SHEAR STRENGTH OF CONCRETE-ENCASED COMPOSITE STRUCTURAL MEMBERS

Transcription

1 SHEAR STRENGTH OF CONCRETE-ENCASED COMPOSITE STRUCTURAL MEMBERS By C. C. Weng, 1 S. I. Yen, 2 nd C. C. Chen 3 ABSTRACT: This study investigtes the sher strength of omposite steel nd onrete members in whih the steel shpe is fully ensed in onrete. Two types of sher filure digonl sher nd sher bond re exmined in this study. Through understnding of these filure modes, new pproh is proposed to predit the sher pities of omposite members. Mjor prmeters investigted inlude steel flnge width, sher reinforement, onrete strength, nd pplied xil lod. To evlute the ury of the proposed pproh, verifition nlysis is mde by ompring sher pities predited by the proposed pproh with previous test results. Furthermore, the sher pities predited by the proposed pproh re lso ompred with those obtined by Amerin nd Jpnese provisions. The results of the nlysis nd omprison indite tht the proposed pproh yields stisftory predition of sher strength nd provides rtionl explntion on the mehnism of sher bond filure. A new term, the ritil steel flnge rtio, is introdued to distinguish the sher bond filure from the onventionl digonl sher filure. INTRODUCTION The omposite steel nd reinfored onrete struturl system n form building rrying the merits of eh mteril. Preventing sher filure is one of the mjor onerns when designing omposite struturl member. The sher filure of onrete-ensed omposite member generlly involves two possible filure modes: (1) the digonl sher filure, whih losely resembles the sher filure of n ordinry reinfored onrete struturl member; nd (2) the sher bond filure (s shown in Fig. 1), whih results in rks long the interfe of the steel flnge nd onrete. For omposite member, the sher bond filure n be ritil when the steel flnge width is lrge nd pprohing the overll width of the omposite setion. Experiments onduted in Jpn hve shown tht sher bond rks long the interfe of the steel flnge nd onrete re responsible for erly filure of some tested onrete-ensed omposite members (Wkbyshi 1988; Zhng 1993). Among the sher design pprohes developed for onreteensed omposite members, the design provisions suggested by the Amerin building speifitions nd by the Jpnese building odes re two widely employed pprohes. In the United Sttes, the design provisions of omposite members n be found in the Amerin Conrete Institute (ACI) (1999) building ode, the Amerin Institute of Steel Constrution (AISC) (1993) LRFD speifition, nd the seismi provisions [Building Seismi Sfety Counil (BSSC) (1997)]. In the ACI ode, the onrete nd the trnsverse reinforement provide the sher resistne of the onrete-ensed omposite member. However, no design provision is vilble to prevent the possible sher bond filure. In the AISC-LRFD speifition (Chpter I), the steel web is responsible for the sher resistne of the omposite member; but the ontribution of the onrete nd trnsverse reinforement is onservtively negleted. In the provisions (Chpter 7), lthough the steel web nd the trnsverse reinforement re tken into - 1 Prof., Dept. of Civ. Engrg., Nt. Chio Tung Univ., 1001 T Hsueh Rd., Hsinhu, 30050, Tiwn. E-mil: weng@.ntu.edu.tw 2 Grd. Res. Asst., Dept. of Civ. Engrg., Nt. Chio Tung Univ., 1001 T Hsueh Rd., Hsinhu, 30050, Tiwn. 3 Asso. Prof., Dept. of Civ. Engrg., Nt. Chio Tung Univ., 1001 T Hsueh Rd., Hsinhu, 30050, Tiwn. Note. Assoite Editor: Amir Mirmirn. Disussion open until Mrh 1, To extend the losing dte one month, written request must be filed with the ASCE Mnger of Journls. The mnusript for this pper ws submitted for review nd possible publition on June 26, 1998; revised April 2, This pper is prt of the Journl of Struturl Engineering, Vol. 127, No. 10, Otober, ASCE, ISSN /01/ /$8.00 $.50 per pge. Pper No ount for the sher resistne of the omposite member, the onrete prt is not inluded. Most importntly, both of the AISC nd provisions do not provide design guidne to void the sher bond filure tht my our long the interfe of the steel flnge nd onrete of onrete-ensed omposite member. In Jpn, the onept of superposition for the sher design of omposite members is dopted in the Arhiteturl Institute of Jpn (AIJ) steel reinfored onrete (SRC) building ode (AIJ 1987). The sher bond filure mode is onsidered in the design ode. Although the Jpnese guidelines re omprehensive for design of omposite members, muh of the guidelines re not pplible to U.S. onstrution due to differenes in design prtie (Riles 1994). It is noted tht 5-yer reserh progrm on omposite nd hybrid strutures (Goel 1997; Nishiym 1998) s phse 5 of the U.S.-Jpn oopertive erthquke reserh progrm ws initited in This progrm ws orgnized into the following four groups: (1) onrete-filled tube olumn systems; (2) reinfored onrete nd steel reinfored onrete olumn systems; (3) hybrid wll systems; nd (4) reserh for innovtion on new mterils, elements, nd systems. The progrm objetives re to develop prtil nlysis nd design proedures for strutures in the first three groups nd fesibility studies of new nd innovtive struturl elements nd omposite systems in the fourth group. However, s for the study on the sher strength of onrete-ensed omposite members, further reserh is needed on the behvior of the sher bond filure mehnism. In light of the bove disussion, this study presents new pproh to predit the sher strengths of onrete-ensed omposite members. The proposed pproh onsiders the possible filure modes of digonl sher filure nd sher bond filure. In ddition, the pproh proposed herein ttempts to FIG. 1. Sher Bond Filure Crks long Interfes of Steel Flnges nd Conrete 1190 / JOURNAL OF STRUCTURAL ENGINEERING / OCTOBER 2001

2 orrespond to the formt of the ACI nd AISC pprohes. To evlute the ury of the proposed pproh, verifition nlysis between sher pities omputed by the proposed pproh nd experimentl results done by other reserhers is mde. Also performed herein is series of prmetri studies to investigte the mjor prmeters tht my ffet the filure mode of omposite member. These prmeters inlude the steel flnge width, stirrup rtio, onrete strength, nd pplied xil lod. A new ftor lled the ritil steel flnge rtio is introdued to distinguish the filure modes between digonl sher filure nd sher bond filure of omposite member. Finlly, the sher pities predited by using the proposed pproh, the AIJ-SRC ode, the ACI ode, the AISC-LRFD speifition, nd the provisions re ompred. The relted sher design provisions of these odes nd speifitions re briefly reviewed in the following setions. AIJ-SRC CODE (AIJ 1987) Aording to the AIJ-SRC ode (AIJ 1987), the sher pity of omposite member is evluted bsed on the method of superposition. Tht is (V ) = V V (1) n omp s u r u where (V n ) omp = sher pity of the onrete-ensed omposite member; s V u = sher pity of steel portion; nd r V u = sher pity of reinfored onrete (RC) portion. Aording to the ommentry on the AIJ-SRC ode, the bond between the steel shpe nd the onrete n be negleted in the ultimte stte. Thus, the sher pity of onrete-ensed omposite member is determined in suh wy tht the steel nd RC portions resist the sher seprtely without bond between them. To determine s V u nd r V u in (1), it is suggested tht smu s u w w F ys V = min, t d (2) l 3 r r u r su Mu V = min l, V (3) where s M u = flexurl pity of the steel portion; l = ler spn length of the omposite member; t w = steel web thikness; d w = depth of the steel web; F ys = yield stress of steel; r M u = flexurl pity of RC portion; nd r V su = sher pity in rv u ontrolled by sher filure of RC portion. To determine rv su in (3), the following formul is suggested: where rv su = min( rv su1, rv su2) (4) rv su1 = B rj(0.5 rfs 0.5wF yh) (5) b V = B j f F (6) B r su2 r s w yh where r V su1 = sher pity in r V su due to digonl sher filure of RC portion; r V su2 = sher pity in r V su due to sher bond filure of RC portion; B = gross width of omposite member; r j = distne between entroids of tension nd ompression in RC portion under flexurl; r = oeffiient relted to sher spn rtio of RC portion, onservtively tken to equl 1.0; f s = sher stress of onrete; w = rtio of trnsverse reinforement; F yh = yield stress of trnsverse reinforement; nd b = effetive width of onrete. ACI BUILDING CODE (ACI 1999) In the ACI building ode, there is no ler guideline vilble for the sher design of onrete-ensed omposite members. It is lso noted tht no speifi provision is inluded regrding the prevention of the sher bond filure of onreteensed omposite members. However, there re vluble provisions involving the sher design of ordinry RC struturl members in the ode. In the sher design of n RC member, the digonl sher filure mode is usully the mjor onern of the design. In the ACI ode, the sher pity of n RC member tht fils in digonl sher n be lulted by using the following equtions: with (V ) = V V (7) n r r AF v yhd V r = 0.67fbd (8) S nd members subjeted to sher nd bending V = 0.17fbd (9) members subjeted to sher, bending, nd xil ompression N u A g V = fbd (10) nd members subjeted to sher, bending, nd xil tension N u A g V = fbd (11) where (V n ) r = sher pity of RC member; V r = sher ontribution of the trnsverse reinforement; V = sher ontribution of the onrete portion; A v = re of trnsverse reinforement within distne S; d = distne from extreme ompression fiber to entroid of longitudinl tension reinforements; S = sping of trnsverse reinforement; f = onrete ompressive strength; b = gross width of RC member; N u = required xil ompression or tension omputed t ftored lods; nd A g = gross re of RC member. AISC-LRFD SPECIFICATION (AISC 1993) For onrete-ensed omposite bems, the AISC-LRFD speifition sttes tht the sher pity should be determined by the properties of the steel setion lone. The sher pity ontribution of the RC portion is onservtively negleted. For onrete-ensed omposite olumns, the AISC- LRFD speifition hs no ler design guideline regrding the determintion of the sher pity of the omposite olumns. It is lso noted tht there is no relted provision to void sher bond filure of the omposite member. SEISMIC PROVISIONS (BSSC 1997) In the provisions, the sher pity of omposite bem follows the relted provisions in the AISC-LRFD speifition. However, the sher pity of onrete-ensed omposite olumn is tken s the sum of the ontribution of the steel web plus the trnsverse reinforement. The sher pities of the steel web nd the trnsverse reinforement n be lulted by the formuls suggested in the AISC-LRFD speifition nd ACI ode, respetively. It is lso noted tht the ltest provisions inlude requirements for sher onnetors for ensed omposite olumns. The existene of sher onnetors between steel nd onrete my help to prevent the sher bond filure of omposite olumn. From the review of the sher design provisions presented in the bove setions, the following observtions re mde: (1) JOURNAL OF STRUCTURAL ENGINEERING / OCTOBER 2001 / 1191

3 for the sher design of onrete-ensed omposite members, the urrent ACI, AISC, nd design provisions re not dequte to prevent the possible sher bond filure long the interfe of the steel flnge nd onrete; (2) lthough the AIJ- SRC ode inludes detiled provisions for the sher design of onrete-ensed omposite members, it is noted tht the formt nd the equtions re omplited nd diffiult to use for engineers who re unfmilir with Jpnese building odes. PROPOSED APPROACH This study presents new pproh ontining the following hrteristis: (1) the new pproh onsiders both filure modes of digonl sher filure nd sher bond filure; (2) importnt prmeters suh s steel flnge width, stirrup rtio, onrete strength, nd pplied xil lod re tken into ount in the proposed pproh; (3) the proposed pproh dheres to the onventionl formt of the ACI ode nd AISC speifition so tht engineers n esily use it. Sher Cpity of Composite Member In the proposed pproh, the sher pity of onreteensed omposite member n be determined s follows: with (V ) = (V ) (V ) (12) n omp n s n r (V ) = 0.6F A (13) n s ys ws (V ) = min[(v ), (V ) ] (14) n r n r1 n r2 where (V n ) s represents the sher pity of steel shpe in the omposite member; (V n ) r denotes the sher pity of the RC portion in the omposite member; A ws = re of steel web; (V n ) r1 nd (V n ) r2 = sher pities of the RC portion in the omposite member ontrolled by digonl sher filure nd sher bond filure, respetively. As indited in (14), the sher pity of the RC portion (V n ) r is determined s the smller vlue of the digonl sher pity (V n ) r1 nd the sher bond pity (V n ) r2. The following prgrphs will introdue how (V n ) r1 nd (V n ) r2 re determined in the proposed pproh. Digonl Sher Cpity of RC Portion It is noted tht Priestley et l. (1994) investigted the digonl sher pity of reinfored onrete olumns nd pointed out the onservtism of the sher design formul suggested in the ACI ode. In ddition, reommendtion tht the ACI sher formul needs to be revised ws proposed. However, before the doption of Priestley s reommendtion by the ACI, the digonl sher pity (V n ) r1 of onrete-ensed omposite member is still lulted by using the urrent ACI sher design formul. Tht is (V n) r1 = AF v yh(d/s) 0.17fBd (15) in whih the first term should not exeed 0.67 fbd. For omposite member subjeted to sher, bending, nd xil ompression, the digonl sher pity is N u n r1 v yh A g (V ) = AF (d/s) fbd (16) Sher Bond Cpity of RC Portion To determine the sher bond pity (V n ) r2 of the RC portion, the sher-frition nlogy is utilized in the proposed pproh. As shown in Fig. 2(), when horizontl sher fore V f is pplied to n RC speimen, the reltive slip of the rked prts uses seprtion of the rked surfes. If there is FIG. 2. Sher-Frition Anlogy of RC Member (ASCE ACI 1973): () Reltive Slip of Crked Prts; (b) Reltion between Compression on Conrete nd Tension in Reinforement trnsverse reinforement ross the rk, it is elongted by the seprtion of the surfes nd hene is stressed in tension. For equilibrium, ompressive stresses ting on the onrete surfe re needed, s shown in Fig. 2(b). It is observed tht the sher fore is trnsmitted ross the rked surfe in the following wys: (1) frition resulting from the ompressive stress ting on the rked surfes; nd (2) interlok of ggregte protrusions on the rked surfes ombined with dowel tion of the reinforement rossing the surfe. Test results on the sher frition behvior of RC members presented by Hofbek et l. (1969) nd Mttok et l. (1972) indited tht the sher frition strength of rked surfe with trnsverse reinforement perpendiulr to the sher plne is given s V = A F KA 0.3fA (17) f f vf yh 1 where f = sher frition oeffiient, tken s 0.8 for onrete sliding on onrete; A vf denotes the re of trnsverse reinforement rossing the sher plne; K 1 represents the empiril onstnt, tken equl to 2.8 MP for norml weight onrete; nd A = re of onrete surfe-resisting sher frition. The first term in (17) represents the frition fore, nd the seond term denotes the sher trnsferred by shering off surfe protrusions nd by dowel tion. Owing to the existene of the steel shpe in onreteensed omposite member, the sher-frition nlogy of omposite member is somewht different from tht of n ordinry RC member. Thus (17) needs to be modified so tht it n be useful for sher design of omposite members. Fig. 3 illustrtes the sher behvior in omposite member subjeted to sher bond filure. Fig. 3() illustrtes the sher bond rks long the interfes of steel flnges nd onrete. Fig. 3(b) displys the sher-frition fore long the rked plne. From Fig. 3(b), the horizontl sher frition pity per unit sping S of the RC portion V hf n be lulted by onservtively ssuming tht the ontribution of the bond stress between the steel flnge nd onrete is negligible. Tht is V = AF KA (18) hf f v yh 1 h 1192 / JOURNAL OF STRUCTURAL ENGINEERING / OCTOBER 2001

4 FIG. 3. Composite Member Subjeted to Sher Bond Filure: () Sher Bond Filure Crks; (b) Sher-Frition Fore V hf long Crked Plne where A h = re of onrete resisting the horizontl sher frition fore within distne S, tken s S b; S = sping of trnsverse reinforement; b = effetive width of the onrete setion to resist sher bond filure, tken s (B b f ); B nd b f re the widths of the gross setion nd the steel flnge, respetively. From (18), the mximum verge sher stress provided by internl sher frition fore on the rked surfe within distne S, 1 n be expressed s V hf = (19) 1 bs The use of b in (19) is to show the ft tht if the steel flnge width beomes lrger nd pprohes the overll width of the omposite setion, the horizontl sher resistne provided by the onrete portion long the interfe of the steel flnge nd onrete will pproh zero. The sher stress resulting from pplied sher fore V r of the RC portion t the lotion of the rked surfe 2 n be omputed from V r Q 2 = (20) Ib where Q denotes the first moment of the onrete re bove the interfe bout the neutrl xis of the RC portion; nd I = moment of inerti of the RC portion. It is noted tht (20) pplies to unrked elsti onrete members nd is only n pproximtion for rked onrete members (MGregor 1997). To simplify the lultion, the verge sher stress is ssumed s uniformly distributed on the effetive onrete re of A v, in whih A v is tken s b d. Thus V r 2 = (21) bd To prevent the sher bond filure, the sher stress resulting from pplied sher fore 2 should not be lrger thn the sher stress provided by internl sher frition fore 1. Tht is Vr Vhf (22) bd bs Substituting (18) into (22) nd with b repled by (B b f ) leds to V AF (d/s) K (B b )d (23) r f v yh 1 f Eq. (23) implies tht the sher bond pity of the RC portion, (V n ) r2, n be expressed s (V ) = AF (d/s) K (B b )d (24) n r2 f v yh 1 f It is importnt to observe tht (V n ) r2 dereses linerly with n inrese of the steel flnge width. The liner orreltion exists beuse the following simplifitions re mde: (1) the sher stress 2 long the interfe of the steel flnge nd onrete is lulted by using the verge sher stress on the effetive onrete re of A v ; nd (2) the ontribution of the bond stress between the steel shpe nd the onrete is onservtively negleted. Consequently, the sher pity of the RC portion of the onrete-ensed omposite member should be the smller vlue of (16) nd (24). VERIFICATION ANALYSIS To investigte the ury nd suitbility of the proposed pproh, verifition nlysis between the test results nd the preditions of the proposed pproh nd the AIJ-SRC ode (AIJ 1987) is mde in this study. The test results listed in Tble 1 were onduted by Zhng et l. (1993). All speimens hd squre setion of mm nd were rein- Speimen number TABLE 1. Dimensions, Mteril Properties, nd Test Results of Composite Members Done by Zhng et l. (1992) B D (mm) Steel setion (d s b f t w t f ) (mm) Stirrups rtio [ w = A v /(B S)] (%) H H H H H Note: All speimens hd onrete over of 15 mm nd reinfored by deformed brs 10 mm in dimeter deployed t four orners; smooth round brs 3 mm in dimeter were used s sher reinforement every 50 mm long sher spn; N u = pplied xil fore; V test = tested sher strengths of speimens. F ys (MP) F yh (MP) f (MP) N u V test JOURNAL OF STRUCTURAL ENGINEERING / OCTOBER 2001 / 1193

5 fored by deformed brs 10 mm in dimeter t four orners. Smooth round brs 3 mm in dimeter were used s stirrups every 50 mm long the sher spn. The ensed wide flnge steel ws built up by fillet welding from steel plte 2 or 3.2 mm in thikness. The test setup is shown in Fig. 4(). A typil rk pttern nd filure mode of the seleted speimens t the ultimte stte re illustrted in Fig. 4(b). From Fig. 4(b), it is observed tht ll speimens listed in Tble 1 filed in the sher bond filure ondition. Tble 2 shows the omprtive results between the test results nd the predited sher strengths bsed on the proposed pproh nd the AIJ-SRC ode (AIJ 1987). The preditions of the ACI, AISC, nd design provisions re not listed in this tble; owing to these provisions does not provide formuls to lulte the sher strength ontrolled by the sher bond filure. From Tble 2, it is observed tht the verge rtios of the predited vlue to the test result re with stndrd devition of 0.05 for the proposed pproh, nd with stndrd devition of for the AIJ-SRC ode. Considering the bove observtion, it is felt tht the sher pity of omposite member n be stisftorily predited by the proposed pproh. In ddition, Tble 2 indites tht the sher strengths predited by the proposed pproh re ontrolled by the sher bond filure mode for ll speimens. However, only the sher strength of Speimen No. 1 predited by the AIJ-SRC ode is ontrolled by the sher bond filure mode. This observtion shows tht the proposed pproh n more resonbly predit the sher filure mode of omposite member thn the AIJ- SRC ode. This is minly beuse the formuls for prediting sher strength of omposite member given in the AIJ-SRC ode [(5) nd (6)] does not involve the xil fore effet on the sher pity of the onrete portion. Although the tested speimens listed in Tble 1 were smll in sle, the writers onsider tht the experiments onduted by Zhng nd Ymd (1993) re still vluble in illustrting the sher filure mehnism of omposite members due to the lk of published reserh reported on lrge-sle test speimens. To further investigte the influene of the sle ftor, it is suggested tht lrge-sle tests on the sher behvior of omposite members will be needed for future studies. PARAMETRIC STUDY Figs. 5 7 summrize the influene of the mjor prmeters, inluding the steel flnge width, stirrup rtio, onrete ompressive strength, nd pplied xil lod on the sher strengths of onrete-ensed omposite members. In these figures, the horizontl xis denotes the rtio of the steel flnge width to the gross width of the omposite setion b f /B, nd the vertil xis represents the sher pity of the omposite member FIG. 4. Physil Test Conduted by Zhng et l. (1993): () Test Setup nd Loding System; (b) Typil Crk Pttern nd Filure Mode of Speimens FIG. 5. Influene of Steel Flnge Width b f nd Stirrup Rtio w on Sher Strength TABLE 2. Comprisons of Sher Strengths Predited by AIJ-SRC Code nd Proposed Method with Test Results Done by Zhng et l. (1992) Speimen number V test Filure mode (V n ) AIJ Filure mode (V n ) prop b Filure mode (V n ) AIJ (V ) V test SB 49.8 SB 45.6 SB SB 51.3 DS d 53.3 SB SB 50.1 DS d 53.3 SB SB 51.1 DS d 53.3 SB SB 53.2 DS d 55.2 SB Averge: Stndrd devition: Coeffiient of vrition: (V n ) AIJ = sher strength predited by AIJ-SRC ode (AIJ 1987). b (V n ) prop = sher strength predited by proposed pproh. SB = sher bond filure. d DS = digonl sher filure. n prop V test 1194 / JOURNAL OF STRUCTURAL ENGINEERING / OCTOBER 2001

6 horizontl lines. This observtion implies tht the steel flnge width rtio does not ffet the sher pity under the digonl sher filure mode. However, if the sher bond filure mode ontrols the sher design, the sher pity drstilly dereses s the steel flnge width rtio inreses. 3. Fig. 5 revels tht the inrese of the stirrup rtio gives rise of both the sher pities of the digonl sher nd the sher bond filure modes. Figs. 6 nd 7 indite tht the inrese of onrete ompressive strength or the pplied xil lod results in n inrese of resistne to the digonl sher filure. CRITICAL STEEL FLANGE RATIO FIG. 6. Influene of Steel Flnge Width b f nd Conrete Compressive Strength f on Sher Strength The ritil steel flnge rtio (b f /B) r is useful in distinguishing between the digonl sher filure mode nd sher bond filure mode. This rtio n be derived from (16) nd (24). Let these two equtions be equl, whih yields bf = Nu f (1 ) F f w yh B K A r 1 g (25) The proposed formul [(25)], revels the following hrteristis of the ritil rtio: (1) the ritil rtio is liner funtion of the stirrup rtio w nd pplied xil lod N u. Also, the ritil rtio dereses with inresing of the stirrup rtio or pplied xil lod; nd (2) the ritil rtio dereses linerly with rdil expression of onrete ompression strength f. From the bove observtions, it is importnt to note tht the ritil steel flnge rtio (b f /B) r of omposite member my beome smller if the stirrup rtio, onrete ompressive strength, or pplied xil lod re inresed. It is likely tht the sher bond filure mode my ontrol the sher design of omposite member if the ritil steel flnge rtio beomes smller. COMPARISONS OF RESULTS PREDICTED BY PROPOSED APPROACH AND EXISTING CODES FIG. 7. Influene of Steel Flnge Width b f nd Applied Axil Lod P u on Sher Strength (V n ) omp. From these figures, it is observed tht the proposed pproh ontins the following hrteristis: 1. For every urve shown in these figures, trnsition point (shown s lrge solid irle) exists between the two envelopes of the digonl sher filure mode nd the sher bond filure mode. The steel flnge width rtio t the trnsition point is given the nme ritil steel flnge rtio (b f /B) r. It is observed tht the sher pity of the omposite member is ontrolled by the digonl sher filure mode when the vlue of (b f /B) rtio is smller thn the ritil rtio (b f /B) r. On the ontrry, the sher pity is governed by the sher bond filure mode when (b f /B) exeeds (b f /B) r. 2. As observed from Figs. 5 7, ll the envelopes representing the digonl sher filure mode pper s broken This study ompres the sher pities predited by using the proposed pproh, the AIJ-SRC ode (AIJ 1987), the ACI ode (ACI 1999), the AISC-LRFD speifition (AISC 1993), nd the provisions (BSSC 1997). Tble 3 lists the dimensions nd mteril properties of the ssumed omposite members used in this study, where speimens re rrnged with vrying steel flnge widths nd stirrup rtios, respetively. Tbles 4 nd 5 summrize the lulted sher pities refleting the influenes of the steel flnge width nd the stirrup TABLE 3. Dimensions nd Mteril Properties of Assumed Composite Members Speimen number B D (mm) b f (mm) w (%) f (MP) Note: Steel setion: H-500 b f (mm); designtion of steel setion: H-d s b f t w t f ; F ys = 343 MP; F yr = 412 MP; F yh = 275 MP; onrete over from steel flnge surfe is 125 mm; onrete over from enter of rebr is 70 mm. JOURNAL OF STRUCTURAL ENGINEERING / OCTOBER 2001 / 1195

7 TABLE 4. Influene of Steel Flnge Width on Sher Cpity of Composite Members Speimen number Design method (V n ) s (V n ) rb Digonl sher Sher bond (V n ) omp Controlled filure mode 1 Proposed 1, ,024 DS d 1 AIJ-SRC 1, ,987 DS d 1 ACI e 1, ,024 DS d 1 AISC nd 1,442 1,442 NA f 2 Proposed 1, ,024 DS d 2 AIJ-SRC 1, ,987 DS d 2 ACI e 1, ,024 DS d 2 AISC nd 1,442 1,442 NA f 3 Proposed 1, ,021 SB g 3 AIJ-SRC 1, ,987 DS d 3 ACI e 1, ,024 DS d 3 AISC nd 1,442 1,442 NA f 4 Proposed 1, ,975 SB g 4 AIJ-SRC 1, ,971 SB g 4 ACI e 1, ,024 DS d 4 AISC nd 1,442 1,442 NA f 5 Proposed 1, ,928 SB g 5 AIJ-SRC 1, ,920 SB g 5 ACI e 1, ,024 DS d 5 AISC nd 1,442 1,442 NA f (V n ) s = nominl sher strength of steel prt, tken s 0.6F ys A ws, exept 0.577F ys A ws for AIJ-SRC ode. b (V n ) r = nominl sher strength of RC prt, tken s smller of digonl sher nd sher bond pity. (V n ) omp = nominl sher strength of omposite member = (V n ) s (V n ) r. d DS = digonl sher filure. e Vlues inlude sher pity of steel web. f NA = not pplible. g SB = sher bond filure. TABLE 5. Influene of Stirrup Rtio on Sher Cpity of Composite Members Speimen number Design method (V n ) s (V n ) rb Digonl sher Sher bond (V n ) omp Controlled filure mode 6 Proposed 1, ,875 DS d 6 AIJ-SRC 1, ,892 SB e 6 ACI f 1, ,875 DS d 6 AISC nd 1,442 1,442 NA g 7 Proposed 1, ,962 DS d 7 AIJ-SRC 1, ,960 DS d 7 ACI f 1, ,962 DS d 7 AISC nd 1,442 1,442 NA g 8 Proposed 1, ,047 SB e 8 AIJ-SRC 1, ,997 DS d 8 ACI f 1, ,047 DS d 8 AISC nd 1,442 1,442 NA g 9 Proposed 1, ,108 SB e 9 AIJ-SRC 1, ,034 DS d 9 ACI f 1, ,132 SB e 9 AISC nd 1,442 1,442 NA g 10 Proposed 1, ,173 SB e 10 AIJ-SRC 1, ,070 DS d 10 ACI f 1, ,214 DS d 10 AISC nd 1,442 1,442 NA g (V n ) s = nominl sher strength of steel prt, tken s 0.6F ys A ws, exept 0.577F ys A ws for AIJ-SRC ode. b (V n ) r = nominl sher strength of RC prt, tken s smller of digonl sher nd sher bond pity. (V n ) omp = nominl sher strength of omposite member = (V n ) s (V n ) r. d DS = digonl sher filure. e SB = sher bond filure. f Vlues inlude sher pity of steel web. g NA = not pplible. rtio, respetively. From these tbles, the following observtions re mde: 1. The sher pities predited by using the proposed pproh nd the AIJ-SRC ode re found to be quite lose. This loseness is ttributed primrily to tht these two pprohes onsider both of the sher bond filure mode s well s the digonl sher filure mode. 2. The vlues predited by using the AISC-LRFD speifition re the most onservtive mong the five pprohes. This is minly beuse the sher pity ontribution of the RC portion is onservtively negleted in the AISC-LRFD speifition. 3. It is interesting to observe from Tble 4 tht the sher pities predited by using the ACI ode re onstnt for ll speimens. For exmple, the vritions of the steel flnge width from 225 to 325 mm (Speimens 1 5, shown in Tble 3) hve no influene on the sher resistne of the onrete portion. This observtion indites tht the urrent ACI pproh does not onsider the effet of the vrition of steel flnge width on the sher pity of onrete-ensed omposite member. It is obvious tht if the steel flnge width beomes lrger nd pprohes the overll width of the omposite setion, the possibility for this setion to fil long the interfe of the steel flnge nd onrete will beome muh higher. 4. In the urrent ACI, AISC, nd design provisions, the influenes of the steel flnge width, sher reinforement, onrete ompressive strength, nd pplied xil lod on the sher pity of omposite members hve not been dequtely ddressed. In this study, the proposed pproh tkes ll these importnt prmeters into ount nd shows their influenes on the sher pities of onrete-ensed omposite members (Figs. 5 7). SUMMARY AND CONCLUSIONS This reserh ttempted to lrify the influene of sher bond filure on the sher strength of onrete-ensed omposite struturl members. Importnt prmeters suh s the steel flnge width, stirrup rtio, onrete strength, nd pplied xil lod were onsidered in the development of new method for the sher strength predition. Eh of the prmeters ws studied in-depth to show its effet on the sher strength of omposite member. In ddition, this study introdued new term lled the ritil steel flnge rtio (b f /B) r, to distinguish the digonl sher filure mode from the sher bond filure mode. It ws found tht when the steel flnge rtio (b f /B) of omposite setion is lrger thn the ritil steel flnge rtio (b f /B) r, the sher pity will be governed by the sher bond filure mode. On the ontrry, the digonl sher filure mode ontrols the sher pity if the rtio of (b f /B) is smller thn (b f /B) r. To evlute the ury of the proposed pproh, verifition nlysis between test results done by other reserhers nd the preditions of the proposed pproh ws mde in this study. The results showed tht the proposed pproh n stisftorily predit the sher pity of omposite member. The sher pities predited by the proposed pproh were lso ompred with the vlues lulted by using ex / JOURNAL OF STRUCTURAL ENGINEERING / OCTOBER 2001

8 isting Amerin nd Jpnese odes. It ws noted tht in the urrent U.S. design prtie, there is no speifi design provision vilble regrding the sher bond filure of fully ensed omposite struturl member. It ws the mjor objetive of the proposed pproh to tke into ount the influene of the sher bond filure long the interfe of the onrete nd steel flnge on the sher pity of omposite member. For future study, tests of lrge-sle speimens need to be onduted to investigte the sher filure mehnism of onrete-ensed omposite struturl members. ACKNOWLEDGMENT The finnil support of the Ntionl Siene Counil of Tiwn, R.O.C., is grtefully knowledged. REFERENCES Arhiteturl Institute of Jpn (AIJ). (1987). Stndrds for struturl lultion of steel reinfored onrete strutures, Tokyo. Amerin Conrete Institute (ACI). (1999). Buildings ode requirements for struturl onrete. ACI , Detroit. ASCE ACI Tsk Committee 426. (1973). The sher strength of reinfored onrete members. J. Strut. Div., ASCE, 99(6), Amerin Institute of Steel Constrution (AISC). (1993). Lod nd resistne ftor design speifition for struturl steel buildings, 2nd Ed., Chigo. Building Seismi Sfety Counil (BSSC). (1997). reommended provisions for the development of seismi regultions for new buildings nd other strutures, Wshington, D.C. Goel, S. C. (1997). U.S.-Jpn oopertive erthquke reserh progrm: Phse 5 Composite nd hybrid strutures. Pro., Summry, Resolutions nd Reommendtions of the 4th Joint Teh. Coordinting Meeting, Dept. of Civ. Engrg., University of Mihign, Ann Arbor, Mih. Hofbek, J. A., Ibrhim, I. O., nd Mttok, A. H. (1969). Sher trnsfer in reinfored onrete. ACI J., 66(2), MGregor, J. G. (1997). Reinfored onrete: Mehnis nd design, 3rd Ed., Prentie-Hll, Englewood Cliffs, N.J. Mttok, A. H., nd Hwkins, N. M. (1972). Sher trnsfer in reinfored onrete Reent reserh. J. Prestressed Conrete Inst., 17(2), Nishiym, I., Goel, S. C., nd Ymnouhi, H. (1998). U.S.-Jpn oopertive erthquke reserh progrm: Phse 5 Composite nd hybrid strutures. Pro., Summry, Resolutions nd Reommendtions of the 5th Joint Teh. Coordinting Meeting, Dept. of Civ. Engrg., University of Mihign, Ann Arbor, Mih. Priestley, M. J. N., Seible, F., Xio, Y., nd Verm, R. (1994). Steel jket retrofitting of reinfored onrete bridge olumns for enhning sher strength Prt 1: Theoretil onsidertions nd test design. ACI Strut. J., 91(4), Priestley, M. J. N., Seible, F., Xio, Y., nd Verm, R. (1994b). Steel jket retrofitting of reinfored onrete bridge olumns for enhning sher strength Prt 2: Test results nd omprison with theory. ACI Mt. J., 91(5), Riles, J. M., nd Pboojin, S. D. (1994). Seismi performne of steelensed omposite olumns. J. Strut. Engrg., ASCE, 120(8), Wkbyshi, M. (1988). A historil study of reserh on omposite onstrution in Jpn. Pro., Compos. Constr. in Steel nd Conrete Conf., ASCE, New York, Zhng, F., nd Ymd, M. (1993). Composite olumns subjeted to bending nd sher. Pro., Compos. Constr. in Steel nd Conrete II, ASCE, New York, JOURNAL OF STRUCTURAL ENGINEERING / OCTOBER 2001 / 1197