Tragfähigkeit fehlerhafter Schweißnähte

Load bearing capacity of welds with defects. Only welds fabricated according to requirements in execution standards are within the scope of actual design codes. These execution standards do not tolerate imperfections like lack of fusion at the weld root even in case of predominantly static loading. In the recent years, steel products with increasing thicknesses are used for steel constructions. The volume of the weld and thus, the costs for welding increases with about the second power of the thickness. Therefore, partial penetration instead of complete penetration and joint preparations with small angles of bevel are applied, if design aspects allow this. As a consequence, lack of fusion at the weld root cannot always be avoided, especially if thick components are welded. There are no design rules for these welds with defects. Therefore, the effect of imperfections on the load bearing capacity of differently fabricated welds is investigated with tests, numerical and fracture-mechanical calculations.     

Schweißen ermüdungsbeanspruchter Altstahlkonstruktionen – Untersuchungen zum Einfluss der Vorbelastung auf die Lebensdauer der Schweißkerbdetails

Welding of existing steel structures – Effect of prior load cycles. When existing structures under fatigue load are to be strengthened or refurbished by welded joints fatigue assessment is required for new welds. For the analysis of existing structures or determining of their remaining fatigue life, experimental investigations were carried out in order to estimate the effect of prior load cycles on the material. Mild steel specimens were preloaded cyclically, then surface treatment was applied and a notch representative for a real weld of a structure was introduced. The results of fatigue tests were compared with fatigue tests on similar non‐preloaded specimens. It has been found that there is no significant effect of prior load cycles if the surface is treated prior to welding and enough fusion penetration depth is given. Therefore, fatigue assessment of new welds on old materials does not need to take into account prior load cycles.     

球罐球壳板组对焊缝清根坡口的磁粉检测

大型球罐压力容器的切片球壳板都采用现场焊接成整体的安装工艺。球壳板厚度通常都在30mm以上,为避免焊后根部和内外表面存在裂纹、未熔合、未焊透、夹渣等缺陷而造成质量隐患,所以在焊接过程中必须对焊缝进行多次磁粉检测,包括焊接前的球壳板坡口检测、焊接过程中焊缝的坡口清根检测、焊后热处理前的焊缝及热影响区检测和水压后的焊缝和热影响区检测。而其中清根坡口磁粉检测则尤为重要。检测结果表明,在球罐赤道带以上焊缝容易产生应力裂纹、未熔合等缺陷,而清根坡口磁粉检测可以有效检测出根部的表面开口和近表面缺陷。     

Determination of elastic modulus of claystone: Nano-/micro-indentation and meso-compression tests used to investigate impact of alkaline fluid propagation over 18 years

Micro-mechanical properties of a claystone were tested after undergoing alkaline perturbation on site(Tournemire,CD borehole)for 18 years.In a saturated context and outside the excavation disturbed zone(EDZ),the claystone exhibits a 11.6-mm black rim at the cement/paste interface,which shows a different mechanical behaviour from the rest of the claystone.Three sets of measurements of elastic modulus were performed using:(i)nano-indentation tests with a constant indentation depth of 2 mm,(ii)microindentation tests with a constant indentation depth of 20 mm,and(iii)meso-compression tests with a constant displacement of 200 mm.The increase of the modulus of deformability in the black rim is between 15 GPa and 20 GPa according to the scale.Moreover,an overall decrease of the modulus of deformability from the smallest to the largest scale is observed in each zone.In view of the mineralogy and petrographic observations,higher values of modulus of deformability in the black rim are related to carbonate content and its distribution.Precipitation of cementitious carbonates as inclusions and very thin partings leads to hardening of the claystone.     

Microstructure and transverse shrinkage stress analysis in GTA welds of P91 steel pipe

In a steam power plant, several components such as boiler tube, condenser and steam lines are made of high creep resistant steel. The P91 steel pipes are generally used in steam power plant because of high creep strength at service temperature of approximately 600oC. In the present research work, the study about shrinkage stresses and their distribution in the four quadrants of P91 pipe weld of 11 mm thickness is reported. The conventional-V and narrow-groove welds were prepared by using the gas tungsten arc welding (GTAW) process. Welding current, arc voltage, groove design, and straining length were the main parameters that affect the transverse shrinkage stresses. In the present research work, the effect of groove design on transverse shrinkage stresses has been evaluated. It also describes the effect of the number of passes on shrinkage. It is concluded that, for a given heat input, the narrow groove pipe weld joint exhibits comparatively less transverse shrinkage stress. Scanning electron microscope (SEM) with field emission gun and optical microscope has been used to characterize the weld fusion zone and HAZs of P91 pipe weldments.

     

Fatigue Strength and Root-Deck Crack Propagation for U-Rib to Deck Welded Joint in Steel Box Girder

Fatigue tests and numerical analysis were carried out to evaluate the fatigue performance at the U-rib to deck welded joint in steel box girder. Twenty specimens were tested corresponding to different penetration rates (80 and 100%) under fatigue bending load, and the fatigue strength was investigated based on hot spot stress (HSS) method. The detailed stress distribution at U-rib to deck welded joint was analyzed by the finite element method, as well as the stress intensity factor of weld root. The test results show that the specimens with fully penetration rate have longer crack propagation life due to the welding geometry, resulting in higher fatigue failure strength. The classification of FAT-90 is reasonable for evaluating fatigue strength by HSS method. The penetration rate has effect on crack propagation angle near the surface, and the 1-mm stress below weld toe and root approves to be more suitable for fatigue stress assessment, because of its high sensitivity to weld geometry than HSS.     

波形反对称软钢阻尼器力学性能试验研究

设计了一种波形软钢阻尼器,针对其滞回力学特性和耗能减震能力,进行了2个波形钢板不同放置形式的波形软钢阻尼器的拟静力试验,试验结果表明波形软钢阻尼器具有稳定的滞回性能和良好的塑性变形能力。其中由于竖向波形软钢阻尼器在水平方向会产生拉压应力场,压缩刚度大,导致其滞回性能和延性均比水平波形软钢阻尼器的差。在整个试验加载过程中,未出现焊缝撕裂现象,说明二氧化碳保护焊可以很好地保证阻尼器整体结构承载和变形能力。利用ABAQUS有限元分析软件建立6个波形软钢阻尼器模型,以试验中的水平波形软钢阻尼器作为基本模型,钢板厚度和波角两个因素作为变量,进行数值分析,结果表明:模拟分析与试验结果吻合较好;当钢板波角为60°时,波形软钢阻尼器力学性能最优;钢板厚度过大会使阻尼器角部应力集中,过早产生局部屈曲,而厚度偏小会使得阻尼器的耗能能力和承载能力不佳,钢板厚度取值6 mm时力学性能最佳。     

丁香特大桥钢箱梁熔透角焊缝的焊接工艺

介绍了丁香特大桥钢箱梁的结构形式、特点以及丁香特大桥钢箱梁熔透角焊缝的焊接工艺。经产品性能试验证明 ,按该工艺施焊的钢箱梁熔透角焊缝的性能能够满足设计和使用要求     

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。     

组合效应对高层钢框架梁柱节点脆性破坏的影响分析

美国北领地震中,不少钢框架梁柱连接出现了意想不到的脆性破坏。观察表明,大部分破坏发生在节点区的梁下翼缘与柱翼缘之间的全熔透焊缝以及相邻板件的焊缝热影响区。由此可知,焊缝质量不良是节点断裂的主要因素。此外,连接缺乏有效的延性也是破坏的一个原因。节点抗震性能试验中多数采用的是钢节点,没有考虑钢梁上的混凝土板。实际结构中,混凝土楼板的存在提高了节点连接的强度和刚度,这也就加剧了下翼缘发生脆性破坏。通过有限元方法,分析了混凝土板组合效应对梁柱节点脆性破坏的影响。     

箱形薄壁构件内隔板电渣焊技术

箱形截面构件薄壁板与内隔板电渣焊接时 ,易产生壁板烧穿和焊缝未熔合现象。通过焊接熔透性工艺试验、调控焊接工艺参数、优选装配坡口尺寸、提高衬条及隔板加工精度 ,保证了电渣焊质量和焊接效率的提高。     

海洋钢结构常见裂纹形式及预防措施

在钢结构焊接时由于主观、客观因素的影响,经常会出现裂纹、气孔、夹渣、未熔合、未焊透、咬边、焊瘤、烧穿、凹坑和弧坑、飞溅等缺陷,在这些缺陷当中,裂纹是焊接生产中比较普遍而又最危险的缺陷,它不仅减少承载截面,产生严重的应力集中,还会在使用中逐渐扩大,最后导致构件的破坏,造成废品,严重的还会带来灾难性的事故。预防裂纹或其它缺陷的产生和焊后外观检验发现缺陷是我们焊接检验工程师义不容辞的责任和使命。     

变截面方钢管轻骨料混凝土柱-H钢梁隔板贯通节点抗震性能试验研究

通过对变截面方钢管轻骨料混凝土柱-H钢梁圆弧扩大头隔板贯通节点和基本型节点进行低周往复加载试验,分析了该类节点的破坏形态、滞回性能、延性、承载力、刚度退化与耗能能力等。结果表明：隔板圆弧扩大头节点先在隔板圆弧扩大区形成塑性铰,随后梁腹板焊接孔开裂,梁翼缘对接焊缝延性拉断;基本型节点在梁翼缘对接焊缝侧边开裂,裂纹扩展迅速至脆断;隔板圆弧扩大头构造明显提高了节点延性和耗能能力,有效降低了节点区焊缝过于密集和焊接热影响区的交叉影响,避免了梁翼缘对接焊缝处的应力集中和过早脆断;隔板圆弧扩大头节点的承载力、塑性转角和耗能能力较基本型节点分别提高16.09%~22.25%、17.34%~63.94%和24.97%~44.32%;加载到节点破坏时,节点域和柱内轻骨料混凝土未发生压碎、剥离、拉裂或滑移破坏,说明该类节点的抗震性能主要受钢梁与隔板间焊缝影响。     

The effects of electro slag welding on material properties of box column plates

The effects of electro slag welding (ESW) on the material properties of box column plates, which is ASTM A572 Gr. 50 steel, were investigated experimentally and numerically. The material properties of the column plates before and after ESW were evaluated by macro-etching observation, micro-structural observation, and CVN impact tests. The temperature distribution of the column plates, with the ESW heat cycle as the heat input, was simulated by using the ANSYS FEM software. It was found that: (1) The CVN values in the through thickness direction of the base metal can be as low as 14J, 8.1J, and 8.1J at 0°C for plate thicknesses of 32, 40, and 50 mm respectively; (2) During the ESW process, the measured peak temperature for a 25×50 mm column plate surface was as high as 1033, 880 and 744°C for plate thicknesses of 32, 40 and, 50 mm respectively; (3) After the ESW heat cycle, the through thickness CVN value decreased by 68% for the coarse grain heat affected zone (HAZ) of the column pate; (4) The FEM thermal conduction model developed was able to simulate the temperature distribution of the steel plate during the ESW process with reasonable accuracy; (5) To avoid welding penetration due to ESW, a minimum plate thickness is suggested; (6) The impact of ESW heat cycle is more significant for thin column plates compared to thick ones.     

Seismic Performance Evaluation of Steel Box-Column Connections with ESW Stiffeners

The purpose of this study is to evaluate the seismic performance of steel box-column connections with electro-slag welding (ESW) stiffeners. Steel box columns have been widely adopted in seismically active areas, such as Japan and Taiwan. It is a common practice to weld diaphragm plates to the inner walls of steel box columns using the ESW process. However, there is still a lack of study evaluating the seismic performance of these steel box-column connections. In the first part of this paper, a literature review examines ESW stiffeners and their impacts on steel box-column connections. In the second part, finite element analysis is conducted on ESW misalignment and eccentricity. The result shows a correlation between connection failures and ESW stiffeners. In addition, ESW fusion diameters can affect the connections more significantly than ESW eccentricities and the thickness of diaphragm plates.

     

大型城市钢箱梁高架桥安装焊缝焊接与质量控制

武汉市二环线汉口段黄埔大街-金桥大道工程中的钢箱梁高架桥长达6200m,钢板厚为14～40mm,各类焊缝总长超过2200km,具有安装量大、结构复杂、熔透焊缝多、制作安装难度大等特点。采取纵向与横向分段相结合的形式,顶底板上对接熔透的一级焊缝较多,均采用陶质衬垫富氩CO2气体保护焊进行焊接和打底焊接;同时,采取合理的焊接工艺与焊接顺序,确保钢箱梁整体安装尺寸的精度;通过对焊缝进行射线、超声波及磁粉等检测,焊缝质量符合设计与规范要求。     

Shear capacity and tension capacity of arc-spot welds for multi-overlap deck panels

Arc-spot welds fabricated in multi-overlap configurations are found in roof deck construction when steel sheets are stacked at a sidelap or endlap. A welding technique that maximizes the quality of arc-spot welds fabricated through several layers of thick sheets is presented. Weld specimens were fabricated through 1, 2 or 4 layers of steel sheets with thicknesses ranging from 0.76 to 1.52 mm (22 to 16 gauge). The most important factors to control during the welding are the current (high intensity), the electrode type (E4311) and the welding technique. Various sheet steel/weld configurations found in roof deck construction were included. Adequate weld quality could be achieved in all cases except that welds were undersized when the ratio of the thickness of the underlying material to total sheet thickness was less than 0.7. A total of 72 tension tests and 107 shear tests were completed. Of those, 31 shear specimens were loaded with a reversed cyclic protocol to examine the behaviour of arc-spot welds subject to seismic loading. All other specimens were loaded under monotonically increasing displacement. The results were compared with the provisions of the CSA S136 North American Specification for the Design of Cold-Formed Steel Structural Members. The CSA S136 equations for shear and tension resistance of arc-spot welds are generally conservative, even for welds fabricated through multi-overlap configurations with total sheet steel thicknesses exceeding the 3.81 mm limit. Nonetheless, modifications to the equation for the effective diameter and to Equations E2.2.1.2-2, E2.2.2-1, and E2.2.2-2 are recommended.     

A study on the material characteristics and the welding properties of the HSA800 steel

In this research, 7 species of material characteristics test and 9 species of welding properties test for FCAW and SAW were proceeded to confirm the various material characteristics and welding properties of HSA800 developed recently. As a result of material test, HSA800 steel satisfied the KS and the criteria of homogeneity for the strength of the steel, confirmed as sound steel having excellent directivity and toughness. Test results of the FCAW and SAW partially satisfied the KS and the criteria of homogeneity for the strength of the steel, and confirmed as having a good weld zones. However, the result of SAW weld zone chemical composition test showed that the P composition is not satisfying the KS. According to the result of weld zone rod and plate tensile test results, the FCAW 1G appeared more better than the FCAW 3G, and the SAW PH2 appeared more better than the SAW PH1.

     

Eine Methode zur Bewertung von Restspalten in Schweißnähten an T‐ und Kreuzstoßverbindungen

A method to assess root gaps in welded seams of T‐ and Cross joints. Design and welding codes require full penetration in case of complete butt splices. This often ends up to time‐ and cost‐intensive repair work for the executing steel work company. Quite recently, classification methods and along with these, a method of tolerating such partial penetrations (here: root gaps) to be considered right from the weld design or planning stage were actually missing, so that additional manufacturing work was preassigned from the outset. Within an AiF‐DASt‐research project [1] an assessment method has been developed basing on an accurate detection of root gaps by non‐destructive testing methods. That method guarantees the demanded structural reliability of a steel structure despite of leaving a weld that actually is to be rejected due to insufficient penetration according to the conventional codes.     

车轮荷载作用下双工字钢组合梁桥横桥向 焊钉拉拔效应

针对双工字钢组合梁在车轮荷载作用下引起的钢混界面横桥向掀起效应导致焊钉出现拉拔应力的问题展开讨论,为分析此效应对双工字钢组合梁焊钉受力的影响从而为焊钉布置提供参考,对2×35 m双工字钢组合连续梁的焊钉拉拔应力分布规律及影响因素进行了研究。分析了6种采用不同单元类型、焊钉模拟方式、接触关系的ABAQUS有限元模型组合梁钢混界面横桥向掀起效应计算结果,通过对比已有文献中的试验结果,确定了合理的有限元模拟方法。基于此方法,分析了车轮荷载作用位置、加劲肋与横梁设置形式对焊钉拉拔应力沿纵横桥向分布的影响; 研究了横梁位置、桥面板厚度与主梁间距比、焊钉横桥向间距对焊钉拉拔应力的影响并讨论了焊钉拉拔应力对各参数的敏感性。结果表明:加劲肋限制了钢梁上翼缘随桥面板变形,导致焊钉产生明显拉拔应力; 焊钉应力沿纵桥向衰减速度很快; 设置横梁能减小双工字钢组合梁的侧向变形,导致焊钉拉拔应力大幅提高,最多能提高317.97%; 焊钉拉拔应力随着桥面板厚度与主梁间距比增大而逐渐减小,随着横梁中心线距钢梁上翼缘距离的增大呈现出先增大、后不变、最后略微减小的趋势,随焊钉横向间距增大出现先增大后减小的现象; 各参数中,桥面板厚度与主梁间距比对焊钉拉拔应力数值的影响最为显著; 根据焊钉拉拔应力分布规律及影响因素,建议应适当加密双工字钢组合梁加劲肋与横梁附近的焊钉。