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标题 输水隧洞预应力混凝土衬砌应力正交敏感性分析
范文 秦敢等
摘要:为了分析输水隧洞预应力混凝土衬砌结构应力对相关因素的敏感性,以穿黄隧洞工程为例,选取张拉控制应力σcon、预应力钢筋与孔道壁的摩擦系数μ、钢绞线孔道局部偏差摩擦系数k以及锚具变形和钢筋内缩值a等4个因素作为敏感性参数,通过正交试验设计法确定计算方案,采用三维有限元方法计算了各因素不同取值时管壁混凝土的应力状态。利用极差分析方法分析了管壁混凝土环向应力和轴向应力对上述4个因素的敏感性。结果表明,在钢绞线张拉完成、充水达到设计水压的两种工况下,管壁混凝土环向应力和轴向应力对这4个因素的敏感性由高到低依次为:μ、σcon、a、k,特别是μ和σcon对管壁混凝土环向应力有显著影响,在数值计算中需要评估或者通过试验验证这2个因素取值的准确性,以保证参数取值反映实际情况以及数值计算结果的可靠性。
关键词:输水隧洞;预应力衬砌;环向应力;轴向应力;正交试验;敏感性分析
中图分类号:TV332 文献标志码:A 文章编号:
16721683(2014)05000105
Orthogonal sensitivity analysis of prestressed concrete lining stress of water conveyance tunnel
QIN Gan,CAO Shengrong,YIN Juan,YANG Fan
(State Key Laboratory of Water Resources and Hydropower Engineering Science,Wuhan University,Wuhan 430072,China)
Abstract:To evaluate the sensitivity of the prestressed concrete lining stress to the related factors,the stretching controlling stress con,friction coefficient between prestressed steel and channel wall,local deviation friction coefficient of strand channel k,and anchorage deformation and steel shrinking value a were selected as the sensitivity factors in this paper based on the background of Yellow River crossing tunnel project.The orthogonal experiment design method was used to determine the calculation scheme,and the stress state of wall concrete was calculated using the threedimensional finite element method with different values assigning to the factors.The sensitivities of hoop stress and axial stress of the wall concrete to the four above factors were analyzed with the range analysis method.The orthogonal experiment results showed that the magnitude of sensitivities of hoop stress and axial stress of the wall concrete to the four factors under the conditions of completed strand tension and water filling reaching design water pressure is in the order of μ,σcon,a,and k,and especially μ and σcon have a significant impact on the hoop stress.Therefore,the value accuracy of the above two factors must be evaluated or validated by the experiments to ensure that the parameter values can reflect the real situation and the results of numerical calculation are reliable.
Key words:water conveyance tunnel;prestressed lining;hoop stress;axial stress;orthogonal experiment;sensitivity analysis
预应力衬砌是通过张拉预应力锚索施加预压应力来抵消隧洞结构承担内水压力所产生的拉应力,使衬砌成为抗裂结构,满足防渗与承载的要求。近年来,随着预应力技术的发展,隧洞预应力衬砌在水利水电工程、输水工程中得到了日益广泛的应用。
针对这种预应力衬砌的结构形式,应用数值模拟的方法对混凝土衬砌结构进行计算分析已经相当普遍[13]。数值模拟结果的准确程度与计算过程中采用的数学模型和计算参数的取值密切相关。在数学模型已经确定的情况下,计算参数取值的合理与否对计算结果有很大影响。但在工程实践中,影响预应力混凝土衬砌强度的因素来源于多个方面,包括材料性能、施工条件和荷载条件等。这些因素有的是确定的,但大部分具有随机性、模糊性、可变性等不确定特点,这就给计算参数的合理取值带来了很大的问题。因此,有必要对影响预应力混凝土衬砌强度的各个影响因素进行敏感性分析,找出敏感因素,并对敏感因素取值的准确性加以评估,从而保证数值分析结果的可靠性。
目前,敏感性分析的普遍方法是单因素分析法,但是该方法是建立在其他因素不变的条件下的[4],不能明确指示某个因素的变动对稳定性的影响程度,因而具有很大的局限性。
正交试验设计是利用数理统计原理处理多因素试验的科学方法,在岩土和边坡工程中得到了广泛的应用[56]。它能够通过代表性很强的少数次试验,揭示各个因素对试验指标的影响程度,确定出因素的主次顺序,找出最优参数组合[7~9]。为此,本文以穿黄工程为背景,采用三维有限元方法,选取主要影响因素作为敏感性参数,采用正交试验设计的分析方法研究预应力混凝土衬砌的环向应力和轴向应力对上述参数的敏感性,进而区分对计算结果影响较大的因素,以期为穿黄隧洞及其类似工程的设计与数值分析提供参考依据。
1 有效预应力的计算与加载
1.1 预应力损失的计算
5 结论
(1)对于管壁混凝土环向应力和轴向应力而言,计算参数的敏感性由大到小依次为:预应力钢筋与孔道壁的摩擦系数μ、张拉控制应力σcon、锚具变形和钢筋内缩值a、钢绞线孔道局部偏差摩擦系数k。μ是影响管壁混凝土环向应力和轴向应力最重要的因素,其参数变化对内衬混凝土应力计算结果有较大影响。因而,要将预应力钢筋与孔道壁的摩擦系数作为主要设计参数,最好结合现场试验确定该值的大小,以保证数值计算结果的合理性。
(2)张拉控制应力是仅次于预应力钢筋与孔道壁的摩擦系数的管壁混凝土环向应力敏感性参数,对其取值的合理性,在设计与计算中也应该慎重对待。
(3)管壁混凝土环向应力和轴向应力对锚具变形和钢筋内缩值、钢绞线孔道局部偏差摩擦系数两个因素不敏感,在当前参数变化范围内,改变上述两个参数的值对有限元计算结果影响不大。
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[8] 张旭辉,龚晓南,徐日庆.边坡稳定影响因素敏感性的正交法计算分析[J].中国公路学报,2003,16(1):3638.(ZHANG Xuhui,GONG Xiaonan,XU Riqing.Orthogonality analysis method of sensibility on factor of slope stability[J].China Journal of Highway and Transport,2003,16(1):3638.(in Chinese))
[9] 方开泰,马长兴.正交与均匀试验设计[M].北京:科学出版社,2001.(FANG Kaitai,MA Changxing.Orthogonal and uniform experimental design[M].Bei jing:Science Press,2011.(in Chinese))
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