Prüfung von Spannbetonbauteilen mit magnetischen Methoden

Die Methoden der magnetischen Streufeldmessung und der magnetischen Restfeldmessung eignen sich gut zur zerstörungsfreien Detektion von Spanndrahtbrüchen in Spannbetonbauteilen. Unter Verwendung eines Jochmagneten mit integrierten Magnetfeldsensoren werden die Bauteile mit mehreren Messfahrten bei verschiedenen Magnetisierungsfeldstärken abgescannt. Die Auswertung basiert auf dem Vergleich von Messungen nach verschiedenen Vormagnetisierungen sowie der Bestimmung der Korrelation mit idealisierten Bügel‐ und Bruchsignalen. Die Nachweisgrenze des Verfahrens wird fallabhängig diskutiert. Die Anwendung in der Prüfpraxis wird an drei Beispielen illustriert. Inspection of Prestressed Concrete Structural Members with Magnetic Methods The methods of magnetic stray field measurement and of magnetic remanence measurment are well suited for nondestructive detection of ruptures in prestressing wires of concrete structural members. Using a yoke magnet with integrated magnetic field sensors, the members are scanned several times with varying magnetization field strength. The signal analysis is based on the comparison of measurements after different premagnetizations as well as on the determination of the correlation with idealized rebar and crack signals. The limits of detection are discussed on a case‐by‐case basis. The application in inspection practice is illustrated with three examples.     

预应力钢压杆的理论及试验研究

日益广泛应用的大跨度张力结构中经常出现一些高度大、负荷重的立柱以支承全部或局部屋面荷载。按常规设计的这些立柱往往截面大,耗材多,成本高,大大抵消了张力屋面的良好经济效益。在钢立柱的设计中采用预应力技术不仅可以达到提高杆件的稳定性和刚度、降低耗钢量及成本的目的,而且还可以改善结构的动力性能,提高其抗震性。 本文研究了预应力钢压杆的静力特性,分析了荷载下的内力分配规律,推导了压杆的临界荷载值及强度极限值,并通过系列模型试验检验了理论分析的可行性及准确程度。     

Durchstanzmodell für Flachdecken mit Faserverbundbewehrung und großen Aussparungen in Stützennähe

Punching Model for Flat Slabs with FRP Reinforcement and large Openings near the supporting Surface Flat slabs with tension bars using glass‐ or carbon fiber reinforced polymer have a substantial lower punching load capacity then conventional steel reinforced plates. This is caused by the dependence of the shear force transportation on the stiffness and therefore on the elastic modulus of the reinforcement, after concrete is cracked: For glass fiber reinforced polymer the elastic modulus has an amount of approximately 35000 N/mm², which isn't more then one sixth of the steel value. Until now designing rules for concrete don't take into account this influence. Following a new developed punching model will be presented, that compared with DIN 1045 [2] and DIN 1045‐1 [3] directly includes the elastic modulus of the bending reinforcement and that also applicates the reduction of the punching load capacity by openings near the supporting surface in a realistic way.     

北京西站主站房预应力钢桁架的理论分析与试验研究

北京西站北主站房１段天桥跨度达４５ｍ，采用了大跨、重载预应力钠行架结构，这是我国首次设计采用的预应力巨型钢结构工程，本文在理论分析、计算比较、１：６大尺寸模型试验及现场工程实测基础上，对该预应力钢桁架进行了较全面的研究，提出了分阶段分组施加预应力的方法；研究了预应力对结构承载力与变形性能的影响；对预应力的建立、损失和分布以及节点刚性等对结构性能的影响也进行了探讨。结果表明，这一预应力巨型钢桁架结构不仅安全可靠，经济合理，技术可行，而且能很好地满足各类功能要求。     

预应力对柱支承扁网壳静力性能的影响

沿柱支承钢扁网壳的拉力环域施加适当预应力能降低结构在使用阶段的变形。以预应力三阶段设计为例分析预应力施加对柱支承扁网壳静力性能的影响。结果发现,预应力可以降低支座水平推力,提高结构刚度,但同时增大了结构在负风压作用时的变形,加大了支座附近杆件的轴力。预应力不能有效提高结构的临界荷载。与其他布索方案相比,折线形索-桁方案对网壳变形控制更有效。     

基于广义梁理论的非线性材料薄壁受压构件屈曲荷载计算方法

提出适用于非线性材料的广义梁理论屈曲荷载计算方法,并对不锈钢薄壁受压构件屈曲荷载进行计算验证。通过定义材料非线性应力应变关系和瞬时弹性模量,对传统线弹性广义梁理论进行修正,建立非线性材料薄壁构件受压屈曲荷载计算方法,推导不锈钢薄板受压局部屈曲、冷弯薄壁不锈钢卷边槽形柱畸变屈曲及箱形不锈钢长柱弯曲屈曲荷载计算公式,并与既有试验数据对比。经验证,线弹性分析方法不适用于不锈钢材料;提出的修正GBT法具有较高精度,且本构关系采用变形法则结果偏于安全,可用于不锈钢等非线性金属材料薄壁构件受压屈曲荷载的确定,为研究和设计提供理论指导。     

预应力轴心受拉钢构件高温性能试验及理论研究

进行了3根预应力轴心受拉钢构件高温试验研究。试验结果表明，高温下预应力轴心受拉构件中内置拉索和钢管所承受荷载比例随温度的变化而不断变化。升温初期拉索张力随温度升高不断增大，预应力轴心受拉钢构件轴向位移平稳发展，在达到峰值后，拉索张力随升温时间的延长而不断降低。在临界状态下，轴向位移增长很快， 预应力受拉构件中拉索均被拉断，外部钢管发生不同程度的颈缩现象。在试验结果的基础上，建立了预应力轴心受拉钢构件的有限元分析模型，得到了高温作用下预应力轴心拉杆中拉索张力和预应力钢杆轴向位移的时程全曲线。参数分析的结果表明：在其他条件相同时，预应力轴心受拉钢构件失效时的临界温度随着荷载比的增加而降低；当预应力比小于08时，预应力比对预应力轴心受拉钢构件失效时的临界温度的影响较小，当预应力比等于08时，预应力轴心受拉钢构件失效时的临界温度显著的提高；在其他条件相同时，预应力轴心受拉钢构件失效的临界温度随约束刚度比的增大而增大。最后对高温下预应力轴心受拉钢构件进行了理论分析，推导出预应力轴心受拉钢构件高温下差分计算方法，并以此为基础编写程序。通过计算结果与试验结果的对比，证明了差分计算方法的正确性。     

Seismic testing and numerical analysis of Y‐shaped eccentrically braced frame made of high‐strength steel

In eccentrically braced frame made of high‐strength steel (HSS‐EBF), link and brace are made from conventional steel whereas other structural members use high‐strength steel. Using HSS for beams and columns in EBF can reduce steel consumption and increase economic efficiency. In this paper, one shake table test of a 1:2 scaled three‐story Y‐shaped HSS‐EBF (Y‐HSS‐EBF) specimen was carried out to study its seismic behavior underground motions with different peak ground accelerations. The dynamic properties, base shear force, displacement, and strain responses of the specimen were obtained from this test. In addition, the finite element models of two 10‐story Y‐HSS‐EBF buildings and one 10‐story conventional Y‐EBF building were evaluated for seismic effects. Nonlinear pushover and dynamic analyses were conducted to compare their seismic performance and economy. The results indicated that the specimen exhibited sufficient lateral stiffness and safety but suffered some localized damages. During the high seismic intensity earthquakes, the links of the test specimen were in inelastic to dissipate the earthquake energy, whereas other structural members remained in the elastic state. Under the same design conditions, Y‐HSS‐EBF used less steel than that of conventional Y‐EBF, which could reduce the amount of steel used in Y‐HSS‐EBF. The Y‐HSS‐EBF is a safe, dual system with reliable seismic performance.     

火灾荷载作用下轴压钢构件临界应力分析

以轴压钢构件为研究对象,探讨火灾场荷载作用下结构钢材料的弹性模量、抗弯刚度、屈服强度的变化规律,且在这些材料基本参数改变的前提下分析了轴压钢构件的临界应力和临界力,最后进行实例数值分析,得出轴压钢构件在火灾高温条件下钢结构材料的弹性模量、抗弯刚度和屈服强度都急剧下降,降幅在火灾持续时间2h左右达50%以上,轴压钢构件的临界应力也快速下降,使钢构件的承载能力下降很快,导致结构破坏。因此,在钢结构设计中,必须考虑火灾高温对轴压钢构件的临界应力和临界力降低的影响。     

Experimental monitoring of the strengthening construction of a segmental box girder bridge and field testing of external prestressing tendons anchorage

Prestressed concrete segmental box girder bridges are composed of short concrete segments that are either precast or cast in situ and then joined together by longitudinally post-tensioning internal, external, or mixed tendons. The objectives of this study are to monitor the construction process of the external prestressing tendons to strengthen the bridge structure and perform a field load test to measure the strain and the deflection of the anchorage devices of the external prestressing tendons to determine the state of these devices after tension forces are applied. The monitoring process of the external prestressing tendons construction includes inspecting the cracks in the diaphragm anchorage and the deviation block devices before the tension forces are applied to the external tendons; measuring the deformation of the steel deviation cross beam during the tension process; measuring the deformation of the box girder after different levels of tension forces are applied; measuring the elongation of the external tendons in each level of the tension; and measuring the natural frequency of the external tendons after the tension process is complete. The results of the monitoring process show that the measured values of the deformation, the elongation, and the natural frequency meet the requirements. Therefore, there is no damage during the construction and the tensioning of the external prestressing tendons. A field load test is performed to the anchorage beam, the steel deviation block devices, and the steel deviation cross beam. The field load test results of the anchorage devices show that the values of the strains, the stresses, and the deflection are less than the respective allowable limit values in the requirements. Therefore, the anchorage devices have sufficient strength, and the working state is good after the tension forces are applied to the external prestressing tendons.     

铝合金轴压构件屈曲荷载计算方法

铝合金轴压构件在建筑工程中有着广泛应用,但由于其材料弹性模量低,稳定问题比钢结构更加突出。文中对铝合金轴压构件进行屈曲分析,提出屈曲模式。采用解析法分析并结合现有轴压构件的各种屈曲理论,给出适合铝合金轴压构件的屈曲荷载计算公式,介绍有限样条法在构件屈曲分析中的应用,并用其验证所提出的各项屈曲荷载计算公式的正确性。     

磁通量传感器及其在桥梁监测中的应用

磁通量传感器是利用铁磁材料的磁弹性效应，建立导磁性能变化与应力、温度的关系，通过测量磁导率变化，测定铁磁材料构件的张力。该种测量方法为无损、非接触性测量法，适用于斜拉索、吊杆、系杆、体外索及预应力筋的内力测定，可用于预应力筋的施工监控，也可用于长期安全监测。文中对磁通量传感器的原理、性能及其在工程中的应用进行了详细的描述。     

2008奥运会羽毛球馆新型弦支穹顶预应力大跨度钢结构设计研究

2008奥运会羽毛球馆屋盖钢结构采用弦支穹顶结构体系,由上弦单层网壳、下弦环索与径向拉杆、竖向撑杆组成。在设计中建立屋盖钢结构和下部看台结构整体有限元计算模型进行结构分析。在综合考虑工程的重要性、结构几何力学特点、预应力损失、施工缺陷等多种因素的基础上,对恒荷载、活荷载、雪荷载、风荷载、温度作用、地震作用等工况进行组合,分别进行结构施工阶段及结构使用阶段的内力、变形和体系稳定分析。在大量计算和分析基础上,对结构几何体系和构件进行了优化设计。在设计中运用单元逐次激活技术,模拟预应力张拉施工过程,并考虑施工临时脚手架刚度的影响进行施工模拟分析。对于索撑节点采用三维实体有限元分析方法,运用接触分析技术,计算索撑节点预应力摩擦损失,并结合施工监测,确定预应力损失值;采用非线性弹簧系统,模拟索撑节点预应力损失并研究了其对整体结构的影响。     

浅谈我国规范中预应力混凝土构件的可靠度与张拉应力的控制

从理论和具体的数据对部分预应力混凝土构件的钢筋应力进行分析,当对构件预应力钢筋的张拉应力值σｃｏｎ不同时,就对构件中的预应力钢筋和非预应力钢筋的应力分配产生影响,从而探讨此类构件的可靠度;并对设计此类构件提出建议。     

采用体外预应力加固简支实腹钢梁的设计计算

体外预应力加固方法是提高钢梁承载能力、改善其受力性能的一种简单易行的方法。本文对体外预应力加固简支实腹钢梁时体外预应力筋的线形布置、预应力损失以及内力增量的计算和体外预应力筋截面面积的确定进行了分析 ,并且对加固后钢梁的设计计算进行了研究 ,最后通过一实例进行了设计计算     

采用体外预应力技术加固钢筋混凝土梁

介绍了采用体外预应力技术加固钢筋混凝土梁的加固设计原理,阐述了体外预应力加固的具体方法,并结合具体的工程实例提出了设计建议,以推广该结构加固技术的应用。     

Verifizierung zerstörungsfreier Prüfverfahren zur Detektion von Spannstahlschäden an Spannbetonbauteilen mit nachträglichem Verbund

Verification of Non‐Destructive Testing Techniques for Detection of Prestressing Steel Damage at Post‐Tensioned Concrete Members For an assessment of the risk potential of existing structures where in the case of prestressing steel damage the load‐bearing capacity could be significantly affected non‐destructive testing techniques which enable reliable evaluation of the condition of the prestressing steels are of utmost importance. During the demolition of the Hohenzollerndamm bridge in Berlin where damage of prestressing wires due to hydrogen‐induced stress corrosion cracking were found in former investigations parts of the girders of the bridge superstructure could be taken out. After non‐destructive investigation by means of two testing techniques based on magnetic leakage flux measurement and one technique based on electromagnetic resonance measurement the single wires were inspected in order to verify the non‐destructive testing results with respect to their reliability. From the results it can be concluded that areas with fractures of several wires could be detected by the two techniques based on magnetic leakage flux measurement.     

Korrosionsmonitoring von Stahlbetonbauwerken als Element des Lebensdauermanagements

Da korrosionsinduzierte Schäden an Bauwerken im Laufe der Zeit zu immensen Kosten führen, sind die sichere Beurteilung des Korrosionsrisikos und eine frühzeitige Erkennung und zuverlässige Vorhersage der Bewehrungskorrosion Schlüsselaufgaben des Bauwerksmanagements korrodierender Spann‐ und Stahlbetonbauwerke. Eine Bewertung des Korrosionszustands wird durch die Bauwerksüberwachung (Monitoring) objektiv möglich. Im vorliegenden Beitrag werden nach einer kurzen Einführung zum monitoringbasierten Lebensdauermanagement die Entwicklung, Erprobung und Optimierung neuartiger kalibrierungsfreier Miniatursensoren zur Erfassung der Bewehrungskorrosion in Betonbauteilen vorgestellt. Mit diesen vielseitig einsetzbaren Korrosionsstellvertretersensoren, die aus mehreren im Bereich der Betonüberdeckung angeordneten, 0,065 mm bis ca. 0,5 mm dünnen Stahldrähten bestehen, kann das Eindringen der Depassivierungsfront in den Beton einfach, zuverlässig und kostengünstig überwacht werden. Basierend auf umfangreichen Untersuchungen im Labormaßstab und der Anwendungserprobung im Zeitraum von mehr als sechs Jahren werden die Erkenntnisse und Weiterentwicklungen der Drahtsensorik präsentiert und diskutiert. Corrosion Monitoring as an Element of Service‐Life‐Management Application of innovative filament sensors for rebar corrosion survey Since corrosion induced damages at civil structures result in enormous costs over lifetime, the assured assessment of the corrosion risk and an early identification and reliable prognosis of rebar corrosion are key tasks of the building management of corroding prestressed and steel reinforced concrete structures. Here an evaluation of the corrosion state is objectively possible by means of Structural Health Monitoring (SHM). In this contribution after a brief introduction of monitoring based service‐life‐management, the development, testing and optimization of novel calibration‐free miniature sensors for the detection of rebar corrosion in concrete members are introduced. By means of these versatile corrosion dummy sensors, made from several 0,065 mm up to 0,5 mm thin steel filaments and mounted within the concrete cover, the penetration of the depassivation front into concrete can be observed easily, reliably and cost effectively. Based upon various investigations in the lab scale and application testing during the time period of six years, the findings and further developments of the filament sensor will be presented and discussed.     

Multi-stepwise thermal prestressing using a cover-plate in steel structures

This paper introduces an innovative prestressing method for steel structures utilizing a multi-stepwise thermal prestressing method (M-TPSM). The proposed prestressing method is founded on a simple concept of thermal expansion and contraction of steel. A cover-plate, a high strength steel cover-plate used as a post-tensioning member in this method, is heated by electrical heaters before it is attached to the main member. After the cover-plate is attached to the main member by using high tension bolts at several points or by welding, the electromagnetic induction heaters are removed, and the resulting contraction force of the cover-plate induces eccentric axial forces to the main member. In this study, a fundamental investigation involving analytical and experimental study is carried out to evaluate the feasibility of the M-TPSM for steel structures. Also, static loading tests were performed on the rolled beam specimens for assessment of the behavior of the steel beam prestressed with M-TPSM.     

Corrosion propagation of prestressing steel strands in concrete subject to chloride attack

A review of research literature suggests that steel corrosion in concrete can accelerate if the corroding steel is under high levels of stress but this important phenomenon has not been investigated thoroughly. Both laboratory tests and field surveys indicate that the effects of corrosion on structural behaviour in reinforced and prestressed concrete structures are different, with the latter having less concrete cracking but more serious structural collapses. The intention of this paper is to investigate the corrosion propagation of prestressing steel strands in chloride-laden environment. A long term experimental program is presented in which the corrosion of twelve prestressing steel strands embedded in concrete was examined. The effects of the level of stresses in the steel and type of steels on corrosion rate are studied. It is found that the corrosion rate of prestressing steel strands in concrete increases with the increase of the level of stresses applied and that the pitting corrosion is the main form of prestressing steel corrosion in chloride-laden environment. The paper concludes that the corrosion of prestressing steel in concrete structures poses higher risk to the structure than that of reinforcing steel in terms of structural collapse.