考虑钢材锈蚀的桥梁焊接节点概率疲劳寿命评估

由于循环外荷载和腐蚀性环境的共同作用,近海桥梁结构易受疲劳破坏.本文提出了一种考虑钢材锈蚀的桥梁结构改进疲劳可靠度评估模型,并基于青马大桥长期结构健康监测数据对其典型焊接节点的概率疲劳寿命进行了评估.通过建立有效截面衰减模型和材料疲劳性能退化函数,利用Miner损伤累积准则的连续概率函数表达式,提出了考虑钢材锈蚀的疲劳可靠度解析模型.同时考虑交通载荷(包括汽车载荷和火车载荷)和台风影响,通过统计分析长期应变监测数据建立了标准日应力谱.采用有限混合分布方法及基于遗传算法的混合参数估计算法,得到了标准日应力谱多模态有限混合分布函数.比较分析了考虑和未考虑钢材锈蚀的焊接节点疲劳寿命失效概率和可靠度指标,研究结果表明钢材锈蚀因素对桥梁焊接节点的疲劳可靠度评估结果有较大影响.     

Low- and high-cycle fatigue behavior of load-carrying cruciform joints with incomplete penetration and strength under-match

The fatigue strengths of load-carrying cruciform joints with incomplete penetration and a strength mismatch between the base metal and the deposit metal were studied. Low- and high-cycle fatigue tests were performed on specimens with five matching conditions and two sizes of incomplete penetration. The test results revealed that the failure life was governed by crack propagation in both the low-cycle and high-cycle fatigue regions, and the crack propagation paths differed according to the matching and loading conditions. In addition, the fatigue strengths of the joints were compared for the degree of strength matching and the size of incomplete penetration in the low- and high-cycle fatigue regions. It was found that the effect of strength matching on the fatigue strength is negligible in the high-cycle fatigue region, but it becomes large in the low-cycle fatigue region and significantly reduces the fatigue life of the specimen in the under-matched joints.     

腐蚀后耐候钢梁栓焊节点的疲劳性能试验研究

裸露使用的耐候钢结构往往在受环境腐蚀的同时还可能承受疲劳荷载.为获得腐蚀后耐候钢梁栓焊节点的疲劳性能,对经过38天乙酸盐雾循环试验后的Q355NHD栓焊节点耐候钢梁试件的疲劳性能进行了试验研究.试验结果显示:腐蚀后的耐候钢梁栓焊节点处的疲劳裂纹均先发生在上翼缘(受压翼缘)过让孔两侧焊趾处,破坏裂纹往往发生在下翼缘(受拉...     

基于细观损伤力学的梁柱焊接节点断裂破坏预测分析

应用细观损伤力学模型预测分析单调荷载作用下梁柱焊接节点的裂纹萌生与扩展。分别依据节点部位的母材、热影响区和焊缝金属缺口试样的单轴拉伸试验，标定材料细观损伤力学模型的参数；通过有限元分析模拟，预测焊接节点的开裂位置以及断裂破坏的过程，与已有试验结果以及基于微孔扩展模型和应力修正临界应变模型的有限元分析结果相比，建议的细观损伤力学模型的有限元分析结果具有更好的预测精度；针对不同焊接孔几何形状对节点断裂性能的影响进行有限元分析，结果表明，孔的几何形状对节点的断裂破坏模式的影响显著，长圆孔比圆孔具有更好的节点延性，开裂延缓，但是两种孔形的节点承载力差别很小。     

桥梁拉索损伤声发射监测及其临界损伤判断

通过拉伸试验,得到了钢绞线整个损伤过程的声发射特征参数,测试结果表明：采用计数、能量、持续时间、幅值和时间的相关点图来综合表征损伤,不但可以跟踪全过程损伤,而且还可以准确判断出断丝信号和非断丝信号以及断丝位置,并发现钢绞线在屈服变形之前,声发射特征参数并不明显,屈服阶段之后,声发射的特征参数逐渐增大,在临近断裂时,声发射特征参数迅速增大。最后采用声发射特征参数时间序列分形理论研究了钢绞线的损伤演化规律,在加载初中期,分形维数变化不大,当钢绞线裂纹进入快速扩展阶段,分形维数出现“最大-最小”变化模式,运用此模式可为钢绞线临界损伤破坏提供一个新的判据。     

高性能桥梁钢典型焊接接头疲劳性能试验研究

针对Q500qE高性能钢两种典型焊接接头,包括对接焊缝和横向角接焊缝,设计疲劳试件。其中对接焊试件包括两种形式,分别为板厚56mm和8mm的对 接焊试件;横向角接焊缝试件的主板厚56mm、附连件厚20mm。对三组试件进行了有限元分析,掌握了试件的应力分布状况及薄弱环节,验证了试件设计的合 理性。随后针对三组试件展开了疲劳试验,掌握了不同类型焊接接头的破坏位置及破坏形式。根据试验结果拟合出了三组试件的S-N曲线,并与普通钢的疲 劳性能进行比较,表明Q500qE高性能钢的这两种典型焊接接头的疲劳强度略高于普通钢。采用目前规范规定的疲劳强度容许值进行抗疲劳设计是合理可行的,并且具有足够的安全余量。     

Prediction of fracture behavior of beam-to-column welded joints using micromechanics damage model

Moment-resisting steel frames often fail by fracture failure of beam-to-column welded joints during a strong earthquake. This paper provides a numerical methodology based on micromechanics damage model instead of traditional fracture analytical methods to investigate the crack initiation and propagation of welded beam-to-column joints subjected to monotonic loading and ultra low cycle loading conditions. Firstly, parameters used in the micromechanics damage model for steel base metal, heat affected zone and weld metal were calibrated, respectively, against uniaxial tension test results and cycle test results of notched specimens. The evolution of void growth in the notched specimens under different loading conditions was compared. Secondly, fracture process of the welded joints subjected to tensile loading was simulated based on the micromechanics damage model. The predicted load displacement response agrees well with the other researcher's test results. Finally, the micromechanics damage model was applied numerically to investigate the ultra low cycle fatigue fracture behavior of the welded joints under constant amplitude as well as variable amplitude inelastic cyclic loading. According to the distribution and evolution of void in the welded joints obtained from finite element analysis, crack initiation and propagation were presented and the number of cycles to fracture was predicted. It is shown that the fatigue life predicted from finite element analysis based on micromechanics damage model agrees well with the other's test results.     

Low cycle fatigue assessments of corner welded joints based on local strain approach

Low cycle fatigue strengths of corner welded joints with single bevel groove welding were studied. Low cycle fatigue tests were performed with three types of specimens which have different sizes of weld root face. The test results indicated that the low cycle fatigue strength of the corner welded joints strongly depends on the weld root size. Then, the fatigue strength of the corner joints was evaluated based on the effective notch strain at the weld root tip which was calculated by elasto-plastic finite element analyses. A unique relationship between the effective notch strain and the fatigue life of the joint was observed regardless of the weld root size. Therefore, it was revealed that the effective notch strain approach is applicable to evaluate the low cycle fatigue strength of the corner welded joints.     

正交异性钢桥面板顶板竖向加劲肋焊接接头疲劳性能试验研究

正交异性钢桥面板的疲劳问题是目前研究的主要热点之一。该文针对国内钢桥面板顶板竖向加劲肋焊接接头的构造细节,通过振动型疲劳试验机开展了18个试件的弯曲疲劳试验,研究了普通角焊缝和熔透角焊缝在不同加载应力幅下的疲劳性能,分析了焊接接头的应力集中系数,并与有限元分析结果进行了对比,得到了普通角焊缝和熔透角焊缝焊接接头疲劳寿命大小;同时采用BS5400、JSSC、Eurocode 3以及我国钢结构设计规范（GB 50017—2003）规定的S-N曲线对试验结果的疲劳强度进行了评定。研究表明：钢桥面板竖向加劲肋焊接接头熔透角焊缝的疲劳性能总体上优于普通角焊缝,对我国钢桥面板竖向加劲肋焊接接头的开裂前的疲劳性能建议采用BS5400-F2的S-N曲线（35MPa）进行设计和评价;并且两者焊接接头的应力集中系数约为2.4左右,其中熔透角焊缝受到焊接工艺的影响其应力集中系数较大,须在焊接后对其进行焊趾表面处理,以进一步提高疲劳性能。     

应力比对16Mn钢焊接接头疲劳强度的影响规律

通过对不同应力比及不同加载方式下16Mn钢焊接接头的疲劳强度的试验结果分析得出：对焊接结构而言,引入参数√[2（1-R）-1]^1,以较好地反映出应力比R对疲劳强度的影响,利用等效应力ΔSR=√[2（1-R）]^-1ΔS,可统一给出不同加载方式及不同应力比R下的S—N曲线,在工程应用上有着积极的意义。     

Q460D高强钢及其焊缝连接疲劳性能试验研究

在疲劳荷载作用下钢结构焊缝区易发生疲劳断裂,通过Q460D高强钢及其焊缝连接的疲劳性能试验研究,结合试验数据,拟合了Smax-N曲线预测其疲劳寿命,根据疲劳损伤理论分析了疲劳破坏程度,并通过断口形貌揭示了疲劳裂纹扩展规律。研究结果表明：Q460D母材具有较高的疲劳抗力;对接焊缝接头Smax-N的95%保证率曲线与ANSI/AISC 360-10的疲劳设计曲线吻合较好;GB 50017—2003的设计曲线能较好预估循环次数大于40万次以上十字接头的疲劳寿命。损伤指标能够较好地表征疲劳破坏过程中构件内部状态的变化,缺口系数越大,损伤发展越快。瞬断前裂纹扩展规律与损伤发展一致,随着损伤发展疲劳条带间距逐渐变大。     

Evaluation of low-cycle fatigue damage in RC exterior beam-column subassemblages by acoustic emission

Since Acoustic Emission (AE) is effective in monitoring the initiation of cracks in materials and structures, it has been widely used as a real-time evaluation technique for damage in reinforced concrete (RC) elements such as beams or columns in moment-resisting frames. This paper investigates its applicability for assessing the low-cycle fatigue damage in RC exterior beam-column subassemblages, which are especially vulnerable parts of the RC frames when subjected to earthquakes. Two 3/5 scale specimens representing connections from the lower and upper part of a prototype building located in a moderate-seismicity area are tested under cyclic loading until collapse. Important differences between the two specimens are observed owing to the different size and amount of reinforcing steel. First, a significant increase in AE activity is observed when the steel reinforcement begins to undergo plastic deformations. Second, by means of the AE improved b-value method, it is clearly shown that the macroscopic fracture processes occur mainly during the loadings paths. Thus, on the basis of AE source location with four sensors situated around the beam-column joint, the AE is successfully correlated with the observed cracks. A strong correlation is also found between the accumulated plastic strain energy dissipated by the concrete and the accumulated AE energy. Based on this fact, a formula is proposed to predict the level of damage and the closeness to failure of an exterior beam-column subassemblage from the AE as recorded by sensors located near the joint.     

Effect of stress ratio on the enhancement of fatigue strength in high performance steel welded joints by ultrasonic impact treatment

In this study, we conducted fatigue tests under various stress ratios using cruciform welded joints to confirm the benefit of Ultrasonic Impact Treatment (UIT) for the fatigue strength of welded joints. The material used in the experiment is the JIS SBHS500 high performance steel for bridges. The fatigue life of the peened weld joint by UIT is significantly longer than that of as-welded joints, especially at a low stress ratio. We also estimated the fatigue life of these cruciform joints by crack growth analysis based on the crack opening and closure simulation using the modified strip-yielding model, accounting for the residual stress distribution created by welding or UIT. These estimation results demonstrate good agreement with experimental results obtained at various stress ratios.     

The fatigue behaviour of welded web attachments

Several superstructures located in the United States contain welded web details possessing low fatigue resistance. The cracking of several steel pier bents on the Dan Ryan Rapid Transit Line in Chicago and small cracks observed in other bridges with similar details has demonstrated that this is true. The objective of this paper is to examine the fatigue resistance of two commonly used web attachments. The first attachment considers a flange plate passing through the web of a girder and attached by welds on one or both sides. The second detail considers flange plates welded on both sides of the girder web.The stress distribution along the eventual crack path is used to predict the fatigue resistance of these details. The predicted fatigue resistance under cyclic load for the detail without web penetration and for details which penetrate relatively thin webs and were attached by welds on each side were in good agreement with other test results on long attachments. The predictions and test results fall within the fatigue limits of cover-plated beam data used to derive design provisions for the AASHTO Bridge Specification (Category). Tests with web penetrations in girders with thick webs typically gave results much more severe. This can mainly be attributed to lack of fusion in the web behind the weld and its adverse affect on the stresses in the weld. The applicability of Category E to such details is dependent upon the thickness of the web to which it is attached and the size of the welds used to connect the flange to the girder web that it passes through.     

Acoustic emission characteristics of concrete-piles

Acoustic Emission (AE) characteristics due to microcracking are studied in full-scale prestressed concrete-piles. By applying AE techniques, fundamental study on the fracture mechanism of the piles under both cyclic and monotonic loads is made. The prestressed concrete-piles are subjected to bending and shear loads. Crack growth is monitored, and three-dimensional (3-D) AE source locations are conducted along with crack classification and crack orientation by SiGMA analysis. The results obtained are compared with those of the pile integrity test (PIT) and visual observation. To investigate AE characteristics of damaged piles, uni-axial load is applied to the damaged RC piles installed in an experimental pit of sand. AE is monitored directly in the RC piles. In addition, indirect monitoring is carried out by using a wave-guide nearby the pile. In both the direct and indirect monitorings, AE sources are located, applying one-dimensional source location. Locations estimated are compared with the real damaged zone. Finally, conditions of AE generation of the damaged RC piles are discussed with respect to crack width and crack orientation.     

Reliability of the bending resistance of welded beam-to-column joints

This paper deals with the reliability of welded beam-to-column joints designed according to EN 1993-1-8. Based on the set of tests of welded beam-to-column joints, the experimental bending resistance has been obtained. The model’s uncertainty has been evaluated based on the comparison of the theoretical and experimental values of the bending resistance. Limit state equations have been defined for each mode of failure. The reliability index for each component of a joint is evaluated by using FORM, SORM and adaptive sampling. The obtained values of the reliability index of the individual components are discussed, as well as the sensitivity factors of basic variables and sensitivities of the reliability index to the mean value and to standard deviation of basic variables. The probabilistic analysis demonstrated that the component method adopted in EN 1993-1-8 has a high reliability level.     

钢筋焊接网疲劳性能试验研究

介绍了钢筋焊接网疲劳S-N曲线的表达方式、疲劳试验条件及试件破坏特征。通过对此次焊接网疲劳试验结果及国外部分数据的分析,以应力幅作为主要参数,取95%的保证概率,得出钢筋焊接网疲劳S-N曲线方程,并与国外的规范曲线进行比较。给出的疲劳S-N曲线方程基本反映了冷轧带肋钢筋焊接网的疲劳特性,可为有关标准规范的编制及工程应用提供参考。根据国外经验,介绍了疲劳荷载下的板类构件,给出了提高抗疲劳性能的几种典型施焊图例。     

线上钢轨焊接接头平直度检测影响因素分析

介绍了影响线上钢轨焊接头平直度检测的两个主要因素,分析了每种因素对平直度检测的具体影响规律,达到预防检测影响因素影响平直度检测结果的效果。轨道交通线路设计目前多采用跨区间无缝线路,无缝线路中钢轨焊接接头成为了线路的薄弱环节,新建轨道交通线路或既有线路大修后,在开通运行前都会进行焊接接头平直度检测,平直度检测的精确性直接关系到列车运行安全和轨道结构使用寿命。     

A review on assessment of fatigue strength in welded studs

Welding is one of the most important and highly developed joining methods; nevertheless unwanted side effects occur like thermal strains and altering of certain material properties induced by heating and melting. These effects lead to distortions and high residual stresses which should be kept to a minimum. To minimize distortion, various strategies are being developed. Stud welding is widely used in steel structures, power plants, and ship buildings due to the significantly technology including highest quality of production processes by continuous electrical control and the efficiency of such a process. Therefore, varying the heat input typically will affect the material properties including yield strength, tensile strength, hardness, and notch toughness in the stud arc welding. Well-defined heat sources offer a reproduced heat input into a highly localized area. The fatigue strength of stud welding has been investigated by performing welding process and microstructural observations. This paper is going to discuss the influence of heat input on the structural changes in stud arc welding.     

细晶花岗岩的声发射特征试验研究

对葡萄牙细晶花岗岩同一岩样进行多次单轴压缩循环加卸载试验,监测试验过程中岩样的声发射活动,记录岩样的变形特征,分析总结声发射与变形之间的相互关系。试验表明,葡萄牙细晶花岗岩在高应力状态下凯塞效应明显,所受应力越高,凯塞效应越弱;在判断岩石凯塞点时,因时间–累计声发射能量曲线中拐点明显,比利用时间–累计声发射事件数曲线更容易、更合理;另外,了解试样的变形特征对解释声发射试验结果是一个有益的补充。