Baltimore Truss Design Based on bamboo

Baltimore Truss Design Based on bamboo

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CHAPTER 1 -INTRODUCTON
Bamboo is often described as very durable; however, this is primarily in reference to the
sustainable growth of the bamboo plant, and not so much about the durability of the bamboo
stems. Proper use, treatment, maintenance and care can ensure excellent durability because
there exist bamboo structures of more than 200 years old.
Bamboo belongs to the family of grasses and doesn't have the same properties as regular
wood.
A bamboo plant has a stem, branches and leaves but that's where the comparison with trees
end. Bamboo is hollow, has no bark or year rings, and doesn't increase in diameter as the
plant gets older.
Bamboo stems grow on average 25 cm per day, and reach their maximum height in just 6-7
months (some tropical bamboo species grow up to 30-40 m). Bamboo stems are mature and
ready for harvest in 3-6 years, after which new bamboo shoots will develop naturally.
Because of its amazing growth rate, it has many different uses, and the fact that bamboo
plants keep emerging without re-planting, it is considered a very sustainable resource.

1.1 Bamboo goes through various checks such as:
1) Compression test
2) Three-point bending test
3) Effects of Oils-Treatments on the Bamboo Appearance and Weight
4) Humidity Test
5) Water Immersion Test
6) Aging Test
7) Tensile Test [This test is mostly avoided in case of bamboos because it is difficult to
hold bamboo while stress is applied].

1.2 Advantages OF Bamboo:
The various advantages of bamboo are mentioned below.
1) Light, strong and versatile.
2) Light, strong, versatile.
3) Environment friendly.
4) Accessible to the poor.
5) Self-renewing resource
6) Fast growing.
7) Highly productive.

1.3 Disadvantages of Bamboo:
1) The major disadvantages of bamboo are as follows:
2) Requires preservation
3) Shaped by nature
4) Durability- bamboo is subjected to attack by fungi, insects; for this reason, untreated
bamboo structures are viewed as temporary with an expected life of not more than 5
years.
5) Jointing- although many jointing techniques exist, their structural efficiency is low.
6) Lack of design guidance and codes.
7) Prone to catch fire very fast by the friction among the culms during wind, and is seen
to cause forest fires.

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1.4 Baltimore Truss Bridges.


Fig 1.1 Baltimore truss as modified version of Pratt truss.

1. The Pratt truss is a very common type, but has many variations. Originally designed by
Thomas and Caleb Pratt in 1844, the Pratt truss successfully made the transition from
wood designs to metal. The basic identifying features are the diagonal web members
which form a V-shape. The centre section commonly has crossing diagonal members.
Additional counter braces may be used and can make identification more difficult,
however the Pratt and its variations are the most common type of all trusses.
2. Charles H. Parker modified the Pratt truss to create a "camelback" truss having a top
chord which does not stay parallel with the bottom chord. This creates a lighter structure
without losing strength; there is less dead load at the ends and more strength
concentrated in the centre. It is somewhat more complicated to build since the web
members vary in length from one panel to the next.
3. When additional smaller members are added to a Pratt truss, the various subdivided
types have been given names from the railroad companies which most commonly used
each type, although both were developed by engineers of the Pennsylvania Railroad in
the 1870s.



Fig 1.2 Various Tension and Compression members in Baltimore Truss Bridges

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Fig 1.3 Schematic of dimensions for Baltimore Truss Bridges

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Chapter 2: Planning of Truss Bridge

Cost analysis:
It is a systematic approach to estimating the strengths and weaknesses of alternatives (for
example in transactions, activities, functional business requirements or projects investments)

Table 2.1 direct and indirect cost


Cost estimation (For 5 days): -

Table 2.2 Labor cost
Skilled labor Unskilled labor Total cost
Rs 500/day Rs 150/day Rs 3250

Table 2.3 Transportation cost
Transportation cost Weight Total cost
100/kg 3kg Rs 300

Table 2.4 Machine and Tools hired cost
Machines used Cost per day No of days used Total cost

Chop saw Rs 150 5 Rs 750
Hand driller Rs 100 5 Rs 500
Radial driller Rs 200 2 Rs 400
Bench sand grinder Rs 100 5 Rs 500
CTM Rs 100 2 Rs 200
Hammer Rs 30 5 Rs 150
Chisel Rs 20 5 Rs 100









Direct cost Indirect cost
1. Cost of material used 1. Cost of machines hired
2. Unskilled labour cost 2. Skilled labour cost
3. Electricity cost 3. Transportation cost
4. Communication and advertisement
cost
Total cost of machine hired Rs 2600/-

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Table 2.5 Electricity cost
Machine Used Electricity Used Cost/Kwh Total cost
Chop Saw 55Kwh(25min) Rs 5 Rs 275
Bench sand Grinder 11.25Kwh(30min) Rs 5 Rs 57
Drill Machine 40.5Kwh(90min) Rs 5 Rs 203
Total Cost- Rs 535

Table 2.6 Material Cost
Material used Quantity Cost Total cost
Bamboo 21.04ft Rs 130/18ft Rs 169
Binding wire 0.5 m Rs 20/m Rs 10
Total cost- Rs 179


Fig 2.1 Tools used while making truss

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CHAPTER 3 – PRE-TEST ANALYSIS

In this chapter we have performed pre-test analysis over a truss. During the process we mostly
focused on the factor which are going to be used during the performance while doing test.

End to end dimension measurement:
As we want whole dimension of assembly vertically as 280mm we calculate it by
considering the diameter of two supporting bamboo and also by considering the fish mouth cut.
The slant truss we cut by using hypotenuse rule and other parts by using geometrical concepts.

Force in individual members:
Firstly, we divided the figure of truss into equal portion section and then we have calculated
the force in individual member by using method of joint and method of separation. We
calculated the forces in each member in terms of p.

Table 3.1 Force in each member:
SR NO MEMBERS LOAD ACTING ON EACH
MEMBER (N)
1 F73 1.O23P
2 F23 0
3 F16 -0.8928P
4 F12 -P/2
5 F17 1.023P
6 F63 -P
7 F27 0


After finding force in each member we done the analysis of what type of force is present in
each member.so we found the force types as compression and tensile in members as shown in
table below.

Table 3.2 Types of forces in each member:
SR NO MEMBERS TYPES OF FORCE IN
MEMBERS
1 F73 Tensile
2 F23 No force
3 F16 compression
4 F12 compression
5 F17 tensile
6 F63 compression
7 F27 No force

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Table 3.3 Dimensions of members:
Sr No Members Dimensions(mm)
1 73 286.5
2 23 500
3 16 500
4 17 286.5
5 63 280
6 27 289.96
7 12 280


Height of the truss is 280 mm.
Length of truss is 1000 mm.


Fig 3.1 Resolution of Various Forces on Baltimore truss members

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Fig 3.2 Schematic of dimensions for Baltimore Truss Bridges

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Chapter 4 – Compression, Tension and Joint test

1. Compression Test
A. Compression test specimens were fabricated by cutting the bamboo sticks in lengths of
10 cm,15cm,20cm,25cm,30cm,35cm.


Fig.4.1-Specimen of various sizes for testing

B. These Specimens were later tested under the compression testing machine.



Fig.4.2-Specimen Compression Testing

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Table 4.1. Observation Table: Compression testing







2.Tension Test


Fig.4.3-Specimen tensile testing for bending test

Sr.
No
Length(mm) OD(mm) ID(mm) A(mm
2
) I(mm
4
) K(mm) Left
0.8Length
λ σ
1. 70 45.325 36.06 904.27 167140.75 13.59 56 4.690 65.46
2 160 46.98 80.27 1013.82 197884.48 13.97 120 8.5898 59.97
3. 200 46.15 30.31 951.21 181207.56 13.80 160 11.59 61.39
4. 250 46.55 30.32 984.38 189521.07 13.87 200 14.41 60.34
5. 300 45.83 25.56 1186.53 195604.14 13.11 240 18.30 55.69
6. 350 47.12 25.15 1247.03 222347.32 13.35 280 20.97 48.34

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Fig.4.4-Specimen tensile testing for bending test


Table 4.2 Observation Table for Tensile Testing of specimen
Sr.No b (mm) t (mm) l (mm) Pu(kg) Mu (mm) Z=bt
2
/6 σ = M/Z
1 40 7 200 36 17658 166.66 105.95
2 42 8 200 80 39240 343 114.28
3 33 8 200 57 27958.5 352 79.42
4 38 6 200 95 46597.5 405.33 114.96
5 29 6 200 24 11772 174 67.65
6 34 9 200 138 65236.5 459 142.12



Result:
Average tensile strength = 104.56 N/mm
2

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2. Joint Test
The joint testing is done on the same machine as that of the tension testing.


Fig.4.5 Tri-Axial Testing Machine



Table 4.3 observations for joints test for various specimens.
Specimen No. Load, P (in kg) Load, P (in N)
1 279 2736.99
2 207 2030.67
3 256 2511.36
4 164 1608.84
5 181 1775.61
6 258 2530.98


Results:
The Average Load is 2199.075 N

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Chapter 5: Fabrication of Baltimore Truss

Various types of joints were used in making truss we studied them with details and tried
to make it from previous made examples. types of general joints are Bevel Cut Bolted
joints, fish Mouth Bolted Joints, Bevel Cut Bolted joints.



Fig-5.1 Fish Mouth Bolted Joints

These joints are made from cutting bamboo into radial drill machine. Its locked with
keys and bolts. Bolts and keys are made from bamboo.


Fig-5.2 Bevel Cut Bolted Joints

Bevel Cut bolted joints are made at 45
o
Angle base joints and further this joint is more
responsible for failure or fractures as per predictions.

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Fig-5.3 Baltimore Truss joints single panel


There are two truss panels which are made by using all above shown joints then two further
panels are joint together to form Baltimore truss bridge.


Fig-5.4 Baltimore Truss Bridge

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Chapter 6: Test Preparation, Test, Results and Discussing

Failure load prediction analysis:

Prediction of Tension Failure:

Maximum tensile force=1.023p
Allowable tensile stress=104.56 N/M
2
Area of member carrying max tensile force: π/4(OD
2
-ID
2
)
We have taken the average area by calculating inner and outer diameters of members by using
above equation
We got the average area as 783.43 mm
2

Maximum tensile stress =F/A=1.023P/Avg. Area = 1.023P/783.43 =σ allowable=104.56n/m
2

P=80073.74N =80KN
This is P allowable for tension failure.

Prediction of Compression Failure:

Allowable compression stress = 48.24 N/M
2

Compression force = 0.8928P
We Calculated the average area by using formula: A=π/4(OD
2
-ID
2
)
We got average area 647.95 mm
2
Therefore, Maximum compressive stress = 0.8928P/647.95 =48.34 KN
Hence P=35082.77N =35.082KN
This is P allowable for Compression failure.

Prediction of Joint Failure:

Average joint tensile strength = ((279+207+256+164+181+258) *9.81) /6= 2199.05N
Maximum tensile force on joint=1.023P=2199.05N
Hence, P=2199.05/1.023=2149N
P=2.15KN, this is p allowable for joint failure
Hence Predicted failure load =2.15KN*2=4.30KN

Results:
By practical analysis we observed that joint starts breaking at 4KN and it totally breaks at 8.5 KN

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Fig 6.1 Tensile and Compression testing on Baltimore Truss
under testing machine for verification of braking stress
theoretical and practical values.

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Chapter 7: Conclusion

1) By performing this civil prototyping course, we got acquainted with various
interesting facts about bamboo and its uses in various structures. Also, we came to
know that role of importance of accuracy in building structures.
2) Proper planning is required right from the sketch till the difficulties we are going to
face problem during actual constructions.
3) At the initial stages of Struss making, reverse engineering needs to be done so that
we can analyses that are already made.
4) There is slight difference between the cost analysis done by us and actual cost.
5) Pretest analysis also needs to be done for verification.
6) Before performing the actual test, there is need to find out different types of failure
of individual members.
7) Test like compression, flexure and joint test we performed on specimen samples of
joints and members respectively. The strength of failure members should be taken
into consideration while designing the truss.
8) The predicted analysis was seen that major failure was seen in joints. There was
discrepancy in theoretical and actual value of failure. In Our case value of failure
exceeded predicted value.

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Reference


Website References


Books Reference

[1]
Environmental Engineering B.C. Punamia(Part I & II), S.K. Garg (Part-I &
II), Peavy, Metcalf & Eddy
[2]
Building Materials Rangwala, M.L. Gambhir
[3]
Strength of Materials /Mechanics of Structure Gare & Timoshenko,
E.Popove, L. Singer, B.C. Punamia
[4] The Book of Bamboo - by David Farrelly













[1] https://en.wikipedia.org/wiki/Truss_bridge
[2] https://prezi.com/h-kihghauqfu/baltimore-truss-bridge/
[3] https://bridgehunter.com/category/tag/baltimore-truss/
[4] http://www.historyofbridges.com/facts-about-bridges/truss-bridge/
[5] https://www.garrettsbridges.com/design/baltimore-truss/

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Team Photographs

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Baltimore Truss Bridge