【作者】 刘赫凯；

【导师】 丁一宁；

【作者基本信息】 大连理工大学 ， 结构工程， 2012， 博士

【摘要】 对称倾角梁是德国学者提出的一种新型的分析管片力学性能的试验模型,在欧洲盾构法施工隧道的研究中已经得到了广泛认可和应用。而盾构管片是盾构法施工隧道的承重主体,因此对其抗裂性、安全性和耐久性要求很高,但传统钢筋混凝土管片自重较大,在运输、安装过程和运营阶段都可能出现局部开裂、破损现象。单纯提高配筋率或局部加固可能由于新拌混凝土工作性能不足,在管片内部配筋密集区域造成混凝土与钢筋无法形成有效粘结和降低混凝土保护层厚度,从而导致管片在复杂应力作用下形成结构裂缝,使得衬砌结构的整体性被破坏,容易发生渗漏和钢筋锈蚀现象,降低了隧道结构的安全性、耐久性和使用寿命。研究表明高性能钢纤维自密实混凝土具有高性能自密实混凝土高工作性和钢纤维混凝土高韧性的特点,采用增强增韧型长钢纤维可明显提高混凝土的抗拉、抗弯性能,因此可以利用结构型长纤维部分替代传统抗剪钢筋,提高箍筋间距,保证混凝土浇筑质量,提高结构的耐久性。但目前国内针对纤维高性能自密实混凝土的研究相对较少,对于利用结构型长纤维替代管片中钢筋的试验研究尚未见报道。鉴于此,本文尝试从钢纤维高性能自密实混凝土工作性能、抗弯性能和韧性、钢筋钢纤维高性能自密实混凝土梁抗剪性能几个方面对钢纤维高性能自密实混凝土的基本材料性能和利用钢纤维部分甚至完全替代箍筋的可行性进行研究。在此基础上,结合国家自然科学基金项目“混杂纤维对管片的裂缝与力学性能的影响”(51078058),对钢纤维自密实混凝土对称倾角梁的力学性能进行试验研究,本文主要从如下几个方面开展研究工作：(1)应用国际上应用较为广泛的自密实混凝土工作度评价方法,采用坍落流动度试验和J-环试验研究了新拌钢纤维自密实混凝土的工作性能。通过工作度试验和材料试验得到了满足工作性能和强度要求的钢纤维自密实混凝土配合比结果。(2)参照国际材料与结构联合会推荐弯曲试验标准(RILEM TC162-TDF)对硬化后自密实混凝土的抗弯性能进行试验研究,对比了不同尺寸、不同掺量端部弯钩型钢纤维对抗弯性能和弯曲韧性的影响。根据弯曲试验结果建议了钢纤维混凝土达到挠度硬化时钢纤维掺量的判定公式。基于开口梁的试验曲线采用反分析方法求解得到不同掺量钢纤维自密实混凝土的应力-裂缝口宽度关系,并基于应力-裂缝口宽度关系预测了受弯钢纤维自密实混凝土矩形梁的荷载-挠度全过程曲线,结果表明曲线预测结果与试验结果吻合良好。(3)为了消除边壁效应对钢纤维混凝土弯曲韧性试验结果的影响,采用截面尺寸为600mm×100mm的开口简支板进行弯曲试验,参考Rilem TC162-TDF中弯曲韧性的评价标准对板试件的弯曲韧性进行评价,研究了钢纤维对开口板弯曲强度和弯曲韧性的影响。并与开口梁试件进行对比,分析了梁式和板式试件弯曲试验结果的差异。(4)以基体强度、钢纤维掺量、钢纤维种类、加载方式、跨度为研究对象,分析了影响钢纤维混凝土梁跨中挠度-裂缝口扩展宽度关系的因素,结果表明当钢纤维掺量低于50kg/m3时：跨中挠度和裂缝口扩展宽度的关系呈线性关系；基体强度、钢纤维掺量和种类对钢纤维混凝土梁跨中挠度和裂缝口扩展宽度的关系曲线的斜率影响较小；跨中挠度和裂缝口扩展宽度的关系曲线的斜率受试件跨度和加载方式的影响。根据试验结果建议了钢纤维掺量低于50kg/m3时钢纤维混凝土受弯试件的跨中挠度与裂缝口扩展宽度的表达式,预测结果与试验结果吻合较好。(5)对钢纤维钢筋自密实混凝土简支梁抗剪性能进行试验研究,分析了钢纤维对试件的荷载-挠度曲线、承载力、破坏模式和裂缝形态的影响。建议了发生剪切破坏试件的韧性评价方法,定量地评价了钢纤维对剪切韧性的影响,结果表明：钢纤维的掺入降低了试件表面弯剪区的裂缝间距和裂缝宽度,钢纤维可以明显提高钢纤维混凝土梁的极限承载力、能量吸收能力和韧性,50kg/m3钢纤维可以将配置构造箍筋的试件从脆性的剪切破坏转化为延性的弯曲破坏。在本文的试验条件下,钢纤维无法完全替代箍筋,而箍筋和钢纤维共同使用时表现出明显的正混杂效应,明显优于单独采用箍筋的情况,因此钢纤维部分替代箍筋是可行的。(6)以钢纤维掺量、配箍率、纵筋率和剪跨比为主要变量,研究了钢纤维对钢筋自密实混凝土对称倾角梁的破坏形态、荷载-跨中挠度曲线和荷载-跨中纵筋应变曲线的影响。结果表明,倾角梁与简支梁试件破坏模式相似,但倾角梁试件的承载力明显高于简支梁试件,而倾角梁试件由于端部轴力作用纵筋应变明显低于简支梁试件；钢纤维可以有效控制倾角梁试件的跨中挠度和纵筋应变,提高试件的抗剪承载力和能量吸收能力,试件的破坏模式明显趋于延性；纵筋率对倾角梁抗剪承载力和能量吸收能力均有影响,影响效果与纤维掺量和配箍率相关；倾角梁试件中利用钢纤维替代构造箍筋是可行的。(7)根据钢筋混凝土梁的抗剪机理和对影响梁试件抗剪强度因素的分析,以抗压强度、纵筋率、剪跨比和钢纤维增强因子为主要参数,通过对142根发生剪切破坏的钢筋混凝土梁和钢筋-钢纤维混凝土梁的试验结果进行回归分析,建立了适用于钢筋-钢纤维混凝土梁抗剪强度的预测经验公式。最后通过分析轴力作用对梁作用和拱作用的增强作用机理,引入增强因子Y来预测钢筋钢纤维倾角梁的抗剪强度,该公式计算结果与试验结果吻合良好。更多还原

【Abstract】 Symmetric inclation beam is a new test method used to investigate the stress state of tunnel segment. It is developed by German scientist and is widely adopted in the investigation of TBM tunnels. Tunnel segment is the main bearing structure for TBM tunnels, thus the cracking resistance, the security and durability is highly desired. While due to the large weight, brittle characteristics and low tensile strength of concrete, traditional RC tunnel segments are prone to crack or damaged during production, transportation, installation and service periods. The poor workability of fresh concrete may reduce the effective bond between matrix and reinforcement and the thickness of concrete cover at high dense reinforcement region with increasing reinforcement ratio and local reinforcement. Cracks often appear in tunnel lining under complex loading conditions, which may damage the integrity of lining structure. The security, permeability, serviceability and durability of the tunnel are strongly influenced by such macro cracks.Fiber reinforced high performance self-consolidating concrete (FRHPSCC) has great potential significance of the high workability of high performance self-consolidating concrete (HPSCC) and high toughness of fiber reinforced concrete (FRC). The macro fiber could improve the tensile and flexural behavior of concrete, replace the steel reinforcement partially, enhance the bar spacing and ensure the ductility of concrete structure. At present the investigation on the workability and mechanical behavior of FRHPSCC is still insufficient, and the experimental study on the application of FRHPSCC in tunnel segment is limited. Therefore, the workability of FRHPSCC, flexural behavior and shear behavior of FRHPSCC beams are firstly investigated in this study. Furthermore, symmetric inclination beam is used to investigate the load-carrying capacity and the toughness of tunnel segment. On this basis and funded by the National Natural Science Foundation-The influence of hybrid fibers on the crack and mechanical behavior of tunnel segment (NO.51078058), the mechanical behavior of FRHPSCC tunnel segment is investigated. The details of the investigation in this dissertation are introduced as follows:(1) The workability of fresh concrete mixture is studied using the wildly used methods in the world, slump flow test and J-ring test. Through the workability test and compressive strength test, the proposed mix design produces the concrete that meet satisfactorily the requirement for workability and strength of SFRSCC.(2) According to RILEM recommendation, flexural behavior of SFRSCC is studied. The influence of fiber size and dosage on flexural behavior and toughness is compared. According to the test results, prediction equation for critical fiber contents to achieve deflection hardening behavior in bending is proposed. Based on the load-deflection curves of notched beam, the a-w relationships of SFRSCC with different fiber contents are derived by inverse analysis method. A model based on σ-w relationship and simple principles of mechanics is proposed to predict the load-deflection behavior. The model is shown to be in good agreement with experimental results.(3) In order to eliminate the influence of wall effect of steel fiber on flexural toughness, a new kind of notched panel with a sectional dimension of600mm×100mm is adopted. Reference to Rilem TC162-TDF, the influence of fiber on the flexural toughness of panels are evaluated. Compared with notched beam, the difference of panel and beam test results is analyzed.(4) The influences of concrete strength, fiber content, fiber type, span and load method on the relationship of central span deflection and CMOD are studied. The results indicate that the deflection-CMOD curves have a linear relationship. The concrete strength, fiber content, fiber type do not show an obvious influence on the relationship between CMOD and central deflection for SFRC member with fiber content less than50kg/m3. The span and load method show clear influence on the gradient of CMOD and central deflection relationship. A relationship for modeling of the central span deflection and CMOD relationship has been proposed, the experimental data of panel test agree well with the suggested model.(5) Shear behavior of simply support SFRSCC beams is studied. The influences of steel fibers on load-deflection curve, load-bearing capacity, crack pattern and failure mode are investigated. Shear ductility indexed are defined and the influence of steel fiber on shear ductility is analyzed quantitatively. The results show that steel fiber can reduce the crack width and space in shear span, and enhance the shear capacity, energy absorption capacity and toughness. The addition of50kg/m3steel fiber can change the failure mode of the beam reinforced with constructive reinforced stirrups from brittle shear to ductile flexure. Stirrups cannot totally replaced by steel fiber. The combination of steel fiber and stirrups shows obvious positive hybrid effect, and the amount of stirrups can be reduced by the addition of steel fiber.(6) The influence of steel fibers on the crack pattern, load-deflection relationship and load-tensile reinforcement strain relationship of symmetric inclination beam is investigated. The main parameters are fiber content, stirrup ratio, tensile reinforcement ratio and shear span ratio. The results show that the failure modes of symmetric inclination beams are similar with their simply supported beam counterparts. The axial force of symmetric inclination beam can enhance the load-bearing capacity and decrease the longitudinal reinforcement strain. Inclusion of steel fiber can restrict mid-span deflection and steel strain, improves the energy absorption capacity and tends to change failure mode to more ductile one. The longitudinal reinforcement ratio show obvious influence on load bearing capacity and energy absorption capacity, according to fiber content and stirrup ratio. The constructive reinforced stirrups can be replaced by steel fibers in symmetric inclination beam.(7) An empirical equation is proposed to predict the shear strength of RC beams and steel fiber reinforced RC beams based on the shear transfer mechanisms and the published experimental data of142beams failed in shear mode. The main variables considered are the compressive strength of concrete, longitudinal reinforcement ratio, shear span to depth ratio and fiber factor. A correction factor to account for the effect of axial force on the beam action and arch action of symmetric inclination beam is included in the equation for predicting the shear strength of symmetric inclination beam. It is shown that the equation predicts with adequate accuracy shear strength of symmetric inclination beams.更多还原