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.

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.

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.

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.

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.

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。

钢筋混凝土黏结-滑移行为敏感性分析及机器学习模型

针对钢筋混凝土黏结-滑移行为,利用ABAQUS有限元软件,构建了基于内聚力模型的钢筋混凝土黏结-滑移有限元模型,通过能量和荷载-位移曲线探究了仿真模型网格敏感性以及内聚力参数敏感性。针对钢筋混凝土黏结强度问题,建立基于非线性自回归动态神经网络模型(NARX)的预测模型,以黏结长度、钢筋直径和加载方式为变量,建立20组数据对钢筋的荷载-位移曲线进行了预测。结果表明,当网格尺寸为6 mm时,可以较理想地平衡预测精度与计算成本;有限元预测结果对内聚力参数的敏感性由强到弱依次为损伤起始强度、断裂能和刚度;所建立的NARX预测精度达到99.6%,有潜力代替量大且耗时的数值模拟和物理试验,实现对钢筋混凝土黏结强度的高效准确预测,为钢筋混凝土黏结强度的预测和设计提供新的便捷途径。

共混GAP基含能热塑性弹性体的氢键行为与力学性能

为了改善GAP热塑性弹性体的力学性能,采用了DSC、低场核磁测试、静态力学测试和动态力学测试的方法对两种异氰酸酯固化的弹性体共混体系的氢键行为和力学性能进行分析,建立微观结构与宏观性能的关系。结果表明,由于分子结构原因,HMDI固化的GAP热塑性弹性体和IPDI固化的弹性体显示出不同的氢键行为和力学性能,通过物理共混得到了兼具抗拉强度及断裂延伸率的弹性体,50℃下抗拉强度高于1.5MPa,-40℃下延伸率不低于300%,相较于纯HMDI固化的弹性体,低温延伸率提升了约150%,IPDI固化的弹性体高温抗拉强度提升了约1.4MPa,说明通过共混可得到性能更为均衡的含能热塑性弹性体。

往复荷载作用下锈蚀钢筋与混凝土黏结性能研究

采用梁式试件进行25次往复荷载(25%、45%和65%极限荷载)作用下锈蚀钢筋(理论锈蚀率为2%、4%和6%)混凝土间黏结性能试验研究。结果表明:钢筋混凝土梁式试件均发生劈裂破坏;钢筋混凝土间的滑移在前十个往复荷载循环周期内基本完成,而后试件加载前后滑移差逐渐缩小,滑移量基本不再增加;在试件所受荷载等级一定时,试件加载端与自由端钢筋混凝土间的滑移随着锈蚀率增加而增大;而控制纵筋的锈蚀率不变,试件纵筋与混凝土之间自由端和加载端的滑移量随着荷载等级的提高而增加明显;往复荷载等级对于试件滑移量的影响较钢筋锈蚀相比更加明显。

Differential bonding behaviors of sodium/potassium-ion storage in sawdust waste carbon derivatives

Sodium-ion batteries(SIBs) and potassium-ion batteries(PIBs) are the most promising alternatives to lithium-ion batteries, and thus have drawn intensive research attention. Porous carbon materials from different precursors have been widely used as anode materials owing to their compatible storage effectiveness of both larger radii sodium and potassium ions. However, the differential bonding behaviors of Na and K ions with porous carbon-based anode are the significant one worth investigating, which could provide a clean picture of alkali ions storage mechanism. Therefore, in this work, we prepare a porous carbon network derived from sawdust(SDC) wastes, to further analyze the differences on sodium and potassium ions storage behaviors in terms of bond-forming process. It is found that, as-prepared SDC anodes could deliver stable sodium and potassium storage capacities, however, there are notable distinctions in terms of electrochemical behaviors and diffusion processes. By virtue of ex-situ XRD and Raman spectroscopy, the phase transition reaction of potassium ions could be well-observed, and the results shows that the multiple intercalated compounds was formed in SDC network during ions insertion, further resulting in slower diffusion kinetics and larger resistance compared to non-bonded process of sodium ions storage. This study provides more insights into the differences between sodium and potassium ions storage, as well as the energy storage mechanism of porous carbon as anodes for secondary batteries.

机构投资者交易与债券收益率——基于银行间债券市场的理论与实证研究

本文基于中国银行间债券市场的日度交易数据,构建以订单流为基础的交易指标,通过包含公开信息和私有信息的债券定价模型以及时间序列聚类的投资组合分析和多种模型分析,对各类机构投资者预测债券收益率变化的能力进行研究。研究发现,在银行间债券市场,保险机构、公募基金、私募基金和境外机构的交易能够预测债券收益率的变化,但在交易券种(国债、政策性银行债)、预测期限、预测能力来源等方面均存在显著差异。本文还对机构投资者的预测能力进行了机制检验。研究发现,在境内机构投资者中,公募基金具备更强的交易预测能力和信息获取与解读能力;境外机构投资者对宏观货币政策信息具有更强的预测能力。本文的研究结果表明,在我国银行间债券市场,机构投资者的交易有助于促进价格发现,增加债券收益率的信息含量,从而提升市场有效性。最后,本文基于实证结果提出相关政策建议。

钢纤维掺量对变形钢筋与超高性能混凝土黏结性能影响

为研究钢纤维掺量对变形钢筋与超高性能混凝土(UHPC)黏结性能的影响,设计、制作了6组18个中心拔出试件,钢纤维体积掺量为0%~5%,室外养护28 d后进行中心拔出试验,观察试件的破坏形态、黏结应力-滑移曲线、最大黏结强度及其对应的滑移等。试验结果表明:随着纤维掺量的增加试件的破坏形态从脆性破坏转变为韧性破坏;纤维掺量对黏结强度影响不大,各组黏结强度均处于60 MPa左右,峰值滑移随着纤维掺量增加而增大;纤维掺量为3%时黏结强度最大,黏结应力-滑移曲线下降段最平缓,韧性最大。建立了黏结强度与抗压强度之间的关系;建议直径16 mm的HRB500型钢筋,在UHPC中最小锚固长度试验值取2.5d;最后给出了黏结应力-滑移曲线上升段计算模型。试验结果可为UHPC材料的工程应用提供参考。

计划行为理论视角下微信用户选择性信息规避行为影响因素研究

[目的/意义]探索微信用户选择性信息规避行为的影响因素,为社交媒体平台设置优化、用户自我调节及成瘾预防法规的完善提供实践启示。[方法/过程]基于计划行为理论,分析与归纳微信用户选择性信息规避行为特征,利用PLS-SEM结构方程模型方法对其影响路径进行实证检验。[局限]未考虑信息类型、推送频率、知识差异及其他外生激励因素的影响。[结果/结论]用户卷入度显著正向影响社会网络联结与心理所有权;社会网络联结显著正向影响心理所有权与信息规避规范;信息规避规范、心理所有权、自我控制能力分别显著正向影响信息规避意向;信息规避意向显著正向影响信息规避行为。

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)A, α = 87.391(5), β = 82.925(5), γ = 81.841(5)°, V = 1204.2(10)A^3, Z = 2, C27H23FN4O5Co, Mr = 561.42, Dc = 1.548 g/cm^3, 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.

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.