Test On Gravity Distortion Effect Of Concrete Filled Steel Tubular Single Arch Rib Under Shaking Tables

The shaking table test is one of the most effective approaches to simulate structural seismic performance and failure mechanisms.Based on the similarity ratio theory,four basic similarity models,namely the strain distortion model,negligible gravity model,real models and artificial mass model,were proposed by scholars.The artificial mass model includes the model with full artificial mass and inadequate artificial mass(hybrid model).The inadequate artificial mass model is the most widely adopted in the shaking table test for the reason that it compensates for the shortcomings of the basic similarity models and takes into account the limited bearing capacity of shaking table.However,the scaled model with inadequate artificial mass cannot accurately reflect the structural seismic performance of a prototype due to the presence of gravity distortion.Significant gravity distortion would be occurred in large-scale models without adequate artificial mass.A number of studies had focused on theoretical analyses of the effect of inadequate artificial mass on scale-model behavior.Although some studies of a scale model without adequate artificial mass were partly carried out in shaking table tests,there are fewer tests on scale models with full complementary artificial mass.The existing research results are still lack of verification.Therefore,based on the relevant factors of gravity distortion(acceleration similarity ratio,structural characteristics and seismic characteristics),the shaking table tests and the finite element parameter analyses of concrete filled steel tubular(CFST)single arch rib model were carried out to study the effect of gravity distortion on the dynamic characteristics and seismic response of the similar model.The main work and conclusions are as follows.(1)Based on the hybrid model similarity theory,a CFST single arch model with a geometrical scale of 1:10 was designed and five different artificial masses were set on it to simulate the different gravity distortion.Several earthquake and artificial waves with five different time compression ratios were input in the shaking table tests to simulate the earthquake loads in longitudinal and transverse directions.(2)Test results of dynamic characteristics test indicated that the gravity distortion has little effect on the instability mode and the first damping ratio of the CFST single arch model.But it has a great influence on the natural vibration frequency.As the complementary artificial mass is inadequate,the maximum error of the natural vibration frequency of the prototype and scale models is more than 20%.The effect of gravity distortion can not be neglected under this condition.(3)The results of seismic response test indicated that the acceleration response of model is reduced under the effect of gravity distortion with the small time compression ratio of input wave.However,it is amplified with the large time compression ratio of input wave.The smaller the time compression ratio of the excitation wave is,the greater the influence of gravity distortion on the displacement response of the model vault is.The gravity distortion has a great influence on the strain response of arch foot section of model.The strain response is inaccurate and unsafe if the gravity distortion is too large.The effect of gravity distortion on is very significant.(4)The results of finite element parameter analysis indicated that the larger the amplitude of seismic wave,the greater the effect of gravity distortion on the seismic response of the model.The larger the rise-span ratio is,the greater the effect of gravity distortion on the natural frequency and acceleration response of the model are,the smaller the influence on the displacement and internal force response is.