1 Introduction
In practice，the generation of thermal stress is a major cause of early age thermal cracking of massive concrete structure.Tensile thermal stresses are generated by restraining of volumetric deformation，while the tensile strength of concrete is very low.Therefore，cracks are widespread in massive structure.High strength concrete is often used in the massive reinforced concrete（RC）structure，which brings more heat of hydration than the dam concrete（ACI318-11，2011）.Consequently，massive RC structures tend to crack more easily due to higher thermal stresses and it is necessary to enhance the requirements of crack width control.Related literatures indicated that only about twenty percent of cracks in massive concrete structure are caused by the external load，while the others are mainly caused by temperature deformation，shrinkage and inhomogeneous deformation，etc（Briffaut，Benboudjema，Torrenti，& Nahas，2013）.
It is important to understand the time-dependent temperature field and thermal stresses field in massive RC structure for assessment of thermal cracking.Many experimental and numerical studies have been conducted to simulate the temperature field and the thermal stress field（Amin，Kim，& Lee，2009；Chu，Lee，& Amin，2013；Sheibany & Ghaemian，2006；Tian& Wang，2012）.In particular，Wilson（1968）initially developed mass concrete structure of temperature field finite element simulation program DOTDICE in 1968，and this program was applied successfully to the temperature field calculation of Dworshak Dam.Moreover，Bazant has made numerous contributions on the creep and shrinkage mechanism as well as the calculation model（Bazant，1972）.In 1985，Tatro and Schrader in the U S Army Corps of Engineers further modified this program（Tohru & Sunao，1996）.
In 1992，P.K.Barrett introduced 3D thermal stress calculation software ANACAP，which brought the smeared crack model of Bazant into temperature stress analysis（Barrett，1992）.South Korean scholars（Amin et al.，2009）simulate the thermal stress in mass concrete using the finite element code DIANA.Further，Jin-Keun Kim（Lee & Kim，2009）has researched deeply in the coupling effect between the heat transfer and the moisture diffusion，concrete creep and early age cracking.However，thermal parameters measured in the laboratory were adopted in the model，which cannot represent the actual concrete thermal properties on site.In this paper，FEM program FZFX3D is improved based on the previous program，and it can reproduce the concrete thermal parameters in the site using the genetic algorithm（GA），which makes the numerical simulation have better accuracy.
Many advanced numerical approaches have been performed to simulate the relationship of reinforcement configuration and cracking behaviour of concrete，in which cracking is caused by external load rather than thermal stress（ACI 207.1R-96，1996；Bazant & Thonguthai，1978；Cusson & Repette，2000）.However，reinforcement configuration methods for limiting thermal cracking have not been effectively improved in massive RC structure.In order to limit the development of thermal cracking，constructional reinforcement should be configured.However，the existing constructional reinforcement designs of massive RC structure have some disadvantages.For instance，thermal reinforcement configuration is based on engineering experience rather than actual calculation.Consequently，a modified method of reinforcement configuration is proposed in this paper.This method is used to calculate the crack width，depth and stress distribution of reinforcement.In addition，this composite method has been applied in the reinforcement optimisation design of a sluice pier structure.