摘要
结构中的混凝土应力和应变都在随着时间而改变,在众多的徐变时间本构方程中,代数本构是最强有利的工具,其精度和关键取决于松弛系数。松弛系数是与时间相关的变量,有工程意义的是松弛系数终值,用计算图来表示它,精度高,使用方便。基于我国公路混凝土桥涵规范的徐变系数模型,按照徐变增量求和本构方程,采用逐步积分的数值方法,对影响松弛系数终值的主要因素进行了参数分析,包括弹性模量、加载龄期、有效厚度、环境湿度和混凝土抗压强度。精细考虑混凝土弹性模量随时间的变量模型,对结果影响不大,故可用28 d弹性模量的常量模型。加载龄期和有效厚度是影响松弛系数终值的两个主要因素,加载龄期越早松弛系数越小,有效厚度越小松弛系数越大。由此给出了松弛系数终值的计算图。应用该计算图,按照代数方法推导了两跨整浇连续梁的徐变次弯矩计算公式,对预制梁现场连接的连续梁采用一个重分布系数来修正徐变次弯矩计算公式。结果表明:若采用Trost提出的定值0.8的松弛系数,对加载龄期早情况的结果偏差大;徐变对整浇连续梁的支座负弯矩没有影响,但对通常的体系转换连续梁影响大,如对预制梁现场连接连续梁产生较大的支座负弯矩,忽略徐变这一与时间有关的因素可能造成安全隐患。
The stress and strain of concrete in structures always change with time, in many creep time constitutive equations, algebraic constitutive equation is the most powerful tool, and its precision and key depend on relaxation coefficient. The relaxation coefficient is the time-dependent variable, and its final value is of engineering significance. It is more convenience and has higher precision by means of calculation chart of final relaxation coefficient. Based on the creep coefficient model of the design code of highway reinforced concrete bridge and culvert in China, according to the incremental constitutive equation of creep, the main factors influencing the final relaxation coefficient, including elastic modulus, loading age, effective thickness, ambient humidity and compressive strength of concrete, are analysed by means of step-by-step integration numerical method. Careful considering the time-dependent model of the elastic modulus of concrete has little effect on the result, hence a constant model of 28-day elastic modulus can be used. Loading age and effective thickness are the 2 main factors that affect the final relaxation coefficient, the smaller the loading age the smaller the relaxation coefficient, and the smaller the effective thickness the greater the relaxation coefficient. The calculation chart of final relaxation coefficient is then given. The calculation formula of the creep secondary moment of 2-span continuous beam is derived according to the algebraic method, and a redistribution coefficient is used to modify it in the case of continuous beam made by a cast-in-situ joint. The result shows that （ 1 ） if the relaxation coefficient of the fixed value 0. 8 proposed by Trost is applied, the result of the early age loading condition is much deviate; （2） creep has no effect on the negative moment of support of continuous beam by integral cast, but has great effect on that of the usual continuous beam by system transformation, such as the cast-in-situ continuous beam using prefabricated beams.
出处
《公路交通科技》
CAS
CSCD
北大核心
2018年第3期36-45,共10页
Journal of Highway and Transportation Research and Development
基金
国家自然科学基金项目(51468026
51668027)
云南省教育厅科学研究基金项目(2017zzx089)
关键词
桥梁工程
徐变
松弛
逐步积分
次弯矩
bridge engineering
creep
relaxation
step-by-step integration
secondary moment
