Experimental Study On Base Isolation

To reduce the cost of isolation system by using common materials and construction site conditions, a hinge pile-artificial soil composite foundation was developed and shaking table tests were taken in this paper. The results show that the reaction of the structure on the compound foundation is quite different from that on the rigid foundation. Comparing with the test results of the structure on the rigid foundation, the acceleration and the shear force of structure reduced obviously, and the natural period and especially the damp, were obviously increased. It means that the new compound foundation absorbs the seismic energy well.On the bases of hinge piles-artificial soil composite foundation, by scaling down the composite foundation, changing the piles into steels, taking a lot of improvement, a new type of steel-asphalt isolation layer, against the characteristics for Earthquake damages and housing conditions in rural areas, was invented. and a national patent named "a kind of isolation layer" was authorized.By making assumptions on steel-asphalt isolation layer applicable to elastic analysis, a simplified model for the first stage of the elastic design was made. According to theoretical analysis, formulas applicable to the first stage of the elastic design of steel-asphalt isolation layer were given, and an example was given to prove the feasibility of theoretical analysis. Specimens were made according to the simplified model of steel-asphalt isolation layer on the first stage of elastic design. By comparing the input El-Centro(1940.5.18) and Taft (1952.7.21)waves and the output waves in shaking table tests, dynamic characteristics of this new isolation layer were studied. The theoretical analysis and tests show that: the acceleration reduction factor of isolation layer is between 0.38~0.55.it's basically proved that the acceleration reduction factor had reached the requirements of the first stage of elastic design and the isolation layer absorbs the seismic energy well.The tests also show that the acceleration reduction factorβais slightly different by inputting different waves. While the amplitude of acceleration increased, theβa decreased to some extent. Natural frequency obtained from Fourier transform using the results of inputting low amplitude White Noise was quit lager than theoretical value. Natural frequency decreased and Damping rate increased after shaking table tests. Natural frequency obtained from Least squares using the results of shaking table waves increased, Damping rate increase and the friction effect of steel-asphalt isolation become more apparent .Comparing to the results obtained from low amplitude White Noise, results obtained from Least squares was More truly reflect the dynamic characteristics of isolation layer during earthquake. The tests also show that : the simplified model for the first stage of the elastic design was not applicable in the second stage of the plastic design.A model considering friction effects for the second stage of the plastic design of steel-asphalt isolation layer during rare earthquake was made. According to some assumptions and using bilinear resilience model on steels, a time history analysis program basis on Wilson -θconsidering friction effects for the second stage of the plastic design of steel-asphalt isolation layer during rare earthquake was made.Specimens without asphalt between brick pier were designed to be test on shaking table. Security reserve and other Failure mode of isolation layer were studied, and the reliability of the model considering friction effects of the layer was studied. The tests show that: the acceleration reduction factor of isolation layer without asphalt between brick pier is between 0.55~0.85.it's basically proved that the acceleration reduction factor had reached the requirements and better than designed value. Comparing with the previous tests shows that, the relative displacement and the acceleration reduction factor of isolation layer without asphalt between brick pier were lager than those with asphalt. The acceleration value obtained from time history analysis program were closed to the tests'.On the basis of the theoretical and experimental analysis, simplified calculation method and limits of relative displacement applied to engineering practice were got, and an example was given. Calculation and experimental results shows that simplified calculation method meet the requirements of the second stage of the plastic design. Combing the related code, construction Steps and related construction requirements of steel-asphalt isolation layer were proposed.In this paper, isolation technology was studied theoretical and experimental. The results provide references for compiling"Technical specification for practical shock isolation technology of rural residential"and the popularization of steel-asphalt isolation layer.