沉管结构预制阶段裂缝控制参数影响分析

混凝土沉管隧道在越江和跨海工程中得到了较广的应用,预制方法从传统的干坞法预制发展为工厂法预制。沉管隧道的混凝土管节在工厂化预制阶段容易因温度梯度、收缩以及约束等原因出现危害性裂缝,影响沉管结构的正常使用和长期耐久性。采用数值仿真和试验研究相结合的方法,基于水化度方法建立了混凝土材料模型,综合考虑混凝土温度变形、自收缩和徐变等时变体积变形以及热-力学边界条件;针对沉管工厂化预制的各个阶段,对配合比、入模温度、养护环境温度、模板、拆模时间、养护时间以及保温养护措施等参数进行了对比分析;在温度场和应力场计算结果基础上,以开裂风险指数为主要判断依据,得到了沉管在预制过程中裂缝控制的关键影响因素。研究结果表明:工厂化预制沉管隧道混凝土管节的入模温度和养护温度是沉管结构预制各阶段的关键裂缝控制影响因素,两者之间的关系对沉管结构的裂缝控制有直接影响,入模温度较高时,可以通过提高养护温度来保证沉管开裂风险指数大于1.4。在冬季时,养护温度的提高使沉管有较好的保温效果,进而降低内外温差和开裂风险;但在夏季还需注意控制其内部最高温度。最后开展足尺节段温控试验,提出入模温度和养护温度的控制措施,并通过温度监测得到较高环境温度下的温度控制指标,以指导工厂化混凝土沉管预制阶段裂缝控制。     

浅谈水泥混凝土路面早期裂缝危害及分类防治

以本地区近年来新建的水泥混凝土路面为例,就其早期出现裂缝的原因、特点、分类及其危害进行了阐述,对如何防止和减少水泥混凝土路面早期裂缝提出了有效的对策.     

关于海工混凝土耐久性问题的探讨

海洋环境下的混凝土结构腐蚀现象十分严重,采用高性能混凝土是解决混凝土腐蚀问题的有效措施,控制高性能混凝土的开裂问题是推广应用高性能混凝土的关键.介绍了海工混凝土应用中存在的几个问题及对策措施.     

某型船用主机汽缸镶台肩套强度分析研究

某船柴油机由于汽缸体缸套装配凸肩出现严重裂纹,在修理时采用镶套的方法进行了修补,文章根据标准对镶套进行常规强度校核和变形的有限元计算,分析表明整个修理方法完全符合要求。     

沥青路面裂缝的条带补缝工艺及补缝机研究开发

针对沥青路面裂缝的修补，通过研究传统灌缝修补工艺存在的不足，开发了条带补缝新工艺，并配套设计了可实现裂缝条带补缝工艺机械化施工的补缝机，为沥青路面裂缝的修补提供了一种修补外观质量和可使平整度更好的新工艺。实践证明：条带补缝工艺对沥青路面的修补效果优于传统灌缝工艺，使用配套的补缝机可实现对沥青路面裂缝的快速一次性修补，具有很好的推广应用价值。     

昆山市震川西路水泥混凝土路面改建设计关键技术

随着交通量的增加和路面状况的恶化，大量的水泥混凝土路面都面临着翻修改建的任务，加铺沥青混凝土罩面是其中最常用的方法之一。为确定经济合理的加铺结构层，保证路面结构强度，延长道路使用寿命，防治反射裂缝是其关键技术。通过介绍震川西路改建的设计及施工方案，为类似工程提供参考。     

基于复杂网络的列车辅助驾驶危险致因传播模型

为了解预期功能安全(SOTIF)相关危险致因在基于智能感知的列车辅助驾驶系统 (IATDAS)中的传播特性，提升针对该类系统的危险控制能力，本文提出基于复杂网络的IATDAS 系统危险致因传播模型。该模型在SOTIF危险致因网络的基础上，提供了全局容量-负载传播机制，能有效刻画IATDAS系统的危险致因传播机制。案例分析结果表明：本文所提模型能够解决复杂致因关系下既有模型与系统实际情况不符的问题，如对于具有较长后续传播路径的致因，本文模型能够刻画其较难导致危险的实际特征；依据本文模型实施传播控制，可以显著降低危险致因的传播速度，如对影响节点范围大、前期影响节点数量增加快的危险因素进行控制时，可使其平均传播速度降低68%，比随机控制策略多降58%。该模型可以为IATDAS系统的SOTIF相关危险控制提供决策基础。     

轨道车辆座椅裂纹分析及改善措施仿真研究

文章介绍了轨道车辆常见座椅分类及其布置,针对某型轨道车辆统计了运行中座椅裂纹分布情况及位置信息,分析了座椅裂纹产生原因,提出了改善座椅裂纹的措施,并通过相应计算及仿真分析验证了座椅裂纹改善措施的可行性。     

Crack growth direction effects on corrosion-fatigue behaviour of offshore wind turbine steel weldments

In this study corrosion-fatigue tests have been conducted on fracture mechanics specimens extracted from an S355 G10+M structural steel welded plate. The tests have been performed on compact tension specimens with the crack tip located in the heat affected zone. The corrosion-fatigue test results from this study have been compared with the data available on the base metal as well as air tests on the same material. Moreover, the obtained results have been compared with the corrosion-fatigue data available in the literature on a wide range of steels and also the fatigue trends for welded joints in free-corrosion condition recommended in the BS7910 Standard. The effect of the specimen orientation, with respect to the weld region, is also examined in this study and it has been found that higher corrosion-fatigue crack growth rates are generally observed in the tests with 0° orientation. The results have also shown that the corrosive environment has significant effects on the fatigue crack growth acceleration at the beginning of the tests; however, as the crack propagates, the environmental damage effect on crack growth behaviour becomes less pronounced. The results presented in this study are discussed in terms of improvement in the structural integrity assessment of offshore wind turbine monopiles.     

The effect of weld residual stress on fracture toughness at the intersection of two welding lines of offshore tubular structure

Due to the spatial complexity and fabrication characteristics of offshore platforms, it is inevitable to encounter overlaps or proximity of weld lines in tubular joints. Several international standards such as American Petroleum Institute (API), American Welding Society (AWS), and American Institute of Steel Construction (AISC) regulate the minimum distance between primary weld beads; however, any logical and detailed background of this limitation has not been presented. For a non-compliant weld joint where the regulation is not met, fracture toughness calculation is a typical index to verify the structural integrity.This research consists of two parts. First, weld residual stress distributions are calculated by a 3D thermo-mechanical nonlinear Finite Element Analysis. Two crossing welds, a T-weld crossing on a butt weld, are simulated in one model. A separate tee and a butt welding simulations are also performed for a comparative purpose. Second, SIFs and J-integral values are calculated at the surface and deepest crack tip locations for four different types of semi-elliptical surface cracks. Four cracks are embedded into the weld model and the residual stress distribution from the 3D thermo-mechanical FEA are mapped to a 3D FE crack model as initial conditions. An additional axial tensile load is also imposed. SIF values are compared with those using the weighting function method for the butt weld model subject to three load cases, i.e., tensile stress only, weld residual stress only, and both of them. From the simulation, a tubular joint containing a chord girth weld intersected with weld beads of brace is found to show lower the SIF values than that having only a girth weld on chord.