Assessing the Bolted Connection Strength of New Zealand Hardwood

Transcription

1 Assessing he Bole Connecion Srengh o New Zealan Harwoo A.R. Abul Karim, P. Quenneville, N. M.Sa on & J.M. Ingham Deparmen o Civil & Environmenal Engineering, The Universiy o Aucklan, Aucklan. 00 NZSEE Conerence ABSTRACT: From publishe lieraure, i was oun ha hrough-bol connecions were ypically applie as a reroi echnique o mos New Zealan unreinorce masonry (URM) builings ollowing he 93 Hawke s Bay earhquake. As connecion ailure by earing ou par o he iaphragm jois was observe in pas earhquakes ue o laeral earhquake loaing, he srengh o he bole connecion in exising inigenous New Zealan imber joiss nees o be assesse. The main objecives o his suy were o evaluae he srengh an o ieniy he possible ailure moes o bole connecions in New Zealan harwoo. Bole connecion ess loae parallel-o-grain were perorme using recycle naive New Zealan Maai an Rimu harwoos because he imber iaphragms in URM builings are ypically consruce using such woo species. From he experimenal suy, i was observe ha he imber bole connecion can ail in eiher ucile or brile moes. The es resuls obaine were compare wih he European Yiel Moel (EYM), he New Zealan imber coe (NZS 3603:993), an a propose se o equaions (Quenneville 009) in orer o evaluae he applicabiliy o hose equaions in preicing bole connecion srengh or New Zealan harwoo. I was oun ha he EYM equaions provie beer preicions han he NZS 3603:993 when compare o he acual capaciy. However, he EYM preicions are only goo in esimaing he srengh o imber bole connecions ha ail uner ucile moe. For he connecions ha ail exhibiing he brile moe, he propose row shear equaion by Quenneville was oun o give beer srengh esimaion. INTRODUCTION Unreinorce masonry (URM) builings are ypically he class o srucures wih he highes risk o ailure uring an earhquake, an he requiremen o seismically upgrae hese earhquake amageprone builings in New Zealan was manae by The Builing Ac 004 (DBH 004). Imporanly, hese URM builings orm a signiican percenage o New Zealan s builing sock an represen he preominan naional archiecural heriage (Russell an Ingham 008). Mos URM builings in New Zealan consis o soli URM bearing walls an lexible imber iaphragms (loor an roo), wih he wall hickness coniguraion over he heigh o he builing ypically reuce by a single lea a each sorey heigh in orer o suppor he iaphragm. The mos common iaphragm seaing meho was o bear he joiss an ransverse beams on a single brick wih wihou embemen. No connecions beween URM walls an iaphragm were ieniie in URM builings consruce beore he 93 Hawke s Bay earhquake an mos ou-o-plane wall ailures were relae o he absence o anchorage beween he walls an iaphragms. Following he 93 Hawke s Bay earhquake, mos URM builings were seismically reroie, which inclue he insallaion o wallloor an wall-roo connecions (Blaikie an Spurr 99). Mos wall-iaphragm connecions ha were insalle as seismic rerois were hrough-bol anchors, use in conjuncion wih a seel bearing plae locae on he exerior o he builing an a bole connecion on he imber iaphragm jois. Typical wall-iaphragm connecion eails can be oun in Abul Karim e al. (009). Figure shows ypical iaphragm eails eermine or exising New Zealan URM builings. Paper Number 4

2 As connecion ailure by earing ou par o he iaphragm jois was observe in pas earhquakes ue o laeral earhquake loaing (Blaikie an Spurr 99), he srengh o he bole connecions in exising inigenous New Zealan imber joiss requires assessmen as hey nee o be properly eaile. The main objecives o his suy were o evaluae he srengh an o veriy he possible ailure moes o he bole connecions in New Zealan harwoo. Base on experimenal aa obaine, a se o esign equaions or preicing he srengh o imber bole connecions is recommene. Thus, eaile seismic assessmen an reroi soluion proceures or wall-iaphragm connecions in exising New Zealan URM builings can be provie. The imber bole connecion ess conuce a he Universiy o Aucklan using recycle naive New Zealan harwoo such as Maai an Rimu are escribe, wih he experimenal resuls compare o several srengh preicion equaions in orer o evaluae heir poenial or calculaing he capaciy o bole connecions, speciically or New Zealan harwoo. a) Jois perpenicular o URM wall b) Jois parallel o URM wall Figure : Typical iaphragm eails (Abul Karim e al. 009) DESIGN EQUATIONS FOR TIMBER BOLTED CONNECTIONS There is agreemen, in principle, wihin he inernaional imber engineering communiy ha crieria in imber esign sanars or eermining he capaciy o bole connecions shoul be base on recognise mechanics moels ha are capable o ieniying each possible moe o ailure (Quenneville 009). Failure moes o be consiere are he ucile bearing ailures an he brile racuring ailures in woo, where he moe wih he lowes esimae capaciy will govern perormance (Quenneville e al. 006). This secion escribes he esign equaions ha are currenly available o preic he capaciy o imber bole connecions.. New Zealan Timber Srucures Sanar (NZS 3603:993) For he purpose o imber bole connecion esign, which is associae wih a ucile ailure moe, Clause 4.4 o NZS 3603:993 can be use. The characerisic srengh o a bol loae parallel o he grain in ry imber, Q kl or a bol in single shear shall be he lesser o: k cj a (Eqn. ) or 0.5 b e cj a (Eqn. ) where k = bol bearing sress acor (Table 4.8 o NZS 3603:993) cj = characerisic bol bearing sress parallel o he grain, MPa (Table 4.8 o NZS 3603:993) a = iameer o a asener, mm b e = eecive imber hickness in a bole connecion, mm (Table 4.9 o NZS 3603:993).

3 Thus, he srengh o a laerally loae bole connecion, N* or wo-member an hree-member connecion ypes is given in Table. In hese equaions, he connecion behaviour is assume o be ucile. A brile ailure is assume o occur only or connecions wih our aseners or more, aken ino accoun wih a value o k 3 less han. Table. Bole connecion srengh or a single bol in ry imber loae parallel o he grain. Type o connecion Bole connecion srengh, N* a) Two-members N * = φ n k k k 3 (k cj a ) (Eqn. 3a) N * = φ n k k k 3 (0.5 b e cj a ) (Eqn. 3b) b) Three-members N * = φ n k k k 3 ( k cj a ) (Eqn. 4a) N * = φ n k k k 3 (b e cj a ) (Eqn. 4b) Noes:. N* is he esign loa eecs on connecion prouce by srengh limi sae loas, N.. φ is he srengh reucion acor (Clause.5 o NZS 3603:993). 3. n is he number o aseners. 4. k is he uraion o loa acor or srengh (Table.4 o NZS 3603:993). 5. k is he acor or he esign o bole connecions in green imber (Table 4.4 o NZS 3603:993). 6. k 3 is he acor or he esign o muliple-bol connecions (Table 4.5 o NZS 3603:993).. European Yiel Moel The European Yiel Moel (EYM), which consiers ucile ailure moes o bole connecions, is associae wih he Johansen s heory. This heory is base on he assumpion ha he maerials (i.e. imber uner embeing sresses an asener uner bening acion) behave as rigi-plasic (Blass 003). Tables an 3 show he possible ailure moes or ouble shear an single shear connecions, respecively. The resisance, R per asener per shear plane o a connecion can be calculae using equaions given in each able. The minimum value will govern he connecion resisance. Table. Possible ailure moes or ouble shear join. Failure moe Resisance, R, per asener per shear plane R = (Eqn. 5) R = 0.5 β (Eqn. 6) ( ) ( ) y 4β +β M R = β +β + β +β (Eqn. 7) β R = M y +β (Eqn. 8) 3

4 Table 3. Possible ailure moes or single shear join. Failure moe Resisance, R per asener per shear plane R = (Eqn. 9) R = β (Eqn. 0) 3 R = β+β + + +β β + +β (Eqn. ) ( ) ( ) y 4β +β M R = β +β + β +β (Eqn. ) ( ) ( ) y 4β +β M R = β +β + β +β (Eqn. 3) β R = M y +β (Eqn. 4) Noes:. β is he raio o he embeing srenghs, β = h, /.. is he embeing srengh corresponing o, MPa. 3. h, is he embeing srengh corresponing o, MPa. 4. an is he imber hickness or asener peneraion o member an, mm. 5. is he asener iameer, mm. 6. M y is he asener yiel momen, Nmm..3 Brile ailure moel Many recen suies (Quenneville an Mohamma 000; Mohamma an Quenneville 00; Quenneville an Bickerike 006; Quenneville e al. 006; Quenneville 009) have ieniie he brile ailure o connecions in imber srucures. The observe brile ailure moes are illusrae in Figure. A se o equaions o preic he ulimae srengh o imber connecions base on each brile ailure moe observe uring ess was evelope by Quenneville (Quenneville an Mohamma 000). The eails o all equaions can be oun in Quenneville (009). However, only he row shear equaion is use in his suy an is escribe below. a) row shear b) group ear-ou c) spliing ) ne ension Figure : Observe brile ailure moes or imber bole connecions loae parallel-o-grain The row shear esign capaciy o a group o owel aseners is given by: R r rs = φ k k RS i min n r (Eqn. 5) 4

5 where: φ = srengh reucion acor k k n r = uraion o loa acor or srengh = acor or he esign o bole connecions in green imber = number o rows in he join as per loa componen RS i min = minimum (RS, RS,, RS nr ) RS i = shear capaciy along wo shear planes o asener row i, in N = ( ) K n a v ls i cr i CF v = member shear srengh, MPa, equal o.9 G.3 G = relaive ensiy o imber or he oven ry coniion K ls n i a cr i CF = acor or member loae suraces (0.65 or sie member, or inernal member) = member hickness, mm = number o aseners in row i = minimum o e an s b or row i (see Figure a), mm = calibraion acor. 3 TIMBER BOLTED CONNECTION TESTS 3. Specimen coniguraions bols plaes imber isplacemen gauge Figure 3: Typical specimen o bole imber connecion loae parallel o he grain in esing apparaus In he laboraory ess, recycle naive New Zealan harwoo such as Maai an Rimu were use because he loor joiss in URM builings are ypically consruce using such woo species. All specimens consise o hree-member connecions wih wo seel sie plaes sanwiching a imber cenre piece as shown in Figure 3. The cross secion o each imber specimen was 50 mm (hickness) 00 mm (wih) an ha a moisure conen o 3% a he ime o esing. mm iameer () bols o 4.8 grae ( y = 30 MPa) were use in all specimens. The seel sie plaes use were 0 mm hick wih an ulimae ensile srengh, u, o 400 MPa. Eleven groups o specimens were ese, where each group consise o a leas en replicaes. Groups an 3 were ese wih boh Maai an Rimu woo species an oher groups were ese wih Maai woo only ue o he limie availabiliy o Rimu woo specimens. All groups ha a single row (n r ), bu varie wih number o aseners (n ) an en isance (e ). The number o aseners varie rom o 4. The majoriy o connecions wih aseners ha a 00 mm bol spacing (s b ) excep or group 9 wih a 50 mm bol spacing. Groups wih a 50 mm en isance were esigne in orer o maximise he number o observaions on he row shear ailure mechanisms, o eermine he calibraion acor o equaion 5 or New Zealan harwoo. Deails o he specimen coniguraion are given in Table 4. 5

6 Table 4. Specimen coniguraion an summary o es resuls. Cross Experimenal Observe e s b s r secion R avg COV R 5h% ailure Group (mm) (mm) (mm) (mm) n r n Species (mm) (kn) (%) (kn) moe Maai 50 x B Maai 50 x B R Rimu 50 x B Maai 50 x B 3R Rimu 50 x B Maai 50 x RS 5 00 Maai 50 x B 6 50 Maai 50 x B 7 00 Maai 50 x B 8 50 Maai 50 x RS Maai 50 x RS Maai 50 x RS Maai 50 x RS Noes: B = Bearing ailure; RS = Row Shear ailure 3. Tes seup All specimens were loae in ension parallel-o-grain an were abricae wih an ienical connecion coniguraion a each en. All aseners were inger igh o allow sel-alignmen, an a monoonic ension loa was applie hrough he sie seel plaes using an MTS loaing sysem. Each specimen was ese a a isplacemen-conrol rae o mm/min unil ailure, when he loa roppe wih no recovery. Boh ens were moniore or loa an slip, an he ulimae loa ha was recore was or he exremiy ha aile. Two isplacemen gauges were use o measure he slip o he woo inernal member wih reerence o he sie seel plae a each exremiy. Each loa-slip aa was collece by a aa acquisiion sysem an recore on a personal compuer. Figure 3 shows a ypical specimen in he esing rame. 4 RESULTS AND DISCUSSION 4. General Each specimen was loae in ension up o he ulimae capaciy o one o he wo exremiies o he connecions. The loa-slip curve o each specimen was ploe an he ulimae loa an he ype o ailure were recore. The experimenal resuls o he eleven groups ese are lise in Table 4. The average experimenal values, R avg, were eermine an he lower 5 h percenile srengh o he experimenal resuls, R 5h%, was calculae assuming a normal isribuion. The preominan moes o ailure observe aer esing are lise in Table 4, where B an RS are esignae or bearing ailure an row shear, respecively. The calculae srengh values (i.e. preicions) or each group o connecions are abulae in Table 5 or comparison. The NZS 3603:993 values represen he srengh o laerally loae hree-member ype bole connecions ha were calculae using equaions 4a an 4b. Equaions 5 o 8 were use o preic he srengh o he connecions base on he EYM. Preicions using he row shear equaion (Eqn. 5) propose by Quenneville or connecions ha ail in a brile moe are also given. All srengh values were calculae or shor erm uraion o loa (i.e. seismic loaing). 4. Failure moes Two ominan moes o ailures were observe uring he connecion ess, which were bearing an row shear ailure. All groups abricae wih an en isance o 00 mm or more aile primarily in a ucile moe (i.e. bearing) unil a seconary brile ailure such as spliing or row shear cause he 6

7 loa o rop suenly as illusrae in Figure 4a. The ominan inal moe o ailure in mos specimens or groups,, 5 an 6 (e 50 mm) was spliing, where ew specimens aile in row shear. However, he inal ailure moe o row shear was observe in groups 3 an 7 (e = 00 mm). Yieling o he aseners was also observe in hese groups o connecions. As expece, groups o specimens wih e equal o 50 mm primarily aile in row shear an very ew aile in spliing. This brile ailure moe is associae o a loa rop a a low isplacemen value as shown in Figure 4b. From boh observaions, one can see ha he moe o ailure is aece by he en isance o he connecions. Figures 4a an 4b show he ypical loa-isplacemen curves or all specimens in groups 5 an 8 ha exhibie ucile an brile behaviour, respecively. In general, he ulimae srengh was also consierably aece by ecreasing he en isance rom 00 mm o 50 mm. The eec o he en isance on he ulimae srengh is bes escribe by comparing he 5 h percenile experimenal values o group wih group 4, as well as group 5 wih group 8. For group 4, he ulimae srengh was abou 0.38 o he srengh o group. The ulimae srengh o group 8 was also lower by a acor o 0.37 compare o group 5. This is consisen wih oher experimenal aa available in he lieraure (Quenneville an Mohamma 000; Mohamma an Quenneville 00). Table 5. Comparison beween es resuls an preicions. Experimenal NZS 3603:993 European Yiel Moel (EYM) Row shear R avg COV R 5h% N * N * N min R Eqn.5 R Eqn.6 R Eqn.7 R Eqn.8 R min R r rs Group (kn) (%) (kn) (kn) (kn) (kn) (kn) (kn) (kn) (kn) (kn) (kn) R R Group 5 0 Group Loa (kn) Loa (kn) Displacemen (mm) a) connecions exhibiing ucile behaviour Displacemen (mm) b) connecions exhibiing brile behaviour Figure 4: Typical loa-slip curves 7

8 4.3 Calibraion acor In orer o eermine he calibraion acor o equaion 5 or New Zealan harwoo, groups 4, 8, 9, 0 an were analyse. As menione previously, hese groups, which ha an en isance o 50 mm, were purposely esigne o maximise he number o observaions o row shear ailure. The average srengh values o row shear ailure (Eqn. 5), R r rs, avg, or each group were eermine. These values were hen ploe agains he average experimenal resuls (see Figure 5). The calibraion acor was eermine when he linear bes ie line o he preicion values (G4, G8, G9, G0, G) mache he linear one-o-one raio line. Figure 5 shows ha he linear bes i line o he preicion values is perecly maching he aoremenione line. Thus, a calibraion acor o 4 was oun in his analysis. 4.4 Preicions vs experimenal Rr rs, avg (kn) 70 Linear (one-o-one raio) 60 Linear (G4, G8, G9, G0, G) G G0 y = 0.99x R = G9 G4 0 G R avg (kn) Figure 5: Preicions vs. es resuls In orer o evaluae he capabiliy o he curren srengh preicion equaions (i.e. NZS 3603:993, EYM, an R r rs ) o esimae he capaciy o bole connecions or New Zealan harwoo, a graph showing he eeciveness o hose preicions versus he es resuls is presene in Figure 6. Any preicion values ploe below he 45 line are consiere o be conservaive. For comparison purposes, Table 6 summarises he calculae raios beween he preicions an es resuls. 75 Table 6. Raios beween preicions an es resuls. Preicions (kn) NZS 3603:993 EYM Rr rs R 5h% (kn) R 5h% N min R min R r rs N min R min R r rs Group (kn) (kn) (kn) (kn) R 5h% R 5h% R 5h% R R Figure 6: Comparison beween es resuls an preicions rom NZS 3603:993, EYM or R r rs By reerring o groups ha aile in bearing, preicions using he curren NZS 3603:993 were oun o be oo conservaive compare o he lower 5 h percenile o he experimenal resuls. The esign values provie by he NZS 3603:993 woul make he choice o bole connecions impracical. Excluing groups 4, 8 an 9 or which he connecions aile in row shear, he raio o he imber sanar values o he es resuls varies beween 0.59 an 0.83, wih an average o Beer preicion values were obaine using he EYM equaions wih he same raio ranges rom 0.85 o.0 an an average o Using he row shear equaion, an accepable esimaion o srengh was oun or groups,, R, 3, 3R, an 7, bu srengh was overesimae or groups 5 an 6 wih ierences o 4% an 7%, respecively. 8

9 A similar comparison was perorme or he groups o connecions ha aile in row shear (groups 4, 8, an 9) as shown in Table 6. Boh he EYM an NZS 3603:993 were clearly over preicing he srengh (i.e. unsae) wih an unaccepable percenage o error. However, goo preicion values were obaine using he row shear equaion, especially or groups 4 an 8 wih raios o 0.99 an 0.98, respecively. The srengh o Group 9 was over preice wih a raio o.38. The use o he EYM equaion in combinaion wih he one or row shear woul hus orm a beer se o equaions o esign bole connecions in URM builings. 5 CONCLUSIONS Base on he experimenal suy conuce, he ollowing conclusions can be rawn:. The srengh an possible ailure moes o New Zealan harwoo bole connecions were successully assesse. Boh srengh an ailure moes were oun o be signiicanly aece by he en isance, e, o he connecions, wih a greaer en isance proucing a sronger connecion.. A calibraion acor o 4 was obaine an applie in equaion 5 in orer o preic he srengh o bole connecions or he row shear ailure moe when occurring in New Zealan harwoo. 3. NZS 3603:993 is ar oo conservaive compare o he 5 h percenile o he acual srengh wih a raio as low as The esign values provie by he imber sanar woul make he choice o bole imber connecions impracical. Beer srengh preicions were achieve using he European Yiel Moel an row shear equaions or bearing an row shear ailures, respecively. Thus, use o he EYM an row shear equaions o esign bole connecions in unreinorce masonry builings is recommene. ACKNOWLEDGMENTS The auhors woul like o express graiue o he New Zealan Founaion or Research, Science an Technology (FRST) or proviing uning or his projec, an o he Minisry o Higher Eucaion (MOHE) Malaysia an Universii Malaysia Sarawak (UNIMAS) or heir inancial suppor o he ocoral suies o he irs auhor. REFERENCES Abul Karim, A. R., Quenneville, J. H. P., M.Sa on, N., an Ingham, J. M. (009). "Srengh Assessmen o Typical Wall- Diaphragm Connecions in New Zealan URM Builings." h Canaian Masonry Symposium ( h CMS 009), Torono, Onario, Canaa. Blaikie, E. L., an Spurr, D. D. (99). "Earhquake Vulnerabiliy o Exising Unreinorce Masonry Builings." Works Consulancy Services, Wellingon. Blass, H. J. (003). "Joins wih Dowel-ype Faseners." Timber Engineering. Thelanersson, S. an Larsen, H. J., es., John Wiley & Sons L., Englan, pp DBH. (004). "The Builing Ac 004". Deparmen o Builing an Housing - Te Tari Kaupapa Whare, Wellingon, New Zealan, 6 p. Mohamma, M., an Quenneville, J. H. P. (00). "Bole Woo-Seel an Woo-Seel-Woo Connecions: Veriicaion o a New Design Approach." Canaian Journal o Civil Engineering, 8, pp NZSI. (993). "NZS 3603:993, Timber Srucures Sanar", New Zealan Sanars Insiue, Wellingon, New Zealan. Quenneville, P. (009). "Design o Bole Connecions: A Comparison o a Proposal an Various Exising Sanars." Journal o he Srucural Engineering Sociey (SESOC) New Zealan Inc., (), pp Quenneville, P., an Bickerike, M. (006). "Eecive In-Row Capaciy o Muliple-Fasener Connecions." CIB-W8 meeing Proceeings, Florence, Ialy, paper Quenneville, J. H. P., an Mohamma, M. (000). "On he Failure Moes an Srengh o Seel-Woo-Seel Bole Timber Connecions Loae Parallel-To-Grain." Canaian Journal o Civil Engineering, 7, pp Quenneville, P., Smih, I., Aziz, A., Snow, M., an Ing, H. E. (006). "Generalise Canaian Approach or Design o Connecions wih Dowel Faseners." CIB-W8 meeing Proceeings, Florence, Ialy, paper Russell, A. P., an Ingham, J. M. (008). "Trens in Archiecural Characerisaion o Unreinorce Masonry in New Zealan." 4h Inernaional Brick an Block Masonry Conerence (4 h IB MaC), Syney, Ausralia. 9