Outline

  • Abstract
  • Keywords
  • 1. Introduction
  • 2. Methodology
  • 2.1. Site-Specific Demand Spectra
  • 2.1.1. Generation of Strong Ground Motion
  • 2.1.2. Generation of Depth Dependent Response Spectra (ddrs)
  • 2.1.3. Conversion of Ddrs to Depth Dependent Demand Spectra (ddds)
  • 2.2. Capacity Spectrum Method
  • 2.2.1. Capacity Curve Through Nonlinear Static Analysis
  • 2.2.2. Conversion of Capacity Curve to Capacity Spectrum
  • 2.3. Performance Point
  • 2.3.1. Procedure 1 (p1)
  • 2.3.2. Procedure 2 (p2)
  • 2.3.3. Modified Effective Damping (βeff)
  • 2.3.4. Reduction of 5 Per Cent Demand Spectrum
  • 3. Demonstration of the Methodology
  • 3.1. Generation of Demand Curve
  • 3.2. Generation of Capacity Spectrum for B1
  • 3.3. Generation of Performance Point for B1
  • 3.4. Generation of Capacity Spectrum for B2
  • 4. Discussions
  • 5. Summary and Conclusions
  • Acknowledgements
  • References

رئوس مطالب

  • چکیده
  • کلیدواژه ها
  • 1. مقدمه
  • 2. روش شناسی
  • 2.1 طیف های تقاضا ویژه محل
  • 2.1.1 تولید حرکت زمینی قوی
  • 2.1.2 تولید طیف های واکنش مستقل عمق ( DDRS )
  • 2.1.3 تبدیل DDRS بع طیف های تقاضا مستقل عمق (DDDS)
  • 2.2 روش طیف ظرفیت
  • 2.2.1 منحنی ظرفیت از طریق تحلیل استاتیک غیر خطی
  • 2.2.2 تبدیل منحنی ظرفیت به طیف ظرفیت
  • 2.3 نقطه عملکرد
  • 2.3 -1 رویه 1 ( P1)
  • 2.3.2 رویه 2 ( P2)
  • 2.3.3 استهلاک ارتعاش موثر اصلاح شده
  • 2.3.4 کاهش 5 درصد طیف تقاضا
  • 3. نمایش روش شناسی
  • 3.1 تولید منحنی تولید
  • 3.2 تولید طیف ظرفیت ساختمان B1
  • 3.3 تولید نقطه عملکرد برای ساختمان B1
  • 3.4 تولید طیف ظرفیت برای ساختمان B2
  • 4. بحث ها
  • 5. خلاصه و نتیجه گیری ها

Abstract

Towards formulating guidelines for performance evaluation of buildings to site-specific earthquakes, studies are reported in literature on the effect of various critical parameters. No study is, however, reported on the effect of depth of soil stratum. In this paper, a methodology is proposed and applied for performance evaluation of buildings for site-specific earthquakes including depth of soil stratum as a parameter. The methodology integrates independent procedures meant for performance evaluation of buildings and site-specific seismic analysis. Application of the proposed methodology enables to determine performance point of a building in terms of inelastic displacement and base shear. Numerical application of the methodology is demonstrated using the particulars of Delhi region. Two typical RC buildings (B1 and B2) with significantly different inelastic behaviour, assumed to be located on soil depths ranging from 10 to 200 m are chosen for the application study. Capacity spectra of the buildings are generated from nonlinear static analysis. Studies indicate that for building B1, with elasto-plastic behaviour, the depth of soil stratum strongly influences demand on inelastic displacement compared to that on inelastic base shear. For building B2, with continuously varying inelastic behaviour, the depth of soil stratum is observed to have significant influence on both the inelastic base shear as well as inelastic displacement. Responses of the buildings are compared with that obtained based on design spectrum of Indian seismic code. For both the cases, inelastic displacements as well as inelastic base shears are underestimated by Indian seismic code for certain depths of soil stratum. Proposed methodology enables the calculation of realistic values of inelastic base shear and corresponding displacement of a building for site-specific earthquakes by considering the actual characteristics of soil stratum.

Keywords: - -

Conclusions

A methodology is proposed for seismic performance evaluation of an existing building for site-specific earthquake and it is demonstrated for Delhi region. Artificial ground motions at rock outcrop are generated for a scenario earthquake of Mw¼8.5. The modified ground motions on top of different depths of representative soil stratum are evaluated. The DDDS for 5% damping ratio are obtained for eight different assumed depths of soil stratum above bedrock. The capacity curves of two buildings B1 and B2 are obtained. Subsequently, the modified effective damping values are evaluated using two procedures P1 and P2. The base shear and roof displacements of B1 and B2 for response spectra of site-specific scenario earthquake and spectra of the DBE of Indian seismic code are compared.

For building B1 which has nearly elasto-plastic behaviour, with soil stratum depths of 30, 50, 75, 100 and 150m, the 5% demand curve intersect the capacity curve in the inelastic region. For 200 m depth 5% demand curve does not intersect the capacity curve. For soil stratum depths above 75 m, the inelastic displacements are more than that of the DBE of IS 1893–2002 [8] DBE. The results indicate that the depth of soil stratum has significant influence on displacement demand compared to base shear demand in buildings which can be idealized as elasto-plastic. For building B2 which has continuously varying inelastic behaviour, with soil stratum depths of 75, 100 and 150 m, the 5% demand curve intersect the capacity curve in the inelastic region. For remaining depths studied, demand curve intersect the capacity curve within the elastic region. Indian seismic code spectra intersect the capacity curve in the elastic region and hence damping modification has not been applied to code spectra for B2. The results indicate that for buildings with continuous variation in capacity spectrum, the depth of soil stratum has influence on the base shear demand as well as on the inelastic displacement demand.

From the studies made, it is clear that considering the design spectra suggested by seismic codes and only the top 30 m soil stratum to include the effects of soil amplification may not ensure safe seismic performance of a building. It is further seen that the site-specific earthquake and the depth of soil stratum have significant influence on the performance of the building both in terms of inelastic displacement as well as inelastic base shear.

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