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FO LDEDPLATESTRUCTURESINPLASTICSA thesis subm itted for the D egree o f D octor o fPhilosophy in the F a c u lty o f E ngineering o f theU n iv e rs ity o f London.byB eza le el Solomon B enjam in,M .S c .( E n g .)(L o n d .), B .E ., D . I . CS tructural Plastics Research U n it,Battersea C o lle g e o f T e ch n o lo g y,London.N o v e m b e r, 1 9 6 5 .

ProQuest Number: 10800474All rights reservedINFORMATION TO ALL USERSThe quality of this reproduction is d e p e n d e n t upon the quality of the copy subm itted.In the unlikely e v e n t that the a u thor did not send a c o m p le te m anuscriptand there are missing pages, these will be noted. Also, if m aterial had to be rem oved,a n o te will ind ica te the deletion.uestProQuest 10800474Published by ProQuest LLC(2018). C opyright of the Dissertation is held by the Author.All rights reserved.This work is protected against unauthorized copying under Title 17, United States C o d eM icroform Edition ProQuest LLC.ProQuest LLC.789 East Eisenhower ParkwayP.O. Box 1346Ann Arbor, Ml 4 8 1 0 6 - 1346

A B S T R A C TThis thesis is an in vestig atio n into the use o f plastics instructures o f the fo ld ed p la te ty p e .Plastics as a structural m a terial has first been c r it ic a llye v a lu a te d w ith p a rtic u la r reference to the types that may be used fo rstructural purposes.The d ifferen ces in the m ech an ical propertiesb etw een these m aterials and c o n ven tio n al m aterials have beenexam ined in d e t a il.C o n ven tio n al design concepts have beensu ita b ly e n la rg e d to take these differen ces into a c c o u n t.Folded p la te structures in plastics b u ilt up from p re fa b ric a te dunits have then been e x a m in e d .The tw o -p la te u n it enables the com pletep re fa b ric a tio n o f a v a rie ty o f structures, p a rtic u la rly o f the compositety p e , and has been selected fo r fu rth er study.The existin g approachto the analysis o f fo ld ed plates has been m od ified for a p p lic a tio n to suchstructures in p la s tic s.This m o dified approach is p a rtic u la rly su itable fo ruse w ith composite fo ld ed p la te structures formed from n o n -p rism atic p la te s .Large transverse d e fle c tio n s o f the structure can be c o n v e n ie n tly taken intoa c c o u n t.This m o d ified approach has been v e rifie d by ex p e rim e n ta l w orkon the roof stru ctu re, the tw o -p in n e d composite fo ld ed p la te portal fram eand a composite fo ld ed p la te b arrel v a u lt .

Folded p la te structures in plastics can be o f single skino r sandwich co n stru ctio n .The properties o f expanded polystyrene andrig id polyu reth an e foam for use as low density cores in such sandwichconstruction have been d e te rm in e d .A prototype composite folded p la te barrel v a u lt ofsandwich construction has been d evelo p ed and tested .S p eciala tte n tio n has been p aid to the connections betw een the fu lly p re fa b ric a te du n its.The costs o f the structure have been b rie fly e x a m in e d .The testresults have been analysed and the th e o re tic a l and e x p erim en talbeh avio ur o f the structure have been com pared.F in a l conclusions have been drawn and suggestions fo r fu rth erresearch have been m a d e .

I should lik e to ackn o w led g e my g ra titu d e toProfessor Z . S. M a k o w s k i, Head o f the D epartm ent o f C iv ilE n g in eerin g , Battersea C o lle g e o f T ech n o lo g y, for his kin dhelp and g u id a n c e .His perspective v ie w o f the problem hasbeen in v a lu a b le .I should also lik e to a ckn o w led g e my g ra titu d e tothe Shell C h em ical C o . L t d ., for the Shell C h em ical C o .research scholarship, for the free supply o f m aterials and forgenerous grants towards the cost o f the p ro to ty p e .A specialword o f thanks is due to M r . R. F . Salmons and D r . E . N a rra c o tto f the Shell C h em ical C o . for th e ir sustained interest in this w o rk .

WORK ACCEPTED FOR PUBLICATIONThe e n tire contents o f this thesis are the work o f the au th o r,done a fte r being registered for the degree o f D octor o f Philosophy, inthe F a c u lty o f E ngineering o f the U n iv e rs ity o f London.Some o f thew ork has since been acc ep te d for p u b lic a tio n as follow s:1.The contents o f C h ap ter 1 have been w ritte n in the formo f a paper e n title d 'An E valu atio n o f Plastics as a S tructural M a t e r i a l '.This has been ac ce p te d for p u b lic a tio n by "The Consulting E n g in e e r" ,London.2.The contents o f Chapters 2 , 3 , 5 , 6 and part o f 7 , in acondensed form w ere read as a paper in c o lla b o ra tio n w ith ProfessorM akow ski a t the co nference 'Plastics in B uilding Structures' held inLondon in June 1 9 6 5 .The paper was e n title d 'The A nalysis of FoldedPlate Structures in P la s tic s .'The proceedings are to be published byPergamon Press la te r this y e a r.3.The contents o f A p p en d ix 1 have been w ritte n in theform o f a paper e n title d 'Expanded Polystyrene and Rigid PolyurethaneFoam Cores in S tructural Sandwich C o n s tru c tio n '.This has been a ccep tedfor p u b lic a tio n by " C iv il Engineering and Public Works R e v ie w " , London.

C O N T E N T SCHAPTERPAG E1.Plastics as a structural m a te r ia l.72.Folded p la te structures in p la s tic s .193.The fo ld ed p la te roof (in te rn a l u n it ).324.The fold ed p la te roof (e x te rn a l u n it).545.The tw o -p in n e d , fo ld ed p la te portalfra m e . 6.The folded p la te barrel v a u lt.7.Tests on a prototype fo lded p la teb arrel v a u l t .79931268.Conclusions.1749.Suggestions for fu rth er res e a rc h .178A P P E N D IX 1.183A P P E N D IX 2 .207REFERENCES.279

7CHAPTER1Plastics as a structural m a te r ia l.1.1In tro d u ctio n :The use o f plastics as a structural m a terial w ill c re a te controversy formany years to co m e.Plastics when used stru c tu ra lly have some advantages -and some disadvantages - as,com pared to co n ven tio n al m aterials such as s te e l,alum inium o r concrete .T h e ir disadvantages, ap a rt from high cost, lie m a in lyin the properties o f the m a te ria l w h ich w ill be considered in g re a te r d e ta il in1 .3 .It w ould th erefo re be a p p ro p riate to discuss b r ie fly firs t, the advantageso f those plastics suitable for structural a p p lic a tio n s .1 .1 .11.A dvantages o f plastics o v e r c o n v e n tio n a l m aterials:Structural plastics have h igher s tre n g th /w e ig h t ratios thanmost o th er en g in ee rin g m a te ria ls .2.They are a ttra c tiv e in appearance and can contributesu bstantially to the a rc h ite c tu ra l b eauty o f the stru ctu re.be made tra n s lu c e n t.They can e a s ilyThey can also be e a s ily pigm ented to g ive desiredcolours to the stru ctu re.3.M a n y plastics have e x c e e d in g ly good corrosion resistance,w hich is fa r superior to th at of many con ven tio n al e n g in eerin g m a te ria ls .4.Plastics are ve ry am enable to p re fa b ric a tio n .This p ro p erty,together w ith th e ir lig h t w e ig h t, makes them ve ry useful m aterials in systemso f industrialised b u ild in g .

In order to be a b le to design in p lastics, it is first necessary tounderstand v e ry thoroughly the m aterial its e lf.To do so is not easy,co m p licated by the fa c t that there are m any, many types o f plasticsused for a v a rie ty o f purposes.H o w ever for structural purposes thereare o n ly a small number o f e ffic ie n t plastics and these w ill now beconsidered in g re a te r d e t a il.1 .2Plastics su itab le for structural ap p lic a tio n s :Plastics can be classified b a s ic a lly into two main groups;therm oplastic m aterials and therm osetting m a te ria ls .Therm oplastic m a te ria ls soften on the a p p lic a tio n of h e a t.They hence e x h ib it considerable creep under load p a rtic u la rly ate le v a te d tem peratures.P o ly v in y lc h lo rid e (p vc) and p o ly m e th y lm e th a c ry la te(Perspex) are exam ples o f therm oplastics that can be used for lig h t structurala p p lic a tio n s .G e n e r a lly th ey are in sheet form and are used re in fo rc e d .They have the advan tag e o f being e a s ily am enable to shaping or m ouldinginto d iffic u lt shapes.They are isotropic and being unreinforced show veryconsistent p ro p erties.Perspex domeshells b u ilt in F in lan d may be g iven asan exam ple of the structural use to w hich these m aterials may be p u t.have a di a m eter o f 19 f t . 4 i n . and a h eig h t o f 6 f t .TheyThey w ere designed fo r asnow load o f 3 0 .7 lb s /s q .ft. and a w ind load o f 2 0 .5 lb s /s q .ft. Therm osetting m aterials once cured, do not soften on the a p p lic a tio no f h e a t.W hen rein fo rced th e y e x h ib it higher strengths and a fa r less

tendency to creep than the therm oplastics.The p o ly e s te r, e p o x id e , andp h e n o lic resins are exam ples o f therm osetting p la s tic s .polyesters are by fa r the most w id e ly used.O f these, theThey are r e la tiv e ly cheap andg ive good properties in rein fo rced la m in a te s .The ep oxid e resins g iveextrem e ly good p ro p erties, but th ey are more expensive than the p o lyesters.The p h en o lic resins g ive good properties w hich are m ain tain ed even a t hightem peratures.They are hence p a rtic u la rly su itable for such w o rk .H o w everp h en o lic resins require hot cures and high la m in a tin g pressures and thislim its th e ir a p p lic a tio n s m ain ly to the aerospace industry.A ll these therm osetting resins cannot be used s tru c tu ra lly by themselvesand have to be rein fo rced w ith su itable reinforcem ent such as glass, c lo th ,paper or asbestos.For high tem perature w o rk , asbestos rein fo rced p h e n o liclam inates are the most s u ita b le .The commonest reinforcem ent is glass.glass reinforcem ent is a v a ila b le m a in ly in three forms:a.Chopped strand mat:The2This is the most im portant type o f glassfibre rein fo rcem en t and consists o f about 2 " long fibres random ly o rie n te d .The resulting lam in ate is hence es s e n tia lly iso tro p ic.b.Rovings:These consist o f a d e fin ite number o f continuous,p a r a lle l, bundled but untw isted strands o f glass.They im part v e ry highd ire c tio n a l strengths and for this reason fin d great a p p lic a tio n as re in fo rc e ments in fila m e n t wound structures such as pipes, tanks, rocket casings e t c .

c.Cloths:strong lam in ates.These are w oven fabrics w h ich g ive e x tre m e lyThey are h ow ever e x p e n s iv e .C lo th rein fo rced lam inatesare anisotropic in th e ir p ro p erties.In single skin construction, the rein fo rced lam inates can be usedby them selves.H ow ever for large spans it is necessary to use structuralsandwich construction in w hich the thin rein fo rced lam inates are bonded toa low density c o re .a x ia lThe facings then take the bending momentforces and the core is assumed to take a ll the shear.and theThe coresthemselves can be o f low density p lastics, and the four m ain types areas follow s:a.R igid p o lyu reth an e foamb.Expanded polystyrenec.Expanded pvcd.Phenolic fo a m .O f these, the rig id po lyu reth an e foam and the p h e n o lic foam aretherm osetting p lastics, the o th er two being therm oplastics.The rig idp olyurethane foam has an ad van tag e o ver the o th er three in that it can befoamed d ire c tly onto the lam inates w hich makes it p a rtic u la rly su itable forinsitu w o rk .Further the p o lyester lam inates can be d ir e c tly 'l a i d 1 on i t .This cannot be done w ith expanded polystyrene as the polystyrene isc h e m ic a lly a tta c k e d .Expanded pvc and p h en o lic foam are not a tta c k e d .H ow ever the surface o f p h en o lic foam has to be sealed in o rder to p reven tthe p en etratio n o f la m in atin g resin into the fo am .