VALENCIA, 13 MAY 2004

Transcription

1 THE DESIGN OF EXTERNALLY BONDED REINFORCEMENT (EBR) FOR REINFORCED CONCRETE STRUCTURES BY MEANS OF FIBRE REINFORCED POLYMERS (FRP) Giovanni Cerretini (Studio Technica) VALENCIA, 13 MAY 2004

2 Introduction Today there are a lot of applications concerning fibre reinforced polymer (FRP) in civil engineering. The aim of this report is to study the exterenally bonded FRP reinforcement for reinforced concrete structures applied to the flexural strengthening and to show a software that has been developed on the basis of the FIB Bulletin 14 specifications.

3 Externally bonded FRP reinforcement for RC structures It s a technique used for the repair, the strenghtening and the retrofit of concrete structures. High resistance of the materials Low specific weight - No modification of structure s weight Small thickness - No modification of volumes Elimination of the need for scaffolding - Reduction in labour cost FRP reinforcement may be taloired to the design requirements - Unlimited availability in FRP sizes, geometry, dimension and stiffness Possibility to design a reinforcing material with specific mechanical properties - Optimization of the reinforcement for its particular stress distribution.

4 Studio Technica Examples of FRP EBR FRP reinforcement of Bridge

5 Examples of FRP EBR Beam-Column intersection

6 Studio Technica Examples of FRP EBR FRP FRP Reinforcement of a roof

7 FRP Materials and FRP Systems FRP (Fiber Reinforced Plastics or Fiber Reinforced Polymer) is a fiber-reinforced composite material, where fibres are merged in polimeric matrix. It s possible to choose between several systems of reinforcement that differ for the type of fibre, for the resin and also for the application techniques. FRP Systems Fibres + Resins + Carbon Glass Aramidic Saturating Resin Adesivhes Primer Putty Fillers Protective Coatings CFRP GFRP AFRP Application Techniques Basic Techniques Special Technicques

8 FRP Systems FRP (Fiber Reinforced Plastics or Fiber Reinforced Polymer) is a fiber-reinforced composite material, where fibres are merged in polimeric matrix

9 Studio Technica Techniques for FRP applications - Basic Technique 1) Application of Putty Filler 2) Application of Primer 3) Application of Saturating resins 4) Application of sheets, fabrics or laminates 5) Application of another layer of saturating resins 5) Application of Protective Coating Resins

10 Studio Technica References CNR ACI 440.2R-02 FIB 14 References CNR - L impiego di Armature non metalliche nel calcestruzzo armato ACI 440.2R-02 - Guide for the design and construction of externally bonded FRP system for strengthening concrete structures FIB 14 - Externally bonded FRP reinforcement for RC structures Betontex FRP Producer

11 Flexural Strengthening Reinforced concrete elements, such as beams and columns, may be strenghened in flexure through the use of FRP compsites bonded to their tension zones, with the direction of fibres parallel to that of high tensile stresses. A lot of studies shows that the greater contribution brought from FRP reinforcement is given at the ultimate limit state (ULS). In this case is possible to obtain a great increment in the bending moment capacity.

12 Bending moment capacity at ULS Bending moment capacity with n layers of FRP reinforcement in a section 25x50cm for various mechanical reinforcement ratios. Betontex GV 330 U-HT, is a high Tenacity CFRP reinforcement produced by Betontex (Italy) Precured System Wet Lay-up Systems Mn! s =1,0 Bending moment capacity (Nm) ! s =0,5! s =0,4! s =0,3! s =0,2! s =0, Number of layers (Betontex GV 330 U-HT) n

13 Full composites action Failure Modes at ULS The failure modes of a reinforced concrete element may be divided into two classes: those where the full composite action of concrete and FRP is manteined until: - the concrete reaches crushing in compression or - the FRP or stell fails in tension Loss of composite action those where composite action is lost due to peelingoff of the FRP g + q embedded steel reinforcement FRP uncracked section cracked section uncracked section Maximum fbending moment Mode 1 Mode 2 Mode 4 Mode 3

14 Lost of composite action - Debonding in concrete on a line along embedded reinforcement in concrete on a line near the surface between concrete and adhesive in adhesive concrete embedded reinforcement adhesive between adhesive and FRP FRP reinforcement in FRP Different interfaces for bond failure and different debonding lines in the concrete Bond failure may occur at different interfaces between the concrete and the FRP reinforcement

15 Peeling-Off, Ripping-Off and Spalling When localised debonding propagates and composite action is lost in such a way that the FRP reinforcement is not able to take loads anymore, this failure is called Peeling- Off Peeling-Off end anchorage flexural crack shear crack normal stresses diverting forces crack Ripping-Off Spalling crack embedded reinforcement shear reinforcement embedded reinforcement

16 Evaluation of the bending moment capacity at ULS To evaluate the bending moment capacity at ultimate limit state (ULS), it s necessary to know the failure mode, the position of the neutral axis and the material s stresses. The design bending moment of the strengthened cross section is calculated based on principles of RC design. Ht Af b Asi As bf hi tf h eo es esi ef ec X Fsi X 0.85 fcd dgx = c R Fs Ff First, the neutral axes depth, x, is calculated from strain compatibility and internal force equilibrium, and then the design moment is obtainde by moment equilibrium.

17 Evaluation of the bending moment capacity at ULS The following assumption are made in calculating the flexural resistance of a section strengthened with an externally applied FRP system: - design calculation are based on the actual dimensions, embedded reinforcing steel arrangement and material properties; - the strains in the reinforcement and concrete are proportional to the distance from the neutral axes; - there is no relative slip between external FRP reinforcement and the concrete surface; the shear deformation within the adhesives layer is neglected ; the tensile strength of concrete is neglected. b Asi hi esi ec X X 0.85 fcd Fsi dgx = c R Ht h Af As bf tf eo es ef Fs Ff

18 Design data - Material properties Elongation "co "cu "su "fu Elastic Modulus Ec = 30 MPa Es = 210 MPa Ef = Mpa Strength at Ultimate fcd fsd ffd

19 Design data - Material safety factors Material Steel reinforcement Concrete CFRP GFRP AFRP Material Safety Factor # (Data: FIB Bulletin 14 end Eurocode 2)

20 Design data - Initial deformation of concrete surface v kn/m deflection Unless all loads on a member, including selfweight and any prestressing forces, are moved before FRP reinforcemeent installation, the substrate to which the FRP is applied present a deformation that reduce the contribution of FRP These strain should be considered as initial strains and should be excluded from the strain in FRP. The initial strain level can be determined from an elastic analysis of the existing member based on cracked section properties.

21 Design data - Shear Forces When FRP reinforcement is being used to increase the flexural strength of RC element, it is important to verify that the reinforced element can resist to the shear forces associated with the increased flexural strength. TRAVE scala 1:50 Sez C - C scala 1:10 1 Foglio n.2 BETONTEX GV 330 U-HT bf = 26 cm L = 110 cm 1 Foglio n.4 BETONTEX GV 330 U-HT bf = 20 cm L = 152 cm 1 Foglio n.2 BETONTEX GV 330 U-HT bf = 26 cm L = 110 cm 1 Foglio n.1 BETONTEX GV 330 U-HT bf = 14 cm L = 220 cm sez B - B Foglio n.1 BETONTEX GV 330 U-HT bf = 14 cm L = 220 cm C B Collegamento Passante Sistema ARDFIX Foglio n.3 BETONTEX GV 330 U-HT bf = 10 cm L = 171 cm passo = 40 cm C B Foglio 1 L = 220, bf = 14 Schema 1 di laminazione 2 Foglio 2 L = 110, bf = Foglio 3 L = 193, bf = Foglio 4 L = 152, bf = 20 4 Tabella Rinforzo Foglio Tipo n L (cm) bf (cm) Sup (cmq) Costo ( /mq) Totale ( ) ,00 Foglio 1 BETONTEX GV 330 U-HT ,40 Foglio 2 BETONTEX GV 330 U-HT ,00 Foglio 3 BETONTEX GV 330 U-HT ,40 Foglio 4 BETONTEX GV 330 U-HT ,20 TAV 1 Trave

22 Depth of the neutral axis and design bending moment From the equilibrium of forces and strain compatibility the depth of the neutral axis is obtained from the following with a Trial and Error procedure. When the position of the neutral axis has been evaluated the resistant moment is obtained from the following: M rd =y T He c L 0.85 f cd b t X ê d GT He c L X ê + e c ÅÅÅÅÅÅÅÅ X ê zs E s A s h + ÅÅÅÅÅÅÅÅ ec X ê zsi Es A si hi +g ec M ÅÅÅÅÅÅÅÅ ê X z f E F A f H t Note: #M coefficient is introduced in ACI 440 to reduce the contribution of FRP reinforcement to the bending moment capcity.

23 ULS verification of Peeling-Off One approach to prevent Peeling-Off is restricting the ultimate tensile strain at ULS. With this approach the bending moment capacity for Peeling-Off ULS may be evaluated as the bending moment capacity in the case of full composite actions. Limitation of maximum FRP force which can be anchored s fa,max =ac 1 k c k $%%%%%%%%%%%%%%%% E f f ctm b ÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅ HMPaL l b,max = $%%%%%%%%%%%%%%%% E f t f ÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅ t f c 2 f ctm (see: FIB 14) FRP strain limitation e fu = f f (ec=0.0065) = E f f fd = min i j k f fk ÅÅÅÅÅÅÅÅÅÅ ; 0.64 $%%%%%%%%%%%%%%%% E f f ctm ÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅ g f t f i j k l b ÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅ l b,max i j2 - k l b y ÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅ z y l b,max {{ z; E f y z {

24 Installation of ARDFIX SYSTEM PARTICOLARE DEL RINFORZO DEL NODO TRAVE COLONNA (Scala 1:25) Primer e Resina Schema di Laminazione PRIMER COLCHEM LC tempo di indurimento 3 ore - tempo di indurimento totale 14 ore Collegamento passante ARDFIX Foglio 2 RESINA COLCHEM LC tempo di indurimento 3 ore - tempo di indurimento totale 14 ore Foglio 2 Foglio 1 Foglio 4 Foglio 3 Rinforzo in Fibra BETONTEX GV 330 U-HT Foglio 3 Fibra di Carbonio HT (Alta resistenza) Tensione di rottura fibra 4800 MPa Modulo elastico Ef= MPa Tensione di rottura di progetto 2667 MPa Peso di fibra nel nastro 200 g/mq TAV 3 Particolare nodo colonna

25 ARDFIX SYSTEM (Patented by ARDEA PROGETTI ITALY) Sistema ARDFIX (brevetto ARDEA srl) Scala 1:5 SISTEMA ARDFIX 1 realizzare un foro ø 12 passante e ripulirlo accuratamente. 2 cospargere di resina la barra e la striscia Barra CFRP ø 8 Foro ø Barra CFRP ø 8 1 A 40 Foro passante ø12 3 ripiegare la striscia sulla barra e inserirle nel foro 4 tagliare il lembo ad U di striscia che fuoriesce sul lato inferiore e ripiegare i lembi che fuoriescono dal foro sul calcestruzzo Striscia CFRP 4 x 42 Elementi del collegamento passante ARDFIX n.1 barra in CFRP ø = 8mm, L = 22 cm 48 n.1 striscia di BETONTEX GV 330 U-HT L = 84 cm, bf = 4 cm Schema di accoppiamento A 3 SEZ A - A TAV 2 Particolare collegamento

26 The Software This software is a tool to design FRP reinforcement It s Platform independant It s available on Internet (Every one who has an internet connection can use it and the upgrades are ready for the use as soon as they are published) The software is available at: Information of BETONTEX FRP at:

27 The Software - Input of Data Request data are grouped in the following sections: Geometry - The user must specify the kind of cross section, the arrangement of embedded steel reinforcement, the width and the thickness of a FRP layer the number of layers. Model Code - The model code used to evaluate Modulus and material s strength Concrete Strain - A positive value means stretching and a negative value means shrinkage #M coefficient reducing factor for the contribution of FRP to the bending moment capacity of the reinforced section Material properties - Materail properties and safety material coefficient. The software use the values specified by the user or the default values of the choosen model code.

28 The Software - Output Data The software gives the following results: Graphical View - a graphical view of the no-reinforced and reinforced section with the number of FRP layers, the position of neutral axis and the bending moment capacity Input Data Summary - a summary of the input data Table Results - a table result with the stress and deformation of section s materials

29 The Software - Results Sezione T x x Asi=0.64cmq x x Asi=0.64cmq As=2.26cmq As=2.26cmq Mrd=12182 N m Af Tot=0.21cmq Mrd=16271 N m Calcolo dello Stato Limite Ultimo (SLU) Modo di rottura x " c x T d GT " f $ f " s $ s " si $ si M RD N/mm 2 N/mm 2 N/mm 2 N m Rottura armatura Rottura armatura

30 Sismic retrofitting of a commercial building in Florence New steel structure A new floor (blu color) will be added to a commercial building in Florence. It s a reinforced concrete structure and with a new steel structure. Structure works fine and there s no problem at serveablity limt state but it s need a reinforcement to increase strength at the ultimate limt state. Reinforced Cconcrete structure

31 Finite Element Model - Stress in column s concrete

32 FEM - Stress in column s steel reinforcement

33 FEM - Stress in beam s concrete

34 FEM - Stress in beam s steel reninforcement

35 Beam Section Actual beam section - This section is not verified at Ultimate Limit State 95 Solution 1 (Traditional) - Incrementation of the section area Solution 2 with FRP - Two layer of BETONTEX GV 330 U-HT layer of FRP BETONTEX GV 330 U-HT

36 Please, visit and try the software Thank You!