Autonomous UAVs for Structural Health Monitoring Using Deep Learning and an Ultrasonic Beacon System with Geo‐Tagging

Visual inspection has traditionally been used for structural health monitoring. However, assessments conducted by trained inspectors or using contact sensors on structures for monitoring are costly and inefficient because of the number of inspectors and sensors required. To date, data acquisition using unmanned aerial vehicles (UAVs) equipped with cameras has become popular, but UAVs require skilled pilots or a global positioning system (GPS) for autonomous flight. Unfortunately, GPS cannot be used by a UAV for autonomous flight near some parts of certain structures (e.g., beneath a bridge), but these are the critical locations that should be inspected to monitor and maintain structural health. To address this difficulty, this article proposes an autonomous UAV method using ultrasonic beacons to replace the role of GPS, a deep convolutional neural network (CNN) for damage detection, and a geo‐tagging method for the localization of damage. Concrete cracks, as an example of structural damage, were successfully detected with 97.7% specificity and 91.9% sensitivity, by processing video data collected from an autonomous UAV.     

爆炸荷载作用下钢框架结构连续倒塌分析

传统数值方法模拟建筑结构在爆炸荷载作用下的结构响应和连续倒塌时,具有计算模型复杂、计算量大的特点,实际应用价值不大。基于将爆炸荷载作用下结构响应分析分两步进行的数值模拟方法,利用非线性显式动力分析软件AUTODYN的Remap技术模拟爆炸波在空气中的传播过程,利用压强测点记录结构构件表面的爆炸压强时程曲线;建立结构精细化有限元模型,并将上一步记录的爆炸压强时程曲线施加于结构构件,利用LS-DYNA显式求解器分析结构在爆炸荷载作用下的动态响应和倒塌过程。将该方法应用于某钢框架结构在爆炸荷载作用下的动态响应和连续倒塌分析。结果表明：钢框架结构具有较好的抗爆性能,在发生1000kg TNT当量及以下规模的室外爆炸时,主体结构能够保证安全;在发生1500kgTNT当量及以上大规模爆炸时,发生次梁塌落等局部破坏,亦可能发生结构连续倒塌。     

Detektion und Lokalisierung von strukturellen Schäden mit Hilfe von geführten Wellen

Detection and localization of structural damages by means of guided waves. The procedure presented serves for an automatic large‐area monitoring of steel structures by means of non‐destructive testing. Piezoceramic members are applied as a cluster to the structure under observation. These elements are used both as sensors and as actuators and initiate guided wave propagation in the structure. Damages are detected by the changed structural response. Beside other methods of signal processing the principle of beamforming is used with the sensor signals. The example of a 6 mm steel plate shows the sensitivity of the developed procedure for damage detection.     

多点输入下基于响应敏感性的单层球面网壳冗余特性研究

结构的响应敏感性是用来描述结构行为与设计参数之间关系的函数,文章基于响应敏感性对结构冗余特 性进行研究,提出基于结构应变能敏感性的冗余度评价方法,即以结构整体应变能对构件材料弹性模量的敏感性 极值作为冗余度评价指标,考虑局部损伤对结构整体的影响。在Dibaj和Penzien求解多点输入响应弹塑性动力方 程的基础上推导多点输入下结构应变能对构件弹性模量敏感性的一整套计算公式,再以此为基础衡量结构构件在 多点输入下的冗余度。以2个跨度23.4m、矢跨比1/2的K6型单层网壳多点输入振动台倒塌试验模型为检验对象, 对比完善结构和人为设置薄弱区结构模型的倒塌过程,表明文中冗余特性评价方法能全面反映结构的整体性能, 可以正确识别结构的薄弱区域和关键构件所在。     

Corrosion damage assessment and monitoring of large steel space structures

Large steel space structures, when exposed to a harsh corrosive environment, are inevitably subjected to atmospheric corrosion and stress corrosion cracking. This paper proposes a framework for assessing the corrosion damage of large steel space structures subjected to both stress corrosion cracking and atmospheric corrosion. The empirical model for estimating atmospheric corrosion based on measured information is briefly introduced. The proposed framework is applied to a real large steel space structure built in the southern coastal area in China to assess its corrosion damage and investigate the effects of atmospheric corrosion on stress corrosion cracking. Based on the results, the conceptual design of the corrosion monitoring system of large steel space structures is finally conducted as the first step for a real corrosion monitoring system.     

Corrosion damage assessment and monitoring of large steel space structures

Large steel space structures, when exposed to a harsh corrosive environment, are inevitably subjected to atmospheric corrosion and stress corrosion cracking. This paper proposes a framework for assessing the corrosion damage of large steel space structures subjected to both stress corrosion cracking and atmospheric corrosion. The empirical model for estimating atmospheric corrosion based on measured information is briefly introduced. The proposed framework is applied to a real large steel space structure built in the southern coastal area in China to assess its corrosion damage and investigate the effects of atmospheric corrosion on stress corrosion cracking. Based on the results, the conceptual design of the corrosion monitoring system of large steel space structures is finally conducted as the first step for a real corrosion monitoring system.     

Polynomial Chaos Representation for Identification of Mechanical Characteristics of Instrumented Structures

Abstract: The modeling of in‐service behavior is of first importance when reassessing complex structures like harbor structures and when performing risk analysis. To this aim, the monitoring of structures allows assessment of the level of loading and to provide more realistic models for mechanical behavior or input values for their parameters. Moreover, for complex structures and due to building hazards, a stochastic modeling is needed to represent the large scatter of measured quantities. In this article, a step‐by‐step procedure for structural identification is presented. A decomposition of random variables on Polynomial Chaos is selected and it is shown to represent better the basic variables in comparison to preselected distribution functions, when considering maximum likelihood estimate. The decomposed variables are used for a stochastic analysis to be further updated with available monitoring data. The model can be used to follow the structure behavior during in‐service or extreme conditions and to perform a reliability analysis. The proposed procedure will be carried out by using available data from the monitoring of a pile‐supported wharf in the Port of Nantes, in France, but it can be generalized to similar monitored structures.     

可恢复功能防震结构研究进展

对于可恢复功能防震理念，要求结构在保护生命的前提下，能够在震后快速恢复使用功能，尽量减少对正常生活和生产的影响。依据该理念，作为可恢复功能城市的基本组成部分，可恢复功能防震结构合理应用摇摆、自复位、可更换和耗能等四种机制，将损伤集中于可更换的耗能构件或部件，从而保护主体结构，使其无损伤或可快速修复。因此，结构功能可在震后及时恢复。利用这些机制，可恢复功能防震结构在材料、构件和体系三个层次具有不同的实现方案，包括摇摆结构、自复位结构、可更换构件/部件结构和复合自复位结构。基于可恢复功能的设计和评估方法，采用恢复时间、经济损失等更加直接的指标，为这一新型结构体系的应用奠定基础。目前，应提出更多的可恢复功能防震结构新体系，而进一步研究该类结构的关键构造和动力特性，提出切实可行的设计方法并形成统一的设计规范，应成为进一步研究的重点。     

Bridge design with reserve and residual reliability constraints

System reliability is evolving as an important design method for selecting components and topology. It should be used to investigate the original intact structure behavior as well as providing sufficient reserve capacity under likely accident and damage scenarios. Highway bridges are an area of special concern since effort to optimize the cost of construction may not provide adequate redundant capacity. The paper describes an example in which a typical girder bridge structure is optimized (both size and girder spacing) to achieve target system performance. System reliability constraints are imposed on the behavior of the intact structure under highway loads. Also, residual system reliability constraints are imposed to control safety under specified accident scenarios corresponding to damage and “lost” members due to corrosion, fatigue, fire or accidental collisions. An optimal design framework for controlling safety under all these life cycle situations is thus provided.     

Plasticity effects on frame member reliability

This paper proposes a computational procedure to correctly construct the nonlinear limit state and estimate the reliability of members in ductile framed structures. Due to the uncertainties in loads and structural properties, the structure could be in one of many different damage states before failure occurs in the member of interest. Since the enumeration of all these damage states and the computation of their effect on member reliability is tedious, the proposed method uses three criteria based on the statistical relationships among the members to efficiently identify those damage states that significantly affect the reliability of the desired member. This is used to determine the polyhedral envelope of the entire failure domain, corresponding to various levels of cumulative damage. The failure probability is then estimated through the union of failure domains defined by each of the linear segments of this polyhedral surface, using second-order bounds.     

Optimized topology extraction of steel-framed DiaGrid structure for tall buildings

This study presents an optimal angle and a topology extraction of diagonal members in a DiaGrid structural system for tall buildings. The angle and topology of diagonal members are achieved by using a computer-oriented SIMP topology optimization. The objective function for the design optimization is to both maximize Eigenfrequency for resisting dynamic responses and minimize mean compliance for static responses. Relative densities subjected to SIMP penalty law are used for both optimization design variables and material properties, and then finite element analysis is carried out by using the relative element density. Frequency and mean compliance sensitivities with respect to relative density are straightforwardly derived by discrete sensitivity formulations. Based on the design sensitivity analysis, an initial topology with a given fixed support is shifted toward a final topology charged by almost voids (0) and solids (1) during every optimization procedure. An optimal DiaGrid topology with the highest stiffness is finally determined to resist both static and dynamic behaviors. Numerical examples with varied fixed support models are studied to find out optimal angles and topologies of diagonal members for a DiaGrid system design.     

用振动参数识别技术对混凝土框架进行破损评估

本文提出了采用振动参数识别技术对混凝土平面框架结构进行破损评估的新方法.该方法是首先采用“残余力向量”识别结构的损伤部位,然后再用振动理论中的加权灵敏度分析的方法识别结构的物理参数,由此识别结构的损伤严重程度.经三榀钢筋混凝土框架的试验结果表明,本文的方法是可行的.     

Estimation of fixity factors of bolted joints in a steel frame structure using a vibration-based health monitoring technique

Framed steel structures frequently have bolted connections to ensure semi-rigid joints that have a significant amount of energy dissipation incorporated in them, to avoid failure of connections and members under cyclic loading, such as wind and earthquake loading. One problem is that due to cyclic action, these bolts may loosen, and compromise subsequent behavior of the structure. A vibration-based health monitoring technique for quantification of the level of loosening of bolted joints in a steel plane frame structure is presented here, to provide a basis for evaluation of the structure state. A numerical model of a plane frame is considered with rotational springs representing semi-rigid joints. A fixity factor is defined in terms of rotational spring stiffness and is considered as a measure of level of loosening of bolts with zero representing fully loose and one representing fully tight condition. Experimental strain time histories are collected and transformed into frequency domain using Fourier transform. A shape co-relation is defined using frequency data obtained from the damaged and the undamaged structures. Using the frequency spectra and shape correlation, an objective function (OF) is developed and minimized by the particle swarm optimization to estimate the fixity factor. It is found that the technique estimates higher value of reduction of the fixity factor in the damaged location, but shows some considerable value at the other springs also. Therefore, the technique is improved using heuristics by identifying probable damage locations prior to applying model updation, in order to estimate the damage severity more accurately. Considering fixity factors at the identified locations as variables, model updating is done for estimation of fixity factors. The improved results clearly indicate actual damage locations and fixity factors for different levels of bolt loosening, and is found satisfactory for possible future application of the technique to multistory framed structures.     

弱连体结构抗震设计方法在虹桥综合交通枢纽工程中的应用

连体结构加剧了结构在地震作用下的受力复杂性,属不规则结构。以上海虹桥综合交通枢纽为工程背景,介绍了弱连体结构抗震设计方法在工程中的应用,并基于LS-DYNA程序开发了用于结构弹塑性时程分析的梁柱纤维单元,通过构件数值滞回加载与试验结果的比较,验证了梁柱纤维单元的适用性。采用多质点层模型进行粘滞阻尼器参数优化分析,并采用整体结构弹塑性模型进行罕遇地震作用计算,评价阻尼器参数设计的合理性和弱连体结构的抗震性能。分析结果表明：该工程弱连接设计是可行的,结构满足抗震性能要求。     

风力作用下深圳市民中心屋顶网架结构的智能健康监测

本文以深圳市民中心屋顶网架结构为工程背景,详细探讨了仅需要有限数量传感器就可实现对风力作用下大跨度复杂体型屋盖网架结构整体工作状态的自动监测和未知损伤的自动诊断的智能方法。此方法的关键技术有:网架结构工作状态的智能监测技术,支承钢牛腿工作状态的智能监测技术,网架结构节点焊缝拉裂损伤的自动诊断技术,有损伤网架结构抗倒塌的实时安全评定技术。通过这些智能方法的应用,成功地实现了在最经济的条件下对整个网架结构的全面健康监测。     

A numerical study based on sequential procedure for optimally placing active controllers

A sequential procedure based on the concept of degree of controllability is developed for optimally placing active controllers in structures. The optimal locations are selected to be located where the largest structural response occurs. This sequential procedure uses time history analysis to determine these optimal locations, and the effect of each additional controller on the next optimal location is considered in every step of the analysis procedure. Force analogy method (FAM) is used to take into consideration any possible structural inelasticity during earthquakes. Different from conventional methods of inelastic analysis using changing stiffness, FAM varies the structural displacement field, and therefore greatly simplifies the computation. Since only initial stiffness is used in the inelastic analysis, it can be easily incorporated into the optimal linear control algorithm using the state space method. Numerical simulation of a six‐storey frame is performed to demonstrate the simplicity of optimal placement procedure while considering structural inelasticity. Results show that optimal locations determined by the proposed sequential procedure have advantages over other locations in terms of control efficiency, where placement of the controllers in these locations reduces the desired overall structural and energy response most effectively. Copyright © 2005 John Wiley & Sons, Ltd.     

Optimal design of steel skeletal structures using the enhanced genetic algorithm methodology

This study concerns with the design optimization of steel skeletal structures thereby utilizing both a real-life specification provisions and ready steel profiles named hot-rolled I sections. For this purpose, the enhanced genetic algorithm methodology named EGAwMP is utilized as an optimization tool. The evolutionary search mechanism of EGAwMP is constituted on the basis of generational genetic algorithm (GGA). The exploration capacity of EGAwMP is improved in a way of dividing an entire population into sub-populations and using of a radial basis neural network for dynamically adjustment of EGAwMP’s genetic operator parameters. In order to improve the exploitation capability of EGAwMP, the proposed neural network implementation is also utilized for prediction of more accurate design variables associating with a new design strategy, design codes of which are based on the provisions of LRFD_AISC V3 specification. EGAwMP is applied to determine the real-life ready steel profiles for the optimal design of skeletal structures with 105, 200, 444, and 942 members. EGAwMP accomplishes to increase the quality degrees of optimum designations Furthermore, the importance of using the real-life steel profiles and design codes is also demonstrated. Consequently, EGAwMP is suggested as a design optimization tool for the real-life steel skeletal structures.     

斜拉桥结构健康监测系统的设计与实现(I):系统设计

结构智能健康监测愈来愈成为重大工程结构健康与安全的重要保障技术,也愈来愈成为重大工程结构损伤积累乃至灾害演变规律的重要研究手段。斜拉桥健康监测系统是由传感器子系统、数据采集与传输子系统、结构分析子系统和数据管理子系统组成的,不同系统的谐调运行需要通过系统集成技术来实现。首先从监测内容、等级和功能等方面研究健康监测系统的总体设计原则;然后,分局部监测变量和整体监测变量研究传感器的最优测点确定方法和原则,提出传感器的选型原则;提出数据采集系统的总线设计方法和方案,研究数据采集系统硬件和软件设计方法;提出数据传输系统的设计原则和方法;给出斜拉桥基于构件和基于结构体系的安全评定设计方法;提出斜拉桥施工监控、成桥试验、运营健康监测和养护管理四位一体系统的共享设计原则;提出系统集成技术的软件设计方法。     

钢筋混凝土框架-剪力墙结构基于能量抗震设计方法的耗能需求计算与设计流程

基于“强墙肢弱连梁”合理耗能机制控制的前提,提出钢筋混凝土框架-剪力墙结构基于能量抗震设计的实施流程。基于大量钢筋混凝土框架-剪力墙结构算例的弹塑性时程分析结果,给出了钢筋混凝土框架-剪力墙结构各构件累积耗能需求的实用计算方法,包括结构总累积耗能EH,EH 在连梁、墙肢和框架梁中的分配,各类构件累积耗能沿楼层高度的分布,同层同类构件的累积耗能分配。结合合理的构件损伤评价模型,建议了钢筋混凝土框架-剪力墙结构各类构件的能力设计方法,将基于能量抗震设计方法落实到构件层次。最后,通过一个20层钢筋混凝土框架 剪力墙结构算例,说明了所建议的基于能量抗震设计方法的具体应用。与时程分析结果的比较表明,所建议方法的构件耗能需求计算结果与时程分析结果吻合较好,且偏于安全。     

Decentralized Parametric Damage Detection Based on Neural Networks

In this paper, based on the concept of decentralized information structures and artificial neural networks, a decentralized parametric identification method for damage detection of structures with multi-degrees-of-freedom (MDOF) is conducted. First, a decentralized approach is presented for damage detection of substructures of an MDOF structure system by using neural networks. The displacement and velocity measurements from a substructure of a healthy structure system and the restoring force corresponding to this substructure are used to train the decentralized detection neural networks for the purpose of identifying the corresponding substructure. By using the trained decentralized detection neural networks, the difference of the interstory restoring force between the damaged substructures and the undamaged substructures can be calculated. An evaluation index, that is, relative root mean square (RRMS) error, is presented to evaluate the condition of each substructure for the purpose of health monitoring. Although neural networks have been widely used for nonparametric identification, in this paper, the decentralized parametric evaluation neural networks for substructures are trained for parametric identification. Based on the trained decentralized parametric evaluation neural networks and the RRMS error of substructures, the structural parameter of stiffness of each subsystem can be forecast with high accuracy. The effectiveness of the decentralized parametric identification is evaluated through numerical simulations. It is shown that the decentralized parametric evaluation method has the potential of being a practical tool for a damage detection methodology applied to structure-unknown smart civil structures.