Dimensional Analysis Of Seismic Responses Of Building Structures Subjected To Near-fault Ground Motions

Near-fault ground motions are characterized with the features that distinctly differ from those of far-field ground motions,e.g.,large-amplitude,long-period velocity pulses and permanent ground motions,and these distinct features caused serious structural damages,casualties and economic losses.Thus,the research on the engineering properties and structural effects of near-fault ground motions has been an important topic in the fields of earthquake engineering and engineering mechanics over the past two decades.With the continuous improvement of infrastructure construction and the sustainable development of urbanization in our country,many engineering structures have been designed and constructed,such as high-rise/super-high-rise buildings,long-span bridges and high-speed railways(highways)etc.It is of importantly academic theoretical significance and engineering application value to deeply study the seismic responses and seismic performance of building structures subjected to near-fault ground motions.The complex time-history characteristics and rich frequency contents in ground motion records as well as the significant record-to-record variability result in the difficulty in recognizing the engineering properties and structural effects of near-fault ground motions.With the ever-increasing database of ground motion records and the rapid improvement of computer performance,an important challenge for the researchers is the right and reasonable presentation of computational results so as to unveil the inherent order in seismic responses.As an essential tool in scientific study,dimensional analysis can construct a dimensionless relationship by nondimensionalizing the physical quantities involved in an engineering problem,and hence reduce the workload of parametric analysis and unveil the general law.It follows that the application of dimensional analysis in the seismic response analysis of building structures under near-fault ground motions is beneficial to present computational results in the most meaningful way,recognize the inherent self-similarity in seismic responses,and construct regression models with much less dispersion to facilitate the development of structural seismic design.Accordingly,this dissertation aims to shed light on the engineering properties of near-fault ground motions and the induced seismic responses of building structures by using dimensional analysis.The main contents are presented as follows:(1)Seismic responses of bilinear single-degree-of-freedom(SDOF)systems subjected to near-fault ground motions are researched by using dimensional analysis.The energetic length scale widely used in the dimensional analysis for seismic responses only depends on the excitation characteristics and is lack of meaningful physical significance.To overcome the defect,the structure-specific intrinsic length scale is proposed,which possesses an unambiguous physical significance.It is shown that the intrinsic length scale can sufficiently reduce the dispersion over the entire frequency-ratio domain and hence contributes to the development of uniform design response spectrum.Therefore,the intrinsic length scale can be used as the length scale in the dimensional response analysis of building structures.Moreover,in the case of intrinsic length scale,the normalized maximum displacement presents two states of complete self-similarity in the normalized yield displacement.Finally,the proposed versatile regression model can sufficiently fit self-similar response spectrum and the corresponding fitted curve can be utilized to predict the seismic responses of structures.(2)Duration effect of near-fault pulse-like ground motions is systematically examined,and the uniform duration is identified as the suitable duration measure to characterize the ground motion duration.Consider the typical elastic-perfectly-plastic,bilinear and rigid-plastic SDOF systems and select as the structural demand measures the maximum displacement and cumulative hysteretic energy.The abovementioned SDOF systems are subjected to the idealized MP pulses wherein the duration effect is decoupled by parametric control,and hence the duration effect of near-fault pulse-like ground motions is qualitatively analyzed.Then,the near-fault strongest pulse-like ground motions are utilized wherein the duration effect is decoupled by equivalent spectrum.In this case,the duration effect is quantitively examined through the correlation coefficients between duration measures and structural demands.It is shown that the duration effect is significant on the cumulative hysteretic energy,whereas that associated with maximum displacement is affected by the hysteretic model.In detail,the duration effect is not significant on the ordinary SDOF systems,except for the sliding displacement of Newmark sliding blocks(rigid-plastic SDOF systems).In addition,the uniform duration always presents the strongest correlation with the structural demand measures and thus is identified as the suitable duration measure to characterize the ground motion duration.Finally,these conclusions are further validated in the case of three shear-type frame structures with stiffness and strength degradation.(3)Influence of the lateral stiffness reduction on the seismic responses and response distribution of flexural-shear beam building structures are investigated in detail.Dimensional analysis indicates that the normalized maximum interstory drift ratio and normalized maximum floor acceleration present complete self-similarity with respect to the normalized building height.Thus,the new concepts of self-similar interstory drift spectrum and self-similar floor acceleration spectrum are proposed to avoid the use of the empirical relationship between fundamental period and building height.It is shown that the lateral stiffness reduction imposes a small influence on the seismic responses and response distribution of flexural-shear beam buildings,except for the significant lateral stiffness reduction.Moreover,the fitted curves of mean self-similar interstory drift spectrum and mean self-similar floor acceleration spectrum can predict the dependable responses of flexural-shear beam buildings.(4)Influences of concentrated constraint(e.g.prestressed tendons)and distributed constraint(e.g.dampers)on the vibration control of rocking wall-frame structures are systematically analyzed.Herein,the widely adopted flexural-shear beam model is utilized to represent the rocking wall-frame structures.Particularly,the closed-form solutions are derived for the dynamic and static responses of the flexural-shear beam with concentrated constraint and distributed constraint.The dynamic properties and static responses of the flexural-shear beam are first examined.Results indicate that the fundamental period of rocking wall-frame structures clearly decreases as the distributed constraint increases.The base moment resisted by the rocking wall remarkably increases with strengthening concentrated constraint,and these two constraints lead to a notable increase in the base shear of the rocking wall.Furthermore,the dynamic response analysis shows that the distributed constraint generally sufficiently suppresses the interstory drift of rocking wall-frame structures but causes a significant drift concentration.The concentrated constraint does not clearly reduce the interstory drift yet sufficiently avoids drift concentration.Additionally,in the case of real ground motions,both constraints generally are detrimental for the control of floor acceleration,especially for the distributed constraint.Therefore,the reasonable measure of vibration control should be utilized in accordance with the responses concerned in practical seismic design of building structures.