锈蚀钢筋混凝土梁抗剪承载力计算的概率模型

该文针对锈蚀钢筋混凝土（RC）梁抗剪承载力计算的传统确定性模型所存在的缺陷,研究建立了锈蚀RC梁抗剪承载力计算的概率模型。首先综合考虑钢筋锈蚀对箍筋屈服强度、配筋率、配箍率、临界斜裂缝倾角、梁有效抗剪截面积等重要因素的影响,结合修正压力场理论和考虑剪跨比影响的临界斜裂缝倾角模型,建立了锈蚀RC梁抗剪承载力计算的确定性模型;然后综合考虑客观不确定性和主观不确定性的影响,结合贝叶斯理论和马尔科夫链蒙特卡洛（MCMC）法,建立了锈蚀RC梁抗剪承载力计算的概率模型;最后通过与试验数据和传统确定性抗剪承载力计算模型的对比分析,验证了该概率模型的有效性和适用性。分析结果表明,所建立的概率模型不仅可以合理描述锈蚀RC梁抗剪承载力的概率分布特性,而且可以校准传统确定性抗剪承载力模型的计算精度和置信水平,具有良好的有效性和适用性。     

考虑力学机制和不确定性影响的钢筋混凝土柱概率抗剪承载力模型

为了克服传统确定性抗剪承载力模型无法合理考虑不确定性因素影响所存在的缺陷,研究建立了一种能够综合考虑力学机制和不确定性影响的钢筋混凝土（RC）柱概率抗剪承载力模型。首先基于桁架-拱模型,综合考虑混凝土、箍筋和拱作用的抗剪承载力贡献以及不确定性的影响,建立了RC柱概率抗剪承载力模型的解析表达式;然后结合贝叶斯理论和马尔科夫链蒙特卡洛（MCMC）法,确定了概率模型参数的后验分布信息,并分析了概率模型参数的先验分布信息以及更新批次对概率模型参数后验分布的稳定性和收敛性的影响;最后利用试验数据验证了该概率模型的有效性。分析表明,随着试验数据的增加,概率模型参数的后验分布可以实现不断更新;概率抗剪承载力模型不仅可以合理描述抗剪承载力的概率分布特性,而且可以校准分析传统确定性抗剪承载力模型的计算精度。     

一种箍筋约束混凝土峰值应力的概率模型

该文首先基于多轴受力情况下混凝土材料的极限强度面和Willam-Warnke五参数破坏准则,结合144组箍筋约束混凝土棱柱体的试验数据,建立了箍筋约束混凝土峰值应力的确定性模型;然后综合考虑主观不确定性和客观不确定性的影响,结合贝叶斯理论和马尔科夫链蒙特卡洛法,建立了箍筋约束混凝土峰值应力的概率模型;最后通过与试验数据和传统确定性模型的对比分析,验证了该概率模型的有效性和适用性。分析结果表明,该概率模型不仅能够合理描述箍筋约束混凝土峰值应力的概率特性,而且能够校准确定性模型的置信水平和预测精度,还可以确定具有预定置信水平的箍筋约束混凝土峰值应力的概率特征值。     

剪切型钢筋混凝土柱抗剪承载力计算的概率模型

现有的钢筋混凝土（RC）柱抗剪承载力计算模型大多属于确定性模型,难以有效考虑几何尺寸、材料特性和外荷载等因素存在的不确定性,导致计算结果的离散性较大,且计算精度和适用性有限。鉴于此,该文结合变角桁架-拱模型和贝叶斯理论,研究建立了剪切型RC柱抗剪承载力计算的概率模型。首先基于变角桁架-拱模型理论,并考虑轴压力对临界斜裂缝倾角的影响,建立了剪切型RC柱抗剪承载力的确定性修正模型;然后考虑主观不确定性和客观不确定性因素的影响,结合贝叶斯理论和马尔科夫链蒙特卡洛（MCMC）法,建立了剪切型RC柱的概率抗剪承载力计算模型;最后通过与试验数据和现有模型的对比分析,验证了该模型的有效性和实用性。分析结果表明,该模型不仅可以合理描述剪切型RC柱抗剪承载力的概率分布特性,而且可以校准现有确定性计算模型的置信水平,并且可以确定不同置信水平下剪切型RC柱抗剪承载力的特征值。     

钢筋混凝土梁抗剪承载力计算的概率模型

传统的钢筋混凝土（RC）梁抗剪承载力模型属于确定性模型,难以有效考虑几何尺寸、材料特性、边界约束条件等因素存在的客观（物理）不确定性和在模型推导过程中存在的主观（模型）不确定性的影响,导致计算结果的离散性较大,计算精度和适用性有限。鉴于此,该文首先结合修正压力场理论和考虑剪跨比影响的临界斜裂缝倾角模型,建立了RC梁的确定性抗剪承载力模型;然后综合考虑主观不确定性和客观不确定性因素的影响,结合贝叶斯理论和马尔科夫链蒙特卡洛法（MCMC）,建立了RC梁抗剪承载力计算的概率模型;最后通过与试验数据和传统确定性计算模型的对比分析,验证了该模型的有效性和适用性。分析结果表明,所建立的概率模型不仅可以合理地描述RC梁抗剪承载力的概率分布特性,而且可以校准传统确定性计算模型的计算精度和置信水平,还可以根据预定的置信水平确定RC梁抗剪承载力的概率特征值,具有良好的计算精度和适用性。     

锈蚀变形钢筋与混凝土粘结应力模型研究

研究了锈蚀对钢筋混凝土无箍筋试件粘结强度的影响,建立了锈蚀导致保护层胀裂前变形钢筋极限粘结应力的理论计算模型,定量地揭示了该阶段粘结强度增强的机理。通过对钢筋肋间混凝土在挤压力、摩擦力及锈胀力作用下的受力分析,从理论上推导了锈蚀钢筋混凝土发生劈裂破坏时的粘结应力计算表达式;给出了摩擦系数等未知参数的取值大小;详细阐述了表达式的求解思路。利用已发表文献的多个试验结果对理论模型进行验证,结果表明计算值与试验值吻合良好。     

Lattice modelling of corrosion induced cracking and bond in reinforced concrete

A lattice approach is used to describe the mechanical interaction of a corroding reinforcement bar, the surrounding concrete and the interface between steel reinforcement and concrete. The cross-section of the ribbed reinforcement bar is taken to be circular, assuming that the interaction of the ribs and the surrounding concrete can be captured by a cap-plasticity interface model. The expansive corrosion process is represented by an Eigenstrain in the lattice elements forming the interface between concrete and reinforcement. Several pull-out tests with varying degree of corrosion are analysed. The numerical results are compared with experiments reported in the literature. The influence of the properties of concrete are studied. The proposed lattice approach offers insight into corrosion induced cracking and its influence on bond strength.     

考虑粘结滑移的冻融损伤纤维梁柱模型研究

伸入梁柱节点以及柱与基础交界处纵向受力钢筋的粘结滑移效应会显著影响构件的侧向变形。为准确评估冻融损伤后钢筋混凝土(Reinforced Concrete, RC)柱的抗震性能，在考虑冻融损伤不均匀分布的纤维模型基础上，以锚固区的粘结滑移效应为研究对象，首先基于拉拔试验建立可考虑冻融损伤分布的粘结强度退化规律，进而根据简化粘结应力分布假设，通过建立控制方程进行理论推导得到冻融损伤粘结滑移计算方法，并与冻融钢筋混凝土拉拔试验数据进行了对比验证。进而基于有限元分析软件OpenSEES，将该文模型嵌套于零长度截面单元中，提出可综合考虑冻融不均匀损伤与粘结滑移效应的纤维梁柱模型，根据6榀冻融RC柱拟静力加载试验数据进行了验证，并与仅考虑冻融损伤的纤维模型进行了对比。结果表明:与纤维模型计算结果相比，采用该文模型计算所得滞回曲线与试验结果吻合更好，在承载力、极限位移和累积耗能等方面的计算误差较小，表明所建模型可更为准确地反映冻融损伤后RC柱的地震响应。     

考虑钢筋锈蚀的复合受扭混凝土箱梁时变承载力研究

对考虑钢筋锈蚀的复合受扭钢筋混凝土箱梁时变承载力进行研究。针对复合受扭混凝土箱梁中混凝土开裂面与钢筋斜交的情况,推导了综合考虑钢筋混凝土粘结滑移效应及正交配筋效应的钢筋修正本构模型。引入钢筋和混凝土材料的时变劣化模型,结合复合受扭钢筋混凝土箱梁的修正板-桁架模型,编制了复合受扭钢筋混凝土箱梁时变承载力的计算程序。与纯扭锈蚀构件和复合受扭构件的试验对比,验证了所提出钢筋修正本构模型的适用性较好。算例结果表明:在假定的一般大气环境和受力条件下,考虑钢筋锈蚀的复合受扭钢筋混凝土箱梁构件100年后抗扭强度降低约15%。     

Bond strength and effective bond length of FRP sheets/plates bonded to concrete considering the type of adhesive layer

Recent experimental results of the FRP–concrete bonded joint using flexible adhesive showed that the most popular analytical models available in the literature underestimate the bond strength and the effective bond length of these experiments. Most of these existing models need to be modified to consider the type of adhesive layer. Consequently, the bond strength model proposed by Chen and Teng (2001) has been modified to consider the type of adhesive layer. An extensive database consisting of about 100 test results of FRP–concrete joint has been assembled to examine the validity of the proposed model taking the type of adhesive layer into consideration. The modified bond strength model is accurately capable of predicting the bond strength and the effective bond length.     

Influence de la position des armatures sur l’adhérence des bétons autoplaçants: interprétation par analyse d’image

Investigation on bond between self-compacting concrete and reinforcement steel have been carried out by means of pull-out tests for different position of bar luring casting. Five positions were studied: horizontal (superior, inferior and median), vertical (loaded in casting direction or against casting direction). Results show that bond strength was highest for bars cast vertically and loaded against the casting direction and the bond strength, cast in horizontal position, decreases when the depth of concrete beneath the bar increases. The ratio between the bond resistance of bars cast vertically and horizontally was about 1.15. An interpretation, using image analysis, was proposed. In fact, we have observed a satisfying correlation between the bond strength and the difference between the percentage of coarse aggregate above and below the bar for different positions.     

拱坝横缝钢筋与混凝土相互作用研究

本文在总结了钢筋与混凝土相互作用研究现状的基础上，建议了一个计算钢筋滑移量、钢筋粘结受力段长度的数值模型，该模型考虑了混凝土保护层厚度、截面混凝土应力分布的影响，并引用有关试验结果进行验证。文末在假定截面应力分布型态和临界混凝土保护层厚度条件下，将模型用于计算小湾拱坝横缝钢筋的滑移量、钢筋临界应力、钢筋受力段长度，计算结果表明用横缝钢筋控制横缝开度的这一工程措施基本可行，且建议的保护层厚度、横缝钢筋布置等均有一定工程参考价值。     

考虑拉伸刚化效应的FRP筋/混凝土轴拉构件变形计算方法

考虑拉伸刚化效应是精确计算纤维增强树脂复合材料(FRP)筋/混凝土构件变形和裂缝的基础。提出了考虑拉伸刚化效应的FRP筋/混凝土拉伸构件变形计算的解析方法。首先,对修正Eligehausen黏结滑移模型(修正BPE模型)进行简化提出四线性黏结-滑移模型。根据该模型推导了拉伸构件在不同拉伸荷载阶段的FRP筋、混凝土应力和变形及黏结力和滑移量的分布表达式。结合混凝土开裂判别方法,提出了FRP筋/混凝土拉伸构件的全过程变形计算方法。通过与已有文献试验结果对比验证了本文方法的准确性。对影响拉伸刚化的一些参数进行了敏感性分析。结果表明,混凝土强度和配筋率对拉伸刚化效应影响不大,FRP筋弹性模量是影响拉伸刚化效应的主要因素。      

Bond and interfacial properties of reinforcement in self-compacting concrete

This paper reports a study carried out to assess the impact of the use of self-compacting concrete (SCC) on bond and interfacial properties around steel reinforcement in practical concrete element. The pull-out tests were carried out to determine bond strength between reinforcing steel bar and concrete, and the depth-sensing nano-indentation technique was used to evaluate the elastic modulus and micro-strength of the interfacial transition zone (ITZ) around steel reinforcement. The bond and interfacial properties around deformed steel bars in different SCC mixes with strength grades of 35 MPa and 60 MPa (C35, C60) were examined together with those in conventional vibrated reference concrete with the same strength grades.The results showed that the maximum bond strength decreased when the diameter of the steel bar increased from 12 to 20 mm. The normalised bond strengths of the SCC mixes were found to be about 10–40% higher than those of the reference mixes for both bar diameters (12 and 20 mm). The study of the interfacial properties revealed that the elastic modulus and the micro-strength of the ITZ were lower on the bottom side of a horizontal steel bar than on the top side, particularly for the vibrated reference concrete. The difference of ITZ properties between top and bottom side of the horizontal steel bar appeared to be less pronounced for the SCC mixes than for the corresponding reference mixes.     

超高性能RPC钢筋网加固混凝土界面粘结性能试验研究

针对现有混凝土加固技术导致的耐久性弱、承载力低的问题,该文基于活性粉末混凝土钢筋网加固混凝土技术(Technical for strengthening concrete structures with reactive powder concrete and bar mesh, RPCBM),展开了双面剪切试验。该文评估了各试件的抗剪强度、破坏形态与荷载位移曲线,系统性地探讨了粗糙度、植筋率、钢筋网规格对RPCBM加固旧混凝土结构界面剪切性能的影响。结果表明：RPCBM加固混凝土结构的界面抗剪强度和延性提升幅度较大,具有良好的粘结性能。在一定范围内,随着粗糙度增大,粘结界面抗剪强度提高;植筋率增高,抗剪强度与延性增强;钢筋网规格是改善界面延性的重要因素。在此基础上,为了更好地计算RPCBM加固混凝土的界面粘结强度,该文基于以上数据建立了粘结界面抗剪强度的模型,提出了综合计算RPCBM加固普通混凝土(Ordinary Concrete, OC)界面抗剪强度的公式,试验结果与理论分析吻合较好,为工程实践中加固材料的选择和改进施工方法提供了理论依据。     

Steel-to-concrete bond after concrete splitting: constitutive laws and interface deterioration

In a previous paper, bond behaviour after concrete splitting was presented as a relevant aspect of the interaction between the reinforcement and the concrete, in r.c. elements characterized by large steel ratios, small concrete covers, small free bar interspaces and high strength steel. Within this framework, the general philosophy and the experimental set-up of an innovative kind of test were presented, and the results of a three-phase research project regarding pull-out, presplit r.c. specimens were shown and discussed. During each test the opening of the preformed splitting crack was kept constant. In the present paper some of the previous test results are briefly recalled in order to work out empirical constitutive laws regarding bond stiffness, bond strength and bond stress as a function of bar slip and of confinement stress, and tangent friction coefficient as a function of the crack opening. Taking advantage of the special bars used in Phase B tests (where the stresses close to the bar are roughly plane and the deformations of the concrete can be examined at the surface of the specimen by means of the moiré technique), the contribution of microcracking and shear strains to bar slip is analysed, as well as the extension of the deteriorated concrete close to the bar. The formulation of suitable constitutive laws is a first step towards a rational design of the transverse reinforcement (i.e. stirrups in an r.c. beam) while the evaluation of the damaged zone within the concrete mass can help in the modellization by finite elements, since bond-related non-linearity may be limited to narrow bands close to each bar.     

Numerical modeling of the rebar/concrete interface: case of the flat steel rebars

This paper presents the methodology used to identify the mechanical behaviour of a steel-concrete interface in the case of a particular steel reinforcement (flat steel). The methodology consists in simulating the statistical mechanical behaviour of reinforced concrete tie-beams, subjected to tension, using a probabilistic discrete approach for the mechanical behaviour of the concrete under axial tension and a deterministic model for the steel-concrete interface. The model proposed for the interface is in the frame of damage mechanics taking into account physical phenomena related to the interface (cohesion and slip). The tie-beams are reinforced by a flat steel rebar with a rectangular cross section of 25 × 3.5 mm. Results of this numerical simulation have been compared to some experimental tests results. These comparisons are performed in terms of global responses (load-displacement curves) and of local responses (crack openings, number of cracks and cracks’ spacing).     

Bond behaviour of reinforcing bars in self-compacting concrete: experimental determination by using beam tests

The force transfer between concrete and reinforcement depends on the bond characteristics between the two materials. Bond influences crack widths and the deflections of RC members and also determines anchorage and splice lengths. Self-compacting concrete (SCC) is characterized by a smaller amount of coarse aggregates when compared to conventional vibrated concrete. To investigate whether this change in mix design has a significant influence on the bond behaviour, a series of beam tests (according to RILEM recommendation RC6) was performed. A total of 36 specimens were cast using 3 different concrete types: one conventional vibrated concrete (CVC) and two powder-type SCC’s. The bond stress—slip behaviour of reinforcing bars with diameters ranging from 12 to 40 mm has been recorded. From these tests, it can be concluded that the bond strength of SCC is even higher than it is for CVC for small bar diameters, but the difference becomes smaller for larger bar diameters.     

Reliability-based bond design for GFRP-reinforced concrete

Most of proposed models available so far associated with the evaluation of design embedded length of fiber reinforced polymer (FRP) rods in concrete are not reliability-based. This paper made an attempt, from the probabilistic standpoint, to determine the design embedded length of a glass fiber reinforced polymer (GFRP) rod in the case of splitting bond failure from concrete. The mathematical model put forward by Orangun et al. for evaluating the average bond strength of reinforcing bars in concrete for splitting failure has been adopted to develop the nonlinear limit state function corresponding to GFRP’s splitting bond failure in which five independent random variables, i.e. concrete strength, GFRP tensile strength, embedded length, GFRP diameter and computational uncertainty factor, are included. As the result of the probabilistic calibration procedures using the Rackwitz–Fiessler method, a non-dimensional factor K associated closely with the design embedded length of a GFRP rod in concrete is proposed to be 0.0306 with the suggested additional target reliability index of 1.10. The effects of some factors on GFRP’s design embedded length have been identified through the following parametric study. Although the calibration process is case-dependent to some extent, the proposed formula is thought to be acceptable for general bond design purposes of GFRP-reinforced concrete components.     

Mechanical reinforcement of concrete with bi-component fibers

For some applications the reinforcement of concrete with fibers is an economical alternative to conventional steel bar reinforcement. Steel fibers have been the first choice for many years because of their high tensile strength and high elastic modulus. Low modulus fibers, such as polyolefin based fibers generally are thought to be less suitable for this purpose.However, it is shown that polyolefin fibers with sufficient tensile strength can, applying a novel bi-component approach, successfully enhance the mechanical properties of concrete. The effect of the introduction of nanoparticles into the fiber polymers and of a fiber surface structuring on the fiber pull-out characteristics and the fiber–matrix bond strength is presented.The performance of bi-component fiber reinforced concrete is studied in 4-point bending and square slab tests. Ductile post-peak behavior of such fiber reinforced concrete is achieved, making this new fiber technology interesting for applications in pre-cast elements, industrial floors and earth quake protecting systems.