《木结构 Timber Engineering》课程教学资源（参考文献）Capacity of Oriented Strand Board Shear Walls with Overdriven Sheathing Nails

Capacity of Oriented Strand Board Shear Walls with Overdriven Sheathing Nails Scott N.Jones'and Fernando S.Fonseca,P.E.,A.M.ASCE2 Abstract:Eight shear wall specimens sheathed with 11 mm structural oriented strand board panels were as embled with overdriver sheathing nails and tested using a nseudo-dynamic cedure specimens used 38x89 mm douglas fir-l arch framing members and 8o coolr,gun-driven sheathing nails Four overdriven nail depths were considered:fush,16,3.2,and 4.8mm.Nails were spaced at 76mm on center along the edges and 305 mm on center along intermediate supports.Edge nailing distance was 9.5 mm.Iwo specimens were con cn a ts c mine a lo cap 0%of the sh n a specime a shear wall.Comp ed to sr mens with flush-driven nails.s gth an reduced 56% D0:10.1061ASCE0733-9445(2002128:7898 CE Database keywords:Shear walls;Nails,Strength;Ductility:Wooden structures. Introduction code deficiencies as well as poor engineering.construction and are sheathing nails il s d h ed t mance Loss of e fop and headush with the surface of the sheathing materil.If a nail is diven per than this ideal depth.the nal is dered to that wood structures are prone to significant (H ditions are depicted in Fig.1.Gray and Zacher (19)repor one 96).F marily fro ce.In the ara of Northridge that was shaken by wit ed the nd docu g the Th team structed with flush-driven nails () sensus wa s that the stru he nage tured to nail framing members together and to slightly overdrive the nails.The overdriv ing allowed members being naile togethe Engincer.Wright Structural Engineers.Inc..7310 Smoke Ranch Rd. to be g la r sheath Provo.Ur 8460 E-mail nalls are us wever,the riving pin mus erepla drive depth to be adiusted at the nosepiece of the gun without the driving pin. ble publication 2000 1.2002.ASCE.ISSN 0733 ne na gun or if th 898/JOURNAL OF STRUCTURAL ENGINEERING/JULY 2002 d05Jn2009to222.65.175.206.Rcd yrigh

Capacity of Oriented Strand Board Shear Walls with Overdriven Sheathing Nails Scott N. Jones1 and Fernando S. Fonseca, P.E., A.M.ASCE2 Abstract: Eight shear wall specimens sheathed with 11 mm structural oriented strand board panels were assembled with overdriven sheathing nails and tested using a pseudo-dynamic procedure. Specimens used 38389 mm Douglas Fir-Larch framing members and 8d cooler, gun-driven sheathing nails. Four overdriven nail depths were considered: flush, 1.6, 3.2, and 4.8 mm. Nails were spaced at 76 mm on center along the edges and 305 mm on center along intermediate supports. Edge nailing distance was 9.5 mm. Two specimens were constructed for each aforementioned overdriven depth. To determine a lower bound on capacity, 100% of the sheathing nails in a specimen were driven to the specified depth. Results from this study indicate that any level of sheathing-nail overdrive will reduce the capacity of a shear wall. Compared to specimens with flush-driven nails, specimens with nails overdriven 1.6 mm suffered 5% loss in strength and gained 1% in displacement capacity. Specimens with nails overdriven 3.2 mm had strength and displacement capacity reduced by 12 and 22%, respectively. Specimens with nails overdriven 4.8 mm fared poorly; strength was reduced 24%, and displacement capacity was reduced 56%. DOI: 10.1061/~ASCE!0733-9445~2002!128:7~898! CE Database keywords: Shear walls; Nails; Strength; Ductility; Wooden structures. Introduction Wood shear walls are the most prevalent lateral-force resisting system in houses and are very popular in low-rise commercial buildings in the United States. Historically, wood shear wall structures have fared very well in seismic events. The ability of a shear wall to deform and dissipate energy in a ductile fashion as it is subjected to lateral loading results in very good seismic perfor￾mance. Loss of life due to the failure of a properly designed and constructed wood shear wall system is uncommon. Collapse of such a structure during an earthquake is equally rare. The January 17, 1994 Northridge earthquake, however, proved that wood structures are prone to significant seismic damage when poor construction practices are prevalent ~Hall 1996!. Fol￾lowing the Northridge earthquake, three teams of engineers, pri￾marily from the City of Los Angeles Department of Building and Safety and the Structural Engineers Association of Southern Cali￾fornia ~SEAOSC!, scoured the shaken area and documented the damage to structures that occurred during the event. These teams were sponsored by the Earthquake Engineering Research Insti￾tute, the National Science Foundation, and the Federal Emergency Management Agency. The general consensus was that the struc￾tural damage incurred in wood buildings was due primarily to code deficiencies as well as poor engineering, construction, and/or inspection practices. Among the more prevalent structural deficiencies found in shear wall construction was overdriven sheathing nails. Overdriven sheathing nails are one of the major structural de- ficiencies in wood shear walls that are constructed with pneumatic nail guns. A properly driven nail should have the top of the nail head flush with the surface of the sheathing material. If a nail is driven deeper than this ideal depth, the nail is considered to be overdriven. Conversely, if a nail is driven more shallow than this ideal depth, the nail is considered to be underdriven. These con￾ditions are depicted in Fig. 1. Gray and Zacher ~1988! reported that in one wood-construction project the plywood shear walls had 80% of the nails driven to 3.2 mm or deeper below the sheathing surface. In the area of Northridge that was shaken by the earthquake, a large number of shear walls were found with over 50% of the nails overdriven. Shear walls with overdriven nails have reduced capacity as compared to those properly con￾structed with flush-driven nails ~Hall 1996!. Pneumatically driven nails are commonly under- or overdriven because of the driving pin. Nail guns were originally manufac￾tured to nail framing members together and to slightly overdrive the nails. The overdriving allowed members being nailed together to be ‘‘pressed’’ firmly and uniformly against each other. Nail guns are often accurate for some conditions, such as driving large 10d nails and 16d sinker. When thinner and shorter sheathing nails are used, however, the driving pin must be replaced with a shorter pin to prevent overdriving. Newer nail guns allow the drive depth to be adjusted at the nosepiece of the gun without replacing the driving pin. In addition, nails are under- or overdriven because guns are not firmly held by the carpenter, framing members are not prop￾erly supported, or framing members have nonuniform density. If the carpenter does not hold the nail gun firmly, or if the framing member being nailed to is not properly supported ~or is perhaps a 1 Engineer, Wright Structural Engineers, Inc., 7310 Smoke Ranch Rd., Suite P, Las Vegas, NV 89128. 2 Assistant Professor, Brigham Young Univ., Civil and Environmental Engineering, 368 Clyde Building, Provo, UT 84602. E-mail: ffonseca@et.byu.edu Note. Associate Editor: David V. Rosowsky. Discussion open until December 1, 2002. Separate discussions must be submitted for individual papers. To extend the closing date by one month, a written request must be filed with the ASCE Managing Editor. The manuscript for this paper was submitted for review and possible publication on October 12, 2000; accepted November 18, 2001. This paper is part of the Journal of Struc￾tural Engineering, Vol. 128, No. 7, July 1, 2002. ©ASCE, ISSN 0733- 9445/2002/7-898–907/$8.001$.50 per page. 898 / JOURNAL OF STRUCTURAL ENGINEERING / JULY 2002 Downloaded 05 Jan 2009 to 222.66.175.206. Redistribution subject to ASCE license or copyright; see http://pubs.asce.org/copyright

nto the sysm The ery 一Rm struction of ood structures.Thus,any practice that underdrives a Underdriving the nails is,therefore,a waste of time and is an avoided practi s om ssed through ne and training appropriate and ap- Fig.1.Nail-drive depths and even futt construction that na tan overdriven.at which point a 3-4%reduction in ultimate loac fush-driven nail shear have overdriven 32mm or with any nail overdriven more.the su ove dcatedoY .Zache and Gra 198 an (1988 13s was conducted on wall specimens with all verdriven nstructed using a95mm CD plywood,the ren issues of overstrength and the adverse effects additional str rd and ar of repaired wall may have on anchorage or adjaccnt nails while the other four spe acceptable for applied loading. such as wind the additiona me with c as led with flush- strength can result in an unplanned failure mechanism for the 32 verdriven acc More recently,Ficcadenti et al.(1996)studied the effects of ngly ove nven 8d ven box hails space at 64 mm o denly at atior vels xpected to in a strong ports.The walls were sheathed thmm-thickCDX ply perform nce wood shear wal The loading sequn used in th ing to Dolan (1999 h se re were que ens were built peop sell (1994)also with s 5096o 27 coupons ands hov applying th tures The coupn tests compared fush-dr ren common nail overdriven na depthand the umer of tested.The ent dep exact depth dvas not ommon nails to she walls with all ails o verdriver only one specimen was 2 les h of the with 20,50 and board (OSB) 80 of the overdriven were.respectiv 4. and 4% sem tnan th with 10d s The well to the maximum load-carrying capa ity of a wal mode that ove not advers se results an rta th the highe 1998 the capac ity,if the failure modes of nail pull through or tearing sell(1994) ed ity of th the specimens was red ced by 1 while capac arch conc to date on coupon and w n f 1985989 and acher (1 that p ng no ance of ood she strength unt ctory.Andreason an JOURNAL OF STRUCTURAL ENGINEERING/JULY 2002/89 20

slightly warped member!, a certain amount of ‘‘bounce’’ will be introduced into the system. The energy lost due to the bounce will cause the nail to be underdriven. Nail guns automated the con￾struction of wood structures. Thus, any practice that underdrives a nail disrupts this automatic procedure because the carpenter must then use a hammer to further drive the nail to a flush condition. Underdriving the nails is, therefore, a waste of time and is an avoided practice. Density of framing members varies along their length and varies from one member to another. If a particular framing member is less dense than another ~which is very likely!, the gun will overdrive the nails in the less-dense framing member. Thus, overdriving is a very common practice. The nail-overdriving problem can be addressed through proper inspection and training. These solutions are appropriate and ap￾plicable to new construction; nevertheless, a significant number of existing structures cannot be easily fixed. To evaluate existing construction and even future construction that may be substan￾dard due to overdriven nails, an engineer must have an under￾standing of the behavior and be able to determine the capacity of shear walls that have overdriven sheathing nails. The nail￾overdriving problem will not be eradicated overnight, however. The issue of pneumatically overdriven nails in wood shear walls has been previously addressed. Zacher and Gray ~1985, 1989! and Gray and Zacher ~1988! reported on 13 shear wall specimens and 15 overdriven nail wood joints. Nine wall speci￾mens were constructed using a 9.5 mm CD plywood; the remain￾ing four specimens were constructed using gypsum board and are not discussed further. Five of the nine plywood specimens were constructed with 8d common nails, while the other four speci￾mens were assembled with staples. Two specimens were as￾sembled with flush-driven nails and three with nails overdriven 3.2 mm. All nails were either flush driven or overdriven accord￾ingly. Testing was conducted using a cyclic, displacement￾controlled loading sequence at 2.0 Hz. Plywood panels failed sud￾denly at deformation levels expected to occur in a strong earthquake, and the results indicated that the performance of wood shear walls with overdriven nails is unsatisfactory. Accord￾ing to Dolan ~1999!, ‘‘These results were questioned by several people and never widely accepted.’’ Andreason and Tissell ~1994! also investigated the effects of overdriven nails by testing 27 coupons and 5 shear walls. Testing, however was conducted using a monotonic loading procedure, which does not correlate well with the seismic response of struc￾tures. The coupon tests compared flush-driven common nails to common nails overdriven to four different depths in various thick￾nesses of plywood. The wall tests compared specimens with flush-driven common nails to shear walls with all nails overdriven by 3.2 mm. The shear wall specimens were sheathed with 12 mm APA rated plywood sheating or 11 mm APA rated oriented strand board ~OSB! structural panels. The OSB specimens were as￾sembled with 8d common nails, while the plywood specimens were assembled with 10d short nails. The results may correspond reasonably well to the maximum load-carrying capacity of a wall but not to the displacement capacity, since testing was conducted using a monotonic loading procedure ~Dinehart and Shenton 1998!. Andreason and Tissell ~1994! observed that overdriven nails reduced the capacity of the specimens. Capacity of the plywood specimens was reduced by 15%, while capacity of the OSB speci￾mens was reduced by 13%. Adequate load factors, however, were retained by all five wall specimens tested. The conclusion from the study was that overdriving will not significantly affect the strength of a shear wall until at least 20–25% of the nails are overdriven, at which point a 3–4% reduction in ultimate load occurs as compared to walls with flush-driven nails. To remedy the problem in a wall with 20% of the perimeter nails overdriven 3.2 mm or with any nail overdriven more than 3.2 mm, the sug￾gestion was that additional nails be driven at a rate of one extra nail for every two overdriven nails. The rationale to support this conclusion and recommendation was not apparent, since testing was conducted on wall specimens with all nails overdriven 3.2 mm. Furthermore, the recommendation did not address seismic issues of overstrength and the adverse effects additional strength of repaired wall may have on anchorage or adjacent structural elements. While increasing the strength of a shear wall may be acceptable for applied loading, such as wind, the additional strength can result in an unplanned failure mechanism for the structure. More recently, Ficcadenti et al. ~1996! studied the effects of overdriven 8d pneumatically driven box nails spaced at 64 mm on center along the edge and 305 mm on center along intermediate supports. The walls were sheathed with 9.5-mm-thick CDX ply￾wood shear walls. The loading sequence used in the testing was a modification of the sequential phased displacement ~SPD! proce￾dure. Two specimens were built with flush-driven nails as control. Three additional specimens were built: one with 20% of the nails overdriven, one with 50% of the nails overdriven, and one with 80% of the nails overdriven. Two important factors must be con￾sidered when determining the appropriateness and applying the results of this testing program: the presumable randomness of the overdriven nail depth and the number of specimens tested. The exact depth of overdrive was not measured but was presumably random: a nail had to be driven at least 1.6 mm past flush to be considered overdriven. Furthermore, only one specimen was tested for each condition. Ultimate average capacity of the specimens with 20, 50 and 80% of the nails overdriven were, respectively, 14, 7, and 4% greater than the average capacity of the walls with flush-driven nails. Because the specimens failed by nail withdrawal, a failure mode that overdriving does not adversely affect, these results are to be expected. These results lead to the inference that the deeper the nail is driven into the framing ~to a certain extent!, the higher the capacity, if the failure modes of nail pull through or tearing out are eliminated. The overdriven nail required more energy to fail ~by withdrawal!, thus increasing the wall capacity. Research conducted to date on coupon and wall specimens with overdriven nails is, therefore, incongruous. Zacher and Gray ~1985, 1989! and Gray and Zacher ~1988! concluded that perfor￾mance of wood shear walls with overdriven nails was not satis￾factory; Andreason and Tissell ~1994! concluded that overdriving Fig. 1. Nail-drive depths JOURNAL OF STRUCTURAL ENGINEERING / JULY 2002 / 899 Downloaded 05 Jan 2009 to 222.66.175.206. Redistribution subject to ASCE license or copyright; see http://pubs.asce.org/copyright

ct the of hear all (196)concluded that overdriven box nails may W12x65 is used as the buttress column and two use n的5。 The loading unit consists of two sidesway cal supp for the force-applying system ded of shear walls with overdriven nails. the force-app to eacl Construction Method and Materials cure according to common construction practice Larch (Dt by ed at 40 net,surface No.2 Douglas 出路 studs was mes The force ing system was fabricated with two TS4X2 X3nhcanT72i5tm 3.3-mm-diam driven each end.The tubes straddle the stem of the ST section,which is s an to he dual end studs through the stem of the ST.which has a vertical slotted holea 10d framing nails that location snge-pin slotted c motion by the center stud (APA 1980).The par nels v 对 AM™q57595 The flanges of the channe of the top channel provides the flat surface needed for specimer es at 203 mm on cente temghanddiphcementepaci,i00%ofihehehmgaS down attachment. n and have been the overdriven nails measurements taken after final nail place structura ment found the nails to be within 0.4 mm of the desired depth. The loading sequence of a wall specimen is s:the actuator applie Test Setup The test fra installed is sche napplied t in Fig.3.The testing frame was designed with two main pur of friction between the stee and the wood.The wall specimen is 900/JOURNAL OF STRUCTURAL ENGINEERING/JULY 2002 dod 05 Jan 2009 to 222.66.175.206.Rodistribu to ASCE l .org/copyright

will not significantly affect the strength of a shear wall until at least 20–25% of the nails are overdriven; and Ficcadenti et al. ~1996! concluded that overdriven box nails may even increase the strength and displacement capacity of shear walls. Clearly, due to the many variables affecting the behavior of shear walls with overdriven nails, the investigations conducted so far are not suf- ficient. Furthermore, testing has not been performed with a level of accuracy that allows bounds to be set on the strength and displacement capacity of a shear wall with overdriven nails. To determine strength and displacement-capacity bounds, it is neces￾sary to test variations of overdriven depth. A series of tests with 100% of the nails overdriven to certain depths have been con￾ducted in this research, resulting in a ‘‘worst-case’’ condition for analysis. Objectives of the testing are to characterize the behavior and to determine limits on the strength and displacement capacity of shear walls with overdriven nails. Construction Method and Materials Eight 2.432.4 m shear wall specimens, schematically shown in Fig. 2, were built according to common construction practice. Studs were 38 by 89 mm net, surfaced dry No. 2 Douglas fir￾Larch ~DFL! spaced at 406 mm on center. Moisture content of the studs was measured immediately after each shear wall test. Those measurements indicated a moisture content varying from 9.7 to 11. Studs were attached to the top and bottom plates using two 3.3-mm-diameter by 78-mm-long ~10d framing! nails driven through the plates into the end grain of the stud. End studs were doubled to allow the required uplift force to be transferred through the studs into a bolted hold down. The dual end studs were fastened together along their length with 10d framing nails at 102 mm on center. The specimens were sheathed with two 11 mm rated sheating OSB structural panels. The panels were installed with the 2.4 m dimension parallel to the studs and were spaced 3.2 mm along the vertical joint at the center stud ~APA 1980!. The panels were attached to the framing members with pneumatically driven, 2.9- mm-diameter 3 60-mm-long ~8d cooler! nails at 76 mm on center along the edges and 305 mm on center along intermediate sup￾ports. Bending yield strength of the 8d cooler nails was obtained by conducting several tests according to ASTM F 1575-95 ~ASTM 1997!. The average bending yield strength of the 8d cooler nails was 704,400 kPa. A nailing edge distance of 9.5 mm was maintained for all specimens. Two specimens were con￾structed for each of the following overdriven nail depths: flush driven, 1.6, 3.2, and 4.8 mm. To determine a lower bound on strength and displacement capacity, 100% of the sheathing nails in a given specimen were driven to the specified depth. The nail gun was set using an adjustable nose piece to underdrive the nails approximately 3.2 mm from their final desired depth. The slightly underdriven nails were then driven to their final depth using a hammer for the flush nails and a hammer and custom punch for the overdriven nails. Measurements taken after final nail place￾ment found the nails to be within 0.4 mm of the desired depth. Test Setup The test frame with a specimen installed is schematically shown in Fig. 3. The testing frame was designed with two main pur￾poses: to ensure that a ‘‘true’’ horizontal force ~or displacement! was applied to the specimen and to prevent out-of-plane motion of the specimen. The frame has a reaction unit and a loading unit. The reaction unit is assembled with wide-flange steel sections. A W12365 is used as the buttress column and two W8331 are used as braces. Steel plates are welded at each end of the braces and at the bottom of the buttress column. The braces are attached to the column with four 19 mm A325 steel bolts. The reaction unit is secured to the laboratory strong floor with three 35 mm dywidag bars. The loading unit consists of two sidesway braces, a force￾applying system, and a force-resisting system. Each sidesway frame was designed as an adjustable ‘‘H’’ frame. Two W8331 wide flange sections are used as uprights. Two structural tubings, TS 63333/8, connect the uprights and provide vertical support for the force-applying system. Two spacers are welded to the tubings, maintaining them parallel to each other and providing a sliding ‘‘window’’ for the force-applying system. Steel plates are welded at each end of the tubings and connected to each upright with four 19 mm A325 steel bolts. The double-tubing system can be attached to the uprights at different elevations according to the height of the specimen to be tested. Each upright is firmly secured to the structural floor with a 32 mm dywidag bar. The H frames are connected to each other with two L43431/4 steel angles. Two 16 mm A325 steel bolts are used to attach each end of the steel angle to the top of the uprights. The force-applying system was fabricated with two TS432 33/8 structural tubes and a ST9327.35 structural tee. The tubes are parallel to each other and are connected with a steel plate at each end. The tubes straddle the stem of the ST section, which is set inverted ~flange down!. The tubes and the ST are connected at midlength. A 25 mm hardened steel pin fits through the tubes and through the stem of the ST, which has a vertical slotted hole at that location. The single-pin slotted connection allows for wall rotation and uplift while maintaining the load in the horizontal direction. Force is always applied horizontally because the tubes are restrained from out-of-plane and vertical motion by the H braces. To provide a smooth riding for the tubes, the two sliding windows in the H braces are dressed with nylon pads to reduce the friction generated by the confinement. Two steel channels, C8318.75, serve as the force-resisting system, or foundation. The channels are stacked and welded to￾gether along their length. The flanges of the channels are perpen￾dicular to the structural floor, and the webs are parallel. The web of the top channel provides the flat surface needed for specimen connection. The channels are securely attached to the structural floor by two 38 mm dywidag bars at each end. The double￾channel unit has been drilled with holes at 203 mm on center along its length, and nuts are welded to the bottom channel at hole locations. Two additional holes are provided in the unit for hold down attachment. The hydraulic actuator is attached to the buttress column and to one of the ends of the force-applying system. All dywidag bars have been posttensioned to attach the testing frame firmly to the structural floor. The testing frame has been aligned horizontally and vertically to a tolerance of 3.2 mm. The loading sequence of a wall specimen is as follows: the actuator applies force ~or displacement! to the tubes of the force￾applying system. The tubes transfer the force through the 25 mm hardened steel pin to the inverted ST section, which is attached to the specimen with bolts. A nonslip 3M™ tape has been applied to the bottom of the inverted ST section to provide a high coefficient of friction between the steel and the wood. The wall specimen is attached to the double steel channel force-resisting system with steel bolts. The nonslip 3M™ tape has also been applied to the 900 / JOURNAL OF STRUCTURAL ENGINEERING / JULY 2002 Downloaded 05 Jan 2009 to 222.66.175.206. Redistribution subject to ASCE license or copyright; see http://pubs.asce.org/copyright

SB Sheathing Pane 76 Shen Fig.2.Shear wall specimen "H"'Frame Nykon Bushin al Tub 入Doble See Channels Fig.3.Testing frame JOURNAL OF STRUCTURAL ENGINEERING/JULY 2002/90 ASCE liconse

Fig. 2. Shear wall specimen Fig. 3. Testing frame JOURNAL OF STRUCTURAL ENGINEERING / JULY 2002 / 901 Downloaded 05 Jan 2009 to 222.66.175.206. Redistribution subject to ASCE license or copyright; see http://pubs.asce.org/copyright

oeemoftedhtelcRi5coiaemoten Con The is shown in Fig 4.The procedure of the specimen to the dou ble steel c anndlforcc-stistngys the d les each ing25.50. system this is a repeate 16 re.the stroke was used.Specimens were attached to 22 tightened an air-impac each at 75.50.and ofthe amplitude of the mm on Each the rresponds to400%of the FME displacemen force-resi mm-eaded hout the rod. oad was applied t ring the arge ment,and time data for the tests.Eleven linear variable diferen anged from Hz(for small amplitude displacements)toH ansducers positioned on and around the specimen and tes large amplitude displacements)due to test equipment limita transducer for string pot)indepen top of the draulic actuator.Measurements were recorded at a rate of 50 Observations samples/s General Trend of the rotate Test Method .th at the and the rotation of the pane 119970 nen.The FME is defined as the firs other words,the na one behavior state to whercas the structura literature and a preliminary test.Dinchart and Shenton (1998 he unZ pping would progres to the point tha or both ested se v wall specimer with similar m were totally deta ted for th A preliminary test of a specimen with assembled with na erdriven 32 and 4.8mm as compared to d using 19 mm as the with flu fact that the imens to be tested could have smalle cap o over na Nail failure he SPD protocol is not flawless There are some conce that f shea s of nai 2 Four mode the sheathing) ear out (the nail tore through the edge of the the dis rresponding to the FM (the na withdrew ng me should b re t that it is the displacemen and fractured).Th nails judged to still have significant ca ir d EME comp (e )For the by the judgment of the individual research ose of diso and because of the difficulties ass e of fail et al 2000)is nation of the pull-through and tear out) modes ether The 902/JOURNAL OF STRUCTURAL ENGINEERING/JULY 2002 105Jhn2009to222.65.175.206.Rd ASCE I

top face of the double steel channels. Excessive uplift of the wall specimen is prevented by two AHD15A hold downs ~Advanced Connector Systems Catalog 1999! that attach the double end studs of the specimen to the double steel channel force-resisting sys￾tem. The force is finally transferred to the structural floor through the dywidag bars securing the double steel channel force-resisting system. For this testing, an 89 kN hydraulic actuator with 162 mm stroke was used. Specimens were attached to the ST with 22 Grade 5, 13 mm bolts, which were tightened with an air-impact wrench. At the double steel channel force-resisting system, speci￾mens were attached with 25 mm A325 steel bolts placed at 406 mm on center. Each AHD15A hold down was attached to the double end studs with 25 mm A325 steel bolts and to the double steel channel force-resisting system with a 32 mm, all-threaded rod. No additional vertical load was applied to the specimens. A PC-based data acquisition system recorded load, displace￾ment, and time data for the tests. Eleven linear variable differen￾tial transducers positioned on and around the specimen and test￾ing frame monitored various specimen and frame displacements. In addition, a linear-motion transducer ~or string pot! indepen￾dently measured the total lateral displacement at the top of the shear wall. Load was measured with the load cell from the hy￾draulic actuator. Measurements were recorded at a rate of 50 samples/s. Test Method The specimens were tested using the sequential phased displace￾ment ~SPD! loading procedure ~Structural Engineers Association of Southern California 1997!. The procedure is a fully reversed, displacement-controlled protocol and is based on the first major event ~FME! of the specimen. The FME is defined as the first significant limit state to occur during a test. In other words, the FME is an event that marks the transition of the test specimen from one behavior state to another, whereas the second structural behavior is altered significantly from the first. The FME for the testing was a specified displacement established from the current literature and a preliminary test. Dinehart and Shenton ~1998! tested several wall specimens with similar material characteristics and used 19 mm as the displacement corresponding to the FME. A preliminary test of a specimen with flush-driven nails was con￾ducted using 19 mm as the displacement corresponding to the FME. Based on the results of the preliminary test and given the fact that the specimens to be tested could have smaller capacity due to overdriven nails, the displacement corresponding to the FME was reduced to 18 mm. The SPD protocol is not flawless. There are some concerns that the protocol causes nail fatigue during testing of shear walls, which has not been observed during earthquakes ~Ficcadenti et al. 1996; Karacabeyli and Ceccotti 1998!. Another concern is the determination of the displacement corresponding to the FME. Al￾though that displacement should be determined through tests, there are no specific guidelines, except that it is the displacement corresponding to the first significant limit state to occur during the test. Thus, the selected FME displacement is usually influenced by the judgment of the individual research conducting the experi￾ments. The Consortium of Universities for Research in Earth￾quake Engineering ~CUREE! protocol ~Krawinkler et al. 2000! addresses these limitations. Current research ~Uang et al. 2000! is being conducted to determine loading-protocol effects on the re￾sponse of wood shear walls. Forthcoming results should significantly aid in determining the appropriate loading protocol to be used in future shear wall tests. The SPD loading procedure is shown in Fig. 4. The procedure consists of 72 cycles of displacement. The cycles are a series of multiples of the displacement corresponding to the FME and start with groups of three cycles, each group representing 25, 50, and 75% of the FME displacement. The procedure, then, is a repeated pattern of seven cycles. The leading cycle of the pattern is a multiple of the FME displacement. Next, three trailing cycles, one cycle each at 75, 50, and 25% of the amplitude of the leading cycle, is applied. The last three cycles of the pattern are at the same amplitude as the leading cycle. This pattern continues until the leading cycle corresponds to 400% of the FME displacement or the applied force diminishes to 25% of the peak force ~strength limit state!. Cycling is preferred to be at 1.0 Hz throughout the testing procedure; however, 0.2 Hz is acceptable during the larger displacements cycles. The actual cycling rate for the testing ranged from 0.6 Hz ~for small amplitude displacements! to 0.3 Hz ~for large amplitude displacements! due to test equipment limita￾tions. Observations General Trend At the beginning of the tests, the two sheathing panels rotated independently of each other in a rigid body motion. Further into the tests, the 3.2 mm gap between the sheathing panels ~along the vertical joint at the center stud! closed up at the top, and the rotation of the panels started to be restrained by bearing and fric￾tion at that location. At the bottom of the panels, the gap did not close. The sheating panels did not sustain any noticeable damage except in the direct vicinity of the nails. The first noticeable dam￾age to the specimens was usually tearing out of one of the four lower corners of a sheathing panel. There was then a progressive failure ~unzipping! along any given edge of the same panel, start￾ing at one of the corners and progressing away from that corner. The unzipping would progress to the point that one or both sheathing panels were totally detached from the studs along two of the edges. Unzipping was more accentuated for the specimens assembled with nails overdriven 3.2 and 4.8 mm as compared to those assembled with flush-driven and 1.6 mm overdriven nails. The pattern also developed earlier in the loading sequence as the overdriven depth increased. Nail Failure Four modes of nail/sheathing failure were observed during the tests: pull through ~the nail head pulled through the thickness of the sheathing!, tear out ~the nail tore through the edge of the sheathing!, withdrawal ~the nail withdrew from the framing mem￾ber without tearing the sheathing!, and fatigue ~the nail fatigued and fractured!. The nails judged to still have significant capacity on completion of the testing sequence were classified as slightly damaged ~e.g., a nail that withdrew only 0.8 mm!. For the pur￾pose of discussion and because of the difficulties associated with distinguishing between some modes of failure ~as they are often closely related!, the pull-through, tear-out, and pull-tear ~combi￾nation of the pull-through and tear-out! modes are grouped to￾gether. The average percentage of nails failing by each mode for each overdriven nail depth is shown in Fig. 5. 902 / JOURNAL OF STRUCTURAL ENGINEERING / JULY 2002 Downloaded 05 Jan 2009 to 222.66.175.206. Redistribution subject to ASCE license or copyright; see http://pubs.asce.org/copyright