thickness of t = 14 mm, end distance of e = 3 mm, side distance of s = 2 mm, longitdinal and transverse hole spacing of p = g = 4 mm. The FR laminates

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1 Jornal of trctral Engineering Vol.56A (March 21) JCE Behavior of ed/bonded joints in pltrded hbrid CFR/GFR composites Ngen Dc Hai*, Hiroshi Mtsoshi** * hd Candidate, Dept. of Civil Engineering, aitama Universit, 255 himo Okbo, akra-k, aitama , Japan ** rofessor, Dr.Eng., Dept. of Civil Engineering, aitama Universit, 255 himo Okbo, akra-k, aitama , Japan This paper presents reslts from experimental and analtical stdies on the behavior of doble lap joints in pltrded hbrid CFR/GFR composites. A nmber of hbrid FR copon and fll-scale beam specimens with ed-onl and bonded-and-ed joints were tested. The reslts show that a combined se of steel s, adhesive bonding and V-notch splice plates in doble lap joints was fond to be an effective method for joining hbrid FR composites. The rogh srface of V-notch splice plates and adhesive bonding contribtes to improve the stiffness of joints. Theoretical analis was carried ot and the reslts showed a good correlation with the experiments. Kewords: hbrid CFR/GFR composites, ed-onl, bonded-and-ed, V-notch 1. INTRODUTION FR composites have been increasingl sed in civil infrastrctre applications de to their advantageos properties sch as high specific strength, lightweight, and corrosion resistance. Recentl, a hbrid FR girder consisting of carbon and glass fibers have been developed. The idea is to se the sperior strength of CFR in the flanges while keeping the material costs low b sing GFR in the flanges and web. A nmber of laborator tests have been condcted to investigate the strctral performance of hbrid FR beam and the reslts showed a possibilit of tilizing this beam as a bridge component 1). However there are still two major isses needed to be frther investigated before appling hbrid FR beam for real bridge application. One is development of joining for hbrid FR composites. The other is evalation of environmental aspects sch as amont of carbon dioxide emission (CO 2 ) and life ccle cost of hbrid FR bridges. As the second step of the ongoing FR research project spported b Japanese government, this std focses on the first isse with emphasis on developing an effective joining method for hbrid FR composites. Joining of FR composite is commonl achieved b adhesive bonding, mechanical fastening or a combination of the two methods. The combination of adhesive bonding and mechanical fastening is often emploed as a safegard against defects within the adhesive laer which ma lead to prematre or catastrophic failre 2). Nmeros experimental and analtical investigations on joining of FR composites have been condcted which mainl focsed on aerospace applications 3-8). However, limited pblished works exist in the field of civil infrastrctre applications. In addition, previos stdies cover a wide range of FR composites with varios fiber architect and matrix tpes, fiber la-p and stacking seqences, etc., which reslt in different behavior of joints. Ths, additional investigations are reqired to fll nderstand the characteristics of joints. This std focses on experimentall and analticall determined behavior of joints of hbrid CFR/GFR composites in small scale (copon) and large scale (beam) tests. A nmber of copon and beam specimens with doble lap ed-onl and bonded-and-ed joints were tested to examine their strength and behavior. The effects of end distance, -torqe, V-notch splice plates and the contribtion of adhesive bonding to the joint strength and failre modes are discssed. 2. COUON TET 2.1 Test pecimen A series of hbrid FR copon specimens with ed/bonded doble lap joints were tested nder tensile loading as shown in Fig. 1. All specimens were ct from the flanges of the large-scale hbrid FR I-beams. Tpical specimens have the same width of w = 8 mm, nominal -23-

2 thickness of t = 14 mm, end distance of e = 3 mm, side distance of s = 2 mm, longitdinal and transverse hole spacing of p = g = 4 mm. The FR laminates consist of CFR and GFR. The angle of CFR was fixed to be zero degree to the longitdinal direction while the angle of GFR was, 9, ±45 degree or Continos trand Mat (CM). All specimens were manfactred sing pltrsion process. Laer composition of hbrid FR copon specimens is shown in Fig. 2. Material properties of the FR laminates are listed in Table 1. Table 1 Material properties of FR laminate arameters Notation CF GF GF GF /9 ±45 CM Yong s Modls * E 11 (Ga) E 22 (Ga) hear Modls * G 12 (Ga) oisson s Ratio * 12 (-) * bscripts 11, 22 and 12 indicates properties of FR materials in longitdinal direction (fiber direction), transverse direction (perpendiclar to fiber direction) and shear direction, respectivel. w e p p e s g s Fig. 1 Test configration Metal Grip Gsset late teel late tainless Bolts d = 1 mm FR Laminate Alminm late CF GF /9 CM GF ±45 Fig. 2 Laer composition of hbrid FR composite Tpical specimens were configred with the same ratios of end distance to diameter (e/d = 3), laminate width to diameter (w/d = 8), side distance to diameter (s/d = 2), longitdinal spacing (pitch) to diameter (p/d = 4), transverse spacing (gage) to diameter (g/d = 4), diameter to splice plate thickness (d/t sp = 1.1), washer diameter to diameter (d w /d = 2.5) and hole clearance (d h d =.5d). tainless steel s were sed with a nominal diameter of 1 mm. The ield and ltimate strength of s are 45 Ma and 7 Ma, respectivel. Holes were machined in the specimens sing diamond tips. The specimens were lateral clamped with s throgh 9 mm thick splice plate in both sides. The torqe was applied exactl at distinct vales b controlling the presetting torqe wrench. The same configration was set for specimens with ed-onl and bonded-and-ed joints. For the bonded-and-ed joint specimens, a preset torqe is applied to the s at the same time with the adhesive. The adhesive was then cred in the experimental room for 24 hors before each test. The mechanical properties of adhesive are shown in Table 2. A nmber of copon specimens with doble lap ed-onl and bonded-and-ed joints were tested to examine their strength and behavior. The effects of end distance, -torqe, V-notch splice plates and the contribtion of adhesive bonding to the joint strength and failre modes are discssed. Copon test variables are listed in Table 3. It is necessar to emphasize that the reslts of copon tests discssed in this paper are onl applicable for a specific case in which the ratio of diameter to laminate thickness is fixed to.7. Table 2 Mechanical properties of adhesive arameters Cring roperties after cring condition (N/mm 2 ) Bending strength 5 Compressive strength 7 Compressive modls 2±2 C 4 Tensile strength 2 Tensile shear strength 1 Table 3 Copon test variables pecimen Tpe Tpe of No. Torqe TAL of splice of (Nm) (mm) joint plate s 2 ED A B Flat n/a A1 BB Flat d A2 BB V-notch.1 TAL1.1 TAL5 BB Flat d TAL E2d-B 2d E3d-B B Flat 2 2 n/a 3d E4d-B 4d E2d-BB 2d E3d-BB BB Flat d E4d-BB 4d T5 5 T2 BB Flat d T3 3 B = Bolted-onl; B = Bonded-and-ed; 1 TAL = Thickness of adhesive laer; 2 ED = End distance (distance from one end of the FR laminate to the center of the nearest hole as shown in Fig. 1) -24-

3 2.2 Test etp and Measrement All tests were condcted sing a Universal Testing Machine (UTM) with a load capacit of 5 kn. The data logger was sed to record load, displacement and strain data. The specimens were clamped b the grips of the testing machine at both ends and the tensile force was applied at the top and bottom end. Clip gages were attached on the both sides of the specimen to measre the relative displacement between the FR laminate and the splice plates. Each specimen was instrmented with back-to-back strain gages attached on the FR laminate and the splice plates. The test setp is schematicall illstrated in Fig. 3. train gage tainless Bolt Fig. 3 Test setp teel late FR Laminate Metal Grip 2.3 Test Reslt and Discssion (1) Load and displacement crve The comparison of load-relative displacement crves of specimens with configration of 6- doble lap joints is shown in Fig. 4. For identification prpose, the specimen with ed-onl will be referred to as specimen A and the specimen with bonded-and-ed will be referred to as specimens A1 and A2 as shown in Table 3. Fig. 4 Load-relative displacement crve Clip Gage 4 Major Major shear/bending (s) Bolt failre 35 debonding (adhesive) Max. (4) 3 (4) (3) Load redction 25 (3) 2 Bearing (plates) 15 hear/bending (s) pecimen A (Bolted-onl) 1 (2) pecimen A1 (Bonded-and-Bolted) 5 (1) (2) Bolts slip into bearing region Note that the relative displacement in the figre indicates the difference in the averaged elongation of clip gages attached on both sides of the specimen (one end of the clip gage is attached on the splice plate and the other end is attached on the specimen). As can be seen, the load-displacement crve of the specimen A can be sbdivided into for stages. For the first stage (1), there was no slip between the splice plates and the FR laminates when the load in the range of to 15 kn. This is de to the effect of the -torqe applied to the s. For the second stage (2), the load-displacement crve behaves linearl when the load increases from 15 to 6 kn corresponding to the relative displacement of.-1. mm. This indicates that the s gradall slipped into bearing region arond the holes of FR laminates. The third stage (3) shows the nonlinear behavior of the load-displacement crve with the range of relative displacement from mm. This might be de to the development of bearing failre in the FR/splice plates combined with shear/bending of the s. The final stage (4) is the load redction after excessive failre strength of s. imilarl, the load-displacement crve of the specimen A1 can be sbdivided into for stages. The first stage shows the slip resistance of joints when the load is approximatel 5 kn. This vale is three times higher than that of the specimen A de to the contribtion of adhesive bonding. It is noted that the hole clearances are filled with the adhesive dring the preparation of specimen A1. However, onl a part of these are filled with the adhesive de to its high viscosit. Hence the second stage exists in the specimen A1 bt the slip is significantl redced compared to the specimen A. Indeed, the second stage indicates linear behavior of load-displacement crve when the load increases from 5-13 kn corresponding to the relative displacement of.5-.2 mm. The third stage (3) exhibits a gradal development of bearing failre in the FR/splice plates together with local debonding of the adhesive laer and shear/bending of s when the load increases from kn corresponding to the relative displacement of mm. The final stage shows the sdden failre of the specimen A1 at abot 345 kn. It is clear from Fig. 4 that the stiffness of the load-displacement crve of the specimen A1 is mch higher than that of the specimen A. This sggests that adhesive bonding can improve considerabl the slip resistance and the stiffness of joints. (2) Effect of Thickness of Adhesive Laer The effect of thickness of adhesive laer was investigated sing specimens with the same configration as specimen A1. Three distinct specimens TAL1, TAL5 and TAL15 were prepared with the thickness of adhesive laer (TAL) of.1 mm,.5 mm and 1.5 mm, respectivel. The load-displacement crve of all specimens is shown in Fig. 5. The figre shows that all specimens have the same failre load and failre mode. The failre modes of these specimens were debonding of adhesive laer and shearing of s. From this figre, it reveals that the stiffness of the load-displacement crve is proportional to the thickness of adhesive laer. The specimen TAL15 had the highest stiffness while the specimen TAL1 had the lowest one. However, it is interesting to note that the specimen TAL15 had almost similar stiffness compared -25-

4 to that of specimen TAL5 before major debonding takes place. This indicates that with the increase in thickness of adhesive laer from.5 to 1.5mm, the increase in joint stiffness is insignificant. The load at which major debonding occrs of specimen TAL5 is higher than that of specimen TAL15. From these reslts, it ma sggest to se the thickness of adhesive laer of.5 mm for bonded-and-ed connection of hbrid FR composite. However, b looking at the load-displacement crve in a smaller scale of the initial loading stage, it is fond that the specimen TAL1 shows a stable behavior while specimens TAL5 and TAL15 exhibit a zigzag behavior. The zigzag behavior ma be cased b stress concentration in the area of the adhesive thickness holders leading to the local debonding of adhesive laer at these positions. In addition, it is not eas to control exactl the thickness of adhesive laer especiall in the constrction site. Hence the soltion of no thickness control (thickness of adhesive laer is approximatel.1-.2 mm) is recommended to se for practical application TAL1 (t =.1 mm) TAL5 (t =.5 mm) TAL15 (t = 1.5 mm) 5 Bonded-and-ed joint (6- configration) Fig. 5 Effect of thickness of adhesive laer (3) Effect of V-Notch plice lates To examine the effect of splice plates on the strength of bonded-and-ed joints, two specimens with the same configration bt different tpes of splice plates were tested. The specimen A1 sing flat splice plates while specimen A2 sing V-notch splice plates (height and spacing of V-notches are.5 mm and 1. mm, respectivel). The original idea of sing V-notch splice plate is to provide more clamping force between the splice plates and the hbrid FR specimen (splice plates bite the specimen) with an appropriate amont of torqe that will not lead to damages at the otermost srface of the specimen. Fig. 6 shows the comparison of the load-relative displacement relationship between specimens A1 and A2. The figre shows that the stiffness of load-displacement crve of these specimens is almost the same p to 13 kn. However, with the contining increases of load, specimen A2 shows higher stiffness than that of specimen A1. The differences in stiffness tend to increase with the increases of load. This ma be de to rogh srface of the splice plate in specimen A2 contribted to improve bonding between the splice plates and the hbrid FR specimen. Indeed, the load at which major debonding of adhesive laer and major shear/bending of s happen of specimen A2 is approximatel 14% higher than specimen A1. This indicates that adhesive laer ma carr almost the load before major debonding occrs. When the adhesive laer fails, the load is carried solel b s. Finall, both specimens A1 and A2 fail de to shearing of s. Major debonding (adhesive) 4 Major shear/bending (s) Bolt failre 35 3 Load redction (4) 25 V-Notch splice plates 2 15 Flat splice plates 1 Bolts slip into 5 bearing region (2) pecimen A1 (Flat splice plates) lip resistance (1) pecimen A2 (V-notch splice plates) Fig. 6 Effect of splice plates (4) Effect of End Distance To investigate the effect of end distance to the failre strength of joints, a nmber of specimens with 2- configration varing end distances (e) from 2d to 4d (where d is nominal diameter of ) were condcted. Two series of specimens with ed-onl and bonded-and-ed joints were investigated. Fig. 7 shows the relationship between load and displacement of ed-onl joint specimens. It can be seen that the specimen E2d-B (with end distance of 2d) has lowest failre load and failed de to shear-ot failre of the FR laminate as shown in Fig. 8. The specimens E3d-B and E4d-B (with end distance of 3d and 4d, respectivel) have almost the same failre load bt different failre modes. The failre mode of specimen E3d-B was shear-ot failre while the failre mode of specimen E4d-B was bearing failre. This indicates that specimen E4d-B is the most appropriate for the ed-onl joints. However, all specimens with bonded-and-ed joints (E2d-BB, E3d-BB and E4d-BB) showed the same failre load and failre mode althogh the end distance was varied as same as ed-onl specimens. The load-displacement crve of bonded-and-ed specimens is shown in Fig. 9. ince the load is mostl carried b the adhesive at the initial loading stage, the load redctions at arond 4-7 kn seem to be cased b the local debonding of the adhesive. The failre mode of these specimens was bearing failre. The differences in failre mode of ed-onl and bonded-and-ed specimens were de to the present of adhesive laer. As previos discssion, adhesive ma carr almost the load before major debonding occrs. The load is then transmitted to the s bt the cold not case the shear-ot failre as ed-onl specimens. This sggests that shear-ot failre was developed gradall bt not sddenl. It is -26-

5 conclded that the effect of end distance on the failre strength of bonded-and-ed joints is not sensitive as that of ed-onl joint and the failre mode of bonded-and-ed specimens is of desirable failre mode. The end distance of 3d is minimm reqirement for designing of joints for hbrid FR composites adhesive laer and bonding strength cold therefore redce. From these reslts, it sggests that the effect of the applied torqe is onl to provide fixation between the splice plates and FR specimen dring adhesive cre. An appropriate amont of torqe needs to be large enogh to fix joint parts and to keep an eqal spreading of adhesive laer. Based on the reslt of this std, it is recommended to se 2 Nm amont of torqe for bonded-and-ed connection of hbrid FR composite. 8 E2d-B (e = 2d) 6 E3d-B (e = 3d) E4d-B (e = 4d) 4 2 Bolted-onl joint (2- configration) Fig. 7 Effect of end distance to ed-onl joint e = 2d e = 3d e = 4d T5 (T = 5 Nm) T2 (T = 2 Nm) T3 (T = 3 Nm) Bonded-and-ed joint (2- configration) Fig. 1 Effect of torqe 12 1 hear ot Bearing Fig. 8 Failre mode of ed-onl specimens 8 E2d-BB (e = 2d) 6 E3d-BB (e = 3d) E4d-BB (e = 4d) 4 2 Bonded-and-ed joint (2- configration) Fig. 9 Effect of end distance to bonded-and-ed joint (5) Effect of Bolt Torqe The same configration of bonded-and-ed specimens sing for the investigation of the effect of end distance was tilized to examine the effect torqe. Applied torqes with vales of 5 Nm (finger tight), 2 Nm and 3 Nm was investigated. Fig. 1 shows the load-displacement relationship of all specimens. The figre indicates that the load-displacement crve of specimen T5 and specimen T2 shows almost the same slope and failre load. However, specimen T3 exhibits slightl lower slope than the others. This implies that large amont of torqe (3 Nm) ma reslt in neqal spreading of 2.4 Theoretical Derivation and Comparisons Althogh the erviceabilit Limit tate (L) of joint ma be defined as occrrence of slip bt the Ultimate Limit tate (UL) mst be cleared becase of the brittle characteristics of hbrid FR composite. resentl, no workable theoretical soltion has been available to determine the behavior of doble lap bonded-and-ed joints of hbrid FR composites. This section is concerned primaril with developing a soltion for prediction of load-displacement relationship of bonded-and-ed joints nder the UL. The behavior of load-displacement is obtained b modifing the theoretical work of Fisher 9-1). The theoretical soltion is based on the following major assmptions: (1) s transmit the entire applied load b shear and bearing once major debonding/slip has occrred; (2) the stress-strain relationship of FR laminate is linear-elastic. The displacements in s and plates are schematicall shown in Fig. 11. The load-displacement relationship is defined b the following eqation: elongationfr elongationsplice 2 where = total displacement, elongation FR, elongation splice = elongation of FR laminate and splice plate in the strip of hole pitch, = displacement of s shear/ bending bearingfr bearingsplice 3 In eqation 3, shear / bending = relative shear and bending -27-

6 displacement of s, bearing FR = bearing displacement in FR laminate, bearing splice = bearing displacement in splice plate Displacement of s is determined sing the modification of the empirical eqation proposed b Fisher 9-1) : 1 1 ln 1 4 N with N obtained b the eqation 7: plastic elongation splice p p n 2AE 1 w wd with 23 ln 1 7 In eqations 5, 6 and 7, = applied load, p = pitch, A FR, E FR and A, E are respectivel gross cross-sectional area and Yong s modls of FR laminate and splice plates, n A = net where, = regression coefficients, = applied load, cross-sectional area of the splice plate,, and, are = ltimate shear load of one, N = total nmber of s. ield and ltimate load/stress of splice plates, w = width of the splice plate, d = nominal diameter of s. The load-carring capacit of bonded-and-ed joints with 2, 4, 6 and 8- configration is shown in Fig. 12. The figre shows a good agreement between the experiments and analsis. The regression coefficients and in eqation 4 were experimentall determined to be 1.2 and.4, respectivel. (a) Joint configration Fig. 12 Load-carring capacit of joint 2-s (Analsis) 2-s (Experiment) 4-s (Analsis) 6-s (Experiment) 6-s (Analsis) 8-s (Analsis) (b) Relationship of hole and displacements Fig. 11 Displacements in s and plates The elongations of FR laminate and splice plates in the strip of hole pitch in eqation 2 was approximated in the elastic range as elastic elongationfr elastic elongationsplice p AFRE p 2AE FR 5 ; with 6 In the inelastic range, the elongation of splice plates can be ince the regression coefficients are experimentall determined, it is possible to appl this theoretical soltion for varios test parameters sch as diameter, characteristics of splice plates and FR laminate (material properties, geometr, and roghness of the srfaces). The theoretical soltion is therefore applicable for doble-lap bonded-and-ed joints with V-notch splice plates which are fond as the most effective joints in this std. 3. FULL-CALE TET OF HYBRID FR BEAM WITH BUTT JOINT 3.1 Test pecimen The reslts of the tensile copon tests were sed for design of the large scale beams with btt joints. The doble-lap bonded-and-ed joint with V-notch splice plate were selected -28-

7 as the joining method for all beams. The end distance of 3d, the amont of torqe of 2 Nm and the thickness of adhesive laer of approximatel.1 mm were applied. The ltimate shear strength of s obtained from the copon tests was tilized to predict the ltimate load of beams as presented in the appendix. A nmber of laborator tests were condcted on hbrid FR I-beams of 95 mm wide, 25 mm high, 14 mm (flange) and 9 mm (web) thick. The hbrid FR I-beams were fabricated with a length of 35 mm. A nmber of beams were ct into halves with each length of 175 mm for joining in the flexral span. Btt joints of the ct beams at flanges and web sing 9 mm thick V-notch splice plates, 1 mm stainless s and a ver thin laer of adhesive were prepared. A torqe of 2 Nm was applied to the s. The adhesive was cred in the experimental room for 24 hors before the test. The hbrid FR beam has the same mechanical properties as that of the copon specimens as listed in Table 1. Details of joints and specimens for fll-scale tests are shown in Fig. 13. Beam test variables are listed in Table 4. Table 4 Beam test variables Length of Total Nmber of Tpe of joined parts length s Beam joint L1 L2 L Flange Web (mm) (mm) (mm) B C n/a n/a 35 n/a n/a B BB B C = Control beam (withot joints); BB = Bonded-and-ed joints (HFR-1) V-notch splice plate (t = 9 mm) FR laminate (a) Cross section 5 V-notch splice plate (t = 9 mm) tainless steel s M Adhesive (b) Elevation Fig. 13 Details of specimen for fll-scale test of joints (HFR-2) Test etp and Measrement The beams were simpl spported and tested in for-point bending at a span of 3 mm with an interior loading span of 1 mm. The test setp is shown schematicall in Fig. 14. Linear Voltage Displacement Transdcers (LVDT) and laser transdcers were sed to measre the deflection of the beams in mid-span section and nder the loading points. A nmber of strain gages were attached in flexral span, shear span and near the loading points to measre the strain distribtions of the beams. A high-speed camera was placed in front of the beams to record the sdden failre. Transdcers Load cell preader beam Fig. 14 Test setp and measrement High speed camera 3.3 Test Reslt and Discssion (1) Load-Deflection Crve The load-deflection crve at mid-span section of beams B, B1, B2 nder for-point bending test is shown in Fig. 15. The reslts show that both beams B and B2 behave linear p to failre. Beam B2 failed at somewhat lower load than beam B. However beam B2 shows higher stiffness than that of beam B de to the present of the splice plates and s in the flanges and web. rediction of ltimate load of beam B1 and B2 was condcted and the reslts showed a good correlation with the experiments (Fig. 15). Details of comptation are shown in the Appendix A. It shold be noted that the flexral strength of beams will decrease abot 1% when the effect of the web splice plates is not taken into accont (as in this std). Hence the good agreement between the experiments and analsis ma be de to the effect of V-notch splice plates. The failre mode of beams B and B2 was crshing of fiber near the loading point followed b the delamination of the top flange. This tpe of failre mode is generall happened otside of the joint and located near the loading point de to the stress concentration 1). It is totall different with the bearing and shear-ot failre which are taken place in the joint as presented in section 2.3. Bearing failre leads to an elongation of holes while shear-ot failre is regarded as a special case of bearing failre. Web bckling in the flexral span was observed in the case of beam B2 de to the constraints of joints in the flanges and web as shown in Fig. 16. B a visal monitoring dring the test -29-

8 of beam B2, it seems that failre did not happen in the joined part as predicted. In contrast, beam B1 was expected to fail in the joined part. Indeed, beam B1 behaves linear p to onl 13 kn. With the contining increases of load, the behavior of beam B1 is nonlinear becase of the major debonding of adhesive laers and the shear/bending of s. The final failre mode of beam B1 was the shearing of s in the bottom flange leading to rotation of the splice plates in the web (Fig. 16) Comptedltimate load (Beam B2) 16 Control beam 14 Comptedltimate load (Beam B1) (Beam B) 12 Beam B1 1 Beam B Deflection (mm) Beam B1 Bolt failre Fig. 15 Load-deflection crve Web splice rotation Beam B2 Fig. 16 Failre mode of beams B1 and B2 Delamination Web crshing (2) Load-train Crve of plice lates Fig. 17 shows the relationship between the load and strain of the splice plates at the top and bottom flanges at mid-span section of beams B1 and B2. In the case of beam B1, both the compressive and tensile strains behave linear to the points that major debonding of adhesive laer and major shear/bending of s occr. Then behavior of strains becomes nonlinear de to the bend/shearing of s. On the other hand, the compressive strain of beam B2 behaves linear p to failre while the tensile strain of beam B2 behaves nonlinear after the major debonding of adhesive laer takes place. It is interesting to note that the load at which major debonding occr in the tension flange splice is alwas lower than that in the compression flange splice. Indeed, load is mostl carried b the adhesive before the occrrence of major debonding and the reslts from the copon tests indicate that high peel stresses at the end of joint in the tension flange splice ma case the prematre debonding. Conversel, peel stresses in the compression flange splice are tpicall not of concern for the separation of joints and the debonding in the compression flange splice ma therefore happen at higher load than that in the tension flange splice. 4. CONCLUION Fig. 17 Load-strain crve of splice plates This paper presented the experimental and analtical stdies on the behavior of doble lap joints in pltrded hbrid CFR/GFR composites. Two tpes of connections were examined inclding ed-onl and bonded-and-ed. The following main conclsions can be addressed: 1. The combined se of steel s, adhesive bonding and V-notch splice plates in doble lap joints was fond to be an effective method for joining hbrid FR composites. The rogh srface of V-notch splice plates and adhesive bonding contribtes to improve the stiffness of joints. 2. The hbrid FR beam with btt joints in flexral span sing the effective joining method showed almost the same strength and stiffness as the beam withot joints. The stiffness of joints was most likel depended pon the bonding strength of adhesive laer while the ltimate load and failre mode of joints were governed b the nmber of s. 3. Theoretical analsis was carried ot and the reslts showed a good correlation with the experiments. ACKNOWLEDGEMENT: This research was fnded b a Ministr of Land, Infrastrctre and Transport of Japan (MLIT) grant-in-aid for scientific research of constrction technolog, which is gratefll acknowledged. AENDI A Major debonding (adhesive) 8 Major shear/bending (s) 6 Beam B1 (Top flange) Major debonding (adhesive) 4 Beam B1 (Bottom flange) Major shear/bending(s) Beam B2 (Top flange) 2 Beam B2 (Bottom flange) train () Bolt failre rediction of Ultimate Load of Hbrid FR Beam with Btt Joint in the Flexral pan Assming that the flanges are carried all of the bending moment and the shear force is resisted b the web alone. In this std, there is no shear force applied in the flexral span and the strength of joint is therefore governed b the magnitde of bending moment. The forces in the tension flange (T) and in the compression flange (C), shown in Fig. A1, are given b: -3-

9 M L T C A1 H t 6 H t where M = bending moment, H = height of hbrid FR beam cross section, t = thickness of the flanges, = applied load and L = span of beam. t C C H Fig. A1 Calclation of flange forces The ltimate load of joint is obtained when the tension and compression force reach the ltimate shear capacit of s: where T M T C N ma N A2 b = ltimate shear load of one, N = total nmber of s in one flange, m = nmber of shear planes (m = 2), A b = cross section area of one, = ltimate shear strength of one. From eqations A1 and A2, the ltimate load of joint can be compted sing the following eqation: 6mAb N H t L A3 Note that bearing load of the hbrid FR composite and splice plate mst satisf the eqation A4: pl Ndt A4 b pl b which d = nominal diameter of, t pl = thickness of FR/splice M T h = H - t plate, b = ltimate bearing strength of FR/splice plate. References 1) Ngen Dc Hai, Hiroshi Mtsoshi, hingo Asamoto, and Takahiro Matsi, trctral Behavior of Hbrid FR Composite I-Beam, Jornal of Constrction and Bilding Materials, Elsevier, in press (29). 2) G. Kell, Qasi-tatic trength and Fatige Life of Hbrid (Bonded/Bolted) Composite ingle-lap Joints, Compos trct 72 (26), pp ) Camanho.., Matthews F. L., tress Analsis and trength rediction of Mechanicall Fastened Joints in FR: a Review, Composites art A 28A (1997), pp ) L.J. Hart-mith, Adhesive Bonding of Composite trctres: rogress to Date and ome Remaining Challenges, J Compos Technol Res 24 (22) (3), pp ) Tate MB, Rosenfeld J., reliminar Investigation of the Loads Carried b Individal Bolts in Bolted Joints, NACA TN 151, Ma (1946). 6) Nelson WD, Bnin BL, Hart-mith LJ., Critical Joints in Large Composite Aircraft trctre, NAA CR-371, Agst (1983). 7) Hart-mith LJ., Design Methodolog for Bonded-Bolted Composite Joints, Technical Report AFWAL-TR , Doglas Aircraft Compan (1982). 8) L.J. Hart-mith, Bonded-ed Composite Joints, J. Aircraft (1985), pp ) J.W. Fisher and J.L. Rmpf, Analsis of Bolted Btt Joints, Jornal of the trctral Division, ACE, Vol. 91, T5, October ) J.W. Fisher, Behavior of Fasteners and lates with Holes, Jornal of the trctral Division, ACE, Vol. 91, T6, December (1965). (Received eptember 24, 29) -31-