frames in space

7/30/2019 Frames in Space

1/17

3 5

STRUCTURES - SPACE FRAME (1)

STRUCTURES (VERSION 1.2)

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.


2/17

3 6



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.


3/17

3 7



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.


4/17

3 8



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.


5/17

3 9



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.


6/17

4 0



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.


7/17

4 1



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.


8/17

4 2



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.


9/17

4 3



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


10/17

4 4



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.


11/17

4 5



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).


12/17

4 6



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.


13/17

4 7



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


14/17

4 8



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


15/17

4 9



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


16/17

5 0



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.


17/17

5 1



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?

frames in space

Documents