Evaluation of FRP and hybrid FRP cables for super long-span cable-stayed bridges

This paper evaluates the safety factors, the applicable lengths, and relative cost of FRP (fiber reinforced polymer) and hybrid FRP cables that are potentially suitable for cable-stayed bridges with a super long-span of between 1000 m and 10,000 m. Following previous studies on 1000-m scale cable-stayed bridges with FRP cables, two kinds of hybrid FRP cables – the previously discussed hybrid basalt and carbon FRP (B/CFRP) cable and the newly-developed basalt and steel-wire FRP (B/SFRP) cable – as well as conventional steel cable, CFRP cable, and BFRP cable are further investigated focusing on their promise in meeting potential requirements for super long-span bridges. Some major results are as follows: (1) a three-stage model for determining safety factors of cables with different kinds and lengths is proposed; (2) a threshold of λ² is suggested to achieve both high material and stiffness utilization efficiency, based on which the applicable lengths for different kinds of cables were evaluated; and (3) hybrid B/SFRP cables and BFRP cables are comparable in cost to steel cables within a 3000 m span, while hybrid B/CFRP cables and CFRP cables demonstrate a superior performance/cost ratio over a longer span.     

应用碳纤维索的斜拉桥地震响应分析

以在建的杭州湾跨海大桥北航道桥为对象,采用强度等效的原则将原桥的钢丝索替换成碳纤维索,利用能考虑拉索局部振动的斜拉桥地震响应分析程序,分析比较了同一地震荷载作用下碳纤维索斜拉桥与钢丝索斜拉桥的振动特性及地震响应差异,并探讨了引起差异的根本原因。结果表明:索桥耦合振动是引起两种拉索斜拉桥的振动特性和地震响应存在差异的根本原因,碳纤维索的自振频率高,发生索桥耦合振动的可能性低于钢索斜拉桥,同一地震荷载作用下碳纤维索斜拉桥的地震响应要较钢丝索斜拉桥有不同程度的降低。     

CFRP拉索设计对大跨度斜拉桥力学特性的影响

以跨度600m～1400m的桥梁为对象,对碳纤维拉索在不同跨径斜拉桥中的适用性和经济性进行了研究。通过活载作用下的最不利内力和变形、抗风性以及弹塑性稳定性、振动特性等方面的对比,分析了碳纤维拉索在各种大跨度斜拉桥中的适用可能性。研究结果表明:碳纤维拉索的刚度虽然低于钢索,但使用这种材料不影响大跨度斜拉桥的结构设计内力,相反由于拉索使用效率的提高和较高的侧向刚度有利于主梁结构的设计。碳纤维拉索的设计安全系数在2.5～3.5之间可以满足桥梁结构设计的强度和刚度要求。但经济性是影响碳纤维拉索适用于跨度小于1000m斜拉桥的重要因素之一。     

CFRP拉索预应力超高性能混凝土斜拉桥力学性能分析

为了探讨碳纤维复合材料(carbon fiber reinforced polymer,CFRP)和超高性能活性粉末混凝土(reactive powder concrete,RPC)在超大跨度斜拉桥中应用的可行性,以主跨1 008 m的大跨度钢主梁斜拉桥设计方案为例,采用拉索的等强度原则将原桥钢索替换成CFRP索,考虑截面刚度、截面应力和局部稳定等要求,将原桥钢主梁替换成RPC主梁,拟订了一座等跨度的CFRP拉索、RPC主梁斜拉桥方案。采用有限元法分别对两种方案结构的静力特性、动力特性、稳定性能以及抗风性能等进行了分析与比较。结果表明:从结构受力性能角度而言,采用超高性能混凝土主梁和CFRP拉索构成千米级跨度混凝土斜拉桥的结构体系是可行的。     

斜拉桥拉索安装亮化灯具的风致稳定性研究

斜拉桥拉索上安装亮化灯具可能存在风致稳定性问题。以某斜拉桥拉索亮化灯具安装的初步设计方案为工程背景,制作了几何缩尺比为1∶1的节段模型,并进行了测力和测振风洞试验,试验结果表明:由于设计方案中两条钢丝的存在,该桥拉索灯具安装的初步设计方案可能会使拉索发生经典驰振。然后,提出了一种灯具安装的建议方案:取消钢丝,将电线直接螺旋固定在拉索表面。通过详细的测振试验表明:建议方案不会使拉索产生不稳定的驰振振动。     

大跨度钢索和CFRP索斜拉桥车桥耦合振动研究

以跨度600m～1400m的大跨度斜拉桥为对象,应用考虑拉索侧向振动影响的车桥耦合振动分析方法研究了钢索和CFRP索斜拉桥的交通振动响应,比较了车辆计算模型、行车速度对计算结果的影响,并分析了斜拉桥的动力冲击系数。研究结果表明,大跨度斜拉桥主梁的振动响应以静位移和长周期振动成分为主,拉索局部侧向振动不明显,车辆计算模型对结构振动响应的影响十分有限,行车速度的提高增加了结构的动力系数,两种拉索材料对斜拉桥在车辆荷载下的振动响应影响很小,斜拉桥的动力系数离散性大且与构件类型有关。     

亮化灯具对既有斜拉索风致振动影响的试验研究

为了装点城市夜景,对既有大跨度斜拉桥进行光彩亮化改造已成为一种趋势,但是安装照明灯具将显著改变斜拉索的气动形状,影响结构气动稳定性。为保证结构的安全及耐久性,通过风洞试验研究了安装灯具后斜拉索的抗风性能,评价亮化灯具对既有斜拉索产生的影响。以三种不同管径斜拉索为研究对象,制作了几何缩尺比为1∶1的节段模型,开展了测力和测振的风洞试验。研究结果表明:灯具的存在将显著改变斜拉索的气动外形,提高其背风侧漩涡脱落的频率,使斜拉索在更低的来流风速下就具备发生涡激共振的可能性。此外,灯具对斜拉索风雨激振的影响较为有限,对斜拉索干索驰振有一定的抑制作用。     

Enhancement of basalt FRP by hybridization for long-span cable-stayed bridge

This paper presents an enhancement method for basalt fiber-reinforced polymer (BFRP) and the corresponding design optimization for application in long-span cable-stayed bridge. Based on previous studies of long-span cable-stayed bridge with FRP cables, the limitations of BFRP cables were first clarified and potential enhancement methods were proposed from both material and structural design perspectives. The basic mechanical properties and fatigue behavior of BFRP and the related hybrid FRP were experimentally studied and the hybrid effect on enhancing both types of properties was assessed. To address the improvement of utilization efficiency of FRP cables, design optimization of various FRP cables were proposed in terms of material enhancement and structural design requirement of long-span cable-stayed bridges. The results show that hybridization of basalt and carbon fibers not only increase the overall potential strength and the modulus but also enhance the fatigue behavior in comparison to basalt FRP. Meanwhile, hybrid basalt fiber and steel-wire FRP exhibits higher initial modulus and maintain high failure strain. Furthermore, design recommendation of FRP cables proposed in terms of lower limit, upper limit of safety factors and practical consideration result in FRP cables achieving higher integrated performance compared to those by conventional design.     

三维覆冰斜拉索风致振动驰振分析

斜拉索偏心覆冰后,气动外形不再稳定,在风的作用下,可能诱发驰振。大幅的驰振将威胁到拉索结构的安全,因此,有必要对覆冰拉索的驰振稳定性进行深入的研究。应用FLUENT中的SST k-ω模型对三维覆冰斜拉索的绕流场进行数值模拟,得到全攻角下的阻力系数、升力系数及驰振力系数,依此判定覆冰斜拉索是否发生驰振,并得到某大跨斜拉桥部分斜拉索的驰振临界风速。结果表明：经过三维模拟计算的覆冰拉索的部分驰振力系数小于零,并且驰振临界风速较小,斜拉索易发生覆冰驰振;与风洞试验和二维模拟数据比较,三维覆冰斜拉索模拟获得的气动力系数比二维更接近试验值。     

On the design and optimization of hybrid carbon fiber reinforced polymer-steel cable system for cable-stayed bridges

This paper addresses the effective use of carbon fiber reinforced polymeric (CFRP) materials in the cable system. As the span length of cable-stayed bridges increases, several technical challenges become more dominant with traditional material. This paper mainly focuses on improving the aerodynamic performance through implementing CFRP composites in the cable system in combination with steel. In order to maximize the improvement, a genetic algorithm (GA)-based optimization procedure is developed to optimize the distribution of CFRP and steel. A numerical example is presented and the results suggest the typical composition of an optimized CFRP-steel cable system for long-span cable-stayed bridges.     

CFRP索斜拉桥动态特性的有限元分析及动态试验

介绍了国内首座CFRP索斜拉桥的工程概况;建立了该桥的三维空间梁壳杆系有限元动态分析模型,进行了结构动态特性有限元分析;进行了环境激励下国内首座CFRP索斜拉桥结构动态特性的测试,结合试验结果对国内首座CFRP索斜拉桥的动态特性进行了分析。同时,将实桥动态试验结果与有限元动态特性分析结果进行了对比分析。结果表明,有限元动态特性分析的低阶频率和振型与试验测得的频率与振型结果基本吻合。笔者等试验及相关研究分析结论可为CFRP索桥梁的动态建模、动态特性分析、抗震抗风设计及CFRP新型缆索材料在桥梁工程中的进一步推广应用提供一定的参考依据。     

斜拉索非线性固有振动特性分析

在考虑斜拉索静平衡时索曲线的基础上，建立了斜拉桥索大幅振动的非线性动力方程，采用傅立叶级数法研究求解了斜拉索非线性固有振动方程。还通过实例计算对斜拉索大幅振动特性进行了讨论分析。     

Stochastic finite element analysis of long-span bridges with CFRP cables under earthquake ground motion

Stochastic seismic analysis of long-span bridges with Carbon fibre reinforced polymer (CFRP) cables are presented in this study through combination of the advantages of the perturbation based stochastic finite element method (SFEM) and Monte Carlo simulation (MCS) method. Jindo cable-stayed and Fatih Sultan Mehmet (Second Bosporus) suspension bridges are chosen as an example. Carbon fibre reinforced polymer cable (CFRP) and steel cables are used separately, in which the cable’s cross sectional area is determined by the principle equivalent axial stiffness. Geometric nonlinear effects are considered in the analysis. Uncertainties in the material are taken into account and Kocaeli earthquake in 1999 is chosen as a ground motion. The efficiency and accuracy of the proposed algorithm are validated by comparing with results of MCS method. It can be stated that using of CFRP cables in long-span bridges subjected to earthquake forces is feasible.     

Carbon Fibre Composites as Stay Cables for Bridges

High tensile strength and stiffness as well as high fatigue life, low weight and excellent chemical resistance are material properties of carbon fibre composites (CFRP) which make these materials interesting for stay cable systems. The key problem to which the application of stay cables as well as tendons is faced is the anchoring. This paper describes the properties of CFRP-wires, the requirements to stay cables or tendons and the development of such a system through calculations and experiments along with a successful field stress test of a CFRP based stay cable.     

表面损伤的斜拉索平均气动阻力特性的试验研究

斜拉索作为斜拉桥的重要受力构件,其风荷载设计在桥梁抗风设计中具有重要意义。斜拉索在生产、运输和安装过程中有可能受到损伤,针对不同程度表面损伤的斜拉索,利用风洞测力试验,研究了亚临界、临界和超临界雷诺数区域损伤程度对斜拉索气动阻力的影响,并得到了表面损伤斜拉索气动阻力的计算方法。结果表明:在一定的风向范围内,斜拉索表面损伤对其气动阻力影响显著,在亚临界区,表面损伤模型阻力系数大于光滑模型;进入临界区后,表面损伤模型的阻力系数则小于光滑模型;在超临界区,二者又比较接近。随着划痕的加深,临界区起始雷诺数提前,且在临界雷诺数区,随着雷诺数的增大,阻力系数减小。对不同损伤程度斜拉索的阻力系数进行拟合,得出相应的计算公式,以方便斜拉索气动阻力的估算。     

Connecting high-performance carbon-fiber-reinforced polymer cables of suspension and cable-stayed bridges through the use of gradient materials

Summary Carbon-fiber-reinforced polymer (CFRP) cables offer a very attractive combination of high specific strength and modulus (ratio of strength or modulus to density), outstanding fatigue performance, good corrosion resistance, and low axial thermal expansion. The high specific strength permits the design of structures with highly increased spans. The high specific modulus translates into a high relative equivalent modulus. This factor is very important in view of the deflection constraints imposed on large bridges. A relative high modulus coupled with a low mass density offer CFRP cables already an advantage for spans above 1000 m. Since 1980 EMPA has been developing CFRP cables for cable-stayed and suspension bridges that are produced as assemblies of parallel CFRP wires. The key problem facing the application of CFRP cables, and thus their widespread use in the future, is how to connect them. A new reliable anchoring scheme developed with computer-aided materials design and produced with advanced gradient materials based on ceramics and polymers is described. Early 1996 such CFRP cables with a load-carrying capacity of 12 MN (1200 metric tons) have been applied for the first time on a cable-stayed road bridge with a 124-m span. Each cable is built up from 241 CFRP wires having a diameter of 5 mm.     

CFRP拉索阻尼特性实验研究和理论分析

为了掌握CFRP拉索的阻尼特性以及建立相应的评价方法,用自由衰减振动试验方法测试了CFRP索、钢索以及CFRP丝、钢丝的阻尼特性,并用能量耗散原理以及振动理论探讨了拉索的结构阻尼和空气阻尼计算方法。结果表明:钢索的阻尼变化与应变能的比例关系明显,实测阻尼值与应变耗能理论计算结果一致,而CFRP拉索的阻尼实测值与理论结果之间存在一定的差异。长度1.8m的单丝阻尼与对应的应变大小相关性不大,应变耗能理论不能评价其阻尼特性,支点产生的阻尼效果不可忽视。     

千米级斜拉桥空气动力学问题

以苏通大桥为背景,对超大跨径斜拉桥的空气动力学问题进行了研究,着重讨论了超大跨径斜拉桥的动力特性、风荷载、基于气弹模型的颇振导数识别、结构体系以及涡激振动特性等一系列问题.研究结果表明,考虑侧向风荷载作用下斜拉索的非线性效应之后,全桥结构的竖向刚度有折减现象.同时发现Fixed-Fixed体系是解决顺桥向风荷载的有效途径,还提出了基于气弹模型的颤振导数识别方法,并就斜拉桥的涡激振动和雷诺数效应进行了探讨.     

斜拉空间网格结构的非线性静力分析

斜拉空间网格结构是塔柱、斜拉索和空间网格协同工作的杂交结构,刚柔相济,受力合理。考虑了不同施工阶段塔柱的弹性支承作用和斜拉索的几何非线性影响,局部修正了网格结构的刚度方程,并将斜拉索施加一定的预拉力,以达到增强结构刚度、减少用钢量的目的。算例分析表明,大跨度屋盖采用斜拉空间网格结构能明显降低杆件内力,减小结构挠度,改善整个结构的受力性能。     

斜拉桥斜拉索的风荷载、风致振动与控制

斜拉索是斜拉桥的主要受力构件之一,其承受的风荷载占大桥总体风荷载的很大比例,准确掌握其风荷载对设计具有重要意义;同时,由于斜拉索的风致振动发生频繁,危害严重,其风致振动的机理是研究热点和难点问题,振动控制措施是设计中需要重点考虑的问题。该文全面总结了斜拉索风荷载计算方法、风致振动的种类和相关机理,介绍了利用气动措施进行振动控制的最新研究成果,为相关的机理研究和斜拉索的振动控制设计工作提供参考。