Structural Subsystemx

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1.

Structural Subsystem


In order to achieve a functional solar kiln it is necessary to construct a suitable structure housing the
drying process. This structure needs to supply a way of transportation for the timber trolley inside the
kiln as well as suitable insulation to preven
t heat loss through its walls. A
way

to measure the mass of
the timber trolley during the drying process

is also requested.

This section will describe and illustrate all
the requirements and functional elements of the structural subsystem

mentioned above
.

This
subsystem can be divided into four sections to provide solutions for the four main functional
requirements

namely, kiln structure, railway structure, weigh bridge and insulation solutions. It is the
responsibility of Stellenbosch’s civil contractor t
he construct the structural subsystem. Al the
information, suppliers and measurable entities to perform this construction is described in detail below.

1.1.

Kiln Structure

The solar kiln structure was designed by SUN engineering and its construction is to be p
erformed by
contractors, KS Builders. KS Builders was the company chosen to build the solar kiln structure, based on
their experience, credibility and cost and time efficiency. SUN Engineering has worked with KS Builders
previously. This section states
the decisions made toward finalising the design of the structure, as well
as how those decisions interlink with the customer requirements. The final design was sent to KS
Builders, in advance, for clarification of any possible ambiguity, as well as to all
ow time for preparation


1.1.1.

Description of the solar kiln structure

This section states the specifications within the final design, and their relation to the customer
requirements. It also includes the different options considered before the specifications w
ere finalised,
illustrating the basis on which the decisions were made.

1.1.2.

Function:

The solar kiln structure was designed to enclose the timber stack while providing insulation and housing
the infrastructure required in the drying process. The structure w
as designed to ensure minimum heat
and moisture losses, as to provide a basis for the control system to control these factors. The structure
was also designed using cost effective materials that are also strong enough for the operation.

1.1.3.

Functional Inter
actions with other Subsystems

The design of the structure was based mainly on the specifications of the subsystems within it. The
external part of the structure, especially the angle of the roof, was designed to accommodate the
collector. The weight of t
he collector formed the basis of the strength calculations done for material
selection. The rest of the external part of the shape was designed to accommodate the ventilation and
the fans. Within the solar kiln, the

positioning of the sensors
and Weigh B
ridge, were considered during
the design process. The Weigh Bridge determined the preparations required on the foundation of the
structure.
The
kiln structure was designed so that it can accommodate the size of the weigh bridge.
Refer to the sections in t
his report, for the specifications of these subsystems.


1.1.4.

Design considerations

In order to select appropriate materials, the following calculations were done. The collector is to be
placed at a 40 degree and for optimum solar collection. Refer to the solar collector
section (??) for

more
specifications. A simplified model was used
for calculation purposes. The simplified model is shown in
figure 1 below. To compensate for the simplification, a safety factor of 1.5 was used in calculation.





Figure 45654

200

20

40°

F
1

F
2

F
4

F
3

F
mass

Beam Section View


The material selected is SANS 1431 GR 350WA, which has a yield strength of 350 MPa. The material,
with the selected dimensions, is therefore strong enough to withstand the load of the collector.
For
more information regarding the chosen material refer to

Appendix 1.


The following materials are generally used for kiln construction within the industry:



Pre
-
cast concrete



Masonry



Aluminium panels



Wood

Pre
-
cast concrete:

This type of kiln structure is most suitable for large operations, that have large forces acting on the
building itself, such as the weight of the solar collector or a large ventilation system. This is a quiet
system, which is most cost effective for appl
ications requiring a volume of more
than 150 cubic meters.




Masonry:

This structure is well suited for long lasting operations. The strength of the masonry is comparable with
that of the pre
-
cast concrete. Therefore this system is suited for heavy dut
y operations, with large
forces acting on the structure itself.

Aluminium panels:

The aluminium structure is easy to erect, for any size operation. This system can also with stand large
forces, as has no cold conductors when insulated. Although easy to

erect and easy to disassemble, it
was found that this system is expensive when compared to same sized kiln structures made from
different materials.

Wood:

The wooden structure is easy to erect, and may be installed quickly. The structure, however, is b
etter
suited for smaller operations as it cannot withstand high forces. The wood structure is also subject to
corrosion and would have to be reinforced after several years of operation.

Final decision

It was decided that a steel frame, with a masonry bo
dy, be used to balance strength and affordability.
The complete wood structure would be the more affordable option, but because of the weight of the
collector as well as the fans, a stronger material was chosen. The complete concrete structure would be
a
ble to withstand the weight of the collector and fans.

For more information regarding the concrete and
masonry materials refer to
Appendix 2 and 3.

Our

intended operation has a capacity of more than 150
cubic meters, which would also make the concrete stru
cture cost effective. The final design was
ultimately chosen based on the lifetime of the structure. The masonry system is better suited for long
life operations.


Figure
1

1.1.5.

Component Listing

Figure 1 below illustrates the final solar kiln design given to KS Builders.


Final design

The final design of the kiln was done based on the 40 degree specification of the collector as well as the
dual flow directions of the fans. To support the collector effectively, additional support beams were
included. The ventilation positioning was dec
ided after considering the flow of the air through the kiln.
The vents were positioned so that air to be expelled is not re
-
circulated through the kiln, and clean air
does not flow directly across the timber stack, which was a customer requirement. The s
ize of the
timber stack and the cart, on which it is to be transported, determined the size of the door frame.
A well
insulated steel sliding door will be used and its dimensions were based on the door frame dimensions.

The length of the solar kiln was det
ermined based on the length of the timber stack. It was also
requested that air is not to flow over the ends of the timber stack. The final length was therefore
chosen so that the end walls channel the air flow over the width of the timber stack. The di
mension
specifications are illustrated in figure 1 above.

Maintenance

The width of the entire kiln structure in includes 2.5 meters on either side of the door frame. This
distance was included, for the fans used for air expulsion support, as well as to
allow human entry for
maintenance purposes. Testing and maintenance on the weigh bridge may therefore occur whilst the
timber stack is in the kiln. The maintenance to be done on the structure over the kiln life time is
minimal, although visual inspection
s should be done every 3 months. Within these inspections, possible
cracks or defects should be noted and investigated.

End of life

The kiln structure has a twenty year lifetime, after which the kiln is to be disassembled. The aim, at the
end of the l
ife of the kiln, is to best restore the surrounding environment to its previous state. The
masonry structure would have to be broken apart, collected and transported of
f

the plant. There are
means of recycling masonry products, and there are factories th
at specialise in this. The steel frame is
to be disassembled and inspected. If it is found that the beams are in a good condition, they may be
used in future structures. Otherwise, the beams may also be transported from the plant to a factory
that specia
lises in steel recycling.

Cost

The table below describes the cost of the structure construction.

Material

Description

Quantity

Cost

Flat beams

Kiln frame

(SANS 1431 GR 350WA)

9 x 9m

2 x 8m

2 x 5m

11 x 6m

2 x 3m

R498.24 per

meter

4 x 3.6m

2 x 1.3m

2 x 6m

Flat plate

Kiln frame

(SANS 1431 GR 350WA)

1 x (9.4 x 1.3)m

R600 per square meter

Bricks

Kiln body

8000 bricks

R1.40 per brick

Concrete

Foundation and brick
laying

156 tons

R760 per ton


Time schedule:

The main time schedules regarding the kiln structure is the time required to procure the materials, and
the time required to build the kiln. The concrete structure is to be laid first, after which the structure
would be erected. The entire kiln construct
ion process would take 3 weeks.

1.2.

Railway Structure

To supply a means of transportation for the timber trolley through the kiln it is necessary to develop a
way of transport. An already existing railway will supply a means of travel to the kiln entrance
,

f
rom
where the trolley needs to be transported to the kiln exit
,

back on the existing rail.

1.2.1.

Technical Specifications

All the technical specifications of the railway system are mentioned below. Decisions were made to
elongate the already existing transportat
ion system.

1.2.1.1.

Track Type

The same I
-
beam type track that is currently in use will be used to transport the trolley through the kiln.
As it is already in use no calculations were made to ensure that the rails can withstand the mass of the
loaded trolley. Two

rails tracks of length 9 m are necessary. A pitch of 1.5 m will be used for rail
construction as requested.

1.2.2.

Component Listing

Two I
-
beam types R412 will be necessary. This type of I
-
beam is priced at R 659.43 per meter of length.

1.2.3.

Railway Functionality

Due to the fact that the same rails, as already used by Stellenbosch Sawmills, will be used for
transportation purposes, minimal calculations and thought were put into its design. The rails will be able
to meet its requirements.

1.3.

Weigh Bridge

In order to effectively control the solar kiln, the control subsystem required the construction of a
structure capable of measuring the timber trolley’s mass inside the kiln. This requirement resulted in the
design of a rail weigh bridge inside the kiln. T
he weigh bridge construction uses
four

load cells to
determine the mass of the trolley. The weigh bridge specifications and boundaries are discussed below.

1.3.1.

Technical Specifications

All technical design specification of the weigh bridge is discussed in the
following sections.

1.3.1.1.

Foundation Requirement

The total size that the weigh bridge will occupy is
4 m (length) x 2.9 m (wide) x 0.89

m (deep). The
specification for the concrete foundation layout is
as follows. A 4.25 m (length) x 3 m (wide) x 0.89

m
(deep) a
rea needs to be laid in the centre of the kiln. A platform area of
850 mm (long) x 650 mm (wide)
x 61.4

mm (high) is needed in the corners of this hole. Four

50 mm diameter and

150 mm deep threaded
holes
need

to be dri
lled in these platforms. Two 1.5

m (wi
de) x 1.5
5
m (long) x 0
.89

m (deep) areas needs

to be left for

installation and maintenance purposes. The foundation

main dimensions are

shown in
figure
3, 4 and 5
.



Figure
2


Figure
3


Figure
4

1.3.1.2.

Weigh Bridge Size

The

weight bridge consists of a 4
m (length) x 2
.9

m (wide) x 0.3 m (high) SAE 1018 steel platform. This
platform will be the
stationary

position of the trolley while the timber is drying inside the kiln. Trolley

rails will be mounted on this platform. The platform dimensions are suitable for the 1.5 m pitch rails.
The platform with the mounted rails is
shown in
figure
6
.


Figure
5

1.3.1.3.

Platform Support

The platform is supported with four bea
ms made of SAE 1018 steel which are bolted to the bottom of
the platform. On the other side of the beams the necessary threaded holes is available for the load cell
attachment. One of the support beams can be seen in
figure 7
.

1.3.1.4.

Load Cells

The load cell mod
ule that will be used in the weigh bridge setup is the 0958 Flexmount Weight Module
supplied by Mettler Toledo. The setup uses four load cell modules in compression. The Flexmount

module was chosen due to the ease of installation and capability of deliveri
ng accurate and reliable
outputs. These modules are also capable of withstanding the force of the trolley (16 tons) acting on
them which makes them suitable for the application.

The specific load cell in each module is the
0743 High Capacity Beam Load
Cell

also supplied by Mettler
Toledo. These load cells are situated within a stainless steel casing with provides excellent corrosion
resistance against the conditions inside the kiln. The load cells are hermetically sealed which ensured
readings
will not

be in influenced by changes in humidity. The safe operating temperatures of the load
cells is between
-
20 °C


65 °C which is ideal for the kiln temperature range.

After installation the system will be calibrated to take into account the weight of the wei
gh bridge
system. The setup of the load cell modules enables the system to discard any readings caused by
thermal expansion and contraction. This is favorable in an environment with fluctuating temperatures.

Each load cell comes with the necessary wires to operate. The wiring will be guided in insulated pipes to
the necessary destination where the control system will use the output.


Figure
6

1.3.2.

Subsystem Interface

The weigh bridge syst
em is interfaced with
one other subsystem
.

1.3.2.1.

Control Subsystem


The final subsystem affected by the weigh bridge is the control system. A way to transport the output
from the weight bridge to the control system must be designed. The information the control
subsystem
needs is as follow.



Rated output of 2 ± 0.005 mV/V



Excitation voltage: 5


15 V AC/DC



Cable length 18.2 m

1.3.3.

Component Listing

This is a brief discussion about the components used in the weigh bridge system including cost, model
numbers, warranty a
nd lifetime.

1.3.3.1.

Platform and Platform Supports

The cost for a platform and supports of the
specified volume is
R 72726
.25. The material type is SAE
1018 steel, a very common steel type.

1.3.3.2.

Load Cells

The cost of one load cell module is R 4988.20. The module use
d is the 0958 Flexmount Weight Module
with a
0743 High Capacity Beam Load Cell inside. Each load cell module has a li
fetime of greater than 1
million

cycles. The guarantee on each load cell module is 10 years.

For more information regarding the
load cells module refer to Appendix A.

1.3.4.

Subsystem Layout

Below is a diagrammatical representation of the weigh bridge.
Figure 6

shown the design of the l
oad cell
supports while figure 7

shown the weigh bridge with the con
crete structure.


Figure
7


Figure
8

1.3.5.

Weigh Bridge Operation

In order to show that the weigh bridge will perform its task a few calculations regarding certain aspects
needs to be shown.

Calculations were done as prescribed by Shigley (
Budynas, 2005: 159).

1.3.5.1.

Load Cell Loads

The compressive load each load cell is subjected to is determined below. The mass of the load timber
trolley
is 16 tons. In order to simplify the calculations the timber trolleys mass was applied to the centre
of the trolley. The mass of the steel platform is also taken into consideration by estimating it as a point
load applied at the centre of the platform.




Timber mass

Platform weight

S1, S2

S3, S4

Figure
9


The deformation of each su
pporting beam was found to be 28.8
5 µm/m which is acceptable. The safety
factors of the supporting beams

to plastic deformation

were determined to be 51 which are very
acceptable.



1.3.5.2.

Platform Strength

To support the fact that the platform will be able to support the timber trolley the following calculation
was done. Maximum bending stress and deformation was our main concerns but the calculations give
us
confidence in the design. The worst case scenario was created by placing the mass of the structure and
trolley in the centre of the platform as shown in figure

11
.



































steel
7840
kg
m
3

TS
400
MPa

YS
220
MPa

E
steel
220
GPa

width
p
4
m

length
p
2.9
m

height
p
0.3
m

Volume
platform
width
p
length
p

height
p


M
platform
Volume
platform

steel


M
trolley
16000
kg

F
platform
M
platform
g


F
trolley
M
trolley
g


F
tot
F
platform
F
trolley


F
one_support
F
tot
4

Area
support
0.13
m
0.13

m


one_support
F
one_support
Area
support


one_support
6.279
10
6

Pa


one_support

one_support
E
steel


one_support
2.854
10
5



n
YS

one_support

n
35.037

length
supports_width
1.95
m

b
3.392
m

h
0.3
m

I
b
h
3
12


F
tot
424.463
kN

M
width_max
F
t ot
lengt h
supports_widt h
2

4

M
width_max
103.463
kN
m



max_bend
M
width_max
I
height
p
2
























max_bend
2.033
MPa

n
bending
YS

max_bend

n
bending
108.19












length
supports_length
3.392
m

b
1
1.950
m

h
1
0.3
m

I
1
b
1
h
1
3
12


F
tot
424.463
kN

M
lengt h_max
F
t ot
lengt h
supports_length
2

4

M
width_max
103.463
kN
m



max_bend1
M
length_max
I
height
p
2









max_bend1
3.537
MPa

n
bending.1
YS

max_bend1

n
bending.1
62.196

F

tot

F

support1

F

support2

Figure
10

1.3.6.

Time Schedule

From receiving the go ahead to manufacture the weigh bridge it will take three weeks to receive all the
materials necessary to construct the structure. Installing the weigh bridge won’t take

longer than five
days. After installation is completed proper testing will be done to determine if the weigh bridge is fully
functional. Testing will take approximately two days.

1.3.7.

Operational and Installation Provisions

The operation of the weight bridge i
s automatic. Provision is made for installation and maintenance
purposes by leaving an entrance, in the form of a hole in the concrete foundation, to the bottom of the
weigh bridge to access parts when necessary. The platform has four attachments for easy
lifting with a
crane during installation. Maintenance occurs once a year and with the weigh bridge package the
supplier supplies two additional load cell modules for unforeseen consequences.

1.4.

Insulation

Insulation within the kiln is necessary to prevent
heat losses and harmful gas emissions to the
surroundings. It is a clinical part in the functionality of the kiln. As the structure is mainly masonry with a
steel frame and insulation material had to be chosen accordingly. Insulation specifications and
bou
ndaries are discussed below.

1.4.1.

Technical Specifications

All technical specifications of the insulation will be discussed below. Four layer of insulation will be used
throughout the kiln structure. Insulation is only supplied to the walls facing the environme
nt.

1.4.1.1.

Wall Insulation

The wall insulation setup is shown in the thermal resistance
diagram, figure 3. The setup consists of outer and inner
masonry walls. Adjacent to these walls are a 100mm air gap.
Separating the air

gap is the CavityLite 16 insulation material
supplied by Insulpro, a South African based company. The
insulation material is 50 mm thick. The insulation material is
non
-
combustible and an excellent insulator. It also has
favourable acoustic properties. Th
e fact that the supplier can
Figure
11

supply the insulation boards to the specified dimensions is favourable as different sized board will be
needed. A total area of 261 m² is required for the wall insulation.

1.4.1.2.

Inner Surface Insulation

The four inner walls of the kiln structure will be insulated using Megaphen insulation material also
supplied by Insulpro.

Megaphen's closed cell structure limits any direct moisture absorption which is
needed in the humid environment. The insulation mater
ial can be produced in any dimensions and
thickness necessary. The thickness of 3 cm specified will be used. A total area of 261 m² is needed to
effectively insulate the inner surfaces.

1.4.1.3.

Object Insulation

To insulate any objects and cold conductors inside
the kiln, Insulpro will supply their Rockwool Flexible
Felt insulation. The insulation is supplied in rolls of dimension 1 m (width) x 5 m (length) x 25 mm (thick).
This insulation material dimension can be altered as needed for a specific application.
All

insulation
materials are listed in Appendix V.

1.4.2.

Subsystem Interface

The insulation system is interfaced with the structure subsystem. The necessary dimensions of the outer
walls are necessary to determine the size of insulation materials needed. This size
is specified in sections
1.1.1 and 1.1.2.

1.4.3.

Component Listing

This is a brief discussion about the components used in the insulation process including cost, model
numbers, warranty and lifetime.

1.4.3.1.

Wall Insulation

The insulation used inside the walls are Cavity
lite 16 and can be seen in figure 3. The price of this
insulation is R 110.65 per square meter. No lifetime of warrantee exists for the insulation material. The
material has a density of 16 kg/m³, a thermal resistance value of 1.25 K/W and a thermal conduc
tivity
value of 0.04 W/m K.

1.4.3.2.

Inner Surface Insulation

The insulation for the inside surface is Megaphen insulation material and can be seen in figure 1. The
price of the insulation is R 133.55 per square meter. No lifetime or warranty exists on the material
. The
thermal conductivity of the material is 0.02 W/m K.

1.4.3.3.

Object Insulation

To insulate the objects inside the kiln the Flexible Felt insulation was chosen. The price of this insulation
material is R 35.16 per

square meter. This insulation is capable of wi
thstanding temperatures up to
650°C which is sufficient for the kiln. No warranty or lifetime exists for this insulation type.


1.4.4.

Subsystem Layout

The figure below illustrates the thermal resistance diagram of the insulation subsystem. The two
masonry walls,

air gaps, wall insulation and surface insulation are visible.









1.4.5.

Subsystem functionality

To show that the insulation methods prescribed above will meet the requirements specified the
following calculations were done. The total resistivity of the air gaps, inner insulation material and
surface insulati
on is calculated below.

Please refer
to figure 3 for

a better understanding.

Calculations
were performed by using heat transfer equations (
Cengel, 2006: 865).













h
air
15
W
m
2
1

C


k
wall_ins
0.04
W
m
1

C


k
inner
0.02
W
m
1

C


L
wall
50
mm

A
surf1
9
m
8

m
9
m
5

m

7.5
m
8

m
2



L
inner
30
mm

R
wall
L
wall
k
wall_ins
A
surf1


R
air
1
h
air
A
surf1


R
inner
L
inner
k
inner
A
surf1


R
tot
R
wall
R
inner

R
air
2



R
t ot
3.335
K
W

Masonry wall

Masonry wall

Air Gaps

Insulation

Inner Wall
Insulation

Figure
12
: Thermal Resistance Diagram


The total thermal resistance to heat conduction from the inside of the
kiln to the environment is 3.335
K/W which is well within the allowable specified range. The insulation is functional.

1.4.6.

Time Schedule

From receiving the contract the required insulation materials will take two weeks to obtain. The
insulation needs to be ins
talled in conjunction with the structure construction and can only start after
the inner walls have been built. The installation of the wall insulation and inner wall insulation will each
take one day. The total installation time for the insulation is depe
ndent on the speed of the structure
construction. Testing will commence during kiln testing to see if the insulation was properly installed.
Testing consists of various temperature readings taken during climate changes inside the kiln.

1.4.7.

Operational and Inst
allation Provisions

The insulation needs no operation. The installation procedure will be scheduled in accordance with the
structure construction schedules due to its dependence on each other. The wall insulation can’t be
maintained as it is in between to
masonry walls. The inner insulation material will be replaced each five
years to ensure proper insulation. Each of the insulation materials used can easily be removed from its
position if the structure needs to be disassembled.


1.5.

Subsystem Cost

Here follows

a detailed cost breakdown for the procurement and construction of the structural
subsystem.

Division

Unit

Cost per unit

Quantity

Price

Structure

Flat Beams

R 498.24 per meter

208 m

103633.92


Flat Plates

R 600 per square meter

12.22 m
2

7332


Bricks

R
1.40 per brick

8000
bricks

11200


Cement

R 760 per ton

156 tons

118560

Railway

Rails

R 659.43 per meter

18.8 m

12397.28

Weigh Bridge

Platform



72726.25


Load Cell

R 4988.20 per LC

4 LC's

19952.8

Insulation

Wall Insulation

R 110.65 per square meter

261 m
2

28879.65


Surface Insulation

R 133.55 per square meter

261 m
2

34856.55


Object Insulation

R 35.16 per square meter

20 m
2

703.2

Construction Cost




100000






Total




510241.65


Appendix A

Microsoft project appendix


Appendix B

Beams


Appendix C

Bricks




Maxibrick


A cost effective and economical masonry unit for single skin walls. Manufactured to strict
dimensional and strength requirements, it offers ease of handling and speed of building during
construction of houses, walls and industrial buildings.


View the product in use.


Height Available


Length Width


Strength


90 mm


290x140


7 MPa




Colours Available:

Grey
-

Special colours made to order





Appendix D

Concrete





Appendix



The relevant technical information of each insulating material
is tabulated below.


Righardts References

Budynas, R.G. 2005. Shigley’s Mechanical Engineering Design, New York: McGraw Hill


Cengel, Y.A. 2006. Heat And Mass Transfer, New York: McGraw Hill



Enrico’s changes can be found within the appendixes, thats

why i didn’t put references in the physical
text, because the text refers to the appendix, and the appendix refers to the website.

Maxibrick building products [online] Available:

http://www
.technicrete.co.za/building/masonry.php

[28 August 2008]


PPC cement products [online] Available:

http://www.ppc.co.za/ppc/view/ppc/en/page1 [28 August 2008]


Introducing SANS 1431 grade 350WA structural steel [online] Available:


http://www.hdgasa.org.za/Journals/indSearchs/S/SANS%201431.pdf

[28 August 2008]


Insulation
Type

Max Operating Temp(°C)

Density(kg/m^3)

Thermal
Resistance

Noise Reduction Coeff

Cavitylite 16

150

12

0.04

0.75

Rockwool

650

60

-

-

Megaphen

150

100

0.02

0.15