Research On The Early Temperature Crack And The Long-Term Excessive Deflection Control Of Long-Span Continuous Bridges

With the increase of bridge span and concrete size, the structures present a characteristic of a large volume of concrete, which causes many diseases and problems to be solved in the bridge construction and operation.This paper is based on a(90+165+90) m large-span PC continuous bridge on the Yellow River, using finite element simulation and combining field measurement, to research and analysis the key problems in the early construction and the late operation about this bridge. The main research work is as follows:(1) According to the design drawings and field practice, this paper simulated the bridge construction process by the Midas/civil and determined the construction camber of the bridge combined with the construction experience and the deflection and stress state of each construction stage by the forward and inversion calculation method. Meanwhile correct thed calculation parameters promptly by the actual conditions to ensure the rationality of the model. Based on the adaptive control method, to test and analysis the linear and stress state of the long-span continuous beam bridges.(2) For the winter bridge box girder crack phenomenon, this paper tested the crack diseases systematically on the spot, combined with curing test block to determine the SFRC and ordinary concrete their early mechanical properties. Given the facts that box girder has a characteristic of massive volume and that temperature measurement points have been placed, the early time-history curves of the concrete box girder can be obtained through actual on-site observation of the forepart temperature field in the SFRC box girder.Building the solid finite element model by using the thermal analysis in the ANSYS, combined with the field measurement, In view of the early web crack of bridge in the winter construction, analysed the properties of early cracks in box girder, and obtained the main causes of the cracks.(3) According to the finite element simulation based on the thermal analysis, this paper compared and analyzed the two kinds of box girder about the early hydration heat temperature field and the stress field of the common concrete and the SFRC, putted forward the effect mechanism of the early cracking resistance of concrete for the SFRC, and proved that the steel fiber reinforced concrete can improve the early temperature crack of box girder.(4) This paper discussed the relationship between the temperature difference of the girder and the early web crack of concrete in winter construction, and obtained the relationship between temperature and temperature stress of box girder by using the control variable method.(5) According to the finite element model of the bridge, this paper studied the different factors under different working conditions of the impact of excessive downwarping disease during the stage of the bridge formation and the late operation of the bridge by using the single variable method. Combined with the change of deflection, the sensitivity of the relative factors was analyzed. According to the characteristics of the bridge structure, the method of using external prestressing in the box can control and reinforce the possible excessive lower deflection of the bridge effectively.