TENSILE LAP SPLICES PART I: RETAINING WALL TYPE. VARYING MOMENT ZONE. Phil M. Ferguson. and. Eduardo A. Briceno. Research Report No.

Transcription

1 TENSLE LAP SPLCES PART : RETANNG WALL TYPE. VARYNG MOMENT ZONE by Phil M. Ferguon and Eduardo A. Briceno Reearch Report No Reearch Project Number Splice and Anchorage of Reinforcing Bar Conducted for The Texa Highway Department n Cooperation with the U. S. Department of Tranportation Federal Highway Adminitration Bureau of Public Road by CENTER FOR HGHWAY RESEARCH THE UNVERSTY OF TEXAS AT AUSTN July 1969

2 PREFACE Thi Part 1 (Reearch Report 113-2) i a progre report on one phae of the general project "Splice and Anchorage of Reinforcing Bar." t cover an invetigation of #11 bar plice (a few ~8) under a condition which model the neceary plice at the bae of the tem of a cantilever retaining wall. While an extenion of the preent work will continue into , the preent finding call for quite ubtantial change from the preent AASHO pecification for uch plice. From the tandpoint of afety it i not deirable to withhold the preent finding for thee later tet. Thi Part 1 of the overall report on "Tenile Lap Splice" will be followed by further part: Part 2: Splice of 414 and ~18 Bar (early 1970) Part 3: The continuation of Part 1 with check on propoed theory, either a a follow-up report or a a report replacing Part 1 (1971) Reearch Report 113-1, entitled "Tet of Upper Anchorage of No. l4 Column Bar in Pylon Deign" by K. S. Rajagopalan and Phil M. Ferguon publiherl Augut 1968, cover another phae. Support ha been provided by the Texa Highway Department and the Bureau of Public Road, U. S. Department of Tranportation. The encouragement and aitance of their contact repreentative are alo acknowledged with thank. The opinion, finding, and concluion expreed in thi publication are thoe of the author and not necearily thoe of the Bureau of Public Road. Eduardo A. Briceno Phil M. Ferguon July 1969

3 SUM MAR Y An invetigation of the trength of cloely paced lap plice in retaining wall tem i reported. Splitting type failure typically occurred, otten tripping the entire cover off of the plice. Thi tudy of 32 pecimen with #11 and #8 bar i continuing into t i concluded in Part A that the 1965 AASHO pecification for plice doe not provide a afe guide unle it i eriouly modified. The neceary immediate modification are developed for the cae of 2 in. clear cover, with a plice length increaing a lateral pacing decreae and the preent pecification adequate only for unuually wide pacing. n Part B a tentative theoretical treatment of lap plice length baed on the everal oberved type of plitting failure i preented. Although thi theory i potentially a coniderable advance over preent knowledge, certain tranition tage and limit mut be better defined before it can be ued with confidence. A portion of the program i directed to thi end.

4 MPLEMENTATON OF RESEARCH RESULTS NTO TEXAS HGHWAY DEPARTMENT OPERATON t i recommended that the deign of lap plice in the tern of retaining wall be increaed from the preent AASHO requirement of 19D (D i bar diameter) for f 40 ki and f' = 3500 pi to the following y c lap length which i a function of the lateral pacing Sand D: L = 19D -T (0.13 D ) ; 19D Thi require the following lap length: D = 3 S 4.2" 4 5.6" 5 7.0" 6 8.5" 8 or more 11. 2" L 54D 40D 3lD 26D 19D Thee length apply where all bar are pliced at the point of maximum moment and aume at leat a 2 in. clear cover provided. Where plice are taggered in location uch that not more than half are pliced at one wall level, their length can be reduced to 0.8 the above. However, thi i not documented well enough to jutify anywhere le than a 19D lap. For higher trength reinforcing bar the plice length L hould be increaed by the factor f 140 (with f expreed in ki). For concrete y y trength le than 3500 pi the value of L hould be increaed by the factor 3500/f'. The two factor could be cumulative. c For clear cover le than 2 in. the lap tabulated above for the larger pacing are probably not adequate, but thi invetigation ha not adequately explored thinner cover. Figure 12 etimate, on very kimpy information, that one bar diameter of clear cover (C/D = 1) might require a 36D plice lap even if the pacing were wide, and the tabulated longer lap at D of 3 or 4. Thee recommendation do not apply to plice in a contant moment length which hould be 15 to 25 percent longer, the exact value not yet cloely defined in term of pacing.

5 N T ROD U C T ON Exiting Splice Requirement For a tenion plice in a reinforced concrete member, a lap plice (Fig. la) i required unle welding or a mechanical plice i ued. the 1965 AASHO pecification and the 1963 AC Building Code ue a reduced value of bond tre for a plice, but the net deign requirement differ ub tan tially. Both The AASHO pecification require a WSD plice length L which i 4/3 a long a required for a uniform bond tre of 0.10 f' (with a maximum c of 350 pi). Since for intermediate grade bar the working value of f f /2, thi lead at ultimate to: y 2 2'0 u L A f y or 2rrD(0.10f')0.75L c For f 40 y For f y ki and 60 ki and L f' c f' c f D/(0.60f') y c 3500 pi, L 19D = 26.S" for tfll = 19" for tis 3500 pi, L 2S.5D = 40.2" for till 2S.5" for tis The AC Building Code (31S-63) ha the ame general requirement, 4/3 the development length, for widely paced plice but the baic USD bond tre permitted i 9.5 ~/D, thu varying with the bar ize. c For cloely paced plice the required length i further increaed by 20 percent. For f = 40 ki, f' = 3500 pi, and cloely paced plice: y c rrd(9. Jf!/D)L (0.75/1.20) rrd2f /4 c y L = f D 2 / ( ft' ) y c 2 2S.5D or 40.2D = 57" for till 2S.5D = 29" for tis For f y 60 ki, all length increae in the ratio 60/40: 1

6 2 60.3D 42.7D 85" for " for 118 Thee length are greatly in exce of the AASHO requirement, epecially for the #11 bar. Top cat bar under both pecification call for lower bond tree and longer plice. The Splitting Problem For bond on deformed bar in general, and for tenion plice in particular, the mot common failure i by plitting of the concrete parallel to the bar axi. The bearing force on the bar lug, intead of being parallel to the axi of the bar, have a radial component which react on the urrounding concrete, like water preure in a pipe, to caue failure by plitting on the weaket plane. n the tem of a cantilever retaining wall the cloely paced plice accumulate thee plitting force with reulting weakne in the plane of the vertical bar. Project Objective The primary objective of thi Part of the invetigation wa to tudy the behavior of the retaining wall type of plice and to formulate modified deign requirement if found deirable. Thi report itelf i preented in two part. Part B i a tentative theoretical analyi which i till under evaluation.

7 3 PAR T A RETANNG WALL SPLCES Scope of nvetigation Thirty-two beam were teted, 27 having #11 bar plice, 4 having #8 bar plice, and 1 having #9 main barn pliced to #11 dowel bar. The percentage of longitudinal teel wa generally 1.67 percent of A432 teel, the beam ize being varied when bar diameter or pacing wa changed. Concrete trength wa typically from 3000 to 4000 pi. Variou lateral pacing of plice and variou arrangement of the pliced bar were ued. Typically two plice were ued in a tet member, but ome pecimen had 3 or 4 plice and ome plice were taggered. Five beam ued the equivalent of tie or tirrup over the plice. Tet Specimen The hape of a retaining wall ection (Fig. lb) i not convenient for teting purpoe. The wall tem wa imulated by a beam length of contant cro ection. The bae of the wall wa replaced (Fig. lc) by a perpendicular (tub) ection projecting from both the tenion and compreion face of the beam, and the beam itelf wa extended with a dummy or loading ection. The beam load wa applied through the tub ection in a manner crudely imulating the flexural compreion from the toe of the retaining wall (Fig. ld). Although the tet pecimen i greatly different from the wall, it behavior around the plice wa planned to be imilar to that of the wall. The loading of the member wa alo implified, uch that a contant hear and linear moment ditribution exited over the plice rather than the more complex oil preure loading aumed on a wall. The variou pecimen detail are hown in Fig. 2 a cro ection and in tabular form in Table 1. The table alo how by ketche the arrangement of bar at the lap.

8 4 ""f""'".'" STEM /USUALLY N CONTACT T L TOE HEEL 'l=====~=--~ BASE """,,,,V",,TVU 'VV' (b) r jo-- --:-: LOAD g"_~ Ol----4f~~L-jLfeo':ft " -~ "WALL" END VARED h ~~~~~~~~~~~======~~ (AND -l-~- L BARS N SMULATED SAME PLANE (VARrED) BASE (e) :-- w rdth b) 6 \ \ \ \ \...---\ \ te \ \ r--=~=r-"'"...l LOAD (d) FG.. TEST CONCEPT (a) BASC LAP SPLCE. (b) CANTLEVER RETANNG WALL WTH TYPCAL STEM BAR SPLCES. (e) TEST SPECMEN TO SMULATE WALL SPLCE. (d) WALL LOADNG COMPARED TO TEST LOADNG.

9 D f--~ 2:~12 ",..., " -VAREO-j 2" r- REGULAR (WTH 8 WTHOUT TES) D S ~ 21 S S 12 1 :" 24" (#26) l,! (# 27) ~~, ~-(rf L 7 " J r-148~ THREE SPLCES (WTH 8 WTHOUT TES) 5 18" - FOUR SPLCES CURVED TOP 2"=C (# 20) t-9"--j STAGGERED SPLCES frl oe S S 2" S"2 (# 19) (#: 28) (# 30) - VARE0-1 ONE BAR CONTNUOUS T ce ~ ruoe S S " (# 25) 1 L..--~:' l') ~ 14..L" THREE SPLCES WTH CURVED SURFACE (WTH TES) 2" L 4 (# 22) (;------'(': 1--17"---1 REDUCED SHOULDERS ~ 20" 1 "(# 23) ~ '... ; L-- -- t- tll---j UNEQUAL BARS 2" o W 0:: <[ > 2.. JD oe~ 2 -! (# 9) (:F 10) (:F 12) -VAREO--l ALTERNATE BAR ARRANGEMENT FG. 2. GEOMETRCAL ARRANGEMENT OF VARABLES N TEST SPECMENS. THE DOWEL BARS NTO TH E "BASEl! ARE UNSHADED. 2"

10 6 TABLE 1. DETALS OF SPECMENS Clear cover i 2.", except 3" for beam 16. Beam No. Width Total Bar Spcg. Splice b h Diam in Bar in. in. in. Diam. f' c Stirrup Bar pi or U-tie Arrangement None B.O B.O @9" None #2@5.2" * None } @7.4" #3@6" @6" o None la a a " 4a *Thi i center pacing; edge ditance maller, to give 6.0D average.

11 7 Preparation and Teting Specimen were cat on their ide from a ready mixed concrete made with high early trength cement (Type ) and Colorado River and and gravel (1.5 in. maximum). The water-cement ratio wa 6.6 gallon per ack, cement factor 4.5 ack per cubic yard, and lump 2 in. to 3 in. The pliced bar were A432 grade deformed bar with tre-train curve hown in Fig. A1 in Appendix. Tie were of intermediate grade with f = 56.5 ki for #3 bar and f = 49 ki for the plain #2 bar. y y Reitance train gage were mounted on the urface of the pliced bar at approximately the quarter point and at the loaded end, ometime on one, ometime in all plice. The bar ize wa uch that thee gave a minimum interference with bond. The pecimen were teted on their ide, upported on 7 in. diameter roller, and loaded by a hydraulic jack againt teel yoke reaction. reaction at the end containing the plice wa monitored by a load cell. ncremental loading wa applied up to failure. The ultimate teel tre f,the ratio k = f f (both baed u u on train reading), and type of failure are tabulated in Table 2, along with other calculation dicued later. The Splice Behavior The member firt cracked in flexure at the higher treed end of the plice, adjacent to the loading tub. The tendency toward the formation of diagonal crack near the loading tub wa not ignificant with thi ize of pecimen, contrary to ome earlier finding with hallow member. Flexural cracking progreed along the plice a load were increaed, with the crack at the outer end of the plice appearing omewhat ahead of neighboring flexural crack. There wa a coniderable tendency for a premature diagonal crack to tart from thi end of the plice unle a few tirrup were preent there. Splitting along the bar developed with increaing load, only on the ide of the beam for cloely paced plice, but for wider pacing firt on the tenion face followed by ide plitting before failure. Four type of failure were oberved, a noted in the lat column of Table 2.

12 8 TABLE 2. TEST DATA AND CALCULATONS Beam No. f u p i f' c pi Spcg. in bar diam. c-c k = f /f u Cover C/D Split cyl. f. t p 1 f~ ratio Calc. ~ f' (cy1) t. p 1 u tet p i Type of Failure Side plit Flex Flexure Flex Flexure Flex Flexure Side plit Flex Flexure Side plit Diag. Ten Diag. Ten. (Near plit) Flex Flexure Diag. Ten. (Near plit) Face-ide plit Face-ide plit Face-ide plit Face-ide plit Face-ide plit Face-ide plit Flexure Side plit Side plit Side plit * Face-ide plit Face-ide plit Side plit Side plit Side plit Side plit Face-ide plit 1a Side plit 2a Face-ide plit 3a Side plit 4a Side plit *Thi i center pacing; edge ditance maller, to give 6.0D average.

13 9 1. Flexure, by yielding of the teel and econdary failure in compreion. 2. Diagonal tenion, tarting from the lower treed end of the plice. 3. Side plit failure, that i, bond plitting all acro the plane of the bar, with little or no plitting on the tenion face, a in Fig Face-and-ide plit failure, that i, plitting firt on tenion face and then all acro the plane of the bar. Flexural failure implie a plice entirely adequate for the beam in which it wa ued. The lowet teel tre at uch a failure wa 71.5 ki. Only three beam failed in diagonal tenion. Each wa premature failure (in term of the AC USD allowable v of 2 f') but two were in c c uch a tage of plitting a to be judged a near plitting failure. The data for all three plot very cloe to thoe of the plitting failure and no ditinction ha been maintained between the two type of failure. t appeared obviou from the plitting behavior that a third kind of plitting failure might be poible when either a wide plice pacing or a thin face cover wa ued. Thi failure would tart a a normal face plit followed by two flatly inclined face plit which would open up a ymmetrical, flat V-groove over the plice. No uch failure occurred in thi erie, but a ingle picture of thi type wa found in the file from earlier plice tet. Splitting failure, except with tirrup, were udden and harply defined, leaving a wide crack at the failure urface (Fig. 3). General nfluence of Splice Spacing A caual inpection of the plitting failure data indicate that the computed average bond tre over the plice length wa coniderably influenced by the lateral pacing of plice. Hhen the ratio of half the average ultimate bond tre relative to the AASHO allowable (WSD) bond tre i plotted in Fig. 4, omitting pecial cae dicued later, all ratio are extremely low. n

14 10 FG.3. SDE SPLT FALURE OF BEAM NO o ~ 1.0 «::> '" w ~ :::) ~ :7~ r 1 L() o 0.6 i ".' '--: tr"'", 0.4 f----_+ ~ # # *11+# '-----_----' ' ' ' SD FG.4. BOND EFFCENCY N TERMS OF AASHO BOND STRESS (0.75 x 0.1 f'c < 0.75 x 350 pi) 7

15 11 Table 2 thi ratio i identified a 0.5u/uAASHO' However, at larger pacing a trend toward normal ratio exit. A omewhat crude but practical overall analyi will firt be preented before preenting in Part B a more theoretical treatment which till lack ome validation. Modification of AASHO Specification for Splice A traight line multiplier to be applied to the allowable AASHO bond tre appear ueful in deigning a better plice. The data of Fig. 4 lead to an average ratio: SD f thi i dropped by 0.08 (roughly one tandard deviation) it become: SD Thi relation could be ued directly with the AASHO bond tre for deign if one would accept a brittle failure mode at the firt yield of the reinforcing. However, good deign mean the avoidance of a brittle failure wherever poible, which i probably bet pecified by lowering the permiible bond tre to 80 percent of the above, leading to a multiplier of 0.13 SD While thi multiplier i le than 1 until id become 8, it hould be noted that preent data top at SD of 6 and are baed on uing 2 in. of clear cover. For practical pacing of retaining wall plice the AASHO pecification for #11 bar i le afe than deirable and for very cloe pacing it i barely afe at ervice load. Alternatively, and to obtain the ame end reult, the plice length a currently pecified by AASHO might be divided by thi ''multiplier'' to give the following for #11 bar, with an abolute minimum of 19D for large pacing: For f y = 40 ki and f' c id S 3500 pi, L Reqd. L = 19D -7- (0.13 id ) Now Specified (for all ize bar and pacing) 3 4.2" 54D D D D 8 or 11.2 or 19D over over 19D 19D 19D 19D 19D

16 12 For f = 60 ki and f' = 3500 pi, 1.5 time the above length are required. y c Thee relation have been verified only for #11 bar, but four ample with #8 bar indicate the ame bond tre multiplier would be appropriate. General Comment By deign thee member were teted to give the neceary L value for retaining wall. For contant moment plice,with equal tree at each end, more length i needed, probably 15 to 25 percent. The data are compared with a emitheoretical analyi in Part B and the reult there look promiing for more general ue when better verified. A few pecial cae of interet are hown on Fig. 5. The "x" mark indicate that either a ingle plice (one bar continuou, in beam #19, #28, and #3a) or a taggered plice (one tarting where the other i complete, beam 1f20) i uually more effective, by 25 percent or more. n the ingle pecimen where #11 dowel were pliced to #9 main bar (beam #23, marked by a triangle) the unit tree in the #9 and #11 bar were about the ame. The trength wa roughly 10 percent lower, which i within the expected catter range. A curved beam face (beam #25), repreentative of a part of a circular pier, including tie typical in uch a cae, howed particularly well when evaluated on the bai of the mot highly treed plice (the one farthet from the compreion face). The theory developed in Part B indicate that a lower tre at one end of the plice i advantageou, but heavy hearing tree may offet thi when the one tre i very low. At large SD ratio a detailed tudy how that the efficiency of a plice drop ome with the increaing length, but thi influence i le than the influence of SD. Data are not adequate to clarify thi point. Where V-tirrup are feaible, the tet indicate a poible 40 to 100 percent gain in tre tranfer, although probably thi device i not practical for wall. Only a few uch tet were made.

17 ~---r r r------' 0 ::t: f) ~ ~ ::::> en Q) ::::> 0.6 t) 0 #8 0.4 "" #8 #118#9 x SNGLE + STR SD FG. 5 BOND EFFCENCY N TERMS OF AASHO. SPECAL CASES MARKED WTH ARROWS.

18 14 Relationhip to AC Code Requirement The data have been analyzed again in Fig. 6 in term of the AC Code proviion for plice. gnoring ingle plice and plice with tirrup, the logic ued in connection with Fig. 4 lead to a bond multiplier of which become unity at SD of SD Although thi m11ltiplier indicate the AC Code i much cloer to the tet data than the AASHO pecification, it i noted that thi correction lead to plice length for #11 bar ome 15 percent greater than the corrected AASHO value. f' = 3500 pi: c For f y For f y 40 ki and L 28.4D 2 /(0.25 SD 0.14) Code for #11, Spac ing id S L For #11 Cloer than id = " 46.7D 2 66D 40.2D D 2 47D 40.2D D 2 36D 40.2D OD 2 30D 40.2D l5.3d 2 22D 40.2D = 60 ki and f' = 3500, 1.5 time thee length are required. c The 15 percent differential appear partially due to greater catter when thee data are related to Jf' and partially to a light unintended c lant to the data caued by a concrete trength f' greater than 3500 pi in c roughly 50 percent of the pecimen. Thi raie the bond ratio under the AASHO pecification which limit the baic allowable bond to 350 pi for f' c of 3500 pi or more. For #8 bar (4 pecimen) the data plot unfavorably low and ugget that L a a multiplier of D might have to be increaed a much a 30 percent above that for the #11 bar. t happen that if the equation above (in 2 term of D and SiD) i multiplied by a 1.3 factor, the L value required for the #8 bar are nearly the ame a the corrected AASHO value. However, four ample are not enough to jutify the recommendation of a pecific correction factor under thi code.

19 ~ t ,1' t-- -+-x_x -tw--"""7'------:i-~-- t_7""' u «::>... -~ f/) Q) ::> #8... _ f------f---_+_- #11 #8 #11 8#9 x SNGLE + STR. 0.2~--~--~--~-----~ SD FG.6 BOND EFFCENCY N TERMS OF AC CODE BOND STRESS (9.5~ /0 )(0.75 /1.2) pi

20 16 Concluion and Recommendation n retaining wall plice at ordinary pacing, the AASHO pecification (1965, 9th Edition) i hown not to be a afe guide unle eriouly modified. Baed on the ue of 2 in. clear cover over the bar, f 40 ki y and f' = 3500 pi, the recommended lap plice length i increaed to c L = 19D...!.. (0.13 SiD ) '7 19D.. which ha been verified for SiD up to 6 for #11 bar and alo eem to fit #8 bar. Conitent with the AASHO pecification, the value of L mut increae linearly with f and with the ratio 3500/f', the latter only where y c f' i le than 3500 pi. c On the bai of only 4 pecimen, taggering of plice or the plicing ot only half the bar at a given cro ection would permit plice length L to be reduced to 80 percent of the above. Thee recommendation do not apply for plice in a.::ontant moment region, which hou1.d be longer a noted in Part B. Nor do they apply fo,: le than a 2 in. clear cover, although Fig. 12 (Part B) ugget very tentatively tha.t C/D == 1 might mean minimum plice length of 36D.

21 17 PAR T B A THEORY FOR SPLCES Radial tree around deformed bar wherever bar tre i changing have long been aumed. Recently Profeor Goto in Japan ha hown experimentally that at high teel tree a tenion bar embedded in a prim of concrete will not only develop tranvere crack in the prim but alo internal crack radiating from each tranvere lug. Thee crack are not perpendicular to the bar but in effect develop a truncated hollow cone of concrete bearing againt the lug. Thee eentially parallel conical hell develop the change in bar tenion by inclined compreive force which are eparated by the inclined crack. Thi eem to be the manner by which tangential plitting tree are developed near ultimate. The following analyi make the implet poible baic aumption, that the radial and longitudinal tre component in the concrete are equal.* Calculation made on thi bai coordinate well with plit cylinder tet trength. The econd aumption i baed on tet data from the train gage reading for thi erie of tet. A documented below, in pite of very different initial and intermediate ditribution, at ultimate the variation in teel tre along the plice i eentially linear from zero at one end to maximum at the other; and thi hold in both direction even when tre at one end i much lower than at the other. Cloe examination of the failed pecimen indicated two plitting failure pattern and pointed toward a third for thinner cover or wider pacing than ued in thi invetigation: 1. At cloe pacing a crack along the plane of the bar which often went o far a to plit off the entire cover over the plice; deignated here a a ide plit failure. *Photolraph made by Profeor Goto would indicate an angle of poibly 50 or 55 degree, which would mean even a larger plitting component.

22 ls 2. Similar to the ide plit failure, except that there firt developed longitudinal crack on the tenion face over the plice and the ide plit developed later to bring about failure; deignated here a a face-and-ide plit failure. 3. Where cover i thin or lateral plice pacing wide, the initial tenion face crack may be followed by the forcing out of a V-wedge of concrete over the bar. No uch failure occurred in thi invetigation, but it how on ome earlier bond tet picture. Thi failure i deignated a a V-type failure. Bar Stre Along Splice Reitance train gage placed at the quarter point of plice indicated the general tre ditribution along the plice. Although ome variation howed between pecimen, Fig. 7a i a typical train record, implified by howing data at only four load level. The final train can be interpreted a the tree hown in Fig. 7b. Although the final tree do not produce preciely traight line (and might vary even more if gage were cloely paced over the 65-in. plice length), it i judged reaonable in the preent tate of the art to conider them traight. The light curve at the upper left i probably the reult of exceive plitting at the higher treed end. The author are inclined to revie their earlier idea of plitting a a totally bad phenomenon to a concept of plitting a a device which accommodate the exceive teel train in uch a way a to develop a near optimum reitance in the concrete over a long length. A horter 33 in. plice at 94 percent of ultimate i hown in Fig. 7c, and a longer plice with (arbitrary) minimum tirrup in Fig. 7d. The dahed line marked "AC" how the change in tre which the AC Code aume will take place. At the wider pacing the AC Code i conervative. Some other failure condition are hown in Fig. S. With one bar continuou (unpliced) in Fig. Sa, the pliced bar take le than 50 percent of the total tenion at the end of the plice and more than 50 percent at midlength. A flexural failure pattern for 4 plice i hown in Fig. Sb, a diagonal tenion failure in Fig. Sc, and a plitting failure in a curved top beam in which the center bar took more than it hare in Fig. Sd.

23 19 Bm. 12 / to' ==========================~-0 A ~ SPliCE LENfTH./J" (a) (b) Bm 'i~')( H) '<l4ri 17' "..fj.fo pi '" " ":.. ". OO'!O of SPLT FA1(RE f:,joo,..' ~ACJ "- Bm. 08,.. 24 '?N, 0 "- '" '" '" 0 t'''' '1.N.:Ttl' CJ. ' (c) (d) Fig.. 7. Stre ditribution along plice. Note that the lat data in (c) are at 94% of ultimate.

24 20 Bm. 3a tc~ O[J #8. Jl 20' '$' 0 [J SPlC LEtf..lH' 1Z' (a) (b) 70 ~~ ~~ '"" ~ V) Z! " A?P ~ tlf J)A(jP!fAL ~.0 eo TEN510N FAL/RE 21 i..331fij p., <» 18' 24' #/1 x--~================~----0 ~ [) ~uu UlftTH, 42..,' (c) (d) Fig. 8. Stre ditribution along plice for pecial cae. (a) One bar unpliced. (b) Nonlinear; flexural failure with data at 90% of ultimate. (c) Some nonlinearity; diagonal tenion failure with data at 90% ultimate. (d) Curved face beam.

25 21 n ome beam gage problem gave le complete record and there were variation not hown in Fig. 7 and 8, but the general pattern eem well-etablihed. The following analye aume bar tree linear from zero to the meaured train (tre) at the other end of the plice. Side Split Failure Although the edge plitting ometime evidenced the preence of hear by a omewhat flat aw-tooth outline, the final failure plane wa eentially a horizontal one (in the plane of the bar). For analyi the unit radial force at the bar wa arbitrarily aumed equal to the unit bond force on the bar urface. Then in Fig. 9, on the higher treed bar u A f u ~L D f u 4L radial unit force Thi lead to a plitting force on the diameter of bar, per unit length, On the other bar, imilarly, the plitting force per unit length i 2 kd f /4L, for a total plitting force on two plice of u ~ 2(1 + k)d f /4L = (1 + k)d2f /2L per inch of length. The concrete u u area reiting plitting i b - 4D or 28-4D for a unit length which give an average plitting tre on the concrete (1 + k)d2f /2L f' u t 28-4D (1 + k)f D u 4(S/D - 2)L Baed on the oberved k and f the calculated value of f ' i tabulated in u' t Table 2 and the next column how the ratio of thi value to the plit cylinder value of f~. (For the face-and-ide plit failure a different relation, developed below, i neceary to calculate f'.) The ratio wa t low where failure in flexure occurred and high where tirrup exited (becaue the ratio at thi time ignore tirrup). The diagonal tenion failure alo indicate by their ratio that plitting wa cloe to it limit. (1)

26 22 -.l C AS fu lmax. M L A kfu -/ LOWER M\ FG.9. SPL TTNG FORCES FOR SDE SPL T FAJLURE 4L FG. 10. FACE - AND - SDE SPLlT FAllURE FG.. V- TYPE FAilURE WHERE CS S VERY SMALL

27 23 Face-and-Side Split Failure The final failure in the face-and-ide plit cae wa almot the ame a in the ide plit cae. Although the firt edge cracking tended to be a little farther from the tenion face, the final failure howed le difference. The analyi aume plitting force a before and lengthwie crack exiting on the tenion face over the plice which prevent tranvere force perpendicular to the crack but which (by aggregate interlock) tranmit ubtantial hear. The chematic arrangement of force on a tranvere ection i hown in Fig. 10, along with ketche of the eparate piece at failure. Symmetry laterally leave two free bodie to conider. On the center free body, ummation of vertical force lead to 2f A ~+2F f' (S - 2D) = 0 rr1 t F (2 ) With the corner free body, if one make the overimplifying aumption that the reulting tree can be baed on PA + Mc/, the limiting tre i (-F + k f A / rr1 ) f' t (0.5S - D) + [(kf A /rr1 )0.25S - F(0.25S + 0.5D)] (0.5S - D)2/6 f the value of F from Eq. 2 i inerted, the equat~on can be rearranged* to f' t f rrd2 '2 (1 + k)s + (2 - k)dj 4:1 (2.5S + D)(0.5S D~ = fd t 2 (1 + k)s~d + (2 - k)d-' L (5S/D + 2)(S/D - 1) (3 ) When a given pacing S i expreed a a multiple of D, or D a a fraction of S, Eq. 1 and 3 ~educe to the form: f ' t = (f D/1 ) x contant, or f (f~1/d) x contant (4) For Eq. 4 the contant for a given pacing S i uch a to lead to a lower f than that given in Eq. 1 for the ide plit cae, that i, the corner free bodie are le efficient than in the ide plit cae. ~\-With experience thi equation can probably be implified. t i overly complex for the aumed accuracy.

28 24 A either of the above failure pattern i conidered with wider and wider pacing, or thinner cover C, it become le probable that a uniform f~ will exit between the plice. At ome pacing for each cover the tre midway between the two plice probably drop to zero and a eparate flat V-type failure over each ingle plice become probable, a ketched in Fig. 11. No uch failure occurred in thi invetigation but an earlier tet howed thi failure which form an upper limit on the poible value of either Eq. 1 or 4. t appear that the ultimate f u hould then vary linearly with the cover C, for plice length and other condition the ame. Comparion of Tet Reult with Thi Theory Although the above relation are undoubtedly overimplified, eentially all the tet reult eem to agree with them within ±15 percent. A mentioned earlier, Eq. 1 or 3, a applicable, wa olved for the plitting tre f~ and thee value are compared in Table 2 to the plit cylinder trength. A number of pecial cae--ing1e plice with one bar continuou, unequal bar pliced, edge ditance le than S/2--were calculated by minor variation of the above procedure. The final ratio of f' /f' in Table 2 are quite reaonable. With tirrup the t(ca1c) t(cy1) computed f~ i overly large, a it hould be ince thi approach (to thi time) doe not include the trength added by the tirrup. Wall Splice Veru Beam Splice The firt tet in the preent erie were tudie of whether four plice at the ame ection, a in a wall of ome width, were different in behavior from a narrower beam with two plice having the ame center-to-center pacing. Unfortunately, thee plice were at a cloe pacing which gave ide plit failure and howed no ignificant differential in their data. The later analyi of the face-and-ide plit cae eem inconitent with probable train in a wall, ince the face-and-ide plit failure require ome lateral movement of the beam corner egment. n a continuou wall the face crack can fonn, but it i difficult to viualize ignificant additional lateral movement.

29 25 Tentatively it i aumed (but till unproven) that in a wall, a wider pacing of plice are conidered, the aumed uniform tenion acro the plitting ection mut become le uniform, making the reitance le efficient, that i, tronger but not tronger in full proportion to the width increae. At ome wide pacing the flat V-type failure will govern and the poibility of the beam-type failure by a face-and-ide plit will be completely bypaed. Thi pacing limit hould be harply dependent on the face cover over the bar. f thi hypothei i correct, wall plice at pacing greater than 4D or 5D will be tronger than the corner plice in a beam which have the ame plice pacing (laterally), that i, tronger than the tet value reported here for SD = 6. nfluence of a Variable Moment over Splice 1ength All thee tet had loading which created a lower bar tenion at one end of the plice than at the other. The theory developed above conider plitting a the reult of both bar tenion, one bar at A f u and the other at ka f, where k i a factor le than unity. Thi reult u in the term 1 + k in both Eq. 1 and Eq. J, and in the latter a econd term, 2 - k, mall enough to be neglected. With thi approximation the total plitting force i proportional to 1 + k.;'( Thi implie that a plice in a contant moment zone mut care for more plitting and hould be deigned for 2f intead of (1 + k)f. With k = 1 in Eq. 1 and 3, thee re1ationu u hip eem applicable for plice in a contant moment zone: Side plit: f' t 2f D f D ~~~ ~ 4(S/D - 2)1 2(S/D - 2)1 (5) Face-and-ide plit: f' t f D r 4S D + 1 ] 1 l (5S D + 2) (S D - 2) (6 ) Deign Chart For any given k value, d ign-type chart can now be prepared chematically, although certain tranition area are till not clarified. *Check on tet data indicate that k = 0 give f value too high for an ordinary development length, probably becaue 1ar~~r hear accompany thi cae and combine with the plitting force.

30 The chart in Fig. 12 for k = 1 i foe a fixed concrete trength and relate the deign ultimate teel tre to plice length and pacing. The data are weighted in uch a manner that the expected ultimate plice trength will correpond to 1.25f when f i entered in the chart for f The y y u ordinate how the dependable deign ultimate tre in ki developed for a plice length of one bar diameter. Then f divided by thi number give y the needed plice length L. The preent chart in Fig. 12 for k = 1 for a given f~ (or poibly ~)is weaket in the upper horizontal limit baed on the V-type failure and in the poible tranition phae which remain to be invetigated. For the ide plit failure the inclined line i traight and for the face-and-ide plit eentially traight. f k { 1, the limit would be parallel line with all f u dotted for k = value higher, a hown The equation line can be eparately compared with the data of thi invetigation, a in Fig. 13. For the ide plit failure mot of the data fall between SD of 3.1 and 3.3 and how coniderable catter. One value at SD of 3.6 fit well. ubtantially below the equation value. plit failure occurred. A #8 bar pecimen at SD of 4 fall For SD of 4.1 the face-and-ide Figure 13 how an average line, a 10 percent reduction line to offet ome of the catter, and the 0.8 factor line to aure trength beyond the can deign of failure. inertion of yield point, hopefully to 1.25f. With thi line the deigner y the plice for a nominal f and till maintain a ductile type y Thi procedure lead to Eq. 7 and 8 from Eq. 5 and 6, by f' = 375 pi (0.375 ki), f' = 3500 pi, and k = 1. t c 26 Side plit: Face-and-ide plit: f (D /L ) f (D/L ) 0.8[0.75S/D - 1.5]0.9 O. 54S /D (7) o 8 ~ 375 (5S/D + 2)(S/D ~ 2.~ 0 9. [. (4S /D + 1) J (5S/D + 2)(S/D - 2) (4S /D + 1) (8 )

31 1.8 Q.. «1.6...J u. 0 ~ 1.4 ~ 0 a: w 1.2 Q.. en ~ en -...J :;:, C) 0.6,,', ~~,,':> /./ LC/D o',,' /...: "+-/ /':-71 -O~;2-( c;o; o.~i- ---; --c>~: ~;.," J~- V-TYPE FAiL: -?'~- EQ.9- ~ / A..." fofo,0 / C).. / O ~(). ~~ ~7 CO'",0\",'<. r~r:.: 12>_ / ~7 Olc:,\,,~ ~(2), c) - ~, 'Q Sfu kfu7,/ ~ -~ 1 ~.., Of;) ~ ~~ --- L ~. ~-~/ /. ~ G ~ ~~ ~ ~~ ~~ C 1- /~~ g,v T " Cd f~ : 3500 pi J S J " ~~ (ft = 't/ 375 pi) ~ k- -l S D = SPACNG DAMETER FG. 12. SKELETON DESGN TYPE CHART, TENTATVE

32 2P 2.2r-----~----~----~~----~----~----~--~ r--+r ~ 1.8 STRRUPS. 6 -t--~--t ~-+-~----+-_ \ ' r r f E Q. 9 - " tn -.J ~ tn "\O~ ~~() Otp \ ,L ,fL---7fL J CODE *. #8 BARS #11 WTH # S / D 5 6 FG.13 DESGN EQUATON VS. TEST DATA

33 29 For the V-type failure the following equation i introduced a the bet preent gue for thi condition, modified by factor a above: V-type: f (O/L ) 0.8[0.375 x 2.67(C/D + 0.5)JO (C/ ) (9) t alo appear that in the ueful range Eq. 8 for the face-and ide plit can be adequately and more imply expreed empirically a Face-and-ide plit: f (O/L ) = 0.34S/ (10) The horizontal limit line repreenting V-type failure for variou C/O ratio (where C i the clear cover) are baed wholly on earlier data, reduced a in the other cae. Thee numerical value are very tentative. They would eem equally applicable a upper limit for either the ide plit or face-and-ide plit cae and appear particularly retrictive when cover i thin. n at leat certain cae, tranition curve a ketched in Fig. 12 are till to be determined and probably will control. For intance, if C/O i large, it appear a wall plice will be defined at low S/O value by Eq. 7. A S/O become 6 or 7, it i almot certain that the reitance to plitting i not increaed proportionately (compare Fig. 11) and the traight line of that equation probably curve (flatten) decidedly. For a beam with two plice, there mut be a tranition from Eq. 7 to Eq. 8 (or 10) and poibly another from the latter to Eq. 9. A ingle empirical lower bound curve could be etablihed for the whole range of S/O value covering all three equation. Such ha not been developed becaue it wa felt that the face-and-ide plit wa probably not proper for wall plice and the eparate curve look promiing for further development. n the coming year thee will be invetigated further. Concluion A tentative plitting theory for plice ha been developed which eem to fit the tet reult with error generally le than 15 percent. Tranition zone between the three eparate cae till need to be defined

34 30 and an aumed difference between wall and beam plice mut be verified or diproved. Work i continuing in thi direction. Until thi work i further advanced, detailed recommendation for deign beyond thoe of Part A are not warranted.

35 31-00 ~ z w a:: 30 t- oo BEAMS 26, 27, 28 ~-40.NCL _. 0 _ 0 _ 2 / OFFSET / / fy = 70 ks :t \.. 25 ee~~s / fy = 65 ki \NC\... / / / / / / / o ~----~----~----~----~------~ STRAN }J- in.lin. FG. A. STRESS-STRAN CURVES FOR RENFORCEMENT