Research On Thermal Stress Theory Of Main Cable Of Suspension Bridge And Structure Temperature Effect

The main cable of long-span suspension bridge is the major bearing structure in bridge, and its performance determines the spanning capacity and bearing capacity of suspension bridge. However, the temperature change has an obvious effect on its internal force and linear. Because the main cable of suspension bridge is composite structure and the thermal mechanism is complicated, when the external environmental temperature changes greatly, the main cable and external environment will make thermal exchange in the form of convection and radiation. The surface temperature of main cable changes rapidly while the internal temperature of main cable changes slowly and with the increasing of diameter of main cable, the lagging phenomenon will be clearer, thus forming clear temperature gradient and leading to great difference between internal and external temperature. This kind of temperature will cause temperature deformation and lead to the change in force and linear of main cable of suspension bridge and even cause extremely great temperature stress. This kind of temperature stress and deformation will have an effect on the safe construction of suspension bridge and later healthy operation. However, the relevant temperature research is less, nor is the relevant computing regulations. Besides, in monitoring the long-span suspension bridge construction, it universally uses measured surface temperature or environment temperature of main cable in replace of the actual temperature of main cable, which will affect the construction security and accuracy of suspension bridge. According to the current situation aforesaid and funded by State Western Traffic Construction Scientific Project Management Center and Traffic Committee of Chongqing City, this thesis makes a systematic research on the temperature field computing, temperature stress deduction and temperature effect of long-span suspension bridge on the basis of the longest-span suspension bridge in Chongqing. The steps are shown as follows:1. Research on thermophysical parameter test and temperature field measurement of main cableIn this thesis, it makes the thermophysical parameter test(apparent thermal conductivity, apparent thermal diffusivity and coefficient of surface heat exchange in natural convection) for main cable model in multiple operating modes. It also makes the steady-state and unsteady-state tests for a series of thermophysical parameters of main cable model, and studies the temperature field test in bridge location(in fine or rainy days) by relying on engineering field environment, thus getting the distribution rules of temperature field of main cable in complicated environments. Besides, it verifies the rationality of test method by way of finite element simulation of model test, which proves that the measured value of the temperature field in the cross section of main cable basically conforms to the computed value and the error is small.2. Research on pervasive computing method of temperature field of main cable of suspension bridgeBy way of analysis of distribution law of main cable and on the theoretical basis of heat transfer theory, general astronomy and solar physics, it studies various factors affecting the solar temperature effect, such as material parameter, solar radiation strength, location in longitude and latitude, weather condition and bridge direction, etc., systematically establishes the boundary conditions for solar temperature field analysis of main cable of suspension bridge and discusses the mechanism of heat transfer between the surface of main cable and external environment and the surface of main cable and interior. Thus, it proposes a set of pervasive computing method of temperature field of main cable of suspension bridge and establishes the computing model of temperature response of main cable in suspension bridge, which can satisfy the value analysis in any complicated conditions.3. Research on computing method of three-dimensional temperature stress of main cable in suspension bridgeThe current analysis for temperature field and temperature stress basically adopts such value methods as finite difference approach and finite element method, which is complicated and needs more efforts, not convenient for actual application. Based on it, it discusses the more simple and actual computing method for the three-dimensional temperature stress of main cable structure in suspension bridge, thus deducing a general computing method for the three-dimensional temperature stress of main cable structure in suspension bridge on the basis of thermoelasticity theory. Besides, it studies the parameters affecting the temperature stress of main cable in suspension bridge and makes computing analysis for the temperature stress of main cable in suspension bridge, and therefore, it can realize the spatial analysis of three-dimensional temperature stress, which replace the three-dimensional problems with two-dimensional problems, only by using structural mechanics method while considering the coupling action between each component of stress caused by Poisson effect.4. Analysis for temperature analysis of main cableBased on the discussion about the temperature field distribution and temperature stress of main cable in suspension bridge, it systematically studies the temperature effect brought by temperature change of main cable, such as structural stress, internal force and deformation, etc., and further discusses the safety and durability of suspension bridge. In the case of project, it systematically computes the temperature field of strand and its effect on internal force, linear and tension difference in the process of erecting strand of main cable in the project, thus providing basis for reducing the deviation of internal force and linear; it also evaluates the effect of temperature change on the internal force and linear of main cable and internal force of bridge tower after the completion of bridge.5. Compute example of temperature field and effectThis research project directly serves the erection and construction of the largest suspension bridge(under construction) in the Southwest. It studies and tests the temperature field of main cable in different seasons of stages of standard strand erection, strand erection of main cable, positioning of cable clamp of bridge and erection of stiff girder, and then computes the temperature field and effect of main cable in the project based on the test conclusions. In the research result, it makes a comparative analysis for the measured temperature data and computed data, adjusts the parameter choice and modifies computing model timely, so as to guarantee the accuracy and reliability of the temperature field of main cable controlled in erection of main cable. In this way, the project-based construction monitoring is successfully made and the height difference between the upper course and lower course and the bridge linear has reached the goal that other similar bridge construction has not reached yet, thus ensuring the construction safety and accuracy.