MATERIALS AND STRUCTURES 2

DES08118

TRIMESTER 2 – 2013

KATE CAVEN

STREET FURNITURE

(Garden Show, (2011)

Street Furniture

1. Introduction

2. Research

3. Development

4. Structural Analysis

5. Component Dimensions

6. Manufacture

7. Material and Finishes

8. Human Scale Analysis

9. Sustainability

10.Final Proposal

11.Design Review

12.Final

Introduction

This design proposal in response to the request for the tender requested by

the city of Edinburgh to provide adequate amount of seating for the

Gardening Show Scotland 2013. My Chosen festival is a garden festival and

one that I am designing for is The Gardening show Scotland which is over

three days and takes place at the Royal Highland show centre in Edinburgh

attracting around 40,000 visitors and over 400 quality exhibitors from across

the UK. The thousands of visitors who visit this festival are walking all day

and need somewhere to sit and relax whilst surrounded by the wonderful

displays this festival has to offer. The seat I am going to design will

accommodate up to four people so that there is plenty of seating for more

than just the normal bench you see at garden festivals. The materials that it

will be made from will be polypropylene plastic as this seating will be left

outdoors for the three days of the show as well as a second material. I want

a simple construction that would mean it can be put together quickly as

there will be a number of these seats to be placed around the festival. The

seat will have to complement its surrounds so I would like to incorporate

plants or flowers to my design.

(Garden Show, (2011)

Research My main component to my design will be made from polypropylene however I

want to choose a second material either wood or a kind of metal. To come to

a decision I want to compare two different kinds of material and their ability to

cope with outdoor conditions.

Teak Bench Cast Iron

• Advantages

• Tough, hard wearing material

• Long lasting

• Heavy duty

• Aesthetically pleasing

• Teak can be cut and shaped very

easily

• Teak wood is characterized by very

tight wood grains, which makes the

furniture extremely durable even

when heavy weights are placed on

top of it (important for a piece of

furniture)

Advantages

• resistance to deformation and wear

resistance.

• Cast iron is extremely strong and

durable when used appropriately

• and protected from adverse exposure

• High resistance to impact

• Secure against - heavy snow falls and

high winds

• Cost effective in long term

• Recyclable

Disadvantage

• Has several different joining

mechanisms

• Expensive

Disadvantages

• Its structure is relatively brittle and

weak in tension.

• Castings may be given a variety of

treatments to reduce rusting and

corrosion in the environment.

• Highly susceptible to corrosion when

exposed to moisture.

• Rusting is a common problem that it is

quite easily recognizable.

• Cast iron requires continual

maintenance

Research

From my research that I have carried out it is clear to me that teak

Is the best option for a quality piece of furniture that would be very robust and

last for years. When researching about cast iron benches they are extremely

strong and again durable so these material have similarities however the iron

benches have several disadvantages. When they are coated with a protective

coating this tends to need regular upkeep to make sure that it does not rust

which leads to the bench looking worn out and unappealing unlike teak which

needs no coating and little maintenance.

As you can see in the picture once

cast iron rusts it looks very

unappealing however the picture of

the teak bench after 12-18 months

without any protective coatings it

has lost its colour due to the sun

however it still looks in good

condition and still has character.

Research

After research I have decided wood will be my second material so I I need to

compare different woods to see which one is most suitable. The major

component of my design will be made from one rotationally moulded

polypropylene component as this has the properties for outdoor conditions.

The table below is my research to determine which wood is more suitable.

TEAK WHITE

OAK

CHERRY RED CEDAR

Advantages:

• Durable in all weather

• Teak does not cause

rust or corrosion

when in contact with

metal

• Teak is strong. It is

naturally oily, which

makes it a very good

material make outside

furniture from.

• Teak is highly

resistant to moisture,

fire, acid and alkalis

• Teak can be cut and

shaped very easily

Advantages

• Great strength &

hardness

• Very resistant to

insect and fungal

• Attractive grain

• Resistant to rot

• Environmentally

friendly

• Resistant to

wear and tear

Advantages

• Medium

strength. • Good bending

characteristics.

• Low stiffness

and medium

shock

resistance.

• Works easily

with hand and

power tools

• Polishes to an

excellent finish.

Advantages

• Cedar is a lightweight

and dimensionally stable

wood that lies flat and

stays straight. Which

means it resists the

natural tendency to

crack.

• naturally occurring oils

give off that distinct

cedar aroma that makes

the wood highly

unattractive to insects,

moths and other pests.

• Its bacterial and fungal

resistance coupled with

the fact that Cedar is

80% the strength of

Oak,.

Disadvantages

• It can be expensive

to buy and because

of the gritty nature of

the wood grain it can

blunt cutting tools

very quickly.

Disadvantages

• Expensive

Disadvantages

• Changes colour

when exposed to

light

• Dries rapidly with

little degradation

if care is taken to

avoid moderate

shrinkage.

Disadvantages

• Moderately priced

• cedar is a softer wood,

it is more susceptible to

dents and dings

Research

Looking at my table of results all four woods have properties that would cope

well with the outdoors however I am going to decide between White Oak and

Teak. White Oak is a very strong and hard material that would take the wear

and tear of the continuous use. It would be suitable for outdoors at the garden

show as it is very resistant to insects, fungal attack and is resistant to rot. As

white oak is a hardwood it is more sustainable and is a renewable source. Teak

is a great material for the outdoors as it can deal with all weather conditions

because of its natural oil and does not need any type of treatment to make it

suitable for outdoor use meaning there is literally no maintenance required. It

has a high level of comfort and outstanding durability. By doing my research on

the two types of woods I have chosen teak because I think it will stand better

than oak in the outdoor conditions . When water penetrates oak it reacts with

the high tannin content within oak, resulting in ‘blackening’ as you can see from

the picture at the bottom, also the levels of rain, wind and sun will make a

difference to how quickly the oak changes colour. I think teak is the desirable

option even if you don’t constantly cover it with a sealer you can let it grey and

it will still perform well . The excellent characteristics of teak are its very low

rate of shrinkage – only half of that of oak making it suitable for my design.

(Oak affected by sun) (Oak affected by rain)

Design Development

By researching my preferred material I can concentrate on my design. I

want my seat to accommodate four people and for several of them to be

placed around the exhibits to provide plenty of seating, they could also be

joined together to make them bigger. My idea was to have a rotational

moulded structure with teak seats. I need to think of a way in which these

teak seats would stay in place without them moving. To keep my rotational

moulded structure from moving It would be filled with water to give it weight

so that it would stay in position. I have designed an area on top of the seat

which can be used for decorative stones or a flower arrangement making the

seat into an exhibit within itself.

From my rough prototypes on sketch up I have thought about how the teak

seats would be inserted. The structure would be rotationally moulded to allow

the teak seats to be slotted in to keep them in position. Teak is not a light

weight material so its not likely for them to slide out however they need to be

secure so I will think of a way of making them remain in the slot.

Development

I have come up with a solution to how the teak seats will be kept secure

In the slot. As you can see in the sectional view below the rotationally

moulded structure will have a push fit system where the piece of wood will be cut

to slot into the seat and this will stop any problems with it sliding out. In the final

design you will not see this as it is not aesthetically pleasing and

ruins the looks so each side will appear as if the wood has not been cut.

(Section view)

This design is straightforward which means it wont be difficult to build on site.

This will be a tool free construction which will save time as there will be several

of these seats around the festival. The cap that opens to fill the structure will be

hidden under one of the teak seats so that you wont see it and makes it easy

and quickly to fill. The seat will be moderately lightweight with consideration to

the size so moving it when empty wont be challenging.

Structural Analysis The structure of my seat is straightforward with next to no major failure

points. My design will be very stable with the main structure being made

from polypropylene and manufactured by the process rotational moulding.

For my structure to be successful the materials have to have the ability to

resist forces that attempt to squeeze or compress the materials together. My

seat will need to take several stresses such as the weight of four people

sitting on the four corners. The main structure is Polypropylene which is

lightweight however it Is a strong material, due to the seats being positioned

on the vertices of the construction the upright outer edges would take the

compressive load of the people that sit on the four corners.

The decorative stones on top of the seat will create a

compressive stress which is why the structure would need to be filled with

water before putting the stones on as it may cause it to bend with the weight.

Partially filling the structure with water before hand allows the structure to be

weighed down and for some of the volume of air to be displaced by water

making this structure less prone to compression as water cannot be

compressed in the same way as air.

The teak also will cause a compressive load by being slotted in

to the structure. The polypropylene will need to cope with the weight when

being fitted. polypropylene can give a little and bend slightly to allow the teak

to slot in however this may cause some stress on the material. The weight of

the teak will also cause compression on top of the plastic structure and then

a person sitting on top of the wood so this is why polypropylene would be an

appropriate material to use because it can be rotationally moulded making it

a strong, sturdy structure as well as being mass produced to make several of

these for the festival.

(Diagram of stresses)

Development

(This is a few

sketches of how the

teak panels will slot

into the structure

using the push fit

technique)

Component Dimensions

These images are from an

assembly that show the

dimensions of the

polypropylene structure and the

teak seat that slots into the

main component.

Manufacture

The seat will be manufactured using the process rotational moulding which

means this will make the major component the structure hollow with the

structure being hollow I will have to fill the seat with water to keep it from

lifting and moving for its position. This plastic will be able to support this

weight due to its high stress properties which I talked about in the structural

analysis. The manufacturing process makes this structure available for

mass production meaning I could make a batch of these seat for the festival

to accommodate thousands of the visitors.

For the seat slots teak is a great material for the outdoors, it is

very easy to work with teak wood and it is manufactured in different types of

shapes and designs as well. The vast majority of commercially harvested

teak is grown on teak plantations found in Indonesia. For my seat I want to

make sure that it is sourced from a company that is environmentally

conscious there are several good suppliers in the UK for example ‘Robbins

timber.’ The teak will be cut to the correct size and shape then the slot will

be CNC machined out so that it is exact. Then the sealer will be put on to

protect the material from sun exposure.

Material and Finishes

The material I will use for this seat has to be suitable for the outdoor conditions

and be tough to handle wear and tear of the thousands of guests that will be

using it. The material that I will use for this seat will be Polypropylene as it has

many good properties that would be appropriate for outdoor conditions. These

properties include, Good resistance to fatigue, Resistance to corrosion,

Resilience against most forms of physical damage, It’s a tough material, Deals

with high stress and also the colour does not fade and will stay in good

condition for longer. Since this seat will take a high volume of people over the

course of the days at the show, by using this material it make its very easy to

maintain as it will be easy to wash down and clean.

I am going to add my second material to this chair to make it more

aesthetically pleasing . This material is teak which I have researched and would

be the most suitable for my design as it will be for outdoors. This is only a three

day event however could be used for other events, or kept in storage when

needed In the future. Teak does not need to be protected. It is a unique wood

that if left in its natural state, is virtually maintenance-free. Over time, untreated

teak furniture which is exposed to the sun will tarnish and turn a silvery, grey

colour however does not harm the strength or quality of the wood. If the seat

was to be left out I could either leave it naturally or apply a teak sealer which

provides protection from the sun and will keep its colour for longer. Teak will add

character to the seat and will attract visitors to it.

Colour scheme

For the colour scheme I have chosen more pastel colours for the polypropylene

such as a pastel green or a beige so that it fits in with its surroundings. I haven't

chose bold and bright colours because colours such as red tend to fade quicker

in sun due to the UV rays. I think the teak and the colours chosen for the main

structure will look visually appealing and provide not only at seat but with its

option to display flowers on the top.

Human Scale Analysis

(Anthropometric Data )

This chair is simply to rest your feet for a little while, its not a seat that

someone will be sitting on for a long period off time. The seat will have to

be at an appropriate height for an average person to sit on. Looking at the

anthropometric data it helps to see what the height, length, width would

be for the seat to be comfortable it also helps determine the size of the

overall seat. I have lowered the back height slightly they however will be

able to lean back and still be comfortable. The reason for this is because

of the middle ‘exhibit’ and so it wasn’t too high up.

Seat Size

Length 430mm

Height 420mm

Width 550mm

Back height 390mm

Sustainability

Sustainability is very important today as we are trying to look after our

environment and It has to be considered when designing my seat so

choosing materials that will last and can possibly be recycled after its finished

with makes the seat more sustainable. Polypropylene is one of my materials,

this material is not incredible sustainable however because it is strong,

durable and very resistant to wear and tear the material is going to last

without the need to replace it regularly and will get many years out of it. It

also has the symbol number 5 which means it can be recycled and possibly

melted down to produce something else as it is only one material this makes

it easier to recycle.

Teak is my other material which again is a durable wood that last

years and years without deterioration in its condition making it sustainable in

the long run. This material also does not need any finish on it, it can be left in

its natural state. Finding a right supplier is key also, I want to make sure that

it is from a company that is also concerned about the environment. I want to

keep to a UK supplier .

Company policy

Our goal is to find manufacturers within the UK, this not only allows us to

improve our economy it cuts our carbon footprint considerably. Our company

policy is to produce the best quality and be as environmentally friendly as

possible. Producing good quality pieces means that it will last for years to

come. A supplier that is eco conscious is important to us.

Final Proposal

I have designed a simple construction that would be straightforward to

set up for the festival which was what I intended to do. The person who

sets this seat up would not need any electrical tools they simply lift the

cap off (which would be under one of the teak panels) partially fill the

seat to give it weight so that it does not move then slot the teak seats

into the structure. The Festival is a very big show and with 40,000

guests, there will be several of these seats positioned around the

exhibits to ensure that the visitors have somewhere to rest their feet.

Part of the design was also to exhibit a flower arrangement or fill the top

with stones however that may take some time but make it very visually

appealing.

Design Review

From the start I wanted to design a seat made from polypropylene and

another material that would accommodate up to four people and be

comfortable enough for visitors to have a short rest from the long walks

around the show. Since this show is very big the seat needed to be simple

to set up but still visually appealing amongst the 400 exhibits the festival

holds. The research helped towards choosing my second material for the

design. I had to consider that the seat will be left outdoors and would need

to be a material that can handle any weather. The material teak was the

perfect material not only because it is durable for the outdoors but is an

elegant and attractive material that would fit perfectly into the festival

theme. Throughout my design development I needed a way of attaching

the teak panels to the plastic structure I wanted to make it as simple as

possible and I came to a solution to use a push fit technique and slot it in

between the plastic structure instead of using any bolts or screws. This

allows the seat to be set up quickly also making this technique hidden so

that it was not visible in the design. The structure being made with plastic it

can tolerate the stress of the push to make it fit which makes this method

possible. The structure is hollow and with the polypropylene being

lightweight it had to be weight down and the solution to this was being

partially filled with water and then the air allowing to be spread out to keep

the stones or weight from on top from bending the plastic. The teak panels

will add weight they will be 50mm each weighing down the structure even

more , even though the polypropylene is strong it could be an issue with

four people sitting on top. This would need to be considered and tested to

make sure that the structure could take the weight - If not I would need to

consider how I could make the structure stronger. This design would be

simple to manufacture, assemble, take apart and be a sustainable seat in

the long term. It will add that extra character to such a extraordinary

festival as well as a pleasant experience to the user.

Final

This is a perfect solution for the

‘Gardening Show Scotland’ as it

fulfils their needs to have an easy

set up seat that is practical as well

adding extra character to this

wonderful festival.

References Images

• Garden Show, (2011), Garden Show [ONLINE]. Available at:

http://www.gardeningscotland.com/gardening-scotland-2011-

gallery/#all/4/grid [Accessed 21 April 13].

• JUST TEAK, (2012), Teak garden bench [ONLINE]. Available at:

http://www.justteak.co.uk/teak-benches/granchester-180cm-teak-bench-

details.htm [Accessed 21 April 13].

• Rendezvous, (2012), Cast Iron Bench [ONLINE]. Available at:

https://www.upbeat.com/rendezvous-bench-cast-

iron/L1364/product.aspx [Accessed 21 April 13].

• Sue Ferris, (2012), Cast Iron Bench [ONLINE]. Available at:

http://www.freshhomeideas.com/diy-projects/eco-friendly-projects/how-

to-restore-a-cast-iron-bench [Accessed 21 April 13].

• Wood finishes direct, (2012), Oak affected by sun [ONLINE]. Available

at: http://www.wood-finishes-direct.com/blog/2009/10/19/what-

everyone-should-know-about-finishing-oak/ [Accessed 21 April 13].

• Wood finishes direct, (2012), Oak affected by rain [ONLINE]. Available

at: http://www.wood-finishes-direct.com/blog/2009/10/19/what-

everyone-should-know-about-finishing-oak/ [Accessed 21 April 13]

• .Tanks UK, (2012), Rotational Moulding Process [ONLINE]. Available at:

http://www.tanksuk.co.uk/process.html [Accessed 21 April 13].

References

Websites

• Properties of Teak, Technology student (2013) Properties of Teak.

[online] Available at:

http://www.technologystudent.com/rmprep08/teaky1.html [Accessed: 24

Apr 2013].

• HooveDesigns, Types of Woods, HooveDesigns (2013) Types of

Woods. [online] Available at: http://www.hoovedesigns.com/woods.html

[Accessed: 23 Apr 2013].

• Sciverse, International Journal of Industrial Ergonomics, Sciverse

(2008) International Journal of Industrial Ergonomics. [online] Available

at:http://www.sciencedirect.com/science/article/pii/S0169814107001746

#fig2 [Accessed: 22 Apr 2013].

• .Tanks UK, (2012), Rotational Moulding Process [online]. Available at:

http://www.tanksuk.co.uk/process.html [Accessed 21 April 13].