Limitations of height-to-width ratio for base-isolated buildings under earthquake

Abstract

The limitation of height-to-width ratio (HWR) for a base-isolated building with elastomeric rubber bearings is of considerable concern to structural design engineers. Guidelines and codes on this type of building have to deal with this issue. Nevertheless, until now, no systematical and quantitative studies have been done on this problem for base-isolated buildings. For this reason, the main objective of this paper is to focus on investigations on the limit of the HWR for the isolated building with rubber bearings under different conditions subjected to earthquake excitations. The simplified formulation is derived to explore the rules of seismic responses for the structural system and some influential factors, such as the site soil conditions, seismic ground motion intensity, period of the isolated system, period of the superstructure and layout of isolators, are studied and discussed. According to the numerical results, it has been found that the effects of site soil conditions on the HWR limit values are important: the softer the site is, the smaller the HWR limit value is under different seismic intensities. The predominant period of an isolated building also plays a considerable role in the HWR limit value, namely, the isolated building with a longer period may have a relatively large HWR value; and the stiffness of the superstructure affects the HWR limit value little. Furthermore, an effective method to improve the HWR limit value is proposed.A time-history calculational method, i.e., the Newmark b method (with coefficients a = 1/2; b = 1/4), is applied to quantitatively analyse the factors influencing the HWR limit of the base-isolated building with rubber bearings. Theses factors include the site soil conditions, seismic ground motion intensity, period of the isolated system, period of the superstructure and layout of isolators. In computations, different structures have been chosen within the range of periods of the practical medium-low-storey buildings.In order to explore the effects of different site soil conditions on the HWR limits of the isolated building, nine seismic acceleration records have been employed, listed in detail in Table 1, which belong to three different types of soil site conditions: hard site, medium site and soft site. Each case of HWR limit at the different sites is calculated with three seismic acceleration inputs. The mean value and variation coefficient (standard variance/mean value) of the results will be given for each site. Effect of site condition and seismic intensityIn this section, the analysis is based on a base-isolated building, whose predominant period is 1·4 s, while 0·65 s before the corresponding building was isolated. Here, the effect of peak accelerations on LIMITATIONS OF HEIGHT-TO-WIDTH RATIO 283

Limit height-to-width aspect ratios for slender base isolated objects of heritage architecture

“…The effectiveness of a base isolation system of a slender rigid object on elastomeric isolators depends also on the height-to-width aspect ratio of the superstructure [8][9][10]. Hino et al [10] present the design of a slender rigid object on elastomeric isolators based on: (a) ultimate state of tensile strength of isolators, (b) ultimate state of drift of the base isolation story under seismic loading, (c) ultimate state of the axial compressive stress of isolators under dead loads and (d) the prediction of overturning moment at the base under seismic loading.…”

A Simple Response Evaluation Method for Base-Isolation Building-Connection Hybrid Structural System under Long-Period and Long-Duration Ground Motion

“…It is well recognized that, while base-isolated buildings are effective for pulse-type ground motions with predominant periods shorter than about 2 s or random earthquake ground motions without clear predominant period (Jangid and Datta, 1994;Hall et al, 1995;Heaton et al, 1995;Jangid, 1995;Jangid and Banerji, 1998;Kelly, 1999;Naeim and Kelly, 1999;Jangid and Kelly, 2001;Morales, 2003;Takewaki, 2005Takewaki, , 2008Li and Wu, 2006;Hino et al, 2008;Takewaki and Fujita, 2009), their earthquake resilience is not clear for long-period ground motions with the characteristic period of 5-8 s Kamae et al, 2004;Ariga et al, 2006). The long-period ground motions with the characteristic period of 5-8 s have been argued in the structural design of base-isolated and super high-rise buildings since the Tokachi-oki earthquake in 2003 and have been treated as one of the most critical inputs for such buildings after the 2011 Tohoku earthquake.…”

Innovative Seismic Response-Controlled System with Shear Wall and Concentrated Dampers in Lower Stories

“…Various types of base-isolation systems have been introduced for pulse-type ground motions (Jangid and Datta, 1994;Hall et al, 1995;Heaton et al, 1995;Jangid, 1995;Kelly, 1999;Naeim and Kelly, 1999;Jangid and Kelly, 2001;Morales, 2003;Takewaki, 2005Takewaki, , 2008Li and Wu, 2006;Hino et al, 2008;Takewaki and Fujita, 2009). But their resilience for earthquake has never been proved in actual situations for longperiod ground motions with the characteristic period of 5-8 s Kamae et al, 2004;Ariga et al, 2006).…”