UHTCC/RC复合梁剪切性能试验研究

超高韧性水泥基复合材料(UHTCC)以其多重细密稳态开裂模式在宏观上展现出拉应变硬化特征,具有优异的裂缝控制能力,可用作修补材料。采用UHTCC替代部分受拉区混凝土对有腹筋UHTCC/RC复合梁进行了剪切性能研究。试验变量为UHTCC层厚度。结果表明:不同UHTCC层厚度的UHTCC/RC复合梁,其抗剪承载力均明显高于RC对比梁;即便配置较密集的箍筋,仍然无法阻止界面剥离,但可以避免界面剥离产生的荷载抖降;UHTCC能够限制和分散上层混凝土中的裂缝。最后,给出了UHTCC/RC复合梁在实际应用中的建议。     

Theoretical analysis on bending behavior of functionally graded composite beam crack-controlled by ultrahigh toughness cementitious composites

Ultrahigh toughness cementitious composites (UHTCC) obviously show strain hardening property under tensile or bending loading. The failure pattern of the UHTCC components exhibits multiple fine cracks under uniaxial tensile loading with prominent tensile strain capacity in excess of 3%, with merely 60 μm average crack width even corresponding to the ultimate tensile strain state. The approach adopted is based on the concept of functionally-graded concrete, where part of the concrete, which surrounds the main longitudinal reinforcement in a RC (reinforced concrete) member, is strategically replaced with UHTCC with excellent crack-controlling ability. Investigations on bending behavior of functionally-graded composite beam crack controlled by UHTCC has been carried out, including theo- retical analysis, experimental research on long composite beams without web reinforcement, validation and comparison between experimental and theoretical results, and analysis on crack control. In addition to improving bearing capacity, the results indicate that functionally-graded composite beams using UHTCC has been found to be very effective in preventing corrosion-induced damage compared with RC beams. Therefore, durability and service life of the structure could be enhanced. This paper discusses the development of internal force and crack propagation during loading process, and presents analysis of the internal force in different stages, moment-curvature relationship from loading to damage and calculation of mid-span deflection and ductility index. In the end, the theoretical formulae have been validated by experimental results.     

Experimental investigation and analysis on flexural performance of functionally graded composite beam crack-controlled by ultrahigh toughness cementitious composites

Based on the concept of functionally graded concrete, UHTCC (ultrahigh toughness cementitious composites) material with excellent crack-controlling ability is strategically substituted for part of the concrete, which surrounds the main longitudinal reinforcement in a reinforced concrete member. Investigations on bending behavior of such a functionally graded composite beam crack-controlled by UHTCC (abbreviated as UHTCC-FGC beam) have been carried out. After establishing a theoretical calculation model, the paper discusses the results of four-point bending experiment on long composite beams without web reinforcement, and validates the theoretical formulae through experimental results of UHTCC-FGC beams with different thicknesses of UHTCC layer. Besides improving bearing capacity and saving steel reinforcements, the results indicate that UHTCC-FGC beams can also effectively control the deformation and enhance the ductility of members. At last, the optimal thickness of UHTCC layer in UHTCC-FGC beams has been confirmed, which can not only save materials and improve mechanical performance of members, but also be very effective in preventing corrosion-induced damage and enhancing the durability of members by controlling crack width below 0.05 mm under service conditions. Supported by the Key Program of the National Natural Science Foundation of China (Grant No. 50438010) and the Research and Application Programs of Key Technologies for Major Constructions in the South-North Water Transfer Project Construction in China (Grant No. JGZXJJ2006-13)     

集中荷载作用下后浇UHTCC简支双向混凝土板的试验研究

在既有钢筋混凝土板的受弯面上浇筑一定厚度超高韧性水泥基复合材料(UHTCC)或混凝土材料制成复合板,通过集中荷载作用下简支双向板试验,考察复合板试件的弯曲破坏形态和底面裂缝的走向特征等。试验结果表明,后浇材料有效提高整体构件的承载力和前期刚度。后浇混凝土复合板与对比混凝土板相比较,韧性改善较小,开裂时中心挠度基本没有变化;而UHTCC后浇层的加入,改善混凝土板的整体韧性,开裂时中心挠度与原构件相比最高可提高至235%。并且UHTCC层有效限制受弯底面裂缝的开裂和扩展,延迟有害裂缝的出现,加载过程中没有出现类似于后浇混凝土复合板的脆性破坏。运用非线性三维有限元软件对试验进行数值计算,通过合理的建模和定义材料属性,对试验结果进行分析预测,包括荷载-挠度曲线、受弯底面的挠度分布和应变分布等。分析结果与试验结果基本一致,表明此方法适用于文中复合板件的计算,为采用UHTCC作为保护层或加固层的复合双向板的设计、分析和优化提供分析依据。     

超高韧性水泥基复合材料与既有混凝土黏结性能

通过共256块超高韧性水泥基复合材料(UHTCC)与既有混凝土黏结而成的立方体试件的劈拉和剪切试验,研究了既有混凝土黏结面粗糙度、抗压强度、黏结面干湿状态以及UHTCC浇筑方位等因素对该2种材料黏结劈拉强度、黏结剪切强度的影响.研究表明:在相同浇筑条件下,各种因素对UHTCC与既有混凝土黏结劈拉强度和黏结剪切强度的影响...     

钢筋混凝土中爆炸破坏效应数值模拟分析

超高韧性水泥基复合材料(Ultra-High Toughness Cementitious Composites,UHTCC)具有优异的韧性和吸能效果,采用UHTCC和UHPC材料制成的功能梯度板具有优越的抵抗爆炸冲击性能。为了更好地研究UHTCC材料在爆炸荷载下的损伤规律,设计出性能优良的防护结构,该文利用LS-DYNA软件对UHTCC功能梯度板接触爆炸进行了数值模拟。探讨了靶体材料、炸药量、配筋情况、能量吸收层厚度对结构抗爆性能的影响。研究结果表明,UHTCC功能梯度板可以有效减少爆炸荷载下的开坑、震塌以及靶体损伤,同时吸收更多的爆炸冲击波,从而达到优良的抗爆效果。配置拉结筋并合理设置能量吸收层厚度能有效减少靶体损伤。     

UHTCC三点弯曲梁裂纹扩展的数值模拟研究

为了探究超高韧性水泥基复合材料(简称UHTCC)断裂性能,选取三点弯曲梁作为研究对象,应用ABAQUS软件中的扩展有限元方法(XFEM)分析模块,模拟分析了加载条件下三点弯曲梁的裂纹扩展过程和规律,并进行了UHTCC力学参数敏感性分析。根据数值模拟结果,分析了三点弯曲梁的起裂荷载、失稳最大荷载、起裂韧度、临界等效裂缝长度、失稳断裂韧度等指标。结果表明,数值模拟结果与物理试验结果总体一致,UHTCC比普通混凝土具有很好的抗开裂能力和延性;在弹性模量、抗拉强度、断裂能参数原值的基础上,分别提高30%和降低30%。分析了3个力学参数对三点弯曲梁的起裂荷载、失稳最大荷载及其对应的裂缝张开位移影响程度。参数敏感性分析结果表明,弹性模量愈小,抗拉强度愈大,材料断裂失稳延性愈明显,而断裂能对断裂失稳延展性影响不明显。研究成果为UHTCC的材料设计、推广应用以及相应的结构分析等具有参考价值。     

喷射UHTCC与混凝土界面的Ⅱ型断裂试验研究

使用喷射超高韧性水泥基复合材料(Ultra High Toughness Cementitious Composites,UHTCC)加固和修补水工混凝土结构具有广阔的应用前景。为评估加固效果,采用喷射UHTCC和既有混凝土制备成的两端无切口剪切型断裂复合试件,开展单边加载剪切型断裂试验,测试两种材料的界面剪切型断裂韧度。对既有混凝土表面分别采用高压水枪冲洗、人工凿毛和涂抹界面剂三种不同的处理方法,并对比研究喷射UHTCC和浇筑UHTCC两种施工工艺,探究不同因素对复合试件界面剪切型断裂韧度的影响。试验结果表明:喷射UHTCC与既有混凝土之间黏结性能良好;界面粗糙度对界面剪切型断裂韧度无显著影响;涂抹界面剂会使界面剪切型断裂韧度显著下降;喷射UHTCC制备的复合试件其界面剪切型断裂韧度高于浇筑UHTCC制备的复合试件。喷射UHTCC技术可对水工混凝土结构进行有效的加固和修复。     

纤维水泥基复合材料轴向直接拉伸试验保证措施研究

直接拉伸试验是获得材料单轴拉伸应力-应变曲线的唯一可行方法,初始偏心是影响单轴拉伸试验结果的关键问题。结合外夹式和粘贴式单轴拉伸试验优点,设计上端球铰连接,下端球铰和销钉共同作用的试验装置,此装置能有效消除试件安装时的初始偏心,并具有轻微偏心的自调节功能,适用于具有应变硬化特征的高韧性、高延性、高能量吸收能力的纤维水泥基复合材料的轴向拉伸试验。对不同厚度UHTCC宽板进行轴向拉伸试验,研究其基本力学参数及应力应变特性。     

超高韧性水泥基复合材料加固混凝土三点弯曲梁断裂过程的研究

该文利用超高韧性水泥基复合材料(UFHTCC)所具备的较好的裂缝控制能力、较高的耗能能力、耐腐蚀性以及与混凝土之间良好的粘结性能,将其浇注在混凝土三点弯曲梁的受拉面,对加固后的混凝土三点弯曲梁的断裂过程进行了研究.首先由界面变形一致的假定,忽略了UHTCC未开裂区域的弹性变形,提出了UHTCC总裂缝宽度Wu的确定方法,...