Study On The Stability Analysis And Diaphragm Setting Method Of Hollow Thin-walled High Pier

With the development of China's transportation industry and the development of the western mountainous area,the bridge in the mountainous area is increasing.The hollow thin-walled flexible high pier has been widely adopted.High pier stability problems have become increasingly prominent because of the loads of high pier are complex,and the set of diaphragm has no unified standard,therefore,it is necessary to make a further study on the stability of high pier structure.The works in this dissertation are as follow:(1)Taking a bridge with rigid frame and five spans and high piers as an example,the whole bridge truss model is established by MIDAS/CIVIL.Consider a hundred years of wind and the temperature gradient,the static analysis is made under the most unfavorable load conditions,then extract the internal force of each pier.A physical model of the high pier is established by ANSYS,the first and the second stability analysis of the high pier is made under the most unfavorable load conditions,the influences of material nonlinearity and geometric nonlinearity on the stability of the high pier were explored.Results show that the top 5 high pier buckling mode is lateral instability,and the calculated stability coefficient is big;the second stability analysis results show that the high pier buckling mode for lateral instability,and the stability coefficient considering geometric nonlinearity is 25%~28%lower than the stability coefficient considering elastic stability analysis of safety system.The extreme decreasing of stability coefficient considering geometric nonlinearity and material nonlinearity shows the significant effect of material nonlinearity on the stability of high pier.(2)Considering three parameters,the concrete strength,the thickness and the height of pier,the first kind of stability analysis of the 3#high pier is made.The results show that the most sensitive influence factors of stability coefficient is the thickness of the high pier.The increase of concrete strength results in small increasing of stability coefficient,and the higher of pier,the poorer the stability of high pier.(3)Based on the theory of elastic buckling of simply supported plates on four sides,the analytical solution of the critical width to thickness ratio is derived:(?).The local stability critical value of C40 concrete high pier rectangular section is b/t?38.3.The second kinds of stability analysis under the condition of the most unfavorable longitudinal load are conducted with the ratio of width to thickness.The results show that the high pier has local instability of width to thickness ratio is less than the critical value,according to the theory of elastic buckling of the critical value of 38.3,indicating that according to a simply supported plate theory of elastic buckling analysis of the thickness ratio of critical value of non-conservative,so the double nonlinear should be considered when the local buckling conditions analysis of high pier is made.(4)Comparing the first five buckling modes of the two models with or without the diaphragm,the elastic stability analysis of high pier with 20cm wall thickness shows that the setting of the diaphragm can change the size and position of the local buckling deformation,which can restrain the local buckling.(5)The influence of different section thickness ratio and diaphragm on the second type of stability of high pier was studied by the nonlinear solid model.The results showed that:for this bridge,the diaphragm can effectively prevent local instability of thin-walled pier.If the flakiness ratio b/t is less than 15,diaphragm is not necessary for the high pier.If the flakiness ratio b/t is greater than 15 but less than30,setting diaphragm can avoid the local buckling of the high pier.(6)The analysis results of three parameters of diaphragm spacing show that:the best diaphragm setting spacing of hollow thin-walled high-rise piers is between0.214 and 0.285 times of pier height,the minimum value of diaphragm thickness ratio should not be less than 5,the reasonable diaphragm aspect ratio is between 10 and 12.