Simulation of Corrosion-Induced Cracking of Reinforced Concrete Based on Fracture Phase Field Method

Accurate simulation of the cracking process caused by rust expansion of reinforced concrete(RC)structures plays an intuitive role in revealing the corrosion-induced failure mechanism.Considering the quasi-brittle fracture of concrete,the fracture phase field driven by the compressive-shear term is constructed and added to the traditional brittle fracture phase field model.The rationality of the proposed model is verified by a mixed fracture example under a shear displacement load.Then,the extended fracture phase model is applied to simulate the corrosion-induced cracking process of RC.The cracking patterns caused by non-uniform corrosion expansion are discussed for RC specimens with homogeneous macroscopically or heterogeneous with different polygonal aggregate distributions at the mesoscopic scale.Then,the effects of the protective layer on the crack propagation trajectory and cracking resistance are investigated,illustrating that the cracking angle and cracking resistance increase with the increase of the protective layer thickness,consistent with the experimental observation.Finally,the corrosion-induced cracking process of concrete specimens with large and small spacing rebars is simulated,and the interaction of multiple corrosion cracking is easily influenced by the reinforcement spacing,which increases with the decrease of the steel bar interval.These conclusions play an important role in the design of engineering anti-corrosion measures.The fracture phase field model can provide strong support for the life assessment of RC structures.

Improved Mechanical Properties of Textile Reinforced Concrete Thin Plate

Textile reinforced concrete （TRC） is especially suitable for the thin-walled and light-weight structural elements with a high load-bearing capacity. For this thin element, the concrete cover thickness is an important factor in affecting the mechanical and anti-crack performance. Therefore, the influences of the surface treatment of the textile and mixing polypropylene fiber into the concrete on the properties of the components with different cover thickness were experimentally studied with four-point bending tests. The experimental results show that for the components with the same cover thickness, sticking sand on epoxy resin-impregnated textile and adding short fiber into the concrete are helpful to improve their mechanical performance. The 2-3 mm cover thickness is enough to meet the anchorage requirements of the reinforcement fiber and the component has good crack pattern and mechanical behavior at this condition. Comparison between the calculated and the experimental Values of flexural capacity reveals satisfactory agreement. Finally, based on the calculation model of the crack spacing of reinforced concrete structures, the crack extension of this thin-wall component was qualitatively analyzed and the same results with the experimental were obtained.

Static behavior of semi-rigid thin-walled steel-concrete composite beam-to-column joints with bolted partial-depth flush end plate:experimental study

A new type of semi-rigid thin-walled steel-concrete composite beam-to-column joint has been proposed in this paper.Five semi-rigid composite beam-to-column joint specimens subjected to hogging moments under monotonic loading were tested to study the static behavior of this new type of joint.The main variable parameters for the five joint specimens were the longitudinal reinforcement ratio and the joint type.The experimental results designated that the magnitude of extension of the longitudinal reinforcement is the most important factor that influenced the moment-rotation characteristic of the new type of joint.The concrete slabs could resist 3.8%-19.1% of the total shear load applied to the cross-sections near the beam-to-column connection.The edge stiffened elements,such as the flange of the lipped I-section thin-walled steel beam,were capable of having considerable inelastic deformation capacity although they had comparatively large width-to-thickness ratios.The shear failure of the concrete cantilever edge strip must be taken into account in practical design because it has significant influence on the anchorage of the longitudinal reinforcement in the new type of external joints.

Fracture model for predicting concrete cover-cracking induced by steel corrosion based on interface bond state

Time-to-cracking of the concrete cover induced by the steel corrosion is one of the critical problems faced by engineers, operators and asset managers in making strategies for the maintenance and repairs of reinforced concrete （RC） structures affected by corrosion. In this paper, a theoretical model for predicting the time-to-cracking is derived by assuming the bond between the steel bar and the concrete as a linear combination of perfectly smooth and bonded. The model takes into account the characteristics of existing exiguous flaws and initial cracks in the concrete before the load acting on RC structures. The validity of the proposed model is prehminarily verified by comparing the obtained results with the available experimental results. A remarkable advantage of the proposed method is its apphcation to the prediction of the service life of RC structures, made of the deformed steel bars as well as the round bars. By determining an experimental constant a, which is related to the interface bond state between the steel bar and the concrete, the service life of RC structures can be predicted using the proposed scheme. Analysis of major factors affecting the time-to-cracking demonstrates that the length of the initial crack affects the service life of RC structures significantly. Moreover, the larger cover thickness and the smaller diameter of the steel bar within a certain range are beneficial to prolonging the time-to-cracking.

Function-Integrative Textile Reinforced Concrete Shells

This paper presents the development and technological implementation of textile reinforced concrete (TRC) shells with integrated functions, such as illumination and light control. In that regard the establishment of material, structural and technological foundations along the entire value chain are of central importance: From the light-weight design idea to the demonstrator and reference object, to the technological implementation for the transfer of the research results into practice. The development of the material included the requirement-oriented composition of a high-strength fine grained concrete with an integrated textile reinforcement, such as carbon knitted fabrics. Innovations in formwork solutions provide new possibilities for concrete constructions. So, a bionic optimized shape of the pavilion was developed, realized by four connected TRC-lightweight-shells. The thin-walled TRC-shells were manufactured with a formwork made of glass-fibre reinforced polymer (GFRP). An advantage of the GFRP-formwork is the freedom of design concerning the formwork shape. Moreover, an excellent concrete quality can be achieved, while the production of the precast concrete components is simple and efficient simultaneously. After the production the new TRC-shells were installed and assembled on the campus of TU-Chemnitz. A special feature of the research pavilions are the LED light strips integrated in the shell elements, providing homogeneous illumination.

多物理场下超薄吸波磨耗层微波加热性能研究

微波加热技术在沥青路面除冰中的应用得到了广泛的关注,然而目前多对沥青路面整体进行微波加热增强,从而导致路表加热效率提升缓慢。为了进一步提高沥青路面路表的微波加热性能,采用碳化硅(SiC)微波增强集料制备了一种超薄吸波磨耗层,通过微波加热以及除冰试验分析了超薄吸波磨耗层的微波加热性能以及加热耐久性,确定了超薄吸波磨耗层的最佳厚度。并采用COMSOL Multiphysics有限元软件建立了多物理场沥青混凝土微波加热模型,分析了超薄吸波磨耗层的设置对微波加热过程中电磁场的强度与分布以及温度场的影响。研究结果表明:在2.45 GHz频率的微波加热下,超薄吸波磨耗层具有良好的微波加热性能,10 mm厚的超薄吸波磨耗层的微波加热效率相比于普通沥青混合料以及整体微波增强的沥青混合料提高了4.47倍和1.40倍。SiC稳定的微波吸收性能保证了超薄吸波磨耗层具有良好的微波除冰耐久性,在经过反复的微波加热除冰后超薄吸波磨耗层的除冰时间仍然可以保持在45 s左右。数值仿真模拟结果表明超薄吸波磨耗层较强的微波吸收能力可以局部增强试件表层的电磁场强度,从而使更高的温度分布在试件表层。超薄吸波磨耗层内部的电场强度和磁场强度分别比普通沥青混合料试件提高了50.9%和15.7%。综上可知,超薄吸波磨耗层的设置可以提高沥青路面表面的微波加热性能。

薄壁钢板局部屈曲关键问题研究进展

钢结构以及钢-混凝土组合结构由于其强度高、耗能能力好、施工方便等优异性能,被广泛应用于工程结构中。然而,随着高强度钢材的应用,薄壁钢板呈现薄壁化、宽厚比随着构件截面尺寸的增大而不断增大的趋势,由于工程结构及荷载的复杂性等因素,钢板过早发生局部屈曲的风险不断加大,薄壁钢板的局部屈曲问题凸显,亟待开展系统性深入研究。对薄壁钢板局部屈曲研究的进展进行了概述,分析总结了现有试验研究和理论研究方面存在的局限性,详细介绍了笔者团队近年来聚焦于薄壁钢板局部屈曲关键问题开展的一系列研究工作及成果。

钢筋混凝土薄壁空心高墩塑性铰长度计算方法

针对我国现行抗震设计规范尚未明确给出钢筋混凝土(RC)薄壁空心高墩塑性铰长度计算方法的问题,首先收集整理了既有RC桥墩塑性铰长度计算方法以及试验数据,分析影响塑性铰计算长度的主要因素;同时对实际桥梁工程采用的RC薄壁空心墩构造参数进行统计归纳.在验证有限元建模方法准确性后,采用ABAQUS软件建立了高度为40~120 m的8种典型RC薄壁空心高墩的精细化有限元模型,并开展非线性推覆分析,得到不同高度桥墩的等效塑性铰长度.最后讨论不同塑性铰长度计算方法的适用性,发现Eurocode 8规范的计算公式精度最高,可用于计算RC薄壁空心高墩的塑性铰长度.

薄壁型钢混凝土梁抗弯性能试验研究

为研究薄壁型钢混凝土(thin-walled steel reinforced concrete,TSRC)梁试件的抗弯性能,设计制作了5根TSRC梁并进行四点弯曲试验,探究不同抗剪螺杆布置方式、截面形式、剪跨比以及混凝土保护层厚度对TSRC梁试件抗弯性能的影响。研究结果表明:TSRC梁的失效模式为薄壁钢管加载点处发生局部屈曲,外围混凝土保护层出现贯通斜裂缝,混凝土保护层沿抗剪螺杆开裂;TSRC梁试件在加载过程中未发生脆性破坏,表现出较好的延性;TSRC梁开裂荷载较小,在0.11P_(u)~0.15P_(u)之间,裂缝总数较少,稳定在6~10条;满跨布置螺杆、增大钢管截面尺寸、减小剪跨比以及增加保护层厚度均可提高TSRC梁试件的承载力。基于试验结果,建立适用于TSRC梁的极限抗弯承载力和抗弯刚度计算公式,可为该构件在实际工程中的应用提供参考。

新型粉煤灰泡沫混凝土墙体轴心受压性能试验研究

利用工业固废粉煤灰制备节能与承重一体的新型墙体,对无冷弯薄壁C型钢外包内置钢丝网片固废粉煤灰泡沫混凝土墙体FW、外包1mm厚冷弯薄壁C型钢内置钢丝网片固废粉煤灰泡沫混凝土墙体CW1、外包2mm厚冷弯薄壁C型钢内置钢丝网片固废粉煤灰泡沫混凝土墙体CW2分别在轴压作用下的破坏形态、荷载-位移曲线及墙体极限承载力进行试验研究。研究结果表明:从破坏形态度角度,FW、CW1及CW2在破坏时,冷拔钢丝、冷弯薄壁C型钢发生屈服,泡沫混凝土破裂;FW大面积泡沫混凝土挤压破碎剥落,破坏严重;CW2破坏时完整性优于FW、CW1。从变形角度,CW1、CW2外包的C型钢能够对墙体内部的泡沫混凝土起到约束作用,墙体的刚度得到提升。从承载力角度,CW2较CW1提升了17.4%,较FW提升了23.7%。对墙体的轴压承载力进行理论计算,与墙体轴心受压试验的实测值相比,二者误差在10%以内且小于实测值,满足国家现行规范、行业技术标准相关要求。

预应力薄壁圆钢管约束混凝土短柱轴压性能初探

为提高薄壁钢管混凝土柱轴心受压性能,提出了预应力薄壁圆钢管约束混凝土柱,即采用对拉螺栓对薄壁圆钢管施加环向预应力,形成对内部混凝土初始约束围压,以提高内部混凝土的轴心抗压强度及承载力性能。为探究其轴向受压性能提升效果,进行了预应力薄壁圆钢管约束混凝土短柱轴心受压试验;并采用ABAQUS有限元计算软件建立了相应的非线性有限元数值模型,基于试验所获得荷载-位移数据,验证了模型的可靠性。在合理可靠试验模型的基础上,进行了不同预应力度(k=0、0.1、0.2、0.3、0.4和0.5)和不同钢管厚度(t=1.5mm、2.0mm、2.5mm和3.0mm)情况下的轴心受压性能影响分析。结果表明:采用对拉螺栓对薄壁圆钢管混凝土柱施加环向预应力,可有效提高其轴心抗压强度、刚度和延性;在合适预应力范围内,预应力度(k=0~0.4)越大,预应力薄壁钢约束混凝土短柱轴心受压性能提升越明显;但较大的预应力度(k=0.5)会让构件在达到峰值荷载后,其承载力降低较为明显,从而使构件延性降低;当预应力度k不变,构件的轴心受压性能随钢管厚度t的增大而增大。

薄壁墙式墩结构装配式方案及其抗震性能分析

针对既有柱式墩预制拼装技术难以应用于截面横纵比大的薄壁墙式墩的问题,提出了一种节段水平并联的新型装配式桥墩结构方案,预制节段采用双向无黏结预应力筋、灌浆套筒及混凝土剪力榫混合连接.依托某国际机场飞机荷载宽幅桥梁工程实例,基于ABAQUS平台分别建立了新型装配式桥墩和现浇桥墩的精细化有限元模型,通过拟静力分析对比研究了2种桥墩抗震性能的差异,并讨论了预应力筋配筋率以及剪力榫埋深对新型装配式桥墩抗震性能的影响规律.结果表明:新型装配式桥墩与现浇桥墩在纵向水平荷载作用下呈现墩底塑性铰充分发展的弯曲破坏形态,而在横向水平荷载作用下则呈现弯剪破坏形态;相较于现浇桥墩,装配式桥墩纵桥向与横桥向水平承载力分别提高68.5%和43.0%,但残余位移分别降低49.2%和67.8%;增大竖向预应力筋配筋率可显著提升装配式桥墩的水平承载力,而增加水平向预应力筋配筋率和剪力榫埋深则对限制节段接缝处的相对变形作用明显.

轻钢-混凝土组合梁极限承载力研究

轻钢-混凝土组合梁作为冷弯薄壁型钢结构体系中主要的受力构件,应具备良好的受弯性能以保证竖向荷载的有效传递。参照冷弯薄壁型钢-混凝土组合梁的抗弯试验,建立试验试件有限元分析模型,通过与试验结果对比,验证了有限元建模方法的可靠性。基于验证后的有限元模型,对组合梁跨度、楼盖梁跨高比以及楼盖梁高厚比等关键因素进行了变参数分析。结果表明,跨度影响组合梁的破坏模式是受剪控制或是受弯控制的重要因素。在设计组合梁时,建议通过减小跨度、增加楼盖梁高度和厚度的方式来提高组合梁的极限承载能力。

双层薄壳钢-混组合桥梁钢塔建造线型控制技术

以安阳至罗山高速公路黄河大桥钢塔为例,双层薄壳桥梁钢-混组合塔建造线形控制是较为复杂的过程,需从横断面的分块设计,双层薄壳单元加工的精度控制,塔节段整体组装(预拼装)精度控制,桥位安装线形采用特征点控制,混凝土时间和浇筑量分别予以控制,针对各工序的控制要点,制定行之有效的实施方案,通过该项目的实践,塔壳的线型满足设计要求,为类似结构桥梁钢塔建造线型控制提供借鉴。

单薄混凝土重力坝的静动力特性研究

混凝土重力坝作为挡水建筑物,已广泛应用于水利水电工程中,但对于体型单薄的混凝土重力坝,在运行过程中,特别是地震荷载作用下,容易出现应力集中和滑动失稳现象。该文依托石城子二级电站工程,采用有限元数值模拟方法,对其压力前池末端的单薄混凝土重力坝开展静动力特性研究,并基于有限元分析成果研究重力坝的抗滑稳定性。该研究成果对类似单薄混凝土重力坝工程具有参考价值。

给排水厂站薄壁混凝土结构质量通病及对策研究

近年来,上海市水务重大工程建设体量大、工期紧,部分厂站薄壁混凝土存在局部渗漏、蜂窝麻面、色差明显等质量问题。为更好地贯彻落实水务工程高质量发展要求,通过对在建典型给排水厂站工程进行深入调研,从人、机、料、法、环五要素对构筑物池体薄壁混凝土质量问题产生的原因进行深入剖析,总结薄壁混凝土结构常见的质量问题,提出现场质量技术措施和管理对策。

引江济淮船闸闸首施工期开裂风险与防裂分析

与混凝土坝相比,船闸闸首、泵站类薄壁大体积混凝土结构体型相对较小,但结构型式与受力复杂、约束明显且采用泵送高性能混凝土浇筑,早期混凝土放热量较常态混凝土大且发热快,施工期比大坝更易产生温度裂缝,其防裂设计成为施工质量控制的难点之一。结合在建的引江济淮枞阳船闸上闸首工程,采用三维有限元法仿真分析手段,模拟真实环境、材料、结构、温控措施的影响,分析结构施工期温度场、应力场以及开裂风险,并提出针对性的防裂措施。研究表明,输水廊道、墩墙、空箱及启闭机房周边大体积混凝土等功能性部位为高风险开裂部位,实现控温浇筑、通水冷却以及表面保温的多措并举且差异化控制,能够大大降低其开裂风险,可为引江济淮工程薄壁结构防裂设计提供参考。

高延性混凝土加固薄壁方钢管短柱抗压承载力研究

针对薄壁方钢管短柱承载力较低的问题,提出了通过外包高延性混凝土的加固方式来提高构件的极限抗压承载力和延性。利用有限元分析软件ABAQUS建立了高延性混凝土加固薄壁方钢管短柱有限元模型,对现有材料进行了材性试验,将结果用于有限元建立本构关系中;采用环氧树脂作为黏结剂,分别考虑了在静力加载作用下不同宽厚比(40、48、67)、不同加固厚度(4、8、12 mm)对高延性混凝土加固薄壁方钢管短桩的极限抗压承载力和破坏模态的影响。有限元结果表明:采用高延性混凝土加固后,构件的极限抗压承载力提升效果可达到30%~50%左右,且加固效果随着宽厚比或加固厚度的增大而愈发明显。理论推导出了高延性混凝土加固薄壁方钢管短柱的承载力理论公式,理论公式与有限元误差可控制在10%以内。

钢管柱外包薄壁装饰清水混凝土施工技术

装饰清水混凝土利用混凝土原色,体现建筑物的品质和格调,沉稳大方,但在空间较大的框架结构的公共建筑中,为保障最大限度地利用空间,柱网尺寸较大,很难实现清水混凝土效果,因此,相关问题催生出了在钢管圆柱外包薄壁清水混凝土的施工做法。文中采用钢管柱外侧设置栓钉、混凝土内配置抗裂钢筋的形式,使混凝土与钢结构完美贴合,同时避免了混凝土裂纹的产生,提升了建筑整体格局,产生了良好的社会效益。

基于ANSYS溶蚀作用下薄壁衬砌混凝土裂缝修复

水工薄壁混凝土在外界温度、作用力、长期软水溶蚀等诸多复杂环境的影响下,易出现开裂现象。本研究以某配水工程实例为背景,首先通过现场检测确定输水隧洞薄壁衬砌混凝土裂缝类型,并提出利用环氧材料对最不利裂缝进行修复的方案。然后运用ANSYS对修复方案进行建模分析,并与现场实际修复情况进行对比,验证了对最不利裂缝的修复,可以降低衬砌结构出现应力集中的概率,阻止水的渗透,延长结构实际使用寿命。