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 layers

3 layers

4 layers

1 seconds

3 seconds

More than 40 seconds

Types of Glues Used Result

Bonding UHU Super Glue

3 second glue

PVA

Did not break

Bends/ 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