INNOVATIVE BRIDGE SYSTEM OF ULTRA HIGH PERFORMANCE FIBRE REINFORCED CONCRETE: EXPERIMENTS, MODELING AND DESIGN

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1 INNOVATIVE BRIDGE SYSTEM OF ULTRA HIGH PERFORMANCE FIBRE REINFORCED CONCRETE: EXPERIMENTS, MODELING AND DESIGN L. G. Sorlli 1,2, P. Fanning 1, F. Toutlmond 2 1 Univrsity Collg of Dublin, Irland 2 Laboratoir Cntral ds Ponts t Chaussés, Franc Abstract Ultra High Prformanc Fibr Rinforcd Concrt (UHPFRC) is a nw gnration of fibr rinforcd cmntitious composit with nhancd mchanical and durability proprty. Th us of UHPFRC in prfabricatd bridg dck dsign was th focus of rcnt rsarch program, which has includd xprimntal tsting at th Laboratoir Cntral ds Ponts t Chaussés (within th Frnch national projct MIKTI) and numrical modling at Univrsity Collg Dublin. Th bridg dck systm drivs from th projct dsignd by th CETE d Lyon Enginring offic. It is a light two way slabs of only 14 cm in quivalnt thicknss, pr strssd in th transvrs dirction, and supportd on longitudinal stl bams. A longitudinal post-tnsioning systm and concrt joints btwn adjacnt moduls provid continuity of load transfr in th bridg span dirction. Th dtaild dsign of this innovativ structur has bn carrid out by applying nwly drawn rcommndations on UHPFRC. Th global rspons to loading and th fatigu rsistanc to global / local loading rprsnt major faturs of th rsarch invstigation. A 3D damag modl has bn implmntd in a finit lmnt mthod to prdict th mchanical bhavior of th pr-strssd moduls during th full-scal xprimnts, including th contact problm btwn th post-tnsiond sgmnts. Sorlli, UHPC Bridg, 1/10

2 1. Introduction Sinc th nd of th 18th cntury, whn mtallic bridgs first bgan to b built, up to th scond half of th 20th cntury, bridg dsign has always bn in th procss of constant and rapid dvlopmnt. Thr wr tims whn th dvlopmnt was basically du to th typs of structurs that appard in modrn bridgs, and thn thr wr othr tims whn it was du to nw matrials. To this dvlopmnt of structurs and matrials w must also add th thortical knowldg of structurs, and procdurs of analysis for dtrmining th safty of bridgs that cam about during th sam priod. In th prsnt priod, promising nw matrials hav appard, spcially mor durabl and with a high proprty to wight ratio: ultra-high prformanc fibr-rinforcd concrt, and fibrrinforcd polymrs. Adaptd dsigns should b dvlopd which fruitfully apply ths nhancd proprtis towards mor fficint and durabl bridg structurs. Ultra High Prformanc Fibr Rinforcd Concrt (UHPFRC) rprsnts a tchnological brakthrough by offring a charactristic comprssiv strngth comprisd btwn 150 to 250 MPa along with a matrix tnsil strngth in xcss of 7 MPa, and outstanding durability charactristics [1, 2]. UHPFRC matrials ar charactrizd by a highly compact cmntitious matrix, th absnc of capillary pors, and th mandatory us of fibr rinforcmnt in th constructiv applications in ordr to nsur nonbrittlnss failur. This tchnology allows dsignrs to build structural lmnts without passiv rinforcmnts and to combin lightnss and xtrm durability in innovativ solutions, as alrady vidnt from th first UHPFRC bridgs [3]. Light wight dcks mad of UHPFRC in composit bridgs ar an altrnativ to convntional stl orthotropic dcks, which ar known to suffr fatigu dgradation, and can xtnd th rang of applications of stl-concrt composit bridgs which nowadays ar ffctivly usd for bridg span btwn 50 m and 100 m. Morovr, th bnfits includ rducd rction costs, rducd construction tims and rsourc savings. By pursuing this trnd of lightnss and durability, th projct considrd in this papr [4] aims to favor innovativ stl-concrt composit applications, which fits th objctivs of MIKTI Frnch R&D national projct. Th UHPFRC bridg dck consists of a thin ribbd slab which is supportd by twin longitudinal stl bams. Th gnral dsign, th dtrmination of rquird pr-strssing tndons, as wll as th dtailing wr basd on AFGC Rcommndations spcific for UHPFRC [2] in complmnt to th Frnch Bridg dsign cods for composit and pr-strssd concrt bridgs. In comparison with classical stl-concrt composit dcks, th UHPFRC solution is vry fficint du to th high comprssion strngth and low crp cofficint, spcially in th cas of hattratd UHPFRC sgmnts. Howvr, som aspcts of th projct appar critical ithr du to limitd xprimntal validation of th dsign provisions or du to th spcific gomtry of th structur. Mor prcisly, 2D slab mchanisms hav not bn xtnsivly documntd for such matrials; most currnt applications hav bn basd on bam structurs [1]. Sinc th capacity of withstanding concntratd loading is crucial in this projct, a bttr undrstanding of th 3D forc distribution within th Sorlli, UHPC Bridg, 2/10

3 ribbd structur is also dsirabl. An xtnsiv xprimntal program on th static and dynamic bhavior of (quasi) full scal bridg moduls has bn carrid out at LCPC Structurs laboratory within th fram of MIKTI [5]. Structural tsts ar complmntd by matrial charactrization, so that dsign ruls and hypothss can b assssd. Th first phas of th tsts prsntd hr concrns strss distribution du to longitudinal prstrssing, and th structural bhavior undr flxural fatigu loading. Th prliminary rsults of th numrical analyss supporting th projct ar also prsntd. 2. Projct outlin 2.1 Dsign of th bridg dck As a pilot projct a road bridg with 3 spans of m, 9 m wid (two 3.5 m wid lans + 1 m sid strips + two 1 m-wid sidwalks) was chosn for this study [4]. Th dsign of transvrs ribs and pr-tnsioning was first dtrmind considring th local and transvrs bnding at srvicability limit stat. Pr-strssing is ralizd by 2 rctilinar T15S tndons along th vrtical axis of ach rib. Th uppr cabls ar anchord from on nd to th othr nd; th lowr cabls ar shathd along th corbls and on supports. In ach transvrs vrtical rib two pr-strssing T15S tndons giv a pr-strssing forc (aftr losss) of about 180 kn ach. Thn th pr-cast moduls ar assmbld by post-tnsioning bfor bing connctd to th longitudinal stl girdrs. Lngth of succssiv sgmnts was limitd to 2.50 m for possibl truck dlivry. Th currnt ribs spacing is 0.6 m from axis to axis in both dirctions. Th slab thicknss is only 0.05 m, whil th total thicknss with th ribs is 0.38 m. Th avrag ffctiv thicknss is about 0.14 m. Th minimum 0.05 m thicknss is critically dtrmind by punching and local bnding rsistanc undr whl loads (100 kn). In th vrification, th 0.09 m currnt thicknss of paving layrs is accountd for, with favorabl load distribution within th bituminous concrt layrs. Th avrag wight of th slab is about 3.9 kn/m². (a) (b) Figur 1. (a) A pr-strssd bridg modul and (b) two pr-strssd bridg moduls tid togthr by post-tnsioning tndons. Sorlli, UHPC Bridg, 3/10

4 Longitudinal global bnding dtrmins th stl girdrs hight and flang thicknss. Morovr, upon th pirs, tnsil strsss in th slabs must b limitd, which is nsurd both by 1 m support lowring and longitudinal pr-strssing. For hat-tratd UHPFRC sgmnts, th crp cofficint is takn as 0.2 and only 14 cabls 7T15S ar rquird to nsur that th maximum bnding tnsil strss is limitd to 15 MPa at th Srvicability Limit Stat (SLS) undr rar load combination, whil for untratd UHPFRC, a consrvativ valu of th crp cofficint qual to 0.8 lads to 17 rquird cabls. Ths cabls could b locatd in btwn all longitudinal ribs, xcpt upon th flangs of th stl girdrs. Honycombs ovr th stl flangs ar filld with fluid grout of class C80/95 whr rgularly spacd studs ar ncasd. Diffrnt typs of intr-modul connction wr considrd, including a cold stitch lmnt within th thin part of th slab, a rinforcd concrt stitch slab in-btwn succssiv transvrs ribs, and local scrwing of transvrs nd half-ribs. Finally, accounting for fild xprinc of in-plac UHPFRC kying [3], a cold joint using castin-plac UHPFRC with shar kys in-btwn transvrs nd half-ribs appars as an adaptd solution. An important dtail of th projct was to dsign th anchoring dtails of th safty barrir as simply as possibl taking bnfit of th dtailing provisions covrd by prsnt tchnical documnts and agrmnts [6]. A longitudinal continuous rinforcd concrt nd bam is to b cast in plac and connctd to th nd ribs of th slab in ordr to diffus th horizontal forc corrsponding to th shock of a truck into th adjacnt sgmnts and to incras th torsion rigidity of th dck for withstanding th inducd momnt (whil th vrtical supports of th barrir ar fixd by typ P pr strssd anchors through a thickr nxt to last rib [6]). 2.2 Exprimntal validation For xprimntal invstigation [5], two quasi-full-scal bridg moduls with a rducd width of 6.1 m and a full-scal lngth of 2.5 m and thicknss wr cast in industrial conditions using two rprsntativ industrial UHPFRC matrials ( Ductal FM and Cracm) with mass dnsity of 2500 and 2800 kg/m3, rspctivly. Thanks to th slf compacting charactr of UHPFRC, no vibration was rquird in th casting phas, whil a gntl viscous flow of th frsh mix allowd as uniform as possibl fibr distribution. Charactristic roughnss of th uppr surfacs is about on millimtr. Aftr transport to th laboratory (Fig. 1a) and positioning of th two sgmnts (Fig. 1b), th kyd cold joint (Fig. 2a) was filld and a longitudinal post-tnsioning was applid using 20 T13 strands. Ralistic vrtical support for a safty barrir was fixd aftr concrting th RC sid bam (Fig. 2b). Bsids load snsors masuring th tnsion in th 20 cabls and LVDT monitoring th joint opning, 18 longitudinal strain gaugs wr locatd to rcord strains in th middl of th sgmnts and clos to th transvrs joint. Thr-dimnsional distribution and volution of comprssiv strsss du to th longitudinal post-tnsioning can thus b Sorlli, UHPC Bridg, 4/10

5 analyzd. Morovr during th bnding tsts, both transvrs and longitudinal dflctions of th spcimn ar monitord by mans of 50 masuring channls. Th two assmbld bridg moduls, with total dimnsions of 6.1 x 5 m, can b usd for many aspcts of th rquird xprimntal validation which consists of th following stps [5]: transvrs bnding with a 4.2 m transvrs span and a loading schm rprsntativ of th Eurocod fatigu axl (two 0.4 x 0.4 m 100 kn-whls at a transvrs distanc of 1.2 m) and rar srvic traffic load (two 0.4 x 0.4 m 150 kn whls at a transvrs distanc of 1.2 m); this stp is spcially dtaild in th prsnt papr; local bnding on a singl honycomb, ithr prviously damagd by fatigu loading or not, undr th sam 0.4 x 0.4 m simulatd whls ; transvrs pushing on th post of th safty barrir typ P, in ordr to chck that fus anchors yild undr a standard 200 kn m momnt bfor any damag of th dck (Fig. 16); th connction of th ribbd slab to th longitudinal girdrs: a standard push-out tst shall prov that th shar capacity of th connction is controlld by th studs yilding, whil th groutd honycombs nsur a satisfactory bond with th UHPFRC slab; th nd anchor blocks for th longitudinal pr-strssing, sinc for ths lmnts, possibly rducd dimnsions and absnc of confining classical stl rinforcmnt, prmittd by UHPFRC proprtis, hav to b approvd aftr a succssful standard tsting procss, as alrady don at th Shrbrook footbridg projct for monostrands [7] or for Millau tollgat 12T15S anchor blocks [1]. In all th bnding tsts, th application of th whl loads is mad by 0.4 x 0.4 x 0.04m stl plats through a 9 cm thick polymr matrial ( Ertalon) block in ordr to rprsnt th distribution inducd by th bituminous concrt paving layrs. Point ball hings ar providd undr th actuator and at th nd of th load distribution bam, in ordr to account for th possibl spcimn flxibility. Complmntary tsts for matrial charactrization with spcimns cast from th sam batch as th ribbd sgmnts hav bn prformd. Young s modulus, comprssiv strngth and flxural bhavior has bn assssd using rcommndd tst procdurs [2]. Post-tnsioning cabls Pr-tnsioning cabls Rinforcd concrt bam Bridg dck (a) (b) Figur 2. (a) Joint btwn two bridg moduls; (b) typ P safty barrir. Sorlli, UHPC Bridg, 5/10

6 3. UHPFRC dsign concpt A ky qustion whn using ultra-high prformanc concrt in building is th availability of dsign cods and charactrization mthods. Unlik convntional rinforcd concrt, th tnsil proprtis of UHPFRC can no longr b disrgardd in th structural dsign mthods. Guidlins for UHPFRC matrials hav bn rcntly drawn by th workgroup of th Frnch branch of RILEM & IABSE [2], daling with matrial prformanc and charactrization tsts, structural dsign, and durability aspcts, aiming to mt this nd. A charactristic lngth (lc) is dfind to transform a strss-crack width σ(w) law into a constitutiv strss-strain σ(ε) law in ordr to modl th strain localization occurring with a strain softning matrial with a continuum mchanics modl. According to th AFGC rcommndations, th charactristic lngth (lc) is assumd as 2/3 of th sction hight (h). Th tnsil part of th σ-ε rlationship can b dducd from xprimntal bnding tsts by invrs analysis [8] including a safty factor K = on th charactristic valus (which taks into account fibr orintation ffcts which may diffr within th structural lmnt from th tstd spcimn). Th tnsil strss-strain rlationship for th ultimat limit stat (ULS) can b dducd by considring an additional safty factor γ bf (qual to 1.05 or 1.3 in th cas of accidntal or fundamntal load combinations, rspctivly), th comprssiv strngth rducd by 15% in cas of sustaind loading, and th maximum comprssiv strain of 0.3 %. Th simplifid strssstrain distribution rlationship is illustratd in Figur 3 (whr w = 0.3 mm 0.3 and w1% = 0.01 H ) for both SLS and ULS limit stats. σ σbc σbc Eij platau only for SLU σ bc = 0.6 fcj σ1% = σ( w1% ) K σbt = σ( w0.3) K Srvicability Limit Stat (SLS) ε= ftj Eij ε = f E + w l ε = f E + w l 0.3 tj ij 0,3 c 1% tj ij 1% c Ultimat Limit Stat (ULS) 3 εlim ε1% ε0.3 ε σbcu = 0.85 f cj ϑγ b εbc εu ε σ1% ftj = ftj γ εu = 310 ε = bf ftj Eij ftj σbt σ1% = σ( w1% ) K γbf ε0.3 = ftj ( γbf Eij ) + w0,3 lc σbtu = σ( w0.3) K γ bf 1% ε = ftj ( γbf Eij ) + w1% lc Figur 3. Strss-strain rlation assumd by th AFGC rcommndations [2]. Sorlli, UHPC Bridg, 6/10

7 4. Numrical analysis of th UHPFRC bridg modl A simplifid damag modl with a constitutiv rlation proprly dsignd for UHPFRC has bn implmntd to hav a first insight into th 3D structural bhavior. As first approximation, a scalar damag variabl was usd to rproduc an isotropic damag volution by calibrating th tnsil strngth dgradation on th dsign guidlins (Fig. 3a). Fractur nrgy (G f ) was assumd as a matrial paramtr of UHPFRC in ordr to guarant msh objctivity undr crack volution (i.., strain localization). A shar rtntion factor was also includd to allow comprssiv strut mchanisms, othrwis nglctd by isotropic damag modls. 4.1 Simplifid damag modl In th isotropic damag modl, th constitutiv rlationship btwn strss and strain is assumd according to th classical form σ = (1 ω) D ε = (1 ω) σ (1) whr σ is th strss tnsor, ε is th strain tnsor, D is th lastic and isotropic matrial stiffnss matrix, σ is th ffctiv strss, and is ω a scalar damag variabl. For th undamagd matrial,ω is st to zro and th rspons is linar lastic. As th matrial is dformd, th initiation and propagation of micro dfcts dcrass th stiffnss, which is rprsntd by th growth of th damag variablω. For ω = 1, th stiffnss vanishs, which corrsponds to a compltly damagd matrial. A loading g(, ε κ) = ε( ε) κ ε ( ε) function g is introducd in th strain spac, whr is a crtain scalar masur of th strain lvl, calld th quivalnt strain, whil κ is an intrnal variabl which controls th damag volution. Damag volvs whn th currnt quivalnt strain rachs th boundary of th lastic domain, i.., loading function g = 0. Th link btwn th variabl κ to th damag variabl ω is basd on th UHPFRC spcific dsign rcommndations [2]. Sinc both th damag ω and th intrnal variabl κ grow monotonically, it is admissibl to postulat th volution law in th (xplicit) form ω( κ) = σ σ σ 0 if κ ε if κ ε (2) ε whr is th limit lastic strain undr uni-axial tnsion. Th modl is simply xtndd to th 3-D by adopting an quivalnt strain corrsponding to th Rankin critrion of maximum principal strss Sorlli, UHPC Bridg, 7/10

8 ε = D : ε = D : ε (3) E E I I = 1 Figur 4a shows th 1-D strss-strain rlation adoptd in th damag modl with th corrsponding damag growth. In this analysis, th xprimntal rsults of four point bnding tsts with small UHPFRC (Ductal ) bams (70*70*280 mm) hav bn mployd [8] to calibrat th paramtrs. Figur 4b shows th fitting btwn th numrical curv and th xprimntal curvs in trms of quivalnt strss vs. dflction aftr th modl paramtr calibration. σ 50 ω 1 ω2 Ε ε (1 ω2) Ε ε ε1 ε2 ε Equivalnt Strss σ [MPa] Exprimntal curvs Numrical curv ε1 ε2 ε Dflction [mm] Figur 4. (a) Schmatic strss-strain rlation and corrsponding damag volution; (b) Comparison of th xprimntal and numrical rsponss undr four point bnding tst in trms of quivalnt strss vs. maximum dflction. 4.2 Prliminary rsults Th modl accounts for th non linar damag du to tnsil micro-cracking as wll as for th contact problm of th ky btwn two adjacnt UHPFRC moduls. Indd, th collaps mchanism may involv possibl opning in th joint connction btwn th two UHPFRC moduls longitudinally post tnsiond by xtrnal cabls. Th matrial bhavior of th tndons is simply assumd to b prfctly lastic-plastic with a yild strngth of 1860 MPa. Th finit lmnt msh consists of nods, linar solid lmnts, and 1520 rbar lmnts. Morovr, 7454 surfac contact lmnts wr usd to modl th joint opning, which in favor of safty is assumd to follow a hard contact law (i.. no friction and cohsion). Th numrical modl prdicts a maximum comprssiv strss of about 5 MPa in th transvrsal dirction of th joint aftr applying th forcs corrsponding to pr-strssing and post- tnsionin, which appars to b in good accordanc with th dsign assumptions basd on a simplifid two way bam modl [2]. Sorlli, UHPC Bridg, 8/10

9 Prliminary finit lmnt analyss hav focusd on th partial clamping (or rotation) of th ribs around th loadd honycombs loadd by a two-whl axl with an intrmdiat countr-flxur. Th prdictd structural bhavior undr global bnding of th bridg moduls is shown in Figur 5 ithr with a 2 whls load in th proximity of th joint (load 9 9) or with a 2 whls load far from th joint (load 10 10). Th structural bhavior has shown to b ductil thanks to th nhancd tnsil toughnss of th UHPC, which is xhibitd by multipl distributd cracks in th ribs. In th cas of th 2 whls load positiond nar th joint lin (load 9 9), th joint opning dos not appar as a critical issu for th global ductility of th structur. At collaps, th maximum strss in th transvrsal tndons is about 1100 MPa, whil th cntral longitudinal tndons ar yilding Load Load Load [kn] limit of linarity Dflction [mm] Figur 5. Global bhavior of th bridg spcimn loadd by 2-whls load in th proximity of th joint and far from th joint. 5. Prliminary conclusions and ongoing rsarch A promising application of UHPFRC to a vry light 2D-ribbd slab with nhancd structural durability has bn dvlopd by applying th spcific UHPFRC dsign rcommndations as wll as considring all rlvant dsign loading cass and aspcts. Exprimntal validations for critical faturs of th projct ar in progrss, and satisfactory fatigu bhavior undr bnding has bn obtaind. Prliminary finit lmnt analyss hav bn prsntd in support of th upcoming xprimntal rsults, Sorlli, UHPC Bridg, 9/10

10 with furthr intntion to optimiz th safty dsign of UHPFRC in thin ribbd structurs. Th dvlopmnt of a micro-mchanics basd modl in ordr to optimiz th structural potntial of UHPFRC will b th focus of th ongoing rsarch [9]. Acknowldgmnts Th projct prsntd was undrtakn within th framwork of Frnch National Projct MIKTI, supportd by th Frnch Ministry for Equipmnt (Résau Géni Civil t Urbain). Thirry Krtz, Tchnical Managr of this National Projct, is gratfully acknowldgd for th launching of this rsarch and innovativ dsign, as wll as Jacqus Rsplndino and Sébastin Boutill (CETE d Lyon) for th dtaild dsign study. Th projct is mostly indbtd to th participation of Eiffag TP and Lafarg. Th first author is gratful to th Mari Curi program within th FP6 Europan Community. Finally, participation of th tchnical tam of LCPC structurs laboratory has bn ssntial for obtaining th xprimntal data. 6. Rfrncs [1] Hajar Z., Lcointr D., Ptitjan J., Rsplndino J., Simon A. (2004) Ultra high prformanc concrts: First Rcommndations and xampls of applications, fib Symposium 2004 : Concrt structurs: th challng of crativity, Avignon, Franc, April, pp [2] AFGC-SETRA, Ultra High Prformanc Fibr-Rinforcd Concrts, Intrim Rcommndations, AFGC Publication, Franc, January 2002 (152 p.). [3] Simon A., Hajar Z., Lcointr D., Ptitjan J. (2002) Ralization of two roadbridgs with Ultra-High Prformanc Fibr Rinforcd Concrt, 6th Int. Symposium on High Strngth / High Prformanc Concrt, Lipzig, Grmany, jun, pp [4] Rsplndino J., Boutill S. (2003) PN MIKTI. Etud d un pont mixt à dall BFUP nrvuré, CETE d Lyon, Tchnical rport, sptmbr (46 p., in Frnch). [5] Toutlmond F. t al. (2005) Innovativ dsign of Ultra-high Prformanc Fibr rinforcd Concrt ribbd slab : xprimntal validation and prliminary dtaild analyss, 7th Int. Symp. on Utilization of High Strngth / High Prformanc Concrt, Washington D.C. (USA), jun, ACI SP-228, H. Russl d., SP , pp [6] Barrièrs d sécurité pour la rtnu ds poids lourds, barrièrs d nivau H2 ou H3, collction du guid tchniqu GC, SETRA, 1999, 161 p. (in Frnch). [7] Ganz H. R., Adlin R. (1997) Mini-anchorags for Ractiv Powdr Concrt, fib Symposium 1997, Lisbon, Portugal. [8] Chanvillard G., Rigaud S. (2003) Complt Charactrisation Of Tnsil Proprtis Of Ductal UHPFRC According To Th Frnch Rcommndations, HPFRCC-4 Symp, Ann Arbor, Michigan, jun. [9] Chuang E., Ulm F. J. (2002) A two-phas composit modl for high-prformanc cmntitious composits and structurs, J. Eng. Mch., ASCE, 128 (12), Sorlli, UHPC Bridg, 10/10