Preliminary Analysis Of R-μ Relationships Of MDOF And Influence Of The Degree Of Statical Indeterminacy On Overstrength

By now, the domestic and foreign researchers have studied comprehensively on R-μ-T relationships of single-degree-of-freedom (SDOF) inelastic systems and acquired the similar conclusions. Because of the influence of designing and detailing, dynamic response characteristics of multi-degree-of-freedom (MDOF) inelastic systems are more complex than that of SDOF systems; the research on the R-μrelationships of MDOF inelastic systems is still in immature stage. Notwithstanding some researchers deem the R-μrelationships acquired from SDOF systems can be used approximately to MDOF systems, but by now there are lack of convictive validate work on it. According to accomplished inelastic dynamic response analysis of MDOF inelastic systems, it is found that MDOF systems have obvious overstrength under earthquake and there are many factors effect on overstrength.Foreign seismic codes take research findings of R-μrelationships acquired from SDOF systems into seismic design and advise three optional R-μrelationships and take into account overstrength coefficient which varies from structure type and degree of statical indeterminacy. If the R-μ-T relationships acquired from SDOF systems can be used in MDOF inelastic systems is not validated, and there is lack convictive explanation for the theoretical relationship of R-μ-T relationships to overstrength of redundant structures.Based on the facts above, the main research work finished preliminarily in this thesis is as follows:①Summary and preliminary commentary of a spot of the main research findings of R-μrelationships and overstrength characteristic of redundant structures.②Through inelastic dynamic response analysis of 3-bay & 6-story reinforced concrete frames systems which are endowed with different design seismic action, review the applicability of R-μrelationships acquired from SDOF systems in MDOF systems.③Review discrepancy among the quantitative R-μrelationships of single-mass point & cantilever column systems, single-story & single-bay frames and 6-story & 3-bay frames.④Analyze overstrength characteristics of reinforced concrete planar frames with different bays, different stories in different intensity zones through dynamic pushover analysis and appraise the analysis results.From the finished research work above, the main conclusions can be drawn as follows:①The R-μrelationships acquired from single-hinge & SDOF systems can be used to a majority of multi-hinge & SDOF systems and MDOF systems, but R of MDOF systems is slightly smaller than that of SDOF systems corresponding to the sameμ.②Single-story & single-bay frames have supreme overstrength. And the number of bays, the number of stories and Intensity Region are not affect overstrength of multi-story and multi-bay significantly, overstrength varies from the control load combination and the column moment capacity amplification measure.③Conservative overstrength of single-story & single-bay frames is up to 2.0, that of multi-story & multi-bay frames is up to 1.5. All constructional elements are not appearing rotate destruction at overstrength ultimate sate above and columns have lower security for preventing inactivation than corresponding beams.Except the obtained main conclusions above, it is found that there are some issues deserve regard to improve seismic measure of Chinese code as follows:①In foreign seismic codes,several Rd and corresponding reasonableμare proposed to offer manifold choice for complex design instances and be propitious to optimize design. In Chinese codes, only one Rd (R_d=2.86) is offered in all Earthquake Intensity Region, which is not impact to several optional R-μrelationships in foreign seismic codes, but the range of application is narrow comparatively and went against assort with performance-based seismic design technique.②The column moment capacity amplification measure in Earthquake Intensity Region 9 can ensure satisfied beam-hinge model and form steady energy dissipation mechanism at major earthquake level for R_d=2.86 adopted by current Chinese codes. It is necessary to enhance the column moment capacity amplification measure to maintain nicer beam-hinge model for R_d>2.86 the potential employed after now.