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.     

Die Geh‐ und Radwegbrücke Kehl – Strasbourg

The Pedestrian and Cycle Bridge Kehl – Strasbourg. The Rhine bridge between Kehl and Strasbourg is the new regional landmark and linking element of the International Gardening Show. The approach to unifying different functions and an architectural endeavour lead to a unique structural system. Two separate decks address the different situations on the river banks and, linked by a platform, form a balcony above the Rhine at midspan. The main bridge is a cable‐stayed structure with a steel pylon and a steel‐concrete composite deck. The approach bridges are continuous girders on steel columns. Both pile and flat foundations are featured in the design. The article describes the structural concept and design, outlines the erection procedure and discusses aspects of the dynamic behaviour of the bridge.     

部分斜拉桥结构性能研究

本文总结了部分斜拉桥的设计参数,同连续梁桥和斜拉桥的结构特性进行了对比,分析了结构刚度的影响因素,对部分斜拉桥适合建造的场合提出了建议,为以后此类桥梁的设计提供了借鉴。     

Performance of Vibration-Based Damage Detection Methods in Bridges

Abstract:   The important advances achieved in the modal identification, sensors, and structural monitoring of bridges have motivated the bridge engineering community to develop damage detection methods based on vibration monitoring. Some of these methods have already been demonstrated under certain conditions in bridges with deliberate damage. However, the performance of these methods for damage detection in bridges has not been fully proven so far and more research needs to be done in this direction. In this article, six damage detection methods based on vibration monitoring are evaluated with two case studies. First, the dynamic simulation and modal parameters of a cracked composite bridge are obtained. Here, the damage detection methods are evaluated under different crack depth, extension of the damage, and noise level. Second, damage is identified in a reinforced concrete bridge. This bridge was deliberately damaged in two phases. In this example, damage detection methods, which do not require comparison between different structural conditions, were applied. In the first case study, evaluated damage detection methods could detect damage for all the damage scenarios; however, their performance was notably affected when noise was introduced to the vibration parameters. In the second case study, the evaluated methods could successfully localize the damage induced to the bridge.     

3D‐Tragwerkssimulationen zur Erfassung der aerodynamischen Beanspruchungen bei der Planung von Brückenstrukturen

On the Modeling of Aerodynamic Effects in the Design Phase of Bridges via 3D Structural Simulations. The use of innovative building materials has led to a trend towards increasingly light and slender structures. Especially for cable‐stayed and suspension bridges, but also for girder bridges, there has been observed a growing dynamic vulnerability. The vibrations are caused, besides pedestrian and traffic‐induced vibrations, mainly by wind action. Apart from local vibrations of cables, the global dynamic behaviour of the bridge deck is of special interest. This paper gives an overview of the analysis methods currently used in practice. Load models which are based on a two‐dimensional treatment of the flow around the cross‐sections and their numerical treatment within the framework of a 3D structural simulation are presented. The experimental measurement of stationary and instationary cross section parameters is briefly recapitulated. Application in engineering practice in both preliminary and final design phases is demonstrated by four examples.     

Spurious mode distinguish by modal response contribution index in eigensystem realization algorithm

Modal identification process has played an important role for civil engineering structures. Among the identification methods, eigensystem realization algorithm is one of the most popular one. However, the noises in practical environment can influent the effectiveness of eigensystem realization algorithm, which can introduce spurious modes due to the overestimated physical order for the structure. This paper proposes a new index named the modal response contribution index (MRCI) for the eigensystem realization algorithm, which can determine the structural physical order and then distinguish spurious mode more precisely. First, the structural responses are divided into different modal response by the well‐known modal superposition theory. Then the square root summation of each modal response is obtained and named as MRCI. A modified stabilization diagram is also presented, which increases the row number of Hankel matrix with the determined order by MRCI. The straight lines formed by the stable points in the modified stabilization diagram designate the structural modal parameters. Finally, one numerical example and the monitoring data of a practical cable‐stayed bridge are employed. The results show that the proposed MRCI and modified stabilization diagram can identify the structural physical mode more precisely.     

大跨度斜拉管线桥的动力特性分析

本文结合一实际工程结构－－斜拉管线桥,从动力分析模型的建立、计算结果与实测结果的比较以及与普通斜拉桥的比较等几个方面研究了这种新型结构的动力特性。结果表明：恒载初始内力对斜拉管线桥的动力特性影响很大;尽管与斜拉桥结构相似,但二者的动力特性却有很大差别。     

模式识别的斜拉桥损伤诊断动力指纹与识别算法

为有效并准确诊断出斜拉桥损伤,对基于模式识别的斜拉桥损伤诊断方法进行了研究。选取易于测试出的低阶模态频率和部分关键点竖向振型数据为动力指纹,无需模态扩展或模型缩聚。研究并采用全因子设计进行动力指纹库的创建,可精确评估设定的损伤因子及其交互作用对损伤识别结果的影响。设计并增加了带随机误差的动力指纹库样本集。编制了基于Matlab的模式识别的多种算法,重点研究了精确度高的多层感知器识别算法及其提高该算法预测准确率的装袋集成算法。最后给出一座单塔双跨双索面斜拉桥的多种识别算法的损伤诊断过程和结果,得到一种可包容测试随机误差的高精确度斜拉桥损伤诊断评估模型。     

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.     

Structural health monitoring of a cable-stayed bridge with Bayesian neural networks

In recent years, there has been an increasing interest in permanent observation of the dynamic behaviour of bridges for long-term monitoring purpose. This is due not only to the ageing of a lot of structures, but also for dealing with the increasing complexity of new bridges. The long-term monitoring of bridges produces a huge quantity of data that need to be effectively processed. For this purpose, there has been a growing interest on the application of soft computing methods. In particular, this work deals with the applicability of Bayesian neural networks for the identification of damage of a cable-stayed bridge. The selected structure is a real bridge proposed as benchmark problem by the Asian-Pacific Network of Centers for Research in Smart Structure Technology (ANCRiSST). They shared data coming from the long-term monitoring of the bridge with the structural health monitoring community in order to assess the current progress on damage detection and identification methods with a full-scale example. The data set includes vibration data before and after the bridge was damaged, so they are useful for testing new approaches for damage detection. In the first part of the paper, the Bayesian neural network model is discussed; then in the second part, a Bayesian neural network procedure for damage detection has been tested. The proposed method is able to detect anomalies on the behaviour of the structure, which can be related to the presence of damage. In order to obtain a confirmation of the obtained results, in the last part of the paper, they are compared with those obtained by using a traditional approach for vibration-based structural identification.     

Image‐based post‐disaster inspection of reinforced concrete bridge systems using deep learning with Bayesian optimization

Many bridge structures, one of the most critical components in transportation infrastructure systems, exhibit signs of deteriorations and are approaching or beyond the initial design service life. Therefore, structural health inspections of these bridges are becoming critically important, especially after extreme events. To enhance the efficiency of such an inspection, in recent years, autonomous damage detection based on computer vision has become a research hotspot. This article proposes a three‐level image‐based approach for post‐disaster inspection of the reinforced concrete bridge using deep learning with novel training strategies. The convolutional neural network for image classification, object detection, and semantic segmentation are, respectively, proposed to conduct system‐level failure classification, component‐level bridge column detection, and local damage‐level damage localization. To enable efficient training and prediction using a small data set, the model robustness is a crucial aspect to be taken into account, generally through its hyperparameters’ selection. This article, based on Bayesian optimization, proposes a principled manner of such selection, with which very promising results (well over 90% accuracies) and robustness are observed on all three‐level deep learning models.     

Kraftbestimmung in Schrägseilen durch dynamische Messung

Force Determination in Stay Cables by Means of Vibration Measurements The knowledge of the actual tensile forces in the cables in the ropes or cables of cable‐stayed bridges or in external tendons is required for the examination and assessment of these elements. The determination of these forces by lift‐off tests with hydraulic jacks is connected with considerable expenditures as well as the danger of damages. But also the accuracies achieved by vibration measurements were, however, not satisfying. For high cable forces and short cables in some cases errors of up to ± 10% of the actual cable force could be determined. Therefore fast and non‐destructive methods for the determination of the forces are required. In this paper, a practicable technology to determine the cable force by means of vibration measurements is illustrated at the Viennese cable stayed bridge crossing the Vienna Donaukanal.     

Die Orinoco‐Brücke in Ciudad Guayana/Venezuela – Doppel‐Schrägkabelbrücke mit Verbundüberbau für Straßen‐ und Eisenbahngüterverkehr

The Orinoco River Bridge at Ciudad Guayana / Venezuela – a twin cable‐stayed bridge with steel composite bridge deck for road plus heavy rail traffic. The Orinoco Bridge at Ciudad Guayana carries a single track railway and a 2 × 2 lane highway across the Orinoco. The river has with low water a width of 1 km and with high water a width of 2 km. The total bridge length of 3156 m is subdivided into – the 1320 m long south approach bridge – the 1200 m long twin cable‐stayed bridge – the 636 m long north approach bridge. The bridge deck is a steel composite box girder and was erected partly by launching and partly by free cantilevering erection. The bridge is founded on large diameter bore‐piles. The paper deals with the design, special aspects of the calculation and the construction.     

Die zweite Geo‐Geum‐Brücke in Südkorea – Schrägkabelbrücke und Vorlandbrücke für Straßenverkehr mit Verbundfachwerkträger

The 2nd Geo Geum Grand Bridge in Korea – cable‐stayed bridge and approach bridge with composite truss girder for roadway traffic. The 2nd Geo Geum Grand Bridge forms part of the fixed connection from the mainland to the Island of Geo Geum in South Korea (Fig. 1). This high level crossing is composed of a 912 m long approach viaduct and a 1116 m long stay cable bridge with a main span of 480 m. The approach viaduct is a continuous girder with regular spans of 120 m. The superstructure of both bridges is a composite truss girder bridge, which carries a 2 lane highway on top and a pedestrian and bicycle way on the lower deck. The main design considerations were function as a high‐way, innovation in design and visual harmony with its surround‐ings. The stay cables are arranged in a single plane at the centre of the bridge, their semi‐fan arrangement with bundled configur‐ation gives a very special and unique appearance.     

斜拉桥成桥初始恒载索力概率确定

传统斜拉桥成桥初始恒载索力的确定方法由于忽略了结构参数的不确定性而不能满足实际工程设计需要。本文从概率分析的角度出发,提出一种新的确定斜拉桥成桥初始恒载索力方法——改进蒙特卡罗法。该方法采用响应面近似计算斜拉桥成桥初始恒载索力。然后,在响应面的基础上,利用传统蒙特卡罗法计算斜拉桥成桥初始恒载索力的统计特征。最后,采用该方法对一座对称式斜拉桥初始恒载索力进行概率性确定。     

Rapid Impact Testing and System Identification of Footbridges Using Particle Image Velocimetry

The rapid impact testing of bridges contains unique advantages. For example, structural parameters, including frequency response function and structural flexibility matrix can be identified; however, additional impact‐testing instruments are required to excite a bridge, restricting the efficiency of the measurement strategy in terms of experimental cost and time. In this paper, a particle image velocimetry‐based method is proposed for the rapid impact testing and system identification of footbridges under pedestrian excitations. The proposed method has shown promising features: (1) pedestrian load is utilized for the impact excitation of footbridges, which is more convenient than the conventional impact‐testing method with additional excitation devices; (2) the human‐induced impact forces under varying jumping scenarios are calculated from image sequences of human motions acquired by a single camera with its noncontact and target‐less characteristics; and (3) both human‐induced impact forces (inputs) and structural responses (outputs) are employed to identify more modal parameters (i.e., scaling factors, modal mass, and structural flexibility). The robustness of the proposed method was successfully validated by a laboratory test of a simply supported beam and field testing of a cable‐stayed footbridge. The proposed method not only could improve the testing efficiency of footbridges, but also could obtain more modal parameters, which can be further utilized for deflection prediction, damage detection, and long‐term performance evaluation.     

超大跨斜拉桥顺桥向地震损伤分析与控制

以一座试设计的主跨1 400 m的斜拉桥为例,采用弹塑性方法并引入地震损伤指标分析了不同强度地震作用下飘浮体系和弹性约束体系的地震损伤与破坏模式;研究了极端地震作用下损伤控制策略对斜拉桥损伤控制效果的影响。结果表明:极端地震作用下,主塔和桥墩分别遭受局部失效和严重损伤,发生了典型的弯曲单塑性破坏;基于Park损伤指数的附加耗能阻尼器的损伤控制策略可显著控制主塔、桥墩地震损伤和主梁位移,满足损伤控制目标要求,改善了桥梁的整体抗震性能。     

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).     

Wiederaufbau der Sloboda‐Brücke Novi Sad

Reconstruction of the Sloboda Bridge in Novi Sad. The Sloboda Bridge in Novi Sad with its free span of 351 m between the pylons has been one of the biggest cable stayed bridges with one cable plan in the world. Begin of April 1999 the bridge has been partly destroyed during a NATO air strike by two Thomahawks hiding the pylon bases. The destroyed bridge is an obstacle for one of the biggest European international waterways and the clearance and reconstruction are necessary in order to allow the free ship traffic.     

上海闵浦大桥的索结构桥梁管养方法

对于索结构桥梁,索力测量、锚固端检查及索皮检查是大桥管养单位检查的重点。以申嘉湖高速上的闵浦大桥为例,详细介绍拉索的索皮索力检测、养护的针对性方案。从结构受力体系出发,结合沉降监测、病害检测、健康监测数据和索力测试的成果,对发现的问题提出了相应的管养办法。