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