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# LIGHT STRUCTURELABORATORY

LABORATORY WORKSHEET

## Force in a statically Indeterminate cantilever

Title
Truss
Faculty : Faculty of Civil and Environmental
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Engineering
Department : Structure And Material Engineering Edition 1
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Title : Force in a statically Indeterminate Effective Date
Cantilever Truss Amendment Date

1.0 OBJECTIVE

1.1 To observe the effect of redundant member in structure and to understand the
method of the analysing type of this structure.

## 2.1 To application the engineering knowledge in practical application.

2.2 To enhance technical competency in structural engineering though laboratory
application.

3.0 THEORY

## In a statically indeterminate truss, static equilibrium alone cannot be used d to

calculate member force. If we were to try, we would find that there would be too
many unknowns and we would not too able to complete the calculations
Instead we will use a method known as the flexibility method, which uses an idea
know as strain energy.
The mathematical approach to the flexibility method will be found in most
structural text books,

## Figure : Idealized Statically In determined cantilever Truss.

Faculty : Faculty of Civil and Environmental
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Engineering
Department : Structure And Material Engineering Edition
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Title : Force in a statically Indeterminate Effective Date
Cantilever Truss Amendment Date

Basically the flexibility method uses the idea that energy stored in the frame
would be the same for a given load whether the frame is from redundant or not.
In other word, the external energy = internal energy.
In practice, the loads in the frame are calculated in its released from ( that is,
without the redundant member) and then calculated with a unit load in place of in
the redundant member and remaining members.
The redundant member load in given by:

## The remaining member force are then given by :

Member force = Pn + f
Where,
P = Redundant member load (N)
l = length of members( as ratio of the shortest)
n = load in each member due to unit load in place of redundant member(N)
F = Force in each member when the frame is release (N)

Figure 2 shows the force in the frame due to the load of 250N. You should be able
to calculate these values from Experiment titled: Force in a Statically
Determinate truss

## Figure 2: Force in the Released Truss

Faculty : Faculty of Civil and Environmental
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Engineering
Department : Structure And Material Engineering Edition
Checking No
Title : Force in a statically Indeterminate Effective Date
Cantilever Truss Amendment Date

Figure 3 shows the loads in the member due to the unit load being applied to the
frame.
The redundant member is effectively part of the structure as the idealized in figure
2

Figure 3: Forces in the Truss due to the load on the Redundant member

3.0 PROCEDURE

1.0 Wind the thumbwheel on the redundant member up to the boss and hand tighten it. Do
not use any tools to tighten the thumbwheel.
2.0 Apply the pre-load of 100N downward, re- zero the load cell and carefully zero the
digital indicator.
3.0 Carefully apply a load 250N and check the frame is stable and secure.
4.0 Return the load zero( leaving the 100N Preload). Recheck and re-zero the digital
indicator. Never apply loads greater than those specified on the equipment.
5.0 Apply loads in the increment shown in table1, recording the strain readings and the
6.0 Subtract the initial (zero) strain reading ( be careful with your signs)and complete table
2.
7.0 Calculate the equipment members force at 250N and enter them into table 3.
8.0 Plot a graph of Load vs Deflection from Table 1 on the same axis as Load vs Deflection
when the redundant removed.
9.0 The calculation for redundant truss is made much simpler and easier if the tabular
method is used is used to sum up all of the Fnl and n2l
Faculty : Faculty of Civil and Environmental
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cantilever Truss

10. Refer to table 4 and enter in the values and carefully calculated the other terms as
Required.
11. Enter your result in to Table 3.

4.0 RESULT

(N) indicator
1 2 3 4 5 6 7 8
0
50
100
150
200
250

## Table 1: Strain Reading and Frame

(N) 1 2 3 4 5 6 7 8
0
50
100
150
200
250

## Table 2 : True Strain Reading

Faculty : Faculty of Civil and Environmental
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Department : Structure And Material Engineering Edition
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Title : Force in a statically Indeterminate Effective Date
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## Experimental Force Theoretical Force

Member (N) (N)

1
2
3
4
5
6
7
8

Member Length
F n Fnl n2l pn Pn + f
1
2
3
4
5
6
7
8

Total

P = Total Fnl
Total n2l

## Table 4 : Table for calculating the forces in the Redundant Truss.

Faculty : Faculty of Civil and Environmental
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Department : Structure And Material Engineering Edition
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Title : Force in a statically Indeterminate Effective Date
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Using the Young s Modulus relationship, calculate the equivalent member force. Complete the
experimental force in table 3. (ignore member 6 at this stage)

## 5.0 DISCUSSION AND CONCLUSION

1.0 From table 3, compare your answer to the experimental values, comment on the
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