Study On Shear Deformation Of Segmental Joint And Its Influence On Pile-soil-bridge System

Continuous rigid frame bridges, as the young bridge family member, has been developed and built rapidly in our and foreign country in recent years, just because of its continuous beam, fixed beam and pier top without support, which leads to traveling comfort. And also it needn't converting structure system to meet the special loading requires of long span bridges.However, a common problem is caused in many long-span continuous frame bridge, which is over-deflection of mid-span section. As we know, over-deflection of this bridge may cause the failure of bridge deck paving, serving life and comfortable traveling in late loading period. So how to control this case becomes an urgent task to improve the property of this kind of bridge. Due to the complexity of the problem and variety of existing reasons, the paper aims at one main factor to study, which is the result of segmental joint shear deformation coming from bad cantilever construction. Although this phenomenon has been put forward by some researchers, but the deep systematic study in theory is lacked. So, the working of this paper may be important to improve the loading property and renovate the design concept of this bridge.The studied content of this paper are as follows:(1) Taking domestic built long-span cantilever constructed box bridge as an example, a three-dimensional finite element model is built. The simulation method of segmental joint and its influence on deflection in cantilever construction is analysed.(2) Using different calculation mode of concrete creep, the influence of shear deflection caused by segmental joint on beam long-term deflection is studied.(3) Based on pile-soil-bridge structure system model, dynamic response of the full bridge structure in deformation and loading properties is researched, particularly the dynamic influence of segmental joint with mobile car load.Based on the analysis above mentioned, the main achievements are as follows:(1)During the beam cantilever construction process, the vertical deflection of beam with segmental joint will be greater than without, because of shear deformation of the joints. The increased deflection value first increases with the increase number of the segment construction, and then it decreases gradually. While in the whole construction procedure, the ratio of joint shear deformation to the corresponding beam deflection without joint is continuously decreasing.(2)According to the two calculation modes of concrete creep proposed in 1985 and 2004, the long-term deflection is calculated, which shows that it is greater by specification in 1985 than in 2004.(3)The existing of segmental joints may have obvious influence on long-term deflection of beam, resulting in the over-deflection. The deflection increasing ratio increases with the concrete age. In the calculation of the example bridge, during the age of concrete, the beam with joints is about 2 times the deflection of that without joints.(4) In pile-soil-full bridge system model, the natural vibration frequency of the full structure is reduced with the consideration of pile-soil action. In same way, the beam stiffness reduction due to joints may cause the reduction of natural vibration frequency too, and also with longer period of vibration and dynamic displacement change.(5) In pile-soil-full bridge system model, the displacement and internal force in all pat of structure with dynamic car loading is larger than with static loading, and the increase ratio is different between the structure with segmental joints and without joints. The result shows that the dynamic response of structure with segmental joints is less sensitive to dynamic loading than without joints.(6) Based on pile-soil-bridge structure with dynamic vehicle loading, the existence of segmental joints may bring different internal force and displacement. Considering the most disadvantageous effect, with the reduction of upper beam stiffness, the deflection of mid-span l will increase, the horizontal displacement of pier and pile heads will reduce, and the maximum bending moment and shearing force of the main beam will reduce, axial pressure of pile bottom will increase.