Research On Construction Reliability Of Mass Concrete Based On Iterative Response Surface Method

With the development of national economy,mass concrete structures are extensively applied in modern civil engineering project.Due to the hydration reaction,the thermal stress inevitably exists in the construction process of mass concrete,even induces the concrete cracking on the surface,impairing the structural safety and the reliability for long term use.In order to ensure the construction safety of mass concrete and prevent the emergence of great cracks,one of the available way is the use of risk and reliability analysis.However,because of the structural complexity of mass concrete and timedependent properties of random variables,the reliability analysis has the following characteristics: 1)the structural performance function is implicit,and the accurate finite element analysis is necessary.2)load effects are generally described by stochastic processes,and the mechanism is complicated due to the thermal-mechanical couple effect.These two characteristics make the reliability analysis method difficult to utilized in the process of mass concrete construction.Therefore,based on the secondary development platform of ABAQUS and the response surface method in reliability analysis,a suitable finite element model for mass concrete and a response surface method with high accuracy and efficiency are presented in this paper.The main contents and research outcomes are as follows:(1)Balancing the accuracy and efficiency is still a challenge in response surface method.In this paper,a new response surface method based on adaptive bivariate dimension-reduction is proposed.Firstly,by combining the cut-high-dimensional model representation(cut-HDMR)and the criterion of delineating the existence of cross terms,an adaptive bivariate cut-HDMR for multivariate response surface function is derived.Secondly,approximating the component functions in bivariate cut-HDMR with polynomials,together with the selection strategy of sampling points.Thirdly,by combining with the criterion of delineating the constitution of component functions,the form of global response surface can be determined and the RSM based on adaptive bivariate dimension-reduction,which comprises two types of sub-methods,is developed.And several examples are presented to verify the accuracy,efficiency and robustness of the proposed method.(2)Based on the secondary development platform of ABAQUS,this paper aims at accurately simulating the temperature field and stress field,with the considerations of behavior variation,thermal-mechanical couple effect and heat transfer condition in mass concrete construction.Firstly,the thermal field subroutine UMATHT is utilized to simulate the temperature field which takes the degree of hydration and equivalent age into account,comprehensively analyzing the effects of temperature and age on the behavior of mass concreter.Secondly,in order to precisely simulate the stress field of mass concrete,a creep function of double power law is considered in the viscoelastic stress field calculation subroutine UMAT,which is based on the maturity theory.At last,the third type of boundary condition and the change of atmospheric temperature are simulated by the subroutine FILM.(3)Because the variables in the process of mass concrete construction are random and uncertain(e.g.concrete strength and conductivity),the deviation will be hold between the results of certainty analysis and practical experience.To overcome this problem,firstly the equivalent extreme-value event is introduced to construct an equivalent performance function for time-dependent reliability analysis of mass concrete construction.Secondly,by combining the finite element model of mass concrete,which is proposed in this paper,the reliability analysis is executed by using the response surface method based on adaptive bivariate dimension-reduction.Finally,the reliability index is employed as quantitative indicators of risk to rationally control the construction process.