ISSN: 0871-7869

Rehabilitation and strengthening

of old masonry buildings

H. Meireles; R. Bento

- Março de 2013 -

Relatório ICIST DTC nº 02/2013

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!Table&of&contents&!Introduction*..........................................................................................................................................................*3!Structural*interventions*related*to*the*foundations*...........................................................................*5!a)! Improvement!of!the!ground!soil!by!Jet9Grouting!.............................................................!5!b)! Improving!the!behaviour!of!foundations!by!enlargement!and/or!consolidation! 5!c)! Strengthening!of!the!foundation!by!using!micro!piles!isolated!or!in!group!or!in!row!6!

Local*interventions*for*structural*improvement*..................................................................................*8!a)! Injections!in!cracks!........................................................................................................................!8!b)! Strengthening!roof!diaphragms!with!plywood!.................................................................!9!c)! Transversal!anchorage!in!walls!...............................................................................................!9!d)! Strengthening!masonry!column!with!jacketing!............................................................!10!e)! Repair!of!damaged!wood!elements!.....................................................................................!10!

Global*interventions*for*structural*improvement*.............................................................................*11!a)! Strengthening!of!masonry!walls!with!reinforced!cement!coating!.........................!11!b)! Strengthening!of!masonry!walls!with!polypropylene!meshing!..............................!11!c)! Strengthening!of!floors!and!improving!the!connection!floor/wall!.......................!12!d)! Strengthening!with!composite!materials!(CFRP!and!GFRP)!....................................!14!e)! The!use!of!horizontal!tie9rods!...............................................................................................!17!f)! Retrofitting!by!post9tensioning!.............................................................................................!19!f)! Strengthening!with!ring!beams!.............................................................................................!21!g)! Retrofitting!by!introducing!RC!shear!walls!.....................................................................!22!h)! Strengthening!with!RC!or!steel!frames!.............................................................................!22!REFERENCES!..........................................................................................................................................!25!

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Introduction!!Men! with! mainly! four! materials! built! the! oldest! constructions! and! these!materials!lasted!thousands!of!years!for!construction!purposes.!These!were!earth!(from! which! bricks! come! from,! for! instance),! stone,! wood! and! natural! plants!fibres.!With!these!four!elements!men!was!able!to!build!spectacular!constructions!some!of!which!are!still! standing!nowadays.!Later! in! the!XVIII!century,!with! the!beginning!of!the!industrial!revolution!in!England,!the!iron!is!burnt!with!coal!and!its! impurities! decrease! giving! rise! to! cast! iron,! to! be! built! in! great! quantities.!While! the! iron! from! Nature! is! very! brittle,! the! cast! iron! is! resisting! well! to!compression,!although!bad!to!tension,!and!can!be!used!as!a!structural!resisting!element!working! in! compression.!With! fewer! impurities,! later! on,!we!have! the!forged! iron/steel! and! later! the! steel,!where! carbon! is!mixed!with! iron! is! small!quantities!to!make!it!become!more!malleable.!The!forged!steel!and!the!steel!are!used!mainly! in! tension!due! to! the!phenomena!of!buckling.! Steel! structures! are!common!nowadays!although!not!in!great!quantity!in!Portugal!when!compared!to!England.! The! last! great! change! occurring! in! construction! materials! was! the!introduction! of! concrete.! In! Portugal! it! started! in! the! 40’s! only! by! introducing!some!concrete!elements,!reinforced!with!steel,!to!build!floors!and!some!columns!such!how!it!is!found!in!Placa!buildings.!Later!on,!in!the!60’s!complete!reinforced!concrete!buildings!were!built!in!Portugal!and!this!is!the!most!common!practice,!nowadays,!to!build!new!buildings.!!!The! old!masonry! buildings! in! Lisbon! that! still! stand! nowadays! are! called! pre9Pombalinos,! Pombalinos,! Gaioleiros! and! Placa! buildings.! They! were! built! with!stone!and/or!bricks,!sometimes!lime,!and!wood,!(Placa!buildings!also!with!a!few!reinforced! concrete! structural! elements).! Foundations! were! built! with! a! large!masonry! footing! sometimes! settled! on! a! base! of! wooden! piles! (Pombalino!buildings).!On!the!ground!floor!one!can!find!masonry!walls,!some!made!of!stone!masonry! others! of! brick! masonry.! It! is! also! possible! to! find! arches! made! of!masonry! very! common! on! the! ground! floor! of!Pombalino! buildings.! The! floors!and!the!roof!are!made!with!wood!joists,!except!for!Placa!buildings!as!previously!referred.!!!The! strengthening! of! old!masonry! buildings! is! an! important! issue! since! these!buildings! constitute! the! historical! centres! of! many! cities! and! thus! deserve!attention!from!the!state!authorities!for!preservation!purposes.!!!When!strengthening!an!old!building,!one!must!focus!first!on!understanding!how!it!is!working,!assessing!its!performance!for!gravity!and!seismic!loads.!Then,!the!problems!and/or!pathologies!must!be!encountered!and!only!then!one!can!start!prescribing!the!necessary!solutions!for!the!rehabilitation!or!strengthening.!!!Old!masonry!buildings!have!common!pathologies!that!are!mainly!related!to!their!age.!For!instance!the!wood!can!be!damaged!due!to!the!changes!and!exposure!to!humidity.! It! can! have! fungus! attack! or! insect! attack.! On! the! other! hand! the!masonry! can! be! also! damaged.! In! case! of! the! masonry! the! most! important!pathologies! have! structural! origin! and! can! be! translated! into! desegregation,!

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crushing,! fracture! and! cracking.! The! most! common! causes! are! related! with!foundation! settlements,! movements! of! thermal! origin,! horizontal! thrusts!transmitted!by! inclined!roofs!or!arches,! the!existence!of!concentrated!and!high!loads! (generally!associated!with!adaptation!of! the!building! to!new!usages)!and!earthquakes!which!have!a!considerable!influence!in!a!material!that!is!both!heavy!and!brittle.!!!The!ageing!of!the!masonry!and!in!particular!its!desegregation!depends!in!a!great!deal!of!the!way!the!masonry!is!protected!by!coating;!the!cracking!or!the!loss!of!these!coatings,!expose!the!masonry!to!the!action!of!the!atmospheric!agents!being!especially!relevant!the!action!of!the!wind!transporting!sands!and!dust!that!give!rise!to!erosion.!!!The! foundation! settlements! are! usually! associated! with! the! construction! of!additional!floors!and/or!the!execution!of!excavations!in!the!adjacent!areas!of!the!building!and!have!has!a!result! the!decompression!and!dragging!of! the!soil.!The!changes!of!the!ground!water!flows!are!also!important.!!!The! iron! was! used! in! old! buildings! mainly! for! small! elements! such! as! nails,!screws! and! elements! with! anchor! shape.! These! were! used! to! connect! wood!elements! between! each! other,! connect!masonry!walls! between! each! other! and!also! connect! wood! floors! with! masonry! walls.! The! main! problem! for! this!material! is! its! corrosion! given! the! lack! of! maintenance! because! of! the!inaccessibility!of!the!elements.!The!risk!of!oxidation!is,! in!first!place,!the!loss!of!useful! cross9section! of! the! elements! and,! secondly,! the! effect! of! destruction!caused! by! the! increase! of! the! volume! of! the! iron! elements! that!may! cause! the!rupture!of!the!masonry.!!!The! existing! pathologies! should! be! tackled.! On! the! other! hand,! the! structural!system!of!the!building!may!be!assessed!and!improved!whenever!necessary.!One!reason! for! improving! the! structural! system! of! a! given! building! may! be,! for!instance,!the!objective!of!changing!its!use!or!merely!an!adaptation!to!nowadays!usages!and!facilities.!For!instance!the!introduction!of!toilets,!the!introduction!of!elevators,!air!conditioning,!the!widen!up!of!rooms,!etc.!!!Moreover,! one! can! think! of! improving! the! structural! system! for! earthquake!resisting!purposes.!It!is!then!very!important!to!understand!very!well!the!original!behaviour! of! the! structure.! It! is! always! essential! to! improve! the! connections!between!the!structural!elements,!e.g.,!between!the!floors!and!walls!(and!frontal!walls!with!walls!in!Pombalino!buildings)!and!between!the!roof!and!the!top!of!the!walls.! In! this! way! these! structural! elements! will! not! separate! when! the!earthquake!strikes!and!will!behave!together.! It! is!usually!also! important! in!any!building! to! strengthen! its! floors! given! the! wooden! floors! are! flexible! in!plan(while! the!masonry! is!rigid)!and!thus! they!do!not! transmit! forces!between!parallel! walls.! The! whole! structure! should! behave! like! a! box! where! all! the!structural!elements!are!having!similar!displacements!and!moving!together.!The!foundations!may!be!improved!also.!!!In! the! following! lines! it! is!presented! separately! structural! interventions,! firstly!

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related!to!the!foundations;!then,!structural!interventions!herein!called!Local!and,!finally,! structural! interventions! that! are! affecting! the! whole! building! (Global)!behaviour.!!

Structural!interventions!related!to!the!foundations!!

a) Improvement!of!the!ground!soil!by!Jet:Grouting!!This!technology!was!first!developed!in!the!70s!but!later!it!had!a!large!expansion!on!the!80s.!It!was!introduced!in!Portugal!in!the!beginning!of!the!90s!due!to!the!construction!of!the!metropolitan!in!Lisbon.!It!consists!in!the!disaggregation!of!a!volume!of! soil,! internally! in! the! ground!without! previous! excavation,!mixing! it!with! cement! grout! introduced! in! high! pressure! (values! between! 200! and! 800!bar)! and! velocity! in! the! order! of! 250! m/s.! This! results! in! a! material! with!mechanical!characteristics!with!higher!values!then!the!previous!ones!for!the!soil!and!with!less!permeability!(Fig.!1).!!!The!advantages!of!this!technique!are:!it!can!be!applied!in!all!types!of!soil!(as!long!as!they!contain!small!sized!material!and!are!not!subjected!to!seepage);!it!can!be!applied! in! difficult! closed! areas! and! it! does! not! give! chance! to! significant!vibrations.!!!

!Fig.&1&The&fases&of&jet–grouting&[Lourenço,&Lectures&UM&]&

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b) Improving!the!behaviour!of!foundations!by!enlargement!and/or!consolidation!

!As!explained!by!Appleton![2003],!the!superficial!foundation!can!be!enlarged!with!concrete! as! is! depicted! in! Fig.! 2.! The! connection! between! foundation! and!concrete!is!made!through!connectors!(“Grampo!de!ligação”).!There!is!the!need!to!excavate!until!the!bottom!of!the!foundation!to!place!the!formwork!(“Cofragem”).!!

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!Fig.&2&Enlargement&of&the&foundation&[Appleton,&2003]&

!Additionally,!the!foundation!may!be!improved!by!filling!the!gaps!between!blocks!with!mortar,!as!can!be!seen!in!Fig.!3.!Visibly,!there!is!the!need!to!excavate!until!the!bottom!of!the!foundation!(“Vala!escavada”)!to!perform!these!tasks.!One!uses!tubes! for! injection! (“Tubos! de! injecção”)! for! the! inner! holes! and! then! closes!cracks!at!the!face!of!the!masonry!(“Selagem!das!juntas”).!!

!Fig.&3&Consolidation&of&the&foundation&[Appleton,&2003]&

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c) Strengthening!of!the!foundation!by!using!micro!piles!isolated!or!in!group!or!in!row!

&The!foundation!layout!present!in!most!of!the!old!masonry!buildings!is!drawn!in!Fig.!4!a).!In!Fig.!4!b)!one!can!see!the!foundation!typical!of!a!Pombalino!building!in!downtown.!This! typology!of!buildings! is!mainly!set!on!an!alluvium!filled!valley!with!a!weak! layer!of!material!over! the!bedrock.!The!small!wood!piles!(average!1.5!m! long)!used! in! these!buildings!are!meant! for!consolidation!of! the! topmost!layer!of!soil!and!cannot!be!seen!as!having!the!same!behaviour!as!nowadays!RC!piles!(which!are!usually!longer,!working!by!point!resistance!and!lateral!friction).!!

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DECivil a) Alargamento da fundação superficial existente

APPLETON, J., Reabilitação de Edifícios Antigos Patologias e tecnologias de intervenção, Edições Orion, 1ª Edição, Setembro de 2003.

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DECivil b) Consolidação da fundação (de alvenaria!) existente

APPLETON, J., Reabilitação de Edifícios Antigos Patologias e tecnologias de intervenção, Edições Orion, 1ª Edição, Setembro de 2003.

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37

DECivil a) Alargamento da fundação superficial existente

APPLETON, J., Reabilitação de Edifícios Antigos Patologias e tecnologias de intervenção, Edições Orion, 1ª Edição, Setembro de 2003.

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DECivil b) Consolidação da fundação (de alvenaria!) existente

APPLETON, J., Reabilitação de Edifícios Antigos Patologias e tecnologias de intervenção, Edições Orion, 1ª Edição, Setembro de 2003.

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&& &a)! ! ! ! ! b)!

Fig.&4&a)&Common&foundations&of&old&masonry&buildings;&b)&Foundations&of&Pombalino&buildings&

!Using!micro! piles! to! strengthen! a! foundation! is! a! solution! reasonably! used! in!Portugal! in!monuments! or! common! buildings.! It! is! for! increasing! loads! in! the!structure,!which! lead! to! increasing! loads! in! the! soil,! or! to!deal!with! settlement!problems.! The! micro! piles! consolidate! the! shallower! layers! of! soil! and! also!mobilize!the!deepest!layers!of!soil.!!!!They!are!composed!of!a!RC!heading,!a!steel!casing!with!8,!10!or!12!meters!long!usually!to!be!filled!with!a!cement!grout!under!pressure.!Inside!the!casing!there!may!be!steel!rods.!Finally,!at!the!bottom!there!is!usually!a!bulb!of!cement.!!!To!be!noticed!that!the!piles!are!only!under!pressure!when!there!is!an!additional!load!in!the!structure.!When!they!are!built!they!do!not!receive!any!load.!!&In!Fig.!5!one!can!see!in!a)!the!machine!to!drill!the!holes!and!in!b)!the!micro!piles!casing!to!be!filled!with!cement!grout.!!

a) b)

Fig.&5&a)&Machine&to&drill&the&holes,&b)&micro&piles&casing&to&be&filled&with&cement&grout&[photos&by&Appleton,&2011]&

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DECivil

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Fundações correntes de edifícios antigos

APPLETON, J., Reabilitação de Edifícios Antigos Patologias e tecnologias de intervenção, Edições Orion, 1ª Edição, Setembro de 2003.

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DECivil

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Fundações de edifícios antigos em solo brando

grade e estacas de madeira

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Local!interventions!for!structural!improvement!!

a) Injections!in!cracks!!The!injections!in!cracks,!internal!or!at!the!face,!of!a!masonry!wall!are!a!solution!of!strengthening!that!is!irreversible.!They!are,!however,!used!frequently!because!they! preserve! the! original! aspect! of! the! exterior! of! the! wall.! It! is! particularly!indicated!for!the!rehabilitation!of!the!masonry!that!has!internal!cracks!connected!between!them.!!For!this!solution!a!cimenticious!based!grout!is!used!or!a!hydraulic!based!grout!or!others!such!as!organic!resins!based!grout.!This!solution!is!based!on!the!injection!in!holes!previously!made!with! injection! tubes!(“tubos!de! injecção”)!and!spread!throughout! the!wall,! to! fill!with! the! grout! the! internal! cracks.! For! the! external!cracks!the!coating!should!be!removed!previously!(“remoção!de!reboco”)!and!the!injection!tubes!may!be!used!also.!Fig.!6!shows!these!considerations.!!!

!a)! ! ! ! ! ! ! b)! ! ! c)!

Fig.&6&(a)&injection&in&external/face&diagonal&crack;&(b)&injection&for&the&internal&cracks;&(c)&side&view&[Roque,&2002]&

!The!aggregate!grading!of!the!grout!depends!on!the!size!of!the!cracks!but!it!can!be!used! a! grout! without! the! sand.! This! technique! shows! improvements! in! the!mechanical!characteristics!of!the!masonry.!It!seems!a!better!application!in!stone!masonry.! To! deliver! a! specific! injection! grout! one! must! carry! on! in9situ! and!laboratory! tests! to! refine! the! grout.! Depending! on! the! used! process,! there! are!several!solutions!for!the!injections:!

1. &Injection& under& pressure:! it! is! frequently! used! in! masonry.! To! avoid!structural!failure!of!the!wall!(that!can!be!in!very!bad!conditions),!the!holes!are!done!from!bottom!to!top!and!from!side!to!centre.!!

2. &Injection&trough&gravity:&it!is!used!to!highly!damaged!walls.!&3. !Injection& trough& vacuum:& it! is! used! in! small! interventions,! mainly!architectural,!statues,!etc.!The!grout!is!very!fluid!(for!instance!resins!can!be!used)![Valluzzi,!M.,!2000].!!

!In! old! structures,! the! inorganic! grouts,! non9cimenticious,! like! hydraulic! limes,!should! be! preferred! because! of! compatibility! issues! with! the! already! existing!mortars.! The! organic!mortars! (polyester! or! epoxy),!more! fluid,! should! only! be!used! when! there! are! needs! for! higher! resistance,! hopefully! without!

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! 9!

compromising!the!compatibility!between!the!materials![Roque,!2002].!!

b) Strengthening!roof!diaphragms!with!plywood!&To! stiffen! and! strengthen! the! roof! diaphragm! (which! may! be! originally! made!only! by! a! single! layer! of! boards! nailed! to! the! joists),! one! can! adopt! an!intervention! that! is! compatible! with! the! original! timber! structure,! by! adding!multilayer! spruce! plywood! panels,!which! are! lighter! and! easier! to! apply! to! an!inclined!plane!in!comparison!to!a!reinforced!concrete!slab,!although!providing!a!significant!stiffness!increase.!One!example!of!intervention![Magenes!et!al.,!2012],!Fig.! 7,! consists! in! adding! 3! layers! of! plywood,! each! 21! mm! thick,! glued! with!polyurethane!glue!and!connected!to!the!purlins!by!means!of!chemically!anchored,!10!mm!diameter!threaded!steel!bars.!After!having!drilled!and!cleaned!the!hole,!a!two9component! epoxy! mixture! is! inserted! in! the! hole! and! then! the! bar! is!introduced! and! rotated! to! distribute! the! resin.! Bars!were! placed! at! a! constant!spacing! of! 30! cm! and! penetrated! into! the! purlins! to! connect! the! upper! plank!layers!with!the!roof!structure.!&

&&

Fig.&7&Scheme&of&the&intervention&on&the&roof&diaphragm,&consisting&in&the&application&of&multilayer&panels&and&chemically&anchored&steel&connectors.&[Magenes&et&al,&2012]!

!To!improve!the!diaphragm!behaviour!of!the!roof,!continuous!steel!plates!(80!mm!wide! and! 5!mm! thick)! were! connected! all! along! the! perimeter! to! the! roof,! to!favour!the!development!of!a!strut!and!tie!mechanism.!The!roof!is!then!completed!by!adding!plain!roofing!tiles!nailed!to!the!multilayer!spruce!plywood!panels.!!!!

c) Transversal!anchorage!in!walls!!The!application!of!transversal!anchorage!in!walls!aims!to!connect!better!the!two!layers!of!the!wall!avoiding!their!separation!from!the!interior!core,!as!can!be!seen!in! Fig.! 8.! The! interior! core! is! usually! constituted!by! rubble! of! low!quality.! The!application!of!such!technique!may!include,!or!not,!binding!material!such!as!grout!(cement,!lime).!!

Simulating an intervention where the roof structure can be temporarily removed, a reinforced concrete

ring beam, 20 cm high and 32 cm wide (as the wall below), was cast at the roof level, on top of the

perimeter façades (Fig. 2, left). The reinforcement consisted in 4!16 longitudinal bars and !8 stirrups

at a spacing of 20 cm, coherently with the prescriptions of the Italian Building Code (NTC08, 2008).

Figure 2. Detail of the reinforcement of the joint at the base of the gable wall (left). Operation of drilling the

timber spreader beam and the concrete ring beam (right)

The original timber roof structure of the unstrengthened building included one 20cm x 32 cm ridge

beam, two segmented 32cm x 12cm spreader beams on top of the longitudinal walls and 8cm x 12 cm

purlins every 50 cm forming the two pitches with 30 mm thick planks.

The strengthening of the roof envisaged the improvement of the connection of the ridge beam with the

gable walls, which consisted of a steel shoe doweled to the concrete ring beam and bolted to the ridge

beam. Timber spreader beams were also doweled to the r.c. ring beam all along the perimeter, by

means of connecting steel bars chemically anchored by epoxy resin. Any discontinuity between the

timber spreader beam and the ring beam was smoothed by the insertion of a plaster layer to create a

continuous contact. The 8 cm x 12 cm joists were reshaped to create a horizontal seat on the ridge

beam and on the longitudinal spreader beams. Steel connecting elements were inserted at the top of

the ridge beam, at the contact between the two opposite purlins. The matchboard was then placed on

top of the timber structure.

To stiffen and strengthen the roof diaphragm (which originally was made only by a single layer of

boards nailed to the joists), it was decided to adopt an intervention that was compatible with the

original timber structure, by adding multilayer spruce plywood panels, which are lighter and easier to

apply to an inclined plane in comparison to a reinforced concrete slab, although providing a significant

stiffness increase. The intervention consisted in adding 3 layers of plywood, each 21 mm thick, glued

with polyurethane glue and connected to the purlins by means of chemically anchored, 10 mm

diameter threaded steel bars. After having drilled and cleaned the hole, a two-component epoxy

mixture was inserted in the hole and then the bar was inserted and rotated to distribute the resin. Bars

were placed at a constant spacing of 30 cm and penetrated into the purlins to connect the upper plank

layers with the roof structure (Fig.3).

Figure 3. Scheme of the intervention on the roof diaphragm, consisting in the application of multilayer panels

and chemically anchored steel connectors.

To improve the diaphragm behaviour of the roof, continuous steel plates (80 mm wide and 5 mm

thick) were connected all along the perimeter to the roof, to favour the development of a strut and tie

mechanism. The roof was then completed by adding plain roofing tiles nailed to the multilayer spruce

! 10!

!Fig.&8&Face&to&face&connector&in&wall&of&two&layers&[Cóias,&2007]&

!

d) Strengthening!masonry!column!with!jacketing!&In! similarity!with! the! case!of! strengthening! the!masonry!walls!with! reinforced!cement!coating,!the!masonry!piers!can!be!strengthened!with!reinforced!concrete!as!an!outside! layer.!The!steels!rods!are!placed! in! the!perimeter!of! the!pier!and!then!the!concrete!is!poured!covering!the!steel!rods.!The!rods!should!be!anchored!to!the!base!foundation!of!the!pier.!!!!

e) Repair!of!damaged!wood!elements!!These! are! repair! techniques! and! not! strengthening! solutions.! The! reduced!existence!of!pieces!of!natural!wood!of!considerable!dimension!nowadays!makes!it! difficult! to! substitute! complete! pieces! of! damaged!wood!with! natural! wood!elements.! In! this! way! one! can! find! several! substitutes! of! wood.! The! damaged!wood! elements! may! be! replaced! by! glued! laminated! wood,! for! instance.! The!damaged!wood!elements!can!be!replaced!also!with!epoxy!resin!mortar!and!this!mortar!has!similar!mechanical!characteristics! to! the!wood!to!be!reconstructed.!In!this!technique,!it!is!advisable!that!the!connection!between!existing!wood!and!mortar!be!enforced!by!mechanical!connectors.! It! is!necessary!also! that! there! is!enough! protection! of! the! mortar! against! fire! given! the! susceptibility! of! this!material!to!high!temperatures.!In!Fig.!9!a)!it!is!depicted!rotten!wood!joists!and!in!Fig.!9!b)!more!rotten!wood!elements.!!&

!a)! ! ! ! ! ! b)!

Fig.&9&a)&Rotten&wood&joists&at&the&connection&to&the&wall;&b)&Rotten&wood&elements&[Cruz,&2012]&

!"#$%&"'()*+,*%&"'-.'/-*0121#*,3&'%&'4*#51.6+1&'!%1718*%&

9::;'<'9::= !"#5$#$5*"'%-'(2)-+*51*'%-'4-%5*

!"##$%$&$'(')#*')*+),"+-"*)*+)(%$&$.(-/"

!! 45->*>-+"'#5*+")-5"*1"?'%-"#1+*%*"'*'21>*5'*"'%17-5-+#-"'7&2@*"'45->*>-+"'#5*+")-5"*1"?'%-"#1+*%*"'*'21>*5'*"'%17-5-+#-"'7&2@*"'%-'A*5-%-%-'A*5-%-

B8&.'&$'"-.'"-2*>-.'A&5'.*#-51*2'21>*+#-CB8&.'&$'"-.'"-2*>-.'A&5'.*#-51*2'21>*+#-C

! "#$%&$'(#)*+,'-*).'(#+,/*0'$&0'/*$.*1

DDEE#&5'F#&5'F661*"?'9::G1*"?'9::G

HH I1>*%&5-"'5I1>*%&5-"'5EE>1%&">1%&" HH I1>*%&5-"'72-JI1>*%&5-"'72-JEE)-1")-1"

20

perda de secção, fractura ou apodrecimento de pavimentos

Introdução de casas de

banho

Apodrecimento das entregas

+ falta de solidarização (apoios curtos,

falta de elementos metálicos)

19

Erros / problemas correntes

Em pavimentos:

• Comprimento insuficiente do apoio das vigas nas paredes

• Falta de contraventamento (ou contrav. solto) entre vigas

• Remoção de apoios ou introdução de paredes divisórias intermédias

! 11!

Global!interventions!for!structural!improvement!!

a) Strengthening!of!masonry!walls!with!reinforced!cement!coating!!In!this!case!(Fig.!10!a)!and!b))!one!places!thin!(less!than!10!cm)!layers!of!coatings!of!cement!reinforced!with!steel!(or!glass!fiber!or!plastic!meshes,!see!section!d))!on!masonry!walls.!The!coating! increases!the!walls!strength!and!ductility.! It!can!be! placed! in! the! outside! or! in! the! inside! or! both,! depending! on! the! most!accessible!areas.!!!To!enable! the!behaviour!of!both!elements!(existing!and!new)! to!work! together!one!places!steel!connectors!on!the!wall.!!!It! is! thought! that! a! wall! of! rubble! (stone)! masonry! with! 0.60! m! of! thickness!reinforced!with!two!layers!of!cement!coating!with!steel!meshes!and!with!0.10!m!thickness!in!total,!may!have!increased!its!strength!in!compression!and!shear!of!3!to!6!times!its!original!strength,!at!least![Appleton,!2009].!&

a)! ! ! ! ! b)!

Fig.&10&a)&Masonry&wall&from&the&inside&with&steel&mesh,&b)&spraying&of&the&cement&grout&into&the&wall&[fotos&by&Appleton,&2011]&

&

b) Strengthening!of!masonry!walls!with!polypropylene!meshing!!!&Polypropylene! meshing! uses! common! polypropylene! packaging! straps!!(PP9bands)! to! form!a!mesh,!which! is!used! to! encase!masonry!walls! (Fig.!11! a)),!preventing!both!collapse!and!the!escape!of!debris!during!earthquakes.!PP9bands!are!used! for! packaging! all! over! the!world! and! are! therefore! cheap! and! readily!available!while! the! retrofitting! technique! itself! is! simple! enough! to!be! suitable!for! local! builders.! PP9meshing! has! been! applied! in! Nepal,! Pakistan! and! more!recently! in! China.! This!method! is!most! readily! applicable! in! terms! of! low9cost!upgrading! of! traditional! structures! to! limit! damage! caused! by! normal!earthquakes!and!give!occupants!a!good!chance!of!escape!in!an!once9in9a9lifetime!large! earthquake.! Non9engineered! masonry! is! widespread! throughout! the!developing!world!and!replacement!of! all! such!dwellings! is!both!unfeasible!and!undesirable,! given! that! they! are! often! the! embodiment! of! local! culture! and!tradition.! It! is! therefore!often!more! feasible! to!consider! low9cost! retrofitting!of!

Abril de 2011pág. 33

!"#$%&%'#()*+,"+"-'!.'.!#-+#/'%0#-+,"+#&1"/#!%#+"+2#,"%!#Reforço de paredes de alvenaria com recurso a lâminas armadas de

argamassa ou microbetão – Edifícios pombalinos em Lisboa

Abril de 2011pág. 33

!"#$%&%'#()*+,"+"-'!.'.!#-+#/'%0#-+,"+#&1"/#!%#+"+2#,"%!#Reforço de paredes de alvenaria com recurso a lâminas armadas de

argamassa ou microbetão – Edifícios pombalinos em Lisboa

! 12!

such! buildings.! Experiments! and! advanced! numerical! simulations! have! shown!that! PP9band! mesh! can! dramatically! increase! the! seismic! capacity! of!adobe/masonry!houses![P.!Mayorka!and!K.!Meguro,!2008].!!&This! is! mainly! achieved! by! increasing! the! structural! ductility! and! energy!dissipation! capacities.! Under! moderate! ground! motions,! PP9band! meshes!provide!enough!seismic!resistance!to!guaranty!limited!and!controlled!cracking!of!the! retrofitted! structures.! Under! extremely! strong! ground! motions,! they! are!expected!to!prevent!or!delay!the!collapse,!thus,! increasing!the!rates!of!survival.!This!method!is!good!for!one9storey!buildings!and!can!be!used!for!a!maximum!of!two!storeys.!To!protect!the!Polypropylene!from!ultra!violate!rays,!mud!plaster!is!used! on! the! outside,! providing! adequate! cover! to! ensure! the! durability! of! the!material![Shrestha!et!al.!2012].!!To!enable! the!behaviour!of!both!elements!(existing!and!new)! to!work! together!one!places!anchorages!throughout!the!wall!(Fig.!11!b)).!!&

&a)! ! ! ! ! b)!

Fig.&11&Implementation&of&PP&band&method&of&retrofitting&in&Kathmandu&Valley&(a)&and&anchorage&throughout&the&wall&(b)&[Shrestha&et&al.&2012]!

&

c) Strengthening!of!floors!and!improving!the!connection!floor/wall!!Traditional!masonry!buildings!have!timber!floors,!and!they!are!typically!flexible.!The! increase!of! the! in9plane! stiffness!of! floors! is! an!evident!and!most!effective!method! of! improving! the! seismic! behaviour! of! old!masonry! structures.! This! is!mainly!because!the!increase!of! in9plane!stiffness!of! floors!enables!the!structure!behaves!like!a!box,!i.e.!enables!the!horizontal!forces!to!be!redistributed!between!the!different!vertical!structural!elements,!and!then!the!horizontal!forces!of!failing!walls!can!be!redistributed!to! the!adjacent!remaining!walls.!A!significant!role! in!the!stability!of!the!entire!building!is!assigned!to!the!floors.!These!structures!are!required,!in!addition!to!an!adequate!performance!level,!a!remarkable!rigidity!and!an! efficient! connection! to! the! supporting! walls,! especially! in! what! concerns!seismic!actions.!For!this!reason,!by!strengthen!a!floor,!on!has!an!opportunity!to!improve!the!behaviour!and!efficiency!of!the!entire!structure.!!

3.2 Polypropylene Meshing Polypropylene meshing uses common polypropylene packaging straps (pp-bands) to form a mesh which is used to encase masonry walls, preventing both collapse and the escape of debris during earthquakes. PP-bands are used for packaging all over the world and are therefore cheap and readily available while the retrofitting technique itself is simple enough to be suitable for local builders. PP-meshing has been applied in Nepal, Pakistan and more recently in China. This method is most readily applicable in terms of low-cost upgrading of traditional structures to limit damage caused by normal earthquakes and give occupants a good chance of escape in a once-in-a-lifetime large earthquake. Non-engineered masonry is widespread throughout the developing world and replacement of all such dwellings is both unfeasible and undesirable, given that they are often the embodiment of local culture and tradition. It is therefore often more feasible to consider low-cost retrofitting of such buildings. Experiments and advanced numerical simulations have shown that PP-band mesh can dramatically increase the seismic capacity of adobe/masonry houses [P. Mayorka and K

Meguro, 2008]. This is mainly achieved by increasing the structural ductility and energy dissipation capacities. Under moderate ground motions, PP-band meshes provide enough seismic resistance to guaranty limited and controlled cracking of the retrofitted structures. Under extremely strong ground motions, they are expected to prevent or delay the collapse, thus, increasing the rates of survival. Experimental verification (full scale) was done in the laboratory of Tokyo University [Nesheli K et al,

2006] and also in Kathmandu, (small scale 1:6) demonstrating reliable performance improvement in the integrity of the structure and preventing material loss. This method is good for one storey buildings and can be used for a maximum of two storeys. To protect the Polypropylene from ultra violate rays, mud plaster is used on the outside, providing adequate cover to ensure the durability of the material.

Fig 3.5 Implementation of PP band method of retrofitting in Kathmandu Valley (left) and anchorage throughout

the wall (right)

A pilot scheme implementing the PP-Band technology in Nepal was conducted in a rural village just outside Bhaktapur, in Nepal, by National Society for Earthquake Technology-Nepal (NSET) in collaboration with Mondialogo Engineering Award Team. The project is titled ‘Improving the Structural Strength under Seismic Loading of Non- Engineered Buildings in the Himalayan Region’ and outlines training courses for rural masons and public demonstrations for community members in the seismically active Himalayan region, to promote seismic resistant building and retrofitting techniques, focusing on polypropylene meshing. The main objective of the project is to disseminate and transfer the PP-band retrofitting technique to the communities who cannot afford other expensive retrofitting technology. The masons were trained through hands on implementation, found to be technically feasible and easily implemented.

! 13!

A! technique! well! spread! for! the! in9plane! reinforcement! of! wooden! floors,!consists!on!placing!over!the!existing!floor!a!concrete!slab,!usually!reinforced!with!a!metallic!net,!and!anchored!to!the!existent!floor!by!pins!or!connectors!fixed!on!the! top! edge!of! the!beams,!which! cross! the!planking! and! are! embedded! in! the!concrete!slab!and!connected!to!the!metallic!net,!see!Fig.!12!a)!and!b).&!

! !(a) (b)

Fig.&12&a)&Example&of&the&reinforcement&of&a&wooden&floor&with&a&cooperating&reinforced`concrete&slab,&(www.tecnaria.com);&b)&Basic&connectors&Tecnaria&(www.tecnaria.com)&

The! structural! particularity! of! this! type! of! intervention! is! the! connection!between!wood! and! concrete,! designed! to! transmit! shear! forces! parallel! to! the!structure,! between! the! beams! and! slab.! There! is! almost! no! advantage! in!overlaying! the!slab!without! linking! it! to! the!pre9existent!structure,!because! the!two! structures!would!work! independently.! Finally,! it! should!be!noted! that! this!reinforcement! technique,!developed! in! the! last!20!years,! allows! to!significantly!increase!the!floor’s!in9plane!bending!stiffness,!however,!it!leads!to!a!weight!gain!for!the!floor,!resulting!in!increase!of!the!seismic!actions.!Thus,!it!is!important!to!limit!the!concrete!thickness!to!5!to!10!cm.!The!technique!is!also!not!reversible.!!!Another! possible! technique! is! the! idea! of! including! on! the! floor! a! horizontal!bracing! composed! of! steel! ties! and! arranged! in! crosses! (Fig.! 13)! and! this!technique!has!been!developed! for!many!decades.! Care! is! taken! to! improve! the!connection!between! the! floor!and! the!masonry!wall!with!L9shaped!steel!plates!(Fig.!13).!On! the!contrary! to! the!previous! technique! this!one!does!not! increase!significantly!the!mass!of!the!floors!and!is!reversible.!!

! 14!

Fig.&13&In`plane&stiffening&with&metallic&diagonals&and&reinforcement&of&connection&floor`

wall&(Pombalino&building)&[photo&from&Edifer]&

!In! the!Fig.! 14!one! can! see! a!photograph!of! the! connection!with!L9shaped! steel!plates!between!wooden!floor!and!masonry!wall.!!

!Fig.&14&Photo&of&the&connection&with&L`shaped&steel&plates&between&wooden&floor&and&

masonry&wall&

!

d) Strengthening!with!composite!materials!(CFRP!and!GFRP)!&It! is! possible! to! strengthen! with! composite! materials! such! as! carbon! or! glass!fibres!reinforced!polymers!piers!and!spandrels!within!walls!and/or!columns!of!masonry.!But!the!application!of!such!method!on!masonry!is!still!scarcely!found.!The! strengthening! improves! flexural! behaviour! or! tension! and! compression!through! increasing! the! confinement! for! instance! in! columns.!The!Carbon!Fiber!Reinforced!Polymer!(CFRP)!or!Glass!Fiber!Reinforced!Polymer!(GFRP)!layers!of!material!are!glued!with!epoxy!resin!to!the!cleaned!surface!of!masonry.!The!weak!element!is!the!masonry!or!the!glued!surface!if!the!biding!is!not!well!done.!There!can! be! placed! also! connectors,! especially! on!walls,! so! that! the!material! is!well!bonded!to!the!masonry.!In!Fig.!15!it!is!shown!the!application!of!CFRP/GFRP!on!a!building,!wall!and!column.!

!"#$"%&

DECivil F) Reforço da ligação dos pisos de madeira com alvenariaexterior com recurso a peças metálicas (cont.):

"'()*+,-+./

0123043(51(6781960:6;

(Edifer)

Fixação de perfis de aço em paredes para reforço de frechais e apoio dos barrotes do pavimento

! 15!

!Fig.&15&Application&of&CFRP/GFRP&on&a&building,&wall&and&column&[Cóias,&2007]&

!In!Fig.!16,!a!wall!specimen!to!be!tested!was!retrofitted!with!two!layers!of!Carbon!Fiber! Reinforced! Polymer! (CFRP)! sheets,! one! in! each! direction,! covering! the!entire! surface! of! the! wall.! CFRP! sheets! are! applied! in! only! one! side! of! the!specimen.! The! first! layer! had! fiber! orientation! parallel! to! bed! joints! and! the!second!layer!had!fibers!oriented!900!with!the!horizontal.!They!were!applied!on!one!side!of!the!wall,!while!the!other!side!remained!with!exposed!block!masonry.!CFRP! was! applied! using! the! wet! layup! procedure.! The! wall! surface! was! first!prepared!prior! to! the!application!of!CFRP.!The!preparation! involved;! i)! surface!cleaning! by! wire! brush,! followed! by! air! pressure! to! remove! loose! mortar,! ii)!application!of!putty!consisting!of!two9component!epoxy!and!silica!fume!to!cover!head!and!bed!joints!and!to!smoothen!the!wall!surface,! iii)!removal!of!any!extra!putty!by!a!plastic!putty!knife,!iv)!after!curing!for!a!day,!inspection!of!the!surface!and!covering!any!noticeable!air!bubbles!with!putty!using!the!same!plastic!knife!and!finally!v)!sanding!the!surface!by!sand!paper!after!two!full!days!of!curing.!&

&Fig.&16&Wall&to&be&tested&in`plane&of&brick&masonry,&strengthened&with&CFRP&[Arifuzzaman&

and&Saatcioglu,&2012]&

!"#$%&"'()*+,*%&"'-.'/-*0121#*,3&'%&'4*#51.6+1&'!%1718*%&9::;'<'9::= !"#5$#$5*"'%-'(2)-+*51*'%-'4-%5*

!"##$%$&$'(')#*')*+),"+-"*)*+)(%$&$.(-/"

!! /-7&5/-7&5,,&'8&.'.*#-51*1"'8&.>&'8&.'.*#-51*1"'8&.>66"1#&"'?@/4A'B/4C"1#&"'?@/4A'B/4C

DD 4*5-%-"A'4*5-%-"A'EE>12*5-">12*5-"FF -')1G*"'%-'8&5&*.-+#&'?81+#*"C-')1G*"'%-'8&5&*.-+#&'?81+#*"C

! "#$%&'%()#($*#+,%

H1#&5'IH1#&5'I661*"A'9::J1*"A'9::J

! "#$%&'%()#(-%.$/.01#.2%

F igure 1.Geometric details of the masonry wall specimen

The wall was built on an I-shaped concrete foundation. The foundation was over reinforced to avoid

any damage during testing. The foundation was designed to accommodate four large holes

(approximately 100 mm in diameter each) to fit the holes in the Laboratory strong floor for securing

the foundation during testing. The foundation concrete was supplied by a local ready-mix company.

The concrete strength that was ordered, was 30 MPa. After casting, the foundation cured at least for

28 days.

The specimen was retrofitted with two layers of Carbon Fiber Reinforced Polymer (CFRP) sheets, one

in each direction, covering the entire surface of the wall. This is illustrated in Fig. 2. CFRP sheets

were applied in only one side of the specimen. The first layer had fiber orientation parallel to bed

joints and the second layer had fibers oriented 900 with the horizontal. They were applied on one side

of the wall, while the other side remained with exposed block masonry. CFRP was applied using the

wet layup procedure. The wall surface was first prepared prior to the application of CFRP. The

preparation involved; i) surface cleaning by wire brush, followed by air pressure to remove loose

mortar, ii) application of putty consisting of two-component epoxy and silica fume to cover head and

bed joints and to smoothen the wall surface, iii) removal of any extra putty by a plastic putty knife, iv)

after curing for a day, inspection of the surface and covering any noticeable air bubbles with putty

using the same plastic knife and finally v) sanding the surface by sand paper after two full days of

curing.

F igure 2.The Masonry wall retrofitted on one side.

! 16!

Once! the!wall! surface!was! ready! for! the!application!of!CFRP!sheets,! the! sheets!were! cut! to! required! sizes! and! applied! on! the! wall! surface.! The! application!involved!the!following!steps:!!

i. Application!of!a!layer!of!two9component!epoxy!on!the!surface.!!ii. Application!of!the!first!layer!of!CFRP!whose!fibres!were!parallel!to!the!

bed!joint,!saturated!in!epoxy.!!iii. Removal!of!extra!epoxy!and!air!pockets!by!means!of!a!ribbed!steel!

roller.!!iv. Application!of!another!layer!of!epoxy!prior!to!the!placement!of!the!

next!layer.!!v. Application!of!the!second!layer!of!CFRP!perpendicular!to!the!bed!joint!

after!saturating!it!in!epoxy!and!following!step!iii.!!!In! the! following! wall! specimen! to! be! tested! under! in9plane! loads,! the! brick!masonry!wall!was!strengthened!with!GFRP!strips!in!both!sides!of!the!wall!(Fig.!17).!!

&Fig.&17&Wall&to&be&tested&in`plane,&strengthened&with&GFRP&[Kabir&et&al,&2012]&

&Furthermore,! Fig.! 18! shows! a!wall! specimen! to!be! tested!under! in9plane! loads!with!the!spandrels!strengthened!with!CFRP!strips!(on!both!sides),!before!testing!(Fig.! 18! a))! and! after! testing! (Fig.! 18! b)).! After! testing! it! can! be! observed! the!debonding! of! the! CFRP! strips! from! the!masonry! face,! implying! a! reduction! in!shear!strength.!!&

&& &a)! ! ! ! ! ! b)!

Fig.&18&(a)&Wall&to&be&tested&in`plane&with&strengthened&spandrels&with&CFRP&(b)&view&of&strengthened&spandrel&after&testing&showing&debonding&of&the&CFRP&[Amadio&et&al,&2012]&

epoxy resin based adhesive (two component epoxy Sikadur 330) was used for bonding the glass fiber

sheet. Cured laminate (GFRP) properties after standard cure are given in Table 2.2 according to the

datasheet made by the manufacturer.

Table 2.2. GFRP properties used in the experimental program

Tensile

strength

Tensile

modulus

Tensile

elongation

90 deg

tensile

strength

90 deg

tensile

modulus

90 deg

tensile

elongation

Thickness ASTM test

method

537 MPa 26.49 GPa 2.21% 23 MPa 7.07 GPa 0.32% 0.5 mm D 3039

The length, height and thickness of these walls were 194, 143, and 16 cm, respectively. Thus, the

aspect ratio of the test walls was about 0.74. The test walls were constructed on a strong reinforced

concrete footing. After allowing the wall to cure (for at least 7 days), a strong reinforced concrete loading beam was built on the top of the brick wall. The foundation and loading beam dimensions

were 240 cm!20 cm!24 cm and 194 cm!20 cm!16 cm, respectively. These test walls had a window

opening in their center. The length and height of this window were 52 and 47 cm, respectively. The unreinforced and GFRP strengthened walls are illustrated in Fig. 2.1. In specimen RBW-X-S1, the

width of the lower and upper diagonal GFRP strips was 15 and 18 cm, respectively. The strengthening

of specimen RBW-X-S2 by means of GFRP was relatively similar to specimen RBW-X-S1, but, it had

two additional vertical GFRP strips with a width of 15 cm at the beginning and end of the surface of two sides.

(a) (b) (c)

Figure 2.1. The unreinforced and GFRP strengthened test walls: (a) URBW; (b) RBW-X-S1; (c) RBW-X-S2

In this experimental study, a gravity load of 41.2 kN was applied along the top of the wall by a loading

beam in a manner consistent with the floor or roof loading. This vertical load generated an average

compression stress of 0.13 MPa and 0.18 MPa in each wall and its piers (adjacent to the window),

respectively. For this purpose, a steel loading basket was constructed. This steel loading basket was filled with 210 lead weights and was subsequently placed on the loading beam. The loading beam

distributed this vertical load uniformly on the top of the wall. Thus, this axial load acting on the wall

was constant during cyclic loading as seen in the walls in real buildings under seismic loading. Horizontal cyclic load was applied manually in the plane of the wall to the loading beam (via steel

plates which were connected to the loading beam during the construction) using two hydraulic jacks

and hand pumps. These jacks could only produce compressive load and were mounted on rigid reaction frames. The loading beam distributed this concentrated load uniformly along the top of the

wall to simulate floor or roof loads used in the actual masonry building construction. The test wall

assembly was laterally supported along its top so as to restrict the out-of-plane displacement of the

assembly. The test setup was similar for all of the test walls.

All these walls were tested under constant gravity load and incrementally increasing in-plane loading

cycles according to (ICC Evaluation Service, Inc., 2007) as shown in Fig. 2.2. The selected loading procedure can simulate the earthquake actions and their effects on the walls. During the test, each wall

was allowed to displace in its own plane. The force required to push the wall and the corresponding

displacement at each load interval were measured. The observed hysteresis response curve for each tested wall specimen is shown in Fig. 2.2.

on provisional supports. A stiff steel element was placed on top of the pier and was connected to the bottom of the pier through six vertical Dywidag steel bars. The steel element was linked to three electro-mechanic actuators adequately fixed to the stiff concrete floor. Two actuators were arranged at both sides of the wall with their axis belonging to a plane perpendicular to the wall and containing the symmetry axis of the specimen, whereas the third actuator was set at the right side of the specimen. Two couples of steel braces were positioned on both sides of the specimen so as to contrast out-of-plane displacements of the wall (Fig. 2.3). Adequate sliding devices were provided at brace-wall interface; a thin layer of PTFE was used to reduce possible friction.

(a) (b)

Figure 2.1. Masonry wall with openings (a); experimental model of the spandrel (b).

(a) (b)

Figure 2.2. Brick specimen with CFRP strips (MS3r) (a); stone specimen with the steel angle (MS4r) (b).

(a) (b) Figure 2.3. Experimental test arrangements: schematic drawing (a), axonometric view (b).

3.1. Samples MS3-MS3r

The relationship between the shear load and the relative transversal displacement of the unreinforced spandrel MS3 is shown in Fig. 3.1a. The test reached a maximum value of about 45 kN in both loading directions. After the peak load a quite rapid reduction in shear capacity was observed and a residual strength value of about 40-50% of the maximum shear was reached at the end of the tests in correspondence of a vertical displacement equal to 0.8% of the spandrel length. In Fig. 3.1b the crack pattern in the spandrel’s back face at the end of the test is shown. As it can be seen the main cracks are diagonal (shear cracks).

(a) (b) Figure 3.1. Specimen MS3: shear load against displacement (a) and crack pattern (b).

(a) (b) Figure 3.2. Specimen MS3r: shear load against displacement (a); crack pattern (b).

The sample MS3 was then reinforced (MS3r) applying horizontal CFRP strips. To close the cracks, after completing the unreinforced tests, a prestress was applied to the specimen using a couple of horizontal steel ties. By means of the steel ties (two Dywidag bars 27 mm diameter) a horizontal compressive force equal to 85 kN was applied to the spandrel. Two couples of horizontal CFRP strips (four CFRP strips, 120x1 mm) were glued on both sides of the spandrel. When the installation of the reinforcement was completed, the steel bars were released. The response in terms of shear load versus the relative vertical displacement of the reinforced specimen is shown in Fig. 3.2a (red line), the black curve is that obtained in unreinforced tests (Fig. 3.1a). A maximum resistance value of about 130 kN was reached (almost three times the resistance achieved with the unreinforced specimen). After the peak load a progressive reduction in shear capacity was observed, especially in one direction. In the other direction, a rapid decrease of resistance was observed, due to the local debonding on CFRP strips. The maximum drift is about 3%, so the increase in ductility was significant with respect to the

! 17!

If!a!building!has!insuficient!shear!capacity!in!a!particular!direction,!the!capacity!of!existing!walls!can!be!increased!instead!of!inserting!an!additional!structure.!In!the!Fig.!19!one!can!see!the!application!of!an!additional!layer!of!material!(CFRP!or!GFRP)!bonded!to!the!surface!of!the!URM!wall!aiming!to!increase!its!strength.!!&

&Fig.&19&Simple&and&visually&interesting&in`plane&strengthening&with&FRPs&[Ingham,&2012]&

!

e) The!use!of!horizontal!tie:rods!!!Tie9rods!in!steel!can!be!used!in!several!applications!of!old!masonry!buildings.!For!instance,!they!can!avoid!or!at!least!decrease!the!probability!of!out9of9plane!failure.!Fig.!20!a)!and!b)!show!the!application!of!horizontal!tie9rods!to!connect!parallel!walls!at!the!level!of!the!floors.!!

&a)! ! ! ! ! b)!

Fig.&20&Using&tie`rods&to&connect&parallel&walls&[A.&Costa,&2008]&

&Tie9rods!can!be!also!used! in!arches! to!absorb!horizontal! impulses! (Fig.!21!and!Fig.!22).!&

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! 18!

&Fig.&21&Utilizing&tie`rods&to&absorb&horizontal&impulses&in&arches&[A.&Costa,&2008]&

!

!Fig.&22&Tying&of&masonry&vaults&with&tie`rods&in&steel&(Santos,&2003)&

!In!Fig.!23!one!can!see!a!failure!of!the!anchorage!of!the!tie9rod!after!an!earthquake,!because!the!plate!was!too!small.!In!Fig.!24!it!is!shown!the!successful!behaviour!of!the!tie9rods,!spaced!close!together.!!

&Fig.&23&Close&up&of&partial&anchorage&failure.&Photograph&of&damage&in&the&2010&Darfield&

(Canterbury)&earthquake&due&to&deficient&anchorages&[Ingham,&2012]&

!

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40/48

An alternative solution, very useful in particular situations, will be the insertion of strengthening components (in steel or timber), glued to the extrados of the masonry, which provides stiffness to the vault and in which the barrier effect is much less sensitive (Fig. 31).

Figure 30 Tying of masonry vaults with tie-rods in

steel (21) Figure 31: Strengthening of masonry vault with

timber ribs glued on the extrados (8)

When blocks have become out of position, an adequate solution will be dismantling, followed by rebuilding in the correct position. In very severe situations, when the shape of the element has been heavily changed, it can be more appropriate to demolish the element, followed by its reconstruction using materials similar to the original ones.

In the case of filled vaults, one possible solution will be the reduction of weight or, if appropriate, the adjustment of its distribution.

In the case of floors made with brick vaults supported on steel beams, an adequate measure to restrict their lateral separation will consist in the placing of tie-rods, in steel, welded onto the bottom flange of the beams.

c) Towers and chimneys

The most common solution for the strengthening of this type of element consists ofn tying them with horizontal ties, usually, steel strips or cables (Fig. 32), or by wrapping them with glued composites (CFRP, GRC, etc.).

In the case of prismatic towers an appropriate measure will be the provision of diaphragms (in concrete or steel), at intermediate levels, for the confinement of the walls. Figure 32: Tying of masonry tower with steel

strips (21)

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!Fig.&24&Successful&anchorages&spaced&close&together.&Photograph&of&building&after&the&2010&

Darfield&(Canterbury)&earthquake&[Ingham,&2012]&

&Finally,!in!Fig.!25!one!can!see!the!utilization!of!tie9rods!in!a!wooden!roof.!!!

&Fig.&25&Using&tie`rods&in&roofs&[M.A.&Parisi&et&al.,&2012]&

&

f) Retrofitting!by!post:tensioning!&A! post9tensioning! retrofit! is! applied! either! by! placing! post9tensioning! tendons!into!cored!cavities!located!at!the!centre!of!the!wall!or!by!placing!post9tensioning!tendons! externally! at! discrete! locations.! The! first! procedure! involves! coring! a!cavity! from! the! top! of! the! URM! wall! right! through! to! the! foundations,! then!placing! a! tendon! into! the! cored! cavity! and! finally! the! application! of! a! post9tensioning!force!to!the!tendon.!From!discussions!with!specialized!New!Zealander!constructors,!one!knows!that!it!is!possible!to!core!a!cavity!up!to!four!stories!with!a! precision! of! +9! 10! mm.! [Ingham,! 2012].! Fig.! 26! a)! shows! the! procedure! of!coring!a!cavity!and!Fig.!26!b)!shows!the!bar!post9tensioning.!!!

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roof covered an important historical building in the town center, the Carli-Benedetti palace, that

suffered severe damage in various parts, like many similar buildings in town.

The strengthening intervention that had been recently performed on the roof may be seen in fig. 5.

This inside view was possible from the opening caused by the unfortunate collapse of a vault. The roof

had undergone intervention with light elements to improve its interior and exterior connectivity and

remove thrusts. In order to appreciate the positive effect of this work, it must be considered that the

earthquake had caused the opening of a significant crack on both sides of the corner corresponding to

the picture. This crack pattern typically evolves into the detachment of the angle and of its subsequent

possible collapse as a rigid block. In this case, the crack was well open up to the mid-height of the

walls, but became narrower and was barely visible at the top, near the roof, indicating that a

restraining action had occurred in this area. The roof action avoided more dramatic damage and

probably collapse of a significant part of the building. The building is currently under repair.

Fig. 5. Low-mass intervention on a timber roof in L’Aquila.

The second case is still under analysis, but it seems interesting because the intervention recognizes a

possible problem in case of horizontal longitudinal motion of the truss top and takes care of it. The

church of St Michele, in Vimercate, near Milano presents a roof structure composed of a series of king

post trusses, which were irregularly spaced because one truss was missing at the intended spacing, an

apparently strange situation which, on the contrary, was found also in other cases (Parisi et al, 2011b).

Fig. 6. Trusses of the church of St. Michael, Vimercate; the bracing element is visible.

! 20!

&a)! ! ! ! ! b)!

Fig.&26&(a)&Coring&operation;&(b)&Bar&post`tensioning&[Ingham,&2012]&

&There! can! be! done! vertical! post9tensioning! for! piers! or! horizontal! post9tensioning! for! spandrels,! as! suggested! by! Meireles! [2012]! for! Pombalino!buildings,!or!both!types.!!The!performance!of!post9tensioned!URM!walls!depends!upon! the! initial! post9tensioning! force,! tendon! type! and! spacing,! restraint!conditions! and! the! level! of! confinement.! Post9tensioning! can! either! be! bonded!when!tendons!are! fully!restrained,!by!grouting!the!cavity!or! left!unbounded!by!leaving!the!cavities!unfilled.!Because!unbounded!post9tensioning!is!reversible!to!some!extent!and!has!minimal!impact!on!the!architectural!fabric!of!a!building,!the!technique!is!deemed!to!be!a!desirable!retrofit!solution!for!URM!buildings!having!important!heritage!value.![Ingham,!2012].!!In!Fig.!27!one!can!see!in!close!up!view!a!post9tensioning!anchorage.!!

!Fig.&27&Close`up&view&of&a&post`tensioning&anchorage&[Ahmad,&2012]&

!According!to!Ahmad![2012]!some!advantages!of!this!technique!for!URM!are:!

a) Reducing!cracking/deflection!under!service!loads;!b) Significant!increase!in!strength!and!ductility;!c) !!!Keep!integrity!of!the!structure!with!minor!changes;!ჼ!d) Reversible;!e) Easy!to!apply.!

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Post-Tensioning

! Advantages:! Reduce cracking/deflection under service

loads

! Significant increase in strength and ductility

! Keep integrity of the structure with minor changes

! Reversible

! Easy to apply

! Keeps external appearance

! Disadvantages:! Not applicable to deteriorated masonry

! Losses due to creep and shrinkage of masonry

! Guiding the tendons is not simple

! 21!

!However!some!disadvantages!may!be:!

a) Not!applicable!to!deteriorated!masonry;!b) Losses!due!to!creep!and!shrinkage!of!masonry;!c) !!!Guiding!the!tendons!is!not!simple.!

!Regarding!the!placing!of!post9tensioning!tendons!externally!at!discrete!locations,!Ma! et! al! [2012]! placed! vertical! and! cross! bracing! struts! at! a! building! in! the!laboratory.!This!is!to!improve!the!shear!capacity!of!the!walls!(Fig.!28).!!

!Fig.&28&Cross&bracing&struts&at&the&first&two&storeys&

&

f) Strengthening!with!ring!beams!&RC!ring!beams!can!be!placed!along!the!perimeter!of!the!walls!in!the!last!floor!if!the! roof! can! be! temporarily! removed! and/or! at! the! level! of! the! floors.! The!behaviour!of!the!different!possibilities!without!or!with!ring!beams!for!flexible!or!rigid! diaphragms! can! be! seen! in! Fig.! 29! a),! b)! and! c).! Out9of9plane! behaviour!should!always!be!avoided!and!the!in9plane!behaviour!of!the!walls!encouraged!for!a!better!performance!of!a!masonry!building.!In!this!case,!the!situation!(c)!is!the!best!situation.!!

&Fig.&29&Behaviour&of&a)&Wood&(flexible)&diaphragm&without&ring&beams;&b)&Wood&diaphragm&

with&ring&beams;&c)&rigid&diaphragm&with&ring&beams.&[Ahmad,&2012]&

B were prestressed using high-tensile thread bar, with a nominaldiameter of 8 mm, a specified tensile rupture stress of 600 MPa,and a yield stress of 355 MPa.

An overview of the two models after construction is shown inFigs. 8 and 9.

3.3. Strengthening schemes

Prestressing tendons were applied to Model B as shown inFig. 10.

The cross-sectional area of the walls along axis B is reduced dueto large openings, which leads to relatively higher compressivestresses of the walls along axis B at lower floors (e.g. storey 1and storey 2) because of heavier dead load and reduced cross-sec-tional area. This limits the increasing margin of shear strengthavailable through the application of prestressing. Therefore, crossbracing struts were additionally applied to the walls along axis Bat storey 1 and storey 2 to improve the shear resistance capacity,as shown in Fig. 11. On the other hand, the walls along axis B atstorey 3 and storey 4 can be applied with considerable prestressingbecause that the compressive stress produced by self-weight wassmaller, thus no additional cross bracings are required. Two groupsof connector plates were used to enable three segments of pre-stressing tendons in the walls along axis B (the connector platesis shown in Fig. 12) achieving different levels of prestressing, as

discussed previously. The first group of connector plates was setin the ring beam beneath the floor slab at storey 2 and the secondgroup was set in the ring beam beneath the floor slab at storey 3(see Fig. 11).

The overview of the completed Model B is shown in Fig. 13.Using Eq. (2), the applied tension forces in the prestressing

tendons at different locations of Model B are obtained, as givenin Table 2.

3.4. Experimental setup

The effective mass (1.0DL + 0.5LL) of the prototype structurewas estimated to be 284,800 kg, so the effective mass of the model

Fig. 10. Planar layout of prestressing tendons for Model B.

Fig. 9. Overview of the two test units sitting side by side. Fig. 11. Cross bracing struts at the first two storeys of Model B.

Fig. 12. Connector plate.

Fig. 13. Overview of Model B on shaking table.

R. Ma et al. / Engineering Structures 42 (2012) 297–307 301

Wall and Diaphragm Interaction

a- Wood ( flexible) diaphragm without ties

b-Wood diaphragm with ties

c- Rigid diaphragm with tie beams

! 22!

&A! reinforced! concrete! ring! beam,! 20! cm! high! and! 32! cm!wide! (as! the! wall! in!!Fig.!30),!was!cast!at!the!roof!level,!on!top!of!the!perimeter!façades!(Fig.!30!a)!and!b))! in! the! experimental! work! of! Magenes! et! al.! [2012].! The! reinforcement!consisted! in! 4φ16! longitudinal! bars! and! φ8! stirrups! at! a! spacing! of! 20! cm,!coherently!with!the!prescriptions!of!the!Italian!Building!Code.!!&

&a)! ! ! ! ! b)!

Fig.&30&Details&of&the&reinforcement&of&the&ring&beam&(left)&and&view&of&the&ring&beam&after&filling&with&the&concrete&(right)&[Magenes&et&al,&2012]&

&

g) Retrofitting!by!introducing!RC!shear!walls!&If! the! rigidity!of! the! slab! is! sufficient! then! lateral! strength!of! a!building! can!be!increased!by!the!placement!of!RC!shear!walls.!A!structural!engineer!can!rapidly!calculate! number! of! shear! walls! and! their! lengths! and! bars! arrangement! by!calculation!of!base! shear.!The! strength!of! the!masonry!building! is!neglected! in!the! calculation! of! the! shear! walls.! In! the! following! Fig.! 31! is! depicted! this!retrofitting!solution!in!a!school!building.!!&

&Fig.&31&Photo&of&the&reinforcement&of&two&perpendicular&shear&walls&[Mahdizadeh et al,

2012]

!

h) Strengthening!with!RC!or!steel!frames!&The! introducing! of! moment! frames! is! a! common! strength! method! aiming! to!increase! additional! horizontal! resistance,! which! can! also! be! used! as! a! local!strengthening! solution.! The! advantage! of! this! system! is! that! it! is! comprised! of!beams! and! columns,! so! is! fully! customizable! and! there! is! space! between! the!vertical!and!horizontal!elements.!Moment! frames!allow! full!visual!and!physical!

Simulating an intervention where the roof structure can be temporarily removed, a reinforced concrete

ring beam, 20 cm high and 32 cm wide (as the wall below), was cast at the roof level, on top of the

perimeter façades (Fig. 2, left). The reinforcement consisted in 4!16 longitudinal bars and !8 stirrups

at a spacing of 20 cm, coherently with the prescriptions of the Italian Building Code (NTC08, 2008).

Figure 2. Detail of the reinforcement of the joint at the base of the gable wall (left). Operation of drilling the

timber spreader beam and the concrete ring beam (right)

The original timber roof structure of the unstrengthened building included one 20cm x 32 cm ridge

beam, two segmented 32cm x 12cm spreader beams on top of the longitudinal walls and 8cm x 12 cm

purlins every 50 cm forming the two pitches with 30 mm thick planks.

The strengthening of the roof envisaged the improvement of the connection of the ridge beam with the

gable walls, which consisted of a steel shoe doweled to the concrete ring beam and bolted to the ridge

beam. Timber spreader beams were also doweled to the r.c. ring beam all along the perimeter, by

means of connecting steel bars chemically anchored by epoxy resin. Any discontinuity between the

timber spreader beam and the ring beam was smoothed by the insertion of a plaster layer to create a

continuous contact. The 8 cm x 12 cm joists were reshaped to create a horizontal seat on the ridge

beam and on the longitudinal spreader beams. Steel connecting elements were inserted at the top of

the ridge beam, at the contact between the two opposite purlins. The matchboard was then placed on

top of the timber structure.

To stiffen and strengthen the roof diaphragm (which originally was made only by a single layer of

boards nailed to the joists), it was decided to adopt an intervention that was compatible with the

original timber structure, by adding multilayer spruce plywood panels, which are lighter and easier to

apply to an inclined plane in comparison to a reinforced concrete slab, although providing a significant

stiffness increase. The intervention consisted in adding 3 layers of plywood, each 21 mm thick, glued

with polyurethane glue and connected to the purlins by means of chemically anchored, 10 mm

diameter threaded steel bars. After having drilled and cleaned the hole, a two-component epoxy

mixture was inserted in the hole and then the bar was inserted and rotated to distribute the resin. Bars

were placed at a constant spacing of 30 cm and penetrated into the purlins to connect the upper plank

layers with the roof structure (Fig.3).

Figure 3. Scheme of the intervention on the roof diaphragm, consisting in the application of multilayer panels

and chemically anchored steel connectors.

To improve the diaphragm behaviour of the roof, continuous steel plates (80 mm wide and 5 mm

thick) were connected all along the perimeter to the roof, to favour the development of a strut and tie

mechanism. The roof was then completed by adding plain roofing tiles nailed to the multilayer spruce

neglected in calculating of these shear walls.

F igure 6: typical retrofitting by shear wall !

Periphe ral shotc rete: This method was achieved by experience of other countries and different experimental tests in masonry buildings. In this method, the peripheral of one story masonry building is shotcreted completely. Bars dimension, arrangements and thickness of shotcrete are determined based on lateral earthquake force. Weight of slab and masonry walls are considered in calculation of base shear, and shear capacity of masonry walls are neglected in calculation of the shotcrete.

F igure 7: typical retrofitting by peripheral shotcrete

Shear Box: Peripheral shotcrete leads to extent change in veneer of building. This leads to considerable increase in total cost of retrofitting. The main advantage of shear wall method on the peripheral shotcrete is concentration of this method on minimum area. However, this concentration needs special foundation and piling. Experiences of this project in Iran show that more than 30% of total cost of project is dedicated to the foundation in this pattern. The shear box method tries to solve the above problems. In this method, masonry walls of four classrooms in four corners of school buildings are completely shotcreted. Bars dimension, arrangements and thickness of shotcrete are determined based on lateral earthquake force. So, total cost of foundation and changing in architecture

are reduced considerably. L ight weight slabs: Strength is not serious problem in these slabs; however, providing stability is the main index for retrofitting of this type of building. 8. PR O V IDIN G ST ABIL I T Y O F AL L M ASO NRY W AL LS Providing stability of structural elements is based on two concepts: First of all, providing general integrity of the building. Secondly, prediction of damage location in earthquakes, and providing the stability of the cracked walls. Consideration of these two concepts is important to propose retrofitting patterns. In some cases providing of sufficient strength leads to providing of these two concepts. In contrast, in other cases it may not happen. As a result, beside of operations to provide strength in building, additional operations should be done to provide stability of elements.

! 23!

access!between!each!side!of!the!frame!and!minimal!spatial!disruption![Ingham,!2012].!&Care! needs! to! be! taken! with! steel! frames! in! particular! to! ensure! stiffness!compatibility!with!the!existing!structure![Robinson!and!Bowman,!2000].!Steel!is!a! ductile! material! but! URM! is! not,! meaning! that! under! earthquake! loads! the!added! stiffness! of! the! steel!might! not! come! into! effect! until! a! load! is! reached!where!the!URM!has!already!been!extensively!cracked.!If!a!steel!frame!is!erected!against!an!existing!wall,! the! frame!needs!to!be! fixed!either!directly! to! the!URM!using!bolted!connections!into!the!wall!or!to!the!diaphragm![Ingham,!2012].!!!Steel! moment! frames! have! a! high! degree! of! reversibility! as! they! rely! on!mechanical! connections! and! relatively! small! ties! to! connect! to! the! existing!structure.!Concrete!frames!are!generally!far!less!reversible.!!&Fig.!32!shows!a!large!new!moment!frame!of!RC!inside!an!URM!building.!!&

&Fig.&32&A&concrete&moment&frame&inside&the&façade&of&a&large&URM&building&in&Wellington&

(Dunning&Thornton&Consultants)&

!Braced!frames!are!also!a!plausible!solution!for!strengthening.!The!key!functional!difference! between! braced! frames! and! moment! frames! is! that! due! to! the!diagonal! braces,! braced! frames!prevent! physical! continuity! between! spaces! on!either! side! of! the! frame.! Braced! frames! are! also! generally! constructed! of! steel!rather! than! concrete! and! are! much! more! rigid! than! moment! frames.! Braced!frames! are! a! very! efficient! method! of! transferring! horizontal! forces! but! have!significant! setbacks! and! their! use! in! façade! walls! is! usually! precluded! by! the!presence!of!windows!as!diagonal!braces!crossing!window!openings!are!generally!considered!to!be!poor!design.!It!is!also!difficult!to!get!a!braced!frame!to!conform!to! an! existing! architectural! character;! however,! they! can!be!used! to! very! good!effect!within! secondary! spaces! and! can! be!made! to! fit! architecturally! in! some!situations!with!careful!consideration.!Generally,!steel!braced!frames!have!a!good!degree!of!reversibility!and!provide!excellent!strengthening!when!appropriately![Ingham,!2012].!!Fig.!33!a)!and!b)!show!braced!frames!inside!two!different!buildings.!!!

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REFERENCES!&Ahmad!Hamid,!2012,!Design!and!Retrofit!of!unreinforced!Masonry!Structures,!FUNDEC!course!on!Lisbon,!February!6,!2012.!!Amadio!C.,!Gattesco!N.,!Dudine!A.,!Franceschinis!R.,!Rinaldin!G.,!2012,!Structural!performance!of!spandrels! in! stone! masonry! buildings,! Proc.! of! the! 15th! World! conference! on! Earthquake!Engineering,!pp!5077,!Lisbon,!Portugal.!!Appleton! J,! 2009,! Técnicas! de! reabilitação! de! estruturas! de! alvenaria,! Seminar! “! Patologia,!Inspecção!e!Reabilitação!de!Edificios!tradicionais”!(in!Portuguese).!!!Appleton,! J.,! Reabilitação! de! Edifícios! Antigos! Patologias! e! tecnologias! de! intervenção,! Edições!Orion,!1ªEdição,!Setembro!de!2003![in!Portuguese].!!!Arifuzzaman!S.!and!Saatcioglu!M.,!2012,!Seismic!Retrofit!of!Load!Bearing!Masonry!Walls!by!FRP!sheets! and! Anchors,! Proc.! of! the! 15th!World! conference! on! Earthquake! Engineering,! pp! 4501,!Lisbon,!Portugal.!!Cóias! e! Silva! V! (2007)! Reabilitação! Estrutural! de! Edifícios! Antigos—Alvenaria,! Madeira—Técnicas!pouco!intrusivas.!Ed.!Argumentum!&!Gecorpa,!Lisbon,!Portugal!(in!Portuguese).!!Costa!A.,!2008,!Notes!from!the!post9graduation!course!on!rehabilitation!of!constructions!–!Stone!Masonry!structures.!!Cruz!H.,!FUNDEC!course!on!Rehabilitation!techniques!of!constructions,!wood!structures,!IST!9!23!Jan!to!3!Fev!2012.!!Ingham,!J.,!2012,!FUNDEC!one!day!lecture!on!the!“Seismic!assessment!and!improvement!of!unreinforced!masonry!buildings”,!IST.!!!Kabir! M.! Z.,! Kalali! A.,! Shahmoradi! R.,! 2012,! Cyclic! Behavior! of! Perforated! Masonry! Walls!Strengthened!with!Fiber!Reinforced!Polymers,!Proc.!of!the!15th!World!conference!on!Earthquake!Engineering,!pp!3734,!Lisbon,!Portugal.!!Lourenço, P. “Reabilitação de edifícios de alvenaria e adobe”. Lectures on the rehabilitation of masonry structures, University of Minho. Ma!R.,!Jiang!L.,!He!M.,!Fang!C.,!Liang!F.,!2012,!Experimental!investigations!on!masonry!structures!using! external! prestressing! techniques! for! improving! seismic! performance,! Engineering!Structures!42!(2012)!297–307.!!Magenes!G.,!Penna!A.,!Rota!M.,!Galasco!A.!!,!Senaldi!I.,!2012,!Shaking!table!test!of!a!full!scale!stone!masonry!building!with!stiffened!floor!and!roof!diaphragms,!Proc.!of!the!15th!World!conference!on!Earthquake!Engineering,!pp!5320,!Lisbon,!Portugal.!!Mahdizadeh!A.,!Borzouie!J.,!Raessi!M.,!2012,!New!Approach!to!seismic!Rehabilitation!of!Masonry!School!Buildings,!Proc.!of!the!15th!World!conference!on!Earthquake!Engineering,!pp!2851,!Lisbon,!Portugal.!!Mayorka!P.!and!Meguro!K,!2008,!"A!step!towards!the!formulation!of!a!simple!method!to!design!PP9Band!mesh! retrofitting! for!Adobe/Masonry!houses",!14th!World!Conference!on!Earthquake!!Engineering,!Beijing,!October!2008.!!Meireles,!HA,!2012,! Seismic! vulnerability! of!Pombalino!buildings,! PhD!Thesis,! IST,!Portugal! (in!English).!

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