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类型 基础研究 预答辩日期 2018-01-26
开始(开题)日期 2015-09-10 论文结束日期 2017-11-01
地点 逸夫建筑馆1501会议室 论文选题来源 国家自然科学基金项目     论文字数 10 (万字)
题目 基于界面粘结性能多尺度分析的UHPC梁计算方法与试验研究
主题词 超高性能混凝土,多尺度分析,界面粘结性能,细观本构模型,受剪承载力
摘要 超高性能混凝土(Ultra-high performance concrete, UHPC)是通过掺和超细掺合料显著提高混凝土的密实度和抗压强度,采用钢纤维提高其抗拉能力,使其为具备超高抗压强度、较强抗拉强度和优越耐久性能的“新型超级混凝土”。当前,世界范围内已逐步将UHPC材料从接缝、剪力连接件等局部附属部位,开始应用于主承力构件,甚至有部分结构开始全部采用UHPC。各国学者对UHPC的研究逐步深入,材料领域的研究多聚焦于采用颗粒堆积理论和加入纳观微观级颗粒优化配合比、从微细观角度揭示不同骨料及纤维对界面粘结性能和材料力学性能的影响、水化硬化机理和流变性能等;结构领域多借助传统经验方法,通过宏观尺度的构件和结构试验进行结构受弯、受剪、抗震、抗冲击和抗爆等研究,在宏观层面建立相应的设计计算理论。材料研究和结构研究存在脱节现象,突出表现在传统的结构设计理论框架下无法合理利用材料领域关于UHPC纳观、微观、细观研究成果。建立两者联系的核心纽带是各组分对结构构件力学性能贡献从细观到宏观的科学定量及界面粘结滑移问题,其中,钢纤维-UHPC基体界面粘结滑移性能是核心问题之一。本文采用多尺度手段,研究了钢纤维与UHPC基体界面粘结性能(微观-细观尺度),基于细观钢纤维-UHPC基体界面粘结性能建立了结构跨尺度(细观-宏观)受弯受剪理论计算模型,并通过试验对提出的理论模型进行了验证。主要研究内容包括: (1)钢纤维-UHPC基体界面粘结性能试验研究(微观-细观尺度) 以纤维倾角、纤维类型和砂骨料最大粒径为参数,进行了90个钢纤维-UHPC基体界面粘结性能试件的拔出试验;采用扫描电镜对破坏界面微观和细观进行观测,结合宏观现象,归纳出两种宏观破坏模式(纤维拔出和纤维拉断)和三种微观破坏模式(界面过渡区破坏、基体破坏和纤维表面划痕破坏);揭示了平直和端勾两种不同钢纤维拔出过程界面粘结破坏作用机制。 (2)基于细观本构的UHPFRC梁跨尺度受弯计算模型(细观-宏观尺度) 基于细观力学分析,揭示了纤维对残余抗拉强度贡献的机理,提出了考虑界面粘结强度和纤维分布、取向以及埋深的超高性能纤维混凝土(Ultra high performance fiber reinforced concrete, UHPFRC)细观本构模型,为预测UHPFRC残余抗拉强度提供新思路,进而建立了UHPFRC梁跨尺度受弯分析模型和受弯承载力理论计算方法。采用9片受弯试验梁结果对提出的理论进行验证,并对不同作用机制的抗弯贡献比例进行了分析。 (3)UHPFRC梁跨尺度受弯计算模型的试验验证 为验证UHPFRC梁跨尺度受弯计算模型,进行了9片矩形截面UHPFRC模型梁试验研究,试验参数包括纤维率、纵筋率、纤维类型和混凝土强度。试验发现纤维“桥联作用”的失效是一个接着一个的,裂缝呈“多而密”的分布特点;提出了一种以极限挠度与弯曲开裂时挠度比值为表达形式的新延性评价指标;UHPFRC梁跨尺度受弯计算模型可准确预测梁体受力全过程曲线和极限承载力。 (4)UHPFRC梁跨尺度受剪承载力计算模型:纤维-基体分离模型(细观-宏观尺度) 针对如何计算纤维抗剪贡献的核心难点问题,提出了全新的有效纤维抗剪区域(Effective Fiber Distributed Region, EDR)思想,即破坏斜裂缝周围一定宽度内的纤维可提供抗剪。基于概率论或纤维拔出荷载-滑移曲线手段确定EDR宽度,进而得到纤维抗剪贡献,并建立跨尺度(细观-宏观尺度)纤维-基体分离受剪承载力理论计算模型(Mesoscale Fiber-Matrix Discrete Model, MFDM),为预测纤维抗剪贡献提供新的思路。建立的模型可以考虑纤维取向、埋置深度和纤维基体间粘结强度等因素,从细观角度反应了纤维抗剪机理。 (5)UHPFRC梁跨尺度受剪计算模型的试验验证 为验证UHPFRC梁跨尺度受剪计算模型,进行了11片UHPFRC梁受剪试验,研究纤维率、纤维类型、配箍率、剪跨比和混凝土强度等参数对UHPFRC梁受剪承载力、裂后性能和裂后变形能力等的影响。首次定义UHPFRC梁的剪切破坏为半延性-半脆性破坏;提出了以极限挠度与剪切开裂时挠度比值为表达形式的新延性评价指标,并对试验梁裂后变形能力和刚度退化进行了评价;UHPFRC梁跨尺度受剪计算模型可很好地预测试验梁受剪承载力。 (6)基于钢纤维混凝土梁剪切数据库(SFRC-SDB)的受剪计算方法评价 广泛搜集国内外钢纤维混凝土(Steel fiber reinforced concrete, SFRC)梁受剪试验数据,建立总数为941的SFRC梁剪切数据库(Shear database, SDB),对SFRC-SDB进行样本整体研究,分析以往试验研究重点及参数分布情况,基于SFRC-SDB详细探讨受剪承载力随各主要影响因素的变化规律,最后对现行规范和抗剪设计方法进行评价。
英文题目 Experimental and Theoretical Study on Design Method of UHPC Beams Based on Multiscale Analysis of Interfacial Bond Behavior
英文主题词 Ultra-high performance concrete,multiscale analysis,interfacial bond behavior,meso-scale constitutive model,shear strength
英文摘要 Ultra-high performance concrete (UHPC) is a new class of super concrete with ultra-high compressive strength, considerable tensile strength and superior durability, in which superfine active admixture is added to improve the compactness and compressive strength and the steel fibers are dispersed to enhance the tensile strength. UHPC has been gradually applied from ancillary facilities, such as joint and shear connectors, to the main structural component, and it is even totally adopted in some structures. Researches in material engineering field mainly focus on optimizing mix proportion by using particle dense packing theory and with the addition of nanoscale particles, investigating the effect of different aggregates and steel fibers on the interfacial bond behavior and material properties, hydrating and hardening mechanisms, rheological property and so on. In structure engineering field, researchers usually use conventional method to investigate the structural behavior under the bending load, shear load, seismic load, impact load and blast load via testing and to establish corresponding design methods at the macro level. It can be concluded that the material researches and structural studies are out of line, especially the nano-scale, micro-scale and meso-scale research achievements of material engineering cannot be utilized appropriately in conventional structural design theory. The core links are the quantification of the contribution of each component on the mechanical properties of structural components from meso-scale level to macro-scale level and the interfacial bond behavior. The bond behavior between fibers and matrix is one of the critical problems. This dissertation presents an experimental investigation and theoretical study on the bond behavior between steel fibers and matrix (micro-scale to meso-scale), and the cross-scale (meso-scale to macro-scale) flexural analysis model and shear strength model of UHPC beams derived from multi-scale analysis. The proposed theories are verified by the experiment results. Details of the study are summarized as follows: (1) Experimental study on the bond behavior between steel fibers and UHPC matrix (micro-scale to meso-scale) 90 pull-out specimens are tested to investigate the bond behavior between steel fibers and UHPC matrix with the parameters of fiber orientation, fiber type and maximum particle size of sand aggregate. The failure interface is observed using scanning electron microscope at a micro-scale. Two macro-scale failure modes, including fiber rupture and fiber being pulled out are observed and three micro-scale failure modes, incorporating interfacial transition zone failure, matrix failure and fiber surface scratching are identified. (2) Cross-scale flexural model of ultra-high performance fiber reinforced concrete (UHPFRC) beams based on a mesoscale constitutive model (meso-scale to macro-scale) The resistance mechanism of fibers on the residual tensile strength is investigated based on the mesomechanics analysis. A mesoscale constitutive model is proposed, taking into consideration uniform distribution, embedment length and orientation of fibers. The proposed model provides an alternative solution for the determination of UHPFRC residual tensile strength. A flexural strength model is subsequently derived on the basis of the proposed mesoscale constitutive model. The proposed model is verified by 9 bending test results and various machanisms on flexural strength are detailed discussed. (3) Experiment verification on the cross-scale flexural model of UHPFRC beams An experimental study is executed to verify the proposed cross-scale flexural model and to assess the flexural performance of UHPFRC beams with the test parameters of the fiber volume fraction, fiber type, longitudinal reinforcement ratio and concrete strength. The failure of the fiber bridging is one by one fiber and the cracks exibit more and fine distribution characteristics. A new ductility index, expressed in the form of dividing the ultimate deflection by flexural cracking deflection, is introduced to characterize the post-cracking ductility capacity. Calculations with the proposed model show good agreement with the test results and the complete loading response of the test beams can be predicted. (4) Cross-scale shear strength of UHPFRC beams: mesoscale fiber-matrix discrete model (meso-scale to macro-scale) To solve the key problem of determining the shear contribution of fibers, a new concept of an effective fiber distributed region (EDR) along the critical diagonal shear crack, where fibers are efficient at providing shear resistance, is proposed. Two methods to determine the width of EDR are proposed based on probability theory and the pullout load slip relationship. Combining the number of efficient fibers and the bond strength of a single fiber, the shear contribution of fibers is derived. A mesoscale fiber-matrix discrete shear strength model is proposed, which offers an alternative perspective in understanding the shear behavior of UHPFRC beams, especially the shear resistance of fibers at a mesoscale level. The proposed model takes into account the fiber orientation, embedment length and bond strength between the fibers and matrix and can reflect the shear force resistance mechanism of fibers. (5) Experiment verification on the cross-scale shear strength model of UHPFRC beams Eleven T-beams, reinforced with high strength steel, are tested to failure to verify the proposed cross-scale shear strength model and to investigate the effect of shear span to depth ratio, fiber ratio, fiber type, concrete strength and stirrup ratio on the shear behaviour, especially post-cracking shear strength and deformability, of UHPFRC beams. The shear failure of UHPFRC beams is firstly defined as semi-ductile, semi-brittle failure. To characterize the post-cracking shear behavior and stiffness degradation of UHPFRC beams, a new ductility index, which is expressed in the form of dividing ultimate deflection by shear cracking deflection, is introduced. The proposed shear strength model could accurately predict the shear strength of UHPFRC beams. (6) Evaluation of shear strength model based on the shear database for SFRC beams The shear test data of SFRC beams are widely collected from literatures, a shear database for SFRC beams (SFRC-SDB) is established with the total number of 941. Based on the analysis of the samples in the SFRC-SDB, the influence of main factors on shear behavior is investigated and the shear strength models are evaluated.
学术讨论
主办单位时间地点报告人报告主题
课题组 2014.11.21 土木馆203 戚家南 万科UHPC人行桥咨询报告进展
课题组 2014.12.23 土木馆203 戚家南 Shear strength of fiber reinforced reactive powder concrete prestressed girders without stirrups
徐州工程学院 2015.01.05 徐州工程学院 戚家南 混凝土结构受剪性能与计算理论
混凝土结构受剪性能与计算理论 2015.04.07 土木馆203 戚家南 Uplift-Restricted and Slip-Permitted T-Shape Connectors
Uplift-Restricted and Slip-Permitted T-Shape Connectors 2017.02.21 土木馆203 戚家南 高强钢筋-超高性能混凝土梁受剪性能:试验与理论
高强钢筋-超高性能混凝土梁受剪性能:试验与理论 2017.02.28 土木馆203 戚家南 Flexural response of HSS-UHPFRC beams based on a mesoscale constitutive model: experiment and theory
课题组 2017.07.17 土木馆203 戚家南 钢纤维与UHPC基体界面粘结性能试验研究
课题组 2017.10.24 土木馆203 戚家南 基于细观本构模型的UHPFRC梁受弯全过程分析
     
学术会议
会议名称时间地点本人报告本人报告题目
ISISS 2015 2015.07.26 清华大学 Influence of draped tendons on crack distribution and shear capacity of externally prestressed concrete beams
Seminar of the Departement of Civil and Environmental Engineering 2016.10.20 田纳西大学 Shear Strength of UHPFRC Beams: Mesoscale Fiber-Matrix Discrete Model
     
代表作
论文名称
Optimization Method and Experimental Study on the Shear Strength of Externally Prestressed Concrete
体外预应力混凝土梁受剪承载力计算方法研究
Shear Behavior of Externally Prestressed Concrete Beams with Draped Tendons
Shear Strength of UHPFRC Beams Mesoscale Fiber-Matrix Discrete Model
Post-Cracking Shear Strength and Deformability of HSS-UHPFRC Beams
Shear capacity of stud shear connectors with initial damage: Experiment, FEM model and theoretical f
 
答辩委员会组成信息
姓名职称导师类别工作单位是否主席备注
刘加平 正高 教授,长江学者 博导 江苏苏博特新材料有限公司
肖岩 正高 教授,千人,长江学者 博导 南京工业大学
艾军 正高 教授 硕导 南京航空航天大学
孟少平 正高 教授 博导 东南大学
万水 正高 教授 博导 东南大学
宗周红 正高 教授 博导 东南大学
郭力 正高 教授 博导 东南大学
      
答辩秘书信息
姓名职称工作单位备注
贺志启 副高 副教授 东南大学