Soft-first-story

Substructure Pseudo-Dynamic Tests on Seismic Response Control of Soft-First-Story Buildings... 

Figure 19.9 shows base shear-story drift hysteresis loops obtained from the tests. Figure 19.10 depicts the shear force-deformation relationships of the tested members during RUN3. The upper part of each figure refers to the piloti frame without a damper and the bottom one to the case with the damper. It can be seen that when the damper is used in the soft-first-story the performance of the piloti frame is good, especially at larger excitation levels. 

The peak lateral load distributions in both tests are shown in Fig. 19.11. Some studies (e.g. Lu et al. 1999) suggest that, in piloti structures the maximum lateral load on each fioor is uniformly distributed, because most of the displacement tends to concentrate in the first story. The results of the present research confirm those findings, even when there is a damper at the soft-first-story. 

The seismic energy response of soft-first-story frames is discussed based on the results of the substructure pseudo-dynamic tests. The total input energy, Ej, and... 

The building is modeled as a 6 DOF shear type model with soft story behavior. This type of behavior is observed in most real buildings that usually have openings and shops at the first story. The mass is assumed uniform at all story levels and equal to m =3.2x1 (Fkg. The lateral stiffiiess is... 

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The two load distributions are schematically shown in Figure 1. The applied lateral load distributions are increased and the response is plotted in terms of base shear V/, vs. top floor displacement D (for example center of mass of the top floor). This is the so-called pushover curve or capacity curve (also shown schematically in Figure 1). The above load patterns are supposed to reproduce static loads equivalent to the seismic action. The two load patterns correspond to a first-mode dominated behavior and to a bottom soft-story response. Other distributions can be used but are typically non considered. 

As in the previous two methods, the pushover analysis is performed first. In general, ATC-40 recommends the distribution of the lateral forces proportional to the fundamental mode pattern. In structures where the response considerably changes after yielding (e.g., in structures with soft stories - see the discussion in section Pushover Analysis Numerical Models and the Lateral Load Pattern ), the adaptive load pattern is required. In high-rise buildings or irregular... 

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