Post-Tensioned Brickwork

Curtin, Shaw, Beck and Bray - W.G.Curtin and Partners.

Liverpool, England SYIIOPSIS

Post-t~nsioned brickwork hn.s been fo !md to be highly cost -C OIl"r~titivc anti

will great.ly increase the applicdtions af structural brickwork. The p,wer

outlined the advantages and method af prestressing brickwork, its advantages

over reinforced brickwork, the authors application af the technique and

discusses briefly the theory, design and construction af p05t~ténsi oned

brickwork.

1. O WTROOUC TlON

Since brickwork 1s strong in compression but relativcly wea.k in tension f'.~iy

a ratio af around 20 to 1) its structura-l application hrts tended to be

confined to such compressive structural elt;ments as r;omrresshely loadfod

Ylalls ",nd columns, arches etc. When, say, walls are subject to bC;lding

due to s1gnificant lateral loading (from retained earth ar water, extreme

wlnd loadlng etc) bending tensile ~tresses resulto To resist the t ensile

stresses the walls require strengthen ing - just thicl.;-ening - is unecono·rtic

and prices brickwork out af the market. The alte rnativc of c h,ln'Jing

the geometric sectlon (J . e. box piers, diaphragm and fin walls, c ruciform

columns etc.) increases the set.::tion l:"Iorl ulus, dec.:rc.,ses tt ,e U:'l,:,- i le !:.t r ~·!·.s

and V"cry considerably extc::nds the structurdI dppti cati on o f bt" ick\\(Jl'k. Sut

the appl.ications are still limited and the design sUl! gO'vcrncd by brick­

work's low tensile strength - and brickwork's high comprcssi .... e strenyth is

under-explolted and under-developed. Post-tens1oning reverscs this and

makes brickwork highly cost-competitive.

Cancrete, too, 1s strong in compression rlnd \\cak in tcnsion - 5 0 c·r'Jln,;,,· rs

rein force it to c .~rt~y the tc::nsi le stresscs or prcst rc- s s it to elj :~ illat.e U,,:m .

It 1s glaringly obviaus that the Sdme b~sic C"Jnt.'cpts can be ;'1pr1ied to brich: ­

work. lhe conccrt 1s not new - r cif.fun:(',1 1, ,' i ckwork \"as IJ 5 C·(j by Moi"'; Cn!!"l' 1

in thc 18~ors .in Engli\nd, by Sir A.l«;'X ,t rHkl' Bt'(:bn~r dt thc t,u"n of tI ,e ccntury

in Inrlj,) "nd it j j not unCOfThnon no .\ in A!,r ·ri ca. Victuri"n Pr' lJin(: ~: I' S rLp~irl;Jj

craC'l<r:"d struct,lres l>y inserUng stC!c l r0ds through the: stnr...turt' , ttlt~n !lr:',1 1· ... ll

and .lnchor ed the rods. As lhe rods (,.'uolecl .1Pd cor.t r ,l dCt1 t l" . .::y ' post. ·tt€' n~i . ) nE-d '

961

the structu re.

Despite these precedents reinfar ced brickwark, and particularly prestressed

brickwark has l agged far behind cancrete. This is hardIy surprising since

relatively feVl' en gineers have appreci ated even pIa in brickwark as a structura l

material, fewer a re taught brickwark structural design and practically nane

have continuously developed prestressed brickwork. There 1s little design

information particularly for prestressed brickwork, even less research carried

aut unde r lh~ supervision af exper1enced engi~eers and almost no papers on

pract ical experience with the techniques - for successful engineers are often

toa busy producing struc tures to produce papers!

2 . 0 REASONS FOR PRESTRESSING

962

The anology "ith -concrete can be pushed toa far - they are different materiaIs

.md the appropriate technologies differ. Prestressed concrete is not nearly

50 cammon as reinfor ced. It ca 11s for high-strength concrete, more sophis~

ticated technol ogy , needs greate r leveI af skilled supervision, 1s more

complcx to dcsign etc. lhe reverse is true in brickwork.

Conere te 15 rclat1vely isotropic and homogenous, it shrinks with age, is

subject to sign i ficant cr eep, under tensile strain minute hair cracks are

cIosely and evenly dis tri buted . Sut bri ckwork 1s not isotropic ar homogenous,

it can expand with age, the creep is reIative ly "lo't\' and the tens ile cracks

~re not 50 minute and they concentrate at the brick/mortar interface .

$0 prestres sed conc rete is more expensive and complex than r einforced but

genera l ly prestressed bri ckwork can be cheaper and simpler than reinforced .

Concrete to be prestressed is often 3 - 4 times as strong as the grade of

conc rete to be reinforc'ed. Host bri c ks have easily 3 - 4 times the strength

of the ir equivalent in conc r et e bIock.

Efficient prestressi ng calIs for structural sect10ns "ith hi gh l/A rat i os

and radius of g)'rati on e . g . Box and I seetions, Tee beams etc . ~ and flOt

solid rc:c t angu lar sections . Sueh sections ilre expens ive to shutter in

('onere te but are sirnp le to form in brick\\"ork .

Tt , an be :..I)o\\n that a p(lst ~ t(>nsionf-d brick bo.\. ~ ~eetion has 60 times the

bc·w.ting reslst.3nce of a flc'rrna l (·q'.J~\'.3 1 r:nt ~olid brick \\,].11! This truly

lua s sÍ\'e inCl'(:.lse in stn:rlgth l'esults in the tC'l.:/.n i que 's c(Js t~ col'~lctitiH~J;(::SS.

•

3 . 0 POST-TEI~S IOIHNG I1ETHOD

lhe site tcchnique 1s simple. To produce, 5ay , a vert. i ca l pre s t r essed

cantilever to resist late ral l oading high-tensi le s t eel r ods ar e anchor ed

in the concrete base, a cavaity ""alI is buil t up a r ound t he r ods and then

ca pped. When the mortar has reached its design strength the rod s ar e

tensioned with a torque spanner and anchor ed at the t op, and tha t , basiça lly

1s t hat. The technique 1s 50 simple that 5mall, country bui lders who

would find r e inforced concrete diffi cult and steclwork fab ri cat.ion and

crection impossible, have very successfully built pos t- tensioncd brick -

work . (lhey were deliberately not told that they were building pos t­

tens ioned brickwork since this would have ma de toem appre oensive and caused

toem to raise their prices. Instead they wer e gi ven help f ul s pec ifi ca tion s

and c lear structural drawings).

Little prac ti cal use seems to ha ve been f ound f or pretens i on i ng , (so f ar ) ,

\'11th its atte ndant complexit ies of numerous te ndons , cur ved duc ts , com­

pli ca t ed fabri cation, curing time etc . (And i n concr e t e the bu l k of pr e~

tens ioning has been used in fa ctory made precast e lements s uc h as f l oor

beams et c .).

The ,maj or appl icati on, by the authors 1, In br ic kwor k has been i n po st ~

t ensioni ng. Quite r easonable l eveIs of prestress can be induced by t he

simpl e t echni que of t orque and for hi gher l eve Is of pr estress a jacking

system can be used.

4.0 ADVAl+TA GES DF PRESTRESSED BR I CK\\'ORK COI-IPARED TO REl I~FDRCED

The case has been di scussed e l sf:\\hc r e (ref .l ) but lt ma)' be hel pfu l to

Dutline lt here. Whllst the author s ' made extens ive use of r ein for ce d

brickwork in the 60's the)' have since the la te 60 ' s mad e mor e a nd more use

of post- t ensloned brickwork. lt i s well ~ knolVn how diffi cult lt 1s t o

ob tni n reliable cost~informat ion, even wi th detailed cos t ~ s lln cy5, 50 t he re

are no ha rd and f a s t r ul es . But i n gene ral pos t~ t.ensjoned bTÍC'k\\ock i s

cheaper than ei ther re i nforc ed br ickwor k ar b-loc kl\ úrk ~ and I' cin f orc:ed

bl ockwork te nds to be cheaper and si ..... pl cr t han rci nfol'ced brick\\()rk . (lhe

authors' fail to unde rstand the British brick ind'Jst r y ' s r e Lltive ly L'lrgc

rc-sCit rch invc s trne nt lnto r c inforced bric \..:\\or k \\hich \\ill tend to aid i t s

ma j or competitor - the concrete bl oc k i ndustry ).

963

964

Prim-lrily brickwork 15 a "\\a111ng l1 material and ve rtical prestre~sed

\\.311in9 is simpler to cons truct and supervise than reinforced . Rein ­

for ceme nt, to act structural l y, must be bonded to the brickwork and this

requires adequate compac tion of good qua l ity grout ar mortar. The

adequa te compaction of grout, keeping graut lifts clear of mortar droppings,

prcvcntion of e~ccssive hydrostatic head, prcvention of grout leakage dnd

trapped air pockets, maintenance of proper caver to the re1nforcement

etc. etc. is not si rnp Ie.

Furthér, since bl' i ck \\ork 15 weak in te:ns i on (and its contribution not

relied upan in design) gé1 the brick\\'ork · bela\-\' the neutra I axis merely

ensures camposite action or provision af cover - 50 much af the brickwork's

valuable compressive strength is \\asted. (In hallaw concrete black\\'ork the

blocks act as permane nt shutters and are relatively s1mple to graut up -

and graut could be cheaper than brickwork). In prestressed b~ickwork ~

the brick",ork i5 in compres5 ion 50 that brickworks' compressive strength

i5 fully cxplaited.

Not only ha ve the authors' found that 1 t 15 generally cheaper I simpler

and mor e 5 t ruc tural I y eff iei ent to pre s tress brick:nork, rather than to

reinfürce it, it i5 also likely that it ",ill be more durable. Since normal

brickwork can crack under bending tensile stress 50 too can reinfor ced

bri ckwork. If significant cracks penetrate the graut the reinforcemen t

ca n cor rade. In pr es tressed br.ic \.;wo rk the tensile stres5es ~ and thus

the tens.ile c rack ing - can be eliminated and this reduces the corrosion

problem.

It is patentl y ob\'ious - to any e~ptriel,ccd cngincc r - that it is p,0re

structurally efficient to prestre5s brick"ork t ~l~n to reinf0rce it and,

too, the applications are wider. lhe above may be hammering home the

obvious ta many experienced engineers but it has been dane si'"lce estab­

lished t echnology t e nds to persist in the fa ce of new. (.\. nd some resear.-:!' (- rs

prefe r t.o clear and ,\iden a t'i'lil blJz~d b) ')the r5 r~the r t !l -3n ') ;;(:, n up a

ne \\ àvc:nue ).

5.0 SOl1E APPLICATIOI~S BY THE AUTHORS

lhe first application by the authors "c"IS for a tall piered ..... all in 1969.

lhe I'.all nas subject to severe wind loading which would have caused

unacceptably high bending tensile stresses 50 the piers were post­

tensioned. (It 1s interesting to note that the fin wall concept, (ref 2),

had not been derived by the duthors at that time - if it had it 1s possi ble

that it would have been used instead)

IJew ideas beget new problems which beget new needs for research. Following

the normal procedure Df the practice in developing a new technique, a

number Df simple site tests were carried out and when the techniques had

becn proven in practice and a sufficiently large contract received by the

authors' practice to afford somewhat more sophisticated r esearch this was

done, (ref.3). The tests were designed not merely to confirm 'ideas' but,

much more importal='ltly, to extcnd the technique by extrapolation of the

test results.

The post-tensioned cavity ..... all technique was applied to a ,.-.ide variety of

structul'C:s but there is a limit to the height and load-be arlng capacity

to which ~uch cavi t y (or solid) \'.a11s can be bull t because of lheir rela ­

tively lo ..... Z/A ratio and radius of gyration.

In the ea rly 170 l s it ~as appreciated, of course, that such sections as the

diaph ragm "ali (ref. 4), fin "ali (ref. 3) and severa I others with their

structurally efficient ~ections \\'ould be ideal for prestress ing. Since" there

\\as no access to adeqlJate rcsearch rcsources or funds to carry out accurate

and refined rescarch into sue h sections - let alene prcstressing them -

pregress WdS somewhat delayed. I-Jevertheless adequat.e site testing by the

authors enabled them t.o bui ld such \\al1s up to a height of 10m. Through

the Brick Development Association,basic research was started in the mid ' 70 ' 5

into the structural behaviour of p]ain diaphragm wa11s (ref.S). The

rcsults \\(~ re gratifying, extrapolated and e>.t e:: nded by furthe r site t c: st.i ng

50 that pl'es tressed dia ph ragrlls , fins etc. \\ere cons tructed. (It r..ay be of

i nterest to note that the authors l practice receÍ\'ed an i:!\\ard for civil

enginc:ering inno\'ation and in add ition H.e first author \\as a\\arded a

AO;ill Svc h :ty I ndustrial Re!'·~ ~ a rch Fel1.ol·.sh ip at t he Uni.\ersity of I-lanch<:slt::: r

I nst itutcof Sci~nce and Tec tlno log)' to (1~ \~lop the "ork).

965

Typi cal of sue h applications ~as for a tall single-storey Sports Hall subjec t

t o se\' e re differential se ttl~ment due to mining subsidence (ref.6). A

diaphragm wall \\as prestressed to eliminate the in-plane tensile stresses

r esul ting from the settlement. Another typical application was to strengthen

an ex isting retaining wall by toothing in and bonding on post - tensioned fins.

A not uncommon appli cation could be when an industrial client needs to

ex te nd an existing steel-framed shed type structure. The existing gable wall

c an be strengthened and provision made for crane gantries and the like by

t he add i tion of post-tensioned fins. If the new gable wall has to be built

50 that at a later date the structure can be still further extended,then

prestressed, or even reinforced, brick box-columns can be built. (Post­

tensioned brick box and other column sections have obvious applications in

industrial 'shed' structures). Cost surveys will almost certainly show

sa\'ings in construction costs and time over the traditional, and unthinking,

use of expensive structural steelwork.

Rec ent r e search, agaln mainly funded by the 8rick Development Association,

at UIHST (ref. 7) on relatively high leveIs of prestress on a tall diaphragm

\\all s how that there is a wide range of applications for the technique.

Pr e l i minary cost studies indica te that post-tensioned brickwork could replace

reinf or ced conc rete retaining walls. The authors hope to start work soon

on a large retaining wall project for a public authority in cooperation wlth

a government research organisation.

Furthe r research work on investigating the collapse mechanism and behaviour

of pos t-tensioned brickwork (ref .8) has stimulated ,the authors application

of the t~chnique to site prefabrication af prestressed box-beams and other

sec ti ons. Resc arch \\orl.: on the problem of the vertical shear strength of

bri ck\\ork, first noticed by the authors' ~nd discussed in ref .S) in diaphragm

and fin \\all design,is being undertaken at Dundee Universi ty with the coopera­

t':'on of t he authors' practice and the BDA.Whilst much work had been done on

s hear, racking etc. this particular problem had not been investigated -

probably beca use it is of Jit.tle ilTlÇ'ortance to the engineer in normal \\al1

des i gn and it does no t l c nd itse lf to easy s olutian by simple site tests.

Though the pr obl e m, f or t~e same s~c tion, 1s eased by post-te nsioning, further

\\ork Id ll be ncccssary to provide firmer guidance on the more advanced of

thc a'Jthors ,llJpl iC03 t ion s and t o e xtend them.

Tt is no t j)(J~s i ~)lc in sli ':- h .) bLief p,1 per lo l ll • .ltli.ne a11 the applicatiorls (this

I.a s b(::(:n s ,~ (:tchi] y c! ·')ne ~rl rc- f.9 a nd lt is I' ro~oscd to do 50 in ref.IO

966

-but i t ma}' be of interest to note that the technique has wide applicdtion

in tall single-storcy structures, opcn-pIan multi-storey buildings, civil

engineering projects etc. The technique has obvious applications in pre­

fabricated brickwork and its full potential has not yet been appreciated .

6.0 THEORY, DESIGI~ Alm COllSTRUCTlON

Basically the theory 15 the same as for prestressed concrete i.e. the

application af comprcssive stress, P/A by prestressing to ellminale the

tensile stress due to bending, r~/z . The well-known equation for combined

f . P + H stress, 15 A _ I

where P

A

prestressing force

cross - sectional area

M

Z

applied bcndin.g moment

section modulus

The design procedure for light to medium leveIs of prestress is dealt "ith

(>1 sc>where (refs 11 and 12) and when further adequa te funding for the authors 1

propo"5ed future research i5 obtained and the work comp1eted and applied the

procedure for high leveis af prestress will be pubUshed.

IIC\l:rtheless it may be of interest to outline the J)rocéd'Jrc hérc .

lhe more criticai design case is f ; P - 11 A I lo eliminate the tcnsile strcs s,

(ar r educe it to ' safe' leveIs) it is necessary to increasc P and a r I.

For f to equal zero P/A must equal H/Z and there P x. (~) ::;: I~. lhe need for

a high l/A ratio is immediately apparent.

'- P + 1·1 lhe co~pressive s~ress f ; ~ I must not e;...ceed the co:npressive str~-qlJth

of the 5ection . lhe compressivc strcngth depends not only on the brick-

"ork's properties but

greater the radius af

areal, indirectl)' and

also on the slenderness ratio af the section. The

gyration, r, ( :: \* ,where I = sE'cond moment of

no t proportiona11y, the grE'ater the C0i7\pressive

strcngth. fo pre\cnt buc~ling inst~bility, ar reduced c08pr~ssi\' e 1oading,

af the compression flange at a lo"er stress than the bric~"ork's potential,

then a hiy~ radius of gyra~ion is advisable . For structural efficicnc~',

economy of 8aterial and labour and "cight-sa\' ing, it is a~p6rent tllat a high

r/l. J'i:ltio is ~ 1so adds.-tble. lhis em bc õ('hicvcd for c,\,);rple \\lth a Tee

967

such scctions are obviously nat structurally efficicnt.

lhe structural efficieney of the prestressing force, P, can of caurse be

greatly increased by applying it eccentrical ly to the centraid af the

seet ion, and it is of course necessary t o eheek the ends of the section for

pr incipIe strcss, local bearing stress , shear 1ag etc. as it is in prestressed

conc r ete . lhis is not 50 simple in brickwork sinee it is an isatr apic .

lhe U.SIJ,'Il losses af prestress mus t b~ allowed for in desiyn and construction .

lhe l os s due to elastic contraction ca n be caleulated if the E value (Youngs

Hodulus) for the brickwork i5 known. But since from the authors experience

the E value can vary between 500 - '1000 times the characteristic strength af

the brickwork, brickwork of t he S<:ime strength ean have different E values

and the heigh t af the section, the methad of loading, etc affect the

E value, such calculations ean be somewhat unreliable . . It is simpler to

cOlnpcnsate for thc l oss on -site by 'toJ1ping-up' thc prestrcss . Losses due

to crcep in the brick\\o rk ean be c rudely assumed to equal hal f that in

eoncrete . Losses due to frietion are non - existent ar minimal in straight

rods in straight voids and anchorage losses are low in post-tensianing

sys tems - and agaln can be co'npcnsated for. lhe losses due to relaxation

af the steel appear to be the s~me in bricl.: \\ork as they are in concrete .

lhere can be gains in prestress due ~o moisture and thermal expansion of

the bricl.:work but .si nce these are likely to be 10w J variable and unc~rtain

i t is suggested that such gains should not be relied upan. lhe designer

should hawever check that such gains do not over -stress the brick",ork and

the roos.

lhe stress di~tribution should be checked at initial stressing, undtr

ap plied laading, after~losses, etc. and particular care IilUSt b~ .€xereised

wi th asymetrical sections wittl eccentric prestress.

SOr.le designc rs have apparently based the design stress on the direet

conp ressive strength , fk

, of the bric~"ork but since the section i5

unde r bendinq action and the length of the 'st.rut' ccti!)n of the comprcssi on

flan ge is short and the brickwork 'restrained' then the authors w01Jld

5ugUCSt that a des ign stress may be based on a \~Iue bct"ecn 1.0 to 1.2~fk

dcpr:nd ing on the ratio af ' diree t and b ~' nrli ng strcss (see ref . 11). ( I n

.lny Cf3 se the facto l-s of sa fe:ty in stl'ucttJra l brick\hH-k are extravaC) :lnt ly

and unnecessa'rily high, in the authors apinion) .

968

lhe const.ruction techniques are again similar to those in concrete in that

phascd se:quence of prestressing ca n be employed (and v.ould prObêibly be

necessary in muI ti-storey construction) . Rod curtailment would be practi c~lly

the same as also would be rod extensioning. Protection of the rods frem

corresion is naturally vital and this can be achieved by painting v.ith

bitumen, or similar, and wrapping in proprietary \\ate rproof tape. Galvani­

sing of the rods is not recommended as stress cracking of the f11m can

occur. lhe rods can also, if thouyht necessary, be protectcd by grouting

but care must be taken to ensure ade:quate and full continuous cover wi th

the correct grade of g r out. Consideration could be given to the use of

stainless steel in conditions of severe exposure . Though such rods are

about four times the cost of normal high-tensile steel rods the 'extra- over'

cost per square rne:tre of completed \~all is not significant and the resulting

structure is still likely to be highly cost competi tive v.ith relnforced

cencrete OI' structural steelwork.

7. 0 RI:SE~RCH IJECOS

It is not proposed to discuss these here since they are dealt \dth in

detail else\\here (ref. 13). Ho\\ever, it may be pertinen t to point out that

\\'hilst much has been done In reinforced brickwork, certainly enough to

give designe r s reasonable guidance, practical l y nothing has been done o~

prestressed brick ..... ork . Huch need s to be done on prestressed brickwork and

it I\lU almost certainly be more \'aluable to the brick industrythan c.on­

tinuing wor k on reinforced brickv.ork. This is not to suggest that such

work should cease, OI' lo denig~te it,but to establish a sense of proporti on

and value of priority . As mentioned above the authors' prac.tice hdS found

a grcdter a ppli ca tion of reinforced masonry to hoIlol\ eoncretc blockwork êind

prcstressed masonry to elay brickwork.

8 .0 CO~<ClUSIOllS

~e are dcaling, in e:f f ~c t, "ith a 'new' struct'Jral material i n pr~strc~~ed

hrick\\ork I\hich r.;,"lS " eS highly ef f h~ien t use of brick\\orl..:s' major arhantaCje

of high C(Jmp J'cs~he strcngth. lhe t~chnique has been fou nd by the autho r s

e'l)erlenrc on sc\e r ~l hundred projects (of a "ide variety of structul"CS

b:lilt by ("V ')lr,'lctrjrs af diff('ring C'i't~ric:r, ce a-,d sizc) to be \ Vry '.:ost

,>'~;) ç-titi\e , sl õ·;)lc ;lnd fast t o t;'[' ( 'ct d;1d dUf.-'lblc uih:1e r the sc:\c"rc'st

969

Eve n with the present knowledge there is a vast scope for its appIication but

the full pot~ntial has not yet been appreciated and much more practical

e>..pericnce combined with appropriate and coopera tive research is nccessary to

achieve this.

Structural brickwork is still an under-developed, under- appreciated and undcr­

researchcd material - post-tensioned brickwork is even more 50 . lt is hoped

that this too short paper will stimulate design engineers and researchers to

expIoit and expIoretogether this vaIuable technique .

9. O REFEREllCêS

1) 'Oa.:elopment , Application and Potential of Reinforced and Pres tresscd Hasonry'

\V.C.Curtin Institution of Civil Engineers , Symposium 14ay '82 London.

2) 'Oesign Df Fin WaIls for Tall Single-Storey Structures'

Curtin, Shaw Beck and Bray B.a.A

3) 'Post-tensioned 8rickwork and the S .C.O. System'

Curtin, Adams and Sldon BCS 1971

4) 'Design Df Diaphragm Walls for Tall Single - Storey Structures'

Curtin, Shaw Beck and Bray B.a.A.

5) 'Brick Diaphragm Walls - Development, Application, Design and future deveIopments .

W.G.Curtln

'Discussion'

lhe Structural Engineer

The Structural Engineer

Feb '80 .

Nov '81.

6) 'Post- Tensi oned Diaphragm \\'al1 subject to di fferential set tlement·

Curtin, Sha\\, Beck and Bra)' Institution of Civil Engineers, Symposi um, Hay 1982, London.

7) 'Behaviour of Post - Tensioned Diaphragm Wal1s'

Curtin and Phipps IBI·1AC '82

5) '8ehaviour of Post - Tcnsioned 8o),.-beams'

Phipps and \\'ise IBI1AC '82

9) 'Brickwork Structure and Form'

10)

11)

W.G.Curtin

'Advanced Structural

Curtin Sha~ 8eck and

International Association of Bridge and Structural Eng ir,.;:e rs Colloquium Sept '81 London.

I·Iasonry

Bray

Design'

Granada Publishing Techníc.al Division, Lend on (in preparation)

'Structural !lasonry Oesigners J.lanudl'

Curtin Sha\\ Beck and I3ray

Granada Publising - Te~hnica l Oivision ~

Dh·ision, London Apri 1 ] S'S2.

)2).. ' Dcv..:.'loí:li"õ;0nt Application and Dc::sign of Post-Tensioned Bricl:\\ork'

13)

970

Curtin,5ha\\ , Bc:ck and ara)' The Structural Errginl!cr (i n prei":<Jcalion)

' Rcsearch on pos t-t ens ioned brick diêplrragm \\ a lls' Curtin and Phipps.

The Structu l'a l EI'Jl~~~r . (in pr cpõration) .