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FRAMES IN SPACE (1): DESIGNING AND
MAKING A SMALL SCALE SPACE FRAME
WHAT YOU W ILL LEARN
After com pleting this un it, you shou ld un derstand:
W h at a fram e is.
The difference between weak and strong fram e structures.
How frame parts can be joined together .
How lightweight fram e parts can be made and assembled.
You sho uld be able to:
Recognise and n ame parts of a structure - e.g. t ies and
struts.
Work to a design brief and write a specification.
Recognise constraints when designing.
Design and m ake a frame structure using roll-tubes.
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A frame structure consists of a nu m ber of parts or com pon ents
jo in ed togeth er to support a load or resist forces. Th e typ e of
frame used to sup port th e tiles or slates in a h ouse roof is an
example of a two d imen sion al frame structure. Other examp les
includ e bicycle fram es and gates.
If you t h ink for a m om en t abou t uses of th e word frame - e.g.doo r fram e, ten t frame - you will realise h ow com m on frame
structures are.
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Many high technology buildings use three dimensional frame
structures - sometim es called space frames.
Th is un it teach es you abou t th ese exam ples and oth er structures
by inviting you to m ake a prototype fram e product for a firm of
structural en gineers. Before lookin g at th is task, you n eed to
know som e basic terms and h ow to u se th em correctly.
The exam ple shows part of a buildin g wh ose outer skin is
suppo rted by an external framework. Tower cran es use a similar
th ree dimensional structure.
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TWO D IMENSIONAL FRAMES
Two dimen sion al fram es are
often referred to as trusses an d
are flat or planar. Theycon sist of slend er strut s and
ties join ed at th eir end point s.
Th e trian gle form ed by th e
three parts of a satellite TV
aerial fram e is an exam ple of a
sim ple tru ss.
Th e example shown h as a wall
plate and a sin gle strut and tie.Because it form s a com plete
triangle, it is rigid an d stable.
Th is m eans th e frame will n ot
chan ge its sh ape wh en forces
act on it un less there is a
structural failure (i.e.
comp on ents parts or joints
break).
If a frame is mad e up from
four parts bolted together as
shown , it lacks rigidity. Wh en
subjected to forces, it ten ds to
beh ave as a parallelogram .
The add ition o f a fifth
(diagonal) component,
h owever, makes it rigid.
The sam e prin ciple is applied
to flat pack furn iture wh ich
incorporates diagonal bracing
to give it rigidity.
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The sim ple bridge truss sh own below is very weak un til two
diagon al strut s are added.
Each roo f truss of a mod ern h ouse cont ains several diagon al
comp on ents. To support a given load, the amo un t of material
used in a roo f truss can b e reduced by good d esign. Modern
trusses use much th inn er and less tim ber than th ose of 20 years
ago an d are said t o b e m ore efficient .
Th e m ore complex trusses used in bridge and buildin g
con struction con sist of a larger n um ber of strut s an d ties - some
of which are placed diagon ally.
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Th e tetrahedron can be repeated m any tim es to provide a
com plex space frame (e.g. on e th at span s a wide gap withou t
support at th e centre). Modern buildin gs sometimes incorporate
space frame structures to lift th em off th e ground or to support
roofs.
THREE D IMENSIONAL FRAMES
Three dimensional frames are
also called space frames or
space tru sses. Th e least
com plex space fram e is a
tetrahedron m ade up of six
components .
Simp le space fram es of th is
type m ay be used for
supporting platform s or other
loads on th e sides of buildings.
Som e examp les are given.
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A designer called Buckminster-Fuller became famous for his
investigations into th e use ofgeodetic space fram es. A geodet ic
frame is a th ree dimen sion al structu re whose parts fit togeth er to
enclose a space.
The example shown uses simple triangular frame elements
repeated m any t imes to create a dom e. Th is kin d of fram e can be
covered in a flexible material for use as a building.
The com pon en ts of space frames can b e joined in a variety of
ways. Th e m ost comm on m ethod s are pin join ts or gusset plates.
In a pin join t, th e pin is usually a steel pin (with h igh shear
strength ) or a bolt. The gusset plate m eth od u ses a m etal plate to
which comp on ents are eith er welded or bolted.
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DESIGNINGAND MAKINGA SPACE FRAME
Evac Geodetics plc is a well kn own firm of consultin g engin eers
wh o advise architects on structural design . In th e course of its
work, Evac makes up scale models of structures for clients.
Th ese show h ow structures will function and what th ey will look
like. Over th e years, Evacs mo del m akers h ave devised a m eth od
of m odelling frames usin g what th ey call roll tube con struction .
Th is is a m ethod of making tubu lar frame com pon ents which
look and beh ave like th e real th ing. Th e following pages h avebeen t aken from Evacs m odel m akers h an dbo ok.
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ROLL TUBES
Roll tubes are made from paper woun d
tightly around a plastic or metal cylinder
called a m and rel. Wh en t h e rolled tube is
slipped off th e m an drel, it is very stiff.
Un like drin king straws, roll tub es con sist of
at least 10 layers of paper m aking up a wall
th ickn ess of at least 1 m m .
Roll tube dimen sions
The in side diam eter (I/D) of a roll tube is th e
outside diam eter (O/D) of the m and rel,
providin g the tu be is tigh tly wound .
Th e outside diameter of a roll tube depen ds on th e nu m ber of turn s of paper.
For a required O/ D of roll tube, th e nu m ber of turn s of pap er requ ired is given by:
No. turns = Required outside diam eter - m andrel diameter paper thickness
2
For exam ple, for a required O/D = 8 m m , man drel O/D = 5mm and paper thickness = 0.1 mm
(ordin ary phot ocopy paper):
Num ber of tu rn s = 8 - 5 0.1 m m = 15 turn s.
2
The approximate length of paper n eeded for a required roll tube is given b y:
Length = no. turns x diameter of m andrel x
For example, num ber of turn s = 15, man drel O/D = 15 m m :
Len gth = 15 15mm 3.142 = 707 mm app roximately.
Th e act u al legt h o f p ap er is: L = n o . o f t u rn s x m ea n d iam e ter of t u be x
= 15 x 16.5 x = 778m m
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MAKING ROLL TUBES
Method 1
Cut th e paper to th e correct length an d
width (allowing extra width for trimm ing
after rollin g). App ly adh esive (e.g. Pritt stick)
to th e paper edge to close the roll.
Carefully wrap th e oppo site edge of th e
paper roun d th e man drel and roll it up over
a flat surface.
Un less th e paper is woun d p erfectly parallel
to t h e m an drel, one en d will spiral inslightly an d th e oth er end will spiral out .
Trim both ends with the type of scissors
shown . Their high m ech anical advantage
en ables th e th ick tu bes to be cut easily and
th e serration s prevent th e tube sliding
between th e blades.
Wh en rolling is comp lete, burnish th e glued
edge with th e back of a spoon - keeping th e
m an drel in side. Slide the tu be off th e
mandrel.
Method 2
For additional strength, adhesive can be
app lied to t h e who le paper surface before
rollin g. Spraym oun t or dilute PVA can be
used.
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Metho d 3
If th e end of a larger diam eter tube is to beleft open - for example, to contain an oth er
sliding tu be - adh esive sh ould b e applied
alon g th e edges of th e paper so th e layers of
pap er at the en ds are glued solidly together.
TERMINATING ROLL TUBES
For m ost space fram e structures, roll tu bes
can be joined u sin g sm all nu ts and b olts.
The tube requires flattening and reinforcing
where a bolt p asses throu gh.
Th e tube is pressed flat and th en p un ched
using a com bined eyeletter an d rivetin g tool.
Reinforcing eyelets are th en inserted an dclosed with th e tool.
The flats on a tub e m ay be parallel to each
oth er or at an y desired an gle. Th e flats canbe m ade to flex or h inge by creasing with a
ruler edge pressed d own very firmly.
FINISHING ROLL TUBES
Roll tubes can be spray paint ed with
cellulose or enam el paint . Alternatively,
coloured paper can b e used in th eir
con struction . Special papers available
includ e th ose with day-glow colour
fin ish es. For o th er m odelling effects or
sim ple labelling, th e pap er can first be passed
through a ph otocopier to print an im age.
(Th is on ly needs to be printed o n th e edge of
th e paper).
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INVESTIGATINGTHE STRENGTHOFA ROLL TUBE
The stren gth o f roll tu bes can be tested. This can be used as th e
basis for a scien tific investigation . The sim plest way to test th e
strength of a roll tube is to supp ort th e tube at th e ends andcontin ue addin g loads to th e cen tre un til the tub e collapses.
Other factors that could be investigated include:
1) The distance between th e supports.
2) The n um ber of turns on th e roll tube. It m ay be easier to
m easure th is in term s of the length of paper used.
3) The th ickness of the paper used.
4) Th e use of various types of glue to bond th e paper in t h e tube.
5) The use of telescopic tubes. It is possible to bridge larger gaps
by m aking telescopic roll tub es (i.e. rolling a tu be aroun d on e
previously made).
For a fair test, only on e factor at a tim e m ust be chan ged (i.e.
when testing th e num ber of turn s, th e distance between th e
supports needs to be constant ).
A roll tube will suppo rt a larger load if th e load is suspen ded from
two lines or wires at th e tube en ds.
Load
Roll tube
Roll tube
Load
String
Set up in t h is way, a roll tube m ade from a sh eet of A4 pap er will
easily suppo rt loads in excess of 25 N. Furth er investigation s
could be carried out t o find out t h e best m eans of supp orting th eload with th e strin g(s).
SCIENCE OPPORTUNITY
Empir ical investigation of strength l eadingto data for plotting a graph.
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MATHEMATICAL ANALYSIS
The results from the
investigations can be plotted
and com pared on a graph. Areth ere lin ks between th e
nu m ber of turns or the
distance between th e supp orts
and t h e load th at causes
collapse?
Load
(N)
Distance between supports (mm)
YOUR TASK
As part of its current advertisin g exercise, Evac is giving away to client s
a small flat-pack gift that can easily be made up into a small piece of
desk furniture - e.g. a pen stand, book-end, desk tidy, clock. Because
roll tubes are associated with the firm, Evac wants the gift to be a
small space fram e kit using mainly roll tubes. You are asked to design
and m ake a prototype gift using roll tube components.
DESCRIBING YOUR TASK
First, you n eed to draw u p a design specification
for your space fram e prod uct. A specification is
a m ore detailed d escription of what a produ ct
will be like, wh at it will do an d wh o will use it.
Here are som e question s to h elp you produce
your product specification:
Wha t will the p roduct do on the desk?
Will the product need any special tools for
its assembly?
How will the space fram e roll tubes be
jo in ed ?
Wh at material will you use for the roll tubes?
Wh at diameter(s) will the roll tubes be?
DESIGN BRIEF
DESIGN SPECIFICATION
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N ylon cord
4mm d iameter
studding
Assorted sheet and
other materials
W HAT YOU HAVE TO WORK W ITH
Before you get on with your d esign work, you n eed to kn ow wh at
m aterials and eq uipm en t are available. Your t eacher will provide
you with some of th e mat erials listed below. Make a n ote of whatth ere is.
A lumin ium sheet (for gussets)
Eyelets
N uts and b olts
A ssorted pap er
DESIGN CONSTRAINTS
Punch Tool
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WORKING OUT YOUR DESIGN
On ce you kn ow wh at m aterials and equipm ent are available, you
need to th ink about som e ideas for th e space frame prod uct.
Set your ideas down on paper .
Play a round with your ideas.
Check your ideas against your specification.
Decide which is the best design.
Do a deta iled drawing of the design.
You will n eed to end up with a workin g drawin g from which you
or som eone else can work to m ark out, make and assemble th eparts.
Before you start, th e followin g n otes will give you som e ideas
about h ow th e space frame produ ct can be design ed and m ade.
Th ey do not give you th e answer tho ugh! You m ust make the
impo rtant decision s and put all th e ingredients together so th at
you end up with an effective product.
SPACE FRAME GEOMETRY
There are a n um ber of well proven space frame geom etries or
shapes. Th e tetrah edron is th e simp lest free-stan din g rigid fram e
an d com prises a series of trian gles. By varying th e length an ddiam eters of th e basic tetrahed ron elemen ts, it is possible to
come u p with some very in terestin g sh apes and p ossible
applications.
NOTE
See Technology Study File 2.
DESIGN PROPOSALS
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If oth er com pon ents are used -
for examp le, a quartz clock
m ovemen t - a special
aluminium or plastic plate can
be made up to conn ect the
m ovem ent to th e tubes.
JOINING ROLL TUBES TOGETHER
Roll tubes can be joined using small n uts an d bolts or gusset
plates. Th e gusset p lates can be cut from th in alumin ium sheet
and pun ched with th e combined eyeletter punch and rivetingtool.
Guessets can also be m ade from th in p olystyren e sh eet. If a
n um ber of iden tical gussets are n eeded, th ey can be m arked ou t
using a tem plate or, for exam ple, by using a CNC m illing
machine.
JOINING ROLL TUBESTO OTHER MATERIALSOR
COMPONENTS
Roll tubes can be joined easily to oth er mat erials using n ut s an d
bolts. Roll tubes can also be used as spacers throu gh wh ich a bo lt
or length of stud din g passes.
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EVALUATING YOUR SPACE FRAME PRODUCT
Th ere are a n um ber of th ings to con sider when evaluating the
success of your prod uct:
Does i t meet the specifica t ion?
Does it meet th e requiremen ts of a space frame; i.e. is it rigid
and stable?
Can it be assembled easily from a kit?
Som e of th ese qu estion s are probably best an swered by seekin g
th e views of oth ers. Can a frien d m ake up your space fram e by
looking at your working drawing?