SHEAR TRA SFER ALO G I TERFACES: CO STITUTIVE LAWS

SHEAR TRA SFER ALO G I TERFACES: CO STITUTIVE LAWS Vasiliki PALIERAKI 1, Elizabeth VINTZILEOU 2 and Konstantinos TREZOS 3 ABSTRACT This paper presents onstitutive laws adequate for prediting the maximum shear load that an be transferred along reinfored onrete interfaes subjeted to monotonially or ylially imposed displaements. A previous empirial formula is modified with the purpose to reah reliable predition of the maximum resistane of various types of reinfored onrete interfaes. The appliation of the modified formula to 8 experimental results from the literature proves the adequay of the proposed laws. I TRODUCTIO In various repair and/or strengthening tehniques, in ase that the intervention onsists in adding a new onrete layer or new RC elements to the existing members of the struture, the onnetion between the new and the old onrete has to be adequately designed and detailed. Various tehniques suggested and used in onstrution, aim to establish a better onnetion between the two different layers, so that the resulting, omposite, element behaves as monolithi. Nevertheless, the shear load to be transferred along the interfaes, depends on the means of onneting the old and the added onrete (use of reinforing bars or anhors, ating as dowels, roughening of the old onrete surfae before asting the new layer) and it is a funtion of the shear slip along interfaes, a prerequisite for the mobilization of the resistane at the interfae. In ase of strutures subjeted to earthquakes, the behaviour of interfaes may beome ritial for the overall behaviour of the struture, due to substantial degradation of the resistane of the interfae under yli ations. On the other hand, in the design of an interfae rossed by reinforing bars or by anhors, one annot additively superimpose the maximum resistane offered by the two main mehanisms (shear frition and dowel ation). The interation between the two mehanisms has to be taken into aount, along with the fat that their maximum resistane is not mobilized for the same value of shear slip. Although, the behaviour of interfaes was experimentally investigated in numerous studies, the available information is not suffiient for the design of interfaes in the ase of RC strutures subjeted to earthquake exitations. An experimental ampaign was arried out at the Laboratory of RC, NTUA, for the systemati investigation of RC interfaes within repaired or strengthened elements. Among the aims of the experimental investigation is also the proposal of onstitutive laws for the aurate prevision of the interfae resistane and overall behavior. In the present paper a summary of the available experimental results is presented, as well as the results of a study that was undertaken with the aim to predit the maximum resistane of RC interfaes under imposed monotoni or yli exitation. 1 Dr., Civil Engineer, National Tehnial University of Athens, Athens, Greee, vasopal@entral.ntua.gr 2 Professor, Civil Engineer, National Tehnial University of Athens, Athens, Greee, elvintz@entral.ntua.gr 3 Assistant Professor, Civil Engineer, National Tehnial University of Athens, Greee, trezos@entral.ntua.gr 1

LITERATURE SURVEY The results of numerous tests on (plain or reinfored) onrete interfaes are reported in the international literature. Tests simulate various ases of interfaes, suh as onstrution joints, onnetions between preast elements, natural raks, et. In most of the tests, interfaes were subjeted to monotonially inreasing load up to failure. Data regarding the behaviour of reinfored interfaes simulating the interfaes between old and new onrete in repaired/strengthened elements, subjeted to yli shear slip are rather sare. The experimental researh arried out by the authors, mainly aims at overing the lak of results regarding the yli behavior of interfaes between old and new onrete, in repaired or strengthened elements. The number of tests performed at NTUA (43 tests on speimens subjeted to yli shear slip, Palieraki, 214) allow for onlusions regarding the behavior of interfaes in yli shear to be drawn. Nevertheless, it is obvious that the tests do not over the wide range of the parameters influening the behavior of the interfaes, e.g., the mehanial harateristis of onrete and steel. In order to formulate a onstitutive law, whih ould be generally applied, experimental results from the literature are re-evaluated. Tests regarding the behavior of interfaes are performed using (a) speimens in the form of beams, strengthened using added onrete, tested in 3-point bending, ausing indiret shear of the interfae, (b) monolithi speimens, tested as onstruted, or raked before being tested, () speimens onstruted in two onseutive phases, simulating interfaes between new and old onrete, as are the speimens tested by the authors, and finally (d) speimens having two interfaes, simulating onnetions between preast onrete elements. In some of the speimens, ompressive or tensile stress is applied perpendiularly to the interfae. The perentage of the reinforement rossing the interfae varies between.14% and 4%, while the most frequently used perentages are in the range of.% to 2%. The different test setups used in order to perform the tests have some ommon harateristis, but may present signifiant differenes, depending on how the interfae is onstruted (in one or two phases) and aording to the purpose of the investigation. One of the most ommonly used test setups is similar to the one used at NTUA (Fig.1). Given that different kinds of test setups an be found in the literature, leading to different results, not diretly omparable in several ases, and given the partiular interest of interfaes between old and new onrete, attention has been paid to the aforementioned ases of interfaes. In total, results from 18 papers, produed between 196 and 212 have been olleted. Results from almost 8 tests regarding interfaes with different dimensions and geometry, overing a wide range of material properties are inluded in the evaluated researh works. F A F Setion A-A C S Bars of 8mm or 12mm diameter R Setion B-B (a) C (b) Figure 1. Tests at NTUA: (a) Geometry of the speimens with three bars rossing the interfae (dimensions in meters), (b) Photo of the test set up, with speimen in the testing position. 2

V.Palieraki, E.Vintzileou and K. Trezos 3 MAXIMUM I TERFACE RESISTA CE-I FLUE CE OF SIG IFICA T PARAMETERES The available experimental results reported in the literature have been re-evaluated and assessed in relation to signifiant parameters, whih, as generally admitted, affet the behavior of interfaes. Shear is transferred along the interfaes mobilizing the mehanism of onrete to onrete frition and the dowel ation of the bars rossing the interfae. The main parameters under investigation are the ompressive strength of onrete, the number and the diameter of the bars rossing the interfae, the anhorage length of the bars rossing the interfae, and the presene of ompressive or tensile stress, ating perpendiularly to the interfae. Given that in the present paper the resistane of interfaes between old and new onrete is investigated, the speimens usually onsist of two parts, onstruted separately. The smaller ompressive strength of the onrete of the two parts of the speimens is the one that governs the resistane of the interfae. The parameters related to the perentage of the reinforement rossing the interfae, an be unified in one parameter, ρf y (where ρ denotes the perentage of reinforement and f y denotes the yield strength of the bars), whih orresponds to the maximum ompressive stress whih an at on the onrete interfae, beause of the tensile stresses to be developed in the reinforing bars of the interfae. In the parameter, the small anhorage length of the bars an be taken into aount, given that for smaller length the tensile stress in the bars is onsidered to be redued. Additionally, in the parameter ρf y, the external ompressive or tensile stress, ating to the interfae is added or subtrated aordingly. As long as it regards the embedment length, it is taken into aount as follows: Most of the speimens are reinfored with bars in the form of losed loops. The bars in this ase, are onsidered to be suffiiently anhored, and able to develop their yield strength. The bars anhored by means of resins are also onsidered to be able to develop their yielding stress. In the ase of bars anhored to the onrete by means of bond, having a small embedment length, the stress to be developed in the bars is onsidered to be smaller than their yielding stress. The tensile stress in the bars, and onsequently the ompressive stress to be developed in the onrete an be alulated aording to Eq. (1): lembfyas σ = (N, mm) (1) A.8lb In Eq. (1), the embedment length that is neessary for the bars to develop their yield strength is taken equal to 8% that presribed by EC2 (Eq. (2)). This is beause, the experimental results obtained at NTUA (Vintzileou and Palieraki, 27, Palieraki and Vintzileou, 29, Zeris et al., 211, Palieraki, 214) have shown that embedment length equal to.8l b is suffiient for the full anhorage of bars used for the reinforement of interfaes subjeted to shear. fydφ lb = (N, mm) (2) 4f bu The effet of the main parameters on the maximum resistane of interfaes is shown in Fig. 2: The resistane of the interfae is plotted against the least of the two ompressive strengths, as well as against the values of the parameter ρf y. In addition, to make the effet of the ompressive strength of onrete more evident, the shear resistane values are reported to the parameter ρf y. The diagrams for the speimens simulating interfaes between old and new onrete learly show that the reinforement parameter is the one governing the resistane along the interfae. The inrease of the reinforement perentage leads to an inrease of the interfae resistane. The influene of the onrete ompressive strength is not so lear. For normal onrete ompressive strength, up to 6.MPa, the inrease of the onrete strength leads to an inrease of the interfae resistane. This trend is not lear for higher values of the ompressive strength of onrete. In ase of interfaes formed within a monolithi element, raked before testing the interfae, this feature an be attributed to the fat that a rak in high strength onrete rosses not only the ement matrix, but also the aggregates, leading to a smoother interfae. In the ase of interfaes between old and new onrete, this ould be also attributed to the different roughness of the interfae.

2 2 1 1 2 4 6 8 1 12 f (N/mm 2 ) 12 Hanson, 196 Mattok, 1976 Vesa, 1978 Noguhi et al., 1984 Bass et al., 1989 Mishima et al., 199 Randl, 1997 Choi et al., 1999 Choi et al., 1999 (2) Valluvan et al., 1999 Kono et al., 21 Kann & Mithell, 22 Papaniolaou & Triantafillou, 22 Nakano & Matsuzaki, 24 Saari et al., 24 Hattori & Yamamoto, 27 Harries et al., 212 NTUA Tests, 27-213 1 1 τu,exp/ρf y 1 8 6 4 2 4 8 12 16 2 ρf y (N/mm 2 ) 2 4 6 8 1 12 f (N/mm 2 ) Figure 2. The effet of the least onrete ompressive strength and the reinforement parameter, ρf y, on the shear resistane of interfaes between old and new onrete. PREDICTIO OF THE MAXIMUM I TERFACE RESISTA CE-AVAILABLE RELATIO SHIPS In the literature, as well as in some Codes, several relationships are given for the predition of the maximum interfae resistane. Those relationships annot always be applied in the ase of interfaes between old and new onrete, in repaired/strengthened elements, beause of the speifi harateristis of the abovementioned interfaes: The quality and the strength of the new and the old onrete may differ signifiantly. The surfae of the old onrete may be smooth or roughened, using various tehniques. The interfae reinforement is anhored in the old onrete by means of resins or other mehanial means, while in the new onrete, the anhorage of the reinforement is ahieved through bond with the onrete. The dimensions of the old, as well as the added part of onrete, are often small, not allowing for full anhorage of the reinforement or/and for suffiient distanes from the edges of the elements. Among all the available relationships, those able to predit the shear resistane of interfaes between old and new onrete are used on a large number of experimental data from various soures. 4

V.Palieraki, E.Vintzileou and K. Trezos Those relationships were proposed by researhers (Pruijssers, 1988, Tassios and Vassilopoulou, 23, Harries et al., 212), or they are inluded in Codes (ACI 318, 211 and CEB-fib Model Code 1, 212). Equation proposed by Pruijssers (1988), Equ. (3): b τ = aρ ( f (3) u y) Where: ρ denotes the reinforement perentage of the interfae f y denotes the yield strength of the steel.46.33 α and b are empirial parameters: a=.822 f m and b=.19 f m f m denotes the ompressive strength of onventional 1mm ubes. It is noted that the relationship is proposed by Pruijssers (1988) for interfaes within speimens onstruted monolithially and raked before testing. Equation proposed by Tassios and Vassilopoulou (23), Equ. (4): τ = β τ + β τ (4) u d d Where β d and β f are ontribution fators for the mehanisms ating along the interfae, namely frition (Equ. (), as proposed by Tassios and Vintzileou, 1987) and dowel ation (Equ. (6), as proposed by Rasmussen, 1962). The formula by Rasmussen is valid for dowels provided with onrete over suffiient for splitting failures to be avoided as desribed herein: 3 2 f f f f τ =.44 σ (N, mm) () where: f denotes the least ompressive strength of onrete σ denotes the ompressive stress ating perpendiularly to the interfae. The ompressive stress may be due to an external ating stress or to the tensile stress of the bars rossing the interfae (=ρf s, f s denotes the tensile stress of the bars), 2 τ =(1.3nd f f )/ A (N, mm) (6) d where: n and d b denote the number and the diameter of the bars rossing the interfae. The ontribution fators for the mehanisms ating aross the interfae (β d and β f ), were determined by Tassios and Vassilopoulou (23) on the basis of experimental results obtained from testing eah shear transfer mehanism separately (Vintzeleou and Tassios, 1987, Tassios and Vintzileou, 1987) and taking into aount the interation between the two mehanisms. Tassios and Vassilopoulou (23), have onluded that for slip values not exeeding.4mm, the ontribution fator of the frition mehanism is equal to.4, whereas that of the dowel mehanism is equal to.7. For large values of the imposed shear slip (s>2.mm), the ontribution fator of the frition mehanism beomes equal to.8, that of the dowel ation remaining equal to.7. When the value of the imposed slip is not known, or for onrete strength higher than 4.MPa, Tassios and Vassilopoulou (23) suggest to use redued ontribution fators, namely.7 and.6 for frition and dowel ation respetively. Given that the values of the imposed shear slip are not known for all the available experimental results, and the onrete strength is for many tests higher than 4.MPa, for the omparison in the urrent paper, the ontribution fators of.7 and.6 for frition and dowel ation respetively are used. Equation proposed by Harries et al. (212), Equ. (7): τ = af +.2ρE.2f (N, mm) (7) u where: E s denotes the elasti modulus of the interfae steel reinforement α stands for an empirial parameter. The value of the parameter is taken into aount aording to the type of the speimen under investigation, i.e.: α=.7 for monolithi, unraked, speimens α=.4 for speimens having a old joint, onstruted in two different phases (the ase of interfaes between old and new onrete) α=. for speimens raked before testing Equ. (7) is a design-oriented equation. Given that the equation is used to predit experimental results, partial safety fators for the materials, namely for onrete and steel, are not used. It has to be b s y

admitted though that avoiding the use of safety fators may not be suffiient for a design-oriented equation. Thus, it is expeted to lead to resistane values smaller than the experimental ones.it is noted that in Equ. (7), the elasti modulus of the steel rossing the interfae is used, instead of its yield strength: Aording to the tests performed by Harries et al. (212), and the steel strains measured during testing, Harries et al. (212) suggest that, in ase of high or medium strength steel (f y >4MPa), the bars do not reah their yield strength. Equations proposed in Codes: ACI 318 (211), equation (Equ. (8)): τ =µα f / A min(.2 f,.1) (N, mm) (8) u s where: µ denotes the frition oeffiient along the interfae; a set of values are speified for different interfae onstrution methods, namely, µ=1.4 for monolithi, raked or unraked, speimens µ=1. and µ=.6 for onrete plaed against hardened onrete, for rough or smooth interfae of the hardened onrete, respetively. Equ. (8) is one of the most ommonly used equations for the alulation of the interfae resistane. It is noted that many researhers, inluding the authors of this paper, have onluded that the upper limits, suggested by the ACI Code, i.e. the limit of.2f or.1mpa are extremely onservative. Based on this observation, the limit of.1mpa is not taken into aount in the following alulations, while instead of.2f, the less onservative, but still on the safe side, limit of.2f is used. It is noted, that also in this ase, the partial safety fators for the materials are not taken into aount. CEB-fib Model Code 1 (212), equation (Equ. (9)): / 3 σn τ.9k f 1 ud = k + µ (k ρ fyd + ) + αf fyd fd β fd b (N,mm) (9) γ where: f k, f d denote the harateristi and the design onrete ompressive strength f yd denotes the design yield strength of steel reinforement rossing the interfae The interation fators k and α F in Equ.(9) take into aount that the reinforement or onnetors are subjet to bending and axial fores simultaneously and the maximum values of eah mehanism our at different slip values. The fator k is hosen aording to the interfae roughness. Finally the fator β is oeffiient, used in order to redue the ompressive strength of a onrete strut. The values of the abovementioned parameters are hosen aording to Table.1. Table 1. Fators for the alulation of the interfae resistane, aording to the interfae roughness (CEB-fib Model Code 1, 212). Interfae Roughness k k α F β Μ f k 2 f k 3 Waterblasted interfaes, R 2.mm 2.3..9..8 1.1 Sandblasted interfaes, R.mm. 1..4.7 Smooth Interfaes 1.4.4. As expeted, the same basi parameters are taken into aount in almost all equations found in the literature, namely: The perentage of the reinforement rossing the interfae, its yield strength, as well as the frition oeffiient depending on the interfae roughness. In some relationships, the onrete ompressive strength is taken into aount, in order to alulate the frition oeffiient, or as an additional part of the equation, denoting the adhesion along the interfae. It is noted that in most ases, (with the exeption of Equ. (4), Tassios and Vassilopoulou, 23) and Equ. (9), CEB-fib Model Code 1, 212), only the ontribution of the frition mehanism is taken into aount, while the ontribution of the dowel mehanism and its interation with frition are ignored. It is noted, that in all investigated equations, no partial safety fators for onrete and steel are taken into aount, given that the relationships are used in order to predit the resistane of tested interfaes. y 6

V.Palieraki, E.Vintzileou and K. Trezos 7 2 Hanson, 196 Mattok, 1976 Vesa, 1978 Noguhi et al., 1984 Bass et al., 1989 Mishima et al., 199 Randl, 1997 Choi et al., 1999 Choi et al., 1999 (2) Valluvan et al., 1999 Kono et al., 21 Kann & Mithell, 22 Papaniolaou & Triantafillou, 22 Nakano & Matsuzaki, 24 Saari et al., 24 Hattori & Yamamoto, 27 Harries et al., 212 NTUA Tests, 27-213 2 1 1 1 1 2 τu,al, pruijssers (N/mm 2 ) 2 1 1 1 1 1 1 2 τu,al, tassios (N/mm 2 ) 2 1 1 2 τu,al,harries (N/mm 2 ) 2 1 1 1 1 1 1 2 τu,al,aci (N/mm 2 ) 1 1 2 τu,al,fib (N/mm 2 ) Figure 3. Comparison between the experimental results, and the resistane of the interfae, alulated using various relationships of the Literature.

In Fig. 3, the values of the shear resistane of interfaes, alulated on the basis of the aforementioned equations are plotted against the respetive experimental values. One may observe the signifiant satter of the results of this omparison. Regarding eah separate equation, one may omment as follows: The preditions aording to Equ. (3) and to Equ. (4) (Pruijssers, 1988, Tassios and Vassilopoulou, 23) are not on the safe side, as they yield systematially interfae resistane values higher than the experimental ones. This is attributed to the fat that both equations were proposed for natural raks and, hene, they do not yield aurate results in ase of interfaes of limited roughness. On the ontrary, Equ. (8), inluded in the ACI Code, applied as desribed previously (taking into aount less onservative upper limits) leads to satisfatory results. Although Equ. (8) neglets the ontribution of dowel ation, the fititiously higher frition oeffiients proposed by the Code ontribute to the alulation of realisti values for the overall shear resistane, Finally, Equ. (9) inluded in the CEB-fib Model Code 1 (212), shows signifiant satter. It should be noted that the values of shear resistane being alulated-for the needs of this omparison-without aounting for partial safety fators seem to be muh on the unsafe side. FORMULATIO OF A MODIFIED RELATIO SHIP Among the numerous relationships available in the Literature, that proposed by Tassios and Vassilopoulou (23), is seleted for further investigation. This hoie is justified by the purpose of the present work: The design of interfaes in repaired or strengthened RC elements is arried out, aording to urrent Codes (e.g. EC8, Part 3), for a given performane level. The shear slip expeted to be imposed to the interfae is a funtion of the design performane level. It is, therefore, neessary to provide the Designer with a formula able to take into aount the ontribution of eah separate mehanism (a funtion of the imposed slip value), as well as the roughness of the interfae, the presene of external normal stress, et. The seleted formula offers this possibility. Thus, taking into aount the available experimental data, the authors of this paper are proposing a set of modified fators to be implemented in Equ. (4): Dowel ation: The ontribution of the mehanism to the overall resistane of the interfae is taken equal to 7% the maximum resistane due to dowel ation (i.e., β d =.7). For bars having an embedment length smaller or equal to 6 times the diameter of the bars (the length is ompared to a length equal to 8 times the diameter of the bar, whih is a length neessary for the full apaity of the dowel to be mobilized), the ontribution of the dowel mehanism is redued by a fator equal to.7. It is to be noted that the ontribution of the dowel mehanism in the overall shear resistane of the interfae is in general rather limited. It is expeted to affet the overall resistane only for small imposed shear slip values, when the ontribution of frition is also small. Frition along the interfae: The most signifiant modifiations to the relationship proposed by Tassios and Vassilopoulou (23) are brought to the part of the frition mehanism. The omparison between the experimental results and the values predited by Equ. (4) show that the ontribution of the frition mehanism annot be aurately estimated, unless signifiant parameters, like roughness of the interfae, presene of external normal stress, as well as type of loading (monotoni, yli or repeated) are taken into aount. First of all, Equ. () is modified: A oeffiient equal to.33 is applied (instead of.44) to aount for frition-dowel ation interation, as well as the fat that the interfae is smoother than the one resulting from a natural rak. Thus, the ontribution of frition is redued by almost 2% and it is alulated aording to the following Equ. (1): τ =.33 σ (N, mm) (1) 3 2 f f Subsequently, on the basis of the re-evaluation of numerous experimental results, the following set of values are suggested for the ontribution of the frition mehanism to the overall resistane of the interfae (Table.2). 8

V.Palieraki, E.Vintzileou and K. Trezos 9 Table 2. Interfaes between old and new onrete: Contribution fators for the frition mehanism. Interfae Charateristis Rough interfae, monotoni loading.6 Smooth interfae with external ompressive stress.6 Smooth interfae.4 Rough interfae, yli loading, imposed shear slip s>1.mm.4 Very smooth interfae.2 Rough interfae, yli loading, imposed shear slip s<.2mm.2 Smooth interfae, no ohesion along the interfae.1 Rough interfae with external ompressive stress.8 Interfae with shear keys.8 β f 2 2 1 1 1 1 1 1 2 τu,al,urrent (N/mm 2 ) 1 1 2 τu,al,safety fators (N/mm 2 ) (a) (b) Figure 4. (a) Comparison between experimental shear resistane and values alulated on the basis of the proposed modified formula (b) Same as (a), taking into aount partial safety fators for onrete and steel (1. and 1.1 respetively). In Fig. 4 (a), the experimental values of the shear resistane are plotted against the values alulated aording to the modified formula, whereas in Table 3, statistial data related to the effiieny of the formulae used for the alulation of the shear resistane of interfaes are provided. It seems that the experimental values are quite aurately predited. The modified formula ould be used for design purposes as well. As shown in Fig. 4(b), when in the modified formula, the design values of ompressive strength of onrete and the yield strength of steel are introdued, the redued predited values of shear resistane of interfaes are adequate for the design of interfaes. Finally, the data inluded in Table 3 prove that the modified formula onstitutes a lear improvement as ompared with other formulae of the Literature. Table 3. Statistial data related to the ratio between alulated and experimental value of the shear resistane of interfaes (τ u,al /τ u,exp ). Equation Pruijssers (1988) Tassios and Vassilopoulou (23) Harries et al. (212) ACI Code (211) fib Model Code 1 (212) Modified formula Average 1.78 1.64.9.6.78.91 Standard Deviation 1.23 1.22.62.36.1.28 Variation 1.1 1.48.38.13.26.8

CO CLUSIO S The numerous experimental data of the literature regarding the shear resistane of RC interfaes are evaluated and used to hek the effiieny of various relationships in prediting with aeptable auray the measured shear resistane values. Among the formulae used in this paper, the formula proposed by Tassios and Vassilopoulou (23) was seleted for further investigation, as it aounts for both shear transfer mehanisms, as well as for their interation. A set of modified oeffiients is proposed, based on a vast database (inluding almost 8 test results). The appliation of the modified formula has proved its satisfatory performane in prediting the shear resistane of interfaes subjet to monotoni and yli shear displaements. REFERE CES ACI Committee 318 (211) Building Code Requirements for Strutural Conrete (ACI 318-11) and Commentary, Amerian Conrete Institute, Farmington Hills, Mih. 3 pp. Bass RA, Carraquillo RL, Jirsa JO (1989) Shear Transfer aross New and Existing Conrete Interfaes, ACI Strutural Journal, 86(4): 383-393. Choi D-U, Fowler DW, Jirsa JO (1999) Interfae Shear Strength of Conrete at Early Ages, ACI Strutural Journal, 96(3): 343-348. Choi D-U, Jirsa JO, Fowler DW (1999) (2) Shear Transfer aross Interfae between New and Existing Conretes Using Large Powder-Driven Nails, ACI Strutural Journal, 96(2): 183-192. EC2, Euroode 2: EN 1992-1 (29) Design of onrete strutures, Brussels: European Committee for Standardization. EC8, Euroode 8: EN 1998-1 (29) Design of strutures for earthquake resistane, Brussels: European Committee for Standardization. Fib (212) fib Bulletin No. 6: Model Code 21 - Final draft, Vol. 1, International Federation for Strutural Conrete, Lausanne, Switzerland, 3 pp. Hanson NW (196) Preast-Prestressed Conrete Bridges 2: Horizontal Shear Connetions, Journal of the PCA Researh and Development Laboratories, 2(2): 38-8. Harries KA, Zeno G, Shahrooz B (212) Toward an Improved Understanding of Shear-Frition Behavior, ACI Strutural Journal, 19(6): 83-844. Hattori Y and Yamamoto Y (27) Shear Transfer Mehanism to bonded Anhors for Exterior Seismi Retrofitting, Proeedings of the 2nd International Symposium on Connetions between Steel and Conrete, Stuttgart, Germany, 4-7 September, Vol. 2: 79-769. Kann LF and Mithell AD (22) Shear Frition Tests with High-Strength Conrete, ACI Strutural Journal, 99(1): 98-13. Kono S, Tanaka H, Watanabe F (21) Interfae Shear Transfer for High Strength Conrete and High Strength Shear Frition Reinforement, Proeeding of the Conferene on High Performane Materials in Bridges, ASCE, Kona, Hawaii, 29 July- 3 August, 319-328. Mattok AH (1976) Shear Transfer Under Monotoni Loading, Aross an Interfae Between Conretes Cast at Different Times, Report SM 76-3, Department of Civil Engineering, University of Washington (Part I of Final Report to ational Siene Foundation, Grant o. Eng74-21131). Mishima T, Suzuki A, Shinoda Y, Maekawa K (199) Nonelasti Behavior of Axial Reinforement Subjeted to Axial and Slip Deformation at the Crak Surfae, ACI Strutural Journal, 92(3): 38-38. Nakano K and Matsuzaki Y (24) Design Method and Compound Effet onsidering deformation of shear transfer elements in preast onrete onnetions, Proeedings of the 13th World Conferene on Earthquake Engineering, Vanouver, Canada, 1-6 August, Paper No. 631. Noguhi H, Ohiai M, Izhuka S (1984) Sliding Shear in Craked Reinfored Conrete Shear Walls Subjeted to Reversed Cyli Shear, Proeedings of the 8th World Conferene on Earthquake Engineering, San Franiso, California, 21-28 July, Vol. 6: 331-338. Palieraki V (214) Seismi behaviour of reinfored interfaes in repaired/ strengthened reinfored onrete elements, Ph.D. Thesis, National Tehnial University of Athens, Greee, 78 pp (in Greek). Palieraki V and Vintzileou E (29) Cyli Behaviour of Interfaes in Repaired/Strengthened RC Elements, "Arhiteture - Civil Engineering - Environment ACEE" Journal, 2: 97-18. Papaniolaou CG and Triantafillou TC (22) Shear transfer apaity along pumie aggregate onrete and high-performane onrete interfaes, Materials and Strutures, RILEM, 3: 237-24. Pruijssers AF (1988) Theoretial and experimental analysis of the behaviour of raked onrete under monotoni and yli shear loading, Heron, 33(4): 1-72. 1

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