Advance in Researches on Bond Behavior for Steel-Corroded Concrete Members

The steel corrosion in concrete is widely reported over the last two to three decades. Much effort has been devoted to researching the causes and mechanisms of reinforcement corrosion and to the questions of durability for concrete structures, but relatively little attention has been devoted to the problem of assessing the effect of bond loss due to corrosion on the structural behavior of corroded elements. From the test results on corroded specimens, the mechanism of degradation in bond behavior between corroded bars and concrete, and the effects of bond loss on structural performances are summarized. Results show that corrosion level, cover depth-W-bar diameter ratio, surface condition of re/nforcement, stirrups, etc. can influence the bond behavior of corroded bars. In addition, the deterioration in bond due to corrosion may induce reduction in bearing capacity, degradation of serviceability, and the loss in ductility for steel-corroded concrete members.

Flexural Bond Behavior of Rebar in Ultra-High Performance Concrete Beams Considering Lap-Splice Length and Cover Depth

This study intends to find out the correlation between the cover depth and the bond characteristics of UHPC through pull-out tests of UHPC specimens with different cover depths and bond tests of rebar using flexural members. In this experimental study, specimens are fabricated with the lap-splice length as test variable in relation with the calculation of the lap-splice length for 180- MPa UHPC. Moreover, specimens are also fabricated with the cover depth as test variable to evaluate the effect of the cover depth on the UHPC flexural members. The load-displacement curves are analyzed for each of these test variables to compute the lap-splice length proposed in the K-UHPC structural design guideline and to evaluate the influence of the cover depth on the flexural members. As a result, the stability of the structural behavior can be significantly enhanced by increasing slightly the cover depth specification of the current UHPC Structure Design Guideline from the maximum value between 1.5 times of rebar diameter and 20 mm to the maximum value between 1.5 times of rebar diameter and 25 mm.

Bond Behavior between Recycled Concrete Containing CDW and Different Types of Steel Bars

The operation of reinforced concrete structures is directly associated with the adhesion between the steel bar and the concrete,which allows the inter­nal forces to be transferred to the reinforcement during the process of load­ing the structural elements.The modification of the concrete composition,with the introduction of recycled aggregate from construction and demoli­tion waste(CDW),affects the steel-concrete interface and can modify the bonding stress,which is also influenced by the type and diameter of the bar used.In this work,the influence of the recycled fine aggregate(RFA)and types of steel bar on the steel-concrete bond was experimentally evaluated using the pullout test.Conventional concrete and recycled concrete,with RFA replacement level of 25%,were produced.Two types of steel rebars(i.e.,plain and deformed)with diameters of 10.0 and 16.0 mm were con­sidered in this paper.The results indicate a reduction in the adhesion stress with the introduction of recycled aggregate,but this trend is influenced by the diameter of the bar used.The use of ribbed bars modifies the stress bon-slip behavior,with an increase in the average bond strength,which is also observed with the reduction of the diameter of the bar.

Influence of layer orientation and interlayer bonding force on the mechanical behavior of shale under Brazilian test conditions

The mechanical behavior of inherently anisotropic shale rocks under Brazilian test conditions are investigated in this study based on experimental studies and numerical simulations. The effects of the weak lamination planes and interlayer bonding force of these layers on the failure strength and fracture patterns are studied systematically. Numerical simulations using particle flow code in two dimensions based on the discrete element method showed a good agreement with the experimental results in the failure strength and fracture patterns. The shale revealed strong anisotropic behavior with the failure strength perpendicular to the lamination plane greater than failure strength parallel to lamination plane. The failure strength of the different interlayer bonding force against the layer orientations changed significantly. Four types of fracture patterns were observed: curved fracture, broken-linear fracture, layeractivated fracture, and central-linear fracture. The observed fracture patterns are either or a combination of tensile and/or shear fractures. Increase in interlayer bonding strength decreased the quantity of micro cracks and this directly led to reduction in the anisotropic behavior. Overall the layer orientation and interlayer bonding force of the shale thus play a very important role in the anisotropic behavior of the shale.

Compressive Behavior of Steel Members Reinforced by Patch Plate with Welding and Bonding

Repair and reinformcement of aged civil steel structures is one of the important issues for maintaining and using them for a long term. For repair and reinforcement of deteriorated civil steel structures due to fatigue and corrosion, patch plate reinforcement is widely applied. Bolting is generally used because of easy quality control and many construction achievements. However, bolting has downsides including holes made and weight increase. Welding is considered to overcome these demerits but in reality the application of welding is unsatisfactory due to the possibility of fatigue crack occurring from the welded part. In this study, a patch plate strengthening system of welded joint assisted with bonding has been proposed. The compressive behaviors of weld-bond jointed specimen were investigated by a series of experiments and FE analysis. It was confirmed that use of welding and bonding was effective to enhance compressive strength of specimen, due to better load-carrying capacity of patch plate compared with sole use of welding.

Reinforcement of Lignin-Based Phenol-Formaldehyde Adhesive with Nano-Crystalline Cellulose (NCC): Curing Behavior and Bonding Property of Plywood

The curing behavior of lignin-based phenol-formaldehyde (LPF) resin with different contents of nano-crystalline cellulose (NCC) was studied by differential scanning calorimetry (DSC) at different heating rates (5, 10 and 20&degC/min) and the bonding property was evaluated by the wet shear strength and wood failure of two-ply plywood panels after soaking in water (48 hours at room temperature and followed by 1-hour boiling). The test results indicated that the NCC content had little influence on the peak temperature, activation energy and the total heat of reaction of LPF resin at 5 and 10&degC/min. But at 20&degC/min, LPF0.00% (LPF resin without NCC) showed the highest total heat of reaction, while LPF0.25% (LPF resin containing 0.25% NCC content) and LPF0.50% (LPF resin containing 0.50% NCC content) gave the lowest value. The wet shear strength was affected by the NCC content to a certain extent. With regard to the results of one-way analysis of variance, the bonding quality could be improved by NCC and the optimum NCC content ranged from 0.25% to 0.50%. The wood failure was also affected by the NCC content, but the trend with respect to NCC content was not clear.

Experimental study about the influence of adhesive stiffness to the bonding strengths of adhesives for ceramic/metal targets

The aim of the investigations presented here was to understand how the stiffness of the adhesive affects the failure of ceramic tiles adhered to metallic backings. The working hypothesis was that varying the adhesive stiffness could have the same effect on the ballistic performance as a variation of the adhesive thickness.Two different projectile/target combinations were utilized for ballistic tests in order to generate extremely different loading conditions. With targets consisting of 6 mm aluminum oxide ceramic and 6 mm aluminum backing, complete penetration occurred in each test with 7.62 mm tungsten carbide core AP ammunition at an impact velocity of 940 m/s. In contrast, with ceramic tiles of 20 mm thickness on 13 mm steel backing,no penetration of the ceramic occurred at the impact of a 7.62 mm ball round at 840 m/s.Four different types of adhesive(high-strength till high-flexible) were tested in both configurations. The elongation of the adhesive layer, the deformation of the metallic backing and the failure of the ceramics were observed by means of a high-speed camera during the projectile/target interaction.The results of the ballistic tests showed that a higher fracture strain caused a larger deformation of the backing compared to adhesives, which exhibit a high tensile strength and low fracture strains.The experimental results indicate that the damage behavior of the ceramic/metal composites depends on the absolute elongation of the adhesive layer. This can be controlled either by the thickness or the stiffness of the bonding layer.

A New Co(Ⅱ) Coordination Polymer Based on a Flexible 1,4-Cyclohexanedicarboxylic Acid: Synthesis, Structure and Thermal Behavior

A new Co（Ⅱ） coordination polymer, [Co（1,4-chdc）（L）（H2O）]n（1）, was synthesized under hydrothermal condition（1,4-H2chdc = 1,4-cyclohexanedicarboxylic acid, L = 2-（4-fluoro-phenyl）-1 H-imidazo[4,5-f][1,10]phenanthroline）. Its crystal structure was determined by single-crystal X-ray diffraction. 1 crystallizes in triclinic, space group P1 with a = 8.790（5）, b = 10.486（5）, c = 13.305（5） ?, α = 87.391（5）, β = 82.925（5）, γ = 81.841（5）o, V = 1204.2（10） ?3, Z = 2, C27H23FN4O5Co, Mr = 561.42, Dc = 1.548 g/cm3, F（000） = 578, μ（Mo Ka） = 0.769 mm-1, R = 0.0415 and wR = 0.1043. In 1, each 1,4-chdc anion bridges two neighboring Co（Ⅱ） atoms to give a chain structure. The L ligands are attached on one side of the chain through chelating the Co（Ⅱ） atoms, and are stacked with those of an adjacent chain through π-π interactions, yielding a double-chain structure. The double-chain structures are linked into a supramolecular layer structure through N–H···O hydrogen-bonding interactions between the adjacent double-chain structures. Moreover, the thermal behavior of 1 was also studied.

Research on the fracture behavior of PBX under static tension

The fracture behavior of polymer-bonded explosive(PBX) seriously affects the safety and reliability of weapon system.The effects of interface debonding and initial meso-damage on the fracture behavior of PBX under quasi-static tension are studied using numerical method.A twodimensional representative volume element(RVE) is established based on Voronoi model in which the component contents could be regulated and the particles are randomly distributed.A nonlinear damage model of polymer matrix relative to matrix depth between particles is constructed.The results show that the simulated strain-stress relation is coincident with experiment data.It is found that interface debonding leads to the nucleation and propagation of meso-cracks,and a main crack approximately perpendicular to the loading direction is generated finally.The interface debonding tends to occur in the interface perpendicular to the loading direction.There seems to be a phenomenon that strain softening and hardening alternatively appear around peak stress of stress and strain curve.It is shown that the initial damages of intragranular and interfacial cracks both decrease the modulus and failure stress,and the main crack tends to propagate toward the initial meso-cracks.

钢筋与混凝土粘结力学性能实验教学设计

该文以增强大学生创新实践能力培养为目标,开展了混凝土结构基本原理课程综合性实验教学研究,设计并实施了钢筋与混凝土的粘结力学性能综合性实验。通过混凝土抗压强度实验、钢筋与混凝土拉拔实验、粘结强度影响因素及钢筋滑移分析等教学内容增强学生对专业知识的理解、掌握及灵活应用,同时提升学生的实践能力及创新能力。实验教学实践表明,该综合性实验教学有效提升了教学效果,学生反馈良好,为高校新工科建设及学生的创新实践能力培养提供了有益参考。

Comparisons of interface microstructure and mechanical behavior between Ti/Al and Ti-6Al-4V/Al bimetallic composites

The microstructure, interface thickness, element distribution and interfacial mechanical behavior of Ti-6Al-4V/Al couples prepared by an insert moulding method were investigated in depth in this paper. Moreover, Ti/Al bonding was also given as a comparison for understanding the interface bonding mechanism. It is shown that there is much thinner compact sub-layer for the interface of the Ti-6Al-4V/Al joint, whose morphology is obviously different from that of the Ti/Al joint. The Ti-6Al-4V/Al interface has been proven to contain a slight content of vanadium. Moreover, both the shear strength and the interface reaction rate of Ti-6Al-4V/Al compound materials are lower than those of the Ti/Al ones.

氯盐环境下UHPC-NC界面黏结性能试验研究

氯盐环境作为一种较为常见的化学侵蚀环境,研究其对超高性能混凝土(ultra-high performance concrete,UHPC)和普通混凝土(normal concrete,NC)界面耐久性能的影响对于UHPC加固混凝土结构和UHPC-NC组合结构的工程应用均具有重大的现实意义.基于此,通过在常规环境以及氯盐环境下的推出试验,获得了干湿循环次数(0次、25次、50次)、氯盐浸泡天数(0 d、50 d、100 d)及界面处理方式(钢丝刷刷毛、高压水射流冲毛、表面缓凝处理)对UHPC-NC界面黏结强度、界面黏结刚度及界面黏结滑移曲线的影响.结果表明:在100 d试验周期内,干湿循环及氯盐浸泡作用造成的界面黏结强度损失率不超过20%;氯盐环境作用时长的增加会导致界面黏结刚度的降低;随着界面粗糙度的增加,UHPC-NC试件的界面黏结强度以及界面黏结刚度均会增加;界面粗糙度的提高有助于界面抗氯盐侵蚀能力的提升.受到界面处理方法的影响,UHPC-NC试件经历干湿循环及氯盐浸泡后,荷载滑移曲线呈现2种不同的形式,分别对应光滑界面(钢丝刷刷毛界面)和其他界面(高压水射流冲毛界面和缓凝剂处理界面).各组试件的黏结滑移曲线在荷载到达峰值前趋于一致;荷载到达峰值后,前者存在荷载骤降段及持荷段,后者则随着滑移量的增加荷载不断降低.根据UHPC-NC黏结滑移曲线特征,提出了黏结滑移建议模型.

Effect of bonding process on the properties of isotropic epoxy resin-bonded Nd-Fe-B magnets

Bonded NdFeB magnets were prepared by compression molding. The effect of preparation technology on their magnetic and mechanical properties was studied through the analysis of density, Br, Hcj, （BH）max, bending strength, and compressive strength of the bonded magnets. The results showed that the magnetic properties decreased with increasing binder content, whereas the mechanical properties increased. Br and （BH）max increased with rising pressure, whereas Hcj decreased. For a fixed mass fraction of the binder, the optimal pressure was 620 MPa and the best thermosetting temperature was 160°C. These conditions made the bonded magnets have the optimal mechanical properties. Scanning electron microscopy （SEM） analyses of the fracture surfaces indicated that the epoxy resin bonded magnets exhibited brittle behavior.

Universal Behavior of Nuclear Fragmentation

We use the bond percolation model to study the multifragrnentation of197Au projectiles interact-ing with Cu target at a bombarding energy of 600 MeV/u.The charge observables and some of their dif-ferential distributions are analyzed.The theoretical results agree well with the experimental data ofALADIN collaboration.This indicates that the percolation model can describe reasonably the universal be-havior of nuclear fragmentation in nucleus-nucleus collisions.

极地低温下混凝土填充GFRP拉挤管黏结性能试验研究

纤维增强聚合物(FRP)管与混凝土之间的界面黏结是二者之间荷载传递的必要条件和共同作用的重要前提.为了探究混凝土填充GFRP管(CFFT)在极地等严寒环境下的黏结性能,在20~-80℃的不同低温条件下,对12个圆形和16个方形CFFT进行了推出试验,得到了GFRP管-混凝土界面的黏结-滑移曲线和典型破坏模式.研究了低温水平(T=20℃、-30℃、-60℃、-80℃)、界面类型(黏砂和未黏砂)、径厚比(D/t=30.0、31.3、37.5、50.0)、截面类型(圆形、方形)和FRP管制造工艺(拉挤成型、纤维缠绕)对黏结性能的影响.试验结果表明:除推出破坏外,部分方形黏砂试件表现为角部开裂;低温改善了GFRP管与混凝土的黏结性能,且20~-60℃温度段对黏结性能的影响强于-60~-80℃温度段;黏砂可显著提高CFFT的界面黏结强度(-60℃下,圆形黏砂试件黏结强度可增加到未黏砂试件的2.18倍,方形黏砂试件黏结强度可增加到未黏砂试件的7.93倍);D/t与黏结强度呈负相关;圆形CFFT的黏结强度高于方形CFFT;拉挤管的黏结强度低于纤维缠绕管,这表明GFRP管-混凝土的界面黏结强度主要受摩擦力(环向约束压力)影响.最后在试验的基础上,提出了CFFT在低温下黏结强度的预测模型.本研究可为CFFT构件在极地低温下的应用提供参考.

Empirical Analysis of Impact of Conversion ofConvertible Bonds on Corporate Performance of Different Industries in China

We apply the methods of principle component analysis (PCA) and Wilcoxon’s signed rank test (WSRT) to study influence of conversion of convertible bonds on corporate performance of different industries in China. In this paper, 33 convertible bonds that were issued by non-financial sectors from 2002 to 2009 in China with the convertible rate more than 50% within a year were selected as a research sample. In order to provide a reference for the parties concerned, the influence of conversion of convertible bonds on corporate performance in different industries was studied from the industrial properties point of review.

隧道支护工字型钢与喷射混凝土粘结滑移性能研究

工字型钢与喷射混凝土的粘结滑移性能对隧道初期支护的协同变形,整体承载能力具有重要影响。该文进行了自然粘结和焊接栓钉两组对照的推出试验,观察试件的破坏特征,获取粘结滑移曲线。在此基础上分析试件的粘结滑移性能,通过函数建立了自然粘结和焊接栓钉试件的粘结滑移本构模型,并提出了特征值的计算公式。试验结果表明:自然粘结试件的破坏模式为纵向劈裂破坏,焊接栓钉试件为拉裂破坏,拉裂缝位置沿栓钉横向排列方向;试件的荷载-裂缝宽度曲线与平均粘结强度-滑移曲线变化规律基本一致,可分为四段:无滑移段、斜线上升段、曲线下降段和水平残余段;在型钢腹板增加栓钉连接件,能有效提高型钢喷射混凝土的特征粘结强度。试验曲线与本构模型曲线对比拟合较高,表明该文提出的本构模型具有较高的精度。研究结果对于隧道工字型钢与喷射混凝土支护结构破坏特征研究及设计提供理论支持。

Numerical Simulation of the Behavior of Cracked Reinforced Concrete Members

Refined non-linear static or dynamic analyses of reinforced concrete structures require the knowledge of the actual force-displacement or bending moment-rotation curves of each structural member, which depend on the crack widths and on the crack pattern, and after all on the slip between concrete and reinforcing steel. For this reason the definition of improved local models taking into account all these local aspects is a fundamental prerequisite for advanced assessment of r.c. structures. A numerical procedure which allows to predict the relative displacement between steel reinforcement and the surrounding concrete in a reinforced concrete element, once assigned the stress in the naked steel bar and the bond-slip law is discussed. The method provides as final outcomes the sequence of crack openings and the individual crack widths, regardless of the particular bond-slip correlation adopted. The proposed procedure is implemented referring to two relevant experimental case studies, demonstrating that it is able to predict satisfactorily actual strain fields and slips along the investigated reinforced concrete elements.

疲劳加载历史对型钢再生混凝土黏结性能的影响

型钢再生混凝土结构既可以实现废弃骨料的再生利用,又具有较高的刚度、承载力及良好的抗震性能,是一种兼顾节能环保与结构性能的新型组合结构。为了研究疲劳加载历史对型钢再生混凝土黏结性能的影响,文章设计了梁式试件,并研制了一种带有球铰的梁式加载装置,先对试件进行了以加载频率和应力水平为关键参数的200万次疲劳加载,而后进行静力加载。试验结果表明:试件最终破坏模式为静力荷载作用下的黏结滑移破坏,证明文章的试件设计和加载方案的有效性。经历疲劳加载后,试件的破坏过程与原静力试验相似;型钢应变和滑移沿锚固长度方向上的分布规律与原静力试验相同,均在荷载上升段呈负指数分布,在荷载下降段呈线性分布;一定范围内,增大应力水平和加载速率,试件剩余承载力降低。