Study On The Equivalent Wind Loads Of The Long-Span Continuous Rigid Frame Bridge With Tall Piers

The stiffness of long-span continuous rigid frame bridge is relatively large during the operational phase, so it has a strong wind resistance. However, in the largest double cantilever state, the stiffness is incessantly declining due to the slenderness trend of the pier, and it makes internal force of pier bottom bigger under the wind load. For flexible bridge structure, internal force under wind loads are consist of two parts:static wind internal force under average wind and dynamic internal force due to wind turbulence buffeting. Static wind internal force belong to static force area. Dynamic internal force need to consider spatial correlation of turbulent wind, dynamic characteristics, the vibration characteristics of the structure, the aerodynamic damping, pneumatic stiffness and pneumatic diversion and other factors. Usually the wind tunnel test or frequency-domain analysis and time-domain analysis are taken to do buffeting analysis. But all the methods are not realistic at the initial design stage. Therefore, it is very necessary to establish a correct and easy way for large-span continuous rigid frame bridge during the construction phase under the wind loads. This method is suitable for the preliminary design of large span continuous rigid frame bridge, but also for wind loads calculation of smaller continuous system bridge.In this thesis, by taking Caijiagou bridge and preliminary design of Balinghe bridge as examples, based on the features of continuous rigid frame bridge with tall piers, the load can be divided into beam wind load and pier wind load. Practical and simplified method of equivalent wind loads to calculate transverse moment and shear of pier bottom and transverse moment and shear of beam are discussed. In order to verify calculated accuracy and the safety of the simplified calculation method, frequency-domain analysis and time-domain analysis and specification method are used to analyze two typical examples.The main work of this thesis are as follows:First of all, take a review of some equivalent wind loads calculation methods, and point out their advantages and defects.The total equivalent wind loads can be divided into three parts:average wind loads, background wind loads; resonant wind loads. We can make a combination of the three responses, then can obtain uniformly distributed equivalent wind loads. According to the gust response factor, we can calculate some response conveniently.Secondly, taking the Caijiagou bridge and preliminary design of Bakinghe bridge as examples, based on characteristics of continuous rigid frame bridge with tall piers in double cantilever state, we can obtain influence function and vibration mode function of the target response, wind loads can be divided into bridge wind loads and pier wind loads, the calculation and simplified process of each parameter are illustrated in the simplified calculation method.Thirdly, using the finite element analysis program ANSYS, frequency-domain analysis and time-domain analysis are used to calculate buffeting-induced responses at the maximum double cantilever stage, which are compared with the wind-resistent design specification results and simplified calculation method rusults. The results show that the calculating using the method given in this paper and the wind-resistent design specification results are consentaneous under average wind load and buffeting force, and they are both larger than the rusults calculated by frequency-domain analysis and time-domain analysis. There are certain safety margin. The rusults demonstrate that the simplified formulas given in this paper are not only very simple but also convenient compared with the theoretical method and wind-resistent design specification, and no graphs or charts are needed.