Neuste Entwicklungen von thermomechanisch gewalzten Feinkornbaustählen – Erfahrungen aus Offshore‐Industrie und Stahlwasserbau

Newest development for thermomecanically rolled steels plates – experiences with offshore constructions and hydropower plants. This article reports about the newest development for thermomechanically rolled steels plates. Steel products with a minimum yield strength of 500 MPa can today be produced by thermomechanical rolling in a thickness range up to 100 mm. The first‐mentioned steel plates are especially characterized by very good fabrication properties, in particular an excellent weldabilty. The article will also describe the first experiences gained with these steel grades in the fields of offshore construction and hydro power plants.     

Elevated-temperature mechanical properties of high strength structural steel S460N: Experimental study and recommendations for fire-resistance design

Fire-resistance design is one of the most important considerations when structural engineers conduct design of steel structures. As a basis of analyzing fire performance of steel structures, elevated-temperature mechanical properties of structural steels are significant for practical design. The recommendations of current European, American, Australian and British standards were mainly obtained from mild steels, which are in question when used to conduct fire-resistance design of high strength steel structures. In order to reveal the elevated-temperature mechanical properties of high strength steel S460N, tensile tests were conducted at various temperatures ranged 20–700 °C. The elevated-temperature reduction factors of elastic modulus, yield and ultimate strengths of S460N were obtained and compared with current design standards and available literature. According to the comparison between this research result on S460N and the available research results in literature on S460N, S460M and various mild steels, it is found that the deterioration of mechanical properties of structural steels at elevated temperature is dependent on steel grades. Thus the recommendations in current design standards are not applicable to high strength structural steels. Further unique predictive equations for the deterioration of high strength structural steel S460 at elevated temperatures were proposed and validated with available literature.     

端部带约束的超高强度钢材受压构件整体稳定受力性能

高强度钢材(屈服强度≥460MPa)已经在国内外多个钢结构实际工程中得到应用,但关于其受压构件整体稳定性的研究还很少,特别是屈服强度超过690MPa的超高强度钢材。针对两种超高强度钢材S690和S960(名义屈服强度分别为690MPa和960MPa),进行了端部带约束的受压构件整体稳定受力性能的试验研究,试验共包括8个试件。基于试验结果,分析该类钢材构件的失稳破坏形态和屈曲承载力,利用经过验证的有限元模型计算其整体稳定系数,并与欧洲规范和我国规范的柱子曲线进行对比分析。结果表明,超高强度钢材受压构件整体稳定系数的试验值要明显高于其所在的b类柱子曲线,甚至比欧洲规范的a0类柱子曲线和我国规范的a类柱子曲线还要高出很多。这说明超高强度钢材受压柱的屈曲强度较普通强度钢材的屈曲强度有明显提高。这些试验研究和有限元分析成果为完善我国超高强度钢材的稳定设计方法和设计理论提供了重要的试验依据和前提条件,并有利于超高强度钢材在我国钢结构工程中得到更广泛的应用和发展。     

Untersuchungen zum Ermüdungsverhalten von Konstruktionsteilen für Mobilkrane

Fatigue behaviour of component sections of mobile cranes out of high strength steel plates. High‐strength structural steels with 960 and/or 1100 MPa minimum yield strength allow a decrease of the investment and operating costs of mobile cranes through lightweight design. However, there still exists an uncertainity for stress resistance under cyclic loads and bearable stresses concerning fatigue behaviour of important crane components. This paper deals for the first time with the fatigue behaviour of crane components examined under realistic load‐time‐cycles derived from realistic crane operating conditions. The results supply important information on the service life. The service life depends in this case strongly from the tension level considerably. The influence of the here applied load‐time‐cycles appears on the other hand small. Additionally, this paper provides a new tool with which the fatigue behaviour of crane components under most different aspects and involved variable combinations can be estimated, consistent with measured values, through a fracture mechanically based model. There can be made important procedure recommendations and hints can be given for a more intense use of high‐strength structural steels for practical application in mobile crane engineering. Inspection intervals and contents can be newly determined. The usage of steels with more than 1100 MPa minimum yield strength in the mobile crane building is evaluated crucially.     

Numerical study on structural performance of corrugated steel plate shear wall with different yield points steel

As a new type of lateral load-resisting system in SPSW systems, corrugated SPSWs (CSPSWs) have been gradually researched and applied. Corrugated plates offer various advantages over flat plates including higher energy dissipation capacity, ductility, out-of-plane stiffness, and improved buckling stability. For seismic control and isolation techniques, low yield point (LYP) steels (LY100, LY160, and LY225) are the reliable and ideal energy-dissipating materials. The low yield point CSPSWs combine high energy-consuming materials with high-performance structures to provide a better solution for ductile and seismic resistance of high-rise and super tall buildings. Currently, there are no design codes addressing the seismic performance of LYP corrugated steel plate shear walls (CSPSWs). This study investigates cyclic behavior and energy dissipation performance of corrugated steel plate yield point (100, 160, 225, 235, and 345 MPa) of different thickness CSPSWs and determine the plate yield point that provides the optimum performance. Results and findings of this study reveal that compared with the ordinary yield strength corrugated steel plates, the low yield point CSPSWs have a larger safety factor of lateral bearing capacity, a fuller hysteresis curve, a strong energy dissipation coefficient, a larger ductility coefficient and a smaller fluctuation range of strength degradation coefficient, and better strength stability. The initial equivalent stiffness of CSPSWs with different yield strengths is the same.     

Ermüdungsverhalten von Mobilkranbauteilen aus hochfesten Baustählen

Fatigue behaviour of component sections of mobile cranes out of high strength steel plates. High‐strength structural steels with 960 and 1100 MPa minimum yield strength allow a decrease of the investment and operating costs of mobile cranes through lightweight design. However, there still exists an uncertainity for stress resistance under cyclic loads and bearable stresses concerning fatigue behaviour of important crane components. This paper deals for the first time with the fatigue behaviour of crane components examined under realistic load‐time‐cycles derived from realistic crane operating conditions. The results supply important information as they indicate that the service life for both steels, even with very high applied stress, is at least 20years. Moreover, it is shown that further improvements of the durability are possible around up to 50% through subsequent treatment of the welds, toughness improvement of the base material and constructive remodelling of the components. Additionally, this paper provides a new design method with which the fatigue behaviour of crane components under most different aspects and involved variable combinations can be estimated, consistent with measured values, through a fracture mechanically based model. Important procedure recommendations and hints can be given for a more intense use of high‐strength structural steels for practical application in mobile crane engineering. Inspection intervals and contents can be newly determined.     

Tests and numerical study of ultra-high strength steel columns with end restraints

High strength steels with the nominal yield strength more than 460 MPa have begun to be applied in the construction of many steel structures, but there are short of sound researches on the major axis buckling behavior of such steel welded I-section columns, especially for the ultra-high strength steels having the nominal yield strength more than 690 MPa. In this paper, the experimental research is described on the overall buckling behavior about the major axis of ultra-high strength steel compression I-section columns with end restraints. In this research 8 columns made from 2 kinds of ultra-high strength structural steels S690 and S960, with nominal yield strengths of 690 MPa and 960 MPa, respectively, were tested. Based on the test results, the finite element analysis (FEA) model was validated to analyze this behavior of ultra-high strength steel columns, and the buckling strength of pin-ended columns fabricated from such steels were calculated by the verified FEA model, which were compared with the design buckling strengths according to the Eurocode 3, the American specification for structural steel buildings ANSI/AISC 360–05, and the Chinese codes for steel structures design GB50017-2003 respectively. It shows that the major axis nondimensional buckling strengths of the ultra-high strength steel compression columns, whose buckling curve is type b according to Eurocode 3 and GB50017-2003, are much higher than that calculated according to the column curve b, even higher than the curve a₀ in Eurocode 3 and the curve a in GB50017-2003 on average, and they are also higher than the design values according to ANSI/AISC 360–05. It is therefore indicated that the buckling strength about the major axis of the ultra-high strength steel I-section columns is improved a lot compared with the ordinary strength steel columns on a non-dimensional basis, and the column curve a₀ and curve a can be adopted to design this behavior in Eurocode 3 and GB50017-2003, respectively. Besides, there is no obvious difference between the major axis nondimensional buckling strengths of the pin-ended I-section columns fabricated from these two kinds of ultra-high strength steels: S690 and S960. These research works will provide the test basis to complete the buckling design method and theory of the ultra-high strength steel columns, and also be helpful for the application of ultra-high strength steel structures.     

焊接热切高强H型钢的残余应力

构件中所存在的残余应力会大大影响钢结构组件的刚度和疲劳寿命。虽然对于低碳钢的结构部件有较多的研究,但由于在常温和高温下应力-应变关系和材料属性的不同,造成了残余应力分布在高强钢构件中与低碳钢焊接而成的构件中的差异。因此,有必要研究由高强钢焊接而成的结构部件中残余应力的分布。对3个屈服强度460MPa的焊接热切高强型钢柱的残余应力进行研究,对不同横截面大小也进行了分析。使用切片法和钻孔法测量,并对两种方法所获得的残余应力进行比较。所测量的残余应力的大小和分布与碳钢中的一致,然而却有相对更小的残余应力比。最后,根据所测量的值,提出一个简化的由热切H型钢焊接而成的460MPa高强钢构件的残余应力分布。     

Residual stresses in welded flame-cut high strength steel H-sections

The presence of residual stress in members can significantly compromise the stiffness and fatigue life of steel structural components. Researches in this area are well documented for structural members of mild carbon steels. Nevertheless, due to the difference of stress–strain relations and material properties under ambient and high temperatures, the residual stress distribution in a high strength steel member is physically different from those fabricated from mild carbon steel. It is imperative to study the residual stress distribution for structural members fabricated from high strength steel. In this paper, the residual stresses of three welded flame-cut H-section columns with a nominal yield strength of 460 MPa but different cross-section dimensions were investigated. Both sectioning and hole-drilling methods were used in the measurement and the obtained residual stresses were compared between the two methods. The magnitudes and distributions of the measured residual stresses are identical with those of carbon steel, however in relatively smaller residual stress ratios. Finally, based on the measurements, a simplified residual stress distribution for 460 MPa high strength steel members with welded flame-cut H-section is proposed.     

Schweißen von Feinkornstählen und deren Eignung für Offshore‐Windenergieanlagen

Welding of fine grain structural steels and there suitability for offshore wind power plants. The investigations show that the high requirements on the mechanical values of a welded joint can be fulfilled by economical process versions of submerged arc welding. The submerged arc tandem twin welding process is predestined for the production of WPP (wind power plant) because of the high value of melting rate and the small expenditure of equipment. The used filler metal is suitable for the production of welded joints with mechanical values which fulfil safely the requirements. Steel grades produced by the TMCP becoming more and more popular for the producers of wind power generator tower because of there better processing and working properties. In comparison with normalized steel grades the TMCP steel grades have e.g. a lower carbon equivalent and higher toughness properties. With increasing clarity of the standards and of the working direction of the European offshore wind power industry further challenges will be appear for the producers of steel, wind power plants and welding equipment. A close cooperation between al partners is inalienable in that case.     

960 MPa高强度钢材轴心受压构件局部稳定试验研究

针对960 MPa高强度钢材轴心受压构件的局部稳定性能,对4个箱形截面试件和4个工字形截面试件进行了轴心受压试验。分析了试件的局部稳定性能,并将试验结果与我国、美国和欧洲钢结构设计规范的相应设计计算结果进行了对比分析,研究各国规范对960 MPa高强度钢材轴心受压构件局部稳定性能设计计算的适用性。研究结果表明：当构件的板件宽厚比相同时,960 MPa高强度钢材构件的局部屈曲后强度要大于460 MPa高强度钢材构件,960 MPa高强度钢材构件应考虑钢材的屈曲后强度;我国现行钢结构设计规范中关于轴心受压构件局部屈曲应力的计算结果不适用于960 MPa高强度钢材构件;在试验钢材板件宽厚比范围内,960 MPa高强度钢材构件的局部屈曲承载力,采用美国规范和欧洲规范的设计计算结果较为准确。     

低屈服点钢在结构耗能减震中的应用

低屈服点钢的力学特点是屈服强度低,强度稳定,变形能力强,因此低屈服点钢的应用成为结构变形耗能的一个重要途径。对低屈服点钢在结构耗能减震中的应用现状进行介绍,提出低屈服点钢在弹性耗能结构中的应用方式,分析该弹性耗能铰的施工技术和耗能机理,为低屈服点钢的应用推广提供借鉴。     

Reduktion der Wanddicken bei Tragtürmen von Windenergieanlagen durch den Einsatz höherfester Stähle

Reduction of plate thickness of wind energy converters made by high strength steels. The design of wind energy converters is significantly defined by the fatigue strength of critical notch details, especially welded joints. The usage of high strength steels leads to no economical benefit because the fatigue strength of welded notch details are defined in design rules independently from the yield strength. The application of post weld treatment methods may increase the fatigue strength of these details significantly. Investigations on high frequency peening methods prove that a doubling of the fatigue strength can be achieved for steel grade S 690. An example of a connection detail is presented where it can be shown that by the application of the investigated methods together with a steel S 690 Q the plate thickness can be reduced to 45%.     

Local buckling of grouted and ungrouted internally stiffened double-plate HPS webs

High performance steel (HPS) is rapidly gaining attention as a desirable material for highway bridge girders largely due to its superior toughness properties and high strength. However, the benefits of using steels with nominal yield strengths of 485 MPa (70 ksi) or greater is restricted by factors such as web stability, deflection, and fatigue design limits, which may govern the design and prevent the effective utilization of the material strength. Therefore, new and innovative bridge design concepts are needed to take better advantage of the enhanced properties of HPS. One design innovation that provides a means of optimizing bridge girders for high strength material utilizes I-girders with double web plates. The web is composed of two steel face plates connected internally by continuous longitudinal stiffening elements. The voids between the face plates may be grouted or ungrouted. The stiffeners permit thin webs to be used, while still allowing the material to reach stresses as high as the yield strength without buckling. In the case of grouted webs, composite behavior increases the out-of-plane stiffness of the web, although bond between the two materials may be unreliable. Nevertheless, it is shown that even in a debonded state, the presence of the grout enhances the buckling capacity of the face plates significantly. Using classical plate buckling theory, design criteria are proposed for bend buckling of the web face plates, considering both the grouted and ungrouted cases. As a means of assessing the anticipated behavior of the plates, upper and lower bounds to the buckling strengths are established. In order to evaluate the ability of classical plate theory to predict the buckling of the face plates, tests were conducted on a series of web panels that simulate a portion of a girder web subjected to flexural compressive stresses. Two of the specimens were ungrouted, two were grouted with a cementitious material, and one was grouted with an epoxy grout. It was confirmed that the presence of grout increased the buckling capacity of the face plates and that the improved bond using epoxy grout served to delay buckling as well, although when the bond broke the failure was sudden. The experimentally determined buckling loads are used to validate the theory.     

Study on nominal values of mechanical properties of high strength steel at elevated temperature and after fire exposure

高强钢高温下和高温后的力学性能是进行高强钢结构抗火设计和火灾后评估的重要基础。我国GB 51249—2017《建筑钢结构防火技术规范》和欧洲规范EC3中针对普通低碳钢提出了高温下屈服强度和弹性模量计算公式，但其不适用于高强钢。国内外学者对高温下和高温后高强钢力学性能已开展了一系列试验研究，但由于钢材强度等级、试验设备、加热速率和加载制度等影响，导致试验结果离散性较大，不能应用于实际工程中。同时不同学者提出的力学性能指标计算式各不相同，均不具有普遍适用性。采用数理统计中t分布与置信区间的方法对高强钢高温下和高温后力学性能试验数据进行统计分析，得到不同温度下力学性能指标具有95%保证率的标准值，拟合出高强钢高温下和高温后力学性能指标的计算式，并与GB 51249—2017和欧洲规范EC3预测结果进行对比。结果表明：自然冷却和浸水冷却条件下，高强钢高温后屈服强度发生明显下降的转折点分别是600℃和 500℃；高温下高强钢的屈服强度折减系数低于普通结构钢；高强钢弹性模量折减系数在作用温度小于600℃时低于普通结构钢的，而在温度大于600℃时高于普通结构钢的。     

高强钢高温下和高温后力学性能指标的标准值研究

高强钢高温下和高温后的力学性能是进行高强钢结构抗火设计和火灾后评估的重要基础。我国GB 51249—2017《建筑钢结构防火技术规范》和欧洲规范EC3中针对普通低碳钢提出了高温下屈服强度和弹性模量计算公式,但其不适用于高强钢。国内外学者对高温下和高温后高强钢力学性能已开展了一系列试验研究,但由于钢材强度等级、试验设备、加热速率和加载制度等影响,导致试验结果离散性较大,不能应用于实际工程中。同时不同学者提出的力学性能指标计算式各不相同,均不具有普遍适用性。采用数理统计中t分布与置信区间的方法对高强钢高温下和高温后力学性能试验数据进行统计分析,得到不同温度下力学性能指标具有95%保证率的标准值,拟合出高强钢高温下和高温后力学性能指标的计算式,并与GB 51249—2017和欧洲规范EC3预测结果进行对比。结果表明：自然冷却和浸水冷却条件下,高强钢高温后屈服强度发生明显下降的转折点分别是600℃和 500℃;高温下高强钢的屈服强度折减系数低于普通结构钢;高强钢弹性模量折减系数在作用温度小于600℃时低于普通结构钢的,而在温度大于600℃时高于普通结构钢的。     

Verbesserung der Ermüdungsfestigkeit höherfester Baustähle durch Anwendung der UIT‐Nachbehandlung

Enhancement of the fatigue strength of welded high strength steels by application of Ultrasonic Impact Treatment (UIT). According to the present state of the art welded high strength steels have the same fatigue strength as welded standard steels. For an effective application of high strength steels in constructions subjected to fatigue are therefore additional efforts necessary in order to improve the fatigue strength, for example by the application of post‐weld treatment methods. However up to the present it is not possible to apply the positive effects of these methods in the fatigue design of steel structures. Within this paper an experimental test program studying the effectiveness of the post‐weld treatment method “Ultrasonic Impact Treatment” (UIT) on the critical construction detail of the transverse stiffener is presented. The test program comprises small scale fatigue tests on the standard and high strength steel grades as well as full size girder fatigue tests. Based on experimental and numerical investigations recommendations for the fatigue design of welded structures treated by UIT are given.     

Seismic performance and cost‐effectiveness of high‐rise buildings with increasing concrete strength

The relationship between the seismic performance and economics of high‐rise buildings when designed to different material strengths is investigated in this paper. To represent the modern high‐rise construction, five 60‐story reinforced concrete buildings with varying concrete strengths, ranging from 45 MPa to 110 MPa, are designed and detailed to fine accuracy keeping almost equal periods of vibration. Detailed fiber‐based simulation models are developed to assess the relative seismic performance of the reference structures using incremental dynamic analyses and fragility functions. It is concluded that a considerable saving in construction cost and gain in useable area are attained with increasing concrete strength. The safety margins of high‐strength concrete in tall structures may exceed those of normal‐strength concrete buildings, particularly at high ground motion intensity levels. The recommendations of this systematic study may help designers to arrive at cost‐effective designs for high‐rise buildings in earthquake‐prone regions without jeopardizing safety at different performance levels. Copyright © 2014 John Wiley & Sons, Ltd.     

Axial capacity of circular hollow section T-joints using grade HSB 600 steel

Because of their structural efficiency and aesthetic appeal, steel circular hollow sections have been used in the construction of a wide range of structures. As more high-rise and long span buildings are built, there has been an increase in demand for high strength steel with sufficient ductility. Steel of grade HSB (High performance Steel for Bridge) 600, with a minimum tensile yield stress (F_y) of 480 N/mm² for all thicknesses, was introduced in the Korea Building Code (KBC 2009, 2009). However, current design standards may not be applicable to circular hollow sections with steel of grade HSB 600 since the current provisions were established based on tests of steels with a yield strength of up to 355 MPa and a yield ratio of up to 0.8. For joints with large deformation, the yield strength can be increased up to 460 MPa with a resistance factor of 0.9. This paper investigates the strength limits and various possible failure modes. Eight full scale circular hollow section T-joints were tested and analyzed to investigate the applicability of current design standards. Two test series depending on the grade of steel, i.e., SHB600 and SS400, with specimens in each series were tested with variations in the ratio of diameter to wall thickness of chord member (D/t) and vertical member (D_t/b_t). All chord members were 3,000mm and vertical members were 1,950 mm in length. For chord members, 750 mm diameter with 12 mm and 26 mm wall thicknesses were used for the tests. For vertical members, 650 mm diameter with 12 mm and 40 mm wall thicknesses were used. The effects of the experimental parameters were evaluated for their applicability to current standards based on the limited test and analysis results of the circular hollow section T-joint.     

Untersuchungen zum Werkstoffverhalten des Feinkornbaustahls S 460 unter erhöhten Temperaturen

Examination of the mechanical properties of the microalloyed grain refined steel S 460 at elevated temperatures. To establish a basis for calculating the load‐bearing capacity of steel members made of S 460 in fire, corresponding to EN 1993‐1‐2 [1], the mechanical properties of the microalloyed grain refined steel S 460 under high temperatures have been examined. Two different kinds of steel have been considered: a normalised rolled S 460 N and a thermomechanically rolled S 460 M, that differ in their chemical composition and the temperature control during the hot‐rolling process. On the basis of transient state tensile tests, material laws have been derived for the temperature range from 20 to 900 °C. The test results show an increased strength of S 460 M at elevated temperatures in comparison to S 460 N. This is a result of the strain hardening caused by the thermomechanical deformation and the precipitates formed by niobium and titanium that constrain creep deformations. The data derived from the tests show that the stress‐strain relationships given in EN 1993‐1‐2 [1] for S 460 overestimate both the strength and the stiffness of the examined S 460 N.