Table 1.Summary of Measured and Calculated Results OD Specimen (mm) (kN)(im) LE N) FLUSH-1 36.8 40.3 37 367 412 2.3 2.6 21 65 68 16 40 34.7 41.5 23 24 1.9 0D116-2 35.1 421 13.9 17.4 0D118- 4.1 32.0 40.6 32 4.1 32.3 32.3 1.8 2.3 18 249 48 4.1 280 181 10 20 1.6 0D316-2 4.1 28.7 20.0 each series of tests is given.P is the average of P for each carrying capacity. of the speci Displacement Capacity and Failure Modes 32,and 4.8 mm,respectively. Given that these are maximum The displacement capacity of a shear wall derives from the syn to shear wall i the to lates s As evclic load is ap a),which torm.Load is the en trans ll syst strength of the sheathing Specimenswithsh-driven cal iven 1.6 of the pane s and c these specimens is clearly evidenced by the hysteresis curves flush-driven nails ing an averag of 81%of the ma 食ordmven de lear hap ens simply because once a tear out oc curs.that nail is no mens,significant damage was not obse ved until the specimens while nail men cle of 3. of the F MEdisplace ils had for sp ero failure,a ng I placem (pul specimens wih and the more du riven 4.8 904/JOURNAL OF STRUCTURAL ENGINEERING/JULY 2002 od05Jhn2009to222.65.175.206.Rodist ASCE I each series of tests is given. Pult is the average of Pmax for each specimen for each configuration. A reduction in Pult is observed for all specimens with over￾driven nails. As compared to the ultimate load of the specimens with flush-driven nails, reductions due to overdriving were 6, 12, and 24% for the specimens with nails overdriven to depths of 1.6, 3.2, and 4.8 mm, respectively. Given that these are maximum expected reductions ~100% of the sheathing nails in a specimen were driven to the specified depth!, the reduction for specimens with nails overdriven 1.6 mm is not significant. For specimens with nails overdriven more than 1.6 mm, however, reductions in strength may seriously compromise structural integrity. Critical displacements (dcri), which correspond to displace￾ments at maximum loads (Pmax), are listed in column 7 of Table 1. For the purpose of this paper, the displacement at failure is defined as the critical displacement. In column 8, the average critical displacement (DC) for each series of tests is given. In column 9, displacement-capacity ~m! values are given. Displace￾ment capacity was calculated by dividing DC by the FME dis￾placement ~18 mm!, which may be thought of as the ‘‘yield’’ displacement. Specimens with flush-driven nails and nails overdriven 1.6 mm exhibited similar behavior. The near-identical behavior of these specimens is clearly evidenced by the hysteresis curves shown in Figs. 6~a and b!. Both specimens with flush-driven nails were able to sustain deformations equal to 350% of the FME displacement while still carrying an average of 81% of the maxi￾mum load during the leading cycle at that displacement level. The specimens with nails overdriven 1.6 mm were also able to sustain deformation equal to 350% of the FME displacement; however, the load of the leading cycle at that displacement level dropped slightly more—63% of the maximum load. For these four speci￾mens, significant damage was not observed until the specimens were subjected to the leading cycle of 350% of the FME displace￾ment. Failure occurred shortly after that leading cycle. Significant reductions in displacement capacity were observed for specimens with nails overdriven 3.2 mm or more. The ob￾served reductions were approximately 22% for the specimens with nails overdriven 3.2 mm and 56% for the specimens with nails overdriven 4.8 mm. As shown in Fig. 6~c!, specimens with nails overdriven 3.2 mm were able to sustain the maximum load for several cycles before a sharp decrease in load occurred. In contrast, as Fig. 6~d! shows, specimens with nails overdriven 4.8 mm reached the maximum load much earlier in the load sequence and sustained that load for only two or three cycles. Failure was sudden and accompanied by an immediate reduction in load￾carrying capacity. Displacement Capacity and Failure Modes The displacement capacity of a shear wall derives from the syn￾ergy between the sheathing panels and nails. Lateral cyclic load is applied to a shear wall via the top plates. As cyclic load is ap￾plied, the top sheathing nails bend and deform as they transfer the load to the sheathing panels. As the sheathing panels deform ~pri￾marily as rigid bodies!, the load is transferred to the bottom sheathing nails as they also bend and deform. Load is then trans￾ferred to the bottom plates by the nails. The capacity of the shear wall to displace or deform in plane continuously originates from the bending of the nails. In an optimum ductile shear wall system, sheathing nails and panels would fail simultaneously. In an actual system, however, displacement capacity is limited by yielding or withdrawing of nails or by the tearing of the panels. The bearing length of nails on the panels and the bearing strength of the sheathing panels are critical factors on shear wall displacement capacity. Due to overstress of the panels and conse￾quent premature panel tear out, the specimens with overdriven nails were unable to reach the displacement levels of those with flush-driven nails. These specimens failed earlier in the loading sequence as nail overdriven depth increased. The increasing per￾centage of nails tearing out of the sheathing ~as shown in Fig. 5 for increasing nail overdriven depth! is a clear indication that displacement capacity decreases with overdriven nail depth. This happens simply because once a tear out occurs, that nail is no longer effective in resisting load or dissipating energy. Nail yielding and withdrawal are ductile modes of failure, while nail pull through and tear out are nonductile. Specimens with flush-driven nails and with 1.6 mm overdriven nails had a significant number of fatigued and withdrawn nails. These types of failures allowed significant bending and yielding of the nail before failure, accounting for the higher displacement capacity of these two specimen types. As the nail overdriven depth increased, there was a marked increase in the nonductile failure modes ~pull through and tear out! and a decrease in the more ductile failure modes ~withdrawal and yielding!. Along with this nail-failure trend follows a significant loss in displacement capacity. At the extreme, virtually all nails in the specimens with the nails over￾driven 4.8 mm that failed did so in pull through or tear out, Table 1. Summary of Measured and Calculated Results Specimen OD ~mm! Keff ~kN/mm! KE ~kN/mm! Pmax ~kN! Pult ~kN! dcri ~mm! DC ~mm! m Vner ~kN! LFner Vubc ~kN! LFubc FLUSH-1 — 3.2 36.8 40.3 3.7 36.7 41.2 2.3 2.6 2.1 FLUSH-2 4.2 36.5 42.0 OD116-1 4.0 34.2 40.8 1.6 4.0 34.7 41.5 2.3 2.4 1.9 OD116-2 4.0 35.1 42.1 13.9 17.4 OD118-1 4.1 32.0 40.6 3.2 4.1 32.3 32.3 1.8 2.3 1.8 OD118-2 4.1 32.6 24.0 OD316-1 4.1 27.3 16.2 4.8 4.1 28.0 18.1 1.0 2.0 1.6 OD316-2 4.1 28.7 20.0 904 / 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