Shear wall test setup 

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... Figure 1 shows the details of the shear wall model. No. 2 spruce pine fir (SPF) 38 × 89-mm lumbers were used as framings members. The 89-mm hand-driven common nails were used as the connectors for framings and studs, and the studs were spaced 400-mm apart. It was estimated that one skilled carpenter can finish the whole process for a 1.22× 2.44-mm shear wall in 25 minutes. The ply-bamboo sheets are typically made with a planner dimension of 2440-mm long and 1220-mm wide, using a manufacturing process similar to producing plywood sheets. They are mass-produced and mainly used as concrete formworks in China now. The market price of ply-bamboo sheets are similar or even competitive compared to plywood panels. For the research reported in this research, 8 to 9-mm thick ply-bamboo sheets with a size of 2.44 × 1.22 m were selected. Tests of panel-frame connections. Tests for panel-frame connectors were performed first. Total 40 monotonic tests with two different nail types used in lightweight timber-bamboo shear walls were performed (Table 1). Furthermore, one cyclic test was performed for each group as a comparison to the monotonic test results. The moisture content of the ply-bamboo panel was about 10%. No. 2 SPF 38× 89 mm lumbers imported from Canada with a moisture content of 9% were used as framing members. 51-mm long 6 d nails with diameter 2.10 mm and 45-mm T shape nails with diameter 1.98 mm were selected as fasteners, for their good constructability. Figure 2 shows the configurations of the test specimen in the test setup. The monotonic tests were performed under deformation control with a loading rate of 2.5 mm/min in accordance with ASTM D1761 standard [4]. The Consortium of Universities for Research in Earthquake Engineering (CUREE) -Caltech loading protocol [5] was adopted for the cyclic tests with a loading rate of 20 mm/min. The reference deformation Δ for cyclic tests was determined from the monotonic tests, as f ollows: find the monotonic deformation Δ m by taking the displacement corresponding to 0.8 F max , and then 0.6Δ m was chosen as the reference deformation Δ . The load-displacement curves obtained from monotonic tests are summarized in Figure 3 and Figure 4. Monotonic results show that the angle between the loading direction and the grain of framing had a significant effect on the strength and stiffness degradation after yielding of the connections. The bearing capacity in perpendicular tests was slightly lower than that in parallel tests, but the degradation of strength and stiffness after yielding of the former was much faster than the latter. The curves of 6 d nail connections in perpendicular tests were similar to those of staple nail connections, while in parallel tests 6 d nail connections showed better bearing capacity and ductility. Figures 5 to 6 show the load-displacement hysteretic responses obtained from cyclic tests, along with the average monotonic curves. The backbone curve obtained from the cyclic test is close to the monotonic one in the positive loading direction. However, the stiffness of the connection, as expected, drops during the reloading phase. It is also noted that the resistance of the connection in the reverse direction was nearly half of the peak load, this degradation phenomena was also noticed during the full scale shear wall test [2]. This asymmetric behavior can be attributed either to some sort of geometrical nonlinearity (the nail shape changes) or to the damage in wood. Also, it is interesting to notice that, at reversal, there is a zero-stiffness branch, possibly due to dragging through damaged wood. The peak load bearing capacity of the two types of connections was approximately 1 kN. The ultimate displacement of parallel specimens was larger than 20 mm, while in perpendicular to grain loading tests it was about 16 mm. The ductility of parallel connections was higher than that of perpendicular connections. Shear wall tests matrix. Table 2 shows the test program of a total of 20 shear walls. Test Groups G1-G3 were tested with the purpose of obtaining the physical characteristics of basic-sized (1.22× 2.44 mm) shear walls, and Groups G4 and G5 to check the performance of walls with a larger length of 2.44 m. Figure 7 shows the test setup for lateral loading experiment of the model shear walls. The apparatus can support the shear wall model as well as limit its out-of-plane displacement by ball-bearing railing devices installed along the loading beam. Racking load can be applied horizontally along the top of the wall, through the distribution beam bolted to the top plate of the model, by a double-acting hydraulic actuator with a load cell and displacement transducer. A computer-controlled data-acquisition system was used to collect the experimental data, consisting of the horizontal displacement of the specimen of the top plate, vertical displacement of both end posts relative to the rigid base, horizontal displacement of the bottom plate relative to the rigid base, and forces in the bolts fastening the connectors to the rigid base. Testing standard ASTM E2126-09 was adopted as the guideline for the monotonic and cyclic tests. The loading speed was 7.5 and 60 mm/min for monotonic tests and cyclic tests, respectively. Lateral load and displacement relationships. Figure 8 summarizes the average load-displacement relationships obtained for the model shear wall groups under monotonic loading tests, in which the influence of different shear wall size, types of nails, and nail-spacing arrangement on the wall performance can be identified. The lateral load and displacement curves obtained reveal that, for 1.22× 2.44-m shear walls, 6 d spiral nails can provide better ductility as well as achievement of their maximum resistance load at larger displacement compared with the walls using staple nails. The initial stiffness of staple nail shear walls was larger than that of 6 d nails but their peak loads were close. For 1.22× 2.44-m T shape nail shear walls, the increase of nails in the center of the wall can improve the deformability of the shear wall but had little effect on the bearing capacity. Figures 9-13 show the load and displacement hysteretic responses obtained for model shear walls subjected to cyclic loading, along with the average force-displacement curves obtained from the three counterpart monotonic shear wall tests. Before the shear walls reach their maximum resistance capacities, the monotonic curves are close to the envelopes of the hysteresis loops, however, the degradation of the hysteresis loops is more severe than the monotonic curves, exhibiting the damaging effects of the cyclic loading. There is not much difference between the hysteretic responses of the 1.22-m walls using either 6 d spiral nails or T shape nails, despite their relatively large differences in responding to the monotonic ...