循环荷载下钢-混结合段性能演化试验研究

为探究特大跨轨道连续刚构桥钢-混结合段在循环荷载作用下的性能演化规律,设计结合段局部1∶2缩尺模型,分别按照设计状态和极限状态施加循环荷载。研究表明：设计荷载循环作用下,每次加载应力-荷载曲线都能够基本重合,且都呈线性关系,说明设计荷载循环作用下结合段的性能基本没有退化。极限荷载循环作用下,每次加载界面粘接均有一定退化,在第6次加载中开裂处混凝土脱空,界面粘接退化严重。前5次加载前段刚度退化不明显,在第6次加载至3 300 kN时,已经退化严重。该文通过对结合段的界面滑移量以及位移量进行分析,研究界面粘接退化以及整体刚度退化,对认识特大跨轨道专用钢-混结合段在偶然极端荷载（如严重超载、地震荷载等）作用下的性能退化规律有很大的参考价值。     

剪切型金属阻尼器恢复力模型研究

剪切型金属阻尼器在新建工程及结构抗震加固工程中已得到了较广泛的应用,其恢复力模型是进行整体结构非线性地震反应分析的基础。为了更准确地描述剪切型金属阻尼器的剪力-变形滞回关系,提出了一种考虑性能退化的新型恢复力模型。通过独立参数控制恢复力模型,以考虑剪切型金属阻尼器在大变形下的强度退化、刚度退化、耗能能力退化等特征。根据所提模型,采用C++语言开发了能够用于剪切型金属阻尼器抗震分析的计算程序,并将其嵌入到结构通用分析软件OpenSees中。使用该模型对现有钢连梁和钢板剪力墙两类剪切型金属阻尼器进行了模拟。结果表明:该文建立的恢复力模型能较准确地模拟试验结果,能够反映剪切型金属阻尼器包括大变形阶段在内的整个变形阶段的滞回性能。该模型可用于安装了剪切型金属阻尼器的整体结构非线性地震反应分析。     

钢管混凝土框架实用荷载-位移恢复力模型研究

根据钢管混凝土柱-钢梁平面框架在恒定轴力与水平低周往复荷载共同作用下的试验结果,分析了钢管混凝土框架典型的水平荷载-水平位移滞回关系曲线的特征。基于非线性有限元理论,对影响钢管混凝土框架荷载-位移骨架曲线的主要因素进行了分析,结果表明:钢管混凝土柱含钢率、钢材强度、混凝土强度、柱轴压比、长细比、梁柱线刚度比及梁柱强度比等参数对钢管混凝土框架的荷载-位移骨架曲线有较大的影响。基于系统的参数分析结果,该文建议了单层钢管混凝土框架的荷载-位移恢复力模型。荷载-位移骨架曲线模型及滞回曲线模型的计算结果得到了试验及精确理论计算结果的验证。     

轴向往复荷载作用下圆钢管混凝土柱恢复力模型研究

为研究钢管混凝土柱的轴向恢复力模型,设计制作了8个钢管混凝土柱试件并对其进行轴向往复加载,分析其受力机理和恢复力特性。基于试验结果,选用退化三线型模型,建立了钢管混凝土柱无量纲骨架曲线模型,并提出其轴拉与轴压方向的峰值承载力和位移的计算方法。鉴于钢管混凝土试件在轴拉与轴压方向受力机理的差异,对滞回曲线的正负向选用不同的滞回规则,建立了相应的卸载刚度函数。据此提出了钢管混凝土柱的轴向恢复力模型,并与试验滞回曲线进行对比,验证了恢复力模型的合理性,所建立的恢复力模型可为斜交网格结构体系的弹塑性分析提供依据。     

考虑土-储罐-液体相互作用的隔震储罐简化力学模型及地震响应研究

为了寻求一种既能减震又能降低成本的储罐结构,提出一种隔震储罐结构体系,根据力的平衡原则推导了滚动隔震装置恢复力模型,得出了复合滚动隔震装置的恢复力模型。基于三质点模型和场地土模型,提出了考虑土-储罐-液体相互作用（STLI）的隔震储罐的简化力学模型和运动方程,并研究了考虑STLI效应和不考虑STLI效应时抗震储罐和隔震储罐在不同场地的地震响应。结果表明：隔震储罐能够有效地降低其基底剪力及倾覆弯矩,但对晃动波高的控制有限,建议在高烈度区,满足晃动波高的前提下,隔震储罐在设计时可以降低烈度。考虑STLI效应后,抗震储罐的基底剪力和倾覆弯矩明显降低,且从Ⅰ类场地到Ⅳ类场地差异率逐渐增大,软土场地降低最为显著。隔震储罐地震响应受STLI效应的影响较小,可以有效地隔断上部结构与场地土之间的耦联,弱化STLI效应对上部结构的影响。     

近海大气环境下锈蚀钢框架梁抗震性能试验及恢复力模型研究

为了研究近海大气环境下锈蚀钢框架梁的抗震性能,对5根钢框架梁进行了近海大气环境加速腐蚀试验和低周反复加载试验,分析了不同锈蚀程度对钢框架梁破坏模式、承载能力、变形能力及耗能能力等的影响。结果表明：随着锈蚀程度的增加,试件底端翼缘屈曲、腹板鼓曲及塑性铰形成所对应的位移逐渐减小;试件承载力及延性显著降低,强度和刚度退化明显,耗能变差。在试验研究的基础上,引入循环退化指数,建立了能够反应强度、刚度循环退化效应的锈蚀钢框架梁恢复力模型;并与试验滞回曲线进行对比,两者吻合较好,验证了该恢复力模型的适用性。研究成果为近海大气环境下在役钢结构的抗震性能评估奠定了试验与理论基础。     

循环荷载作用下粉砂岩疲劳流变损伤模型研究

针对现有流变模型难以有效描述循环荷载作用下岩石变形及疲劳损伤演化特征等问题,开展了粉砂岩循环加卸载试验,分析了不同上限荷载下岩石的流变规律与疲劳特性。基于Kachanov蠕变损伤理论建立损伤变量,引入一个带应变触发和应力阈值的黏塑性元件,与Burgers模型串联构建循环荷载作用下岩石疲劳流变损伤模型;将正弦波应力函数替换流变微分本构方程中的恒定应力,推导岩石在循环荷载下的一维、三维微分型损伤本构方程,再根据叠加原理得到模型的黏弹塑性流变损伤方程。适用性验证表明,新建模型不仅可以精确地反映循环加卸载过程中粉砂岩的衰减、稳态流变阶段,还可以有效地描述上限荷载高于疲劳强度时的加速流变阶段。通过粉砂岩疲劳损伤流变全过程定量化分析,提出加速流变阶段的临界损伤阈值和破坏失稳判据,并给出加速流变阶段的启始时间、持续时间及疲劳寿命预测方法,模型对岩体工程长期稳定性评价具有一定的理论指导意义。     

PVC-CFRP管混凝土柱-钢筋混凝土环梁T型节点拟静力试验与弯矩-曲率恢复力模型研究

开展11根PVC-CFRP管钢筋混凝土柱-钢筋混凝土环梁T型节点低周反复加载试验,分析环梁尺寸、环筋配筋率、CFRP条带间距、梁纵筋配筋率、轴压比等因素对其破坏形态、滞回性能、骨架曲线等影响。结果表明：节点破坏经历初裂、通裂、极限和破坏四个阶段,节点的弯矩-曲率滞回曲线包括弹性段、弹塑性段和平稳段,节点滞回环饱满,显示出良好的抗震性能。基于软化混凝土本构关系模型,考虑各因素对骨架曲线特征点的影响,提出骨架曲线特征点简化计算公式。基于退化三线型恢复力模型,给出卸载刚度计算公式,提出节点滞回规则,建立预测精度较高的环梁节点弯矩-曲率恢复力模型。     

结构钢材循环荷载下的本构模型研究

在抗震分析中,钢材在循环荷载下的一维本构模型是结构抗震设计时进行结构弹塑性地震响应分析的基础.为了更为准确地模拟结构的地震反应,并能够在实际工程中应用,该文提出了结构钢材Q235B、Q345B 在循环荷载下的单轴简化本构模型,其中包括：单调加载曲线、循环骨架曲线以及滞回准则,通过建立数学模型对钢材循环荷载作用下的反应进行描述.根据提出的模型并基于大型通用有限元软件ABAQUS 提供的用户子程序接口UMAT,开发了适用于结构分析的钢材单轴循环本构模型.通过与多种加载制度下钢材反应的试验数据进行对比,进而证明该文所提出模型的正确性以及适用性,保证其用于钢结构体系在地震作用下弹塑性时程分析时的精度和可行性.分析结果表明：钢材在循环荷载下的反应与在单调荷载下的反应有很大的差别,循环荷载下的骨架曲线对于准确的数值模拟起到重要作用;钢材在循环荷载下的滞回准则也与现通用有限元软件中的本构模型有较大区别,这对于抗震计算设计的准确性有一定的影响.     

金属橡胶材料恢复力的三维模型

以大量试验数据分析为基础,提出了一种构建金属橡胶弹性恢复力三维模型的方法。通过对试验数据插值拟合处理与理论分析的方法,得到了恢复力关于位移和速度的二元解析方程,认为恢复力由线性正刚度弹性力、非线性阻尼力和与速度平方有关的非线性负刚度弹性力三部分组成,并对这三部分的实际物理意义进行了分析。试验结果表明,本模型对金属橡胶弹性恢复力的表述更加直观,分析更加准确,克服了现有模型简单和参数辨识复杂的缺点。     

考虑损伤效应的弯曲破坏型腐蚀RC柱恢复力模型

出于氯盐腐蚀钢筋混凝土（reinforced concrete,RC）结构弹塑性分析的需要,对6根RC框架柱试件进行加速腐蚀试验,而后进行拟静力试验,观察人工气候环境下锈蚀钢筋的表观损伤,并分析不同腐蚀程度和轴压比对RC框架柱破坏形态和抗震性能的影响。在此基础上,引入双参数损伤模型,确定模型参数取值,进而定量化揭示腐蚀RC框架柱损伤发展规律。此外,通过理论分析与试验回归相结合的方法,建立考虑腐蚀与轴压比影响的RC框架柱骨架曲线模型。引入基于损伤的循环退化指数,提出能够反映加载、卸载、再加载、下降四阶段性能退化的滞回规则,进而建立弯曲破坏型腐蚀RC框架柱恢复力模型,并验证其有效性。结果表明,骨架曲线计算值与试验值误差总体在10%以内,累积耗能计算值与试验值误差总体不超过20%;由于计算再加载曲线线性特征,再加载阶段与试验结果存在一定误差,但滞回曲线整体上吻合较好、误差较小,说明建立的恢复力模型能够较为准确地反映弯曲破坏型腐蚀RC框架柱抗震性能。     

Modelling the compression behavior of ground tire rubber

The purpose of this paper was to study elastomer powder from crushed used tires (CUTs). In particular, the behavior of the green density of elastomeric powder was analyzed by varying compaction pressure. In the Anglo‐saxon bibliography, this powder is known as ground tire rubber: ground tire rubber (GTR). The density of the tyre was made using a hydrostatic balance, the analysis of grain size using cribbing sieves, and the measures of compression parameters by means of a Universal Testing Machine. The main goal was to obtain a behavior model of ground tire rubber along different compaction pressures. This model was used to predict optimum compaction pressures in order to achieve the highest density. This was the first step to obtain recycled products when sintering processes are applied, evidently if thermal compression was used as a manufacturing process. This established model predicted the evolution of green density versus compaction pressures very accurately.     

The use of deconstructed tire rail pads in railroad tracks: Impact of pad thickness

Deconstructed end-of-life tires are an abundant waste material that can be used to manufacture rail pads. Since tire layers are deconstructed, there is no need to shred and grind them up, which has the advantage of reducing economic costs as well as environmental impacts. However, the mechanical performance of this material can be affected by various design parameters, particularly, the thickness of the rail pad. This research study assessed the impact of thickness on the mechanical performance of deconstructed tire rail pad when subjected to loads simulating the passing of trains. The objective was to produce rail pads specifically designed for railway systems of various types and demands. Accordingly, the static and dynamic response was evaluated as well as the fatigue strength of rail pads of different thicknesses. In this sense, thicker rail pads were found to be more flexible and with a greater capacity to damp loads. The results of the study showed that for high-speed railways, the most suitable rail pads were those with a thickness of 7.5–9.0 mm, whereas pads with a lesser thickness were more suitable for conventional railroad tracks.     

Sound insulation property of wood–waste tire rubber composite

The sound insulation property of wood/used tire rubber composite panel (WRCP) was investigated. A four-microphone method was used to measure the sound transmission losses of three different composite panels: WRCP, commercial compound wooden floorboard and commercial wood-based particleboard. The WRCP was manufactured in the lab with commercial urea–formaldehyde (UF) and polymeric methylene diphenyl diisocyanate (PMDI) adhesives. The test results indicated that sound insulation property of WRCP is better than that of commercial compound wooden floorboard and wood-based particleboard. In addition, the acoustic insulation of WRCP is significantly affected by the amount of rubber crumbs and PMDI adhesive used in the composite. An increase in the usage of recycled tire rubber crumbs and the dosage of PMDI adhesive significantly improve the soundproof property of the WRCP. Moreover, the microstructure of WRCP was examined using a scanning electron microscope (SEM). The sound insulation effect is also dependant on the microstructure of the interface zone of wood/rubber and densification of WRCP. The continuous interfaces are formed in the presence of sufficient UF and PMDI adhesives resulted in better soundproof WRCP.     

UV modification of tire rubber for use in cementitious composites

The use of recycled rubber as a possible aggregate in concrete is known to result in a reduction of compressive and flexural strength. This paper summarises the results of initial studies on the effect of surface-treating rubber crumb (obtained from discarded tires) with ultraviolet (UV) radiation, with the aim of mitigating such losses. Investigation focussed on changing the surface energy, and therefore the bond strength, between cement and rubber. To identify the most effective UV wavelength for this purpose, a water retention test method was utilized, resulting in the selection of the UV-C wavelength range for treatment. Additionally, specimens containing rubber, treated for different time periods, were subjected to flexural testing. As expected, the addition of untreated crumb rubber resulted in a degradation of flexural strength, however exposure to UV-C generated, at best, values only 6% weaker than those of rubberless specimens, indicating the benefits of the investigated surface treatment.     

Pull-out analysis of laser modified polyamide tire cords through rubber matrix

Today with regard to the increased tire failure accidents, strengthening the tire cord adhesion to rubber compounds to reduce the tire blow-out risks is being of great importance. The main aim of this research is strengthening the adhesion of tire cord to the plastic/rubber matrix by the use of laser treatment method to achieve a high performance material. In this study, the polyamide (known as nylon 66) tire cord was prepared and the surface treatment was performed by CO₂ laser, prior to Resorcinol formaldehyde latex (RFL) dipping.To obtain the ideal irradiation condition, surface roughness was evaluated by image analysis using both Fractalyse2.4 and Mountainsmap7 Software. The cord parameters such as count, twist, strength and toughness and also H-Test, FTIR and XRD analysis were tested before and after laser treatment. The results showed that cord count, twist and strength did not have any significant changes. However, the other parameters such as cord elongation, shrinkage and toughness were changed so that enhanced adhesion properties. FTIR and XRD analysis revealed that the crystalline structure of irradiated cords has been decreased.The results showed that laser treatment increases the interfacial shear strength of rubber/fiber without reducing strength of cords. Finally, a mechanical model of failure based on pull-out method was used to investigate the effect of laser treatment on the adhesion strength of cord/rubber. Thus, an index of laser intensity was introduced which would be capable of predicting the influence of any laser treatments on interfacial shear strength between cords and rubber.     

Study of microcellular injection-molded polypropylene/waste ground rubber tire powder blend

Microcellular polypropylene/waste ground rubber tire powder blend processing was performed on an injection-molding machine with a chemical foaming agent. The molded samples produced based on the design of experiments (DOE) matrices were subjected to tensile testing and scanning electron microscope (SEM) analyses. Molding conditions and waste ground rubber tire (WGRT) powder have been found to have profound effects on the cell structures and mechanical properties of polypropylene (PP) and waste ground rubber tire powder composite samples. The result shows that microcellular PP/WGRT blend samples exhibit smaller cell size and higher cell density compare with polypropylene resin. Among the molding parameters studied, chemical foaming agent weight percentage has the most significant effect on cell size, cell density, and tensile strength. The results also suggest that tensile strength of microcellular PP/WGRT composites is sensitive to weight reduction, and skin thickness.     

Prediction of properties of polymer concrete composite with tire rubber using neural networks

The neural network method was used to investigate the influence of filler and resin content on the mechanical properties of polymer concrete with powdered tire waste. The mechanical strengths of 10 experimentally determined combinations using mixed epoxy resin, aggregates and tire powder as filler were optimized using direct neural modeling and inverse neural modeling, by imposing a minimum cost (content in resin). Direct neural modeling gave the optimum composition for obtaining maximum values for compressive strength, flexural strength and split tensile strength. Inverse neural modeling analyzed the possibility of obtaining maximum values of mechanical properties by variations in the dosages of the epoxy resin and tire powder. Neural network modeling generated the mixes with the lowest cost and maximum strength. The modeling method has shown that two mechanical properties can be simultaneously optimized in the investigation domain. From direct modeling, the maximum compressive strength was obtained for a composition with 0.215 (fraction weight) epoxy resin and 0.3 (fraction weight) tire powder. Maximum flexural strength was obtained for experimental values of 0.23 epoxy resin and 0.17 tire powder with a severe reduction noted for smaller resin dosages. The maximum split tensile strength was obtained for a resin dosage of 0.24 and tire powder dosage of 0.17.