基于NCHRP496收缩徐变模型的连续刚构桥时效分析
发布时间：2018-11-25 15:16
【摘要】：国内外大跨径预应力混凝土连续刚构桥在运营多年后相继出现跨中下挠和梁体开裂,裂缝和变形的相互耦合更加剧了桥梁的病害,严重影响到桥梁结构的安全和正常使用性能。考虑预应力筋松弛和混凝土收缩徐变相互耦合的预应力损失计算中,分析方法的正确性和收缩徐变预测模型的准确性决定了计算结果的精度性。研究表明,收缩徐变预测模型的误差会比计算方法带来的误差更明显。国内外广泛采用的混凝土收缩徐变预测模型,是基于大量的普通混凝土长期试验数据经统计学方法拟合的公式,与目前广泛使用的高强度混凝土结构不符。为研究混凝土收缩徐变预测模型对连续刚构桥预应力损失和预拱度的影响,选取NCHRP 496报告提供的高强度混凝土收缩徐变预测模型和现桥规中JTG D62-04预测模型,以薛家坝2#大桥为主要分析对象,开展了基于高强混凝土收缩徐变模式的预应力损失与预拱度的数值计算研究:①系统归纳现广泛使用的各种收缩徐变预测模型和基于高强度混凝土试验的预测模型NCHRP 496。根据实际指定条件,对比分析各种模型的预测值差异和特点,主要分析构件理论厚度和混凝土强度因素对各种预测模型的影响,重点对比JTG D62-04和NCHRP 496因混凝土强度的变化所引起的预测值之间的差异;②基于按龄期调整的有效模量法,开展考虑混凝土收缩徐变、预应力筋松弛和普通钢筋相互作用的截面应力时效重分布计算方法的研究,推导出相应的预应力长期损失的计算公式;③重点依托实际工程薛家坝2#大桥,利用Midas/Civil有限元分析程序,对比分析JTG D62-04和NCHRP 496对结构长期预应力损失和竖向挠度的影响差异。以赫章特大桥作为辅助算例,验证计算分析结果的正确性和适用性。研究表明,现行桥规JTG D62-04收缩徐变预测模型未能准确考虑高强度混凝土的影响。JTG D62-04有高估高强度混凝土徐变特性和低估收缩应变特性的趋势,并且低估了因混凝土收缩徐变引起的长期预应力损失值,造成施工预拱度的设置偏小,这在一定程度上解释了桥梁跨中下挠过大的普遍现象。因此,为了能够准确分析高强度混凝土收缩徐变效应,建议规范JTG D62-04提供的收缩徐变预测模型需针对高强度混凝土加以修正完善。
[Abstract]:Long span prestressed concrete continuous rigid frame bridges at home and abroad have appeared in succession after many years of operation of mid-span deflection and beam cracking. The coupling of cracks and deformation exacerbates the disease of bridges, which seriously affects the safety and normal performance of bridge structures. The accuracy of the calculation results is determined by the correctness of the analytical method and the accuracy of the prediction model of shrinkage and creep in the calculation of prestress losses which are coupled with the relaxation of prestressed tendons and the shrinkage and creep of concrete. The results show that the error of the model is more obvious than that of the calculation method. The widely used concrete shrinkage and creep prediction model at home and abroad is based on a large number of ordinary concrete long-term test data fitted by statistical method, which is not consistent with the widely used high strength concrete structure. In order to study the influence of concrete shrinkage and creep prediction model on the prestress loss and precamber of continuous rigid frame bridge, the high strength concrete shrinkage and creep prediction model and the JTG D62-04 prediction model provided by NCHRP 496 are selected. Taking Xuejiaba2# Bridge as the main analysis object, Numerical calculation of prestress loss and pre-arch degree based on shrinkage and creep mode of high strength concrete is carried out. 1 various kinds of shrinkage and creep prediction models used widely and NCHRP 496 model based on high strength concrete test are systematically summarized. According to the actual specified conditions, the differences and characteristics of the prediction values of various models are compared and analyzed. The influence of the theoretical thickness of components and the strength of concrete on the prediction models is mainly analyzed. The difference between the predicted values of JTG D62-04 and NCHRP 496 caused by the change of concrete strength is compared. (2) based on the age-adjusted effective modulus method, the calculation method of cross-section stress aging redistribution considering the interaction of concrete shrinkage and creep, prestressed tendons relaxation and ordinary reinforcement is studied. The formula for calculating the long-term loss of prestressing force is deduced. (3) based on the actual project of Xuejiaba2# Bridge, the difference of the influence of JTG D62-04 and NCHRP 496 on the long-term prestress loss and vertical deflection of the structure is analyzed by using Midas/Civil finite element analysis program. The accuracy and applicability of the calculation results are verified by taking the Hezhang Bridge as an auxiliary example. The results show that the current JTG D62-04 shrinkage and creep prediction model of bridge gauge can not accurately consider the influence of high strength concrete. JTG D62-04 has the tendency of overestimating the creep characteristics of high strength concrete and underestimating the shrinkage strain characteristic. The long-term prestress loss caused by shrinkage and creep of concrete is underestimated, and the setting of pre-camber is small, which to some extent explains the common phenomenon of excessive deflection in bridge span. Therefore, in order to accurately analyze the shrinkage and creep effect of high strength concrete, it is suggested that the prediction model of shrinkage and creep provided by JTG D62-04 should be modified and perfected for high strength concrete.
【学位授予单位】：重庆交通大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：U441;U448.23
本文编号：2356560
[Abstract]:Long span prestressed concrete continuous rigid frame bridges at home and abroad have appeared in succession after many years of operation of mid-span deflection and beam cracking. The coupling of cracks and deformation exacerbates the disease of bridges, which seriously affects the safety and normal performance of bridge structures. The accuracy of the calculation results is determined by the correctness of the analytical method and the accuracy of the prediction model of shrinkage and creep in the calculation of prestress losses which are coupled with the relaxation of prestressed tendons and the shrinkage and creep of concrete. The results show that the error of the model is more obvious than that of the calculation method. The widely used concrete shrinkage and creep prediction model at home and abroad is based on a large number of ordinary concrete long-term test data fitted by statistical method, which is not consistent with the widely used high strength concrete structure. In order to study the influence of concrete shrinkage and creep prediction model on the prestress loss and precamber of continuous rigid frame bridge, the high strength concrete shrinkage and creep prediction model and the JTG D62-04 prediction model provided by NCHRP 496 are selected. Taking Xuejiaba2# Bridge as the main analysis object, Numerical calculation of prestress loss and pre-arch degree based on shrinkage and creep mode of high strength concrete is carried out. 1 various kinds of shrinkage and creep prediction models used widely and NCHRP 496 model based on high strength concrete test are systematically summarized. According to the actual specified conditions, the differences and characteristics of the prediction values of various models are compared and analyzed. The influence of the theoretical thickness of components and the strength of concrete on the prediction models is mainly analyzed. The difference between the predicted values of JTG D62-04 and NCHRP 496 caused by the change of concrete strength is compared. (2) based on the age-adjusted effective modulus method, the calculation method of cross-section stress aging redistribution considering the interaction of concrete shrinkage and creep, prestressed tendons relaxation and ordinary reinforcement is studied. The formula for calculating the long-term loss of prestressing force is deduced. (3) based on the actual project of Xuejiaba2# Bridge, the difference of the influence of JTG D62-04 and NCHRP 496 on the long-term prestress loss and vertical deflection of the structure is analyzed by using Midas/Civil finite element analysis program. The accuracy and applicability of the calculation results are verified by taking the Hezhang Bridge as an auxiliary example. The results show that the current JTG D62-04 shrinkage and creep prediction model of bridge gauge can not accurately consider the influence of high strength concrete. JTG D62-04 has the tendency of overestimating the creep characteristics of high strength concrete and underestimating the shrinkage strain characteristic. The long-term prestress loss caused by shrinkage and creep of concrete is underestimated, and the setting of pre-camber is small, which to some extent explains the common phenomenon of excessive deflection in bridge span. Therefore, in order to accurately analyze the shrinkage and creep effect of high strength concrete, it is suggested that the prediction model of shrinkage and creep provided by JTG D62-04 should be modified and perfected for high strength concrete.
【学位授予单位】：重庆交通大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：U441;U448.23
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相关期刊论文 前2条
1 潘钻峰;吕志涛;刘钊;;考虑收缩、徐变和松弛相互影响的预应力长期损失计算[J];现代交通技术;2010年05期
2 杨旭;汪维安;张俊琪;;布柳河大桥收缩徐变模型的比选[J];科技资讯;2006年24期
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