 3 kg the intermediate members broke, but the bridge didnt collapse. Since the intermediate part distributes the forces to other members, the bridge lacked strengthening in the middle. And also it requires cross bracing in the mid-range which allows the forces to be distributed equally to all the other members. This was analysed and upgraded in the final model.

Fettuccini Bridge Final ModelThe final model is an improved version of the prototype. The immediate members are strengthened to be able to withstand the direct force pulling from the bottom. Cross bracing is added in the mid-range to allow the forces to be distributed equally to all the other members.The bridge is tested with loads of accumulated weights pulling from the bottom of the bridge. The bridge is balanced on the edge of two tables. A piece of wood is placed in the centre to soften the point of impact on the bridge. Aluminium foil warp is used to wrap around the bridge at the centre to hold the bag where the weights are loaded. The weights are gradually increased until the bridge fails and buckles.

The bridge starts to buckle when the load in the bag is increased to 11kg. The force at the centre is the strongest, so the bridge starts to collapse at the centre.

The collapse begins inwards and the fettuccini is crushed.

The whole bridge is brought down in an instant.

In comparison to the prototype, the newly enhanced and improved bridge is able to withstand more than three times the weight, which is 8kgs more. Previously it was able to withstand only 3kg, but now it is able to withstand up to a total of 11kg. This shows how important it is to strengthen the immediate members of the bridge, and to enable an equal distribution of forces to all the other members of the bridge.

ConclusionThrough this truss bridge design, construction and testing, we have gained much understanding of the analysis of truss bridges. Based on the research of the precedent studies and experiments that were done, we have developed an understanding of the tension and compressive strength of construction materials and the force distribution in a truss. This understanding has enabled us to evaluate, explore and improve the attributes of construction materials as well as to explore and apply the understanding of load distribution in a truss. We are also able to evaluate and identify tension and compression members in a truss structure, and explore different arrangement of members in a truss structure. Finally through this project, we are able to design a perfect truss bridge which has a high aesthetic value and is made of minimal construction material.

AppendixExercise : Truss analysis

A total of 6 different truss systems which carry the same loads are analysed to determine which truss arrangement is the most effective and why.

The following are the task distribution for the cases:Case 1 : Chan Kah Leong, LeonCase 2 : Ng Sueh YiCase 3 : Yasaanth KirishnamoorthyCase 4 : Tan Hui XianCase 5 : Ahmad Farhan Shah Bin Syed AmanullahCase 6 : Nur Fazlin Binti ZulkifliThe analysis and calculations of trusses are attached after this page.

References:

Magee, A.D. (2007). A Critical Analysis of the Forth Bridge. Department of Architecture & Civil Engineering, University of Bath.Railway-technology.com. (n.d.). Forth Rail Bridge, Firth of Forth, Scotland. Retrieved from railway-technology website: http://www.railway-technology.com/projects/forth-rail-bridge-firth-scotland/

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