Critical problem in EB-FRP technique

Transcription

1 Critical problem in EB-FRP technique Unle only a mall amount o FRP i ued, ull utilization o FRP material tenile trength cannot be realized.

2 Failure o a trengthened member - a premature, udden and brittle detachment o FRP rom the concrete ubtrate. Thi weaket link o bond undamentally limit the eicacy level and reliability o the method.

3 Current Technology: FRP trength tranmitted into concrete through adheion. Weak interace by urace adheion Problem remain when a tronger adheive ued - peeling o a thin concrete layer. Low trength utilization ratio - lower than 0% o the FRP trength. Limited application due to limited increae in trength.

4 Previou olution to the problem Additional U-jacket FRP trip bonded to beam ide at the plate end Brena et al. (003), Ritchie et al. (99), Swamy and Mukhopadhyaya (999), Smith and Teng (003), Teng et al. (00). 4

5 End anchorage Anchoring FRP trip at end with large mechanical anchor, or FRP U-jacket FRP Plate RC Beam Anchorage Block Adheiveilled Bore Mild Steel Bolt

6 Mechanically Fatened (MF) FRP ytem Lamanna et al. (00, 00, 004). 6

7 Mechanical atening o FRP (MF-FRP) Mechanical atening - a conventional and eective way. Not applicable to normal FRP abric/laminate, due to low bearing trength. A pecial FRP SaStrip TM that poe certain bearing trength but or temporary trengthening

8 Near-urace mounting (NSM) Inerting FRP bar or trip into concrete cover. Steel bar RC beam Saw-cutting may cut exiting reinorcement bar. NSM Bar Limited increae in bond trength.

9 U-jacket Wrapping FRP trip with U-haped trip that may increae the bond trength by 30% (Ye et al. 005) Ye, LP, Lu XZ, and Chen, JF. Deign propoal or the debonding trength o FRP trengthened RC beam in the Chinee deign code. Proc. International Sympoium on Bond Behaviour o FRP in Structure (BBFS 005), Hong Kong, pp

10 Fiber anchoring Fiber anchor pike can increae the lexural capacity o trengthened beam by 35% (Ekenel et al. 006). Contruction inconvenient Ekenel, M., Rizzo, A., Myer, J.J., and Nanni, A. Flexural atigue behavior o reinorced concrete beam trengthened with FRP abric and precured laminate ytem, J. Compoite or Contruction 006; 0(5):

11 Interlocking-anchorage Interlocking key - cutting tranvere hallow groove and illed with epoxy. U-jacket at the end. Increaing bond trength by % (Grace 00) Grace, N.F. Improved anchoring ytem or CFRP trip, Concrete International ACI, 00; 3(0):

12 The tate-o-the-art Ater more than one decade o extenive R&D work all over the world, international leading expert conclude: No eicient method i available yet to avoid IC debonding ailure (Ye et al. 005) Ye, LP, Lu XZ, and Chen, JF. Deign propoal or the debonding trength o FRP trengthened RC beam in the Chinee deign code. Proc. International Sympoium on Bond Behaviour o FRP in Structure (BBFS 005), Hong Kong, pp

13 No olution or the problem? A imple tet: A lea mounted by two pin A lea mounted by a taple Increae in bond trength by replacing two pin with a taple: 740/5*00%= 59%

14 A New Patented Technology HB-FRP Normal adheive bond augmented by a pecially mechanical atener Conventional anchor replaced by taple

15 Laboratory Teting

16 No atener FRP debonding With the atener - FRP rupture

17 Applied load (kn) Tet reult Flexural trength increae: > 4 time Bond trength increae: > 6 time Additional bond: proportional to atener number Higher increae expected HB-FRP 6 plie debond EB-FRP plie debond HB-FRP plie FRP break Mid-pan diplacement (mm) HB-FRP 4 plie FRP break Batch A tet Batch B tet

18 Mechanim Concrete ubtrate Puh againt atener and concrete pulled out FRP Perpendicular movement FRP longitudinal lip HB FRP: lip caue paive preure, hence riction No bearing reitance i required or FRP, hence applicable to any FRP laminate Dierent rom the mechanim or SaStrip - bearing

19 Mechanim o HB-FRP joint Free end FRP trip Mechanical atener Loaded end (a) Adheive l Concrete ubtrate F= F a +F m (b) b b (c) (d) (e) τ a (x) τ m (x) τ a (x) τ m (x) L e L e Le a a a3 m m m3 F a F m F m τ mequ (x) Homogenizing 9

20 Load-lip repone or HB-FRP joint Baed on equilibrium, contitutive and compatibility condition, governing equation or adheive joint can be expreed a ollow 0 when x=0, l t b E F when x=l max max max 0 '' t E t E t E e e Energy Method Homogenizing

21 max 3 max max ) B B B C B t b E B B C B t b E B C B t b E C B t b E F l meq l l meq l l meq l l meq l e e t E B max B max 3 B 3 max 4 B where, Load-lip repone or HB-FRP joint Energy Method

22 Load capacity o HB-FRP joint Ininite bond length F P l u 0 lim 3 max C t E t b E meq Finite bond length No cloed-orm olution but can be obtained numerically by olving the econd order dierential equation (governing equation).

23 Numerical Modeling o the hybrid bonding cheme Hybrid bonding cheme Modeling Numerical reult

24 Interacial hear tre(mpa) Interacial hear tre(mpa) Numerical imulation reult EB-FRP: one bond tre block, moving to plate end at debonding Ditance to mid-pan (mm) HB-FRP: many bond tre block, one or each anchor Ditance to mid-pan(mm)

25 Deign Equation Pu Pa P Pd () where P u - total bond trength; P a - adheive bond trength; P d - dowel trength; and P - rictional bond trength given by P N m a in which - rictional coeicient, = 0.96; N a - vertical pullout reitance o one atener; and m number o atener.

26 Concluion The current adheive bond technology relie on the tenile trength o concrete which i weak and unreliable. Furthermore, it cannot igniicantly increae the trength o trengthened tructure. One eaible, and probably the only undamental, olution to thi problem i to enure that the FRP take root in the concrete ubtrate The new HB-FRP technology can increae the bond trength by many time. It can be applied to tructure where large increae in trength i needed. It i applicable to any exiting commercially available FRP abric, plate, laminate or heet.

27 Reerence paper. Wu YF, Huang Y. Hybrid bonding o FRP to Reinorced Concrete Structure. Journal o Compoite or Contruction 008; (3): Wu YF, Wang ZY, Liu K, He W. Numerical Analye o Hybrid-Bonded FRP Strengthened Concrete Beam, Computer-Aided Civil and Inratructure Engineering 009; 4: Yun YC, Wu YF, Tang WC. Perormance o FRP bonding ytem under atigue loading. Engineering Structure 008; 30(): Wu YF, Yan JH, Zhou YW, Xiao Y. The ultimate trength o reinorced concrete beam retroitted with hybrid bonded FRP, ACI Structural Journal July/Augut 00; 07(4). CityU patent - One US patent - granted - One China patent iled Deign guideline - Recommended in the propoed Hong Kong Guide or the Strengthening o Concrete Structure uing FRP Compoite.

28 Better olution? Brittlene o FRP material oten caue problem in engineering application. A trong, light, yet ductile material poee great advantage. Thank to the advance in material cience, uch material are nowaday available. Example: nanotructured teel material.

29 True tre (MPa) Surace Nanocrytallization Technology Surace Mechanical Attrition Treatment (SMAT) (Lu and Lu, 999; Tong et al., 003) i a recently developed procee to orm nanocrytallized urace layer. Current poible trength o SMATed SS y = 700 MPa. SMAT proce Actual trength o a two-ply CFRP trip (t mm) u = 4300x0.65x=49 MPa Concluion: SMATed SS can have a higher trength than CFRP, yet with a ductile pot-yield behavior - ideal or tructural rehabilitation SMAT 304 SS 00ball+0min SMAT A Normal received 304 AISI304 SS SS o mm thickne True train (%) SMATed 304 tainle teel

30 Flexural Strengthening Uing SMATed teel Steel plate Bottom o RC beam Concrete crew Strengthened bottom ace o beam 400 Tet etup Repone curve

31 Advantage With the trength o FRP, and the ductility o teel No debonding by making ue o hybrid bond mechanim without additional teel capping plate. Steel plating HB-FRP

32 Additional advantage Avoiding detachment o externally bonded reinorcement uing the nano-treated material

33 Debonding caued by cracking B Beore cracking: Point A and B are bonded together Point A on concrete urace Point B on FRP trip

34 Debonding caued by cracking B Ater cracking: Point A and B eparated cauing relative movement hence debonding A A B

35 Debonding proce SP5 without nano-treatment debonded in the tet Steel plate train ditribution or SP5

36 Debonding proce SP6 with nano-treatment did not debond Steel plate train ditribution or SP6

37 Concluion High trength teel heet can replace FRP or RC rehabilitation with much increaed ductility. Nano-treatment can be utilized to avoid debonding

38 Thank you!