桥面铺装对钢桥面板疲劳应力幅的影响

钢桥面板厚度小,铺装层的相对刚度较大,钢桥面板疲劳设计时,应该考虑铺装层与钢桥面板的共同作用。假设桥面铺装与顶板没有相对滑移,采用有限元方法探讨了桥面铺装弹性模量和厚度对正交异性钢桥面板疲劳应力幅的影响。     

南京长江第四大桥钢桥面铺装疲劳性能试验研究

结合南京长江第四大桥钢桥面铺装实体工程,开展铺装层混合料20℃疲劳性能试验。为了使试验结果能够更真实地反映主桥铺装的实际情况,直接采用主桥铺装使用的混合料成型试件,其中,带钢板复合梁试件为施工现场摊铺、碾压成型。室内试验对铺装结构单层采用劈裂疲劳试验,选择0.2、0.3、0.4、0.5、0.6这5个等级的应力水平,对组合结构采用带钢板复合梁疲劳试验,荷载水平为6 kN、7 kN、8 kN,并通过回归分析得到疲劳方程。     

钢桥面铺装用环氧沥青相容性研究进展

环氧沥青是一类具有优异高温、低温及耐疲劳性能的正交异性钢桥面铺装材料。由于石油沥青在溶解度参数、介电常数、密度等方面均与环氧树脂有较大差异,因此解决石油沥青与环氧树脂间的相容性问题是实现高性能钢桥面铺装用环氧沥青国产化制备的前提。本文从对沥青进行顺酐化改性、选择与沥青相容性好的固化剂以及添加增容剂三个方面综述了近年来环氧沥青相容性的研究现状,最后指出了环氧沥青钢桥面铺装中存在的问题并进一步明确了下一阶段应在耐疲劳性、耐候性以及施工便易性等方面提升环氧沥青的综合性能。     

钢桥面铺装损伤病害的调查及分析

钢桥面铺装病害产生的原因包括外部因素和铺装自身因素,外部因素主要是铺装温度、交通荷载、桥面板刚度;铺装内部自身因素主要包括混合料的胶结料性能、混合料级配类型、混合料配合比、施工控制质量等因素。本文针对我国典型的钢桥面铺装:双层SMA、浇注式、环氧沥青铺装进行病害调查,分析引起病害的原因,为制定病害处治方案提供依据。     

微动疲劳损伤失效分析

介绍了微动疲劳损伤失效的现象，影响因素，鉴别特征，并举例说明。     

粘贴GFRP的钢桥面铺装层的剪切性能

大跨径钢桥由于桥面板厚度薄,容易出现推移、开裂等诸多病害。在桥面钢板上粘贴一定厚度的玻璃钢（GFRP）薄板,形成复合铺装结构,以提高铺装层刚度,延长铺装层使用寿命。采用ANSYS有限元软件,计算分析复合铺装结构的层间剪切应力分布状况,研究GFRP薄板的模量等对铺装结构受力的影响。结果表明,粘贴不同模量GFRP后,铺装层的应力、应变均出现了不同程度的变化。铺装层与钢板粘结处剪应力为未粘贴GFRP的1．44倍;剪应变减小为0．11％。但粘贴GFRP后铺装层层间最大剪应力和剪应变均大于未粘贴GFRP的铺装层,实际工程中应注重提高沥青铺装层的高温抗变形性能。     

双相钢的疲劳行为（下）

评述了近年来国内外有关双相钢疲劳行为方面的文献资料,并提出了尚待解决的问题。     

复合浇筑式钢桥面铺装车辙评估模型研究

根据南京长江第四大桥钢桥面铺装试验研究成果,对复合浇筑式沥青混合料性能进行了分析研究,通过系统分析动稳定度与温度、汽车轮载、车速及行车道间的关系,结合南京地区汽车超载情况的研究,提出并建立了复合浇筑式钢桥面铺装的车辙评估模型。     

大跨径钢桥面铺装技术施工要点分析

近些年来,随着我国经济的发展,经济交流及商业活动尤为频繁,尤其是在南方经济发达区域,需要建设一些大跨径的桥梁来提高经济交流的速度,在桥梁的建设过程中大跨径钢桥面铺装技术是一项全世界的技术难题。本文主要对树脂沥青组合体系钢桥面铺装技术在施工过程中需要注意的要点进行介绍。     

正交异性钢桥面疲劳开裂研究

正交异性钢桥面板的钢结构桥梁在车辆荷载作用下易出现疲劳开裂,为了解决这一问题,该文采用在正交异性钢桥面板上设置薄层RPC(Reactive-Powder-Concrete)超高性能混凝土层,将钢桥面转变成组合桥面,从而提高了桥面刚度,能有效改善结构受力状态,且不会增加桥梁上恒载重量。通过对某大桥的计算分析表明:采用组合桥面后,车辆荷载作用下的钢桥面应力大幅度下降。钢桥面疲劳敏感点处的拉应力降幅达到71.32%~72.39%,大幅度的提高了钢桥面的抗疲劳寿命;薄层RPC面板的高强度和高韧性,完全能满足组合桥面的最大拉应力10.08MPa的强度要求,成为钢桥面上的永久结构层,可以大幅度降低钢桥面板的开裂风险。     

Fatigue damage of medium carbon steel under sequential application of axial and torsional loading

Fatigue tests were conducted on S45C steel under fully reversed strain control conditions with axial/torsional ( at ) and torsional/axial ( ta ) loading sequences. The linear damage value (n₁/N₁+n₂/N₂) was found to depend on the sequence of loading mode ( at or ta ), sequence of strain amplitude (low/high or high/low) and life fraction spent in the first loading. In general, at loading yields larger damage values than ta loading and the low–high sequence of equivalent strain leads to larger damage values than the high–low sequence. The material exhibits cyclic softening under axial cyclic strain. Cyclic hardening occurs in the torsion part of ta loading, which elevates the axial stress in the subsequent loading, causing more damage than in pure axial fatigue at the same strain amplitude. Fatigue life is predicted based on the linear damage rule, the double linear damage rule, the damage curve approach and the plastic work model of Morrow. Results show that overly conservative lives are obtained by these models for at loading while overestimation of life is more likely for ta loading. A modified damage curve method is proposed to account for the load sequence effect, for which predicted lives are found to lie in the factor‐2 scatter band from experimental lives.     

Effect of pavement design parameters on the behaviour of orthotropic steel bridge deck pavements under traffic loading

This study evaluated the effect of the pavement design parameters on the behaviour of orthotropic steel bridge deck pavements under traffic loading using a three-dimensional finite element model. Four types of paving materials were considered in this analysis: polymer concrete, epoxy asphalt concrete, polymer-modified stone mastic asphalt concrete and mastic asphalt concrete. The maximum transverse tensile strain was developed at the bottom of the pavement under a tyre of dual tyres or on top of the pavement between two tyres. From the sensitivity analysis, better interface bonding between the deck plate and pavement led to a significant enhancement of bottom-up fatigue cracking resistance, especially for 40-mm-thick pavements. As pavement temperature increased from ? 20 to 60°C, critical tensile strain increased significantly, and corresponding locations moved from the bottom to the top of the deck pavement.     

Cumulative fatigue damage of stress below the fatigue limit in weldment steel under block loading

To investigate the cumulative fatigue damage below the fatigue limit of multipass weldment martensitic stainless steel, and to clarify the effect of cycle ratios and high‐stress level in the statement, fatigue tests were conducted under constant and combined high‐ and low‐stress amplitude relative to stress above and below the fatigue limit. The outcomes indicate that neither modified Miner's nor Haibach's approach provided accurate evaluation under repeated two‐step amplitude loading. Moreover, effect of cycle ratios has been determined. Additionally, the cumulative fatigue damage saturated model is established and validated. Cumulative fatigue damage contributed by low‐stress below the fatigue limit in high stress of 700 MPa is higher than that with 650 MPa at identical conditions (fatigue limit 575 MPa). Thus, high stress affects fatigue damage behaviour below the fatigue limit. A new predicted approach has been proposed based on Corten‐Dolan law, whose accuracy and applicability have been proven.     

Fatigue life prediction of a structural steel under service loading

Fatigue life prediction techniques for variable amplitude load histories are reviewed. The fatigue crack growth rate and crack closure responses of BS4360 50B steel are determined for a service load history experienced by a gas storage vessel. Crack propagation rates are found to be independent of specimen thickness. Crack growth is successfully predicted by linear summation using the Paris law; no significant improvement is achieved by incorporating crack closure into the analysis. The particular choice of cycle counting technique is also found to have an insignificant effect on the predicted fatigue life. The load-interaction model proposed by Willenborg et al correctly indicates the absence of retarded growth, whilst the Wheeler and Führing models erroneously predict retarded crack growth.     

Fatigue life estimation of notched specimens of modified 9Cr-1Mo steel under uniaxial cyclic loading

Accuracy in the estimation of low cycle fatigue life of modified 9Cr-1Mo steel notched specimen by different analytical methods such as linear rule, Neuber’s rule, strain energy density method and numerical method such as finite element analysis have been studied in this investigation. The fatigue tests on notched specimens having notch radius of 1.25 mm, 2.5 mm and 5.0 mm were carried out at 823 K with net stress amplitudes of 250 MPa, 300 MPa and 350 MPa. The fatigue tests on smooth specimens were carried out with strain amplitudes ranging from ±0.3% to ±0.8% with a strain rate of 3 × 10^?3 s^?1 at 823 K to evaluate the fatigue life of notched specimen through strain-life approach. In order to predict the cyclic stress response of the material, Chaboche non-linear hardening model was employed considering two back stress components. Predicted hysteresis loops for smooth specimen were well in agreement with experimental results. Estimated fatigue lives of notched specimens by analytical methods and finite element analysis were within a factor ±16 and ±2.5 of the experimental lives respectively.     

Fatigue life estimation under random loading using the energy criterion

A procedure for estimating the useful life of a component for a given (admissable) probability of fatigue fracture origination under random loading is presented. The method uses material constants obtained from the S/N and cyclic stress/strain curves, standard deviation and probability density distribution of the loading process and a macroblock of harmonic cycles obtained by applying the rainflow cycle counting method to the random loading process. Theoretical and experimental lives are found to exhibit good agreement.     

Stochastic modelling of low-cycle fatigue damage in 316L stainless steel under variable multiaxial loading

In the present study, a stochastic model is developed for the low-cycle fatigue life prediction and reliability assessment of 316L stainless steel under variable multiaxial loading. In the proposed model, fatigue phenomenon is considered as a Markov process, and damage vector and reliability are defined on every plane. Any low-cycle fatigue damage evaluating method can be included in the proposed model. The model enables calculation of statistical reliability and crack initiation direction under variable multiaxial loading, which are generally not available. In the present study, a critical plane method proposed by Kandil et al . ( Metals Soc., London 280, 203–210, 1982) maximum tensile strain range, and von Mises equivalent strain range are used to calculate fatigue damage. When the critical plane method is chosen, the effect of multiple critical planes is also included in the proposed model. Maximum tensile strain and von Mises strain methods are used for the demonstration of the generality of the proposed model. The material properties and the stochastic model parameters are obtained from uniaxial tests only. The stochastic model made of the parameters obtained from the uniaxial tests is applied to the life prediction and reliability assessment of 316L stainless steel under variable multiaxial loading. The predicted results show good aggreement with experimental results.     

Fatigue of bonded steel interfaces under cyclic shear loading and static normal stress

Hybrid joints that combine mechanical fastening and bonding provide potential joining alternatives for high strength steel structures. An experimental and analytical research program has been initiated to assess the static and cyclic Mode II shear strength of epoxy bonded steel interfaces subjected to static normal (Mode I) pre-stress. During cyclic loading, shear stress vs. interface displacement could be divided into elastic and inelastic regions with a power law equation describing the inelastic curve. Hysteresis loop shape varied with normal stress, shear stress and accumulated fatigue cycles. A shear stress amplitude threshold equal to about 50% of the fracture shear stress was observed.     

Fatigue failure modes of rib-to-deck joints under the multiaxial stress states caused by various wheel loading characteristics

Orthotropic steel bridge decks (OSBDs) are characterized by overall structural asymmetries and severe local stress concentrations; meanwhile, complicated service loadings always cause relevant rib-to-3deck (RD) welded joints in multiaxial stress states. Under such circumstances, a full-scale OSBD model was established. Six loading cases were applied, and the multiaxial fatigue deviation was calculated to represent the multiaxial stress state of the bridge deck. Based on the effective traction structural stress method, the most unfavorable loading case for the failure mode of the RD joint under a multiaxial stress state was analyzed, and the failure mode transition in the process of wheel load movement was discussed. The results indicated that the fatigue failure mode of the RD joint was determined by the transverse loading locations. In-between-rib loading can cause the initiation of toe-rib cracks. Cracks are prone to occur under over-rib loading and riding-rib loading, and the arrangement of diaphragms can increase the risk that the fatigue crack originates from the weld root.