(201IINEEA1 - 201IIN1A11)
INTRODUCTION TO ENGINEERING
DESIGN 1A
INDIVIDUAL DESIGN PROJECT
EGG PROTECTION DEVICE
CHARUMBIRA TINASHE B.
219063251
ABSTRACT
Concrete egg protection device will be a small structure designed to withstand a monitored
number of blows directed from above to protect an egg that will lie below it. To protecting the
egg from any damage, the structure needs to be strong enough and be able to withstand all
blows. The egg protection device (EPD) design will be constructed using specified materials
and within the dimensions stated.
IDENTIFYING THE PROBLEM
According to Hammond (1996), a large egg is 57-64 grams in mass and is a very fragile object
which does not require much force to break it and on average It takes around 25N to crack.
An egg protection device has to be designed using only concrete, admixtures and aggregates.
This structure must be strong enough to withstand a normal falling mass so as to protect an egg
that will be below it. A certain number of blows will be applied from above, and the blows will
be increased after each success. The blows will start at a height of 1m with a mass of 1kg then
2kg and 3kg successfully, a 4kg mass will then follow falling from a height of 0.8m then a 5kg
mass at 0.6m and finally a 5.5kg mass at 0.4m above the device.
DEFINING THE PROBLEM
Designing and building the highest impact-load resistant, concrete Egg Protection Device
(EPD) with the supplied materials within the dimension/mass restrictions by protecting an egg
from directed falling masses from above using an overlapping concrete structure.
INTRODUCTION
Designing and egg protection device that can withstand blows and protect egg below by coming
up with a shape that is able to resist and stand firm against a normal force.
RESEARCH & PREPARATION
Previous EPD competitions
In 2017 the Pretoria Portland Cement (PPC), sponsored Inland Branch Egg Protection Device
competition was held on September first. The total participants were 270 pupils from 4
institutions which are:
1. University of Johannesburg
2. University of Pretoria
3. University of the Witwatersrand
With a total of 40 egg protection devices, only 21 passed, meaning 19 of them were not within
the required dimensions and/or masses.
In 2018, sponsored again and hosted by Pretoria Portland Cement (PPC), the competition was
held on August 31st. a total of 34 egg protection devices were submitted but 13 of them were
not within the required specifications of mass and/or dimensions, making the number of those
that competed back to 21devices. The winners of the year’s competition set a new record,
increasing from the previous by one, adding to a total of 54blows.
CONCEPTUALISATION
On generation of the design concepts, a focus was made to make all designs adhere to the
project’s maximum and minimum values of both the mass and dimensions. This would ensure
a fair ground for the judgements and evaluations of the design concepts in accordance to the
Egg Protection Device Design Rules. In each design a concentration was also made in making
sure that the feet of the structure were made is a way that would ensure that the designed
structure stands on a flat surface on its own with no other supporting structures or any external
forces. The concepts drawn are also in 2Dimensions only, since it is only a concept and not the
final plan so they are only showing a side view of the concept design. The one that comes as
the final design amongst the evaluated projects will then be further developed.
Concept 1
Figure 1: concept design 1
This design was based on the strong structure of the triangle which will transfer the impact
force directly to both the side supports and the ground. This design utilizes the ground as a
support and also the sides. The design also minimizes the shear forces involved in the legs of
the structure
Concept 2
Figure 2: concept design 2
The second design is an Arch. This design mostly uses the ground normal force as a support
and less on the sides. But the structure is also good in the sense that it utilises its elasticity to
when hit as intended. Arch structures are more elastic under compression as supported by Wen
(1987). This also as an advantage as we bare more concerned on the structures ability to change
the momentum of the falling mass to zero.
Concept 3
Figure 3: concept design 3
The structure is unique but for this design the structure will be thin so as to fit within the
maximum mass limit of 5.5kg. This also implies that the strength of the structure is greatly
reduced and the centre bridge where the guided mass strikes is likely to experience a positive
bending moment and break.
SYNTHESIS
Limitations
•
•
•
Structure will be built with only Concrete, Admixtures and Aggregates.
Device will also be limited to specified maximum and minimum dimensions.
mass of structure will be 5kg
Figure 4: Image of dimensions from EPD document rules
Table 1: Concrete Density, Modulus of elasticity and Compressive strength
Kind of Concrete
Density (kg/m3)
Modulus of Elasticity Compressive Strength (
N/mm2)
×103 (N/mm2)
Ordinary
2200–2300
25–35
20–50
Light-weight
1400–1900
10–18
15–30
Aerated
500–800
1.5–2.2
3–8
Concrete Density - an overview | ScienceDirect Topics (Elsevier, 2020)
Since structure has to have a maximum mass of 5kg and ordinary cement of around 45MPa is
going to be used for the larger part of the concrete structure hence it is safe to take a density of
2300kg/m3.
𝜌=
𝑚𝑎𝑠𝑠
𝑀
=
𝑣𝑜𝑙𝑢𝑚𝑒 𝑉
And since both mass and density have maximum values therefore the volume also has a
maximum value which can be found using the equation:
𝑉𝑚𝑎𝑥 =
𝑀𝑚𝑎𝑥
𝜌𝑚𝑎𝑥
Where the maximum volume and density are known, therefore
𝑉𝑚𝑎𝑥 =
5kg
= 2.173913043 × 10−3
2300kg/m
= 2.17 × 10−3 𝑚3
The maximum volume is 2.17×10-3m3 and therefore the dimensions of the concrete structure
should make up a volume less than that of 2.17×10-3m3.
EVALUATION of CONCEPTS
Table 2: Evaluation of all concepts
I
Design 1
R
R×I
Design 2
R
R×I
Design 3
R
R×I
9
7
4
9
10
5
7
8
4
7
7
6
7
6
4
3
36
49
28
54
70
30
28
24
319
9
6
6
6
6
6
8
7
81
42
24
54
60
30
56
56
403
7
5
7
4
3
4
5
8
63
35
28
36
30
20
35
64
311
Production cost
Maintenance cost
Time to complete the project
Score
-6
-2
-3
5
1
4
-30
-2
-12
-44
7
2
5
-42
-4
-15
-61
8
4
3
-48
-8
-9
-65
Net score
70
Design Criterion
Positive
Originality
Practicability
Manufacturability
Reliability
Performance
Durability
Appearance
Uniqueness
Score
Negative
275
342
246
Design 2 As the Final Solution
Overall, the second, design 2 has the highest score of 342 followed by the first design with a
score then lastly the third design. This then indicates that the second design, the arch like
structure, having the highest score of 342 is going to be the final solution and design in this
paper.
OPTIMASATION
To make sure that we have a structure which is exactly under the 5.5kg maximum value, the
calculations made will make use of a maximum mass of 5kg. The feet of the structure have
been expanded by increasing the contact surface area at the bottom to ensure that the structure
stands on its own without toppling. To make sure that the structure has a mass just below 5kg
and also maintain its arch like structure, the inside of the structural design is curved, giving it
a spherical inside look.
In order for the structure to stop the falling masses efficiently, the structure must do Work
against the Kinetic energy of the falling mass (Sjoblom, Hartness, and Cordell, 1988). In
addition to the shape, a more elastic type of concrete will be used at the feet of the structure so
as to make use of the structure’s elasticity to increase the impulse, this increases both the length
moved during the collision and the impulse, known as the change in momentum.
Since modulus of elasticity(E) =
𝑆𝑡𝑒𝑠𝑠
𝑆𝑡𝑟𝑎𝑖𝑛
=
𝜎
=
𝜎𝐿
𝜀
Where 𝜀 =
𝑐ℎ𝑎𝑛𝑔𝑒 𝑖𝑛 𝑙𝑒𝑛𝑔𝑡ℎ
𝑜𝑟𝑖𝑔𝑖𝑛𝑎𝑙 𝑙𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑚𝑎𝑡𝑒𝑟𝑖𝑎𝑙
=
𝑥
𝐿
𝑥
𝐸=
𝜎𝐿
𝑥
𝑥=
𝜎𝐿
𝐸
Since 𝜎, L are constants, in order to produce a large length moved during collision the modulus
of elasticity needs to be small, but the change in length (𝑥) should not be too great and should
not to exceed the breaking point, hence it might be safer to use the light weight cement with
an E of 10–18×103 N/mm2 than the aerated cement (Benazzouk, 2006). Also, in addition to
that, generally the arch structure is elastic owing to its circular-like shape, further increasing
the distance moved during collision (Podio-Guidugli, 1990).
Material and design process
•
•
Since the top surface is getting hit directly by the falling guided mass, it should be
strong for it not to fracture and therefore the feet of the concrete structure will be made
up of light weight with a mixing ratio of 8 parts sand, 8 parts cement and 8 parts
aggregates to 5 parts water.
Mixing ratio of a 45MPa concrete grade is 1-part Cement + 3-parts coarse sand + 3parts aggregates (AFRISAM, 2020).
Using a 200l drum, an arch shell can be made using the measurements from above using a
welding machine, pliers and a few other tools.
Pour into container up to the point where the feet start. Concrete generally cures in 28days but
sets in 24-48 hours (Bernardo, 2006). To make the structure strong and make sure that the there
are no extra joining complications of the two, between the legs and the feet of the structure and
so by pouring on top of the wet legs it joins the two parts neatly, ensuring that the feet are flat
at the bottom. Thus, the application of the light weight cement is done after 30hours.let the
structure cure and solidify then gently open the metal shell using a welding machine.
Figure 5: Feet of EPD from AutoCAD 3D
•
Since structure has to be strong and withstand falling masses, the cement type has to be
strong. A 45MPa type cement will be strong, cheap and locally available.
Shape
•
•
An arch appears to be strong (Habbal, 2003) and according to Conde, Díaz-Vilariño,
Lagüela and Arias (2016) it is also elastic allowing larger impulses to be experienced.
Foot structure should have about the same height as the fixed base plate, to try to
minimize avoid fracturing caused by the sheer force acting within the foot.
Figure 6: Image of foot of egg protection device and fixed base plate from EPD document rules
PRESENTATION
Figure 7: Final 3Dimensional design for the Egg Protection Design in 3D (AutoCAD 3D image 1)
Figure 8: Final 3Dimensional design for the Egg Protection Design in 3D (AutoCAD 3D image 2)
Figure 9: Drawing of Views (AutoCAD 2D images)
EGG PROTECTION DEVICE
DRAWN BY : TINASHE
CHARUMBIRA B.
360mm
435,36mm
360
450mm
435,36
450
DATE
14/04/2020
DRAWING NUMBER 003
SCALE
1:1
PROJECTION
UNIVERSITY OF JOHANNESBURG
The height of the feet makes use of the base plate using it as a form of support from the
horizontal forces. The flat top of the structure has an inclined edge and according to Wienke,
and Oumeraci (2005), this distributes an impact force to a greater area and then into the arch
like structure then to the more elastic feet. The feet of the structure should make use of the
maximum dimensions of both length and width but in order to counter for errors the dimensions
of the feet are just a little less than the maximum values.
Figure 10: Final Design Specification from AutoCAD 3d
Volume of structure is =2079682.3995mm3 = 2.08×106mm3=2.08×10-3m3
Maximum volume is = 2.173913043 × 10−3 = 2.173913043 × 10−3 ×
10003 𝑚𝑚3
𝑚3
= 2173913.043𝑚𝑚3 = 2.173913043 × 106 𝑚𝑚3
= 𝟐. 𝟏𝟕 × 𝟏𝟎𝟔 𝒎𝒎𝟑
𝑴𝒂𝒔𝒔 𝒐𝒇 𝒔𝒕𝒓𝒖𝒄𝒕𝒖𝒓𝒆 = 𝝆 × 𝑽 = 𝟐𝟑𝟎𝟎 × 𝟐. 𝟎𝟖 × 𝟏𝟎−𝟑 = 𝟒. 𝟕𝟖𝟒𝒌𝒈
Volume of structure is under the maximum required volume and within a good range, therefore
the expected mass of the whole structure should be under the maximum mass of 5kg.
CONCLUSION
With the structure just below the 5kg mark, it is safe to say that the mass will be within the
ranges required. The structure also makes use of the elasticity of the arch shape hence provides
a greater impulse and would look forward for the structure to withstand a considerable number
of blows
REFERENCES
AFRISAM,
2020,
High
Strength
Cement,
29
March
<https://www.afrisam.co.za/products-services/cement/high-strength-cement>
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<https://www.sciencedirect.com/topics/engineering/concrete-density>
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2020,
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