Experimental bond behaviour of GFRP and masonry bricks under impulsive loading

Expe imen al Bond Beha iou o GFRP and Mason y B icks unde Impulsi e Loading João M. Pe ei a a*, Paulo B. Lou enço a a ISISE, Depa men o Ci il Enginee ing, Uni e si y o Minho, Guima ães, Po ugal * Co esponding au ho : Depa men o Ci il Enginee ing, Uni e si y o Minho, Campus de Azu ém, Guima ães, 4800-058, Po ugal; email: jpe ei a@ci il.uminho.p Abs ac : Fib e Rein o ced Polyme s ha e become a popula ma e ial o s eng hening o mason y s uc u es. The pe o mance o his echnique is s ongly dependen on he bond be ween he FRP and he subs a e. Unde s anding he s ain a e e ec on hese ma e ials and s eng hening echniques is impo an o p ope design and p ope modelling o hese sys ems unde impac s o blas loads. This wo k aims o s udy he beha iou o he bond be ween GFRP and b ick a di e en s ain a es. A D op Weigh Impac Machine specially de eloped o pull-o es s (single shea es s) is used wi h di e en masses and di e en heigh s in oducing di e en de o ma ion a es. The s ain a e e ec on he ailu e mode, shea capaci y and e ec i e bond leng h is de e mined om he expe imen al esul s. Empi ical ela ions o dynamic inc ease ac o s (DIF) o hese ma e ials and echniques a e also p esen ed. Keywo ds: GFRP, Mason y, Impac , D op Weigh , S ain a e, DIF 1. In oduc ion Di e en loading condi ions migh lead o di e en s ain a es. Quasi-s a ic loading p oduces s ain a es o a ound 10-5 s-1, while impac s and blas loading p oduce s ain a es o well o e 100 s-1. When subjec ed o dynamic loading condi ions, ma e ials can ha e a much di e en beha iou when compa ed wi h hei s a ic beha iou (Meye s [1], Hie maie [2], Ngo e al [3], S a ogin and Ta aso [4]). Mos esea ch wo k on s uc u al esponse and damage unde impac and blas loading assumes ypically s a ic ma e ial p ope ies (Baylo e al [5], Mo eland e al [6]. In ecen yea s, composi es ma e ials such as ib e ein o ced polyme s (FRPs) ha e been inc easingly accep ed as e ec i e s eng hening echnique o ci il enginee ing s uc u es, pa icula ly in he case o ein o ced conc e e and mason y (Bakis e al [7], Pampazopoulou e al [8]). The e ec i eness o hese s eng hening echniques is s ongly dependable on he bond beha iou be ween he subs a e and he FRP ab ic. S udies on he in luence o he s ain a es on he bond beha iou o hese s eng hening sys ems a e sca ce and canno be ound easily in he li e a u e. Recen ly, Al- zubaidy e al [9] s udied he bond beha iou be ween CFRP ab ics and s eel pla e join s unde ensile loads wi h de o ma ion a es up o 5 m/s. This wo k concluded ha he use o mul i-laye ein o cemen was ine ec i e and he e ec i e bond leng h was no a ec ed by he de o ma ion a e. They ha e also shown ha he ailu e modes ob ained unde impulsi e egime we e simila o hose ob ained unde quasi-s a ic loading egime. Shi e al [10] s udied he bond beha iou be ween FRP lamina es and conc e e using double-lap shea bond es s up o s ain a es o 0.1 s-1. These au ho s showed ha o s ain a es o 0.1 s-1 he inc ease in he ul ima e shea s eng h is 1.3 imes he quasi- s a ic alue. These au ho s also concluded ha he in luence o he s ain a e is mo e p onounced o weake conc e e, and i is no signi ican ly a ec ed by he p ope ies o bonding adhesi es and he ype o FRP composi e. Simila conclusions we e ob ained by o he au ho s when s udying he bond beha iou o di e en FRP lamina es and conc e e (Li e al [11], Shen e al [12]). In o de o ully unde s and he in luence o he s ain a es in hese s eng hening sys ems and o de elop empi ical ela ions able o es ima e he esponse o hese ma e ials unde high s ain a es, i is necessa y o s udy he subs a e and he ab ic independen ly and he s eng hening sys ems i sel . Dynamic beha iou o common cons uc ion ma e ials such as conc e e (G o e e al [13]) o ein o cemen ba s (Mal a and Ross [14]) ha e been s udied in ecen yea s, being al eady in oduced in o some s anda ds (CEB-FIP [15], UFC 3-340- 02 [16]) in he o m o a dynamic inc ease ac o (DIF) which ep esen s he a io be ween he dynamic and s a ic p ope y. Howe e , e y limi ed s udies can be ound in he li e a u e o mason y ma e ials. Recen ly, Hao and Ta aso [17], Pe ei a e al [18], Lou enço and Pe ei a [19] and Asp one e al [20] s udied his e ec on mason y componen s (clay b ick, s one and mo a ) and mason y specimens. I was shown ha Dynamic Inc ease Fac o s (DIF) up o 2.54 and 2.17, we e ob ained o he comp essi e s eng h o clay b icks and mason y a a s ain a e o 200 s-1. Simila alues we e ob ained o he Young’s modulus. Rega ding he ensile beha iou o hese ma e ials, DIF up o 3.1 o he ensile s eng h o mo a join s we e ob ained a a s ain a e o 1 s-1 and DIF up o 3 we e ob ained o he ensile s eng h o he es ed s ones. Composi e ma e ials we e also s udied unde high s ain a e e ec s in ecen yea s and some o hese s udies (Gu usideswa and Velmu ugan [21], Okoli [22] and Co ei a and Peixinho [23]) show ha a s ain a es o 500 s-1, DIF up o 2 can be ob ained o Glass Fib e Rein o ced Polyme (GFRP) s ips. In his pape , an expe imen al campaign on he in luence o he s ain/de o ma ion a e on he mechanical bond beha iou o GFRP-b ick sys ems is desc ibed. The es s we e pe o med wi h a D op Weigh owe de eloped speci ically o his pu pose. This equipmen is able o pe o m single-lap shea bond es s unde impulsi e egime using a d op hamme being eleases a a speci ic heigh . Bo h ma e ials a e s udied independen ly p e iously – clay b ick and GFRP s ips – and in his pape he bond beha iou o he s eng hening sys ems is s udied unde high de o ma ion a es. 2. Clay b ick unde high s ain a es S udies on clay b icks unde high s ain a es we e pe o med p e iously and we e p esen ed in de ail by Pe ei a e al [18] and Lou enço and Pe ei a [19]. These b icks we e o he same ma e ial used in he single-lap shea bond es s p esen ed in he nex sec ion. A d op weigh impac machine was used o pe o m he comp ession es s a di e en s ain a es. Two di e en ways we e used o measu e he de o ma ion p o ile: a) a Fas Cam ideo came a using a ge s in he specimen and ideo acking so wa e; b) s ain gauges in all aces o he specimen Pe ei a e al [18], Lou enço and Pe ei a [19]. The esul s ob ained by Pe ei a e al [18] and Lou enço and Pe ei a [19] can be seen in Figu e 1. I is clea ha hese ma e ial show s ain a e dependency. A a s ain a e o 200 /s Dynamic Inc ease Fac o s o 2.54, 2.43, 1.30 and 5.95 we e epo ed o he comp essi e s eng h, Young’s modulus, s ain a peak s eng h and comp essi e ac u e ene gy, espec i ely. The ob ained esul s a e in ag eemen wi h o he s udies (Hao and Ta aso [17]). The empi ical equa ions able o es ima e hese mechanical p ope ies o s ain a es up o 200 /s, as ollows (Pe ei a e al [18], Lou enço and Pe ei a [19]): Fo he comp essi e s eng h:  (   )  =   1                                                    1  − 5     <   󰇗 < 2     0 , 3344 ln (  󰇗 ) + 0 . 7682                    2     <   󰇗 < 200                     (1) Fo he Young’s modulus:  (  )  =   1                                                    1  − 5     <   󰇗 < 2     0 , 3105 ln (  󰇗 ) + 0 . 7848                    2     <   󰇗 < 200                     (2) Fo he s ain a peak s eng h:  (   )  =   1                                                    1  − 5     <   󰇗 < 2     0 , 0673 ln (  󰇗 ) + 0 . 9533                    2     <   󰇗 < 200                     (3) Fo he comp essi e ac u e ene gy:  (   )  =   1                                                    1  − 5     <   󰇗 < 5     1 , 3419 ln (  󰇗 ) − 1 . 1597                    5     <   󰇗 < 200                     (4) 3. GFRP unde high s ain a es Co eia and Peixinho [23] es ed GFRP s ips unde di e en s ain a es. The es ed GFRP s ips we e o he same ma e ial used o he single-lap shea bond es s p esen ed in he nex sec ion. Two di e en es ing equipmen s we e used allowing wo di e en s ain a e le els. A Se o-hyd aulic es ing machine (Ins on, 25 kN capaci y) was used o lowe loading speed (0.02 mm/s), while a high-speed se o-hyd aulic es ing machine (Zwick, 20 kN capaci y) was used o loading speed o app oxima ely 6000 mm/s. Rega ding he high-speed es ing equipmen , his includes a slack- esponse b acke , allowing he pull- od o accele a e be o e commencing o load he specimen; he in e nal measu ing sys ems o he equipmen we e used, including piezo-elec ic load cell and e ical displacemen ansduce o he s oke o he pull- od. The nominal s ain a es ob ained in he es s was calcula ed by di iding he linea speed o he es ing machine by he pa allel leng h o he specimen. The esul s ob ained by Co eia and Peixinho [23] can be seen in Figu e 2 and he s ain a es a ied om 0.655 /s o 446 /s. I is clea ha his ma e ial shows s ain a e dependency. The obse ed dispe sion in he expe imen al esul s is somehow expec ed conside ing he impulsi e na u e o he expe imen s and he handmade building p ocess o he specimens. In he highe s ain a e es s a highe ensile s eng h was ob ained, a e aging 1862 MPa, while o he lowe s ain a e es s only a ensile s eng h o 1030 MPa (a e age) was ob ained. This ep esen s a Dynamic Inc ease Fac o o abou 1.8 o s ain a es o abou 500 /s. These esul s a e in ag eemen wi h p e ious s udies ega ding simila ma e ials and simila es s (Gu usideswa and Velmu ugan [21], Okoli [22]). 4. Bond beha iou o GFRP-b ick unde high s ain a es In his wo k i is in ended o s udy he e ec o high s ain a es in he bond beha iou o GFRP-b ick s eng hening sys ems. The main objec i e is o de elop empi ical ela ions, based on expe imen al esul s, able o ela e he maximum bond capaci y wi h he slip a e. These empi ical ela ions a e based on he DIF (Dynamic Inc ease Fac o ). Du ing he es s bo h he load p o ile and slip p o ile a e necessa y. The load p o ile ela es o he quasi-s a ic e e ence allowing calcula ing he DIF (Eq. 5) and he slip p o ile allows calcula ing he slip a e as he g adien o he slip- ime cu e. Simila p ocedu es we e used p e iously (Hao and Ta aso [17], Pe ei a e al [18], Lou enço and Pe ei a [19]).  =   (  )   (  −  ) ,  (  ) 󰇗 (5) Di e en es se ups ha e been used o cha ac e ize he bond beha iou o conc e e-FRP sys ems, some being al eady implemen ed in in e na ional s anda ds such as he Ame ican Conc e e Ins i u e (ACI 440). In he case o mason y-FRP sys ems, due o he lack o s anda d es se ups, simila se ups ha e been used o s udy his phenomenon (Ghiassi [24]). Single-lap shea bond es s consis in imposing a load in he FRP s ip, along i s longi udinal di ec ion (Figu e 3a). Usually, he composi e is applied o one o he aces o he subs a e, lea ing enough FRP s ip ee o be connec ed o he ac ua o s. Ghiassi [24] s udied he bond beha iou o GFRP-b ick sys ems using single-lap shea bond es s unde quasi-s a ic condi ions. These es s we e pe o med wi h simila specimens o hose s udied in his wo k, using he same ma e ials. These es s unde quasi-s a ic egime we e pe o med using a se o-hyd aulic ac ua o wi h a 50 kN maximum capaci y. The es specimens we e placed in a s eel suppo s uc u e (Figu e 3b), specially designed o his pu pose. The load p o ile was measu ed using a load cell and he slip was measu ed using se e al LVDTs placed along he ein o cemen (Figu e 3c). Fi e es s we e pe o med (Figu e 4) a e aging a maximum load o 9.22 kN (Figu e 4a) and a maximum slip o 1.43 mm (Figu e 4b). These es s we e pe o med unde a slip a e o a ound 10-5 mm/ms. These esul s a e used in his wo k as he quasi-s a ic e e ence o he DIF calcula ion. In o de o s udy he bond beha iou o hese sys ems unde high s ain a es, a new es se up was de eloped based on he d op weigh concep . This new es ing equipmen and he ob ained esul s a e p esen ed in he ollowing sec ions. 4.1. Tes ing equipmen A d op weigh owe speci ically de eloped o single-lap shea bond es s was used o he dynamic es ing (Figu e 5a). This owe allows a d op heigh up o 3 me e s and a d op weigh wi h a minimum o 14 kg. The load p o ile was measu ed a he ee end o he GFRP s ip using a load cell speci ically o dynamic applica ions – VETEK VZ101BH (Figu e 5b). This load cell is connec ed o a Na ional Ins umen s Acquisi ion Sys em. This acquisi ion sys em is composed o a SCXI-1000DC chassis (Figu e 5c), a SCXI-1600 da a acquisi ion and con ol ca d o PC connec ion and a gene ic inpu module SCXI-1520 wi h a SCXI- 1314 moun . The SCXI-1600 limi s he sampling speed o 200 kS/s (200 samples pe millisecond), which was ound o be enough e en a a la e s age whe e 4 channels whe e used a he same ime, allowing an acquisi ion equency o 50 kHz pe channel. The de o ma ion beha iou o he specimen was measu ed in wo di e en ways. Fi s , a Fas Cam ideo came a was used. I is a PHOTRON Fas Cam APX – RS (Figu e 5d) wi h a maximum ame a e o 250 000 ames pe second. This equipmen allowed he isualiza ion o he es in slow mo ion and he measu ing o he slip. This slip measu emen was possible using a ge s in he specimen a a speci ic loca ion and pe o ming a acking sweep o hose a ge s in he ideo (Figu e 6a). To pe o m he acking sweep, he TEMA T acking So wa e ( : 3.1-005) was used. Wi h he ela i e posi ion o he a ge s, he slip a each ins ance was calcula ed. The second me hodology used o ob ain he de o ma ion beha iou was using s ain gauges. The s ain gauges used we e BFLA-5-8-3L (Figu e 6b) om TML and we e he same used in he quasi- s a ic es ing pe o med by Ghiassi [24]. 4.2. Specimens p epa a ion The applica ion o GFRP ein o cemen usually in ol es wo s eps: a) p epa a ion o he subs a e su ace and b) applica ion o he ein o cemen . The p epa a ion o he subs a e su ace, in his case clay b ick, should be aken wi h special a en ion in o de o ob ain a good bond be ween he wo ma e ials (Ju an es [25]). The b icks used in his s udy, 200x100x55 mm b icks, we e simila o hose al eady s udied and cha ac e ized p e iously by Pe ei a e al [18], Lou enço and Pe ei a [19] and Ghiassi [24] unde di e en condi ions. Ini ially he b icks we e g inded (app oxima ely 7 mm) in he ace whe e he ein o cemen was applied, in o de o imp o e he mechanical and chemical bond capaci y o he applica ion (Ghiassi [24]). A e his ini ial ea men he b icks we e washed and placed in an o en a 100 ºC o a pe iod o 24 hou s. A e his pe iod he specimens we e emo ed om he o en and cleaned wi h comp essed ai , making su e ha he su ace was kep clea o any small pa icles. Wi h he su ace p epa ed, he ein o cemen applica ion can be ini ia ed. Fi s ly, a p ime is applied, only in he bonded a ea ( he es o he su ace is p o ec ed wi h duc - ape) (Figu e 7a). The applied p ime was a MAPEWARP PRIMER 1 and he bonded a ea can be seen in Figu e 7b. The GFRP ein o cemen was composed o glass ib e MAPEWRAP UNI-AX and MAPEWRAP 31 epoxy. In o de o apply he ein o cemen , he p ocedu e was he ollowing: a) Cu he glass ib es wi h he equi ed dimensions (400x50 mm) and place wo me allic shee s in one end o he ib es o b acing (Figu e 7b); b) In he b ick su ace a laye o epoxy is applied using a b ush; c) In he ib es a laye o epoxy is also applied and he ib es a e placed in he co ec posi ion. In o de o ha e ull con ac be ween he ib es and he su ace a oam oll is used; Cons uc ion – S a e-o - he-a Re iew. 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S eng hening and ein o cemen o ein o ced conc e e s uc u es using CFRP composi es. PhD- hesis, Uni e si y o Po o, Po ugal, 1999. [26] Oli ei a DV, Basilio I, Lou enço PB. Expe imen al bond beha iou o FRP shee s glued on b ick mason y. Jou nal o Composi e o Cons uc ion 2010; 14(3):312-323. [27] Lou enço PB, Ra sanjani SH, Pe ei a JM. A cons i u i e h ee-dimensional in e ace model o mason y walls subjec ed o high s ain a es. The wel h In e na ional Con e ence on Compu a ional S uc u es Technology, I aly 2014. Table cap ions: Table 1 – Impac es s on GFRP-b ick specimens. Table 2 – Compa ison be ween ideo equipmen and s ain gauges esul s. Figu e cap ions: Figu e 1 – DIFs o clay b ick mechanical p ope ies (Pe ei a e al [18], Lou enço and Pe ei a [19]). Figu e 2 – GFRP s ips ensile s eng h a di e en s ain a es by Co eia and Peixinho[23]. Figu e 3 – Single-lap shea bond es s: a) es schema ic; b) s eel suppo s uc u e; c) LVDT posi ioning (Ghiassi [24]). Figu e 4 – GFRP-b ick quasi-s a ic esul s: a) o ce- ime p o ile; b) slip- ime p o ile (Ghiassi [24]). Figu e 5 – Tes se up: a) d op weigh owe se up; b) load cell; c) acquisi ion sys em; d) ideo equipmen . (1) Pho on ideo equipmen ; (2) D op weigh owe ; (3) load cell; (4) hamme ; (5) specimen; (6) acquisi ion sys ems; (7) PC; (8) S ain gauges. Figu e 6 – De o ma ion acquisi ion: a) a ge s o ideo acking; b) s ain gauges. Figu e 7 – Specimens: a) specimen p epa a ion; b) specimen geome y; c) inal aspec o he specimens. Figu e 8 – Examples o impac es esul s: a) o ce- ime p o ile; b) slip- ime p o ile; c) o ce-slip p o ile. Figu e 9 – Examples o ailu e modes: a) o al de achmen o he ab ic; b) pa ial de achmen o he ab ic. Figu e 10 – Dynamic inc ease ac o o shea capaci y a di e en slip a es. Figu e 11 – Examples o s ain gauges signal acquisi ion: a) o al de achmen o he ab ic; b) pa ial de achmen o he ab ic. Figu e 12 – Example o slip- ime p o ile ob ained om s ain gauges. Figu e 13 – Dynamic inc ease ac o o shea capaci y o GFRP-b ick a di e en slip a es. Table 1 – Impac es s on GFRP-b ick specimens. Specimen D op heigh (cm) PHOTRON Load cell DIF Failu e mode (De achmen leng h) Maximum slip (mm) Slip a e (mm/ms) Maximum o ce (kN) Quasi - s a ic [19] 1.49 2E-5 9.22 1.00 To al I37 11 0.19 0.06 12.65 1.37 Pa ial 5cm I41 15 0.32 0.07 14.97 1.62 Pa ial 5cm I7 16 0.17 0.08 14.66 1.59 Pa ial 7cm I25 14 0.14 0.09 13.16 1.43 Pa ial 5cm I1 17 0.29 0.10 14.94 1.62 Pa ial 6cm I20 16 0.45 0.13 14,85 1.61 Pa ial 6cm I40 19 0.49 0.15 15.96 1.50 Pa ial 7cm I26 21 0.41 0.25 16.81 1.82 To al I3 18 0.53 0.44 17.66 1.92 Pa ial 5cm I31 25 0.76 0.57 16.65 1.81 To al I46 30 0.84 0.74 17.15 1.86 To al I44 31 0.87 0.77 17.64 1.91 To al I36 28 0.58 0.83 15.64 1.70 To al I30 37 1.00 0.87 17.29 1.88 To al I49 36 1.28 1.32 18.73 2.03 To al Table 2 – Compa ison be ween ideo equipmen and s ain gauges esul s. S ain Gauges PHOTRON Specimen Max Slip (mm) Slip a e (mm/ms) S ain a e (/s) Max Slip (mm) Slip a e (mm/ms) Fo ce (kN) DIF I41 0.31 0.10 2.6 0.32 0.07 14.97 1.62 I40 0.36 0.23 2.5 0.49 0.15 15.96 1.73 I46 0.86 0.70 3.7 0.84 0.74 17.15 1.86 I30 0.56 0.98 7.4 1.00 0.87 17.29 1.88 Figu e 1 – DIFs o clay b ick mechanical p ope ies (Pe ei a e al [18], Lou enço and Pe ei a [19]). Figu e 2 – GFRP s ips ensile s eng h a di e en s ain a es by Co eia and Peixinho[23]. a) c) b) Figu e 3 – Single-lap shea bond es s: a) es schema ic; b) s eel suppo s uc u e; c) LVDT posi ioning (Ghiassi [24]). a) b) c) Figu e 4 – GFRP-b ick quasi-s a ic esul s: a) o ce- ime p o ile; b) slip- ime p o ile (Ghiassi [24]). a) b) Figu e 11 – Examples o s ain gauges signal acquisi ion: a) o al de achmen o he ab ic; b) pa ial de achmen o he ab ic. Figu e 12 – Example o slip- ime p o ile ob ained om s ain gauges. Figu e 13 – Dynamic inc ease ac o o shea capaci y o GFRP-b ick a di e en slip a es.