摘要
装配式空心板桥由于其预制、安装、施工工艺简单、工程造价较低,同时板桥具有建筑高度最小等优点,所以在中小跨径桥梁中得到广泛地应用。但从已建成桥梁的运营状况来看,也存在一些较为典型的病害。通过调研分析表明,影响空心板桥正常使用和结构安全最突出的问题是由于横向联系结构偏弱,单板刚度较低所造成的,而究其根源,空心板桥铰缝破坏是主要原因。空心板间铰缝处混凝土破碎、脱落、大面积渗漏,除引起梁本身破坏外,还可引起桥面铺装、伸缩装置、桥梁支座等的破坏,使桥面平整度降低,甚至出现桥面铺装拥起、破碎、脱落等现象。这不仅严重地影响了行车的舒适性,增加了行车的安全隐患,还大大降低了桥梁结构的整体承载力。
本文通过调研分析和阅读大量的相关文献对空心板桥铰缝破坏的原因、一般特征及其危害性进行了探讨和研究。简要介绍了基于ABAQUS有限元方法分析空心板桥所涉及到的非线性理论及其处理办法,本文主要包括材料非线性和接触条件非线性,非线性材质采用Newton-Raphson方法来解决,接触条件非线性采用了满足Coulomb摩擦定律罚函数公式进行处理。铰缝中的混凝土和钢筋用ABAQUS有限元提供的混凝土塑性损伤模型和经典的金属塑性模型分别实现。
建立实桥模型并与静载实验实测数据进行对比,由此验证了采用三维有限元程序ABAQUS6.8对考虑铺装层影响的空心板桥进行数值模拟和仿真研究是可行的、合理的和有效的,得到桥面板和铰缝的接触面采用滑动摩擦体系与实际相符。
利用有限元程序ABAQUS6.8对有限元模型进行如下分析:
(1)横向和纵向荷位对铰缝受力性能的影响,通过变化横向和纵向荷位,得到铰缝受力的最不利位置,并对不利荷载位置作用下的铰缝受力性能(包括沿纵向和跨中截面板高方向)进行深入细致的分析。
(2)对不同跨径空心板桥进行对比分析,在相同荷载,相同作用位置其荷载横向分布系数也是不相同的,跨径越小,横向荷载分布系数越不均匀。同一编号的空心板桥纵向正应力随跨径增大而增大。从荷载传递率来看,随着跨径的增大,荷载传递率逐渐增大。
(3)超载是对空心板桥铰缝结构各项指标中影响最大的因素,超载比例的增大会引起各项应力的增大,而且可能使铰缝混凝土的拉应力超过其抗拉强度,造成破坏。
(4)摩阻系数跟桥面的粗糙程度、车辆的速度、车辆的轮胎样式等因素有关。通过改变摩阻系数实现水平荷载的变化,并对比分析其对铰缝结构应力及变形的影响,发现水平荷载对铰缝结构中沿桥跨纵向的应力影响很大。
(5)沥青混凝土铺装层厚度改变对铰缝结构的各项应力影响较大,增加铺装层厚度将减小铰缝结构的纵向拉应力最大值,其余应力随着铺装层厚度增加,在10cm～12cm之前衰减幅度很大,之后衰减幅度逐渐减缓。其中剪应力衰减较大,当厚度由4cm增加到20cm时,剪应力衰减最大近90.4%。可见,增加铺装层厚度对于降低铰缝结构剪应力效果明显。
(6)沥青混凝土弹性模量随外界气温变化和荷载作用时间的改变变化很大,分析证明沥青铺装层的模量变大时,各应力均呈减小状态,而且增加铺装层弹性模量对铰缝结构的剪应力影响较大。
(7)当铺装层厚度一定时,桥面铺装材料采用刚性的钢筋混凝土和钢纤维混凝土对铰缝结构受力性能更为有利。
(8)通过改变铰缝结构弹性模量模拟不同等级的铰缝混凝土,发现随着铰缝弹性模量增加,铰缝结构的最大正应力及剪应力都呈现单调增加趋势,铰缝的竖向位移减小。
(9)铰缝结构泊松比的变化对铰缝的各应力及挠度影响不明显。
(10)桥面板与铰缝结构的接触状态比较复杂,研究发现接触条件变化对铰缝剪应力影响较大,铰缝结构和桥面板之间的良好粘结,对铰缝结构的受力性能有利。
(11)通过改变梁体密度,发现在跨径和截面相同的情况下,减轻自重,对铰缝结构受力性能有利。
(12)对铰缝常见加固方案进行对比分析,发现施加横向预应力筋效果最好。其次是加粗铰缝钢筋,但是采用该方法加固时不容易施工,不过在设计中适当加粗钢筋对新建桥梁还是有现实意义的。再次是铰缝底部及顶部增加钢板的方案,这两种方案不仅加固效果明显,而且施工也方便。
中小跨径装配式空心板桥在内蒙古地区应用十分广泛。不过从已建成桥梁的使用状况来看,铰缝破坏病害比较突出。故本论文研究成果将及时服务于正在蓬勃发展的西部地区中小跨径桥梁工程建设,对提高工程质量,保证空心板桥的结构安全度及耐久性,减轻高速公路养护阶段的工作量以及节省大量的养护资金,促进当地社会经济的发展,都具有迫切性和重要意义。
Fabricated concrete hollow slab bridges are applied widely in bridge engineering, because of its simple prefabrication and construction craft, lower cost and lowest construction height etc. However, some typical diseases have been found according to the operation condition of some bridges. Through analysis of research studies show that the most prominent problems that should impact the normal use of hollow slab and its structural safety are due to the weaker horizontal ties、the lower veneer stiffness, and the root reason of the damage of the bridges is the destroy of hinge joints. Hinge joints between hollow concrete slab broken off, large areas of leakage, it might cause the damage of beam itself, and also cause the damage of bridge deck, expansion join, and bearing, even though leading to the lower deck flatness, bridge deck over, broken off and so on. This is not only seriously affected the traffic comfortable, an increase the traffic safety problems, but also greatly reduce the bearing capacity of overall bridge.
In this dissertation, a large number of relevant literatures and research analysis of the damaged reasons and the general characteristics for the hollow slab bridge hinge joints are discussed. The nonlinear theory and its approach are introduced to hollow slab bridge with ABAQUS finite element method. The article involved material nonlinearity and contact conditions nonlinearity,the non-linear material uses Newton-Raphson method to solve, the contact conditions use the penalty function formula of Coulomb friction law to deal with. The concrete damaged plasticity model and the classic plasticity metal models of ABAQUS finite element are provided for hinge joint concrete and steel respectively.
Contrast the test results with the calculation results, hollow slab bridge numerical simulation is feasible, reasonable and effective for ABAQUS6.8. It is feasible for using sliding friction contact system to simulate the contact conditions of slab and hinge joints.
With Finite Element Method ABAQUS6.8, the analysis is included:
(1)For changing the transverse and longitudinal load positions. The most unfavorable position of loading was found. And the mechanical property of hinge joints has been analyzed under those unfavorable conditions.
(2)Hollow slab bridges of different span are analyzed in the same load, The transverse distribution coefficient of the different length hollow slab is not the same, the smaller the span was, the greater the transverse distribution coefficient is. In the same number slab, the vertical stress increases with the span. As the span increasing, the load transfer rate was increasing gradually.
(3)The effect of the overload is the biggest factor to hollow slab bridge, the overload proportion increasing can enlarge each stress, even lead to the hinge joints destroy because the tensile stress would surpass concrete tensile strength.
(4)Friction coefficient is related to the bridge floor rough degree, vehicles speed, vehicle tyre style. The horizontal load equal to the vertical load multiplied the friction coefficient. In this dissertation we discuss the influence about stress and deformation of the hinge joints under the change horizontal loads. .
(5)Thickness change of asphalt concrete pavement has a greater impact to the stress of hinge joints, increasing the thickness of pavement layer will reduce the maximum vertical tensile stress, and the remaining pavement thickness in 10cm ~ 12cm ,the stress decay rate is big, and then decay rate become gradually slower. Attenuation of shear stress in which is larger, when the thickness changed from 4cm to 20cm, the maximum shear stress decay nearly 90.4%. Obviously, increasing the thickness of pavement layer structure is effective method to reduce the shear stress of hinge joint.
(6)Elastic modulus of asphalt concrete pavement will change greatly with the outside temperature and load period, with the elastic modulus of asphalt concrete pavement enlarging, all the stress are reduced, and increased elastic modulus of pavement impacts the shear stress largely in hinge joints structure.
(7)When thickness of pavement is a certain, using rigid reinforced concrete and steel fiber concrete as the bridge deck pavement material have more favorable mechanical properties for the hinge joints structure.
(8)The different grades of concrete is simulated by changing the elastic modulus of hinge joints, it is found in the study: with increasing elastic modulus, the greatest stress is increasing, the vertical displacement is decreasing.
(9)The affect of stress and deflection in hinge joints structure are not obvious by changing Poisson’s ratio of hinge joints concrete .
(10)The contact state is complex for bridge deck and hinge joints. It is found that the contact state is obviously effect for the shear stress of hinge joints. Improving the contact state, hinge joints structure will have favorable mechanical properties.
(11)By changing the density of hollow slab bridge, It is showed that the favorable mechanical properties is obtained by reducing dead weight for hinge joints structure in the same span and cross-section cases.
(12) The common programs of the hinge joints reinforcement were analyzed, it is found that exerting lateral tendons has the best affect, followed by bold steel hinge joints, but the first method is not easy to construction, using bold in design is appropriate to the newly building bridge. Secondly the program of increasing the steel plate at the bottom and at the top of the hinge joints was discussed, these two programs has effective reinforcement and convenient construction.
Small and medium-span fabricated hollow slab bridge is widely used in China and Inner Mongolia province. However, when the bridge has been completed and operations, there are also some the more typical diseases of hinge joints. The research conclusion of the dissertation must be serving for the small and medium span bridge in the western region projects, improve the quality of the projects and ensure the structure safety and durability of the hollow slab bridge, reduce the workload of the highway conservation, as well as substantial saves conservation funds, and develop the promotion of local socio-economic. It is an immediate problem and has an important meaning.
引文
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