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Lab assignment – CVEN2303
Submission due by 2pm 5th of August
You need to show and submit all your working solution either handwritten or typed.
You can use Matlab (or other software) to invert the structural matrix or for your entire
solution procedure. You need to upload a copy of your code or Excel sheet if used.
If you are using Matlab, it is expected that you add some titles/subtitles and comments to
the different sections of your code.
It is expected to add one or two pages of handwritten or typed Flowchart of your coding
or solution procedure, that will simply reflect the various stages taken in your code.
For part 1.3, it will be good to include differences between the theoretical and measured
results in percentages. That will prepare you to discuss the differences between the
results.
Introduction
In this assignment students are expected to calculate axial forces of a Warren truss and a
basic Roof truss using the stiffness method, and then to compare with experimental results.
The test videos can be watched on moodle (might take a while to upload). A guide for using
Matlab (optional) is also available on moodle.
Warren Truss
The Warren truss under investigation is illustrated in Figure 1, which consists of eleven
300mm long truss members that create 5 equilateral triangles as shown. The distance between
the supports is 900mm.
Figure 1: Warren Truss
2
The truss is simply supported with a pin support located on the left, and a roller support
located on the right. For consistency, use the members numbering as shown in Figure 2.
Figure 2: Reference system for Warren truss structure
The pin support is located at Position L0; the roller support is located at Position L3; the
vertically downwards load F is applied at Position L2.
Basic Roof Truss
The basic roof truss under investigation is illustrated in Figure 3, which also consists of
eleven truss members as shown. The length of members 2, 6 and 10 shown below is 300mm.
The distance between the supports is 900mm. The height of the truss measured from the
centre of the supports to the Position U1 (Refer to Figure 4) is 259.8 mm (150√3 mm).
Figure 3: Basic Roof Truss
3
Figure 4: Reference system for roof truss structure
The truss is simply supported with a pin support located on the left, and a roller support
located on the right. For consistency, use the members numbering as shown in Figure 4.
Assume that member 3 is perpendicular to members 1 and 4 and that member 9 is
perpendicular to members 8 and 11. The pin support is located at Position L0; the roller
support is located at Position L3; the vertically downwards load F is applied at Position L2.
Part 1.1 (70%): Calculate theoretical axial forces of the Warren and Roof trusses
Use the stiffness method to calculate the axial forces of all members in the Warren truss and
the Roof truss under a load that is applied at Position L2 with a magnitude of 300 N
downwards. You may use any computer software to do the calculation.
The material of the truss member is acrylic, and its elastic modulus is E = 2500 N/mm2. The
cross-section area of each truss member is A = 250 mm2.
Part 1.2 (10%): Determine experimental axial forces of the Warren and Roof trusses
From the measured strains, the experimental member axial forces can be obtained using:
N = EA??
where E is the elastic modulus of the material, A is the cross-section area, and ? is the
measured strain which is multiplied by 106. Therefore, in order to get the actual value of
you need to multiply the measured value by 10-6.
Part 1.3 (20%): Results discussion
Compare between the theoretical and experimental results and discuss four possible reasons