SE 310 Design of Structures and Mechanisms, Fall 2021
Project I
Due November 28, 2020 (Sunday, EOD)

Cell phone towers are elevated, high powered antennas that transmit radio frequency (RF)
signals to mobile devices in the surrounding area. They enable phone communications
across large areas. With increasing amount of cell phone usage, these towers are gaining
more importance. During natural calamities these structures have to support load without
collapse. During wars, the terrorists/enemies tend to destroy these towers to disrupt
communication lines. So, our task is to design a strike resistant cell phone tower, which
implies that if one of the truss elements is damaged, the entire structure is still stable.


Figure 1. Cell phone tower truss structure

Loads: The loads acting on the cell tower are of two kinds: horizontal load D and vertical
load W. The horizontal loads may be due to extreme wind conditions, and the vertical loads
may be due to the combination of the antenna weight and other loads. The vertical loads
are fixed at 80 kN, while the horizontal loads D = Last five digits of your UIN applied in
N. The height of the truss structure is 50 m. Design a truss structure with a square cross
section that supports these loads.

Design objective
Maximize the quality of the structure by minimizing the following function:

where n is the total number of joints, m is the number of elements, xi2 is the cross sectional
area, and li is the length of the element. The quality function is total volume of the structure
penalized by the number of joints introduced in the structure.

Design variables
1) Number of joints, n > 3
2) Length of each elements li (i.e., location of joints)
3) Cross sectional area xi (square cross section)
å+=
m
ii lxnC
1
2)1(

Design parameters
1) High strength steel (600 MPa yield strength) with Young’s modulus E = 200 GPa,
and density r of 8000 kg/m3
2) Square cross section, i.e., Ai = xi2
3) Effective length of each truss element is equal to the actual length of the truss,
i.e., leffective = li
4) Factor of Safety for stress and buckling: 4 (For each truss, calculate the internal
load. If the truss is in compression, then evaluate the critical buckling load. If the
critical buckling load is less than the internal load / safety factor, the truss is
assumed to fail).

Boundary conditions
1) All the joints on the ground should be pin joints.

Design constraints
1) Each of the truss elements should satisfy design constraints (stress, strike
resistance and slenderness ratio).
2) Slenderness ratio constraints should be less than or equal to 500 in both
tension and compression
3) Top of the tower where the antenna is mounted should be 50 m above the ground
at least.
4) Width of the tower on the ground should be at least 5 m and no more than 20 m on
the ground.
5) Between the top joint and the ground, there should exist at least one joint in the
middle level.
6) Joints should be separated at least 2 m apart.

What to submit
General requirements:
• Use a word processor to write the reports.
• Drawings should be clean and legible.
• Put a front cover page with title, name, date, course number.
• Final report: Finding an optimal design.
o Table of contents with page numbers and section headings
o Introduction and problem description.
o Drawing of the proposed design solution with joint and member
numbers.
o In your quest for an optimal design, you may have to try out several
candidate solutions. You are encouraged to use the excel sheet with the
python code introduced in class to quickly evaluate these solutions. You
are required to try and compare at least two feasible solutions and
compare them for its quality factor. The best solution must be
analyzed using the python code and checked for its effectiveness.
o Printouts of tabulated data for member forces and joint deflections from
python that use the same member- and joint-numbering scheme as in the
worksheet. All the work can be done by hand, or python; but all work
must be shown. Due to the nature of trial-and-error for this project, you
are advised to use the excel input files and python for validation.
o Design process description: Explain how you obtained the final design.
o Conclusions & Recommendations.
o Submit your report as a PDF file and attach the outputs of your excel
sheet and/or python scripts. The files will be uploaded and checked in
python.

Grading will be based on:
1) Correctness of the analysis and adherence to the design constraints (80 pts max),
2) Quality of your proposed design compared to the best value (20 pts max). This part
includes a relative comparison with your peers. Thus, collaboration with your
classmates is not allowed.
Note that if the final design violates any of the design constraints (e.g., stress constraint,
slenderness ratio constraint, etc.), it will be ineligible for the economy of the design credit
(20 pts) plus it will lose a large portion of credit under 1) above.





































































































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