Experimental study and analysis on fatigue stiffness of RC beams strengthened with CFRP and steel plate

The objective of this work is to investigate the fatigue behavior of reinforced concrete(RC) beams strengthened with externally bonded carbon fiber reinforced polymer(CFRP) and steel plate. An experimental investigation and theoretical analysis were made on the law of deflection development and stiffness degradation, as well as the influence of fatigue load ranges. Test results indicate that the law of three-stage change under fatigue loading is followed by both midspan deflection and permanent deflection, which also have positive correlation with fatigue load amplitude. Fatigue stiffness of composite strengthened beams degrades gradually with the increasing of number of cycles. Based on the experimental results, a theoretical model by effective moment of inertia method is developed for calculating the sectional stiffness of such composite strengthened beams under fatigue loading, and the calculated results are in good agreement with the experimental results.

Properties and strengthening mechanism of brush plated nanoparticle reinforced composite coatings

Nanoparticle reinforced nickel matrix composite coatings, such as n-Al2O3/Ni, n-SiO2/Ni, n-SiC/Ni and n-TiO2/Ni, were fabricated by brush plating technique. Hardness, wear resistance and contact-fatigue resistance of the composite coatings were determined, and strengthening mechanism of the composite coatings was discussed. Results show that the composite coatings have superior properties to the Ni metal coating. Compared with properties of brush plated Ni metal coating, the composite coatings have hardness over 1.5 times and wear resistance capability of about 2.5 times. The strengthening mechanism of the composite coatings mainly includes fine-crystal grain effect, nanoparticle dispersion effect and dislocation effect.

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...

Interface failure of segmental tunnel lining strengthened with steel plates based on fracture mechanics

Segmental tunnel lining strengthened with steel plates is widely used worldwide to provide a permanent strengthening method.Most existing studies assume an ideal steel-concrete interface,ignoring discontinuous deformation characteristics,making it difficult to accurately analyze the strengthened structure’s failure mechanism.In this study,interfacial fracture mechanics of composite material was applied to the segmental tunnel lining strengthened with steel plates,and a numerical three-dimensional solid nonlinear model of the lining structure was established,combining the extended finite element method with a cohesive-zone model to account for the discontinuous deformation characteristics of the interface.The results accurately describe the crack propagation process,and are verified by full-scale testing.Next,dynamic simulations based on the calibrated model were conducted to analyze the sliding failure and cracking of the steel-concrete interface.Lastly,detailed location of the interface bonding failure are further verified by model test.The results show that,the cracking failure and bond failure of the interface are the decisive factors determining the instability and failure of the strengthened structure.The proposed numerical analysis is a major step forward in revealing the interface failure mechanism of strengthened composite material structures.

Experimental Study on Tensile Properties of Steel Plate Bonded by CFRP

The tensile properties of five groups of composite specimens, which consist of steel plate bonded by CFRP,were experimentally researched. The failure types, performing characteristics and failure mechanism of the composite specimens were investigated in detail. The influence of different ratio of CFRP on bearing capacity, loading-strain curves, compound modulus, rigidity and ductility of the composite specimens was analyzed. The experimental results indicate that the composite specimen can work harmonically and the steel plate does not break in tension. Comparing with steel plate, the bearing capacity and the rigidity of the composite specimens increase and ductility decreases. The bearing capacity increases sharply with the increase in the number of layers of CFRP. With the increase in CFRP, the yield strength increases slightly and ductility decreases. The experimental researches can provide a theoretical basis for engineering application of combination strengthening.

Evaluation of straightening capacity of plate roll straightener

Straightening machine is widely used for improving the quality of the defective mild steel plates.In general,the capacity of straightening machine is affected by material properties,the initial shape of the incoming plate and the plastic ratio.The mechanics model describing the capacity of the machine was developed.The deviation of the straightening capacity curves was studied.Then,the presented model was evaluated by comparative study to filed production data.Finally,the influences of overstretch,straightening speed,strengthening coefficient,elastic modulus,width of the plate on the straightening capacity were studied.It is convenient to determine whether the plate can be straightened or not by a series of straightening capacity curves.The straightening speed,width of the plate and elastic modulus of the material are more sensitive to the straightening capacity than the strengthening coefficient.

Characteristics of Paleoproterozoic Subduction System in Western Margin of Yangtze Plate

Paleoproterozoic subduction strongly occurred in the western margin of Yangtze plate. The basalticandesite volcanics of Ailaoshan Group and Dibadu Formation had been formed during paleo QinghaiTibet oceanic plate subduction under the paleoYangtze plate. Their trace element geochemistry suggests that their forming environments are continentalmarginarc and back arcbasin respectively. Consequently, the Paleoproterozoic subduction system in the western margin of Yangtze plate was established. Ailaoshan Group and Dibadu Formation came from an enriched mantle source that was contaminated by crustal sediments carried by subducted slab, and formed the Paleoroterozoic metamorphic basement of western margin of Yangtze plate. Ailaoshan Group is actually western boundary of Yangtze plate.

基于电接触强化的铝合金表面电刷镀镍层改性研究

[目的]对铝合金进行表面处理可提高其硬度和耐磨性,拓宽铝合金材料在机械零件方面的应用。[方法]采用电刷镀技术在1060铝合金表面制备Ni镀层,再通过电接触强化技术对Ni镀层进行改性。采用扫描电子显微镜和维氏硬度计考察了Ni镀层电接触强化前后的微观组织和显微硬度。通过摩擦磨损试验对比了1016铝合金及Ni镀层电接触强化前后的耐磨性。[结果]经电接触强化后,Ni镀层内部的裂纹及孔洞类缺陷减少,晶粒间隙减小,致密性提高,显微硬度增大到524.4~560.3 HV0.1范围内。1016铝合金在摩擦磨损试验后存在较深的犁沟和剥落,耐磨性较差。Ni镀层的耐磨性优于1016铝合金,但在摩擦过程中会发生剥落。经电接触强化的Ni镀层在摩擦过程中摩擦因数平稳,表面只是轻微擦伤,耐磨性最佳。[结论]结合电刷镀镍和电接触强化技术可显著提高铝合金的表面性能。

不同界面下梁端直剪型锚栓钢板剪切承载力试验研究

开展梁端直剪型锚栓钢板剪切承载力加固试验研究。试验序列包含1个对比试验段、5个剪切承载力加固试验段。试验参数包括界面条件和钢板高度。结果表明:受力过程中钢板与混凝土之间的黏结界面终会剥离,不同黏结界面不影响剪切承载力;增加钢板高度和配套的直剪型锚栓数量能有效提高混凝土梁的剪切承载力。直剪型锚栓钢板剪切承载力加固存在2种机制,约束机制通过限制斜裂缝宽度提高剪切承载力,而组合受力机制通过钢板将一部分剪力直接传入支座。加固钢板高度较小时以约束机制为主,加固钢板高度较大时,2种加固机制联合发挥作用。

粘铝合金板加固RC梁抗弯性能试验及正截面承载力

为了探讨铝合金板厚度与端部U形铝合金箍板构造对RC梁破坏机理及抗弯性能的影响,对16根铝合金板加固RC梁进行了4点弯曲静力加载试验。在试验梁底铝合金板的表面以及试验梁跨中截面的顶面、侧面粘贴应变片,在试验梁底跨中、梁顶两端支座布置百分表。为了推导铝合金板加固RC梁的正截面承载力计算式,基于试验得到的破坏机理,通过引入6个基本假定,分析了5种不同破坏模式的相对受压区高度。建立了各破坏模式下铝合金板加固RC梁的正截面承载力计算式,并将其与引入文献中的试验结果进行了对比分析。结果表明:试件破坏形态包括适筋破坏、端部铝合金板与结构胶剥离、端部铝合金板与梁剥离及中部铝合金板剥离4种情况;当端部设置U形铝合金箍板时,可有效抑制端部铝合金板发生剥离,使钢筋与铝合金板的材料性能得到充分发挥,试件承载力与延性明显提升;当铝合金板厚度分别为2~6 mm时,试件承载力随铝合金板厚度的增加而提高;端部设置U形铝合金箍板可有效防止端部铝合金板发生剥离,但试件仍可能会出现中部铝合金板剥离现象;当试件出现适筋破坏特征时,试件抗弯承载力的计算值与试验值比值均在1以下。本研究所提计算式具有明显的规律性和适用性,可为工程实际设计提供参考。

HPC端部加强双钢板组合剪力墙的抗震性能

为研究高性能混凝土端部加强双钢板组合剪力墙受力机理及破坏形态,以轴压比、腹部普通混凝土强度等级为关键参数,设计了4片普通试件,7片HPC端部加强试件,运用ABAQUS构建其有限元模型,研究其抗震性能。结果表明:同轴压比下,HPC端部加强试件相比普通试件屈服荷载提高16.30%,峰值荷载提升13.40%;随着轴压比提高,HPC端部加强试件峰值荷载和屈服荷载分别提高7.22%和2.72%,随着轴压比减小,HPC端部加强试件延性提升22.26%;提高腹部腔体混凝土强度等级,HPC端部加强试件的屈服荷载和峰值荷载分别提高13.01%和11.14%,延性提升16.91%。

钢板-UHPC组合加固损伤RC梁的受弯性能试验研究

为研究钢板-超高性能混凝土组合加固损伤钢筋混凝土梁的受弯性能,对1根RC梁及2根加固梁开展了试验研究,并对其承载力、挠度、应变、裂缝发展情况等进行了分析。结果表明:相较于未加固RC梁,加固梁在抗裂性能、刚度及极限承载力方面有了大幅提升,其中开裂荷载分别提高2.71倍、3.19倍,承载力分别提高了54%、65%,刚度提升近1倍。由于破坏模式均为新老混凝土界面剥离破坏,极限状态下钢板及钢筋均未达到屈服强度,未能充分发挥材料性能,在加固设计中应避免此类破坏的发生。此外,基于桁架模型理论对钢板-UHPC组合加固梁剥离承载力进行了理论推导,建立了理论计算公式。结果表明:基于桁架模型理论建立的剥离承载力公式计算值与试验结果吻合,相对差值在10%以内,此理论模型可靠。

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.

碳纤维板加固H型钢梁抗剥离夹具研制及应用试验

外贴碳纤维板是钢梁抗弯加固的常用方法,但其端部易因界面应力集中导致剥离破坏,严重影响高性能材料的有效利用,特别是结构加固后的安全服役.为此开发出一种适用于H型钢梁的简易夹具——C形槽板夹,以加强碳纤维板的端部锚固.通过多根带夹碳纤维板加固梁的静力加载试验,验证了此夹具的可靠性,并考察了碳纤维板伸入剪跨段长度与剪跨段长度之比及锚固方式(纯粘、端锚和混锚)对加固效果的影响.研究发现端锚加固不同于纯粘,只要梁的控制截面仍在夹具之间,碳纤维板的极限应力、加固效果及利用效率均随其长度缩短而提高,当碳纤维板长度分别为600、750 mm时,前者极限应变和承载力比后者分别高27.3%和8.1%.由于钢梁表面处理质量较差,混锚加固梁均发生突然剥离,后期退化为端锚加固梁,因而相比端锚加固梁加固效果改善不大,需要提高表面处理质量再做类似研究.尽管如此,相比纯粘加固梁,混锚加固梁采用C形槽板夹后剥离破坏被延迟,抗弯性能大为改善.试验过程中还用压电阻抗法对界面剥离情况进行了检测,结果符合实际.

倒角结晶器铜板镀层崩边原因分析及控制

针对倒角结晶器窄面铜板镀层崩边问题,从结晶器传热、铜板结构、镀层性能等角度分析原因,提出采用激光熔覆技术对铜板表面进行强化的解决方案,并开展了工业试验进行验证。研究结果表明:铜板角部温度高、镀层厚度大、镀层与铜板热变形差异大、在线调宽状态下铜板侧面清渣不彻底是影响镀层发生崩边的重要原因。采用激光熔覆技术后,倒角窄面铜板的过钢量由5万t提高到10万t以上,当过钢量达到8.7万t时,熔覆层仍未出现角部崩边、剥落及因磨损过大引起的局部露铜现象。

CFRP板加固既有石楼板抗弯性能试验研究

为改善既有石结构中石楼板的抗弯性能,避免其发生脆性断裂,提出了采用CFRP板加固技术对石楼板进行抗弯加固,并对未加固的素石板和CFRP板加固后的石楼板进行受弯试验,对比不同厚度及宽度CFRP板对石板受弯性能的影响。结果表明:利用CFRP板加固石板能够显著改善石楼板的最终破坏形态,破坏形式由素石板的脆性断裂转变为CFRP板加固后石板的弯曲破坏,CFRP板加固石板在破坏前具有一定的变形能力;CFRP板能够显著提升石楼板的抗弯承载能力,CFRP板加固石板的极限荷载较素石板提升了60.15%~128.59%,且CFRP板的加固效果随着CFRP板的厚度及宽度增大而提高;CFRP板能有效阻碍石楼板板底裂缝的产生,提高了石材的极限拉应变,从而增大石楼板的开裂荷载。受拉区石材的极限拉应变随着CFRP板厚度和宽度的增大,提升了66.92%~187.48%,CFRP板加固石板的开裂荷载较素石板提升了13.33%~54.07%;通过理论计算,建立了CFRP板加固石楼板的受弯承载力计算公式,理论计算结果与试验结果符合较好。

电磁成型工艺对钛合金表面强化性能的影响

为提高TC4钛合金板材表面硬度,用电磁成型工艺,通过改变冲击电压、冲击次数、驱动片等参数对TC4钛合金板材进行试验。用高精度维式硬度计、有限元模拟、数据拟合软件等对试验结果进行分析。结果表明:电磁成型工艺可一定程度强化TC4钛合金表面,经强化处理的TC4钛合金板材,硬度最大为377.2HV,比原始硬度提升了约10.94%。此外,不同试验条件对试验结果的影响不同。冲击电压过大及冲击次数过多都使试件的硬度低于原始试件。

波纹钢加固盖板涵受力机理及影响参数数值研究

为明确波纹钢加固盖板涵的受力机理以及不同设计参数对结构承载力和刚度的影响,本文依托波纹钢加固的跨径4m的盖板涵的实体工程,在考虑原涵洞的二次受力状态以及界面接触属性的基础上,利用两步法建模的方法分析了原涵洞退化程度、界面处理方式、波形参数、填充层强度和厚度等参数对加固后的承载能力、刚度、破坏状态的影响,并分析了波纹钢加固盖板涵的受力体系。结果表明:波纹钢在设计值状态下的应力主要由湿重状态下的混凝土的侧压力产生;利用波纹钢对盖板涵加固后承载能力提高25~85倍,刚度提高26~136倍。结合面的处理方式和混凝土填充层的厚度对承载力和刚度的影响显著,波形参数、混凝土强度对承载力和刚度的影响较小;波纹钢不是承受荷载的主要部件,给结构提供足够的支撑作用,使得结构从单一的盖板破坏转变为多位置的共同破坏,结构的承载力和延性得到明显的提升。

超高性能混凝土板加固足尺钢筋混凝土梁抗剪性能

为进一步研究超高性能混凝土(ultra-high-performance concrete,UHPC)预制板加固钢筋混凝土(reinforced concrete,RC)梁的抗剪性能,开展了3根足尺RC梁的试验研究,包含1根对比梁和2根UHPC预制板加固梁,关注UHPC板及其内嵌CFRP板条对RC梁抗剪性能的影响。试验结果表明:试验梁均发生受剪破坏,但加固梁的承载力、刚度和延性均明显提高,其中,因内嵌CFRP板条提高了UHPC板的抗裂性能,极限荷载及对应位移分别提高了30.8%和28.5%;螺杆力学锚固发挥了侧向约束作用和销栓作用,在一定程度上提高了UHPC板的贡献。同时,通过建立非线性有限元模型对试验梁进行了数值分析,模拟结果与试验结果吻合度高,表明模型所选的本构关系及相关参数合理,可用于预测UHPC板加固RC梁的全过程受力行为。

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.