Quasi-plane-hypothesis of strain coordination for RC beams seismically strengthened with externally-bonded or near-surface mounted fiber reinforced plastic

The application of fiber reinforced plastic（FRP）,including carbon FRP and glass FRP,for structural repair and strengthening has grown due to their numerous advantages over conventional materials such as externally bonded reinforcement（EBR） and near-surface mounted（NSM） strengthening techniques.This paper summarizes the results from 21 reinforced concrete beams strengthened with different methods,including externally-bonded and near-surface mounted FRP,to study the strain coordination of the FRP and steel rebar of the RC beam.Since there is relative slipping between the RC beam and the FRP,the strain of the FRP and steel rebar of the RC beam satisfy the quasi-plane-hypothesis;that is,the strain of the longitudinal fiber that parallels the neutral axis of the plated beam within the scope of the effective height（h 0） of the cross section is in direct proportion to the distance from the fiber to the neutral axis.The strain of the FRP and steel rebar satisfies the equation：ε FRP =βε steel,and the value of β is equal to 1.1-1.3 according to the test results.

Mode-I fracture and durability of FRP-concrete bonded interfaces

In this study, a work-of-fracture method using a three-point bend beam （3PBB） specimen, which is commonly used to determine the fracture energy of concrete, was adapted to evaluate the mode-I fracture and durability of fiber-reinforced polymer （FRP） composite-concrete bonded interfaces. Interface fracture properties were evaluated with established data reduction procedures. The proposed test method is primarily for use in evaluating the effects of freeze-thaw （F-T） and wet-dry （W-D） cycles that are the accelerated aging protocols on the mode-I fracture of carbon FRP-concrete bonded interfaces. The results of the mode-I fracture tests of F-T and W-D cycle-conditioned specimens show that both the critical load and fracture energy decrease as the number of cycles increases, and their degradation pattern has a nearly linear relationship with the number of cycles. However, compared with the effect of the F-T cycles, the critical load and fracture energy degrade at a slower rate with W-D cycles, which suggests that F-T cyclic conditioning causes more deterioration of carbon fiber-reinforced polymer （CFRP）-concrete bonded interface. After 50 and 100 conditioning cycles, scaling of concrete was observed in all the specimens subjected to F-T cycles, but not in those subjected to W-D cycles. The examination of interface fracture surfaces along the bonded interfaces with varying numbers of F-T and W-D conditioning cycles shows that （1） cohesive failure of CFRP composites is not observed in all fractured surfaces; （2） for the control specimens that have not been exposed to any conditioning cycles, the majority of interface failure is a result of cohesive fracture of concrete （peeling of concrete from the concrete substrate）, which means that the cracks mostly propagate within the concrete; and （3） as the number of F-T or W-D conditioning cycles increases, adhesive failure along the interface begins to emerge and gradually increases. It is thus concluded that the fracture properties （i.e., the critical load and fracture energy） of the bonded interface are controlled primarily by the concrete cohesive fracture before conditioning and by the adhesive interface fracture after many cycles of F-T or W-D conditioning. As demonstrated in this study, a test method using 3PBB specimens combined with a fictitious crack model and experimental conditioning protocols for durability can be used as an effective qualification method to test new hybrid material interface bonds and to evaluate durability-related effects on the interfaces.

Investigation on the Moldability of HDDR NdFeB Bonded Magnet Prepared by Compression Molding Method

The phenomenon of uneven density distribution is inevitable in the process of preparing bonded magnets with complicated shape or with large geometric size by compression molding due to the friction among magnetic powder grains and between magnetic powder and the die wall, which reduces the pressure along the compression direction. In order to improve the density distribution homogeneity, the thin wall rings with composition of HDDR NdFeB prepared by compression molding were selected as the investigated object in this study. It was systematically investigated on the effect of addition level of lubricants and the addition methods of lubricants and strengthener on magnet density, density distribution and on magnet strength. By means of joint addition of lubricants and strengthener, which increases the magnet density and improves the magnet density distribution under the precondition of keeping the magnet strength unreduced. Thus the moldability of the bonded magnets is improved.

Lagged strain of laminates in RC beams strengthened with fiber-reinforced polymer

Based on the theory of concrete structure, a new expression was derived for lagged strain of fiber-reinforced polymer （FLIP） laminates in reinforced concrete （RC） beams strengthened with FRP. The influence of different preloaded states and nonlinear stress-strain relationship of compressed concrete were both taken into account in this approach. Then a simplified expression was given by ignoring tensile resistance of concrete. Comparison of analytical predictions with experimental results indicates satisfactory accuracy of the procedures. The errors are less than 8% and 10% respectively when the tensile resistance of concrete is or not considered. While the maximum error of existing procedures is up to 60%.

Study on Interactive Computer Program for Seismic Appraisal and Seismic Strengthening of R.C. Frame Structures

In many cases, seismic appraisal of existing structures is carried out by the two step method and seismic strengthening of R.C. frame structures is solved just based on rough calculation or experience of designers, which may lead to either lack of safety or too conservative in design. According to some related criteria and experts experience, a computer program is developed specially for seismic appraisal and seismic strengthening of R.C. frames (not more than 10 storeys) in this paper. Because the progra...

Review on Bond Properties between Wood and Fiber Reinforced Polymer

Retrofitting of existing ancient and modern timber structures has been an important project recently.And it triggers a need of excellent strengthening methods,so does the strengthening of newly built architecture.Traditional strengthening methods have shortcomings such as high costing and destroying the aesthetic of the structure,many of which can be overcome by means of using fiber reinforced polymer(FRP)composites.However,the behavior of FRP-towood systems has yet to be thoroughly researched compared with their FRP-toconcrete or FRP-to-steel counterparts.As FRP retrofitting and strengthening timber structures has a promising future,better understanding of their failure modes will enable more precise designs balancing safety and cost.Three of the most common FRP-to-wood systems in the literature are discussed in this paper,namely,the externally bonded reinforcement(EBR),the near-surface mounted(NSM)and the glued-in rods(GiR)techniques.Debonding of the FRP from the substrate is one of the most common failure modes,which exhibits the significance of the interface bond between FRP laminates and wood.Hence,bond properties and behavior of FRP-to-wood composite systems are described,parameters influencing the composite action are summarized in this paper,previous works on the bond interface of FRP and timber element are reviewed and future topics are also suggested.This work can provide a reference for future research and engineering applications.

Experimental research and numerical simulation of RC beams strengthened with bonded steel plates

It is a common method to strengthen the damaged RC structures with bonded steel plates. At present the ultimate bearing ca- pacity of RC structures strengthened with bonded steel plates is calculated mostly using the theory based on the test. Four beams, including one reference beam, two strengthened concrete beams in primary force and secondary force respectively, and one strengthened concrete beam which was not anchored enough, were tested under four-point bending (4PB) in order to get the data of strain of longitudinal bars, bonded bottom steel plate in tension and deflection of beams in the middle span. The experimental program was supported by a three-dimensioned finite analysis using ABAQUS. At the end of experiments and finite analysis, it is concluded that the investing strengthening technique can significantly improve the load-carrying capacity and the phenomenon of stress concentration at the end of interface, as well as the damage at interface, can be well simulated with cohesive element provided by ABAQUS.

CFRP板纵向加固RC柱在水平低周循环荷载下的力学性能研究与应用

开发了一种纵向粘贴CFRP(Carbon Fiber Reinforced Polymer,碳纤维增强复合材料)板的RC(Reinforced Concrete,钢筋混凝土)柱抗弯加固系统,该加固系统由纵向粘贴在柱表面的预制CFRP板和防止柱底CFRP板脱粘的混凝土加厚层组成.为研究纵向粘贴CFRP板对RC柱的抗弯性能影响,设计并开展了5根足尺矩形RC柱的水平低周循环加载试验.研究结果表明:粘贴CFRP板加固能有效延缓柱的开裂;柱的破坏模式得到明显改善;相较于未加固柱子,粘贴1层CFRP板和2层CFRP板加固的RC柱极限承载力分别提高了15.1%和17.4%;加固后柱的抗弯承载力和刚度得到提高,但增加CFRP板的层数对极限强度和刚度没有显著影响,反而会降低柱的延性,相较于仅采用增大柱底截面的方式加固的对照柱,粘贴1层CFRP板和2层CFRP板加固的试验柱的延性系数分别降低16.2%和35.1%;试验过程中,由于柱与基础节点承载力的限制,CFRP的最大应变仅达到极限应变的24%,抗拉强度未得到充分发挥.该加固方法已在某医院加固工程中得到应用,跟踪研究表明,加固后柱子的抗弯承载力有明显提升,加固方法得到工程业界的认可.

湿热环境下外贴CFRP加固RC梁抗弯性能有限元分析

本文研究了湿热环境下外贴CFRP加固RC梁抗弯性能。首先,基于已有的FRP-混凝土界面双参数黏结滑移模型,引入湿度和温度对断裂能G_(f)、界面刚度B的影响系数,建立了湿热环境下界面黏结滑移模型。然后,利用该界面模型对一组湿热条件作用下的试验梁进行有限元数值模拟,将模拟结果与试验结果进行对比分析,验证模型的正确性。最后,使用已验证的有限元模型深入分析不同湿热条件下CFRP与混凝土的宽度比和CFRP的加固量等因素对钢筋混凝土加固梁抗弯性能的影响。结果表明:本文建立的CFRP-混凝土黏结滑移模型,可以有效地模拟湿热环境下的界面性能;湿热条件下的加固梁主要发生剥离破坏,且随着湿热环境恶化,加固梁受弯承载力和对应的挠度明显下降;湿热环境下,可以通过适当增加CFRP与混凝土的宽度比和CFRP的加固量提高加固梁的受弯承载力。

高强韧可重构C―N键交联弹性体的制备与性能

首先以双(甲苯磺酰氧基)丙烷(BTP)为交联剂使丁苯吡橡胶(VPR)交联,生成基于对甲苯磺酸吡啶鎓盐的C―N键交联丁苯吡橡胶(VPR-BTP),然后引入铜离子(Cu2+),制得基于C―N键和Cu2+-吡啶配位键的双重动态键交联弹性体VPR-BTP-Cu。通过红外光谱、X射线光电子能谱仪、动态热机械分析仪、透射电镜等研究了Cu2+含量对VPR-BTP-Cu的结构与性能的影响。结果表明:BTP能够有效交联VPR,VPR-BTP-Cu具有良好的重构能力;同时,Cu2+的引入大幅提高了VPR-BTP的力学性能;当Cu2+的质量分数为9%时,VPR-BRP-Cu的强度和韧性分别比VPR-BTP提高了6.6和6.3倍。此外,VPR-BTP-Cu表现出可重构形状记忆功能。

网络形成体平均键能对化学强化典型盖板玻璃力学性能的影响

探讨了在典型盖板硅酸盐玻璃组分中改变网络形成体的平均键能强度对化学强化后该玻璃的应力特性、抗弯性能和抗冲击性能的影响规律,并分析其影响机理。结果表明,随着Al_(2)O_(3)和/或ZrO_(2)取代SiO_(2)的量的适量增加,玻璃网络形成体的平均键能强度减小,玻璃结构中Na^(+)和K^(+)的迁移更容易,相同化学强化工艺条件下,化学强化后玻璃的离子交换深度增加,表面层压应力下降;然而,化学强化后玻璃内部产生的压应力合力随网络形成体的平均键能强度的减小呈现逐渐增大的趋势,其抗弯性能和抗冲击性能也增强。

Dissimilar-metal bonding of a carbide-dispersion strengthened vanadium alloy for V/Li fusion blanket application

Carbide-dispersion strengthened(CDS)vanadium alloy is a kind of advanced structural material for V/Li fusion blanket.The welding technology for the alloy is very important for its application in fusion reactors.In the present study,preliminary investigation on dissimilar-metal bonding by hot isostatic pressing(HIP)was carried out for the CDS V alloy by joining with the conventional V-4Cr-4Ti alloy.Microstructural characterization for the bonding interfaces and mechanical tests for bonding property evaluation were analyzed for the HIP joint.The results show that after the HIP,the grain size of the V-4Cr-4Ti base metal(BM)obviously increases,while the grain size near the interface is much smaller than that in the V-4Cr-4Ti BM.This is the reason why the hardness near the interface is larger than that of the V-4Cr-4Ti BM.By shear test evaluation,the HIP joint possesses good bonding property with sound strength and ductility.Because there is no phase transformation during HIP,no post-bond heat treatment(PBHT)is necessary for the dissimilar-metal joint.

粘贴钢板加固偏压H型钢长柱承载力试验研究

为了研究粘贴钢板加固对H型钢长柱承载力的影响,以粘贴钢板厚度和施加荷载偏心距为变量,制作了3根未粘贴钢板加固H型钢长柱和6根在翼缘纵向通长粘贴钢板加固的H型钢长柱,加固前后钢柱长细比均大于30,并对其进行压弯试验。通过对试验测得的柱中腹板应变、柱中翼缘应变、柱中侧向位移及试验现象进行分析,研究粘贴钢板加固对于H型钢长柱受力稳定性能的影响。结果表明:未经加固的H型钢长柱稳定性较差,在荷载下降段时发生空间弯扭破坏;经过加固的H型钢长柱试件稳定承载力提升显著,胶层在达到极限承载力之前粘接牢固,在荷载下降段时胶层发生剥离,试件发生平面内整体弯曲失稳破坏;并且在其他条件相同情况下,加固试件的偏心距越小,承载力越高,粘贴钢板厚度越大,承载力提升幅度越大。

CFRP加固钢板在海洋环境下的黏结性能实验研究及数值模拟

海洋环境对碳纤维增强树脂复合材料(CFRP)-钢板的黏结性能有着严重影响。为评估CFRP-钢板黏结界面在海洋环境腐蚀下的黏结强度,采用双搭接接头,开展了5种不同黏结长度试件在NaCl溶液中腐蚀7~21天的实验研究。使用数字图像相关技术(DIC)对CFRP的轴向应变分布进行监测,同时使用扫描电子显微镜(SEM)和能谱仪(EDS)观测CFRP表面微观信息及元素含量的变化。结果表明,随着腐蚀周期的增加,CFRP表面的Na^(+),Cl^(-)元素含量逐渐增加,引起电荷补偿,电解液渗入界面导致自由体积膨胀,从而造成界面黏结强度下降。腐蚀后的试件均发生CFRP-胶层的界面失效,不同黏结长度试件的极限荷载均随腐蚀周期的增加而降低。腐蚀7~14天后,黏结界面的延展性降低;腐蚀21天后界面软化段消失,呈现出明显的脆性破坏特征。基于Fickian理论以及黏结滑移本构参数,建立了CFRP-钢板的有限元模型,分别模拟了海水在黏结界面间的扩散特征及界面Ⅱ型剥离过程,数值结果和实验结果吻合较好。

加劲钢板与混凝土黏结面抗剪性能研究

为研究预应力混凝土梁加固所用的外贴加劲钢板与混凝土黏结面的抗剪性能,开展了钢混黏结面推出试验及有限元分析。通过推出试验测得黏结面的剪力-位移曲线、抗剪强度和破坏形态。对比有、无加劲肋试件的抗剪强度,得出加劲肋对黏结面剪切受力性能的影响。通过参数化分析,得出影响黏结面抗剪性能的关键设计参数。研究结果表明,加劲钢板与混凝土通过A级胶相连的抗剪黏结强度约为2 MPa,极限滑移变形约为0.2 mm,胶黏层与钢板剪切粘结失效为其破坏模式。将黏结强度由2 MPa提高至4 MPa,黏结面抗剪强度提高约38%,提高黏结强度可改善黏结面抗剪性能。加劲肋会增大黏结面的局部剪应力,降低黏结面抗剪强度,加固设计中宜考虑加劲肋对黏结面抗剪强度的削弱作用。

文化润疆视域下篮球思政示范课师资力量及教学质量研究

研究采用文献资料、专家访谈以及实地调研等方法,从文化润疆角度,对篮球课程思政师资力量及教学质量进行研究。研究认为,文化润疆与篮球课程思政建设是相互促进、相互影响的逻辑关系,文化润疆能够对篮球课程思政建设起着重要引导作用。提高师资力量以及教学质量有助于促进立德树人建设、培养高素质人才以及探索篮球课程思政新模式。今后应重点加强师资队伍建设,重视多部门协同联动,构建系统化课程思政教学评价体系。

文化润疆工程下的和若铁路站房建筑设计

铁路站房是地标性建筑,在多种文化汇集的地区,如何将各种文化的主要特点与站房建筑设计相融合是建筑设计的难点。以和若铁路站房建筑设计实践为例,分析其时代风貌与文化内涵相结合的措施,地域文化与现代交通建筑理念相融合的方法,总结出“文润和若”的设计理念。和若铁路站房建设是推进践行文化润疆工程、繁荣建筑创作的具体实践,推动交通建筑与地域特色建筑相结合,可为站房建筑设计提供一定的参考。

Sino-Russian Ties Strengthened by Economic Bonds

The China-Russia strategic partnership has become increasingly successful-intertwined with growing trade and economic ties As the two largest countries on the Eurasian Continent, China and Russia have established stable and coordinated relations through bilat-

异种金属层状复合材料累积叠轧工艺的研究进展

综述了异种材料累积叠轧技术,介绍了累积叠轧的工艺原理及异种材料累积叠轧试样的宏观结构和力学性能研究进展,分析了层状复合材料累积叠轧工艺的复合机理和强化机制,最后展望了异种材料累积叠轧工艺的应用和发展并对进一步的研究提出了建议。

FRP片材与混凝土粘结性能的精细有限元分析

FRP-混凝土界面粘结性能是外贴FRP片材加固混凝土结构技术的关键问题。基于FRP与混凝土界面面内剪切试验,采用精细单元有限元模型对其界面粘结性能进行了研究。在该模型中,混凝土和FRP片材都使用非常小的单元加以模拟,通过调整混凝土材料的本构模型来考虑单元尺寸的影响。FRP单元和混凝土单元直接连接,通过混凝土单元的断裂破坏来模拟FRP和混凝土界面的宏观剥离破坏过程。通过与大量面内剪切试验结果对比,验证了该精细有限元模型的正确性,并基于精细有限元分析结果,对界面剥离破坏机理进行了讨论。