海上风电混凝土承台温度特性监测与仿真分析

Monitoring and simulation analysis of temperature characteristics of concrete pile-cap foundation for offshore wind turbine

多桩承台是海上风电基础的主要形式之一,为大体积混凝土,如果产生裂缝,会因海水侵蚀影响承台耐久性。温度荷载是产生裂缝的主要原因,温度控制是防裂的主要手段,目前承台混凝土的温度控制设计参照水运部门的相关规范。为了把握海上风电承台的温度特性,对河北乐亭菩提岛、福建福清兴化湾两个海上风电场共28个基础承台的温度过程进行了现场观测,对实测温度数据进行了统计分析,并以兴化湾典型承台为代表进行了温度场仿真分析。结果表明:(1)承台混凝土发热快,水化热温升高,2~3 d即达到最高温度,最大水化热温升可达60℃以上,致使内部最高温度可达90℃以上;(2)内外温差大,实测最大内外温差可达40~45℃;(3)降温速率快,温度降幅大,实测最大降温速率达到5℃/d以上;(4)仿真分析结果表明,承台浇筑3个月后温度即可降至准稳定温度,内部最大温度降幅可达80℃以上,比表面的温度降幅高30℃,这种温度变化会在承台表面产生压应力,在内部产生拉应力,存在内部产生裂缝的风险。上述几个温度指标均已远远超出设计采用的水运部门相关规范规定的温控标准,因此有必要在进一步研究温度应力规律的基础上研究标准的适应性,制定适应于海上风电混凝土承台的温控标准和措施,并编制相应规范。

Multi-pile cap foundation is one of the main forms of offshore wind turbine and consists of mass concrete;of which the durability is to be affected by seawater corrosion after the occurrence of cracking. Temperature load is the main cause of cracking, and then temperature control is the main method to prevent cracking. At present the concrete temperature control of the pile-cap foundation is designed with the reference of the relevant criteria from the water transport sectors concerned. In order to understand the temperature characteristics of the pile-cap foundation for offshore wind turbine, the in situ observations are made on the temperature processes of total 28 pile-cap foundations for two offshore wind farms, i.e. Puti Island Offshore Wind Farm in Laoting County of Hebei Province and Xinghua Bay Offshore Wind farm in Fuqing County of Fujian Province, and then the measured temperature data are statistically analyzed, while the simulation analysis of the temperature field is carried out through taking the typical pile-cap foundation for Xinghua Bay Offshore Wind farm as the representative. The results show that(1) the temperature rise of the concrete of the pile-cap foundation is rapid with high hydration heat temperature rise, which can reach the maximum temperature within 2~3 days and the temperature rise of hydration heat can reach above 60 ℃, thus can make the internal maximum temperature reach to above 90 ℃;(2) the inside and outside temperature difference is large and the measured internal and external temperature difference can reach to 40 ℃~45 ℃;(3) the rate of temperature drop is rapid with large temperature drop amplitude and the maximum measured temperature drop rate can reach to above 5℃/d;(4) the simulation analysis result exhibits that the concrete temperature of the pile-cap foundation can drop to the quasi-stable temperature after three months of the concrete placement and the maximum internal temperature can reach to above 80 ℃ and 30 ℃ higher than the surface temperature drop amplitude. The temperature change can produce compressive stress on the surface of the pile-cap foundation and produce tensile stress inside the pile-cap, thus a risk of internal cracking is there. If all the above mentioned temperature indexes far exceed the temperature control standards specified in the relevant criteria from the water transport sectors concerned, it is necessary to study the adaptabilities of those criteria on the basis of the further study on the law of temperature stress, make the temperature control standards and measures adaptable to the concrete pile-cap foundation for offshore wind turbine and establish the corresponding specifications as well.