Sign Support Design Project
Team Hydra
Chris Byrne, Michiko Matsumoto Li, Kevin Stewart, Aoyong Tan, Yue You
MME 312 Section A. Spring Semester
Miami University: School of Engineering
Dr. Jeong-Hoi Koo
3 May 2013
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Abstract
The objective of this project was to create an alternative design for sign support structure
on a single lane parkway in Cincinnati, Ohio. Four separate designs were initially created and
finally came to the final design which would be the basis for all the analysis (Appendix, Figure
8). Materials were researched to find what best coincided with the design. Three materials were
selected: Aluminum 6061-T4, Stainless Steel 304, and Glass Fiber Reinforced Polymer
Composite. Upon further investigating material properties, the material selection was narrowed
to Aluminum 6061-T4 and Stainless Steel 304. The design was created in Abaqus and the
material properties were applied to the model. After analysis was completed, the steel exhibited
less stress and deflection as expected (Figures 1 and 2). When compared, although the steel
displayed less stress and deflection, Aluminum 6061-T4 exhibited minimal stress and deflection
and was much cheaper (Figures 3 and 4). Aluminum 6061-T4 was chosen as the final material
because it met the desired standards and was a much cheaper alternative than Stainless Steel 304.
The end product made with Aluminum 6061-T4 and the design created yielded the desired
results.
Introduction
The aim of this project was to design a new sign support structure for a single lane
parkway in Cincinnati. The sign in question is made of aluminum 2014-T6 and is 3 meters wide
by 2 meters high and with a thickness of .001 meters. This sign is to be anchored to a single post
with a circular cross section and can be either solid or tubular. Using the concepts learned from
this course our goal was to determine a better design than the one currently being used. We
would have to keep in mind the stresses and deflections from the wind, and also the structures
own weight. Thermal degradation was also something we would keep in mind for the design.
Our main objective was to design a structure that minimizes cost, but still soundly
support the sign. This required emphasis on which material we would use for the supports, as
well as thicknesses and length of each support. If we minimized the amount of metal used, our
total cost will do the same. Another objective was for the design to be easily assembled. This
meant that we would try to use standard size pieces rather than having to heavily rely on cutting
and welding to achieve the pieces we need. A positive for using standard size pieces means that
production will be efficient as well, which leads to a faster construction time and lower labor
costs.
After researching a few overhead highway designs used determined that there was some
room for improvement. In most designs, there was an overuse of material used to support the
sign. Our design would be able to do the same job while using less material while still
conforming to highway regulations. These regulations required the sign to be high enough to
avoid being struck by larger trucks, and also be able to withstand high winds. We expect to be
able to design a stable structure to support the sign while keeping costs to a minimum. From our
design and analyses using modeling software, we will show our design is a viable option to what
is being used now.
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Design and Analysis Results
Design Summary
At our first meeting we brainstormed design concepts, keeping in mind our objectives
and goal. Our first design utilized two beams, one being parallel to the ground and the second
anchoring the far end to the top of the support pole (Appendix, Figure 5). We determined that
since we were utilizing a triangular shape, the sign would not be able to be secured in a way to
prevent bending from the wind. The next design iteration we came up with was a u-shaped beam
with a support in the middle (Appendix, Figure 6). Although it was unique, it would not work
since we would be using too much material and it would be harder to manufacture. The third
design we came up with featured two parallel beams attached to the support pole with a cross
support in the middle (Appendix, Figure 7). Although this would be a sturdy design, we opted
against it since we could achieve the stability with less material. The fourth design, which would
be a basis of our selected design, featured two beams attached at one end to the pole and pinned
in the middle (Appendix, Figure 8). This design looked good at first but it had a few problems.
One of which was it would be harder to secure the beams where they cross since they were not
keyed. We decided to cut a notch halfway through both beams where they cross so that lock
together and allow for the sign to lay flat. The two beams could be welded to join them with
minimal work. This design utilized the least amount of material, and could be produced and
assembled fairly easily since it only requires two cuts and a weld. Based on these qualities, we
chose this design. Before this design was modeled and analyzed in Abaqus, materials had to be
chosen to test.
Material Alternatives and Selection
The material selection was one of the most imperative considerations affecting the sign
support structure design. There were series of measurements and calculations conducted in the
decision making. A research shows the U.S. Transportation Department has been using
aluminum for transportation implementations since the 1950s. However, there were still several
alternative materials considered on this design.
The objectives of the materials selection were based on the following four factors: (1) a
series of physical and mechanical properties of the materials, strength, stiffness and ductility, (2)
the load resistance of the wind [1], (3) chemical corrosion resistance, and (4) the cost and
application. Decision making later maintained these four factors. There were four alternative
materials researched for the sign structure design.
We started the research from aluminum which is frequently used in many applications.
The material we picked was 6061-T4 (See from Appendix). Based on the specification that
Matweb.com offered, aluminum has excellent joining characteristics, relatively high strength and
workability. The application of 6061 was easily perceived from hardware. 6061-T4 has relatively
high tensile strength. Its modulus elasticity is 68.9 GPa and a shear modulus of 26 GPa. Its
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density is 2.7 ×103 kg/m3. The modulus of elasticity and shear modulus factor greatly into the
decision whether the sign could resist the pressure from the wind. Its aging temperature is 160
°C, which means the material will maintain its strength under this temperature. Aluminum 6061T4 also has good chemical corrosion resistance to bear aggressive environment. [3]
The second material we choose was Stainless Steel 304. The use of stainless steel is also
relatively common in daily life due to its high tensile strength, high corrosion resistance. Based
on the data that Matweb.com offered, the density of stainless steel is 8.00 ×103 kg/m3. It has a
UTS of 500 GPa, yield strength of 215 GPa, range of modulus of elasticity is 193-200 GPa, and
its shear modulus is 86 GPa. The research shows that stainless steel has high strength and good
workability, which fulfills the requirements of fabrication. Its high ductility could help sign
structure perform a stable dynamic behavior against the wind. Stainless steel 304 is also a low
carbon steel, which means it possess a low susceptibility and high corrosion resistance.
The third material we considered were Glass Fiber Reinforced Polymer Composites
(GFRPs). A research article shows that GFRP composites are feasible to use for crack
connections of sign structure due to its decent mechanical properties [2]. Thus, we took it into
consideration as one of the options in this circumstance. GFRP has a range from 19 GPa to 31
GPa of modulus of elasticity [2]. And its shear modulus is around 15 GPa [4]. It has low density
compare to metals. The other advantages based on its mechanical property are good resistance on
corrosion and under different environmental conditions. And research shows that GFRP
composites have been adopted in various civil engineering projects such as composite beams and
joints which could resist applied load. [2]
The Feasibility Comparison and Cost
The very first two materials we considered for this design were steel and aluminum. The
comparisons were conducted after the research. The list below ranks the orders of different
property. The final decision was generated from the multiple considerations below.
Density: Stainless steel 304 > Aluminum 6061-T4 > GFRP composite
Tensile/ Shear Strength: Stainless steel 304 > Aluminum 6061-T4 > GFRP composite
Corrosion Resistance: GFRP composite > Aluminum 061-T4 > Stainless steel 304
General Cost: GFRP composite [5] > Stainless steel 304 > Aluminum 6061-T4
Due to the comparison above, we concluded Aluminum 6061-T4 would be the most
feasible material to build the sign structure. It has enough tensile strength and shear strength
which fulfilled the requirements. The density is relatively low compare to Stainless steel 304.
Since, the demand of certain weight is not the factor we considered. However, lower weight of
the material would be easier to transport and construct. The corrosion resistance is another nonnegligible factor. It relates to the lifetime of any fabrication. Aluminum 6061-T4 has relatively
stronger on corrosion resistance compare to Stainless steel 304. And GFRP perform as the most
stronger on corrosion resistance among those three. The last option we need to consider is the
cost of the materials. Aluminum 6061-T4 has lowest cost among those three which would reduce
the total expense of building a sign structure.
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Our cost estimation was based on the market price. According to a material supplier in
Ohio (McMaster.com), cost to build a 0.5 inch thickness, 18 meters (in total) fabrication sign
structure would approximately cost 2,500 USD in total, not include workers wage.
Stress/Deformation Analysis
To ensure the Aluminum was the best choice not only on paper, the model was first
analyzed for stress and deflection using the mechanical properties for Stainless Steel 304.
Figure 1. Stress Analysis (Stainless Steel 304)
Figure 2. Deflection Analysis (Stainless Steel 304)
After Stainless Steel, the structure was then analyzed with the mechanical properties for
Aluminum alloy 6061-T4. The analysis gave favorable results towards the Aluminum being the
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better option for its strength relative to its cost (Figures 3 and 4)
Figure 3. Stress Analysis (Aluminum 6061-T4).
Figure
4. Deflection Analysis (Aluminum 6061-T4)
From Figure 3 and Figure 4, we can know that the largest stress happened near the bottom of the
pole which is 1.482*106Pa. Compare this to the yield stress of the Aluminum 6061-T4, which is
145MPa, the stress that acting on the pole is really a small number. Also, the largest deflection
happened on the 2nd chord at the furthest point from the pole, which is 2.842*10-3m. Figures 8,
7, and 9 in the appendix show the deflection in the x, y and z directions. Note that the deflection
is shown with signs to indicate their direction, therefore, the max deflection is the magnitude of
these numbers: In x-direction is 2.795*10-3m; in y-direction is 4.872*10-4m; in z-direction is
3.488*10-4m. Overall, the volume of the whole structure is about 0.3441m3 and the mass is
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929.082kg. When comparing the analysis of the stainless steel and aluminum or compared, the
following conclusions were made:
1. There is almost no difference between the Max Stress.
(1.471*106 Pa for steel vs. 1.482*106 Pa for aluminum)
2. There is a significant difference between the overall Max deflections.
(9.311*10-4 m for steel vs. 2.842*10-3 m for aluminum)
3. There is a significant difference between the total masses.
(2715.83kg for steel vs. 929.082kg for aluminum)
Hand Calculation Comparison
To analyze the mechanical properties of the designed sign support structure, we basically
focus on the Stress, Deflection, and Angle of twist. We assume the only external force is
produced by the wind on the area of the sign based on the weather condition of Cincinnati and
neglect the wind force acting on the chord and pole since the area are very small compare to the
sign.
By setting a 3D model of the sign support structure, the weight of the sign and the pole
will create the normal stress to the section we chose (Appendix, Figures 15 through 19). And not
only the wind force but also the moment of Z-axis will create the shear stress to the section .The
moment acting on X-and Y-axis will create bending stress. Based on the parameters we set up,
we can obtain the bending stresses are
σx=FwWC/2I
σx)max=183.86kPa
σY=PlC/2I
σy)max=747.19kPa
Then, it is easy to conclude that the maximum bending stress occur at the edge of the circular
section, where the distance is the outer radius of the tube. The only one normal stress, which
shows below will give the pole compression time
σz=ρ(l+a)g+Fw/A
σz)max=240.05kPa
So the maximum normal stress happens at the most bottom of the pole. The shear stresses
produced by moment along Z-axis and shear force acting along negative X-axis are
τz=2.25PC/J
τz)max=220.63kPa
τx=PQ/It
τx)max=240.5kPa
It is obviously that the maximum shear stress also happens on the edge of the circular section.
After the maximum values were obtained, we chose four points on the circular section to
analysis according to the direction and magnitude of each stress. Then by using Mohr circle
analysis we got the maximum and the minimum normal stress, shear stress and twist angle will
lead the extreme value.
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Then based on the material property we calculated the maximum angle of twist, which is
a very small value of 0.00024rad and within the range of twist angle to reach the maximum
value. We can analyze all the points on the circular section by using Abaqus.
Besides, to consider the elongation based on the difference of the temperature, we found
out the highest and the lowest normal temperature in Cincinnati, which is 103F and -22F, the
thermal strain we calculated are very small, which can be neglected. Also there will be a
deflection on the portion where the sign attached on the pole, the total deflection is 1.3mm,
which can cause the pole to deflect and cause the sign lower. But based on such a small
deflection compared to the whole structure we can neglect it.
Conclusions
From all of the research done on materials the Aluminum 6061-T4 appeared to be the
best choice for our structure design when considering strength and overall cost. After further
hand calculations and loading analysis in Abaqus, this was proved true. Although Stainless Steel
304 had lower values of stress and deflection, the aluminum alloy still had minimal stresses and
deflection and was much more cost efficient. Concepts from Mechanics of Materials were
integral for every part of this project. Stress analysis had to be performed in each beam, bolt,
and point of attachment. This stress analysis included all different analysis such as bending
stress, normal stress, and shear stress. Concepts for finding deflection also had to be used in
order to make sure the sign structure was not bending too much and possibly lower and hit a
semi-truck passing under. Overall this project was a very good test of all skills learned in
Mechanics and was very interesting relating those skills into a real life application.
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References
[1] Kaczinski MR, Dexter RJ, Van Dien JP. Fatigue-resistant design of cantilevered signal, sign and
light supports, NCHRP Report 412, Transportation Research Board, National Research Council:
Washington, DC; 1998.
[2] Pantelides, Chris P.. "Repair of Cracked Aluminum Overhead Sign Structures with Glass Fiber
Reinforced Polymer Composites." (2003): 9. Print
[3]Metals Handbook, Vol.2 - Properties and Selection: Nonferrous Alloys and Special-Purpose
Materials, ASM International 10th Ed. 1990.
[4] Federal Highway Administration. "Behavior of Fiber-Reinforced Polymer (FRP) Composite Piles
under Vertical Loads." [Online] April 2011.
<http://www.fhwa.dot.gov/engineering/geotech/pubs/04107/chapt2.cfm>.
[5] Chakrapan, Tuakta. Use of fiber reinforced polymer composite in bridge structure. (2004): 68.
Print
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Appendix
Table 1. Properties of Aluminum 6061-T4.
Density
2.7×10 kg/m3
3
Tensile Strength,
Ultimate
241 MPa
Tensile Strength,
Yield
145 MPa
Modulus of
Elasticity
68.9 GPa
Poisson Ratio
0.33
Shear Modulus
26.0GPa
Aging
Temperature
160 °C
177 °C
Rolled or drawn products; hold at
temperature for 18 hr
Extrusions or forgings; hold at
temperature for 8 hr
Table 2. Properties of Stainless Steel 304.
Density
8×10 kg/m3
3
Tensile Strength,
Ultimate
505 MPa
Tensile Strength,
Yield
215 MPa
Modulus of
Elasticity
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193-200 GPa
Poisson Ratio
0.29
Shear Modulus
86.0GPa
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Table 3. Properties of Glass Fiber Reinforced Polymer Composites.
Figure 5. Deflection Analysis x-direction (Stainless Steel 304)
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Figure 6. Deflection Analysis y-direction (Stainless Steel 304)
Figure 7. Deflection analysis in z-direction (Stainless Steel 304)
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Figure 8. Deflection analysis in x-direction (Aluminum 6061-T4)
Figure 9. Deflection analysis in y-direction (Aluminum 6061-T4)
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Figure 10. Deflection analysis in z-direction (Aluminum 6061-T4)
Figure 11. Design 1
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Figure 12. Design 2.
Figure 13. Design 3.
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Figure 14. Final Design
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Figure 15. Structure Parameters and Calculation Assumptions.
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Figure 16. Stress Calculations.
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Figure 17. Stress Calculations Continued.
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Figure 18. Mohr's Circle Analysis.
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Figure 19. Stress and Deflection Calculations of Structure and Bolt.
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Table 4. Dates and Time Spent in Meetings.
Dates
Minutes
10-Apr
60
17-Apr
60
25-Apr
120
1-May
90
2-May
240
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