## 5 Results and Discussion
### Case-II Building  
The code specified drift for the governing performance level (i.e., 2 percent) and design drifts are not exceeded for any of NTHA drifts (Figure 11). The result shows the method is conservative in attaining the design drifts for the LS performance level. This is because secant stiffness of the frames obtained based on the 2-percent drift is higher than that from 4-percent drift. As a result, elastic higher-mode periods are obtained that produce significant elastic force effects since periods are on the rising and constant plateau of the design acceleration response spectrum. Thus, design for these force effects gives the frames higher strength than required. NTHA drifts decrease as the story increases although this is not the case for the design drift profile (Figure 11). Less discrepancy is obtained between NTHA and design displacements as well as NTHA and design drifts at the lower stories (Figures 11 and 12). NTHA displacements and drifts of the frames show less identical response compared to the Case-I building. The difference of the mean story displacements between the frames at the extreme ends of the buildings (for example, at the 5 th story for frame A and E) is 6 percent, at the 13 th story for frame A and D 10 percent, and at the 20 th story for frame A and C 11 percent (Figure 13a).  
Figure 9: (**a**) Mean story displacement for Case-I; (**b**) Mean drifts for Case-I.  
Figure 10: Usage ratio for the members of Case-I. (**a**) Case-I frame A&E-beams’ usage ratio; (**b**) Case-I frame B and D-beams’ usage ratio; (**c**) Case-I frame C-beams’ usage ratio; (**d**) Case-I frame A and E-columns’ usage ratio; (**e**) Case-I frame B and D-columns’ usage ratio; (**f**) Case-I frame C-columns’ usage ratio.  
Figure 11: Case-II drift. (**a**) Case-II frame A’s drift; (**b**) Case-II frame B’s drift; (**c**) Case-II frame C’s drift; (**d**) Case-II frame D’s drift; (**e**) Case-II frame E’s drift; (**f**) Case-II center of mass’s drift.  
Figure 12: Case-II story’s displacements. (**a**) Case-II frame A’s displacement; (**b**) Case-II frame B’s displacement; (**c**) Case-II frame C’s displacement; (**d**) Case-II frame D’s displacement; (**e**) Case-II frame E’s displacement; (**f**) Case-II center of mass displacement.  
Beam usage ratios for the frames range from 0.4 to 0.45 with an average of 0.43 (Figure 14a-e), while for the columns the usage ratios vary between 0.02 and 0.033, and the mean is 0.03 (Figure 14f-j). The ranges show that similar seismic demands are imposed on each frame, which indicates that uneven responses of frames due to floor rotations (global torsion) are insignificant. Conservatism for the ranges can be minimized by redesigning members, but since the aim is to check the performance of the procedure without redesigning members, it can be inferred that the safety is ensured using the proposed design procedure.  
In general, low mean NTHA outputs are produced compared to the design outputs. Factors affecting the outputs include the following:  
* To reduce computational effort and time, the design should not be done for each member. Members having similar analysis outputs must be grouped in one category, and design has to be performed for the maximum output from the category.  
Figure 14: _Cont._