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x p e r im e n t a l a n d a n a l y t ic a l s t u d ie s f o r t h e c h o ic e o fr e p a i r t e c h n i q u e s a p p l ie d t o h i s to r ic b u i ld i n g sM . R . V a l l u z zi 1 L . B i n d a a n d C . M o den a 1(1 ) D i par t i me n t o d i C os t r uz ion i e Tr as por t i , Un i v e r s i t fi d i P ado v a , v ia M ar z o l o 9 , 1 -3 51 31 P ado v a , I ta l y(2 ) D i par t ime n t o d i Inge gne r i a S t r u t tur a l e , P o l it e c n ic o d i M i l ano , P i az z a L . D a V i nc i 32 , 1 - 20 13 3 M i l ano , I t a l y

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A B S T R A C T R I~ S U M g:A s tudy conce rn ing the appli cat ion of d i f fe ren t repa i rt echniques on dam aged h i s tor i c maso nry bui ld ings is p re -

s e n t e d . I n p a r t i c u l a r , t h r e e t e c h n i q u e s a r e c o n s i d e r e d :i n j e c ti o n s , j a c k e t i n g , a n d r e p o i n t i n g o f b e d j o i n t s r e i n -forc ed by stainless steel wires.Th e resu l ts o f an ex per ime nta l re sea rch ca r r i ed out inthe l a s t yea rs on some s tudy cases a re shown . Lab ora toryand in s i tu t e s t s a re inc luded and the in t e rpre ta t ion o f them e c h a n i s m s o f f ai lu r e b y m e c h a n i ca l a n d n u m e r i c a l m o d -els is also given.

C e t r av a i l pr e n t e u ne ~ t ude r e la t i v e a l ' app l i c a t ion de s d if f ~ -r e n t e s te c hn i que s de r ~par a t i on s ur l e s ouv r age s h i s tor i que s de m af o n-n e r ie e n d o m m a g E n p a r t ic u l ie r , t r o i s t e ch n i q u e s s o n t p r i se s e nc ons i c ~r a t ion : l e s in j e c t ions , l e s pa r d s ar m s e t l e r e mpl i s s age de s

j o i n t s h o r i z o n t a u x d e m o r ti e r r e n fo r c p a r d e s b a r r e s d ' a c i er i n o x y -dab l e . Le s r u l t a ts d 'u ne r e che r c he e x p i me n t a l e e f f e ct u au c our sd e s d e r n i e s a n n 6 e s s u r q u e lq u e s c a s d ' 6 tu d e s s o n t e x p o s . L e se s s a i s e n l abor a t o i r e e t i n s i t u y s on t i nd us e t l 'i n t e r pr 6 t a ti on de sm a n i s m e s d ' e n d o m m a g e m e n t e s t 6 g a l e m e n t d o n n 6 e p a r d esm o d k l e s m ~ c a n i q u e s e t n u m 6 r i q u e s.

1 . I N T R O D U C T I O NThe l a s t s e i smic event s tha t occur red in Umbr ia andM a r c h e ( t w o r e g i o n s i n t h e c e n t r a l p a r t o f It a ly ) h a v ecaused damage a l so to bu i ld ings w hich had previously be enretrofi tted. Th e m ost di ffused repair techn iques applied tohis torical bui ldings w ere the subs t i tution of t imb er f loorsand roofs wi th concre te s t ruc tures and the appl ica tion ofj acke t ing or grout in j ec t ion to the poor ly con nec ted s tonew a l l s . S e v e r a l c a s es o f fa i l u r e h a v e o c c u r r e d t o t h e s erepai red bui ld ings e i the r due to a po or des ign o f the in t e r -vent ion o r to a poo r appli cat ion of the t echn ique [1] .I n s u c h c o n n e c t i o n , t h e a u t h o r s h a v e d e v e l o p e d a ne x p e r i m e n t a l r e s e a rc h o n g r o u t i n j e c ti o n a n d ja c k e t i n gt e c h n i q u e i n o r d e r t o p r o d u c e g u i d e l i n e s f o r t h e d e s i g n -e rs c o n c e r n i n g :( i ) t he pre l iminary s tudy of the ex i s t ing wa l l s to be ca r -r i e d o u t i n l a b o r a t o r y a n d o n s it e, i n o r d e r t o c h e c k t h eappl icabi l ity o f the te ch niq ue to th e specif ic case;( ii ) t h e l a b o r a t o r y s t u d y o f th e n e w m a t e r i a ls t o c h e c kthe i r feas ib i li ty an d com pa t ib i l i t y w i th the s t ruc ture an dmate r i a l s to be repa i red ;

iii) t h e o n s it e c o n t r o l o f th e i n t e r v e n t i o n .The resu l t s a l ready reached by the re sea rch a l low tof o r m u l a t e r e c o m m e n d a t i o n s t o t h e p r o f e s s i o n a l p e o p l eo n h o w t o d e c i d e w h e t h e r t h e t e c h n i q u e s c a n b e a p p li c a-b le to the bu i ld ings they h ave to repa ir .F u r t h e r m o r e , a s tu d y i s p r e s e n t e d c o n c e r n i n g a t e c h -n iqu e for cau t ious s t rengthe ning o f the wa l l s o f mass ivebui ld ings . Anc ien t towers a s we l l a s de fens ive wa l l s andheavy p ie rs a re in fac t f requent ly s e r ious ly damaged byheavy dead loads and cyc l i c s t re s ses due to t empera turev a r i at io n s a n d l o w d y n a m i c f or ce s a s b e ll r i n g i n g a n d l o ww i n d s . T h e t e c h n i q u e i s b a s e d o n h o r i z o n t a l j o i n t r e i n -forcement wi th s t a in les s s t ee l w i res appl i ed to the mos td a m a g e d a r ea s ; t h e a i m i s t o c o n f i n e t h e m a s o n r y d i la -t ion caused by h igh com pres s ive s tre sses.

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9 ' J " 0,ut on szte e s ti n g . S h e ts a R I L E M F e l lo w and a m e mbe r ~ fR IL E M A s so ,c ia teMember .1 6 8 - M M M C o m p u t e r m o d e lli ngo f mechanical behaviour o f

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w or ld . N ev er the les s , s ever a l va r iab les have to b e taken in toa c c o u n t fo r a c o r r e c t d e s ig n a n d e x e c u t i o n o f t h e i n t e r v e n -t i o n . F i rs t o f a ll t h e k n o w l e d g e o f th e w a l l s e c t io n i n o r d e rto check i t s in jectab il ity , s econd ly the se lec t ion of the g r ou tw i t h a p p r o p r i a t e p r o p e r t i e s a n d a d e q u a t e c o m p a t i b i l i t yc h e m i c a l a n d p h y s ic a l) w i t h t h e o r i g in a l m a s o n r y . T h a n ,t h e p r o c e d u r e o f i n j e c ti o n it s el f c h o ic e o f t h e n u m b e r a n dd i s t r i b u t i o n o f t h e i n j e ct o r s, i n j e c t i o n p r e s s u re , t i m e o fe x e c u t i o n ) . F in a ll y , t h e c h e c k i n g a n d c o n t r o l o f t h e c o n s o l -ida t ion e f fec tiveness u s ing spec i fic inv es t iga t ion techniqu esb e f o re , d u r i n g a n d a f te r t h e i n t e r v e n t i o n .A l l t h o s e t as k s r e q u i r e s p e c if i c c o m p e t e n c e a n d e x p e -r i e n c e , a s w e l l a s th e s u p p o r t o f r e s ea r c h o n m a t e r i a l s, o fl a b o r a t o r y s i m u l a t i o n s a n d o f i n s i tu t e s ts .Mos t spec i f ic p r oblems r e la ted to gr out in jec t ions a r ec o n n e c t e d t o t h e u n c e r t a in t ie s o n t h e m a s o n r y m o r p h o l -ogy e .g . f or s tone w a ll s the lack of in f or m at ion o n the s ized i s t r ib u t i o n o f v o i d s a n d t h e u n e v e n f e a tu re s o f t h e s e c t io nc a n c o n t r i b u t e t o w o r s e n t h e p u r s u e d m o r e f a v o ra b le c o n -d i t io n s . T h e p r e s e n c e o f v o i d s o f d i f fe r e n t s iz e c an c o m p l i -c a te t h e c h o i c e o f t h e p r o p e r g r a i n s i ze o f t h e g r o u t : t h em ix , in f ac t, can ha r d ly pen e t r a te in to c r acks th in ne r thant h e g r a i n s i z e o f t h e b i n d e r p a rt ic le s; o n t h e o t h e r h a n d , t h ein jec t ion o f a f r ee mate r ia l in to l a r ge vo ids can ind uce seg-r e g a ti o n a n d c o n s e q u e n t s h r in k a g e . M o r e o v e r , t h e p r e s-e n c e o f s t o n e s a n d m o r t a r s f r o m v a r i o u s o r i g i n c a n i nc re a set h e d i f fi c u l ty in c h o o s i n g t h e o p t i m a l c o m p o s i t i o n o f t h em i x ; t h i s i s d u e t o t h e d i f f e re n t ra t e o f w a t e r a b s o r p t io n o fthe in jec te d mate r ia l , M i lch can even an t ic ipa te the se t t ingphase be f or e a pr o per d i f f us ion in to the w a l l . F ina lly , thei n j e c t i o n p r e s s u r e s h o u l d b e s u f f i c ie n t l y l o w i n o r d e r t oavoid e i the r a i r t r appin g in to th e c r acks and smal l vo ids ore v e n t h e w a l l d i s ru p t i o n .

A s o m e w h a t c o m p l e t e e x a m p l e o f d e s ig n a n d e x e c u -t i o n o f w a l l re p a i r m o n i t o r e d b y t h e a u t h o r s i s g i v e n b y t h er e s t o r a t io n o f t h e m e d i e v a l C a s tl e o f E s t e P a d u a , I ta ly ).T h e s t r u c tu r e , w h i c h c o m p r i s e s d e f en s e c u r t a i n w al ls a n dt o w e r s , w a s s u f f e r i n g w i d e d e t e r i o r a t i o n p h e n o m e n a d u eto the e nvi r o nm enta l exposu r e , and r evea led sever e c r ack-i n g p a t t e rn i n s o m e p o r t i o n s. T h e i n t e r v e n t io n w a s a c o m -b i n a t i o n o f d i f f e r e n t te c h n i q u e s : b u t t r e s s i n g , r e b u i l d i n g ,addin g of s tee l r e inf or ce me nt , g r ou t in jec t ions [ 2] .

A s f o r t h e i n j e c t i o n t e c h n i q u e , t w o d i f fe r e n t g r o u t sw e r e c o n s i d e r e d a n d a s e r ie s o f i n j e c t a b i l i t y te s t s w e r ep e r f o r m e d o n c y l i n d e r s c o n t a i n i n g m a t e r i a l s s a m p l e df r o m t h e c u r t a i n w a l l s t o c h a r a c t e r i z e t h e m o s t s u i t a b l eg r o u t s ; m o r e o v e r , t h e e f f e c ti v e n e s s o f t h e t e c h n i q u e w a sc h e c k e d b y a w i d e i n s i t u in v e s t i g a t i o n c a m p a i g n [ 3] .

F i g . 1 s h o w s t h e g r a i n s i ze d i s t r i b u t i o n o f t h e t w ogr outs con s ide r ed in the exper im enta l s tudy: the M labeledon e i s a specia l mic r o s pozzo lan ic cem ent , w her eas theF type i s an hy dr a ted l ime w i t h addi tives. T he r epr esen ta -t iv e r a n g e s o f v a ri a t io n a r e 0 . 9 - 2 0 g m f o r t h e f o r m e r , a n d0 .9- 100 gm f or the la t t e r . The tw o mate r ia l s w er e s tud ieddur ing a pr ev ious r esea r ch [ 4] . F ig . 2 g ives the r esu l t s o fc o m p r e s s i o n t e s t s c a r r i e d o u t o n c y l i n d e r s i n j e c t e d w i t ht h e a b o v e - m e n t i o n e d m a t e r i a l s, i n t e r m s o f s t re s s -s t ra i nd iagr ams r esu l ts a re r e la ted to a r a t io w a te r /b ind er = 1 andt h e d a s h e d l i n e s r e p r e s e n t t h e v o l u m e t r i c s t r a i n ) . T h eh i g h e s t c u r v e s a r e c o n n e c t e d t o t h e m i x t u r e M , w h i c h

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t r a n sp a r e n c y a l o n g t h e h o r i z o n t a l li n e A - A t h e s ym b o lsx ind ica te in F ig . 3 the t e s t ing poin t s ) a re g iven in F ig . 4 .I t can be not i c ed tha t: a ) in the f i r st appl i ca t ion the sonict e s t w a s a b l e t o d e t e c t a n a r e a c o n t a i n i n g l a r g e v o i d sindica ted as A -A in F ig . 3) , cor resp ond ing to a prev iousb a d r e p a i r a f t e r a lo c a l c o l la p s e ; b ) a n i n c r e a s e o f t h eve loc i ty was de tec ted a f t e r the in j ec t ion , e spec ia l ly in them o r e d e t e r i o r a t e d p o r t i o n s o f t h e w a l l , w h e r e a b e t t e rd i s t r ibu t ion of the m ix ture i s pos sib le .T h e s e r e s u l t s c a n b e c o m p a r e d w i t h t h o s e o b t a i n e dby the rada r te s ts appl i ed a long the s ame pa r t A- A of thew a l l F i g . 3 ) b e f o r e t h e i n j e c t i o n F i g . 5 a) a n d f o u rm o n t h s l a t e r F ig . 5 b ), w h e n t h e w a l l s w e r e d r y . T h i sw a s d o n e t a k i n g i n t o a c c o u n t t h e s i g n if i ca n t s e n si ti v it yo f t h e p r o c e d u r e t o t h e m o i s tu r e c o n t e n t . H o w e v e r , i th a s b e e n p o s s i b l e t o d e t e c t t h e g e n e r a l m o r p h o l o g y o fthe wa l l: i n fac t , t he pos i t ion o f the wid e por t ions w i thl o w d e n s i t y w a s d e t e c t e d , c o n f i r m e d b y t h e p r e v i o u ssonic t e s t s . Af te r in j ec t ion the dens i ty inc reased in thecent ra l pa r t o f the wa l l l eav ing s ti ll l ower den s i t ie s in th elateral parts as in F ig. 4b.

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3 J A C K E TIN G O F M A S O N R Y W A L L ST h e c o n s o l i d a t io n o f d a m a g e d w a l ls b y j a c k e t i n g is al a rge ly d i f fused t echnique in I t a ly ; i t can be appl i ed , a sw e l l a s t h e i n j e c t i o n s , b o t h f o r s t o n e a n d f o r b r i c km a s o n r i e s . T h e t e c h n i q u e i s b a s e d o n t h e a p p l i c a ti o n o f at h i n c o n c r e t e s l a b , i n c l u d i n g u s u a l l y s m a l l g r a i n s i z eaggrega tes an d prope r addit ives to prev ent shr inkage an dt o i m p r o v e t h e a d h e s i o n w i t h t h e w a l l , r e i n f o r c e d b y as tee l ne t . T he re inforced p las te r s l ab should be p laced onbo th s ides o f the wa l l and a series of t ransversal s teel t iesi s p l aced ac ross the th i cknes s of the w a l l t o co nn ec t thetwo ex te rna l l aye rs.S u c h a n i n t e r v e n t i o n p r o v i d e s a r e le v a n t i n cr e a s e o f

the s t rength a nd of the s ti ffness of the w a l l; t ho se e f fect sc a n b e u n f a v o r a b l e i f t h e i r c o n t r i b u t i o n i s n o t w e l l c o n -s ide red in the des ign phase and , ove ra ll , t he ex ecut io n oft h e t e c h n i q u e i s n o t c o r r e c t . T h e m o s t n u m e r o u s f a il ur eso f th i s t e c h n i q u e w e r e f o u n d i n t h e c a se o f m u l t i p le l e a fs t o n e m a s o n r y w a l l s m a d e w i t h i r r e g u l a r s t o n e s , w h e r et h e e x e c u t i o n o f t h e t ie c o n n e c t i o n t h r o u g h t h e w a l l i sve ry d i f f i cu l t [1] .A n y w a y , th e m e c h a n i c a l b e h a v i o r o f t h e c o n s o l i d a te dwal l is depend ing , o f course , o n s evera l pa ramete rs : t het h i ck n e s s o f t h e s la b s, th e a m o u n t o f r e i n f o r c e m e n t , a n dthe ti e s d i s t r ibu t ion d iam ete r and spac ing) , whi ch a rerespons ib le for the ach ievable u l t ima te load . Moreover ,t h e e f f i c i e n c y o f t h e t e c h n i q u e i s s tr o n g l y d e p e n d e n t o nl o c a l m e c h a n i s m s a c t i n g a t t h e i n t e r f a c e l e v e l, l ik e t h eshea r transmis s ion be tw een th e s l ab and the or ig ina l wa l ldue to the sur face in t e r locking .

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A n u m e r i c a l s t u d y o n t h e i n f l u e n c e o f th e a b o v e -m e n t i o n e d p a r a m e t e r s o n c o n s o l i d a t e d w a l ls , ba s e d o nt h e e x p e r i m e n t a l r e s u lt s o b t a i n e d i n a p r e v i o u s re s e a r ch( [ 5 , 6 ] ) h a s b e e n c a r r i e d o u t i n r e c e n t y e a r s f r o m t h eU n i v e r s i t y o f P a d u a [ 7] .A f i n it e e l e m e n t s t w o - d i m e n s i o n a l m o d e l ( pl an es tr a in ) h as b e en ad o p ted to sch em at ize r ea l ly tes ted wal l s .T h e o r i g i n a l w a ll s, h a v i n g d i m e n s i o n s 1 5 0 x 1 0 0 x 5 0 c m( t w o c o n c r e t e b e a m s , 3 0 c m h i g h w e r e a l s o b u i l t a t t h et o p a n d a t t h e b a s e o f th e w a l l t o d i s t r i b u t e t h e l o a d s) ,were su b jec ted to d i r ec t in s i tu co mp ress io n tes t s , b e fo rea n d a f t e r s t r e n g t h e n i n g . T h e s t r e n g t h e n i n g e l e m e n t i s as lab o f 5 cm an d a se ries o f 5 | 2 t i e - ro d s .O n t h e b a s is o f th o s e f e a t u r e s t w o r e f e r e n c e m o d e l s ,o n e f o r t h e n o n c o n s o l id a t e d c o n d i t i o n a n d t h e o t h e r f o rt h e c o n s o l i d a t e d o n e , h a v e b e e n c o n s i d e r e d . A q u a r t e r o ft h e t h ic k n e s s o f t h e c o n s o l i d a t e d p a n e l w a s m o d e l e d ,

t a k i n g i n t o a c c o u n t t h e d i l a t a n c y a n d t h e s h e a r t r a n s m i s -s i o n b e t w e e n t h e o r i g i n a l w a l l a n d t h e s l a b s a t t h e i rin ter face [7] .F i gs . 6 a n d 7 s h o w t h e e v o l u t i o n o f t h e p l a s t ic z o n eu n d e r c o m p r e s s i o n l o a d s f o r t h e o r i g i n a l a n d t h es t r e n g t h e n e d w a l l r es p e c ti v e ly . I t c a n b e n o t i c e d t h a t t h eo r i g i n a l w a l l re a c h e s a s u d d e n a n d w i d e p l a s t ic i z a t io nu n d e r l o w e r v a l u e s o f s t r e s s e s , w h e t h e r t h e p r e s e n c e o ft h e s t r e n g t h e n i n g e l e m e n t s ( s l a b s a n d t i e s ) i s a b l e t oi n c r e a se t h e s t r e n g t h o f t h e w a l l a n d t o k e e p t h e p l a s ti -c i z a t i o n i n t h e v i c i n i t y o f t h e t i e , b e f o r e i t s d i f f u s io nt h r o u g h t h e c o r e o f t h e m a s o n r y .F i g. 8 s h o w s a d i re c t c o m p a r i s o n b e t w e e n n u m e r i c a la n d e x p e r i m e n t a l r e s u l ts o f t h e d i s p l a c e m e n t - s t r e s s t r e n df o r t h e o r i g i n a l (a ) a n d t h e c o n s o l i d a t e d w a l l ( b ). A ss h o w n i n F i g . 8 a, b e f o r e t h e c o n s o l i d a t i o n t h e w a l l w a ss u b j e c t e d t o c y c l ic c o m p r e s s i v e t e s t. T h e v a l u e s o f t h e

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S o m e c o n c l u s i o n s c a n b e d r a w n : f i r s t o f al l, t h e u l t i -m a t e s t r e n g t h a n d t h e s t i f fn e s s o f t h e w a l l is g e n e r a l l yi n c r e a s i n g w i t h t h e a m o u n t o f s t e e l ti e s ( a ) ; i n f a c t , a s aco n se q u en c e o f th e p las t ic izat io n o f th e m aso n ry , th e t ie sy ie ld an d th e co llapse o cc u r s as a r esu l t o f in s tab i li ty p h e-n o m e n a o f t h e s la bs . A s l i g h t d e c r e as e o f t h e u l t i m a t es t r e n g t h h a s b e e n o b s e r v e d w h e n t h e s l a b t h i c k n e s sin creases (b ) ; th i s i s d u e to a g lob a l in stabi li ty p h en o m en o nw h i c h c a n b e p r e v a l e n t w h e n t h e t h i c k n e s s in c re a se s . I nF i g . 1 0 t h e t w o p o s s i b l e w a y s t o t r a n s f e r t h e a c t i o n sb e t w e e n t h e m a s o n r y a n d t h e s la b s a re g i v e n . I f t h e p r e s -s u r e is c o n s i d e r e d u n i f o r m l y d i s t r ib u t e d a t t h e t o p o f t h em aso n ry ( case a ) th e u p p e r t i e is th e m o s t lo ad ed so th e s labsu ff e rs th e co llapse as in d ica ted in th e f ig u re ; o th erwise , i fth e v er t ica l lo ad i s co n s id e red co n ce n t r a ted a t th e in te r f aceb e tw een th e s lab an d th e w ai l ( case b ) , th e lo w es t t ie i s th ef ir s t t o y i e ld . T h o s e t w o m e c h a n i s m s a re o f co u r s e c o m -

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P r o c e e d i n g i n t h e d e s c r i p ti o n o f t h e r es u lt s a s s h o w ni n F i g. 9 , t h e h e i g h t o f th e w a l l se e m s t o h a v e a g r e a ti n f l u e n c e o n t h e s t r e n g t h a n d t h e s t if fn e ss o f t h e c o n s o l -ida ted wa l l s (c ) . Thi s i s due to a d i f fe ren t pos t -e l a s t i cphase evolu t ion : in the re fe rence m od e l , i n fac t , t he p las -t ic z o n e s t ar ts f r o m t h e u p p e r o u t e r e l e m e n t s a n d j o i n sd i a g o n a ll y t h e l o w e r e l e m e n t s , w h e r e a s in t h e m o d e l s o fthe t a l le r pane ls a cen t ra l co re n o t y e t in p las ti c phase hasbee n fou nd e ven nea r the fa ilu re load ( see F ig . 11) .Th e com bina t ion of d i f fe ren t s lab th icknesses w i th d i f -ferent s teel areas (d) deno ted a loss of s t iffness o f the m od elw i t h t h e l o w e s t s t e e l a r e a . H o w e v e r , t h e u l t i m a t e l o a dincreases because o f the red uc t io n o f the s l ab th i cknes s ,wh ich redu ces the e f fec t desc r ibed in F ig . 10b . Th e resu l tscon f i rm the im por tanc e o f the s tee l quant i ty in inc reas ingthe s t rength a nd the s t iffness in the plas t ic phase.F inal ly , i t has bee n o bse rved tha t in the t al l pane l s thei n c re a s e o f s t e el p r o d u c e s a n i n c r e a s e o f s t r e n g t h a n ds ti ffness (e ) . More ove r , t he inc rease of the s l ab th i cknes sl eads to a remarkable inc rease on s t rength ( f ) due to a

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M a t e r i a ls a n d S t r u c t u r e s / M a t 6 r ia u x e t C o n s t r u c t io n s Vol.35 June2002

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I I I I II l l U lI I I I I II I I I I II l l U lI I I I I In imn 1 . 8F i g . 11 - T y p i c a l p l a s ti c z o n e e v o l u t i o n f o r h i g h w a l l s ( m o d e l H 3 ,s t r e s s e s i n M P a ) .col lapse mec han i sm tha t happen s as a re su l t o f the loca lf l exure of the s lab .

4 . US E O F R E I N F O R C E M E N T I N B E D J O I N T ST h e b e d jo i n t r e i n f o r c e m e n t t e c h n i q u e h a s b e e nr e c e n t l y p ro p o s e d t o c o u n t e r a c t t h e t y p ic a l d a m a g e o fovers tressed ma son ry s tructures . T he extern al parts of thebed jo in t s a re excava ted for few cent ime te rs by us ing co m -m on recessing tools and , after the re info rcem ent bars arep laced inside, t he jo in t s a re re f i l led by a rep oin t ing m ate r -ia l in o rde r to re-es tabl ish the in tegri ty o f the w al l.Recent s tud ies ( [8 , 9 1 h a v e d e m o n s t r a t e d t h e i n f l u -e n c e o f t im e - d e p e n d e n t p h e n o m e n a ( c re e p ) in m a ss iv emasonry s t ruc tures l ike towers , p i l l a r s and heavy loadedwalls . D ue to the p revalent dead loads , those s t ructures are

suffe ring a typ ica l mechan ica l damaging represented b y aseries of vert ical , thin bu t ve ry diffused cracks , w hic h canlead the s t ruc ture to a n exces s ive s ta te o f de format ion andt a pos sib le su dden and u nex pec ted co l lapse. Moreo ver ,cycl ic loads can act on those s t ructures du ring their l ives,l ik e w i n d , t h e r m a l a n d h y g r o s c o p ic e x c u r s io n s , a n d b e l losci l la t ions . Al though not caus ing subs tant ia l varia t ion ofs tre sses they can cont r ibu te to w orsenin g the dam aging bya fat igue act ion o n th e masonry.T h e p r o p o s e d t e c h n i q u e c a n b e p e r f o r m e d a t o n es id e o r b o t h s id e s o f t h e w a l l , d e p e n d i n g o n t h e t h i c k n e s sa n d t h e t y p e o f t h e m a s o n r y . T o i m p r o v e t h e a n c h o r i n go f t h e o u t e r l e a f a n d t o i m p r o v e t h e g l o b a l b e h a v i o r inload bea r in g wa l l s, t r ansversa l p ins can be p laced . In pa r -t ic u l a r, i n m u l t i - l e a f m a s o n r y w a ll s t h e c o n n e c t i o nb e t w e e n t h e r e i n f o r c e m e n t s c a n p r e v e n t t h e d e t a c h m e n to f t h e o u t e r l e a f u n d e r c o m p r e s s io n .T h e a p p l i c a ti o n o f t h e t e c h n i q u e i n v o l v e s m a n ya s p e c ts a s f o l lo w s : t h e p r e l i m i n a r y p r e p a r a t i o n o f t h ej o i n t s , t h e c h o i c e o f t h e r e i n f o r c e m e n t i n t e r m s o f m a t e -r i a l ( s t ee l ba rs or p l a t e s , o r FRP l amina tes can be used)a n d o f sp a ci ng a n d a m o u n t , t h e t y p e o f r e p o i n t i n g m a t e -r i a l, a n d t h e a e s t h e t i c o f t h e w a l l fa c e . T h e p r o p o s e dt e c h n i q u e d o e s n o t s h o w p a r t ic u l a r d i f f ic u l t y o f a p p li c a-t i o n ; s o m e s p e c i a l c a r e i s r e q u i r e d i n s o m e o p e r a t i v ep h a se s ( c u t t i n g o f t h e b e d j o i n t , c l e a n i n g , p r e - w e t t i n g ,r e f il l a n d a d e q u a t e c u r i n g ) b u t i t c a n b e p e r f o r m e d e a si lya n d q u i c k l y . N e v e r t h e l e s s , u n l i k e t h e c o n s o l i d a t i o ni n t e r v e n t i o n s p r e v io u s l y m e n t i o n e d , s u c h a t e c h n i q u e i s

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m a t e r i a l t 6 0 m m 1 bF i g . 1 2 - H o r i z o n t a l ( a ) a n d v e r t i c a l ( b ) s e c t io n s o f t h e s t r e n g t h -e n e d p r i s m s .p a r t i c u l a r l y i n d i c a t e d f o r t h e a p p l i c a t i o n t o b r i c km a s o n r y s t r u c t u r e s . I n f a c t , t h e a v a i l a b i li t y o f r e g u l a rc o u r s e s o f e l e m e n t s a n d m o r t a r j o i n t t h i ck n e s s a ll ow s t h ee a s ie r p o s i t i o n i n g o f t h e r e i n f o r c e m e n t i n t o t h e g r o o v e scut in the face of the wa l ls .In ord e r to s tudy the m echan ica l ef fec t s of th i s t ech-n iqu e a s e ri es o f l abora tory t e s ts and a FE m od e l ing haveb e e n p e r f o r m e d b y t h e P o l y t e c h n ic o f M i l an a n d t h eU n i v e r s i t y o f P a d u a [ 1 0 ]. B r i c k - m a s o n r y p a n e l s ( 1 1 0 x5 0 x 2 5 c m ) h a v e b e e n t e s t e d u n d e r c o m p r e s s i o n , t h e nr e p a i r ed b y t h e m e n t i o n e d t e c h n i q u e (2 | s te e l b a rsh a v e b e e n i n s e r t e d e v e r y t h r e e m o r t a r c o u r s e s ) a n df i n a l l y s u b j e c t e d t o f u r t h e r c o m p r e s s i o n t e s t s . F i g . 1 2shows the de tai ls o f the t e s t ed pane ls ; i n or de r to pro videt h e p r o p e r a n c h o r i n g t h e b a r s w e r e f o l d e d a n d f i x e d b yres in in to the shor t e s t s ides of the pane l s.

A f t e r c o n s o l i d a t i o n a r e d u c e d c r a c k p a tt e r n , e s p e -c i a l l y o n t h e r e i n f o r c e d s i d e o f t h e w a l l , w a s n o t i c e d .M o r e o v e r , n o i m p r o v e m e n t o f t h e s t r e n g th w a sd e t e c t e d . O n t h e c o n t r a r y , a r e d u c e d d i l a t i o n o f t h erepa i red pane l s aga ins t the non consol ida ted ones and ar e d u c e d d i l a t io n o f t h e c o n s o l i d a te d f a ce s o f t h e r e p a ir e dpane l s were d e tec ted (F ig . 13) .T h e r e s u l t s o b t a i n e d b y a F E m o d e l ( t w o d i m e n -s i o n a l- p l a n e s t re s s) p r o v i d e d f u r t h e r i n f o r m a t i o n a b o u tt h e g l o b a l b e h a v i o r o f t h e p a n e l s . I n p a r t ic u l a r , d u e t othe p resence o f the s tee l ba rs, t he m od e l de tec ted a s ig-n i f i c a n t r e d u c t i o n o f t h e t e n s i l e s tr es se s i n t h e b r i c k s( a r o u n d t h e 4 0 ) a s s h o w n i n Fi g. 1 4 ( d u e to t h e s y m -m et ry of the pane l , t he re sul ts a re re fe r red to the up perl e f t qua r t e r o f the wa l l) .A s p r e v i o u s l y d e s c r ib e d , t h e i n j e c t i o n a n d j a c k e t i n gt e c h n i q u e s a re a b l e to m o d i f y b o t h t h e s t re n g t h a n d t h e

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Fig. 15 - Damage d pillar of the church.

Fig. 13 - Typical s tress-strain diagram for the consolidated panels: comparisonwith the or iginal panels a) and curves detected for every side b) .

and th e propagation of the existing crack patternby the confinement of the high compressedzones of the structure. The improvem ent of thestrength is a secondary effect, often not achiev-able for the l imited por t ion of thicknessinvolved by t he intervention and anyway oftenunrequired for the particular damage of themasonry. However, the possible combinatio n ofthis techn ique with re buildin g where bricks areparticularly damaged) and/or inject ions espe-cially for mult i-lea fmasonry walls having a hig hpercenta ge of voids in th eir inn er layer), canimprove the load carrying capacity of the damaged com-pressed walls and consequ ently reduce the cracking.The above-mentioned technique has been recentlyapplied on some historical structures located in Italy.Fig. 15 shows the critical cracking situation of one of theheaviest pillars orS. Sofia church in Padua; it can be seenthat reinforcement rings were necessary to reduce thefailure hazard. Fig. 16 shows a view of the rebar inserted

in the previously excavated join t, and th e positio n of the

Fig. 14 - Princi pal tensile stress dist ribut ion before left) ndafter r ight) consolidation stresses in MPa).deformability especially the jacketing) of the walls in arelevant way.On the contrary, the here-described intervention isparticularly aim ed to reduce the dilation of the m asonry Fig. 16 - Phase of inser tion of the rebar .

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M a t e r i a ls a n d S t r u c t u r e s / M a t 6 r ia u x e t C o n s t r u c t i o n s V o l . 3 5 J u n e 2 0 0 2

t r a n sv e r s a l p i n . T h e t e c h n i q u e w a s e a si l y a p p l i e d w i t h n oi n f l u e n c e o n t h e a e s t h e t i c a sp e c t s o f t h e m a s o n r y . I n t h i sc a se s t u d y t h e b e d j o i n t s r e i n f o r c e m e n t t e c h n i q u e h a sb e e n a p p l i e d t o g e t h e r w i t h t h e i n j e c t i o n o n t h e m o s td e t e r i o r a t e d p i ll a rs . A n y w a y , a f t e r c o n s o l i d a t i o n , t h es t ee l ri n g s w e r e r e m o v e d .

5 C O N C L U S I O N S

F i n a ll y , t h e e x p e r i m e n t a l a n d n u m e r i c a l r e s u l t s o f t h ee f f ec t i v en e s s o f a c o n s o l i d a t i o n t e c h n i q u e b a s e d o n t h ei n s e r ti o n o f r e in f o r c e d s t ee l b a r s in b e d m o r t a r j o i n t sh a v e s h o w n t h a t t h e m o s t s i g n i fi c a n t re s u l t c o n c e r n s t h er e d u c t i o n o f t h e t e n s i l e s t re s s es in t h e b r i c k s a n d o f t h ed i l a t i o n o f t h e w a l l . S u c h t e c h n i q u e r e v e a l e d i ts s u i t a b i l-i t y f o r m a s s i v e s t r u c t u r e s s u f f e r i n g c r e e p d a m a g e , w h e r et h e c r a c k in g d e v e l o p i n g c a n b e s l o w e d d o w n o r s t o p p e d .

T h e r e s u l t s o f d i f fe r e n t s t u d i e s o n t h e a p p l i c a t i o n o f an u m b e r o f c o n s o l i d a t i o n t e c h n i q u e s f o r h i s to r i ca lm a s o n r y s t r u c t u r e s h a v e b e e n p r e s e n t e d . I n j e c t i o n s ,j a c k e t i n g a n d r e i n fo r c e d r e p o i n t i n g p e r f o r m e d b y th ei n s e r t i o n o f st e el b ar s i n t h e m o r t a r j o i n t s h a v e b e e nc o n s i d e r e d .

T h e i m p o r t a n c e o f th e d e s i g n a n d o f t h e s i te c o n t r o lo f t h e i n t e r v e n t i o n h a s b e e n p o i n t e d o u t , a s w e l l a s t h en e c e s s i ty t o u s e p r o p e r m e t h o d o l o g i e s t o i n v e st i ga t e t h ee f f i c ie n c y o f t h e i n t e r v e n t io n .A s f o r g r o u t i n j e c t i o n s , t e s t o f i n j e c t a b i l i t y a r e r e c -o m m e n d e d t o s t ud y t h e c o m p a t ib i l it y o f t h e g r o u t w i t ht h e e x i s t i n g m a s o n r i e s , a s w e l l a s t h e u s e o f n o n - d e s t r u c -t i v e m e t h o d s f o r t h e c o n t r o l a n d t h e e v a l u a t i o n o f t h ee f f e c t iv e n e s s o f t h e t e c h n i q u e .

A r e s e a r c h b a s e d o n e x p e r i m e n t a l t e s t s a n d n u m e r i c a ls t u d y o n t h e a p p l i c a t i o n o f t h e j a c k e t i n g t e c h n i q u e t om a s o n r y w a l l s r e v e a l e d s o m e u s e f u l i n d i c a t i o n s f o r t h ed e s i g n o f t h e i n t e r v e n t i o n . I n p a r t i cu l a r , t h e r e l e v a n t r o l eo f th e p r e s e n c e o f a n a d e q u a t e n u m b e r o f ti e s a n d t h eb e h a v i o r i n t h e p o s t - e l a s t i c p h a s e u p t o f a i l u r e h a v e b e e nc l a r i f i e d . H i g h m a s o n r y w a l l s , f o r e x a m p l e , h a v e a g o o db e h a v i o r w h e n t h e t i e - r o d s a re c l o se r o n e a n o t h e r i n t h eu p p e r a n d l o w e r z o n e s r a t h e r t h a n i n t h e c e n t r a l o n e .A l s o t h e s l a b ' s t h i c k n e s s h a s a n i m p o r t a n t r o l e i n t h e s ew a l l s b e c a u s e t h e i r f l e x u r a l s t i ff n e s s is i n c r e a s e d .D e c r e a s i n g t h e w a l l ' s h e i g h t , i t w o u l d b e b e t t e r n o t t oin c r e a s e th e s l a b th ic k n e s s , to a v o id a c o l l a p s e b y in s ta b i l -i t y r a t h e r t h a n i n f l e x u r e . M o r e o v e r , t h i s t e c h n i q u e h a s al i m i t e d a p p l i c a t i o n p o t e n t i a l t o s o m e w a i l s : f o r e x a m p l e ,t h e p r e s e n c e o f l a rg e h a r d s t o n e s i n t w o - l e a f w a l l s c a nc o m p l i c a t e t h e i n s e r t i o n o f t i es , so t h e s t u d y i n a d v a n c eo f t h e w a l l t y p o l o g y c a n b e s u g g es t ed .

R E F E R E N C E S[1] Bin , L. , Gambarotta, L. , Lagom arsino, S. , Mo dena, C. andSegnalini, O ., 'Montesanto and Roccanolf i his torical centers atrisk', I t a l i a N o s t r a l l d o p o t e r r e m o t o Bollett ino 355 (1999) (avail-able only in Italian).[2] M oden a, C., 'Criteria for cautiou s repair of historic buildings', in'Evaluation and Strengthening of E xisting Masonry Structures ',L. Bin C. Mo dena Ed., RILEM , 1997, 25-42.[3] Mod ena, C., B in , L. and Anzani, A., 'Investigation for the

design and control o f the repa ir interventio n on a historical stonemasonry wall ', Proc. of the 7th Int. C onf . on Structural Faultsand P,.epair, Edinb urgh, U K, 1997.[4] Laefer , D., B aronio, G., Anzani, A. and Bin , L. , 'Measurementof grout injection eff icacy or s tone mason ry walls ' , Proc. o f the7th N orth A merican Conf. , U.S.A, 1996.[ 5 ] Ge lmi , A . , M o d e n a , C . , Ro s s i , P . P . a n d Z a n in e t t i , A . ,'Mechanical characterization of s tone m asonry structures in oldu r b a n n u c le i ', P r o c . o f th e 6 th N o r th Ame r ica n M a s o n r yCon ference, Philadelphia, Pennsylvania, U.S .A., 1993.[6] M oden a, C. and Bettio, C ., 'Ex perim ental characterization andmodelling o f injected and jacketed masonry walls ' , Proc. I talian-French Sy rup. on Strengthening and Repair of Structures inSeismic Area, Nice, France, 1994, 273-282.[7] M oden a, C., Zavarise, G. an d Valluzzi, M. R ., 'Mod elling of stonemasonry walls s trengthened by r . c . Jackets ' , Proc. Com puterMe thods in Structural Mason ry,vol. 4, 19 98, 285-292.[8] Binda, L., Gatti, G., Man gano, G., P oggi, C. and Sacchi Landriani,G., 'The collapseof the civic ow er of Pavia: a surveyof the materi-als and stru cture', M a s o n r y I n t e r n a t i o n a l 6 (1) (1992) 11-20.[9] M irabella, G., Bin , L. and Anzani, A., 'Experim ental investiga-tion into effects of persis tent and cyclic oads on the masonry ofancient towers ' , Proc. of the 7th In t. Con f. on S tructural FaultsRepair , Edinburgh, UK , 1997, 339-347.[10] Binda , L . , Modena , C. , Val luzz i , M. R. and Zago, R. ,'Mechanical effects of bed join t s teel reinforcement in histor icbr ick masonry s t ruc tures ' , Proc . o f the 8 th In t . Conf . onStructural Faults and Repair , London, U K, 1999 (on CD -Rom ).

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experimental and analytical studies for the choice of

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