Failure Mode Under Strong Earthquake And Fragility Analysis Of Typical RC Frame Structures On Slope

In recent years,buildings constructed in mountainous area are increasing significantly.However,compared with conventional structures,seismic design of mountainous building structure is more complex,and the research of seismic-design theory is seriously lagging behind the needs of engineering practice.At present,the seismic design of mountainous building structure still refers to the current seismic code,and the design mainly relies on the experience of engineers.Earthquake is a kind of sudden natural disaster.From the investigation of Wenchuan Earthquake,mountainous buildings were damaged with different degrees.To find measures and methods to improve the seismic performance and the study of failure mode under strong earthquake and seismic vulnerability of mountainous building structure are urgently needed.RC step-terrace structure is the typical representative of mountainous building structure.The thesis carried out systematic and in-depth research on the plane of multi-layer step-terrace structure,mainly from failure mode under strong earthquake and vulnerability analysis and aftershocks additional damage,etc.The main research work and achievements are as follows:(1)The seismic response of typical soil slopes with different slope heights and inclines was analyzed from the peak ground acceleration,amplification coefficient of response spectrum and characteristic period.Based on the analysis results,the response spectral parameters of the seismic design of mountainous buildings were determined.The research on the seismic input of the mountainous building structure was supplemented,which provides the reference for the relevant content of seismic code.(2)By comparison with the results of quasi-static test of the whole structure,the correctness and rationality of the non-linear-field calculation model and the related parameters were verified.The RC step-terrace structure was designed with reference of seismic design code GB50011-2010.The influence of the magnification of the upper ground motion on the failure mode of the step-terrace structure was studied from the maximum displacement angle,the hinge rate of the rod end,the rod yield depth and the damage degree of the rod end.The results show that the magnification of the upper ground motion would increase the interlayer displacement angle and the hinge rate of the rod end,deepen the rod yield depth and aggravate the damage degree of the upper ground poles,which is also very unfavorable to the lower ground poles.(3)Considering the magnification of upper ground motion,the failure modes of the RC step-terrace structures under different number of layers and crosses were compared.The influence of ductility factors,such as column section size,column concrete strength,column longitudinal reinforcement ratio and characteristic values of column stirrups,on the failure modes of the step-terrace structures was further studied.The results show that the number of layers and crosses impacts the maximum displacement angle,the hinge rate of the rod end,the rod yield depth and the damage degree of the rod end.The damage of upper ground poles can be reduced obviously by strengthening the ductility of pole end section.(4)The failure modes of the step-terrace frame structure under far-field and near-field ground motions were compared.And the Incremental Dynamic Analysis method was used to calculate the vulnerability of step-terrace structure and the general structure under far-field and near-field ground motions.The vulnerability and anti-collapse ability of each structures under far-field and near-field ground motions were compared.The influence of the number of layers and the number of crosses on the vulnerability of the step-terrace structure was analyzed.The results show that the maximum displacement angle,rod hinge rate,rod end yield depth,rod end damage degree and vulnerability under near-field ground motions are higher than those of far-field ground motions.In addition,the number of layers and crosses have considerable impact on the results.By comparison with the general structure,it is found that the collapse probability of the step-terrace structure under the near-field ground motion is much higher.(5)The influence of PGV/PGA of the near-fault ground motion on the seismic response of the step-terrace frame structure was studied.The results show that with the increase of PGV/PGA,the maximum displacement of the structure,the maximum interlayer displacement angle,the maximum shear of the upper ground and the maximum shear of the upper base are increased.The correlation between PGV/PGA and the maximum top displacement and maximum interlayer displacement is more obvious.Under the near-fault ground motions with wide acceleration-sensitive areas,the effect of high-order modes on the step-terrace structures is more significant than the far-field ground motions.(6)The influences of ductility factors and other measures on vulnerability and anti-collapse ability of the step-terrace frame structure under the near-field ground motions were studied,and the measures to improve vulnerability under the near-field earthquake were proposed.(7)The damage accumulation degree of the step-terrace frame structure and the ordinary frame structure under the main-aftershock earthquakes was studied.The failure states of the structures under different combinations of main shocks and aftershocks were studied from the point of structural energy dissipation,damage components and the growth of failure index at weak layers.The results show that the growth amplitude of each parameters of the step-terrace structure is obviously larger than that of the ordinary structure.The innovations of this paper are as follows:(1)The influence of typical soil sloping terrain on peak ground acceleration PGA,amplification factor of spectra β and characteristic period Tg under horizontal ground motion was studied.The conservative value of the magnification coefficient under the horizontal seismic ground motion was given,which can be used as the reference for the seismic input of the mountainous building structure.(2)The failure mode of the step-terrace frame structure and the influence of the ductility factors on the failure mode were studied.The vulnerability and anti-collapse ability of the step-terrace structure and the general structure under far-field and near-field ground motions were compared.The results that the anti-collapse safety reserve capacity of the step-terrace structures is obviously smaller than that of ordinary structures under near-field ground motions were shown.And the measures to improve the vulnerability of the near-field earthquakes of the step-terrace structures were discussed,which can be used for the compilation of the design codes for the mountainous building structures.(3)The failure accumulation degree of the step-terrace frame structure and the ordinary frame structure under the main shocks and aftershocks was studied.The failure states of the structures under different combinations of main shock and aftershock were systematically studied from the point of structural energy dissipation,damage components and the growth of failure index at weak layers.It was concluded that the influence of aftershocks on the structure of mountainous step-terrace structures was obviously larger than that of general structures,which can be used for the compilation of the design codes of mountain building structures.