Comparison study of precise monitoring techniques applied to engineering specimens tested under dynamic loading

Initially, the thesis shows a state of the art for structural health monitoring techniques and procedures. Different types of instrumentations and sensors employed under different requirements, which are presented with the view to monitor a variety of structural issues resulted by numerous conditions. It also presents examples from the literature following the proposed monitoring strategy as a novel pattern. These show how close-range digital photogrammetry and strain gauges have been employed in the past with the view to obtain strain evaluation assessments of the relevant monitored structural elements. Based on three surveys which have been carried out in a historical masonry church in Athens (Greece), the methodology of the thesis is generated with the experimental framework being also formed. Eight experiments have been carried out, five of them at the Advanced Structures Laboratory (CEGE – UCL), one at the Concrete Laboratory (CEGE – UCL) and two of them at the Earthquake and Large Structures Laboratory (EQUALS – University of Bristol). Two scale engineering specimens are employed for the experimental needs, both are scaled down using as a prototype element, the north-eastern wall of the studied church. The five experiments which are carried out in CEGE, are made on small scale masonry specimens, of 1/17th scale and the two experiments in EQUALS are made on large scale masonry specimens, of 1/5th scale. All the seven experiments are dynamically loaded. The only static loaded experiment is carried out at the Concrete Laboratory and it is made on a masonry specimen. Through the comparison of the two monitoring methods, close-range digital photogrammetry (CRDP) and strain gauges (SG), is concluded that both methods can capture a change in strain, on the tested specimens, when a crack is occurring

Non-contact monitoring of railway infrastructure with terrestrial laser scanning and photogrammetry at Network Rail

Current monitoring practices in the railway industry primarily rely on total station and prism based methods. This approach requires the installation and maintenance of prisms directly onto the structure being monitored which can be invasive and expensive. This thesis presents the outcomes of an industrial based doctorate, motivated by the Network Rail Thameslink Programme, to investigate the potential of terrestrial laser scanning and photogrammetry as an alternative non-contact and “target-less” solution to monitoring railway infrastructure. The contributions made by this thesis in the context of Network Rail requirements include: a laboratory based exploration of the state of the art in target and surface-based measurements; a validation of conventional, terrestrial laser scan and photogrammetric surveys of a deforming set of brick arches; and a novel prism-less method of track measurement using terrestrial laser scanner data. The complete project has been carried out as part of the highly complex and dynamic £900m London Bridge Redevelopment Project. The thesis comprises of a review of existing monitoring system performance and highlights challenges in the adoption of this technology through interviews of leading professionals in the monitoring industry. Laboratory tests utilise network adjustment prediction and analysis to compare state of the art total station, terrestrial laser scanning and close-range photogrammetry instrumentation to both target and target-less deformation monitoring scenarios. The developed tests allow the performance of each technique to be assessed within the context of state of the art and Network Rail operational practice and are extensible to developments in each of these technologies. Results demonstrate performances to sub-millimetre level and are validated through the use of a Leica AT401 laser tracker. Each technique is then explored within the London Bridge Redevelopment Project through a series of live monitoring sites where their ability to either augment or replace existing survey techniques is evaluated. Results from the on-site monitoring of historic brick arch structures demonstrate surface measurements compatibility at the millimetre level, highlighting close agreement between instrument performance established in the laboratory. A key use of prism-based techniques is in the determination of engineering track parameters where costly prism systems, both in terms of installation and subsequent maintenance, attached to the track are a key concern. Here laboratory validated track surface measurement, with terrestrial laser scanning, has been deployed on a 15 metre long dual track site and shown to be highly capable of replacing prism systems for the determination of accurate track geometry. This work has included a novel optical non-contact measurement process utilising individual rail cross section designs to automatically extract relevant track geometry parameters within 1mm of prism-based methods. The method offers excellent potential for incorporation into an automated track monitoring system. Outcomes from the thesis have been published in peer-reviewed journals and conferences

Digital Photogrammetry for Long-Term Monitoring

Digital photogrammetry has established itself as an effective tool for documenting cultural heritage in the twenty-first century. With portable equipment and a relatively short amount of time, an incredible amount of surface data can be captured for an object and stored as point clouds. This richness of data raises questions of whether it should be used for analytical purposes in addition to documentation. This thesis researches using close-range, digital photogrammetry to describe physical change over time. The image sets were captured, point clouds created in Agisoft, and analyzed using CloudCompare to identify any dislocations. Three-dimensional changes that are not easily measured or observed were chosen as the focus of this research and they were broken into three typologies: cracking, erosion, and warping. Each was recreated using a proxy experiment and gave different degrees of analytical data for The degree to which these changes can be detected will drive what sort of analytical conclusions can be drawn. This comparative photogrammetry can identify areas of change that may be easily ignored by the humane eye due to their slow, gradual rate of change. When these two points in time are compared directly in the form of two high resolution point clouds, minute changes become discreet and take shape. Once the shape becomes a pattern, material condition could begin to be speculated. With two well executed data sets, it is possible to detect and visualize the changes between two experimental models. The challenge lies in understanding how CloudCompare understands these changes and then translating that language into analytical decisions about the condition of the material. The speed, ease, and relatively low cost of photogrammetry makes it very effective at homing in on areas of concern

Monitoring 3D vibrations in structures using high resolution blurred imagery

This thesis describes the development of a measurement system for monitoring dynamic tests of civil engineering structures using long exposure motion blurred images, named LEMBI monitoring. Photogrammetry has in the past been used to monitor the static properties of laboratory samples and full-scale structures using multiple image sensors. Detecting vibrations during dynamic structural tests conventionally depends on high-speed cameras, often resulting in lower image resolutions and reduced accuracy. To overcome this limitation, the novel and radically different approach presented in this thesis has been established to take measurements from blurred images in long-exposure photos. The motion of the structure is captured in an individual motion-blurred image, alleviating the dependence on imaging speed. A bespoke algorithm is devised to determine the motion amplitude and direction of each measurement point. Utilising photogrammetric techniques, a model structure s motion with respect to different excitations is captured and its vibration envelope recreated in 3D, using the methodology developed in this thesis. The approach is tested and used to identify changes in the model s vibration response, which in turn can be related to the presence of damage or any other structural modification. The approach is also demonstrated by recording the vibration envelope of larger case studies in 2D, which includes a full-scale bridge structure, confirming the relevance of the proposed measurement approach to real civil engineering case studies. This thesis then assesses the accuracy of the measurement approach in controlled motion tests. Considerations in the design of a survey using the LEMBI approach are discussed and limitations are described. The implications of the newly developed monitoring approach to structural testing are reviewed

Innovative Methods and Materials in Structural Health Monitoring of Civil Infrastructures

In the past, when elements in sructures were composed of perishable materials, such as wood, the maintenance of houses, bridges, etc., was considered of vital importance for their safe use and to preserve their efficiency. With the advent of materials such as reinforced concrete and steel, given their relatively long useful life, periodic and constant maintenance has often been considered a secondary concern. When it was realized that even for structures fabricated with these materials that the useful life has an end and that it was being approached, planning maintenance became an important and non-negligible aspect. Thus, the concept of structural health monitoring (SHM) was introduced, designed, and implemented as a multidisciplinary method. Computational mechanics, static and dynamic analysis of structures, electronics, sensors, and, recently, the Internet of Things (IoT) and artificial intelligence (AI) are required, but it is also important to consider new materials, especially those with intrinsic self-diagnosis characteristics, and to use measurement and survey methods typical of modern geomatics, such as satellite surveys and highly sophisticated laser tools

Fifth International Conference on SALT WEATHERING OF BUILDINGS AND STONE SCULPTURES:

These proceedings report on the 5th edition of the conference, after Copenhagen (2008), Cyprus (2011), Brussel (2014) and Potsdam (2017), and it is the first time the conference is held in hybrid form, due to the COVID-19 pandemic. It is a challenge to organize an event in such an uncertain situation and to make it as attractive and interactive as the previous editions. We hope to meet your expectations! I’m very glad, that despite the situation, the interest for the conference is strong: we have received more than 40 contributions from 18 countries from all over the world. This confirms the relevance of the problem of salt weathering for the built cultural heritage and stone artifacts in a wide range of environments. Moreover, the broad spectrum of approaches to the subject presented in these proceedings highlights the importance of the interaction between different disciplines as well as between fundamental research and practice of conservation. I wish this conference to contribute to this fruitful exchange, and to generate new research ideas, whilst strengthening and broadening interdisciplinary collaborations. On behalf of the organizing committee, I’m looking forward to welcoming as many as possible of you in Delft. We hope that, next to participation to the conference, you will find some free time to visit the city. You can stroll along the canals, enter a windmill, visit the Prinsenhof museum and the Blue Delft Factory, admire the architecture and sculptures in the Old and New Church and, if you are looking for a real Dutch experience, you can rent a bicycle and visit the surroundings! This event would not have been possible without the collaboration of several persons. I would like to thank, on behalf of us all, the Scientific Committee for carefully reviewing the papers and contributing thereby to the high quality of the published contributions. My personal thank goes to the organizing committee who significantly contributed to the organization of this event and to the preparation of the proceedings. Last but not least, I’d like to thank the Cultural Heritage Agency of the Netherlands for co-sponsoring the event and RILEM (International Union of Laboratories and Experts in Construction Materials, Systems and Structures) for contributing to the dissemination

"Ponte do Arco", analisi di un ponte in muratura. Analysis of "Ponte do Arco" masonry arch bridge

I ponti in muratura godono di peculiarità specifiche che determinano una certa complessità nell’affrontare la valutazione del loro comportamento sotto le diverse azioni, statiche o dinamiche, e quindi della loro sicurezza; infatti, essi sono costituiti da numerose parti che interagiscono tra loro (volta, timpano, riempimento ecc.). Tale lavoro si propone di fornire un approccio generale che si addentri negli ambiti previsti per ottenere una valutazione fondante del comportamento del pont

Integrated HBIM-GIS Models for Multi-Scale Seismic Vulnerability Assessment of Historical Buildings

The complexity of historical urban centres progressively needs a strategic improvement in methods and the scale of knowledge concerning the vulnerability aspect of seismic risk. A geographical multi-scale point of view is increasingly preferred in the scientific literature and in Italian regulation policies, that considers systemic behaviors of damage and vulnerability assessment from an urban perspective according to the scale of the data, rather than single building damage analysis. In this sense, a geospatial data sciences approach can contribute towards generating, integrating, and making virtuous relations between urban databases and emergency-related data, in order to constitute a multi-scale 3D database supporting strategies for conservation and risk assessment scenarios. The proposed approach developed a vulnerability-oriented GIS/HBIM integration in an urban 3D geodatabase, based on multi-scale data derived from urban cartography and emergency mapping 3D data. Integrated geometric and semantic information related to historical masonry buildings (specifically the churches) and structural data about architectural elements and damage were integrated in the approach. This contribution aimed to answer the research question supporting levels of knowledge required by directives and vulnerability assessment studies, both about the generative workflow phase, the role of HBIM models in GIS environments and toward user-oriented webGIS solutions for sharing and public use fruition, exploiting the database for expert operators involved in heritage preservation

Physical model tests and numerical simulation for assessing the stability of tunnels

Nowadays, numerical modelling is increasingly used to assess the stability of tunnels and underground caverns. However, an analysis of the mechanical behaviour of existing brick-lined tunnels remains challenging due to the complex material components. One promising approach is to carry out a series of small-scale physical tunnel model tests representing the true behaviour of a prototype under extreme loading in order to validate and develop the corresponding numerical models. A physical model test is advisable before any field study, which might be dangerous and costly. During the tests, advanced monitoring techniques such as the laser scanning and photogrammetry would be used to register tunnel deformation and lining defects. This investigation will show how these may substitute or supplement the conventional manual procedures. Simultaneously, numerical models will be developed, primarily using FLAC and UDEC software, to simulate the physical models after comparing their results. In this way, numerical simulations of physical models would be achieved and verified. These numerical models could then be applied to the field study in the future research, enabling accurate prediction of the actual mechanical behaviour of a masonry tunnel, in combination with advanced monitoring techniques