B U I L D I N G S T R U C T U R E [ A R C 2 5 2 3 ]

F e t t u c c i n e T r u s s B r i d g e A n a l y s i s

G e r t r u d e L e e ( 0 3 0 6 2 6 5 )

K e e T i n g T i n g ( 0 3 1 0 0 1 9 )

M e e r a N a z r e e n ( 0 3 0 9 6 3 0 )

N u r u l J a n n a h J a i l a n i ( 0 3 1 0 2 1 0 )

S o n i a M a n y i e ( 0 8 0 1 A 6 5 7 0 4 )

T A B L E O F C O N T E N T

I N T R O D U C T I O N

M E T H O D O L O G Y

P R E C E D E N T S T U D Y – H E N S Z E Y ’ S W R O U G H T I R O N B R I D G E

A N A L Y S I S

S t r e n g t h o f M a t e r i a l s

T r u s s A n a l y s i s – I n i t i a l t o F i n a l D e s i g n

T E S T I N G

T r u s s S t r u c t u r e A n a l y s i s

R e a s o n f o r B r i d g e F a i l u r e

S u g g e s t i o n t o S t r e n g t h e n B r i d g e

C O N C L U S I O N

A P P E N D I X

R E F E R E N C E S

I N T R O D U C T I O N

For this project, we were assigned in a group of 5 to carry out precedent study of a truss bridge. Using the knowledge from the research, we

are required to design and construct a fettuccine bridge of 750mm clear span and maximum weight of 200g.

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.

Upon the agreement of the bowstring truss as our topic of interest, the Henszey’s Wrought Iron Bridge was chosen as our precedent study.

The report will be based on the compilation of our research on the bowstring truss and the application of our understanding to the

construction of our fettuccine bridge.

Bridge Requirement:

• 750mm clear span and maximum weight of 200g.

• Only fettuccine and glue are allowed.

• Loads have to be point load.

• Must be able to withstand each weight that is put on for 10 seconds.

M E T H O D O L O G Y

In order to complete the project, the following methods were carried out:

Precedent Study

Gives an understanding of a truss bridge. The connections, arrangement of members and truss type are focused on. Based on the study, we

would then adopt the desired truss design into our own fettuccine bridge design.

Material and Adhesive Strength Testing

Before constructing the bridge, the physical properties of the fettuccine is to be understood. Therefore, we have tested the behavior of the

materials when subjected to either tension or compression.

Model Making

In the beginning, simple sketches of the trusses were made. Once decision was made, a CAD drawing of 1:1 scale was generated to ease the

process in creating a more accurate model.

Structural Model

The truss is analyzed by determining which members are in tension or compression. The structural analysis is done using the same method

as that of the truss analysis exercises (appendix).

Precedent Study - Henszey’s Wrought Iron Bridge

Figure 1 is a picture of Henszey’s Wrought-Iron Bridge, a single span wrought

iron bowstring truss bridge. The bridge is named and based after Joseph

Henszey’s patent design in 1869, a prominent engineer during his time. The

durability and longevity of surviving metal bridges built in the United States

from the 1800s is truly impressive. The ability of these bridges to defy time

itself in a way that no modern bridge today can is due to a variety of reasons.

The wrought iron used during this period was actually more rust-resistant and

long-lasting than the steel used today. Some bridges were overbuilt by

engineers who may have not been able to calculate the design of a bridge,

while in contrast

A B O U T T H E B R I D G E

Figure 1

others may have been designed by engineers who were very skilled and creative and were able to come up with a bridge design that was

uniquely effective. After design, skilled craftsmen would carefully fabricate the parts for these bridges, producing a well-built structure that

would be ready to stand for over a century. All of these types of things might be applicable to the long life that Henszey's Wrought Iron

Bridge has enjoyed, however some might find cause to question the skills of the craftsmen who fabricated this bridge. Today, Henszey's

Bridge serves as a pedestrian walkway for students, faculty, staff and visitors on the campus of Central Penn College, Cumberland,

Pennsylvania. The bridge symbolizes the high-quality, hands-on education that the college provides to connect students to their career

dreams.

T E C H N I C A L F A C T S O F H E N S Z E Y ’ S W R O U G H T - I R O N B R I D G E

Figure 2 Span Layout

Figure 2 shows the span layout of the bridge at 92 foot 4 inches (28.14m) from end shoe to end shoe with each truss subdivided into eight

panels. The approaches are formed by stone wing wall which rise to the level of the roadway and are fitted with pipe railings. The span

carries a 15 foot clear roadway of wood plank deck with a 4” by 4” wheel guard (Figure 3). U1 to U7 represents the top chords positions

while L0 to L8 represents the lower/bottom chords positions. All members and chords are wrought iron, but there are also cast iron

components for the bridge's connections, floor beams, and bearings. The cast iron components increase the rarity and significance of the

bridge.

The top chords are fashioned from 7 15/16” x 5/16”cast Phoenix sections, between which is a

riveted a stem plate 11 ¼” x 5/16”. Stiffening bars, 2” wide and 5/16” thick are inserted horizontally

through the stem plate regular intervals and are riveted to the outer flanges of the Phoenix

sections (Figure 4).

Figure 3 Foot Clear Roadway

Figure 4 Phoenix Section with Stem Plate and Stiffening Bars

Figure 5 Top Chord Overview

The top chords are fashioned from 7 15/16” x 5/16”cast Phoenix sections, between which is a riveted a stem plate 11 ¼” x 5/16”.

Stiffening bars, 2” wide and 5/16” thick are inserted horizontally through the stem plate regular intervals and are riveted to the

outer flanges of the Phoenix sections (Figure 4).

Figure 6 Top Chord ConnectionsFigure 4 Phoenix Section with Stem Plate and Stiffening Bars

Figure 7

The vertical posts of each truss consist of pairs of T-bars 3” x 1/2” x ½” which by means of flanges at the

bottom are riveted to the upper flange of each floor beam and the plates are riveted to the top chord (Figure

7).The deck is suspended from the top chord, thereby placing all verticals in tension.

The bottom chords consist of pairs of flat bars 4 ¾” x ½” with turnbuckles, on which rest the I-beam floor

beams which carries the I-beam stringers on which the flooring is laid (Figure 10).

Figure 9 Cast Iron Bottom Chord ConnectionsFigure 8 Bottom Chord Connections

The bottoms chords is also in tension as a result of the horizontal thrust exerted by the arched top chord. When a load passes

over the bridge, the load is conveyed to the vertical posts. As the posts are placed in greater tension, the segment of top chord

between the two posts is placed in compression. The flat verticals between posts of the bridge thus appear to have been

installed in order to counteract the tendency of a given arched segment of the top chord to buckle upward under the force of

the added compression.

Figure 10(a) Lower/Bottom Chord Connections to Flooring and Upper Chord Figure 10. Bottom Bracing at Lower Chord 2 and Lower Chord 6.

Figure 12 View of under the BridgeFigure 11 King Post under Floor Beam

In conclusion, the trusses for the Henszey’s Bridge are rather shallow. This is because the ratio between the maximum truss depth

(8 feet) and the overall length (92feet) is only about 1:11. Due to the arch configuration, deflection and vibration increases

especially when the outer end of the trusses are considerably shallower. Therefore, to decrease deflection, inverted king posts are

used below the floor beams (Figure 11). Moreover, placement of camber rods below each beam in a king-post configuration also

reduces lateral movement of the upper chords under live loads.

A N A L Y S I S

Materials used for this project are:

1. San Remo Tubular Spaghetti

S T R E N G T H O F T H E M A T E R I A L

Based on our research, the properties of the fettuccine are below:

1. Ultimate tensile strength = 2000 psi

2. Stiffness (Young’s modulus) E= 10,000,000 psi

(E=stress/strain)

Failure occurs when ultimate tensile strength is exceeded. As the length of the fettuccine increases,

the maximum load a fettuccini can carry before it breaks decreases.

2. UHU Super Glue

UHU super glue dries relatively quickly but is slightly flexible when dry. Moreover, the required

rigid glue joints can be achieved. PVA glue is not a suitable adhesive. Since it is water based, the

spaghetti is softened by the glue. Glue joints take forever to dry. Once dry, joints are not very

strong.

E X P E R I M E N T A T I O N O F T H E S T R E N G T H O F M A T E R I A L S

Types of Beams Numbers of Layers Result

L-beam 1 layer all sides Flattens and bends

L-beam 2 layers all sides Bends

I- beam 3 pieces Breaks at 5 seconds

I- beam 5 pieces Did not break

I- beam 6 pieces Did not break but heavy

Lamination 2 layers3 layers4 layers

1 seconds3 seconds

More than 40 seconds

Types of Glues Used Result

Bonding UHU Super Glue3 second glue

PVA

Did not breakBends/ flexible

Twists and breaks

Based on the results, it can be concluded that the I-beam made up of 5 pieces of fettuccines is the strongest. Moreover, 4-layered

lamination has also proved quite strong. The C-beam, L-beam and joists on the other hand, either buckled or twisted when tested.

Therefore, we have chosen to use I-beams and laminated fettuccine in our bridge. Finally, as an adhesive, UHU super glue turned

out to be the best option.

Bowstring Truss was selected as our fettuccine bridge design.

T R U S S A N A L Y S I S – F R O M I N I T I A L T O F I N A L D E S I G N

Figure above is a Typical Bowstring Truss

Figure below shows how the tension, compression and buckling may occur to the beams of a bridge while in this case, the fettuccines.

We have found that for a regular fettuccine (diameter = 2mm), maximum load is approximately 4.5kg. Moreover, a structure that relies on

bending strength to support a load has very little strength. Triangles is the best design for trusses as there are no bending moments in

triangular element(truss strength depends on bending strength of members)

Bowstring Truss was selected as our fettuccine bridge design.

T R U S S A N A L Y S I S – F R O M I N I T I A L T O F I N A L D E S I G N

The initial design of the fettuccine truss bridge weight was 286g. It was tested. Load was added until the bridge fails. The bottom bracing

deflected downwards when more weight was added and broke when it reached its limit. The other parts of the bridge was still in tack. It is as

shown below.

Front Elevation of Initial Fettuccine Bridge Design

Side Elevation of Initial Fettuccine Bridge

Design

Besides being advice to test the bracing, as our bridge is weight, 286g, more than the requirement of the brief,

which is 200g, we were also advice to decrease the amount of fettuccines used at the truss of the bridge. From

the advice that was given, we designed a new bridge.

The final design of the fettuccine bridge weight was 198g as we have decided to adjust our final design to lesser bracings which, reduces its

weight. Instead of making all the truss X-bracing(diagonal), we decided to make the three most middle trusses diagonal to each other while

the rest triangular. In order to make the middle bracing stronger, we made the middle bracing that was holding the load the strongest by

sticking more fettuccines together. We also decreased the length of the bridge

Front Elevation of Final Fettuccine Bridge Design

Final Fettuccine Bridge Design

P R E - T E S T I N G

We have chosen the truss member based on the required force to withstand tension and compression after referring to past material testing

as well as the precedent study to make appropriate joint connections.

TRUSS STRUCTURE ANALYSIS (Mock Up Model for Initial Design)

Failure Analysis:

The material needed to sustain the loads for this model was overwhelming. From our first testing, 2 fettuccine was placed in the middle for

bracing to hang the load. The bridge weighing at 284g was able to withstand 1.45kg of load. Using the same model and with minor

adjustments (placing 2 bracings, both shaped as I-beam), the model now weighing 286g was able to withstand 2.5kg of load. While the

bridge did not break during the first testing, its weight is way over the requirement of 200g.

Based on the calculation, we have found that although the weight has increased, the extra support and strength from the I-beams increases

the efficiency of the bridge.

First testing on First Mock-Up Model

Load: 1.45kg

Weight of bridge: 284g

Efficiency = (load) ^2 / mass of bridge

Efficiency =0.007

Second testing on First Mock-Up Model

Load: 2.5kg

Weight of bridge: 286g

Efficiency = (load) ^2 / mass of bridge

Efficiency = 0.02

P R E - T E S T I N G

After decreasing the number of trusses, the length of span of the bridge and the amount of fettuccines used, this is the result of the bridge.

Load = 198g

Mass of bridge = 4.2kg

Efficiency = (Load) ^ 2/mass of bridge

Efficiency =

TRUSS STRUCTURE ANALYSIS (Mock Up Model for Final Design

Failure Analysis:

For the final model, critical, tension and compression members were reduced. The diagonal bracings are only for the three most middle

trusses while the rest are triangular. From the truss analysis, triangular members are the obvious choice as these members has no bending

moments.

T E S T I N G

During the testing day, the 2 tables were 750mm apart from each other. The bridge was tested with a bucket and water as the load. The

water was poured into the bucket until the bridge fails.

During the testing, as water was poured into the bridge, one of the trusses popped out. As more water was poured in, the bridge started to

tilt. The bridge broke and was only able to withstand 2.648kg of load.

Load = 198g

Mass of bridge = 2.648kg

Efficiency = (Load) ^ 2/mass of bridge

Efficiency = 0.04

TRUSS STRUCTURE ANALYSIS

R E A S O N F O R F A I L U R E O F B R I D G E

1. Decreasing the amount of compression and tension members and misinterpretation of compression and tension members.

We decreased the amount of members in order to fit to the 200g bridge requirement but then we forgot about how

decreasing the number of members affect the compression and tension between the remaining members on the bridge.

Besides that, we also misinterpreted which member will have compression and tension force acting on it.

Tension

Compression

All the vertical members before was thought to be compression members

LOAD

2. The members are too far apart

As the members of the bridge was too far apart, it fails to support the compression force that was acting on the members.

The further the members are from each other, the amount of compression force that is acting on one member is more

resulting in the deflection of the base of the bridge.

Too far apart

3. The height of the bridge

The height of the bridge is too tall as the members are too tall. The taller the members, the weaker are the members in

withstanding the compression force of the bridge. As shown in the diagram above, the bridge started tilting due to the load

that was exerted on the bracing that was holding the load.

S U G G E S T I O N S T O S T R E N G T H E N B R I D G E

1. Decreasing the height of the bridge.

By decreasing the height of the bridge, the bridge will be more firm as the height of the bridge affects the stability of the bridge. The

shorter the members in the bridge, the stronger the members resulting on a more solid bridge.

2. Decrease the length between each members and add more members

By decreasing the length between each members and adding more members, the force distribution will be more equal and also it will be

more solid compared to when it is further apart.

HEIG

HT

C O N C L U S I O N

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.

Therefore, we would consider our truss bridge model a success. This is due to the fact that for the final model, the material and weight

lessened from 286g to 198g. Consequently, this produces better efficiency as the weight of load carried increases from 2.5kg to 4.2kg. We

were able to discover the strategy in achieving better efficiency by doing testing according to the maximum load the bridge can sustain.

Moreover, we have discovered that time management and teamwork is crucial in producing a bridge that is not only aesthetically appealing

but also of high quality during a limited time.

A P P E N D I X

Exercise: Truss analysis

A total of 5 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: Kee Ting Ting

Case 2: Gertrude Lee

Case 3: Meera Nazreen

Case 4: Nurul Jannah Jailani

Case 5: Sonia Manyie

The analysis and calculations of trusses are attached after this page.

Case 1: Kee Ting Ting

Case 2 : Gertrude Lee

Case 3 : Meera Nazreen

Case 4: Nurul Jannah Jailani

Case 5 : Sonia Manyie