Fiber Reinforced Concrete, Chalmers research - an exposé

Transcription

1 Seminar Fibre reinforced concrete and durability: Fiber Reinforced Concrete, Chalmer reearch - an expoé

2 From micro to macro - or mall-cale to large-cale

3 Chalmer reearch (PhD & licentiate): Carlo Gil Berrocal. Corroion of teel bar in fibre reinforced concrete: corroion mechanim and tructural performance. PhD thei, 217. Jona Ektröm. Concrete Structure Subjected to Blat Loading: Fracture due to dynamic repone. Licentiate Thei, 215. (PhD defence November 1 th ) Natalie William Portal. Uability of Textile Reinforced Concrete: Structural Performance, Durability and Sutainability. PhD thei, 215. David Fall. Steel Fibre in Reinforced Concrete Structure of Complex Shape: Structural Behaviour and Deign Perpective. PhD thei, 214. Ulrika Nytröm. Modelling of Concrete Structure Subjected to Blat and Fragment Loading. PhD thei, 213. Anette Janon. Effect of Steel Fibre on Cracking in Reinforced Concrete. PhD thei, 211. Peter Harryon. Indutrial Bridge Engineering Structural development for more efficient bridge contruction. PhD thei, 28. Ingemar Löfgren. Fibre-reinforced Concrete for Indutrial Contruction a fracture mechanic approach to material teting and tructural analyi. PhD thei, 25.

4 Fibre-reinforced concrete σ l l w f ct w Fibre contribution FRC Reidual tenile tre Concrete l w.5 mm w c.3 mm w c = l f / 2 Schematic decription of the tenile behaviour When fibre-reinforcement i added an additional material property have to be taken into account, i.e. the σ-w relationhip, or the fibre bridging or the reidual tenile trength.

5 Material teting approch The approach i baed on three tep: 1) Material teting (fracture mechanic baed) 2) Inver analyi σ-w relationhip 3) Adjutment of σ-w relationhip conidering the number of fibre in the pecimen

6 Material teting UTT groove (cat) cube pecimen piton with Three-Point contant Bending cro- Tet head diplacement load cell WST tarter notch (cut-in) teel loading device with roller bearing wedging device Direct method RILEM TC 162-TDF Clip gauge linear upport F p Indirect method

7 Mateial teting & tructural analyi Material teting Invere analyi Sectional analyi Structural analyi

8 Analytical model non-linear hinge d x R δ Stre, σ c, [MPa] Strain, ε c, [1-3 ] Concrete Stre-train relationhip σ (ε) f ct E c ε σ ( w) f ct 1 b 2 w 1 Concrete Stre-crack opening relationhip Moment a 1 a 2 w c w σ Reinforcement Stre-train relationhip ε N M a w M N h / 2 h / 2 a ε ε c (y) θ * θ / 2 d1 y y σ σc (ε,y) σc (w,y) Curvature Non-linear hinge model

9 Comparion: experiment / analyi Load Lat [kn] Load Lat [kn] [kn] S1:2 7-15/7 (Mix 1) FE 'bond-lip' FE 'embedded reinforcement' Analytik Experiment Midpan Nedböjning deflection [mm] [mm] S4:2 7-15/7 (Mix 4) FE 'embedded reinforcement' FE 'bond-lip' Analytik Experiment Midpan Nedböjning deflection [mm] [mm] Q Exp. [kn] Q Exp. [kn] FE analye -2 R 2 =.982 Correlation:,99 Analytical Bi-linear -2-4 Q Model [kn] -4-6 R 2 =.882 Correlation:,94 Q Model [kn]

10 Comparion conventional v. FRC Lat Load [kn] FRC: 59 kg/m 3 & φ7-15 Plain: φ Midpan Nedböjning deflection [mm] [mm] Load-deflection rel. FRC: 39 kg/m 3 & φ7-15 Plain: φ Moment [knm] M φ7-15 Conventional φ1-15 crack opening M FRC 6 kg/m 3 φ7-15 FRC 4 kg/m 3 Comparion: crack opening Crack opening [mm]

11 Effect of fibre on the cracking proce Crack u N N N Force N Impoed deformation N Impoed deformation N cr Tenion tiffening N cr N cr Stadium II (neglecting tenion tiffening) u Large reinforcement ratio u Small reinforcement ratio When cracking i caued by an external applied force the crack width depend on the applied force. If cracking i caued by an impoed deformation the force in the member depend on the actual tiffne and the crack width on the number of crack formed. However, mot code do not ditinguih between thee two cae. u

12 Force induced cracking N cr N cr Crack l t,max r,max l t,max Crack New crack A c Can be ued to derive the crack pacing expreion A (+ effect of concrete cover & pacing) φ σ fb τ bm σ ct f ct Force acting on the concrete: τ π φ(.5 ) + σ A bm r,max fb c = f ct A c l t,max.5 r,max Stre introduced to concrete through bond, σ c (x) Fibre bridging tre, σ fb (w) σ ct f ct Total concrete tre, σ ct (x,w) Poible location of new crack

13 Force induced cracking = ct fb f f k σ 1 eff r k k k c k, ,max ρ φ + = According to EC 2 the crack pacing can be calculated uing the following expreion: + = eff f m r k k k k c k, , ρ φ Thi can be modified to take into account the effect of fibre (the reidual tenile trength ) by introducing a new coefficient (k 5 ): ( ) m c m m m r w,,, ε ε = and the crack width can be calculated a: ( ) ( ) ( ) ( ) ( ) eff ef eff ct f t t m c m E f k k k,,,, ρ α ρ σ ε ε + + = e.g. DAfStb (UA SFB N 171):

14 Experiment LVDT Q Q A h=225 d=2 Roller C L 18 2 ELEVATION A Roller b=15 Reinf. Tet erie without and with fibre reinforcement (type Dramix RC-65/35 from Bekaert) and amount of conventional reinforcement. A-A Fibre doage Reinforcement Beam Serie [vol-%] and [kg/m 3 ] Number and diameter [mm] [No.] 1 V f = % ( kg/m 3 ) 3 φ V f =.5 % (39.3 kg/m 3 ) 3 φ V f =.25 % (19.6 kg/ m 3 ) 3 φ V f =.5 % (39.3 kg/ m 3 ) 3 φ V f =.75 % (58.9 kg/ m 3 ) 3 φ 6 3

15 Reult 1 Average crack pacing [mm] φ8 V f = % φ8 V f =.5% φ6 V f =.25% φ6 V f =.5% φ6 V f =.75% V f =.5% and φ 8 Experiment Model Gutafon, M. and Karlon, S. (26): Fiberarmerade betongkontruktioner Analy av prickavtånd och prickbredd. MSCe thei 26:15, Dep. of Civil & Environmental Eng., Chalmer Technical Univerity, Göteborg, Sverige, 26.

16 Reult Moment [knm] Non-linear hinge model DAfStb Crack width [mm] V f =.75% and φ 6 Moment [knm] V f =.5% and φ Crack width [mm] V f =.5% and φ 8

17 Effect of Steel Fibre on Cracking in Reinforced Concrete Focu on: Combined reinforcement, i.e. teel bar + (teel) fibre Crack control Service tate Invetigation of: Cracking proce, i.e. crack width and crack pacing. Bond-lip relationhip Material propertie

18 Experiment: tenion rod L N N Tenile member Axial force, N N y2 N y1 Yield load for reinforcemen t bar Fibre reinforced concrete N cr N c N Concrete Reinforcement bar For invetigation of the cracking proce Digital Image Correlation Relative elongation, δ / L

19 Bond-lip relationhip Normalized bond tre τ/f c a 1.b Active lip [mm] For confined condition, the fibre (teel fibre, Dramix RC-65/35-BN) howed no effect on the bond-lip relationhip. For unconfined condition (i.e. plitting crack) the fibre provide confinement and inhibit plitting crack.

20 Bond-lip relationhip confinement effect Bond tre [MPa] Serie.25 Exp Confined Split-tirrup Slip [mm] Serie 1.b Exp Confined Split-tirrup Slip [mm] Serie.5 Exp Confined Split-tirrup Slip [mm] Serie φ-tirrup [mm] Bond tre [MPa] Serie 1.a Exp Confined Split-tirrup Slip [mm] Correponding tranveral reinforcement: S v [mm] K tr [%] a b

21 Cracking & tenion tiffening ε (x) ε c (x) ε Tenile load [kn] Tenion rod Reinf.,5 1 1,5 2 2,5 Deformation [mm] ε m ε cm 66 kg 78 kg 35 kg 14 kg kg Crack width [mm] β i ued to calculate the average teel train between crack Reult how higher β and that at high fibre doage almot contant and no degradation. kg kg 35.5 kg 781.a kg 661.b kg Bond factor β [ - ] Load [kn] a. - β c b. -β FRC a. b Member train [ - ]

22 N(σ ) N(σ ) Retraint induced cracking combined reinf. l Crack, modelled a non-linear pring w(σ ) N(σ ) N(σ ) Bond-lip relationhip => crack width a a function of the teel tre: w 2 φ σ E E 1+ E.826 ( σ ) = φ.22 f cm Force acting on un-cracked part (with only bar reinforcement) N(f ft.re ) N(f ft.re ) Force acting on un-cracked part for N(σ ) N(σ ) combined reinforcement (fibre and bar reinforcement), with f ft.re a FRC N(σ ) N(σ ) reidual tenile trength c A A Engtröm, B. (26): Retraint cracking of reinforced concrete tructure, Chalmer Univerity of Technology. ef σ E Friction between lab and ub-bae i neglected

23 The repone during the cracking proce can decribed with the following deformation criteria: N ( σ, f ft. re ) l ( 1+ ϕef ) + n w( σ ) = R ε c l E A c I where N(σ, f ft.re ) i the force acting on un-cracked part, n i the number of crack and R i the degree of retraint. N(σ, f ft.re ) can be calculated a: N ( σ, f σ A + f A A ft. re ) = ft. re ( ) ef If N(σ, f ft.re ) i larger than the force required to initiate a new crack, N 1, more crack will be formed. However, if it i maller only one crack will be formed. The force required to initiate a new crack, N 1, can be calculated a: E N f A + 1 A 1 = ctm ef c E Engtröm, B. (26): Retraint cracking of reinforced concrete tructure, Chalmer Univerity of Technology.

24 Exemple A reinforced lab on grade, 2 meter long, with full retraint (R=1). Reinforced with φ 8, 1 or 12 (.2% < ρ <.8%) 25 1 m c = 3 2 m Material propertie, concrete C3/37 (vct.55): Tenile trength: f ctm = 2.9 MPa (f ctk,.5 = 2. MPa) Reidual tenile trength: MPa < f ft.re < 2.5 MPa Creep coefficient: ϕ ef = 2.5 Concrete hrinkage: ε c = 6 1-6

25 Exampel crack width with combined reinforcement Reidual tenile trength [MPa] ρ =.8% Crack width [mm].6% C 3/37 φ 12.5%.3%.4% Reidual tenile trength [MPa] ρ =.8%.6% Crack width [mm].5% C 3/37 φ 1 The normal / recommended reinforcement ratio i typically.4-.6%. A conervative etimate on the reidual trength with teel fibre: 2 kg/m 3 =>.8 MPa reidual trength 3 kg/m 3 => 1.1 MPa reidual trength 4 kg/m 3 => 1.3 MPa reidual trength.3%.4%

26 Concrete tructure quare and boring?

27 TailorCrete-Rationeldeign and production of tructure with complex geometrie

28 TailorCrete-Rationeldeign and production of tructure with complex geometrie

29 Tailorcrete Intereting reult regarding: - Load reditribution - Membrane action

30 Blat and Fragment Impact effect of fibre From PhD thei, by Jona Ektröm, to be preented November 1 th

31 Blat and Fragment Impact effect of fibre From PhD thei, by Jona Ektröm, to be preented November 1 th

32 Durability Effect of fibre on corroion Crack morphology no fibre Crack morphology with fibre