Study On Seismic Behavior Of Strengthened Masonry Structure And Its Response To Nonstationary Earthquake Motion

According to current technical specifications, seismic strengthening of thebuildings was applied for masonry buildings which designed without adequatedetailing following seismic code in parts of country. Masonry strengthening with RCbeam-column was mostly used. These buildings are available at present. Whetherthese strengthened masonry buildings can satisfy the seismic fortification criterionneed to be further studied. The non-stationarity of earthquake motion is shown both inamplitude and frequency content. Current research on non-stationarity is mostly intime domain, meanwhile non-stationarity in frequency domain has not been fullystudied. The effect of non-stationarity on the structural seismic response has not beenstudied comprehensively. This thesis wants to assess seismic behavior of masonrybuildings and evaluate the retrofit effect of masonry strengthened with RCbeam-column. The influence of non-stationary characteristics on masonry seismicresponse is analyzed using pseudo-dynamic test.Three groups of brick masonry buildings were designed and constructed, includingmasonry strengthened with RC beam-column, masonry with tie-column andring-beam according to the requirements of present codes, common masonry withoutseismic fortification measures. The earthquake motions with frequency stationarityand non-stationarity are taken as seismic input in each group of masonry. Totally, sixapproximate full-size models of masonry buildings were constructed and dynamiccharacteristics tests, pseudo-dynamic tests and pseudo-static tests have carried out.In this thesis, two kinds of earthquake motion input were adopted. One is artificialsynthesized earthquake acceleration time-history with amplitude non-stationary butfrequency stationary. The other is real strong motion record with non-stationarity bothin amplitude and frequency. In order to contrasting the test results, adjustments to theoriginal record are made to ensure that peak value of the two acceleration time-historyis equal, the time reaching the peak is similar, and arias intensity and spectral intensityare close.Through dynamic characteristics tests, natural frequencies, damping ratios andmode shapes of the six masonry buildings were obtained. The similarities anddifferences of dynamic characteristics of three types’ masonry were concerned. Pseudo-dynamic tests of homogeneous structure under different earthquake motioninput were carried out to compare and investigate the structural response includingdisplacement, acceleration, restoring force. Seismic response of different structureunder same earthquake motion were analyzed and contrast. The hysteretic cures,skeleton curves, stiffness degradation curves, maximum resistance and ultimatedisplacement of the buildings were obtained from pseudo-static tests of the sixmasonry buildings. The deformation capacity, stiffness degradation and failure patternof different structure were contrasted and studied. The method of non-dimensionalrepresentation and normalized regression analysis are provided in the skeleton curvesand the stiffness degradation.Also, this article discusses the feasibility of using two methods of phase differencespectrum and evolutionary power spectra to synthesize non-stationary earthquakemotion. The Short-time Fourier Transform (STFT) of the simulated earthquakeacceleration time-history was analyzed. The issues in synthesis effects of the twomethod can be for the engineering application and further research.