西部干寒地区日照辐射及骤然降温引起的FRP加固混凝土箱梁温度效应研究

The domestic and foreign researchers made a great deal of experimental research and theoretical analysis on mechanical properties and functional performance of concrete structures reinforced by FRP, and achieved fruitful research results. However, in their studies, a few studies involved the box girder reinforced by FRP, and the study on temperature effects of concrete structure reinforced by FRP is not deep enough. Considering climatic characteristics of radiation intensity of sunshine, large temperature difference between day and night, and small relative humidity in dry and cold areas of the western China, the temperature field of concrete box girder reinforced by FRP is established caused by solar radiation and sudden drop in temperature respectively, by way of indoor and outdoor tests and analysis of radiation heat transfer theory and heat conduction theory.Based on an analysis of the measured temperature effect, the general laws of the longitudinal and horizontal temperature stress, as well as the interface temperature stress between FRP and concrete would be got. Then the control differential equations of the concrete box girder reinforced by FRP under the effect of temperature are to be established so as the numerical solution and analytical solution can be got.At last, some simplified formula would to be explored which can make the design and calculation easier, and can be applied to calculate the interface temperature stress between FRP and concrete.This project will be helpful to determine the temperature gradient of the concrete box girder reinforced by FRP reasonably and can provide a reliable basis to the design of reinforcement for the dry and cold areas of the western China.

国内外研究者对FRP加固混凝土结构的力学及使用性能进行了大量的试验研究与理论分析，并取得了丰硕的研究成果，但涉及FRP加固箱梁的研究较少，对FRP加固混凝土结构温度效应的研究也不够深入。本项目考虑西部干寒地区日照辐射强、昼夜温差大、相对湿度小的气候特点，通过室内外试验和辐射换热及热传导理论的分析，建立日照辐射及骤然降温引起的FRP加固混凝土箱梁温度场。通过对实测温度效应的分析，总结FRP加固混凝土箱梁纵、横两向温度应力及FRP-混凝土界面温度应力的一般规律。应用复合薄壁箱梁理论，建立FRP加固混凝土箱梁温度作用下控制微分方程，进而获得加固梁体温度效应的数值解和解析解。探求一种便于设计计算的FRP加固混凝土箱梁温度应力及FRP-混凝土界面温度应力的简化计算公式。本项目的研究将为西部干寒地区，FRP加固混凝土箱梁温度梯度模式的合理确定及加固设计计算提供可靠依据。

考虑到西部干寒地区日照辐射强、昼夜温差大、相对湿度小的气候特点，项目组对CFRP加固混凝土箱梁温度场及温度效应开展了三方面的研究。.（1）日照辐射引起的CFRP加固混凝土箱梁温度场及温度效应的研究。.CFRP加固混凝土试验箱梁比未加固构件表面最高温度高出4~5℃，导致了箱梁截面竖向温差增大，其最大温差出现在14时~16时。不同日照辐射条件作用对CFRP加固混凝土箱梁的竖向温度梯度存在一定的影响。所建立的神经网络预测模型，可简单快速地预测出西部干寒环境下CFRP加固箱梁日照辐射温度场。.温度正应力与未加固箱梁相差很大。在顶面粘贴CFRP后，顶板承受温度应力全为受压，底板拉应力大于未加固箱梁的底板拉应力。.（2）骤然降温引起的CFRP加固混凝土箱梁温度场及温度效应的研究。.CFRP加固试验梁和未加固试验梁的温度梯度模式和温度值可取一致，顶板可拟合为折线形，腹板可拟合为二次抛物线形。拟合得到的温度梯度模式与现行《公路桥涵通用设计规范》规定的降温温差模式区别较大，主要表现在规范未考虑底板负温差，与英国规范BS-5400中规定的降温模式较为接近。.CFRP加固的顶面混凝土随着温度的降低温度应力持续增大，底板温度应力也由拉应力转变为压应力。.（3）日照辐射下CFRP加固混凝土箱梁温度自应力及CFRP-混凝土界面温度应力的研究。.基于复合材料力学，运用能量变分原理，建立了CFRP加固箱梁的日照辐射温度自应力及界面温度应力的控制微分方程。分别推导了CFRP加固简支箱梁温度自应力及其界面温度剪应力的计算公式。.在纵向位移函数为二次抛物线的假设下，混凝土自应力沿纵向呈双曲线变化，沿横向呈抛物线变化。跨中区域混凝土温度自应力最大，而纵向端部附近区域CFRP温度自应力最大。在CFRP-混凝土界面温度纵向剪应力为6次函数的假设下，界面剪应力变化较大，纵向端部应力集中现象明显，最大值在腹板位置。.本项目的研究为西部干寒地区，CFRP加固混凝土箱梁温度梯度模式的合理确定及加固设计计算提供可靠依据。