Regen‐Wind‐induzierte Schwingungen – Ein Berechnungsmodell auf der Grundlage der neuesten Erkenntnisse

Rain‐wind induced vibrations – a calculation model based on recent investigations. Rain‐wind induced vibrations of slender structural members with circular cross sections, as of bridge‐cables or hangers of tied arch bridges may occur when these members are exposed to both wind and rain. This vibration phenomenon is known to bridge‐engineers after the spectacular closing of the Erasmus Bridge shortly after inauguration and the damages at hangers of the Dömitz Bridge across the river Elbe. For the onset of rain‐wind induced vibration various parameters as the intensity of rain, the wind velocity and the wind direction in relation to the slope of the member play an important role. Vibrations once die away, when the intensity of rain or the wind velocity change significantly or the wind direction varies. Rain‐wind induced vibrations are self‐induced vibrations where the inducement mechanism from the variation of the position of the rain rivulets interacts with the movements of the cables or hangers. This type of vibration is not novel, however the mechanism has so far not yet been sufficiently investigated to produce a calculation model that allows predicting the magnitude of the vibration amplitudes.     

Vereinfachte Methoden zur Berechnung der dynamischen Antwort von Eisenbahnbrücken bei Zugüberfahrt

Simplified methods to calculate the dynamic response of railway‐bridges under crossing trains. In this paper, two different methods to calculate the dynamic response of single‐span bridges under moving forces are presented. The work is focused on beam bridges with constant cross‐section in underdamped condition. In the first method, referred to as “Impulse‐method”, the effective impulse resulting from the load is approximated by simple analytical functions. The bridge is modelled as a single degree of freedom system by means of modal analysis. For this simplified system describing bridge and load, closed analytical formulae to calculate the dynamic response can be set up. The “Impulse‐method” is exemplified by the HSLM‐A1 load train given in Eurocode 1 (EC1). In the second method the response spectrum analysis widely used in earthquake engineering is adopted for the present problem. The calculation of response spectra for beam bridges under the HSLM‐A load models is demonstrated. An example shows how this method is deployed.     

Regen‐Wind‐induzierte Schwingungen – ein State‐of‐the‐Art Report

Rain‐wind induced vibrations can occur, when rain and wind simultaneously act, for instance, on the cables of cable‐stayed bridges, on inclined steel hangers of arch bridges or on the backstays of guyed masts. As a result of wind and gravity, the rainwater forms small rivulets, which flow down on the surface of these structural members. The rivulets disturb the wind flow around the dry cross section and cause a modified unsymmetrical distribution of the surrounding wind pressure, which leads to periodic exciting forces. Due to the movement of the cable and the wind forces, the position of the rivulets varies on the cable surface. This constellation can lead to aeroelastic excitation with large amplitudes. Rain‐wind induced vibrations can reduce the life cycle of a structure seriously, because the initialising wind velocity of rain‐wind induced vibrations is significantly lower than the design wind velocity and thus has a high probability of occurrence. In this paper, the further researches and investigations up to now dealing with rain‐wind induced vibrations are summed and commented.     

Baupraktische Sicherheitsnachweise gegen winderregte Schwingungen von Brücken und Türmen

Practical assessment of safety against wind‐induced vibrations of bridges and towers. Development and present state of the practical assessment of safety against wind‐induced vibrations of suspension and cable‐stayed bridges as well as towers are explained and compared with the in situ behaviour of three numerical examples from practice.     

Entwicklungen im Stahlverbundbrückenbau – Autobahnbrücken mit einteiligen Verbundquerschnitten

Developments of steel‐composite bridges – motorway bridges with one‐piece composite cross‐sections. On design orders of the German Bundesministerium für Verkehr, Bau‐ und Wohnungswesen (BMVBW) motorway bridges have to be built with two superstructures – one for each carriageway. To get satisfying solutions in design of motorway bridges across valleys too, the authority decided in 1997 that it should be possible to build one‐piece steel‐composite bridges, provided that special suppositions are respected. The acceptance based on the condition, that it is possible to repair the reinforced concrete slap of the one‐piece superstructure as well as separated superstructures. The extensive maintenance of traffic has to be guaranteed all over the repair period. Since 1997 DEGES erected six bridges with one‐piece steel‐composite cross‐sections, three further bridges are under construction. Although the superstructures are designed for the state of the partly replacement of the reinforced concrete slap and therefore they are over dimensioned for the using‐state, these one‐piece superstructures are economic if they have a height of more than 50 m over the bottom of the valley. The following essay describes the one‐piece steel‐composite cross‐sections and gives constructive hints to their components.     

Der Stabbogen bei stählernen Straßenbrücken – Entwicklungstendenzen der letzten 50 Jahre – Teil I

The strut arch in using of steel road bridges mainly in Germany – trends of developments into the last 50 years. By the presentation is given a survey about the development of the designing the arch construction for steel road bridges inclusive the constructive details. In the detail are considerd the suspensions with their connections, the cross‐sections of the arch, springing arch, arch model and the roadway‐constructions into different phases. At last of the investigation are presented some typical erection‐examples.     

Neues BAW‐Merkblatt zur Bewertung der Tragfähigkeit bestehender massiver Verkehrswasserbauten

New BAW Code of Practice for the assessment of the load bearing capacity of existing solid hydraulic structures Many of Germany's solid hydraulic structures, i. e. structures made from concrete, reinforced concrete or masonry, are of above‐average age. For example, about a third of all locks for which the Federal Waterways and Shipping Administration (WSV) is responsible is more than a hundred years old. In other words they have exceeded the design lifetime of 100 years that is nowadays the requirement for such structures. Not only existing locks, but also numerous weirs and canal bridges show static characteristics, such as construction methods or very large cross sections, that are no longer common practice today. If any alterations are made to these structures, or if they exhibit visible damage, it is essential to re‐assess the statics of the supporting structure and perform new calculations to verify its conformity with stability requirements. This re‐assessment can be done with a new BAW‐Code of Practice „TbW”. In contrast to bridges and buildings, no adapted regulations have been released until now for re‐assessing the statics of existing solid hydraulic structures.     

Adaptive Flüssigkeitstilger für Vertikalschwingungen von Ingenieurstrukturen – Teil 2 – Feldversuche

Adaptive tuned liquid column dampers for structures, part II – field tests. Due to increasing dynamic actions and the trend to slender structures the damping of vibrations gains in importance. One of the effective methods to reduce vertical structural vibrations is the application of classical tuned mass dampers (TMD), which are damping the vibration response of excited natural frequencies. The areas of application reach from civil and mechanical engineering to aeronautics. In addition to part I (laboratory tests) this paper shows the first application of tuned liquid column dampers (TLCD) to a vibration‐prone steel constructed railway bridge. The fluid mass is guided in a U‐tube. A gas spring enables tuning of the natural damper frequency and energy dissipation is given by turbulence effects in fluid and gas flow. In case of the TLCD there are no mechanical parts for tuning necessary. At first the mechanical model of the bridge‐TLCD coupled system is presented and the equation of motion is derived. Furthermore optimal tuning is performed. The considered railway bridge is analyzed numerically by a finite element model, including the modelling of the TLCD. The installation process of the TLCD to the railway bridge is described in detail and measuring results are presented. It is shown that the application of TLCD's to railway bridges effectively reduces bridge vibrations.     

Das Schwingungsverhalten der Fußgängerbrücke am Stern‐Center in Potsdam

Dynamic behaviour of the Stern‐Center footbridge in Potsdam. The footbridge at the Stern‐Center in Potsdam has been opened seven years ago. Ever since, both bridge administrators and pedestrians discomfortingly observed distinct vibrations while crossing the cable stayed bridge. The performed investigation aimed at identifying the bridge's dynamic behaviour and its according causes by measuring, as well as developing an appropriate FE‐calculation model that sufficiently describes the dynamic impacts.     

Der Stabbogen bei stählernen Straßenbrücken – Entwicklungstendenzen der letzten 50 Jahre – Teil II – Fortsetzung aus Heft 2/2005 und Schluß

The strut arch in using of steel road bridges mainly in Germany – trends of developments into the last 50 years. By the presentation is given a survey about the development of the designing the arch construction for steel road bridges inclusive the constructive details. In the detail are considerd the suspensions with their connections, the cross sections of the arch, springing arch, arch model and the roadway‐constructions into different phases. At last of the investigation are presented some typical erection‐examples.     

Stahlverbundbrücken mit begehbaren Kastenträgern

Steel‐Composite bridges with box girders which are to be inspected on foot. In the last years the development in shaping of cross sections of bridges over a valley shows a tendency to some special types in dependency on the site, which were built again and again. These are the cross sections with one trapezoid box girder, consisting of a steel trough and a concrete slab, which is to be inspecting on foot as well as cross sections with two airtight welded box girders of steel, connected with the concrete deck slab, too. All the bridges with these cross sections are so designed that there is only a composite effect in longitudinal direction. To realise an economical bridge building, there has to be taken some typical design criterions into consideration for each type of cross section. The following paper describes these design criterions for cross sections with one trapezoid box girder and points out the optimal cross section and the economical area of application.     

Holzbrücken – Erkenntnisse zum Feuchteverhalten in den Tragquerschnitten aus Langzeitmessungen

Timber bridges – Long term monitoring results of moisture diffusion in the load carrying cross‐sections Timber road bridges have been built worldwide for centuries. The high performance of wood is approved through many constructions. However, there are still doubts about using wood by the planning engineer, which reduce the number of realized projects. The moisture induced stresses in cross‐sections according to the varied ambient climate are mainly investigated under laboratory conditions. The results show that the moisture content changes differently over the cross‐section and leads to moisture induced stresses. The discussion about methods for the assessment of the moisture induced stresses in timber bridge cross‐ections is continuing. Results observed in the long term monitoring of seven timber bridges provide first guidelines for practitioners. For all constructions, the moisture content was measured regarding the ambient micro climate. As result, the influences according to the ambient micro climate are not insignificant. Positive is that the directly measured moisture content is less compared to the equilibrium moisture content calculated from the data of a close by meteorological station. The analysis of the moisture gradient over the cross‐section allows the definition of an active or passive zone.     

Structure‐aware 3D reconstruction for cable‐stayed bridges: A learning‐based method

A powerful deep learning‐based three‐dimensional (3D) reconstruction method for reconstructing structure‐aware semantic 3D models of cable‐stayed bridges is proposed herein. Typically, conventional bridge semantic 3D model reconstruction methods are not robust when low‐quality point clouds are used. Furthermore, they are suited particularly for their respective fields and less generalized for cable‐stayed bridges. Hence, a structure‐aware learning‐based cable‐stayed bridge 3D reconstruction framework is proposed. The encoder part of the network uses both multiview images and a photogrammetric point cloud as input, whereas the decoder part uses a recursive binary tree network to model a high‐level structural relation graph and low‐level 3D geometric shapes. Two actual cable‐stayed bridges are employed as examples to evaluate the proposed method. Test results demonstrate that the proposed method successfully reconstructs the bridge model with structural components and their relations. Quantitative results indicate that the predicted models achieved an average F₁ score of 99.01%, a Chamfer distance of 0.0259, and a mesh‐to‐cloud distance of 1.78 m. The achieved result is similar to that obtained using the manual reconstruction approach in terms of component‐wise accuracy, and it is considerably better than that obtained using the manual approach in terms of spatial accuracy. In addition, the proposed recursive binary tree network is robust to noise and partial scans. The potential applications of the obtained 3D bridge models are discussed.     

Zur maßgebenden Verkehrslaststellung bei Schrägseilbrücken

Appropriate traffic load cases for steel and composite cable – stayed bridges. A significant problem in the global analysis of bridge structures is to find the most unfavourable position of the traffic loads for each cross‐section. In practice usually those traffic load cases are chosen which maximise one part of stresses at the cross‐section (often expressed in form of internal forces). First of all a simple method is presented to find out the most unfavourable traffic load position, also applicable for complex interaction formulae including web buckling. Secondly an example of a cable‐stayed bridge is analysed. For two significant sections of the bridge deck the results are presented. The stresses due to the conventional practical procedure are compared with the more accurate ones. The behaviour is explained by the corresponding influence lines. Based on these results some proposals for practical work are given. The presented procedure is also applicable to other types of construction works and materials (e.g. reinforced concrete).     

Großversuch WILD‐Brücke – versuchsgestützte Bemessung einer UHPC‐Bogenbrücke

Full‐Scale Experiment Bridge WILD – Design of an UHPC Arch Bridge based on Experiments The outstanding durability of UHPC makes this material predestined for the construction of bridges. In Austria UHPC is introduced into the practice of road bridges through the realisation of the bridge WILD. The cross section of the arch, which spans 70 m, is just 6 cm thick and doesn't contain any passive reinforcement. The design is based on international recommendations on the one hand and on specific experiments on the other hand. This paper deals with the evaluation of two full‐scale laboratory tests. The setup is configured for getting a broad field of results as it is necessary for approval tests. In this way, all critical design states, which are also determined by calculation, are investigated experimentally. Furthermore, the experiments cover secondary effects, which don't have any verification through practical experience but can clearly be seen in FE‐results. The test results are carefully interpreted and explained by the use of simple mechanical models. The final examination of the results is figured out by means of comparison between calculation and experiment.     

Die Bauweise der dichten Kleinkästen im Verbundbrückenbau

The system of closed small‐sized box girders in the construction of composite bridges. In short time the system of closed small‐sized box girders has found wider application in the building of composite bridges. In the design of bridges with medium spans are often problems to be solved, in which this method is successful in competition with the other systems of composite bridges and also with concrete bridges. The characteristics of the system in construction and erection are described and the resulting conclusions for the design considerations are put together. The possibilities of application are discussed in comparison with the other competing systems and the potentials for further development are reported on.     

Zum Tragverhalten von Stützen semi‐integraler Brücken

Load‐bearing behaviour of columns of integral bridges – realistic calculation of columns of integral bridges for the ultimate limit state Due to the complex and interactive load‐bearing behaviour, calculation of integral bridges is more expensive than the calculation of bridges with its superstructure uncoupled from the substructure. Apparently conservatively chosen reinforcement ratios lead to increased stiffness of the columns and thus inherently increased the constraining forces. Therefore, a greater reinforcement ratio is not imperatively connected with a better load‐bearing behaviour of the columns. To better understand the load‐bearing behavior of integral bridges, it is necessary to consider the physical non‐linearity in the calculation. In this contribution, the non‐linear behaviour of integral columns is examined by varying the cross section dimensions and the reinforcement ratios. The results are analyzed with regard to the columns ductility and the constraining forces. Finally, this contribution offers conceptual proposals, which can be used for the dimensioning of integral bridges.     

Besonderheiten bei der Beurteilung des Ankündigungsverhaltens von Spannbetonbrü

Particularities in Interpretation of the Preannouncement Behaviour of Prestressed Concrete Bridges by Applying the “Crack‐before‐Collapse‐Criterion”. Part II: Number of Tendons, Maximum live Loads In respect of the failure older bridges are often constructions without sufficient preannouncement behaviour with regard to the “crack‐before‐collapse‐criterion”. These bridges, especially bridges with tendons endangered to stress‐corrosion‐cracking, bear risks of failure. Additionally to the particularities in interpretation of the preannouncement behaviour of prestressed concrete bridges by applying the “crack‐before‐collapse‐criterion” part I: temperature loads, relocation of internal forces further investigations were performed to evaluate the existing risk for the owner. Considerations with regard to the number and type of tendons as well as maximum portion of live loads lead to an assessment of the danger for bridges. Proposals for further proceeding with critical bridges will be discussed based on different assessment‐criteria. Instructions to investigate structures according to DIN 1076 are presented to recognize cracks and damages due to failure caused by stress‐corrosion‐cracking.     

曲线弯梁桥振动分析方法

利用广义坐标法和能量原理推导了曲线梁桥的振动控制微分方程,解释了曲线梁桥振动理论与直线梁的异同点,并推导了质量矩阵。在推导过程中考虑了截面扭转中心与截面形心的不一致,随后给出了曲线梁动力分析的有限元方法,并完成了电算程序的编制。最后通过实例分析验证了本文所提理论和计算方法的正确性。     

Die Stahlverbundbrücke über die Müglitz im Zuge der Autobahn Dresden–Prag – Entwurf und Ausführung

The composite bridge across the Müglitz on the highway Dresden–Prag. Design and construction. The bridge across the Müglitz transfers the newly built Federal Highway A17 over the small town Dohna near by Dresden. The bridge has a total length of 310 m and crosses a railway, a state highway and the river Müglitz. The bridge dominates the townscape. Extensive design investigations were performed to find the technically and aesthetically right solution for the given situation. Chosen and built was a continuous girder bridge as a composite structure with a span sequence of 45 – 55 – 55 – 55 – 55 – 45 m. The construction is composed of two bridges, one for each carriageway. Each superstructure has two airtight steel box girders, which are in composition with the concrete deck slab. To give the bridge a differentiated view, the main girders are built with shallow but significant haunches and emphasized stiffening boxes in the bearing zones. In the design of the composite columns these criteria reappear in the widening of the column heads and the eight‐cornered cross‐sections. Special consideration was given to a simple fabrication and an unproblematic erection with as far as possible reduced welding at the site. The article covers the planning and the building of the bridge. In addition experiences made in building other bridges with airtight box girders are reported.