optimizing the design process for frp shell structures
TRANSCRIPT
OPTIMIZING THE DESIGN PROCESS FOR
FRP SHELL STRUCTURESP2 Research framework
ABSTRACT FRP materials can greatly benefit the built
environment. With FRP more complex designs are
possible and larger structures and spans can be
realised. However to fully benefit from the
advantages of FRP in shell structures a new design
process is needed, that is adapted to get the full
potential out of FRP shell structures
Kirolos Abdalla ‐ 4023722
Main mentor: Joris Smits
Second mentor: Arie Bergsma
External Examinator: Olindo Caso
Date: 26/06/2015
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Contents
1 1.1 The Fibres 3 1.2 The Polymer 3 1.3 The Composite Material 4
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2.1 Shaping process 5 2.2 Case study 6
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3.1 Problem statement 7 3.2 Objective 7 3.3 Research question 9 3.4 Scope 10
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4.1 Methodology 11 4.2 Architectonic shape 12 4.3 Geometrical design and optimization 13
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5.1 Time planning 16
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Introduction The Industrial revolution started a chain reaction in the building environment. This was made
possible by the use of new materials and the implementation of conventional materials in innovative
ways. By using steel in a constructive matter and glass, buildings became taller and more elegant
through their transparency.
However since the industrial revolution only little has changed in the usage of building materials.
Materials have been improved and by this taken to their very limit, but little new materials have
been introduced that had a large impact on our recent building methods. Especially in the
constructive part of buildings. This very strange if compared to other fields in engineering. In most
fields of engineering, materials are one of the main subjects that keep being developed to meet the
design requirements. In architecture a lot of design are restricted to the limitations of the used
materials. Of course the design assignments of architecture are on a much larger scale than designs
in the automotive industry and budget is a very serious restriction in the architectural field, but new
materials can help develop architectural designs.
One of those materials are fibre reinforced materials. Fibre reinforced materials are composite
materials, meaning they are made of two or more materials. In this case they are fibres, that
reinforce a polymer. This result in a very light and strong material, that can be shaped to meet the
design requirements. The automotive industry already uses this material due to the fact that is very
strong, light and all shapes are possible. One of the first cars that was produced in this way, was the
hemp car from Henry Ford, that did not get dented when hit on by a hammer. Until now FRP
materials are not widely used in the building environment. Small application in building envelopes,
window frames and supplying extra strength in steel beams are already being used. However very
little constructive elements are built in FRP. This report will first focus on what FRP materials are and
what their advantages are. Then it gives a problem statement on why FRP materials are still not
being used in the building environment. Eventually this will result in a research question, what the
starting point of the graduation design will be.
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1.1 The Fibres Because FRP’s are a composite material they exist out of multiple components. This results in a large
variety of different sorts of FRP materials, with different properties. The fibres are divided in 4 groups
according to the source of their base material(Knippers, 2011). These are natural fibres, organic
fibres, inorganic fibres and metal fibres. Except for the natural fibres, they all have to go through a
melting and stretching process to be created. Because of this process that aligns the structure of the
material lengthwise, the fibres become much stronger and flexible than their original form(Gardiner,
2009). After being stretched the fibres are bundled, which is called a roving and twisted together to
create a yarn. This yarn is measured in kilo. 1 [k] = 1000 fibres. This is important to measure the
strength of the eventual FRP. Metal fibres will be excluded because they are not fit to make FRP
materials. Their surface is to smooth for the polymer to create a good connection.
Constructors give their preference to fibres that have a minimal elongation(Knippers, 2011), or a high
young’s modulus. The tensile strength is also of importance in these fibres when it comes to creating
constructive components. When looking to the different fibres it shows that natural fibres have to be
excluded too, because of their very low young’s modulus they are not suited to create constructive
elements in buildings. This leaves us with two groups of fibres. However cost is a very important
limitation in building components. Aramid fibres for example have very good qualities to be used in
constructive components, but are very expensive. When comparing all the fibres together the most
effective fibre to use is the E‐Glass type fibre("CES Edupack 2014," 2014), made out of alumino‐
borosilicate glass. Carbon fibre is expensive compared to e‐glass, but can be added to the parts
where extra strength is needed.
In conclusion the main disadvantages of the fibres are their cost in comparison to other conventional
materials. Also the fibres are very strong, but only in their length direction. This means that the fibres
should be supported at their ends.
1.2 The Polymer Equally important as the fibre, the polymer or matrix that forms the composite. In order to fully
understand the working of this composite material, the forming of the polymer needs to be
explained. Polymers in most cases synthetic materials that can be divided in to three
groups(Knippers, 2011). These groups are the thermosets, elastomers and thermoplastics. All three
groups have specific properties and usage, but sometimes properties can be shared. The most
common definition of these 3 groups are:
Thermoplastics
No cross connection in the material
Low melting point
Melts when heated, so recycling is possible
Mostly used for packaging materials
Image 1: Different fibres (L to R) glass, metal, aramid and hemp
Image 2: Thermoplastics
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Elastomers
Do have cross connections
Not recyclable
Very elastic, not suited for constructive elements
Mostly used to divide loads (Car tires, levellers)
Thermosets
Lot of cross connections
Not recyclable
Stronger and more rigid than other types
Buns when heated
Because attachment to the fibre is of great importance in FRP’s(Mallick, 2007) the polymer should
have a lot of cross connections. This means that thermosets are the best option when creating FRP’s.
This means also however that the building component is not recyclable. Mixtures of polymers do
exist to create materials with different properties, also additives could be mixed with the polymers to
adjust them according to the design specification. These could result in the following
properties(Knippers, 2011):
Cost reduction
Colourings (Have a large impact on heat storage and reflectivity of the material)
Increasing the durability
Reduce brittleness
Fire retardants
Improving outer surface for coatings
Thermosets are therefore the choice to create FRP’s, because of their many cross connections, strong
properties and the ability to shape them to meet the design requirements.
Of course using thermosets comes with a few disadvantages. The main disadvantage of the polymer
is its inability to be recycled. Some recycling is possible(Koo Young & Seung Hee, 2012) but is still
difficult.
1.3 Composite material Concluded that the most suitable material to create FRP’s are glass fibres and a thermoset. By using
the CES edupack program a selection of different polymers and fibres can be made. Here it shows
that the best solution to use FRP’s in buildings is a combination between the E‐glass fibre and
unsaturated polyester resin. This composite is one of the cheapest FRP’s, but still maintains a high
young’s modulus and is very well to shape.
The positioning of the fibres in this material determine in which way the loads could be carried.
Fibres can be placed in both directions, but this will result in a loss of strength (Mallick, 2007).
Therefor the positioning of the fibres should be done according to the different loads that will work
on the design.
Image 3: Elastomers
Image 4: Thermosets
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2.1 Shaping process Another important aspect for producing FRP components is the shaping process itself. The chosen
process has a large impact on many different factors that determine how the finished product will
look like. A few important factors are:
Production cost
Freedom of shape
Design limitation (Thickness, connections, symmetries etc.)
Margins (Margins for connections)
The production process should therefore be chosen according to the design specifications (Wu &
Burgueño, 2006). In some cases the design needs to be changed to the limitations of the design
process. Most methods in designing FRP components are based on moulds, where the fibres are
placed and the polymer is either poured or sprayed on. This can be done by hand or by machine, for
example vacuum devices that ensure a good distribution of the polymer. The eventual designed
shape determines here the chosen production process. It is clear however that the use of moulds is
very important in shaping FRP components. It is also clear that more moulds equal an more
expensive structure. It is interesting to research in this stage if the design shape can be achieved
with less moulds. This reduces the cost of the production process and the whole structure.
Furthermore the production process of FRP’s are pre‐fabricated. This is a very important factor and
advantage in the use of FRP’s in buildings. Because FRP components are made in a controlled
environment, it is less likely for mistakes to occur in components. The impact on building sites and
their surroundings are also a lot less, because on site the structure only needs to be assembled. This
reduces the time spent on a building site and the nuisance that comes with it.
The last stage of the production process is the transportation. Because FRP is relatively light in
comparison to other materials, large object that can be lifted by crane are a possibility. However
transport is equally important. Transportation of very large object via road, will come with a lot of
trouble and cost. Therefor it is very important to divide the structure in the best possible way to be
able to transport them and design the best possible connection to assemble the components back to
each other on the building site.
In conclusion the shaping process has a very large influence on the FRP components. The main
disadvantage is the more different components there are, the higher the cost. This is due to the fact
that more moulds have to be made, that comes with high costs. Since this projects only focusses on
optimizing the design process for the FRP shells new production methods like the Kine‐Mould
(Schippers et al., 2014) will not be taken in to account.
Image 5: Loadbearing only in the direction of the fibre
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2.2 Case Study An interesting case study is the Chanel pavilion from Zaha Hadid Architects. This building houses an
exhibition area and is demountable for transportation. The unique shape of the building was very
difficult to make in materials other than FRP. With the use of FRP the building also became lighter,
this was a great benefit since the building is demountable for transport over the world.
The panels for the Chanel pavilion were produced by Sage One. This company made use of CNC
milled moulds to shape the moulds for the FRP panels. All of the 400 hundred panels used in this
pavilion were different of shape. Therefor 400 different moulds had to be made. This comes at a
price since the production of the building cost one million euros, which is reasonable compared to
the benefits it had from the FRP panels.
Image 6: Different shaping processes (L to R) Hand lay‐up, Resin infusion moulding, RTM, Spray up
Image 7 & 8: Chanel Pavilion by Zaha Hadid Architects (Photograph by Stefan Tuchila)
Image 9: Production of the FRP panels for the Chanel Pavilion
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3.1 Problem statement Eventually the main problem statement focusses on the advantages of FRP that are not utilised and
the high cost that comes with the making of FRP structures that require a complex shape as shell
designs. This is mainly due to the use of moulds that increase when the design is more complex.
More moulds equal an higher production cost. Therefor the problem statement can be summarized
in the following sentence:
“In the current design process it is not economically feasible to create FRP shell structures and
therefor the advantages of FRP materials are not utilised.”
The problem statement can be divided in several sub problems that would need to be resolved:
Current design methods do not offer room for new materials.
With the traditional design and building process, there is little space for the usage of FRP materials
(Kendall, 2007). FRP materials require a lot more knowledge about the material and more research
(Wu & Burgueño, 2006). Also to improve the qualities of FRP roof structures the process itself needs
to be pre‐fabricated and workers should be highly skilled to work with such materials.
It is very expensive to create shell structures from FRP.
Although FRP materials offer a lot of advantages in comparison to other materials, they do come
with a higher initial cost (Berg, Bank, Oliva, & Russell, 2006). It is very important for clients and
contractors to research whether the advantages of FRP are worth the high initial costs.
FRP materials are not recyclable.
It is important to state that this problem will not be a focus point in the graduation process, but does
need to be taken in to account when designing structures with FRP. Because of its difficult nature to
recycle. Recycling does exist in some terms and is officially recognized by the European
Union(Fibercore, 2011), but requires a lot of work. FRP materials are because of this not suited for
the design of temporarily buildings or buildings with a short lifespan.
3.2 Objective The main objective of this graduation project focusses on the Delft Central Station. The Delft central
station was recently completed. In this project a whole new tunnel was made to lead the train
underground. A whole new office building is made that houses the municipality and acts as the new
central station. In front of this building the bus station is placed. This bus station, which is also on the
side of the old central station, is fairly busy. It has direct connection to different large cities outside
delft like Rotterdam, Den Haag and Zoetermeer. For this graduation project a shell structure out of
FRP will be made, to cover this bus station. This project will mainly focus on the engineering of the
shell structure. Of course at first it will be a difficult architectonical assignment to determine the right
shape of the structure. There are a lot of difficult architectonical challenges that need to be solved
first to finalize the right shape. The eventual shape should be of value for the bus station. This means
that it should give value on an architectonical level to both buildings, old and new as well as
providing shelter for passengers and not be an obstruction to the passengers or other flows.
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Demands for the project can be described as followed on different levels
Architectonical level
FRP monolithic roof structure
Connects both old and new Central Station
Does give value to both buildings in an architectural way
Does not obstruct any of the flows in the Delft Central Station
Technical level
FRP monolithic roof structure
Area to cover is about 200 m2 (40 x 50 m)
No usage of enforcements other than FRP
Shape provides its own structure
All components must be pre‐fabricated
Transportation by truck
Only existing production processes will be taken in to account
Finished product
The finished product will exist of a design for a new FRP roof structure for the Delft Central station.
This roof structure will connect both old and new central station and the shelter the bus station and
its passengers. It is very important that this FRP roof has an advantage for the passengers that make
use of the bus station. This roof is designed to match the flows of the passengers and not the other
way around.
The main focus point will be the engineering of the FRP roof structure. This includes technical
drawings for the production of the FRP roof structure, detailed drawings of the different connections
that need to be made and calculations to determine the right shape and thickness of the whole
structure. Eventually the conclusion of this project will provide a toolbox of what the design process
for FRP roof structures should look like. It discusses for which project FRP would be most suited and
which obstructions could occur when designing FRP structures.
Image 10: impression of a roof structure for the Delft Central Station
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The other important aspect of this report is the cost. FRP roof structures are very expensive. Therefor
the advantages of these structures should be evaluated to see if they are worth their costs. This
evaluation is presented in a form of comparison with other roof structures that are built in
conventional materials. This will give a good overview on how well FRP roof structures will perform in
the current building environment.
3.3 Research question The main research question for this graduation project will be:
“How can an optimised design process help create a FRP roof structure with a large span for the Delft
bus station?”
With these research question there are several sub questions that need to be answered first. These
sub question eventually answer the main research question.
What are the advantages of FRP roof structures?
How does the flow of pedestrians and other users of the Delft Central station look like?
What are the regulations for such structures?
How can the shape be geometrically optimized?
How can the roof shape give value to its surroundings (Delft Central Station)?
How can such a structure be build/transported? (Shaping Process)
What are the cost of such a structure?
What happens to the structure when it reaches its end of its lifespan?
How well do FRP roof structures perform compared to conventional materials?
Image 11: Impression of a FRP shell structure for the Delft Central Station
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3.4 Scope Architectonic Design
Focusses only on the Delft Central station
Creates a roof for the bus station
Does not obstruct any flows
Does not degrades its surrounding buildings in value
Shape eventually determined through computer simulations and studies
Technical design
This focusses on the elaboration of the structure in detailed drawings
This includes foundation and support, connections and shape
Calculations of the structure through computer software
Production process
The production process focusses on existing methods, that are already being used to produce
FRP components
Whole structure is pre‐fabricated
Transportation of the panels are an important factor
Cost
Cost estimation of the structure will be made on current prizes of materials and production
An estimation of the cost of a similar structure will be made for an evaluation structure
Toolbox will be focussed on these factors
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4.1 Methodology The method that will be used for the design process will continue to reflect to previous drawn conclusions. The whole research and design is based on several sub research questions that need to be answered before the process can continue. The conclusion of research question 1 is necessary input for research question 2. It is therefore important to keep reflecting to the previous drawn conclusion and in the end it is of importance to evaluate the whole design with the individual conclusions of the sub questions.
Image 12: Design scheme
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4.2 Architectonic shape
In order to determine the right shape for the shell structure an analysis has to be made of the
different flows in the Delft Central station. In this analysis all the flows are mapped out, including
pedestrians, cyclists, busses and trams. The roof structure should benefit these flows here by offering
them shelter instead of being an obstacle.
From this analysis the location of the different supportive elements could be determined. The roof
structure here should benefit these flows by offering them shelter, not be an obstacle for them.
Out of this comes a foot print for the
shape of the FRP roof structure. The
shape can be made by lifting the
lines up, where the flows pass
through.
Image 13: Different flows in Delft Central Station
Image 14: Determining the location of the supports
Image 15: Determining the shape for the roof structure
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4.3 Geometrical design and optimization
By using a parametric design software as Grasshopper, we can create shell design that eventually can
be optimized. One of the possibilities to create such a design is by defining a surface area first, this
could be the one found in the flows of Delft Central Station.
After defining a surface area, Grasshopper can generate a grid on top of this. This grid contains the
points that will create the shell shape. Using a smaller grid will result in a smoother and more
accurate shape, but would require the computer more time to render.
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To lift the area up we can use a spring simulator like Kangaroo. This simulates springs that push the
surface upwards. This is similar to hanging a cloth on all ends and let gravity shape the cloth. In this
stage we can specify the stiffness of the materials, anchorpoints, elasticity, forces etc.
Eventually Grasshopper can calculate a shell design that would be formed. Here it show that the
more points are added on the grid, the more accurate of a result will be generated.
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When the desired shape is made, the points could be patched to create a 3d object of the shell.
This 3D object can be analysed. Here there is a curvature analysis by Rhino that shows where the
maximum curves are. Red being positive curves and blue being negative curves. The shape can also
be exported to other programs that can calculate the stresses, moments and loads for the structure.
From here the shape can be altered to improve the loadbearing structure of the FRP shell.
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5.1 Time planning
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