【作者】 徐丰；

【导师】 张海龙；

【作者基本信息】 华中科技大学 ， 桥梁与隧道工程， 2009， 博士

【摘要】 温度作用在混凝土箱梁桥中产生的应力和应变可以与恒载或活载效应相当，是导致该类桥梁结构在施工与运营期间产生裂缝的重要原因之一，因而对该类桥梁结构的安全性、耐久性和适用性均有显著影响。本文将混凝土箱梁桥温度效应的起因归结为气候因素、人为因素和材料自身因素三大类，并以ANSYS为软件平台，采用三维有限仿真技术，对混凝土箱梁桥各种因素所导致的温度效应进行了全面分析。全文主要工作如下：(1)构建了辐射历计时系统，提出了辐历时角的概念，重新定义了太阳高度角和方位角的取值范围，使这两个角度随辐历时角的日变化和年变化具备单值性，在此基础上提出了一套适用于土木工程三维日照热分析的太阳位置计算公式。(2)建立了以箱梁轴向方位角为变化参数的温度场分析有限元模型，按照箱梁外表面与外界环境热量交换的不同特性对模型的热边界进行分类，根据箱梁外表面的动态热平衡条件求取外表面各类热边界的辐射气温及其随辐历时角的变化规律。借助ANSYS内嵌的辐射矩阵生成器AUX12基于半立方体法的单元“遮挡与可见性”判断的功能，实现了箱梁外表面在任意辐历时刻日影单元与非日影单元的区分与选择，进而实现了箱梁外表面动态热边界的模拟。采用这种办法对不同地理位置上各种轴向方位上的混凝土箱梁模型进行了温度场的时程计算和参数分析，并作了实桥验证。(3)提出了截面竖向温差梯度模式的线性度概念。通过对比现行设计人员常用的简化计算方法和三维实体有限单元法计算同一混凝土连续箱梁桥在同一温差梯度荷载作用下的温度应力计算结果，指出由前者计算得到的温度应力值在分析模型的大部分部位都小于后者，文章分析了这种差别产生的原因。(4)对气温骤降作用下混凝土箱梁桥的温度效应进行了参数分析，得到了箱梁截面的特征长度、冷空气对箱梁表面的对流换热系数以及气温骤降的剧烈程度对箱梁温度应力的影响规律。采用“单元生死”技术模拟了沥青摊铺机在桥面的行进过程，分析了高温沥青摊铺作业过程中箱梁内部的温度分布和应力特征。(5)按照松弛系数法的有限元格式，借助ANSYS的二次开发功能，写出了用以计算大体积混凝土结构水化热阶段温度应力的命令流。该命令流考虑了混凝土材料在水化热阶段所具备的包括抗拉强度与弹性模量随龄期增长以及徐变与收缩性质的时变特性。对一实际大型桥梁工程箱梁零号块水化热阶段的温度场和温度应力进行了仿真分析。更多还原

【Abstract】 It is known that temperature stresses and strains are comparable to that induced by thedead load or vehicle load upon concrete box-girder bridges.As one of the most importantfactors that lead to the occurrence of cracks in concrete bridges during construction oroperation period,temperature effect may deteriorate the safety,durability and adaptabilityof the bridge structures.Tracing from different originations the temperature effect ofconcrete box-girder bridge is classified into three categories:climatic temperature effect,artificial temperature effect and material temperature effect (the third one here representsthe effect caused by the hydration heat released by the cement-based concrete materials intheir hardening phase).Taking the general finite element modeling package ANSYS asplatform,a wide variety of thermo-mechanical problems of concrete box-girder bridge areanalyzed by simulating the structure in 3 dimensions.The main works are as follows:(1)A new timing system named Radiation Calendar is established.In RadiationCalendar the ranges of solar altitude angle and azimuth angle are redefined,which makesthe angles calculated from the improved formulas single-valued varying to RC hour angle.These improved formulas may be used conveniently when the 3D structural temperatureeffect caused by the solar radiation is to be quantified.(2)A parametric finite element modeling of a box-girder segment with any axialdirection is established.The external surface of the segment model is divided into differentareas according to their different characteristics reflected in the heat exchange betweenthese areas and thermal surroundings.By solving the equations that describes the heatequilibrium between these surface areas and thermal surroundings the valves of equivalentradiation air temperature and their variation to RC hour angle can be obtained.Taking useof the ANSYS auxiliary processor (AUX12)that supports the application of Hemi-cubemethod,the recognition of the elements exposed to and shaded from the sunlight is realized.So the thermal conditions that vary not only to time but also to spatial position can be lively simulated.Following these methods,parametric analysis of the transient temperature fieldof box-girder segments located in different geographical positions and axial directions arecarried out.In a comparison the simulation results agree well with the observed values froma practical engineering.(3)The definition of linearity of vertical gradient temperature forms is proposed.Through comparing the results calculated from the solid finite element model,theprevailing simplified method through which the thermal stresses are calculated in usualdesign work is proved to be lack of safety from the overall.The reasons for the differencebetween these two series of results are expounded.(4)Sudden drop of air temperature causes stresses in the body of box-girder bridge.To investigate the characteristics this kind of temperature effect,the parametric analysisabout the influence of characteristic length of cross section,convective heat transfercoefficient and severe degree of temperature drop on the magnitude of temperature stressesare performed.High temperature asphalt pavement is another factor that changes thetemperature field of box-girder in short time.Making use of the elements’“death and birth”function,the course of asphalt pavers’marching along the girder is simulated,throughwhich the temperature distribution and the stresses caused by asphalt paving is analyzed.(5)According to the relaxation coefficient method finite element scheme,takingtime-varying and age-varying properties of concrete into account,a program written inAPDL is proposed to calculate the temperature stresses in massive concrete structuresduring early ages.Through this section of APDL a calculation of temperature field andtemperature stress distribution of an original segment of a long span continuous box-girderbridge is implemented.更多还原