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and “DA” stands for Double All, meaning all brackets in the panel are double sided. Based on Figure 6, the designer can specify, for example, the “3DE” configuration for the entire story, etc. It should be noted that for the case of the wall panel with only 2 brackets , configurations DE and DA are identical. The maximum number of 16d nails that can be put in a single bracket is 6, due to the limitation of the bracket to floor connection strength. These typical walls will be used later in the design of the 10-story CLT building. Figure 5: Calibrated model compared with test (with gravity) The calibrated hysteretic parameters for three types of connectors are listed in Table 2, including the Simpson Strong-tie HTT-16 hold-downs installed at corners of CLT walls and 16d spiral nails with D=3.9mm and L=89mm with Simpson Strong Tie 90mm x 105mm x 105mm Bracket commonly used in CLT construction in Europe. The parameters listed for the 16d nails are for a single nail connection. The 16d with step joint is the equivalent nail parameter to be used for multiple panelled walls with step joints. With the numerical model and connector parameters calibrated, the loaddeformation curve or the hysteresis curve for any CLT wall configuration with specific connectors can be developed. This provides a useful tool to generate CLT wall backbone curves that will be used in PBSD and tables with lateral load design values that are needed for force-based design of CLT structures. Table 2: Calibrated CLT connector parameters Connector Type Hysteretic Parameters (N, mm) K0 r1 r2 r3 r4 HTT-16 4378 0.002 -0.3 1 0.05 16D-SN 140 0.005 -0.2 1 0.01 16D-SN+step joint 158 0.001 -0.3 1 0.03 F0 F1 X a b HTT-16 40032 1779 51 0.75 1.1 16D-SN 3558 178 64 0.5 1.1 16D-SN + step joint 2669 89 41 0.5 1.1 2.4 TYPICAL WALL CONFIGURATIONS Several typical CLT wall configurations were considered in this study as shown in Figure 6. It is assumed that a structural CLT wall in the multi-story building will have 2, 3, or 4 brackets attached at the bottom of the wall, providing connection between the wall and the floor panel. The size of a single panel can vary from 0.96 m (4 ft) to 1.83 m (6 ft). It is assumed that for walls longer than 1.83m, multiple1.22 m (4 ft) panels are to be combined together and each panel will have bracket configuration as shown in Figure 6. The notation “S” stands for Single sided brackets for each location, “DE” stands for Double sided brackets at the End of the panel, Figure 6: Typical wall configurations 3 DIRECT DISPLACEMENT DESIGN (DDD) OF CLT BUILDING 3.1 CAPSTONE BUILDING FLOOR PLAN The floor plan of the NEESWood Capstone structure, a six-story light frame wood apartment building tested at Japan’s E-Defense shake table in 2009 [10], served as the model to develop the 10-story CLT structure, i.e. similar floor plan. The elevation and floor plan are presented in Figure 7. The building foot print is about 12 x 18 meters, with total height of 27.4 meter. All floor plans are identical except for the top story, where a penthouse unit may be integrated. The seismic weight of the building was assumed to be 2.2kN/m 2 for the first story, 1.4kN/m 2 for the roof, and 2.1kN/m 2 for all other stories. The total building weight is 4,537kN (462 metric tons). Given the floor plan, the wall selection is constrained in that only a limited amount of wall segments can be placed in each story. The design began by identifying the total usable wall segment length in each direction from the architectural floor plan. The numbers in Figure 7 show the maximum amount of CLT wall panel segments one can put in any particular line of the floor plan, which may or may not be fully utilized in the design process as the designer may choose to select some walls as “non-structural partition” and only apply minimal connections. The exterior walls are shown with window openings removed from the wall line. However, for CLT panels the windows are typically pre-cut into
the wall panel, so the window opening will not significantly affect the strength of the outside wall segments. For the interior, the door openings do interrupt the CLT walls (due to the height of the door openings) so these walls are broken into smaller segments. Note that the X direction is the longitudinal direction in the floor plan while the Y direction is the shorter direction. curve. The backbone curve for CLT walls used in the design can be readily obtained using the simplified model and calibrated connector parameters obtained earlier. Thus DDD can be utilized to design the CLT building presented in this paper. Detailed description of the DDD procedure can be found in [12]. The basic philosophy of DDD is to identify the required story lateral resistance at prescribed drift levels enabling the designer to select shear walls that satisfy this requirement. Three performance objectives were adopted in the design of the CLT building, limiting the maximum inter-story drift under different hazard levels. Because the inter-story drift level correlates well with seismically induced damage to a building, the performance objectives outlined in Table 3 will also ensure minimal damage during these earthquake events. Table 3: Performance Objectives Seismic Hazard Performance Expectations Inter-story Drift Limit Non-exceedance Probability 50%/50yr 1% 50% 10%/50yr 2% 50% 2%/50yr (MCE) 4% 80% Based on the performance objectives, the target point for the backbone curve for each story was identified using DDD. Design of the CLT building was conducted by choosing the CLT wall configuration for each story to produce a backbone curve that will satisfy (be larger than) the corresponding target point. The CLT walls selected for each story in both directions are listed in Table 4. The resulted backbone curves for all stories were plotted in Figure 8, together with the target points for these stories resulting from DDD. Table 4: Wall selection based on DDD Figure 7: CLT building architectural plan and wall segments location 3.2 PERFORMANCE OBJECTIVE AND DIRECT DISPLACEMENT DESIGN Direct Displacement Design (DDD [11]) was the design approach employed in the NEESWood research project to design the NEESWood Capstone building for prescribed drift limits under different levels of seismic intensity. It was validated through full scale shake table test of a six-story light frame wood building. In fact, the DDD method can also be applied to any lateral resistance system which has a clearly defined backbone CLT walls in X-direction 3.66 m 4.88 m 6.1 m ST # Con. # Con. # Con. 1 2 4DA 2 4DA 8 4S 2 2 4DA 2 4DA 8 4S 3 2 4DA 2 4DA 7 4S 4 2 3DA 2 4DA 7 4S 5 2 3DA 2 3DA 7 3S 6 2 3DA 2 3DA 7 3S 7 2 4S 2 3DA 7 3S 8 2 2S 2 2S 7 3S 9 2 2S 2 2S 7 2S 10 0 -- 2 2S 5 2S CLT walls in Y-direction 1.53 m 1.83 m 2.44 m 6.1 m ST # Con. # Con. # Con. # Con. 1 4 4DA 2 4DA 14 4S 1 4DA 2 4 4DA 2 4DA 14 4S 1 4DA 3 4 4DA 2 4DA 14 4S 1 4DA 4 4 3DA 2 3DA 14 3S 1 4DA 5 4 3DA 2 3DA 16 3S 1 3DA 6 4 3DA 2 3DA 14 3S 1 3S 7 4 3DA 2 3S 14 3S 1 3S 8 4 2S 2 2S 14 2S 1 3S 9 2 2S 2 2S 10 2S 1 2S 10 0 -- 2 2S 8 2S 0 -- In Figure 8, note that only targets for the level 3 design are shown in the Figures since this case controls the
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