A, asphalt commercial concrete bridge deck disease analysis
1, structural theory and design
In the structural theory of (1) bridge, the calculation, analysis and discussion of deck pavement are almost zero, and only the recommended thickness is given in the current code, which has been used in various grades of highways for decades. With the increase of traffic volume, the existing pavement has not adapted to the increase of heavy and ultra-heavy vehicles and the increase of vehicle speed. Bridge deck pavement directly bears the impact of wheel load, and it partially or completely participates in the deformation of main girder structure, so bridge deck pavement is a complex dynamic system, and the stress distribution is affected by various forms of main girder and the structure of pavement itself.
(2) Article 3.2.2 of the current bridge code stipulates ... If there is no accurate calculation method, the box girder can also be treated with reference to the provisions of the T-beam. Judging from the design of many box girders, most designers treat box girder components as T-beams. Although the actual stress of box girder is close to T-beam, it is different from T-beam, especially for continuous box girder. Especially in recent years, the bridge deck of box girder is getting wider and wider, and the ratio of bridge span to bridge width is getting smaller and smaller. It is more and more inappropriate to design the reinforcement of box girder according to the slender members of T-beam, which makes it difficult for the reinforcement of box girder skeleton designed according to beam to play its due role like the main reinforcement of T-beam under actual stress. Therefore, the assumed state of the design is inconsistent with the actual stress state of the box girder.
(3) With the development of material industry and the improvement of bridge load-bearing structure, the main girder of bridge can meet the stress requirements with flexible structure, and the lateral width of long-span bridge of high-grade highway is getting wider and wider. Especially in the design and calculation, the longitudinal calculation and analysis of the main girder are emphasized, and the lateral stiffness of the bridge is not paid enough attention. The lateral structural measures are unfavorable, which makes the bridge deck pavement share too many secondary internal forces.
(4) For bridge structures such as continuous beam bridge, arch bridge and cantilever beam bridge, due to the negative bending moment or tension generated by the load, the bridge deck pavement is pulled, which leads to cracks in the negative bending moment area, thus causing the damage of the bridge deck pavement.
(5) In the traffic organization and management of expressway, due to the different lane functions, the operation of the bridge structure is always in an unbalanced load state, which makes the operating stress level of the main lane pavement much higher than that of the overtaking lane, thus accelerating the fatigue of the main lane pavement. Especially with the development of private transportation industry, in order to pursue short-term economic benefits, shippers have doubled the load, axle weight and wheel weight of automobiles by changing the carriage structure, such as lengthening the carriage and heightening axle springs. These vehicles have caused serious damage to the pavement, overloaded the bridge structure locally, and accelerated the disease development of the main lane pavement. Therefore, in the design, according to the actual distribution of vehicle load in operation, the stress of bridge deck pavement should be calculated on the basis of clarifying the stress of bridge structure.
2, the construction technology
(1) The pavement thickness is small. Because it is impossible to accurately predict the settlement of the bracket and prestressed inverted arch in the superstructure of the bridge, or because the construction technology is not well controlled, it is difficult to match the elevation of the top surface of the main girder with the design value during construction. Generally, it is adjusted after measuring the elevation of the top surface of the main girder to ensure the thickness of the bridge deck. If the adjustment is not good, it will cause uneven thickness of the road surface and reduce the thickness in some places.
(2) The cleaning of the beam top is unfavorable, resulting in poor combination between the pavement and the main beam.
3, the influence of bridge deck waterproof layer
Because the strength of flexible waterproof layer is different from that of main board and pavement, its existence makes the superstructure form a rigid-flexible-rigid plate stress system according to the modulus, and the flexible interlayer in the middle will increase the tensile stress at the bottom of bridge deck. Once the pavement on the waterproof layer cracks, under the dynamic load of the wheel, the gap between the two becomes bigger and bigger until it falls off loosely. In addition, the use of waterproof layer greatly increases the probability of pavement shear failure.
4. Constraints of bridge deck pavement
The bridge deck pavement is constrained by the bridge structure, and its boundary conditions are very different from those of the general pavement. In addition, the coupling effect of beam deflection, torsion and other deformations has a negative impact on the working performance of pavement.
2. Discussion on the design method of bridge deck pavement
At present, the research on bridge deck pavement is not mature, and the existing research mainly focuses on material design and pavement technology, with little research on theoretical analysis and structural calculation.
Judging from the existing structural analysis methods, three-dimensional isoparametric element model is mainly used for analysis, and at present, three-dimensional eight-node and twenty-node elements are mostly used.
Reasonable finite element model is the premise of calculation and analysis. Judging from the current research situation, there are mainly the following aspects that need to be discussed urgently.
For bridge deck pavement, how to assume and simulate interlayer contact is a very important problem in finite element modeling. For the case without waterproof layer, we can learn from the treatment of composite pavement. In a word, how to simulate interlayer contact, especially how to consider the influence of waterproof layer, is the key problem to establish a reasonable finite element model, and also the focus of studying pavement structure design theory. It is necessary to combine theoretical calculation with experimental analysis, compare the calculated results with the experimental and measured results, and find a model that is consistent with the actual stress of the structure.
Bridge deck pavement is a special pavement structure. How to simplify the load model reasonably and how to distribute the load in the horizontal and vertical directions is also directly related to the accuracy of the calculation results.
Another important problem that needs to be studied is the deflection and other deformations of the bridge under the load, what influence these factors have on the mechanical characteristics of the pavement, and how to consider these influences, which is also an aspect that bridge deck pavement is different from general composite pavement. At present, there is no special discussion in China.
To solve the problem of bridge deck pavement reasonably, we need to start with theoretical analysis and structural calculation. The correct theoretical basis is fundamental, and the reasonable mechanical model is the key. By comparing the calculation analysis with the actual measurement, the above problems such as contact model and load simplification can be well solved, and the influence of other factors can be clarified. It is also necessary to strengthen the study of model scale and convergence conditions; If possible, strengthen the research on its dynamic performance. Based on the analysis of pavement failure forms, the key factors are determined, the control indexes are put forward, and the corresponding failure criteria are established, which provides a basis for design. To achieve this goal requires a lot of basic research work.
In this paper, the early diseases and their causes of flexible deck pavement of reinforced concrete bridges are analyzed, the main methods of structural analysis of deck pavement in China are summarized, some problems that should be paid attention to in finite element analysis are put forward, and the main research direction in the future is pointed out.
It is urgent to speed up the further research on asphalt commercial concrete bridge deck pavement, so as to clarify the calculation model, mechanical characteristics and related parameters of each structural layer of bridge deck pavement and provide guidance for bridge deck pavement design. At the same time, strengthen the research on the material performance index and detection technology of various pavement materials, and develop new materials to adapt to the failure mechanism of bridge deck; In addition, it is necessary to improve the pavement technology and construction quality, ensure the accuracy of the design model, and fundamentally solve the early damage problem of bridge deck pavement.
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