EXPERIMENTAL AND NUMERICAL ANALYSIS OF TEXTILE REINFORCED CEMENT COMPOSITES AS TENSILE REINFORCEMENT IN CONCRETE SHELLS.

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1 EXPERIMENTAL AND NUMERICAL ANALYSIS OF TEXTILE REINFORCED CEMENT COMPOSITES AS TENSILE REINFORCEMENT IN CONCRETE SHELLS. Evy Verwimp 1,2, Tine Tysmns 1, Svetln Verruggen 1 nd Mrijke Mollert 2, 1 Deprtment of Mechnics of Mterils nd Constructions (MeMC), Vrije Universiteit Brussel. 2 Deprtment of Architecturl Engineering (ARCH), Vrije Universiteit Brussel. Astrct: Textile reinforced cement (TRC) composites re incresingly studied s mteril for structurl sty-in-plce formwork for concrete structures, ecuse elements with low thickness nd reltive high mechnicl cpcities cn e produced. Current envisioned formwork pplictions - ems, sls, columns - do not exploit nother dvntge of TRC s, nmely tht the flexile textile reinforcement llows n exclusive freedom of form. With TRC, freeform moulds re esily prefricted to serve s structurl formwork for shells, fcilitting the construction on site. This pper investigtes the contriution of TRC formwork to the lodering ehviour of concrete shells. Tests re performed on TRC reinforced sphericl shell of 2m spn nd 200mm height, sujected to distriuted lod. The experiment is compred to numericl simultion performed in the finite element softwre Aqus. The test shows promising results for TRC s reinforcement s the TRC lyer contriutes significntly to the concrete section. The finite element model shows similr ehviour s monitored during the test. This model llows to further develop the design methods for concrete shells with sty-in-plce TRC formwork nd reinforcement. With the use of TRC composites, more efficient nd fster construction method for concrete shells is just round the corner. INTRODUCTION The construction of concrete shells is one of the chllenges in civil engineering in western regions. Firstly, the current formwork methods for concrete shells, i.e. timer moulds [1] nd fom locks [2], re lour intensive nd/or mteril wsting. Currently, reserch is performed on lterntive formwork methods like flexile frics [3], [4] pneumtic formwork [5] or hyrid cle-net nd fric formwork [6]. These systems re flexile enough to esily relize curved surfces, however they still experience reltively lrge deformtions when csting concrete. Secondly, the plcing of the rigid trditionl steel reinforcement limits the curvture, is lour intensive nd therefore increses the cost. Recently, lterntive reinforcement methods sed on fire textiles re investigted in concrete shells, nmely fire nd textile reinforced cements (FRC / TRC), like demonstrted in [7] nd [8]. However, these lterntive methods do not solve the formwork prolems discussed efore. Considering these issues, we developed n inventive formwork solution, which exploits the properties of textile reinforced cement (TRC) composites. These TRC composites re composed of continuous fire system, textile, which is impregnted with cementitious mtrix. While this cementitious mtrix is wet, the impregnted textile remins flexile (Figure 1) nd cn e shped onto ny (reusle) mould, like e.g. pneumtic formwork (Figure 1). The low weight of the thin TRC lyer compred to the concrete, which is normlly directly cst onto these moulds, prevents lrge deformtions nd thus ensures finl shpe closely pproximting the initilly designed shpe. 53

When the concrete is hrdened the sty-in-plce formwork gets n dditionl structurl function, i.e. s (prtil) tensile reinforcement of the finl concrete structure.

2 Figure 1: While the cementitious mtrix is wet, the textile remins flexile (), nd cn e shped on e.g. (reusle) pneumtic formwork (). After hrdening of the cement, thin composite is otined which is rigid enough to withstnd the csting of the concrete. When the concrete is hrdened the sty-in-plce formwork gets n dditionl structurl function, i.e. s (prtil) tensile reinforcement of the finl concrete structure. The structurl cpcity of TRC sty-in-plce formwork ws lredy demonstrted for em elements in [9] nd [10]. This pper presents the experimentl nd numericl nlysis of TRC reinforced concrete dome. Firstly, the plin concrete dome, reinforced y the sty-in-plce TRC formwork, is sujected to point lod. Secondly, the experiment is numericlly simulted within the finite element softwre Aqus. Finlly, the experiment nd the model re compred nd conclusions re drwn. EXPERIMENTAL ANALYSIS OF A TRC REINFORCED DOME Mterils nd experimentl setup During the test, TRC composite consisting of textile mt of 300g/m² rndom E-glss fires impregnted with Inorgnic Phosphte Cement - IPC (18 % fire volume frction) - [11] is used in comintion with concrete. Their mechnicl properties re found in tle 1. Tle 1: Properties of the concrete nd TRC composite used for the experiment. Properties concrete Compressive chrcteristic strength Properties TRC 50 MP Compressive chrcteristic strength 80 MP Tensile chrcteristic strength 4.1 MP Tensile chrcteristic strength 40 MP Young modulus 35.7 GP Young modulus stge 1 18 GP Young modulus stge 3 4 GP The mechnicl ehviour of glss fire textile reinforced IPC (GFTR-IPC) differs significntly in compression nd tension ecuse of the rittle mtrix. In compression, the composite is ssumed to e liner elstic until filure [12], ut in tension, it shows lredy nonliner ehviour t low tensile stresses - round 7 MP - (Figure 2) due to the low tensile filure strin of the mtrix reltive to tht of the fires. 54

Figure 2: GFTR-IPC is liner in compression nd nonliner in tension [13] The geometry nd experimentl setup of the concrete dome re shown in Figure 3.

To restrict the horizontl displcement the edge is encircled with wooden pnels.

Figure 4 shows the production process of the TRC reinforced concrete sphericl dome. The glss fire mt is plced in fom mould () nd impregnted with cementitious mtrix (IPC) ().

3 Figure 2: GFTR-IPC is liner in compression nd nonliner in tension [13] The geometry nd experimentl setup of the concrete dome re shown in Figure 3. The concrete dome hs spn of 2 m, height of 200 mm, concrete thickness of 20 mm nd it is reinforced with 5 mm thick TRC. The shell is sujected to point lod (ϕ100 mm) on the top. To restrict the horizontl displcement the edge is encircled with wooden pnels. Figure 3: The sphericl dome is sujected to point lod, strins re mesured y strin guges t five different loctions. Figure 4 shows the production process of the TRC reinforced concrete sphericl dome. The glss fire mt is plced in fom mould () nd impregnted with cementitious mtrix (IPC) (). To otin TRC formwork of 5 mm, ten lyers of mts re needed. After hrdening, the composite is turned nd strong nd stiff formwork is otined (c). A rougher contct surfce - y dding lyer of smll stones - is creted to ssure the ond (d). Ruer rulers re plced on the formwork to control the concrete thickness during csting (e nd f). The shell is tested fter 31 dys. c 55

d e f Figure 4: Production process of the dome with mixed TRC-concrete section. The experiment is monitored y strin guges nd Digitl Imge Correltion (DIC).

Strin guges re plced on oth the TRC lyer (so in etween the TRC formwork nd concrete efore, lue lines Figure 3) nd on top of the concrete (red lines Figure 3), oth in meridionl nd hoop direction.

during testing of the TRC-concrete shell The verticl deformtion of the top centre, mesured y the lod cell, of the TRC reinforced concrete dome is shown in Figure 5. The curve is liner up to 17.

4 d e f Figure 4: Production process of the dome with mixed TRC-concrete section. The experiment is monitored y strin guges nd Digitl Imge Correltion (DIC). For the DIC, two res of pproximtely 400 x 400 mm (light lue squres in Figure 3) were monitored y two 3D cmer systems. Strin guges re plced on oth the TRC lyer (so in etween the TRC formwork nd concrete efore, lue lines Figure 3) nd on top of the concrete (red lines Figure 3), oth in meridionl nd hoop direction. The nomenclture of the strin guges is defined y three prmeters: 1 M: meridionl direction 2 Position (see Figure 3) 3 C: on concrete lyer H : hoop direction S : 45 direction R: on TRC lyer Results during testing of the TRC-concrete shell The verticl deformtion of the top centre, mesured y the lod cell, of the TRC reinforced concrete dome is shown in Figure 5. The curve is liner up to 17.5 kn, where first drop occurs. In n initil ssumption this could indicte tht the shell remins intct up to this drop, where fter crcks initite within the concrete mteril until the ultimte lod of 18.7 kn. Finlly, the lod decreses to constnt vlue of 2 kn, where the test ws stopped. Figure 5: Lod progress shows two dropping points (t 17.5 kn nd t 18.7 kn). Figure 6 shows the shell fter testing. During the experiment visile crcks initited from the top long rdil lines, exctly where the ruer rulers were plced while csting. Herefter, circulr crck initited round the point lod. When the constnt lod of 2 kn is reched, no other visile crcks were formed. After the test, the concrete lyer proved to e 56

The strins monitored y the strin guges re shown in Figure 7,, c nd d.

5 completely deonded from the TRC shell, indicting the loss of composite ction etween oth (Figure 6). Figure 6: Crcks formed long the rdil lines were ruers were plced () nd deonding of TRC nd concrete (). The strins monitored y the strin guges re shown in Figure 7,, c nd d. c d Figure 7: Strin guges show similr trends s long s no crcks re initited. Figure 7 shows the meridionl strins on positions 2 nd 4, on qurter spn of the dome. The strins on the TRC lyer (M2R nd M4R) re oth in compression nd hve the sme 57

6 curve up to 13 kn. From here on the xisymmetric ehviour clerly vnishes, indicting the initition of dmge, proly y concrete crcks. This phenomenon ws however not oserved in Figure 5, where the initil constnt stiffness is retined until lod of 17.5 kn. A possile explntion for this phenomenon cn e found in the crck ridging cpcity of the TRC sty-in-plce formwork, s is lredy oserved for TRC externl em reinforcement [14] nd [15]. Surprisingly, the strins on the concrete lyer (M2C nd M4C) do not exhiit similr ehviour, not even efore the initition of the crcks. Considering the similr evolution of M2C to M2R nd M4R, it cn e ssumed tht mesurement error occurred for M4C. The hoop strins on position 2 nd 4 re shown in Figure 7. Until the first crck, the strins on the TRC lyer (H2R nd H4R) re in tension nd ehve similr. The concrete lyer lso ppers in tension (H2C), however it shows rekpoint t 8 kn, which is gin not noticed in lod-deflection ehviour (Figure 5). The tension in the hoop direction explins the first concrete crcks, induced long the rdil lines. Comprison of Figure 7 nd indictes the expected ixil stress stte of the shell, s the meridionl strins re in compression nd the hoop strins re in tension. Figure 7c shows the strins on the centre top of the TRC lyer. S3R nd M3R ehve opposite nd H3R shows no similrities. However, similr ehviour is expected on the top in n xisymmetric geometry. This discrepncy cn e explined y imperfections: i.e. lod not perfectly in the middle, strin guges not perfectly plced t the centre, etc. However these strins remin limited in comprison with the ones otined t qurter spn. The meridionl nd hoop strins ner the edge (position 5) re shown on Figure 7d. The meridionl strins on oth lyers (M5C nd M5R) re in tension until 10 kn, where fter they switch to compression. For the hoop strins on oth lyers (H5C nd H5R) the opposite phenomenon occurs. However up to 10 kn this oservtion is opposite to the expecttions, which re similr to Figure 7 nd, nmely meridionl strins in compression nd hoop strins in tension. This cn possily e explined y the lterl supports of the shell; the zone ner the edge moves up due to the centrl loding. This effect leds to tension in the rdil direction nd compression in the hoop direction until the first concrete crck. Up to concrete crcking the strins re s expected. Here fter the xisymmetry is lost nd the ehviour ecomes unpredictle. The initition of crcks is however well noticed in the strin curves y severl rekpoints t 10 nd 13 kn, indicting tht the crcks re proly initited t lower lod thn 17.5 kn, which ws initilly ssumed sed on the constnt stiffness in the lod-deflection curve. The tensile strins in the TRC remin limited up to shell filure nd do not exceed 400 με, which flls within the first liner prt of the TRC stress-strin digrm (Figure 2). Thus, no stresses higher thn 7 MP re otined, which is only 17.5 % of the tensile strength of the TRC (40 MP). The DIC oservtions show qulittive results concerning the displcements over the surfce of the shell. The verticl displcement of severl points during loding is shown in Figure 8. All points follow the sme trend, nmely downwrd displcement followed y sudden upwrd displcement. The upwrd movement indictes the deonding of concrete nd TRC, induced y the crcks in the concrete. These rekpoints pproximtely correspond to the two min drops in the lod-deflection curve t 17.5 kn (400s) nd 18.7 kn (800s) (Figure 5). 58

7 Figure 8: Displcement of the concrete lyer is first downwrds nd then upwrd NUMERICAL ANALYSIS OF A TRC REINFORCED DOME The experiment is simulted using the finite element (FE) softwre Aqus nd the experimentl results re compred with the numericl ones. Model uild-up The numericl model of the dome is uilt up in two prts, which re plced on ech other s two lyers; the TRC lyer is modelled s shell prt with continuous shell section nd the concrete lyer is modelled s solid prt with continuous solid section. For the TRC lyer two types of liner elements re used, nmely the 3-node S3 nd the 4- node S4R elements, which re elements for douly curved thin or thick shells with reduced integrtion. For the concrete lyer, the 8-node C3D8R elements re used, which re liner ricks with reduced integrtion. Mesh convergence ws checked for this geometry; in the end, elements with seed of pproximtely 30 mm were used, chosen s compromise etween ccurcy nd clcultion time. The mteril ehviour for oth the concrete nd TRC lyer re modelled with the Concrete Dmged Plsticity (CDP) model, which is inuilt in Aqus. Woznik proved in [13] tht the CDP model predicts the TRC mteril s ehviour the est. As the concrete is cst on the TRC lyer, the ond etween the two mteril lyers is not perfect nd is therefore tken into ccount in the numericl model. The ond is modelled y the inuilt cohesive ehviour in Aqus, which hs the possiility to include the dmge of the ond. The prmeters needed for modelling the ond re descried in [16]. The dome s edge is re- 59

8 stricted in three directions. The model is loded y its self-weight nd point lod, which grdully increses to 20 kn, t the centre top with dimeter of 100 mm. Numericl results The comprison of the mesured strins during the experiment with the numericlly clculted strins re shown in Figure 9 nd. The numericl results re represented y dotted line. The numericl model predicts generl trend well, nmely the ixil ehviour of the shell, which mens the meridionl strins re in compression nd the hoop strins in tension. Moreover, the order of mgnitude is lso well predicted. However, individully some differences re oserved. Figure 9: Comprison of the experimentl nd numericl results shows similr trend nd order of mgnitude is well predicted. Figure 9 shows the meridionl nd hoop strins on position 2, t qurter spn of the dome. For oth strins the generl trend nd order of mgnitude is well predicted, ut the progress of the experimentl nd numericl curves re different. The hoop strins on the TRC lyer re lrger thn those on the concrete lyer, which proves opposite in the experiment. Figure 9 compres the numericl nd experimentl meridionl nd hoop strins ner the edge, on position 5. Up to the concrete crcking the numericl simultion fils to predict the strin distriution, s the inverted strins re oserved in the experiment. This devition cn e ttriuted to locl phenomen ner the edges of the shell (s discussed ove), which re not tken into ccount in the numericl simultion. Due to the presence of nodes, in the numericl model ner the lod ppliction zone, i.e. top centre, which encounter stress concentrtions, these results re not represented. The comprison of the numericl nd experimentl verticl deformtion of the top centre is shown in Figure 10. The numericl clculted deformtion corresponds well to the first prt of the lod-deflection curve of the experiment, however fter 17.5 kn the numericl curve linerly continues nd shows no dropping point s ws oserved during the experiment. 60

Figure 10: Numericl clculted deformtion of the top centre corresponds well to the first prt of the loddeflection curve of the experiment The numericl model did not predict deonding of the two mteril

9 Figure 10: Numericl clculted deformtion of the top centre corresponds well to the first prt of the loddeflection curve of the experiment The numericl model did not predict deonding of the two mteril lyers, s the contct sher stress never exceeded the llowle sher stress of 2.8 MP (Figure 11) [16]. However, note tht the ond model is very complex nd currently is intensively studied y Woznik [16], this is possily lso the reson ecuse of the discrepncy. Figure 11: Contct sher stress on the contct surfce is smller thn the llowle sher stress oth in the x- direction () nd y-direction (). CONCLUSIONS This pper studied the experimentl nd numericl nlysis of TRC reinforced concrete dome. The dome - 2 m spn, 0.2 m height nd 20 mm thick - is reinforced with 5 mm thick TRC nd sujected to point lod on the top. The results of the experiment showed interesting results concerning oth the production nd the ehviour during loding. Firstly, visile crcks formed long rdil lines during the test exctly where the ruer rulers were locted while csting the concrete. Oviously, this phenomenon must e tken into ccount nd every djcent segment of concrete must e csted directly next to ech other. In this wy good dhesion nd homogenous ehviour of the concrete shell is ssured. Secondly, deonding etween the concrete nd TRC lyer occurred sooner thn expected. However, ll mesurements clerly indicte composite ction etween the TRC nd concrete efore the crck initition. As longs s deonding does not occur, the forces cn e trnsferred through the contct surfce nd the TRC form work works s tensile reinforcement. The experiment ws simulted with the finite element softwre Aqus. In generl the numericl model predicts the sme trends nd order of mgnitude for the mesured strins, except for those ner the edge, where exctly the opposite phenomenon occurs. The verticl deformtion of the top centre is lso reltively well predicted up to deonding of oth constituents. However, some notle differences re seen etween the experimentl nd numericl nlysis. These discrepncies cn e explined y the experiment which filed 61

10 much fster thn expected. The erly deonding of the two lyers ws not foreseen nd lso not predicted y the numericl model. For this reson, it is difficult to vlidte the numericl model, thus the production nd experiment must e improved. Simultneously, the numericl model needs further development to exclude the stress concentrtions ner the lod ppliction zone nd to mke sure the model corresponds to the experiment. These interesting nd promising results encourge the further reserch on TRC reinforced concrete shells, where fter setup meliortion nd model verifiction, other shell geometries cn e exmined. REFERENCES [1] A. Weilndt, Rolex Lerning Center in Lusnne: From Conceptul Design to Execution, Proceedings of the Interntionl Assocition for Shell nd Sptil Structures, Vlenci, Spin, 2009, [2] Nedcm, Spencer Dock Bridge Dulin (Mrch 2014). URL [3] N. Cuerg, T. Tysmns, S. Adrienssens, J. Wstiels, M. Mollert, B. Belkssem, Shell Elements of Textile Reinforced Concrete Using Fric Formwork: A Cse Study, Advnces in Structurl Engineering 15 (4) (2012) [4] M. West, Thin-shell concrete from fric moulds (Mrch 2014). URL [5] P. vn Hennik, L. Wgemns, Revivl of pneumtic formwork for the construction of monolithic (irregulr) shells, Proceedings of the Interntionl Assocition for Shell nd Sptil Structures, Montpellier, Frnce, [6] D. Veenendl, P. Block, Design process for prototype concrete shells using hyrid cle net nd fric formwork, Engineering Structures 75 (2014) [7] T. Tysmns, S. Adrienssens, J. Wstiels, O. Remy, Textile reinforced cemencomposites for the design of very thin sddle shells: A cse study, Proceedings of the 18th Interntionl Conference on Composite Mterils, Jeju Islnd, South Kore, [8] D. Ehlig, F. Schlditz, M. Frenzel, M. Curch, Textile concrete n overview of executed projects, Beton- und Sthletonu 107 (2012) [9] S. Verruggen, O. Remy, J. Wstiels, T. Tysmns, Sty-in-Plce Formwork of TRC Designed s Sher Reinforcement for Concrete Bems, Advnces in Mterils Science nd Engineering (2013). [10] S. De Sutter, O. Remy, T. Tysmns, J. Wstiels, Development nd experimentl vlidtion of lightweight sty-in-plce composite formwork for concrete ems, Construction nd Building Mterils 63 (2014) [11] EP B1, Inorgnic Resin Compositions, Their Preprtion And Use Thereof. [12] H. Cuypers, Anlysis nd Design of Sndwich Pnels with Brittle Mtrix Composite Fces for Building Applictions, Doctorl Thesis, Vrije Universiteit Brussel, Brussel, Belgium, [13] M. Woznik, T. Tysmns nd J. Vntomme, Finite element modelling of glss fire reinforced composites with Inorgnic Phosphte Cement mtrix: Comprison of inuilt Aqus concrete models. Proceedings of the 19th Interntionl Conference on Composite Mterils, Montrél, Cnd, [14] S. Verruggen, T. Tysmns nd J. Wstiels, TRC or CFRP strengthening for reinforced concrete ems: An experimentl study of the crcking ehviour. Eng Struct, Vol.77, p.49-56; [15] S. Verruggen, Reinforcement of concrete ems in ending with externlly onded textile reinforced cementitious composites. PhD thesis, Vrije Universiteit Brussel; 2014 [16] M. Woznik, T. Tysmns, J. Vntomme nd S. De Sutter, Numericl simultion of the ond ehviour of high-performnce fire-reinforced cement composites during the doule-lp sher test. Proceedings of Interntionl RILEM Conference on Strin Hrdening Cementitious Composites (SHCC3), Dordrecht, Netherlnds,

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