Dissipative CLT-Based Seismic Upgrading System for RC-Framed Structures: Experimental Characterization, Numerical Modelling, and Design Guidelines

Ea hquake Enginee ing & S uc u al Dynamics RESEARCH ARTICLE Dissipa i e CLT-Based Seismic Upg ading Sys em o RC-F amed S uc u es: Expe imen al Cha ac e iza ion, Nume ical Modelling, and Design Guidelines F ancesca Ba bagallo1E ika Liccia dello1Edoa do Michele Ma ino1Claudio Mazzo i2Luca Pozza2 1Depa men o Ci il Enginee ing and A chi ec u e, Uni e si y o Ca ania, Ca ania, I aly 2DICAM Depa men , Uni e si y o Bologna, Bologna, I aly Co espondence: F ancesca Ba bagallo ( [email p o ec ed]) Recei ed: 14 June 2024 Re ised: 11 Feb ua y 2025 Accep ed: 17 Feb ua y 2025 Funding: This pape was ca ied ou in he amewo k o he “Ene gy and seismic a o dable eno a ion solu ions” (e-SAFE) p ojec , which has ecei ed unding om he Eu opean Union’s Ho izon 2020 esea ch and inno a ion p og am unde g an ag eemen No. 893135. Keywo ds: exis ing buildings | ic ion dampe s | seismic ene gy ehabili a ion | seismic s eng hening | imbe ABSTRACT This pape in es iga es a seismic e o i echnique named e-CLT, which is pa o he solu ion o in eg a ed seismic and ene gy ehabili a ion o buildings de eloped in he amewo k o he esea ch p ojec e-SAFE unded by he Eu opean Union’s Ho izon 2020 esea ch and inno a ion p og am. Acco ding o his echnique, he RC s uc u e is cladded by means o CLT panels equipped wi h ic ion dampe s, o inc ease la e al s i ness, s eng h, and ene gy dissipa ion capaci y. The e ec i eness o he e-CLT sys em has been p o ed by a ull-scale expe imen al es . A ini e elemen nume ical model o he RC ame wi h e-CLT sys em has been de eloped and calib a ed based on he expe imen al esul s. Hence, guidelines o he design o seismic s eng hening o mul i- s o ey RC amed building s uc u es by e-CLT sys em ha e been d awn based on he esul s o a pa ame ic analysis conduc ed on a se o RC case s udy ames ep esen a i e o a a ie y o exis ing buildings no designed o seismic esis ance. 1 In oduc ion In he second hal o 20 h cen u y, ein o ced conc e e (RC) s uc u es sp ead wo ldwide. Howe e , mos o hese buildings p eda e mode n code p o isions, bo h in e ms o s uc u al and ene gy equi emen s. In Eu ope, mo e han 75% o he land is occupied by esiden ial buildings and mo e han 40% o hese a e mul i-s o ey RC amed s uc u es cons uc ed be o e he 1960s o he 20 h cen u y [1]. These s uc u es a e expec ed o exhibi poo seismic esponse, and hei ene gy pe o mance is so inadequa e ha hey a e liable o 36% o he o al ene gy consump ion and CO2emissions in Eu ope [2]. An explica i e example o his issue is o e ed by he I alian e i o y. Acco ding o he la es census o I alian esiden ial buildings [3], mo e han 70% o he cu en esiden ial buildings we e ealized be o e 1981, when seismic zona ion included only 25% o he I alian e i o y. These buildings su e om high seismic ulne abili y, as d ama ically demons a ed by ecen seismic e en s [4, 5]. In addi ion, almos 90% o he I alian building s ock was cons uc ed be o e 1991, ha is, be o e he en o cemen o he i s egula ion on he mal pe o mance c i e ia [6]. To boos a compelling ansi ion owa d a esilien and sus ainable socie y, Eu opean egula ions on cons uc ion wo k [7] ha e been adding equi emen s o keep he cons uc ion pe o mances in ac and ex end i s se ice li e as long as possible [8]. The e o e, he ehabili a ion o hese build- ings is a eal need and, as a ma e o ac , du ing he las 30 yea s he a e o e o i in e en ions inc eased om 20% o 40% and i is expec ed ha his end will s eadily inc ease in he nea u u e. This is an open access a icle unde he e ms o he C ea i e Commons A ibu ion License, which pe mi s use, dis ibu ion and ep oduc ion in any medium, p o ided he o iginal wo k is p ope ly ci ed. © 2025 The Au ho (s). Ea hquake Enginee ing & S uc u al Dynamics published by John Wiley & Sons L d. Ea hquake Enginee ing & S uc u al Dynamics, 2025; 54:1775–1796 h ps://doi.o g/10.1002/eqe.4334 1775 o 1796 Con en ional uncoupled ehabili a ion echniques aim o enhance he seismic pe o mance o he he mal one [9]. Fu he mo e, he majo i y o he con en ional echniques equi e he addi ion o de ices ha occupy space o ins alla ion, need in asi e ins alling wo k ha o ce eloca ion o occupan s and cause ac i i ies dis up ion. Hence, new app oaches a e equi ed o p omo e en i onmen al economic–social sus ainable ene gy and seismic e o i in e en ions. Among he in eg a ed app oaches cu en ly unde de elopmen , he “double skin” app oach is one o he mos p omising. I consis s o he supe imposi ion o a second ex e nal s uc u e designed o enhance seismic and he mal pe o mance o he building. The main ad an age o his solu ion is ha i s ins alla ion akes place om he ou side o he building, hus educing o he minimum he dis up ion o he dis u bance o occupan s. Di e en cons uc ion echniques and ma e ials ha e been p oposed o he second skin. Fo example, Takeuchi e al. [10] de eloped a s eel dissipa i e açade, Ma ini e al. [11] p oposed a second skin wi h s eel shea walls and he possibili y o in oducing dissipa i e membe s, Fe an e e al. [12]in es iga ed an in eg a ed solu ion based on s eel exoskele on. RC second skin has been de eloped as well, such as he new RC in illed ame connec ed o he exis ing s uc u e p oposed by Man edi and Masi [9] o he cas -in-si e RC ame sys em endowed wi h EPS modules de eloped by Pozza e al. [13]. An al e na i e app oach is ollowed by Bou nas [14], who p oposes he use o Tex ile Rein o ced Mo a jacke s o inc ease he ou -o -plane load capaci y and he ene gy abso p ion capaci y o in ill walls in RC ames. In he ide owa d he eco iendly ma e ials, he use o wood as a s uc u al ma e ial has ecen ly gained p ominence. In pa icula , c oss-lamina ed imbe (CLT) is a sus ainable solid wood-based cons uc ion ma e ial wi h low mass and excellen s uc u al pe o mance. CLT panels consis o an odd numbe o s acked c osswise laye s o so wood boa ds, bonded by s uc u al adhesi e [15], ha can sus ain loads in all di ec ions [16]. CLT panels a e p oduced o a high deg ee o p e ab ica ion, allowing e icien on-si e ins alla ion. No wi hs anding he ligh weigh na u e o CLT, i is cha ac e ized by a high in-plane la e al s i ness and s eng h. Fu he mo e, he possibili y o combining CLT panels wi h duc ile join s makes he use o CLT appealing in ea hquake-p one a eas [17, 18]. Thanks o hese ea u es, he use o CLT panels has been ecen ly ex ended o seismic e o i o RC exis ing s uc u es, basically ollowing he second skin app oach al eady men ioned. S azi e al. [19] p oposed he encasemen o CLT panels wi hin he RC ame bays, as a eplacemen o mason y in ills. Diagonal es s we e conduc ed on con ined and no con ined CLT panels, while he e ec o he CLT panels on RC s uc u es was nume ically in es iga ed on a single-s o ey one- bay RC ame. Also, Smi oldo e al. [20] p oposed o eplace he exis ing mason y in ill o RC ames wi h a CLT panel, which was inse ed in o he ame and ixed o RC membe s by a imbe sub- ame. The imbe sub- ame and he RC ame a e connec ed by conc e e sc ews, which a e designed o emain elas ic. The duc ile componen o he sys em is he connec ion be ween he imbe panel and imbe sub- ame. The p oposed echnique was in es iga ed by pusho e analysis on single-bay single-s o ey ames and he nume ical esul s showed an inc ease in e ms o la e al esis ance and maximum displacemen s. Al hough bo h s udies demons a ed he good pe o mances p o ided by he CLT in ills, in eal exis ing s uc u es he inse ion o he CLT panels in place o in ill walls would equi e qui e la ge demolishing wo k and a no negligible dis u bance o occupan s. In his ega d, Smi oldo e al. [21] conduc ed an expe imen al s udy on an RC ame o in oduce a less in asi e op ion, i.e., CLT panels a e applied o he building açade, wi hou emo ing he mason y in ills, and as ened o he ou e ace o RC beams by dowel- ype connec o s. Howe e , he expe imen al es s e idenced ha also his ex e nal con igu a ion equi es qui e in asi e wo ks on he mason y in ill panels, which mus be cu o a oid in e ac ion be ween RC columns and he walls. Fu he mo e, he dowel- ype connec o s ans e ed he shea o ce om he CLT panel o he columns, which mainly sus ained he damage mechanism. Sus e sic and Dujic p oposed he combina ion o CLT panels wi h a “nano” insula ion laye o c ea e an ou e shell ha is connec ed o he exis ing s uc u e by s eel ancho b acke s [22]. The echnique was expe imen ally es ed on a wo-s o ey one-bay RC ame wi h mason y in ills and nume ically in es iga ed on a h ee-s o ey wo-bay RC ame [23–25]. The dissipa i e capaci y is delega ed o he s eel angula b acke s. Howe e , i is s a ed ha such a connec ion would equi e modi ica ions o be applicable in eal s uc u es. Indeed, i equi es access om he inside o he building [22]. Badini e al. [26] p oposed he use o CLT walls pe pendicula ly o he açade. The wall is connec ed o he RC ame by s eel b acke s, while pos - ensioned s eel endons a e in oduced be ween CLT panels o inc ease he dissipa i e capaci y. Howe e , he impac o he o ces ansmi ed by he ex e nal s uc u e o he exis ing RC membe s may imply he educ ion o he capaci y o RC membe s and he need o addi ional in e nal local in e en ions. In his amewo k, his pape p oposes an inno a i e in eg a ed seismic and ene gy sys em, named e-CLT. The concep o his sys em was d a ed in [27] and i s de elopmen as a seismic upg ading ool is pa o he mul idisciplina y Ho izon 2020 inno a ion esea ch p ojec e-SAFE (ene gy and seismic AF o d- able Eno a ion solu ions) [28]. This pape p esen s he esea ch ac i i y o his p ojec in he ield o seismic upg ading and he ela ed ou comes. The e-CLT sys em is based on he idea o endowing exis ing RC- amed buildings wi h a second pe o m- ing skin made o p e-assembled and cus omizable componen s. The e-CLT sys em is composed o p e ab ica ed CLT panels supe imposed o he ex e nal wall and connec ed o he RC beams by ic ion dampe s. Each dampe connec s he CLT panels o wo consecu i e loo s o he in e media e RC beams and consis s o wo s eel p o iles: he ancho p o ile is connec ed o he RC beam by ancho bol s and o he o he p o ile, named ee p o ile, by slo ed holes and p e ensioned high-s eng h bol s. The ee p o ile ecei es he shea o ce om he CLT panel placed abo e and ansmi s i o he ancho p o ile by means o he ic ion exe ed on he con ac su ace. The componen s o he dampe a e shaped so as o decouple he CLT panel’s e ical mo emen s om hose o he dampe s. In case o a seismic e en , wo possible scena ios may occu : I he seismic ac ion is mode a e, he dampe s igidly connec he CLT panels o he RC s uc u e, hus making a ailable addi ional la e al s i ness and s eng h. This is help ul o a oid damage in non-s uc u al componen s. On he o he hand, i s ong seismic ac ions occu , he dampe s ac i a e and dissipa e pa o he inpu seismic ene gy by sliding. This educes he damage o 1776 o 1796 Ea hquake Enginee ing & S uc u al Dynamics,2025 10969845, 2025, 6, Downloaded om h ps://onlinelib a y.wiley.com/doi/10.1002/eqe.4334 by Uni e si ã Di Ca ania, Wiley Online Lib a y on [03/10/2025]. See he Te ms and Condi ions (h ps://onlinelib a y.wiley.com/ e ms-and-condi ions) on Wiley Online Lib a y o ules o use; OA a icles a e go e ned by he applicable C ea i e Commons License s uc u al componen s and p e en s he building om collapsing. I is no ewo hy ha he ac i a ion o he dampe s de ines an uppe bound o he o ce sus ained by he CLT panels, hus p e en ing hei ailu e e en in case o unexpec edly s ong g ound mo ions. The e-CLT sys em p esen s se e al ad an ages wi h espec o o he sys ems. The e-CLT panels can be combined wi h non-s uc u al p e-assembled panels made o ligh weigh wooden ames and p o ided wi h high-pe o ming windows. The e-CLT sys em is designed o allow a quick and easy ex e nal ins alla ion, which can be pe o med by mobile li ing equipmen , hus a oiding cos s and ime needed o he sca olding se - up. Di e en pa s o he sys em, such as ancho p o iles, a e sui able o p e-assembly p ocess o si e. Fu he mo e, since he ins alla ion p ocess akes place om he ou side, he dis u bance o occupan s is minimized and ope a i i y dis up ion is a oided. The dampe , conside ing i s size, is sui able o ins alla ion on mos common RC amed buildings. Fu he mo e, i is ins alled ou side he building and he dampe inspec ion and main enance a e also eased by s ing cou ses, which can be easily emo ed. Compa ed o s udies a ailable in he li e a u e, he pape has a wo old inno a i e goal: on one hand, o demons a e and quan i y he bene i s p o ided by he e-CLT sys em o he s uc u al esponse o an RC ame, based on expe imen al es s; on he o he hand, o assess he impac o he e-CLT sys em on he s uc u al pe o mance o a se o ealis ic RC buildings, by means o ini e elemen nume ical models and inc emen al nonlinea dynamic analysis (IDA). To his end, he esea ch ollowed h ee main s eps: (1) he e ec o he e-CLT sys em on he seismic esponse o RC ames was expe imen ally ep oduced, (2) a eliable nume ical model o he RC ame wi h e-CLT sys em was de eloped, and (3) he seismic pe o mance o mul i-s o ey RC ames wi h di e en e-CLT con igu a ions was in es iga ed, so as o p o ide guidelines o he design o seismic upg ading by e-CLT. Fi s , he esul s o wo quasi-s a ic cyclic es s ca ied ou on wo in illed RC ames (wi hou and wi h e- CLT), a e p esen ed. The es s cha ac e ized he cyclic esponse o he s uc u al sys em and p o ided da a o he calib a ion o nume ical model. In pa icula , he a ailabili y o wo es s allowed he calib a ion o he nume ical models o he RC ame and he e-CLT sys em in wo s eps. To ex end he s udy o ac ual buildings wi h RC amed s uc u es designed acco ding o old (non-seismic) egula ions, a se o mul i-s o ey RC ame models is de ined. Inc emen al dynamic analyses and pusho e analyses a e ca ied ou on hese ame models o in es iga e he seismic de iciencies o exis ing RC- amed buildings and he capabili y o pusho e analysis in de ec ing such de iciencies. Hence, IDAs a e ca ied ou on he RC ame models equipped wi h e-CLT. Th ee di e en con igu a ions o e-CLT a e conside ed: he local na ow con igu a ion, he local ex ended con igu a ion, and he sp ead con igu a ion. The esul s o IDA led o iden i ying he mos e ec i e con igu a ion, ela ing i o he ou come o pusho e analysis (design analysis), and quan i ying he bene i s ha can be gained by e-CLT. In he nume ical in es iga ion, bo h duc ile and agile ailu e modes o s uc u al membe s a e checked. The seismic pe o mance o he models is analyzed in e ms o he dis ibu ion o seismic demand and demand- o-capaci y a io along he heigh , agili y cu es, and mean annual equency o exceedance o Nea Collapse and Signi ican Damage limi s a es. The inal sec ion d aws he design p o isions o he seismic upg ading o RC s uc u es by e-CLT. 2Expe imen al Tes ing o he e-CLT Sys em The expe imen al campaign is ca ied ou a he CIRI-EC labo a o y o he Uni e si y o Bologna and is de o ed o (1) cha ac e izing he cyclic esponse o a mason y in illed RC ame s eng hened by he e-CLT echnology and (2) p o iding physical e idence ha he componen s o he seismic upg ading sys em pe o m as in ended, e en a e epea ed and se e e cycles o loading. To his end, wo RC ame specimens we e es ed in eal scale, in bo h uns eng hened and s eng hened con igu a ions, unde quasi-s a ic cyclic loading. 2.1 Specimen Desc ip ion Two iden ical one-s o ey–one-bay RC ames a e es ed in he wo in es iga ed con igu a ions. The RC ames eplica e he ypical cons uc i e ea u es o I alian buildings o he ‘70s and a e designed in compliance wi h he building code en o ced in 1974 [29] conside ing g a i y loads only. De ails on he design o he RC ames may be ound in [30].Thespanleng his equal o 4.0 m and he in e -s o ey heigh is 3.2 m. Columns ha e 300 ×300 mm c oss sec ion, while a 300 ×400 mm c oss sec ion is adop ed o beam. The RC ames a e in illed wi h a single laye 120-mm- hick mason y wall ealized wi h ex uded hollow blocks and aligned wi h an ex e nal su ace o he ame (Figu e 1a). Comp ession es s we e pe o med on cube and cylinde samples collec ed du ing he cas phase o he wo ames. The a e age alues o he cylinde comp essi e s eng h o s eng hened and uns eng hened ames a e 21.9 and 21.4 MPa, espec i ely. Tensile es s we e un on h ee s eel eba specimens collec ed om he s eel lo and he a e age yielding s eng h was equal o 534.6 MPa. The e-CLT sys em was cons i u ed by a 100 mm hick CLT panel (5 laye s o 20 mm hickness) connec ed o he RC ame by means o a s eel appa a us (Figu e 1b). The wo uppe componen s o he s eel appa a us a e ancho ed o he uppe RC beam and suppo he CLT panel, while he wo bo om componen s a e mechanical ic ion dampe s ac i a ed by he ela i e displacemen be ween CLT panel and bo om RC beam. 2.2 Expe imen al Se up and Tes P o ocol A speci ically designed se up is de eloped o ca y ou quasi- s a ic es s o he wo specimens (Figu es 1and 2). The RC ame is ancho ed o he s ong loo while a ho izon al displacemen is imposed o he op RC beam by means o a 500 kN MTS se o-hyd aulic jack ancho ed o he conc e e eac ion wall. The ancho ing sys em o he bo om RC beam is ealized by igid s eel b acke s and pos - ensioned dywidag ba s and i ually a oids also he ho izon al sliding o he RC ame o e he s ong loo . Fu he mo e, he s eel b acke s aligned on he RC columns se e as a as ening sys em o he e ical ba s used o apply he axial o ce o he columns. The axial o ce, equal o 250 kN, is applied o each column by means o hyd aulic jacks placed o e hem and cons ained by ans e se s eel beams as ened o he bo om b acke s desc ibed be o e. The e ical load applica ion sys em is designed wi h od end pins and conical nu s, which allow cyclic la ge displacemen s in he ho izon al di ec ion. The applied e ical o ces ep oduce he axial o ce caused by he 1777 o 1796 10969845, 2025, 6, Downloaded om h ps://onlinelib a y.wiley.com/doi/10.1002/eqe.4334 by Uni e si ã Di Ca ania, Wiley Online Lib a y on [03/10/2025]. See he Te ms and Condi ions (h ps://onlinelib a y.wiley.com/ e ms-and-condi ions) on Wiley Online Lib a y o ules o use; OA a icles a e go e ned by he applicable C ea i e Commons License FIGURE 1 Geome y and pho os o specimens: (a,c) uns eng hened and (b,e) in illed s eng hened RC ame, (d) membe s c oss sec ions. FIGURE 2 Tes se up: (a) global scheme and (b) pho o o labo a o y es ing sys em (s eng hened con igu a ion). g a i y load o he seismic design si ua ion in he i s s o ey columns o a h ee-s o ey esiden ial building. The ho izon al displacemen applica ion sys em is composed o a s eel ie made up o s i ened ans e se s eel pla es placed a he wo ends o he uppe RC beam and connec ed h ough pos - ensioned dywidag ba s. The se o-hyd aulic ac ua o is connec ed o one end o he ie and is cons ained o he eac ion wall. The en i e es sys em is ans e sally s abilized by means o a la ice s eel sys em allowing o he ho izon al and e ical displacemen s only o he op RC beam h ough sphe ical olle s. This ans e se s abiliza ion sys em a oids possible ou -o -plane displacemen o he RC ame, in pa icula in he case o he s eng hened con igu a ion, wi h he e-CLT panel eccen ically ixed wi h espec o he ho izon al o ce alignmen . The measu emen sys em depic ed in Figu e 2is composed o : (1) wo ho izon al ansduce s eco ding he base displacemen (LVDT 1) and he op displacemen (LVDT 2) espec i ely; (2) a ho izon al ansduce eco ding he ela i e displacemen be ween he ic ion dampe and he base RC beam (LVDT 3) and (3) a LOAD CELL eco ding he o ce in he ac ua o . The RC ame d i is calcula ed as he di e ence be ween he ho izon al displacemen s o he op and base RC beams eco ded du ing he es using LVDT 2 and LVDT 1, espec i ely. Mo eo e , 1778 o 1796 Ea hquake Enginee ing & S uc u al Dynamics,2025 10969845, 2025, 6, Downloaded om h ps://onlinelib a y.wiley.com/doi/10.1002/eqe.4334 by Uni e si ã Di Ca ania, Wiley Online Lib a y on [03/10/2025]. See he Te ms and Condi ions (h ps://onlinelib a y.wiley.com/ e ms-and-condi ions) on Wiley Online Lib a y o ules o use; OA a icles a e go e ned by he applicable C ea i e Commons License TABLE 1 Ho izon al loading p o ocol. S ep o loading 1 2 3 4 5 6 7 8 9 10 11 D i ampli ude (mm) ±1±2±4±8±16 ±24 ±32 ±48 ±64 ±80 ±96 D i a io (%) ±0.03 ±0.06 ±0.13 ±0.25 ±0.50 ±0.75 ±1.00 ±1.50 ±2.00 ±2.50 ±3.00 Loading a e (mm/s) 0.02 0.05 0.10 0.20 0.20 0.30 0.40 0.50 0.70 1.00 1.20 No. o cycles 33333333333 (a) (b) (c) -300 -200 -100 0 100 200 300 -125 -75 -25 25 75 125 ]Nk[F D i [mm] S engh ened Uns engh ened -150 -100 -50 0 50 100 150 -125-100 -75 -50 -25 0 25 50 75 100 125 ]mm [ i D Sliding [mm] 0 50 100 150 200 250 300 1 2 4 8 16 24 32 48 64 80 96 ]Jk[y g e nede a p is s iD D i [mm] S engh ened Uns engh ened FIGURE 3 Cyclic esponse o he uns eng hen and s eng hen ames: (a) load-d i hys e esis loops, (b) RC d i e sus e-dampe sliding, (c) dissipa ed ene gy. he ic ion dampe sliding is eco ded o he s eng hened con igu a ion using LVDT 3. Figu e 2shows a comp ehen- si e scheme o he se up and a pho o o he expe imen al equipmen . The specimens a e loaded in wo phases: i s , he e ical o ces a e applied and g adually inc eased up o he a ge alue o 250 kN in o ce con ol, hen he ho izon al displacemen is cyclically applied. In he second phase, he e ical o ces a e kep cons an , by con olling he hyd aulic p essu e o he jacks, while d i cycles o inc easing ampli ude a e applied by con olling he di e ence in he ho izon al displacemen s o he uppe and lowe beams. Du ing he en i e cyclic loading phase, he o ce in he ac ua o is measu ed using he LOAD CELL. The ho izon al loading p o ocol is designed aking in o accoun he displacemen capaci y o he e-CLT sys em. I is summa ized in Table 1, which lis s d i ampli ude, d i a io, loading a e, and a numbe o cycles o each s ep o he cyclic loading. 2.3 Tes Resul s All he componen s o he e-CLT sys em beha ed as in ended, up o he end o he es . Indeed, he CLT panel emained elas ic and did no expe ience ins abili y o any kind o local damage e en unde he la ges imposed d i , ha is, 3% o he s o ey heigh . Hence, i e icien ly ans e ed he ho izon al o ce om he op beam o he wo ic ion dampe s a he bo om o he panel. The dampe s ac i a ed as planned unde he push exe ed by he CLT panel and slid al e na i ely back and o wa d dissipa ing ene gy. A he end o he es , he s eel appa a us was dismoun ed and he single componen s (pla es, sc ews, bol s, and aluminum shim laye s) we e accu a ely examined. No sign o yielding o o he ype o damage was de ec ed, hus p o ing ha he s eel appa a us and as ening sys em beha ed elas ically o he whole du a ion o he es . Figu e 3a compa es he load-d i hys e esis loops ob ained o he uns eng hened ( ed line) and s eng hened (black line) con igu a ion. I is e iden ha he RC ame wi h he e- CLT sys em exhibi s ini ial la e al s i ness and peak s eng h signi ican ly la ge han hose o i s uns eng hened coun e pa . Mo eo e , he s eng h deg ada ion (i.e., di e ence be ween he o ce achie ed a he 1s and he 3 d epea ed cycles) esul s gene ally lowe o he s eng hened con igu a ion, especially o la ge d i le els. Figu e 3b shows he slippage be ween he wo pa s o he ic ion dampe e sus he d i o he RC ame eco ded du ing he es . A a ia ion o he RC ame d i while he dampe slippage emains cons an ( e ical b anches in he g aph) iden i ies a e e sal o loading. This occu s when he o ce ansmi ed by he CLT panel o he dampe empo a ily becomes lowe han he dampe ic ion o ce and he a ia ion o he slippage s ops. A e he e e sal, when he o ce in he dampe a ains again he alue o he ic ion o ce, bo h d i and slippage s a a ying simul aneously again. Hence, he heigh o he e ical b anches o he g aph ep esen s he po ion o he d i ha canno be ans o med in o slippage because o he de o mabili y o he panel and o he ic ion dampe as ening sys em. The small heigh o he e ical b anches o he g aph obse ed in Figu e 3b demons a es ha a 100-mm- hick CLT panel is s i enough o ans o m almos he whole d i in o slippage (abou 80%, since o d i sligh ly lowe han 100 mm he slippage is abou 80 mm), hus o cing he dampe s o dissipa e ene gy e icien ly. This esul s in a big posi i e impac o he e-CLT sys em on he ene gy dissipa ion capaci y (compu ed acco ding o [31]). Indeed, he a ea enclosed by he hys e esis loops (dissipa ed ene gy) o he s eng hened ame is much la ge han ha o he uns eng hened ame (Figu e 3a). The 1779 o 1796 10969845, 2025, 6, Downloaded om h ps://onlinelib a y.wiley.com/doi/10.1002/eqe.4334 by Uni e si ã Di Ca ania, Wiley Online Lib a y on [03/10/2025]. See he Te ms and Condi ions (h ps://onlinelib a y.wiley.com/ e ms-and-condi ions) on Wiley Online Lib a y o ules o use; OA a icles a e go e ned by he applicable C ea i e Commons License RC in illed ame + e-CLT RC membe s In ill panel CLT panel F ic ion dampe s In illed RC ame e-CLT sys em FIGURE 4 Desc ip ion o elemen s o he nume ical model. compa ison be ween he ene gy dissipa ed a he end o each loading s ep by he s eng hened and uns eng hened ames (Figu e 3c) quan i ies he imp o emen o dissipa ion capaci y p o ided by e-CLT, which can be e en 200% o ha o he uns eng hened ame. 3 Nume ical Model o he Tes Specimen A plane nume ical model o he es specimen is implemen ed in OpenSees [32] and de eloped in o wo “mac o-sys ems”: he in illed RC ame and he e-CLT sys em (Figu e 4). Each pa o he nume ical model is i s desc ibed, and hen he alues o mechanical pa ame e s a e calib a ed so ha he cyclic esponse o he nume ical model ma ches he expe imen al one. 3.1 Desc ip ion o he Nume ical Model The nume ical model o he in illed RC ame includes columns, beams, and in ill panels, and i is assumed ixed o he g ound. Fo RC columns and beams, nonlinea beha io is supposed o be limi ed o plas ic hinge egions a membe ends, while he emaining pa o he elemen emains elas ic. They a e modeled as beamWi hHinges elemen wi h he modi ied Gauss Radau in eg a ion ule [33]. The leng h o plas ic hinge Lpl is se equal o he dep h o he c oss sec ion and he c oss-sec ion o e Lpl is disc e ized in o ibe s. Speci ically, he conc e e pa o he c oss-sec ion is subdi ided in o ibe s ha ing 5 mm dep h and wid h equal o he wid h o he c oss-sec ion, while single ibe s a e used o model eba s. The Ken –Sco –Pa k cons i u i e law (Conc e e01 uniaxialMa e ial)[34] and he elas ic–plas ic cons i u i e law wi h kinema ic ha dening (S eel02 uniaxialMa- e ial)[32] a e assigned o he conc e e and he s eel ibe s, espec i ely. A pai o diagonal usses is used o model he in ill panel. Unde he e ec o ho izon al o ces, only he comp essi e b anch is ac i e, while he ensile one p o ides a minimal non- ze o s i ness necessa y o nume ical s abili y. Al hough his modeling app oach o in ill panels is a he simple, i is ecog- nized o ep oduce sa is ac o ily he global esponse o ames unde ho izon al o ces and is deemed an accep able comp omise be ween compu a ional bu den and accu acy o esul s [35]. As p oposed by Panagio akos and Fa dis [36] and Cela ec e al. [37], he o ce-displacemen ela ionship o he diagonal usses is de e mined o eplica e he shea o ce-d i ela ionship o he in ill panel. This ela ionship consis s o ou b anches: he i s b anch co esponds o he linea elas ic beha io up o he i s c acking o he in ill, he second b anch uns om he i s c acking up o he maximum s eng h, he hi d b anch is he pos -capping deg ading b anch, and uns om he maximum s eng h o he esidual s eng h, inally, he ou h b anch is ho izon al and co esponds o he esidual s eng h. Fo each b anch, he alues o s i ness and maximum o ce a e de e mined acco ding o he equa ions p oposed in [37]. The abo emen ioned mul ilinea o ce-displacemen ela ionship is con e ed in o an equi alen s ess–s ain ela ionship. The alues o s ess–s ain couples o he h ee co ne s o he en elope, bo h in he posi i e and nega i e loading di ec ion, a e assigned o he usses by he Pinching4 uniaxialMa e ial implemen ed in OpenSees. The e-CLT sys em is composed o he CLT panel and ic ion dampe s (Figu e 4). The CLT panel is modeled by means o six equi alen usses: wo e ical usses, wo ho izon al usses, and wo diagonal usses (Figu e 5). All usses a e elas ic and ha e c oss-sec ion wi h he uni a y a ea. The axial s i ness o he usses is calib a ed o p o ide he same in-plane s i ness o he CLT panel. To his end, he elas ic modulus o he e ical and diagonal usses Ecand Eda e calib a ed so ha he ho izon al and he e ical displacemen s o he uss model a e equal o hose o he ac ual CLT panel subjec ed o wo ho izon al o ces applied on he op co ne s o he panel (Figu e 5). Consis en ly, he elas ic modulus o he ho izon al usses Ebis calib a ed so ha he ho izon al displacemen o he CLT panel simula ed by usses is equal o ha o he ac ual CLT panel subjec ed o wo opposi e ho izon al o ces applied on op o he panel (Figu e 5). The displacemen demands o he ac ual CLT panel a e de e mined by a second “suppo ” nume ical model, which simula es only he CLT panel by a single shell elemen wi h elas ic o ho opic ma e ial. The Young and shea moduli in he h ee mu ually pe pendicula di ec ions o he shell elemen s depend on he mechanical cha ac e is ics o he conside ed CLT panel. F ic ion dampe s a e simula ed by ze o-leng h elemen s loca ed a he beam- o-column in e sec ion (Figu e 4). The beha io o ic ion dampe s in he ho izon al di ec ion is desc ibed by an elas ic-plas ic beha io (S eel01 uniaxialMa e ial in OpenSees), whose yielding s eng h ep esen s he ic ion o ce ha ac i a es he dampe s. In he e ical di ec ion, he dampe can mo e eely. The concen a ed g a i y loads on columns a e hose applied du ing he expe imen al es and a e equal o 250 kN. The ho izon al loading applica ion sys em o he expe imen al es is simula ed by a uss elemen wi h s eel elas ic modulus and c oss- sec ion a ea equal o ha o he s eel ie used in he es . The uss connec s wo addi ional ex e nal nodes ha a e o mally coinciden wi h he RC beam ends. Each addi ional node is connec ed o he co esponding node o he beam end by a ze o- leng h elemen ha eac s only in comp ession wi h e y la ge axial s i ness. Two opposi e ho izon al o ces equal o 320 kN a e applied a each end o he beam o eplica e he p es ess o ce applied in he es . 1780 o 1796 Ea hquake Enginee ing & S uc u al Dynamics,2025 10969845, 2025, 6, Downloaded om h ps://onlinelib a y.wiley.com/doi/10.1002/eqe.4334 by Uni e si ã Di Ca ania, Wiley Online Lib a y on [03/10/2025]. See he Te ms and Condi ions (h ps://onlinelib a y.wiley.com/ e ms-and-condi ions) on Wiley Online Lib a y o ules o use; OA a icles a e go e ned by he applicable C ea i e Commons License H L h h Shell elemen h Ho izon al displacemen equilib ium Ve ical displacemen equilib ium H L h h Shell elemen h 1) Fo ces wi h same di ec ion Ho izon al displacemen equilib ium 2) Fo ces wi h opposi e di ec ion FIGURE 5 E alua ion o he axial s i ness o equi alen usses simula ing he CLT panel. (b)(a) (c) D i [mm] D i [mm] D i [mm] FIGURE 6 Expe imen al e sus nume ical cyclic esponse o he uns eng hened ame in e ms o o al base shea - op displacemen : (a) sub- componen app oach, (b) nume ical model o RC ame (la ge ampli ude displacemen s); (c) nume ical model o RC in illed ame (low ampli ude displacemen s). 3.2 Calib a ion o he Pa ame e s o he Nume ical Model To calib a e he mechanical ea u es o he desc ibed nume ical model, he esul s p o ided by he expe imen al es , in e ms o base shea and op displacemen , a e assumed as a ge s. Two cal- ib a ion p ocesses a e ollowed in se ies: Fi s , he cha ac e is ics o he RC ame and he in ill panel a e de e mined based on he esul s o he cyclic es on he in illed RC ame (wi hou e-CLT sys em). A e wa d, he ea u es o he e-CLT componen s a e calib a ed o ma ch he expe imen al esul s o he s eng hened specimen (wi h e-CLT). In he i s calib a ion p ocess, he mechanical cha ac e is ics o bo h RC membe s (columns and beams) and in ill panels a e deduced om he same expe imen al es , ollowing a “sub- componen ” app oach (Figu e 6a). This app oach is based on he expe imen al obse a ion ha , o la ge displacemen demand, he s i ness and s eng h o he in ill panel d as ically dec ease in almos all RC amed s uc u es subjec ed o ho izon al o ces. This allowed he de e mina ion o he mechanical pa ame e s o he RC membe s assuming as a ge he cyclic esponse unde he la ges displacemen ampli udes, when he s i ness and s eng h o he in ill panel has become negligible. In his s ep, he nume ical model includes only he RC membe s and he maximum comp ession s eng h o conc e e Fcm is se equal o 21.65 MPa, i.e., he mean comp essi e s eng h ob ained om he conc e e comp essi e coupon es s. The co esponding Young’s modulus Ecm is calcula ed as 2 Fcm/εc2 and i is equal o 21950 MPa. Howe e , o ake in o accoun he e ec o conc e e c acking, he momen o ine ia o he sec ion is educed o 50% and 80% o Ig o beams and columns, espec i ely [38]. The con inemen e ec on he co e o he membe c oss sec ions is neglec ed because he specimen is ep esen a i e o RC s uc u es designed wi hou seismic p o isions, ha gene ally ha e ew s i ups. The s ains a maximum comp ession s eng h εc0 and a c ushing s eng h εcu a e assumed equal o he con en ional alues 2 ×10−3and 3.5 × 10−3, espec i ely. The esidual conc e e comp essi e s eng h is calib a ed based on he esul s o he ull-scale expe imen al es ca iedou on heRC ameandse equal o6MPa,abou 30% o he peak alue. The ension s eng h o conc e e is i ually ze o. As o s eel, Young’s modulus Esis assumed equal o 1781 o 1796 10969845, 2025, 6, Downloaded om h ps://onlinelib a y.wiley.com/doi/10.1002/eqe.4334 by Uni e si ã Di Ca ania, Wiley Online Lib a y on [03/10/2025]. See he Te ms and Condi ions (h ps://onlinelib a y.wiley.com/ e ms-and-condi ions) on Wiley Online Lib a y o ules o use; OA a icles a e go e ned by he applicable C ea i e Commons License TABLE 2 Lis o pa ame e s o nume ical model. Conc e e 01 S eel 02 Maximum conc e e comp ession s eng h Fcm =21.59 MPa Yielding s eng h Fym =400 MPa Young modulus Ecm =21950 MPa Young modulus Es=210,000 MPa s ain a maximum comp ession s eng h εc2 =0.002 Kinema ic ha dening a io b=0.001 s ain a c ushing s eng h εcu =0.0035 Residual conc e e comp essi e s eng h =6MPa In ill panel (Pinching 04) Thickness w=120 mm Floa ing poin s de ining he eloading o he cyclic esponse: DispP =0.5, Fo ceP =0.5, uFo ceP =0, DispN =0, Fo ceN =0, uFo ceN =0 Young modulus Ew=1979.7 MPa Shea modulus Gw=791.9 MPa C acking s eng h 0.23 MPa Floa ing poin s con olling he cyclic deg ada ion: gK1,gK2,gK3, gK4,gKLim =1; gD1 gD2 gD3 gD4 gDLim =0, gF1 gF2 gF3 gF4 gFLim =0.5 Pos -capping deg ading s i ness pa ame e α=0.035 Residual s eng h pa ame e β=0.02 Equi alen usses o CLT F ic ion dampe s (S eel 02) Elas ic modulus o diagonal uss Ed=13840.3 MPa Yield s eng h (ac i a ion o ce) 25.7 MPa Elas ic modulus o e ical uss Ec=172423.5 MPa Ho izon al s i ness =299.6 kN/m Elas ic modulus o ho izon al uss Eb=329436.1 MPa Ve ical and o a ional s i nesses =0.0 210,000 MPa while he yielding s eng h ym is equal o 400 MPa. The kinema ic ha dening a io bis se equal o 0.001, while no iso opic ha dening is p esen . Based on he ma ch wi h he expe imen al esul s o he RC ame, he alue o he yielding s eng h is assumed lowe han ha p o ided by he coupon es . This s a egy allowed he nume ical model o ake in o accoun he s eng h deg ada ion caused by he ins abili y o longi udinal eba s ha occu ed du ing he expe imen al es a la ge displacemen demand. These pa ame e s led o he cyclic esponse plo ed in Figu e 6b by he ed line, which is in qui e good ag eemen wi h he expe imen al esponse (black line) a e he comple e c ushing o in ills. Once he mechanical pa ame e s o he RC membe s ha e been de e mined, he nume ical model is in eg a ed wi h he equi alen diagonal usses simula ing he in ill panel. In his second s ep, he ea u es o he in ill panel a e de e mined so ha he nume ical model ma ches he expe imen al esponse when low-medium displacemen ampli udes a e applied, and he in ill panel has no been signi ican ly damaged ye . The mechanical p ope ies a e assigned acco ding o he da a p o- ided by he expe imen al es s. Hence, he hickness is equal o 120 mm, Young’s modulus and shea modulus a e equal o 1979.7 and 791.9 MPa, espec i ely, while c acking s eng h is equal o 0.23 MPa. The pa ame e s αand β, which ule he pos -capping deg ading s i ness and he esidual s eng h, a e calib a ed o ma ch he cyclic esponse o he in illed ame p o ided by he es , and alues α=0.035 and β=0.02 a e ound. Since he expe imen al esul s o he in illed ame showed cyclic deg ada ion o s eng h and s i ness unde cyclic loading, he alues o he loa ing poin s de ining he load- ing/ eloading o he Pinching4 uniaxialMa e ial a e epo ed in Table 2. The second calib a ion p ocess is de o ed o he de e mina ion o he mechanical pa ame e s o he usses, simula ing he CLT panel, and he ic ion dampe s, so ha he s uc u al esponse p o ided by he nume ical model is in acco dance wi h he expe imen al esul s o he s eng hened RC ame. Wi h ega ds o he CLT panel, he elas ic moduli Ed,Ec,Ebo he diagonal, e ical, and ho izon al usses a e se equal o 13840.3, 172423.5, and 329436.1 MPa, espec i ely. These alues we e de e mined by scaling by 0.50 imes he elas ic modulus o he usses ha we e equi alen o he es ed CLT panel modeled by a shell elemen (C24 class). The la e was cha ac e ized by an elas ic o ho opic beha io wi h elas ic moduli equal o 6748, 4622, and 370 MPa in he X,Y,andZdi ec ions, espec i ely. Figu e 7a shows he ela ion be ween d i o he ame and sliding o he dampe loca ed a i s base. I can be obse ed ha he d i inc eases linea ly wi h he displacemen o he dampe . The ed and black lines show ha he esul s p o ided by he nume ical model and expe imen al es a e in good ag eemen . As o he dampe , he pa ame e s ha need o be de ined a e he yield s eng h o he elas oplas ic ma e ial and i s elas ic modulus. The expe imen al es shows a qui e asymme ic esponse o he dampe subjec ed o he cyclic ho izon al o ce, wi h a peak posi i e and nega i e s eng h equal o 29.44 and −22.04 kN, espec i ely. The yield s eng h assigned o he dampe in he nume ical model is se equal o 25.7 MPa, which is he a e age alue be ween he posi i e and nega i e s eng hs p o ided by he es . The elas ic modulus was calib a ed so ha he esponse o he nume ical analysis i ha o he expe imen al es , and i is se equal o 299.6 kN/m. The esponses o he dampe p o ided by he expe imen al es and he nume ical model a e epo ed in Figu e 7b,whe e he sliding o he dampe has been plo ed as a unc ion o he o al applied o ce. The wo plo s show ha he nume ical model is able o p edic accu a ely he esponse o he expe imen al es . 1782 o 1796 Ea hquake Enginee ing & S uc u al Dynamics,2025 10969845, 2025, 6, Downloaded om h ps://onlinelib a y.wiley.com/doi/10.1002/eqe.4334 by Uni e si ã Di Ca ania, Wiley Online Lib a y on [03/10/2025]. See he Te ms and Condi ions (h ps://onlinelib a y.wiley.com/ e ms-and-condi ions) on Wiley Online Lib a y o ules o use; OA a icles a e go e ned by he applicable C ea i e Commons License (b)(a) (d)(c) -150 -100 -50 0 50 100 150 1257525-25-75-125 D i [mm] Sliding [mm] Expe imen al Nume ical -300 -200 -100 0 100 200 300 1257525-25-75-125 F [kN] Sliding [mm] Expe imen al Nume ical -300 -200 -100 0 100 200 300 1257525-25-75-125 F [kN] D i [mm] Expe imen al Nume ical 0 50 100 150 200 250 300 968064483224168421 Dissipa ed ene gy [kJ] D i [mm] Expe imen al Nume ical FIGURE 7 Compa ison o expe imen al e sus nume ical cyclic esponse o he s eng hened ame in e ms o (a) op displacemen e sus sliding o he dampe , (b) o al o ce e sus dampe displacemen , (c) o al base shea e sus op displacemen demand, (d) dissipa ed ene gy. Once he calib a ion o he pa ame e s is concluded by checking he local esponse o CLT membe s and dampe s, he en i e nume ical model is ully de ined. A lis o all he calib a ed pa ame e s is epo ed in Table 2. Hence, he global esponse in e ms o base shea and op displacemen o he ame is obse ed (Figu e 7c). The seismic esponse o he s eng hened ame is cha ac e ized by a peak o esis ance, a ound 200 kN, and a e y high elas ic s i ness due o he in ill. A e he c acking o he in ill panel, he s i ness and he la e al s eng h dec ease and end o hose o he RC ame wi h CLT and dampe s. The nume ical model ( ed line) is able o es ima e he peak s eng h and he elas ic s i ness p o ided by he expe imen al es (black line) accu a ely as well as he cyclic esponse o he ame a e c acking o he in ills. Indeed, he calib a ed nume icalmodel can accu a ely p edic he ene gy dissipa ed by he specimen du ing each cycle o imposed displacemen , wi h a maximum e o a he ending cycle lowe han 13% (Figu e 7d). 4Case S udy Buildings A se o case s udies is de ined o encompass RC- amed buildings cha ac e ized by s uc u al ea u es and seismic sho comings common in he Medi e anean building s ock. Fi s , he p oce- du e ollowed o design he RC membe s is p esen ed and all he con igu a ions o he case s udy buildings a e de ailed. Hence, he nume ical model de eloped o analyze he case s udy is desc ibed. 4.1 Design o Case S udy Buildings Since mos o he exis ing RC buildings we e cons uc ed be ween he middle and he end o he 20 h cen u y, when seismic codes we e no in o ce ye o seismic zona ion was s ill unde e olu ion, hey a e a ec ed by di e en le els o seismic de iciencies. Following his obse a ion, i s , a e e ence case s udy ame is designed o g a i y loads only. This is ep esen a i e o hose buildings ha we e no o iginally concei ed o ace seismic o ces bu we e a e wa d included in seismic-p one a eas. This building is i e-s o ey high and has a ec angula plan layou (Figu e 8) wi h dimensions equal o 28.8 and 15.5 m in he X-andY-di ec ion, espec i ely. The loo decks a e ealized by RC jois s a anged along Y-di ec ion connec ed by a 40 mm hick slab, and a e suppo ed by he ou se en-bay ames o ien a ed along he X-di ec ion. Only wo ames a e disposed along he Y-di ec ion, o close he pe ime e o he plan layou . Since he majo i y o beams a e disposed along he X-di ec ion and columns oppose hei s ong ine ia axis mainly along he X-di ec ion, he la e al s i ness and s eng h along he X-di ec ion a e signi ican ly la ge han hose along he Y-di ec ion. Such a di e ence in he wo di ec ions o he building is a ea u e ha o en cha ac e izes s uc u es designed wi hou seismic p esc ip ions. The dis ibu ion o la e al s i ness and s eng h is symme ic wi h espec o bo h axes passing h ough he geome ic cen e o he plan layou , meaning ha he s uc u al esponse o ho izon al seismic o ces is pu ely ansla ional. Dead and li e loads on s uc u al elemen s a e de e mined acco ding o he nominal alues p o ided in [39]. The allowable s ess me hod is ollowed o size he c oss sec ions and s eel ein o cemen o membe s, as p esc ibed by he I alian code en o ced in 1974 [29]. Columns a e designed conside ing axial o ce only, while beams a e designed o bending momen and shea o ce. The in e nal axial o ce No columns and he dis ibu ed loads es ing on beams a e e alua ed acco ding o he ibu a y a ea concep . The cha ac e is ic comp essi e cubic s eng h Rck o conc e e is equal o 25 MPa (co esponding o cylinde s eng h ck equal o 20 MPa o s eng h class C20/25). S eel g ade Feb38K wi h a cha ac e is ic yield s ess yk =375 MPa 1783 o 1796 10969845, 2025, 6, Downloaded om h ps://onlinelib a y.wiley.com/doi/10.1002/eqe.4334 by Uni e si ã Di Ca ania, Wiley Online Lib a y on [03/10/2025]. See he Te ms and Condi ions (h ps://onlinelib a y.wiley.com/ e ms-and-condi ions) on Wiley Online Lib a y o ules o use; OA a icles a e go e ned by he applicable C ea i e Commons License X- ame models Y- ame models (a) (b) (c) Uns eng hened ame Sp ead e-CLT Local ex ended e-CLT Local na ow e-CLT 0 1 2 3 4 5 6 0% 1% 2% 3% 4% N Δ 0 1 2 3 4 5 6 0.0 0.5 1.0 1.5 2.0 N θ / θ NC Columns 0 1 2 3 4 5 6 0.0 0.5 1.0 1.5 2.0 N θ / θ NC Beams 0 1 2 3 4 5 6 0.0 0.5 1.0 1.5 2.0 N VEd/V Rd Columns 0 1 2 3 4 5 6 0.0 0.5 1.0 1.5 2.0 N V Ed /V Rd Beams 0 1 2 3 4 5 6 0% 1% 2% 3% 4% N Δ 0 1 2 3 4 5 6 0.0 0.5 1.0 1.5 2.0 N θ / θ NC Columns 0 1 2 3 4 5 6 0.0 0.5 1.0 1.5 N θ / θNC Beams 0 1 2 3 4 5 6 0.0 0.5 1.0 1.5 2.0 N V Ed /V Rd Columns 0 1 2 3 4 5 6 0.0 0.5 1.0 1.5 N V Ed /V Rd Beams FIGURE 13 Dis ibu ion along he heigh a he a ainmen o NC limi s a e in he uns eng hened in illed ame o (a) d i demand; (b) cho d o a ion D/C a io o columns and beams; (c) shea o ce D/C a io o columns and beams. building, while in he Y- ame model, wi h espec o he o he wo e-CLT con igu a ions, i p o ides a simila o a lowe e ec on he seismic esponse. The dis ibu ions along he heigh o he uns eng hened ba e and pilo is building o maximum d i demand, cho d o a ion D/C a io in columns, and cho d o a ion D/C a io in beams a e plo ed o he ela ed PGA capaci ies in Figu e 15a–c, espec i ely. The analysis o he d i demand and he cho d o a ion D/C a io in columns shows ha X- ame models o bo h ba e and pilo is buildings in he uns eng hened con igu a ion expe ienced concen a ion o damage a one o wo s o eys, while a seismic demand a he dis ibu ed along he heigh is obse ed in he Y- ame models. When applied in he sp ead o local ex ended con igu a ion, he e-CLT sys em in he X-di ec ion success ully educed (by abou 40%) bo h he d i demand and he cho d o a ion demand o columns o he s o eys wi h he la ges displacemen demands. I e-CLT sys em is loca ed acco ding o he local na ow con igu a ion, d i demand and cho d o a ion demand in columns o he X- ame model concen a e a a single s o ey ( he hi d in he ba e building and he ou h in he pilo is building) and become e en la ge han hose o he buildings in he uns eng hened con igu a ion. This beha io s ems om he ac ha he e-CLT sys em was loca ed only a he ou h s o ey in he ba e building and he hi d s o ey in he pilo is building. Thus, he maximum seismic demand shi om hese s o eys o he adjacen ones, making he local na ow con igu a ion no e ec i e om a global poin o iew. In he Y- ame model, he local na ow con igu a ion shows he leas impac on he seismic esponse (abou 15% educ ion on maximum d i and cho d o a ion demands). Wi h ega ds o beams, he e-CLT sys em leads o a educ ion o he cho d o a ion demand in beams only in he Y- ame model (−36% and −43% wi h sp ead con igu a ion in he ba e and pilo is building, espec i ely), whe e he displacemen demand was a he dis ibu ed along he heigh and he beams expe ienced a cho d o a ion demand compa able o ha o columns (as shown in Figu e 9). 1790 o 1796 Ea hquake Enginee ing & S uc u al Dynamics,2025 10969845, 2025, 6, Downloaded om h ps://onlinelib a y.wiley.com/doi/10.1002/eqe.4334 by Uni e si ã Di Ca ania, Wiley Online Lib a y on [03/10/2025]. See he Te ms and Condi ions (h ps://onlinelib a y.wiley.com/ e ms-and-condi ions) on Wiley Online Lib a y o ules o use; OA a icles a e go e ned by he applicable C ea i e Commons License Ba e ame (wi hou in ills) Pilo is ame X- ame models (a) (b) Y- ame models (c) (d) Uns eng hened ame Sp ead e-CLT Local ex ended e-CLT Local na ow e-CLT 0 0.2 0.4 0.6 0.8 1 0 0.2 0.4 0.6 0.8 P(LS) PGA [g] 0 0.2 0.4 0.6 0.8 1 0 0.2 0.4 0.6 0.8 P(LS) PGA [g] 0 0.2 0.4 0.6 0.8 1 0 0.2 0.4 0.6 0.8 P(LS) PGA [g] 0 0.2 0.4 0.6 0.8 1 0 0.2 0.4 0.6 0.8 P(LS) PGA [g] FIGURE 14 F agili y cu es o NC limi s a e o he case s udy buildings be o e and a e he in oduc ion o e-CLT. Gene ally speaking, in he s eng hened X- ame models, espe- cially in he case o in illed and pilo is building, he sp ead o local ex ended con igu a ions (1) educe he d i demand con- cen a ion ha cha ac e izes he esponse o he uns eng hened coun e pa and (2) lead o an inc eased o he cho d o a ion demand in he columns o he s o eys wi h lowe d i demands, which a e o ced o pa icipa e in he dissipa ion p ocess. Thanks o he la ge numbe o RC membe s in ol ed in he dissipa i e p ocess and he addi ional con ibu ion o he dissipa i e capaci y p o ided by he dampe s, he esponse o he ame is d as ically educed, and he PGA capaci y is signi ican ly enhanced. In he case o Y- ames, whe e damage is no localized a a ew s o eys e en in he uns eng hened con igu a ion, he e-CLT sys em educes he cho d o a ion demand mainly hanks o he addi ional sou ce o seismic ene gy dissipa ion gi en by he dampe s, hus he bene i achie ed by he ame is less ema kable. 7.2 Mean Annual F equency o Exceedance o Case S udy Buildings a NC and SD Limi S a e The seismic esponse o he analyzed case s udy buildings is also assessed in e ms o mean annual equency o exceedance o he NC and SD limi s a e conside ing he X-andY- ame models. Fo all he conside ed cases, Figu es 16 and 17 show he a io o he mean annual equency o exceedance λo SD and NC limi s a es wi h espec o he ele an limi alues λ eq equi ed by [45]. I λ/λ eq o e comes uni y, he co esponding e i ica ion is no ul illed. The a io λ/λ eq is e alua ed conside ing he ou agg ega ion ules conside ed o he cons uc ion o he agili y cu es: only duc ile ailu e modes in all membe s, bo h duc ile and agile ailu e modes in all membe s, o all ailu e modes only in columns o all ailu e modes only in beams. The la ges alue among he ou a ios is he one ha quan i ies he seismic pe o mance o he ame. The ed his og am e e s o he building in he uns eng hened con igu a ion, while he ha ched his og ams e u n he seismic pe o mance achie ed by he in oduc ion o e-CLT in he local na ow (g ey hin ha ch), local ex ended (black hin ha ch) and sp ead (black hick ha ch) con igu a ions. When seismic exci a ion ac s in he X-di ec ion (Figu e 16), he building in he uns eng hened con igu a ion is a om ul illing ei he he NC o he SD limi s a e and shows alues o λ/λ eq always much la ge han 2.0. The e-CLT in he local na ow con igu a ion inc eases he alues o λ/λ eq, hus esul ing in an ine ec i e in e en ion, which con i ms he conclusions o Sec ion 7.1. Consis en ly, e-CLT in bo h he sp ead and he local ex ended con igu a ions signi ican ly enhances he seismic pe o mance o all he conside ed cases and dec eases he alue o λ/λ eq o he uns eng hened buildings by mo e han 50%. Fu he mo e, he ull upg ading, ha is he alue o λ/λ eq igo ously lowe han one, a bo h SD and NC limi s a es, is achie ed o all he conside ed buildings when he e-CLT sys em is loca ed acco ding o he local ex ended con igu a ion. In he case o seismic exci a ion ac ing in he Y-di ec ion, he buildings in he uns eng hened con igu a ion ul ill o a e e y close o ul illing NC and SD limi s a e e i ica ions. Anyway, he in oduc ion o he e-CLT sys em leads in all he cases o a signi ican educ ion o λ/λ eq,up oalmos 46%wi h espec o he building in he uns eng hened con igu a ion. 8P inciples and Guidelines o a Design P ocedu e Based on he esul s o he expe imen al es s and nume ical in es iga ion, a design p ocedu e is p oposed in his Sec ion. The nonlinea s a ic me hod o analysis, which is a well-known 1791 o 1796 10969845, 2025, 6, Downloaded om h ps://onlinelib a y.wiley.com/doi/10.1002/eqe.4334 by Uni e si ã Di Ca ania, Wiley Online Lib a y on [03/10/2025]. See he Te ms and Condi ions (h ps://onlinelib a y.wiley.com/ e ms-and-condi ions) on Wiley Online Lib a y o ules o use; OA a icles a e go e ned by he applicable C ea i e Commons License Ba e ame X- ame models Y- ame models Pilo is ame X- ame models Y- ame models (a) (b) (c) Uns eng hened ame Sp ead e-CLT Local ex ended e-CLT Local na ow e-CLT 0 1 2 3 4 5 6 0% 1% 2% 3% 4% N 0 1 2 3 4 5 6 0.0 0.5 1.0 1.5 2.0 N / NC Columns 0 1 2 3 4 5 6 0.0 0.5 1.0 1.5 2.0 N / NC Beams 0 1 2 3 4 5 6 0% 1% 2% 3% 4% N 0 1 2 3 4 5 6 0.0 0.5 1.0 1.5 2.0 N / NC Columns 0 1 2 3 4 5 6 0.0 0.5 1.0 1.5 2.0 N / NC Beams 0 1 2 3 4 5 6 0% 1% 2% 3% 4% N 0 1 2 3 4 5 6 0.0 0.5 1.0 1.5 2.0 N / NC Columns 0 1 2 3 4 5 6 0.0 0.5 1.0 1.5 2.0 N / NC Beams 0 1 2 3 4 5 6 0% 1% 2% 3% 4% N 0 1 2 3 4 5 6 0.0 0.5 1.0 1.5 2.0 N / NC Columns 0 1 2 3 4 5 6 0.0 0.5 1.0 1.5 2.0 N / NC Beams θ Δ Δ Δθθ θθ θθ θθθθ θθ θθ θθ FIGURE 15 Dis ibu ion along he heigh a he a ainmen o NC limi s a e in he uns eng hened ame o (a) d i demand; (b) cho d o a ion D/C a io o columns; (c) cho d o a ion D/C a io o beams. p o essional ool also allowed by seismic codes, is used o he p edic ion o he seismic esponse. In pa icula , he p elimi- na y seismic assessmen o he uns eng hened building can be pe o med by pusho e analysis, which is able o es ima e he collapse mechanism and he co esponding dis ibu ion along he heigh o he d i demand. Hence, he loca ion o he e-CLT sys em can be de e mined. I he d i demand is concen a ed a one s o ey (o a ew s o eys), he e-CLT sys em ollows he local ex ended con igu a ion. Ins ead, i he d i demand is widesp ead among he s o eys, he e-CLT sys em can be loca ed acco ding o he sp ead con igu a ion. A he selec ed s o eys, he numbe and loca ion o CLT panels depend on a chi ec u al ea u es o he açade, pa icula ly he numbe o spans wi hou la ge openings. A his s age o he design p ocedu e, he ac i a ion o ce o he dampe s is assumed equal o a easonable alue, o example, ha o he expe imen al es , and he s i ness o CLT panels is assumed in ini e. Hence, a second pusho e analysis is pe o med o assess he seismic esponse o he RC ame wi h he e- CLT sys ems so a designed. Gi en a a ge alue o PGA, he co esponding seismic demand o he s eng hened building is de e mined by nonlinea s a ic me hods o analysis (e.g., Capaci y spec um me hod o N2 me hod). I he a ge limi s a e has been o e come, he ac i a ion o ce o he dampe has o be inc eased, so ha he la e al s eng h o he s eng hened building inc eases in u n. E en ually, he pusho e analysis can be i e a i ely epea ed un il he s eng hened building sa is ies he a ge limi s a e. A e he ac i a ion o ce o he dampe has been designed, he size o he CLT panel and he s oke o he dampe can be de e mined o ul ill he d i demand a he a ge limi s a e. Speci ically, o ensu e ha he dampe s ully ac i a e and 1792 o 1796 Ea hquake Enginee ing & S uc u al Dynamics,2025 10969845, 2025, 6, Downloaded om h ps://onlinelib a y.wiley.com/doi/10.1002/eqe.4334 by Uni e si ã Di Ca ania, Wiley Online Lib a y on [03/10/2025]. See he Te ms and Condi ions (h ps://onlinelib a y.wiley.com/ e ms-and-condi ions) on Wiley Online Lib a y o ules o use; OA a icles a e go e ned by he applicable C ea i e Commons License Ba e ame (wi hou in ills) In illed ame Pilo is ame e a s imilCNe a s imil DS Uns eng hened ame Sp ead e-CLT Local ex ended e-CLT Local na ow e-CLT 0 0.5 1 1.5 2 2.5 θ θ+V Col Beam / eq -66.7% -67.7% 0 0.5 1 1.5 2 2.5 θ θ+V Col Beam / eq -54.8% -47.4% 0 0.5 1 1.5 2 2.5 θ θ+V Col Beam / eq -69.2% -68.3% 0 0.5 1 1.5 2 2.5 θ θ+V Col Beam / eq -74.3% -64.0% 0 0.5 1 1.5 2 2.5 θ θ+V Col Beam / eq -58.4% -58.3% 0 0.5 1 1.5 2 2.5 θ θ+V Col Beam / eq -67.9% -66.4% FIGURE 16 Ra io o mean annual equency o exceedance o X- ame models. Ba e ame (wi hou in ills) In illed ame Pilo is ame NC limi s a e SD limi s a e Uns eng hened ame Sp ead e-CLT Local ex ended e-CLT Local na ow e-CLT 0 0.5 1 1.5 2 2.5 3 θ θ+V Col Beam λ / λ eq -28.6% -1.3% 0 0.5 1 1.5 2 2.5 3 θ θ+V Col Beam λ / λ eq -30.2% -43.5% 0 0.5 1 1.5 2 2.5 3 θ θ+VCol Beam λ / λ eq -1.8% -26.3% -33.7% 0 0.5 1 1.5 2 2.5 3 θ θ+V Col Beam λ / λ eq -5.2% -24.8% 0 0.5 1 1.5 2 2.5 3 θ θ+V Col Beam λ / λ eq -40.4% -45.9% 0 0.5 1 1.5 2 2.5 3 θ θ+V Col Beam λ / λ eq -10.0% -42.7% -31.1% FIGURE 17 Ra io o mean annual equency o exceedance o Y- ame models. dissipa e ene gy, he in-plane s i ness o he CLT panel mus be se la ge enough o minimize he de o ma ion o he panel i sel and u n he d i demand mainly in o sliding displacemen o he dampe s. Hence, he CLT panel can be sized so ha he ho izon al ela i e displacemen be ween i s bo om and op sides induced by he ac i a ion o ce o he dampe s is equal o a small a e o he maximum d i demand a he a ge limi s a e. In u n, he s oke o he dampe is se equal o he di e ence be ween he d i demand a he a ge limi s a e and he ela i e displacemen be ween op and bo om sides o he panel. Since he CLT panels a e expec ed o emain elas ic du ing he seismic ac ion, s eng h and s abili y o he panels ha e o be e i ied as well. 1793 o 1796 10969845, 2025, 6, Downloaded om h ps://onlinelib a y.wiley.com/doi/10.1002/eqe.4334 by Uni e si ã Di Ca ania, Wiley Online Lib a y on [03/10/2025]. See he Te ms and Condi ions (h ps://onlinelib a y.wiley.com/ e ms-and-condi ions) on Wiley Online Lib a y o ules o use; OA a icles a e go e ned by he applicable C ea i e Commons License Once he e-CLT sys em has been ully designed (loca ion, numbe , size o CLT panels, ac i a ion o ce, and s oke o he dampe s), he s uc u al esponse o he s eng hened building can be assessed by pusho e analysis. I he d i demand o he s eng hened building a he a ge limi s a e s ill o e comes he capaci y, he ac i a ion o ce and/o he size o he CLT panel can be inc eased. Wi h ega ds o he uppe connec ions, hese can be ealized by con en ional mechanical and/o chemical ancho s widely a ail- able in he ma ke . The connec ion can be designed as las s ep o he design p ocedu e, o sus ain (1) he e ical eac ion o ce due o he sel -weigh o he CLT panel, plus (2) he ho izon al eac ion o ce ha esis s he ac i a ion o ce o he dampe s, plus (3) he e ical eac ion o ce ha a ises o balance he momen caused by he eccen ici y be ween o ce ansmi ed by dampe s and ho izon al eac ion o ce o connec ions. These o ces a e ob ained om he h ee igid body equilib ium equa ions o he CLT panel. The s eng h o he connec ions can be e i ied acco ding o p esc ip ions a ailable in seismic codes. 9 Conclusions The pape p oposes he e-CLT sys em as a e o i sys em sui able o an in eg a ed ene gy and seismic app oach o upg ading exis ing RC- amed building s uc u es. The quasi-s a ic expe - imen al es s ca ied ou on wo ull-scale one-s o ey one-bay RC in illed ames, wi hou and wi h e-CLT, demons a ed ha he e o i sys em beha es unde cyclic loading as planned. In pa icula , du ing he loading p o ocol, (1) he ic ion dampe s, connec ing he CLT panel o he RC beam, success ully ac i a ed and slid, (2) he CLT panel and he ic ion dampe as ening sys em sus ained he o ce deli e ed by he dampe emaining in he elas ic ange o beha io , (3) he join ac ion o CLT panel and dampe p o ided he RC ame wi h addi ional la e al s i ness, la e al s eng h and, e en mo e, ene gy dissipa ion capaci y. The ac i a ion o he dampe occu ed o he alue o o ce assumed in design and i s cyclic esponse was s able, wi hou app eciable s eng h deg ada ion e en a e many cycles o loading and unloading. A he end o he es , he dampe did no exhibi e idence o yielding, local ins abili ies, o ano he kind o damage, hus con igu ing i as a damage- ee de ice ha does no need o be eplaced e en a e a s ong g ound mo ion. A nume ical model o he RC in illed ame equipped wi h e- CLT sys em has been de eloped in OpenSees en i onmen and calib a ed based on he esul s p o ided by he expe imen al es s. A p ocedu e based on a sub-componen app oach was es ablished o he calib a ion o he model. The p ocedu e led o he calib a ion o he pa ame e s con olling he esponse o he componen s o he RC ame +e-CLT in subsequen s eps. Fi s , he mechanical p ope ies assigned o he elemen s simula ing he RC membe s a e calib a ed assuming as a ge he cyclic esponse, unde la ge ampli ude displacemen s, o he uns eng hened RC in illed ame (wi hou e-CLT). In he second s ep, he pa ame e s o in ill panel a e calib a ed o i he expe i- men al esponse o he uns eng hened RC ame unde low and in e media e ampli ude displacemen s. In he hi d ( inal) s ep, he pa ame e s ha con ol he beha io o he CLT panel a e calib a ed based on he expe imen al esponse o he ame wi h e-CLT. The cyclic esponse p o ided by he nume ical models i s well he expe imen al esponse o bo h he uns eng hened and s eng hened RC ame o low, in e media e, and la ge displacemen cycles: elas ic beha io , c acking o in ill panels and subsequen la e al s eng h deg ada ion, esidual s eng h o RC ame +addi ional s eng h p o ided by e-CLT. Finally, unning he nume ical model equi es a low compu a ional bu den, which makes i sui able o model mul is o ey buildings and pe o m ex ensi e pa ame ic in es iga ions. A pa ame ic analysis was conduc ed on i e-s o ey ames wi h h ee di e en con igu a ions o in ills (ba e ame, wi h ull heigh in ills, and pilo is ame) and wo di e en ypes o global nonlinea beha io (d i and cho d o a ion demand concen a ed a ew s o eys o widesp ead along he heigh o he ame). The esul s allowed he quan i ica ion o he impac o he e-CLT sys em on he seismic esponse o ealis ic RC buildings and p o ided basic guidelines o he design o seismic upg ading by e-CLT. I was ound ha he e ec i eness o he con igu a ion o e-CLT is ela ed o he global nonlinea beha io o he RC building o be s eng hened. The local ex ended con igu a ion (e- CLT in oduced in he s o ey whe e he d i demand is maximum plus one s o ey below and one s o ey abo e) is sui able o upg ade RC amed buildings wi h a concen a ion o d i demand a a ew s o eys. Ins ead, i he d i demand is widesp ead along he heigh o he building, he sp ead con igu a ion (e-CLT in oduced a all s o eys) should be p e e ed. The pusho e analysis can p edic he ype o global nonlinea beha io o he building o be s eng hened and, he e o e, can be used o selec he mos app op ia e con igu a ion o e-CLT. The applica ion o e-CLT on amed s uc u es wi h concen a ion o demand led o an inc ease o PGA capaci y by up o 40% and educed he mean annual equency o exceedance o he conside ed limi s a es by up o 74%. When e-CLT was used o upg ade amed s uc u es wi h widesp ead seismic demand, he inc ease o PGA capaci y and he dec ease o mean annual equency o exceedance o he conside ed limi s a es we e up o 15% and 46%, espec i ely. The hi d con igu a ion o e o i , named local na ow con igu a ion (e-CLT sys ems s ic ly in oduced in he s o ey whe e he d i demand is maximum), esul ed o be he leas e ec i e and somewha de imen al. Indeed, on one side, he e-CLT sys em educed he seismic demand a he s o ey whe e i was in oduced bu , on he o he hand, shi ed he seismic demand o he adjacen s o eys, which expe ienced an ab up and signi ican inc ease in he d i demand. Hence, he e-CLT sys em esul ed o be a p omising seismic upg ading echnique and he pa ame ic analysis conduc ed on ealis ic buildings con i med his esul . In he end, based on he expe imen al and nume ical esul s, p inciples and s eps o design seismic upg ading by e-CLT a e p o ided. Acknowledgmen s This pape was ca ied ou in he amewo k o he “Ene gy and seismic a o dable eno a ion solu ions” (e-SAFE) p ojec , which has ecei ed unding om he Eu opean Union’s Ho izon 2020 esea ch and inno a ion p og am unde g an ag eemen No. 893135. Nei he he Execu i e Agency o Small-and-Medium-sized En e p ises (EASME) no he Eu opean Commission is in any way esponsible o any use ha may be made o he in o ma ion i con ains. 1794 o 1796 Ea hquake Enginee ing & S uc u al Dynamics,2025 10969845, 2025, 6, Downloaded om h ps://onlinelib a y.wiley.com/doi/10.1002/eqe.4334 by Uni e si ã Di Ca ania, Wiley Online Lib a y on [03/10/2025]. See he Te ms and Condi ions (h ps://onlinelib a y.wiley.com/ e ms-and-condi ions) on Wiley Online Lib a y o ules o use; OA a icles a e go e ned by he applicable C ea i e Commons License Da a A ailabili y S a emen The da a ha suppo he indings o his s udy a e a ailable om he co esponding au ho upon easonable eques . Re e ences 1. Buildings Pe o mance Ins i u e Eu ope (BPIE), Eu ope’s Buildings Unde he Mic oscope. A Coun y-by-Coun y Re iew o he Ene gy Pe o mance o Buildings (Buildings Pe o mance Ins i u e Eu ope, 2011). 2. A. Ma ini, P. Passoni, P. Ri a, P. Neg o, E. Romano, and F. 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