考虑施工需求的混凝土结构耐久性定量设计参数协调取值方法

Construction demand based consistent method for quantitative durability design of concrete structures

由传统耐久性设计方法所确定的混凝土结构一维和二维扩散区的耐久性定量设计参数取值往往互不相同,导致混凝土的制备和施工浇筑存在困难。鉴于此,提出了考虑施工需求的混凝土结构耐久性定量设计参数的协调取值方法。首先考虑氯离子扩散系数的时变特性,推导了混凝土结构中一维和二维扩散区氯离子浓度分布的时变解析模型;然后分析了混凝土结构角部箍筋弯折对混凝土附加保护层厚度的影响,并依据不同扩散区耐久性定量设计参数的协调一致性要求,建立了箍筋协调弯弧内半径的计算表达式,进而提出了混凝土结构耐久性定量设计参数的协调取值方法,从而满足对于同一截面上具有不同扩散区的构件能够一次性完成混凝土浇筑的施工需求。分析表明,该方法基于箍筋协调弯弧内半径和耐久性定量设计确定混凝土结构的耐久性设计参数取值,使混凝土结构能够在规定的腐蚀环境作用下满足预定的设计使用年限要求,从而克服传统耐久性设计方法所存在的缺陷。

Durability design parameters for one-dimensional(1 D)and two-dimensional(2 D)diffusion regions of concrete structures obtained by traditional durability design methods are generally different,which induces difficulty in the preparation and placement of concrete.In order to overcome this disadvantage,a construction demand based consistent method of quantitative durability design parameters for concrete structures was proposed.Firstly,analytical models for concentration distribution of chloride ion in both 1 D and 2 D diffusion regions of concrete structures were derived considering the time-dependent behavior of chloride diffusion coefficient.Then formula of additional concrete cover depth induced by bending stirrup in the 2 D diffusion region of rectangular section was developed according to the geometric relations of stirrups after bending.Finally,the consistent bending radius of stirrup were determined and the consistent method of durability design parameters for concrete structures was established according to the consistent durability between 1 D and 2 D diffusion regions,which satisfies the construction demand of concrete component with different diffusion regions.The analysis results show that the proposed method not only takes into account the influence of bending radius of stirrup on durability of 2 D diffusion zone,but also provides an efficient way to achieve consistent durability between 1 D and 2 D diffusion regions of concrete structure.Furthermore,the proposed method can determine the potential combinations of concrete cover depth,initial chloride diffusion coefficient and its ageing factor to meet the predefined service life,which achieves the quantitative durability design of concrete structures and overcomes the disadvantages of traditional durability design methods.