Stochastic petri-net models to predict the degradation of ceramic claddings

A stochastic Petri-net formalism is proposed to predict the degradation of ceramic claddings over time in order to understand how different environmental exposure conditions contribute to the overall degradation of these claddings. For that purpose, the degradation condition of 195 ceramic claddings located in Lisbon, Portugal, is evaluated through in situ visual inspections. In the first part of the study, a stochastic deterioration Petri-net model is proposed for the entire sample. In the second part, the original sample is divided according to the environmental exposure conditions, evaluating the influence of these conditions on the deterioration process of ceramic claddings. Four main degradation agents are analyzed: exposure to moisture; distance from the sea; orientation; and wind–rain action. The results reveal that Petri nets can accurately describe the deterioration process of ceramic claddings, providing relevant information regarding the performance of these claddings through their life cycle and according to the environmental exposure conditions to which they are subject. These results are extremely relevant for different practitioners: the approach allows the adoption of more sustainable and durable solutions at the design stage, as well as improving the durability of the ceramic claddings by performing optimized maintenance plans and strategies

Stochastic maintenance models for ceramic claddings

The authors gratefully acknowledge the support of the CERIS Research Institute, IST, University of Lisbon and the FCT (Foundation for Science and Technology), through the projects SLPforBMS (PTDC/ECM‐COM/5772/2014) and Best Maintenance-Lower Risks (PTDC/ECI-CON/29286/2017).Maintenance decision-making involves a series of multiple objectives, some of them contradictory. Usually, stakeholders intend to find the optimal maintenance strategy, to minimize the economic burden, while simultaneously maximizing the buildings’ performance. In this study, a condition-based maintenance model, based on Petri nets, is proposed to evaluate the consequences of alternative maintenance strategies to maintain and improve the performance of ceramic claddings. This maintenance model is a full life-cycle model that integrates the stochastic assessment of the degradation condition of the claddings, and also inspections, maintenance and renewal processes. Three maintenance strategies are considered: (i) major intervention only; (ii) combination of minor and major interventions; and (iii) combination of cleaning operations, minor and major interventions. The uncertainties associated with the degradation process, as well as with the definition of the effects of maintenance actions are considered by modelling the transitions times in Petri nets as random variables. Considering the complexity of Petri nets, the statistical descriptors of the performance of the assets (e.g., mean condition, probability of applying maintenance) were computed using Monte Carlo simulation. The impact of the different maintenance strategies in the claddings’ service life is discussed, comparing the different alternatives also from an economic point of view.publishersversionpublishe

Probabilistic analysis of degradation of façade claddings using Markov chain models

In this study, the time-dependent stochastic degradation of three types of claddings is analysed. For this purpose, 203 fac¸ades with stone claddings(directly adhered to the substrate), 195 with adhered ceramic claddings and 220 with painted surfaces were analysed. All the fac¸ades are located in Lisbon, Portugal. Their degradation condition was assessed through an extensive field work. Based on the data gathered, Markov chains are used to predict the degradation of claddings and to understand, in some detail, how the characteristics of the claddings contribute to the overall degradation. The results show that the distance from the sea and exposure to damp are significant to the degradation of all types of cladding. The type and size of stone plates also influence the degradation of stone claddings. The exposure to wind-rain action has a high impact on the degradation of ceramic claddings. The models proposed provide useful information on the probability of failure of the claddings; these results are fundamental in the context of insurance policies and in the definition of building maintenance plans

Anomaly diagnosis in ceramic claddings by thermography - A review

With the increasing importance given to building rehabilitation comes the need to create simple, fast and non-destructive testing methods (NDT) to identify problems and for anomaly diagnosis. Ceramic tiles are one of the most typical kinds of exterior wall cladding in several countries; the earliest known examples are Egyptian dating from 4000 BC. This type of building facade coating, though being quite often used in due to its aesthetic and architectural characteristics, is one of the most complex that can be applied given the several parts from which it is composed; hence, it is also one of the most difficult to correctly diagnose with expeditious methods. The detachment of ceramic wall tiles is probably the most common and difficult to identify anomaly associated with this kind of cladding and it is also definitely the one that can compromise security the most. Thus, it is necessary to study a process of inspection more efficient and economic than the currently used which often consist in semi-destructive methods (the most common is the pull off test), that can only be used in a small part of the building at a time, allowing some assumptions of what can the rest of the cladding be like. Infrared thermography (IRT) is a NDT with a wide variety of applications in building inspection that is becoming commonly used to identify anomalies related with thermal variations in the inspected surfaces. Few authors have studied the application of IRT in anomalies associated with ceramic claddings claiming that the presence of air or water beneath the superficial layer will influence the heat transfer in a way that can be detected in both a qualitative and a quantitative way by the thermal camera, providing information about the state of the wall in a much broad area per trial than other methods commonly used nowadays. This article intends to present a review of the state of art of this NDT and its potentiality in becoming a more efficient way to diagnose anomalies in ceramic wall claddings

Anomalies detection in adhesive wall tiling systems by infrared thermography

Adherent tiling systems are widely used all over the world as wall cladding because of their aesthetic and technical characteristics. However, anomalous behaviours often occur; compromising the overall behaviour of facades, and possibly raising safety risks. The need to create expeditious, non-destructive and accurate methods of inspection that can encourage these systems’ inspection and maintenance fomented a research study on infrared thermography’s capacity of early detect anomalous zones in adhesive tiling systems, such as detachments or presence of humidity, in controlled in situ conditions, proving it as a valuable diagnostic tool.authorsversionpublishe

Use of Petri Nets to Manage Civil Engineering Infrastructures

Over the last years there has been a shift, in the most developed countries, in investment and efforts within the construction sector. On the one hand, these countries have built infrastructures able to respond to current needs over the last decades, reducing the need for investments in new infrastructures now and in the near future. On the other hand, most of the infrastructures present clear signs of deterioration, making it fundamental to invest correctly in their recovery. The ageing of infrastructure together with the scarce budgets available for maintenance and rehabilitation are the main reasons for the development of decision support tools, as a mean to maximize the impact of investments. The objective of the present work is to develop a methodology for optimizing maintenance strategies, considering the available information on infrastructure degradation and the impact of maintenance in economic terms and loss of functionality, making possible the implementation of a management system transversal to different types of civil engineering infrastructures. The methodology used in the deterioration model is based on the concept of timed Petri nets. The maintenance model was built from the deterioration model, including the inspection, maintenance and renewal processes. The optimization of maintenance is performed through genetic algorithms. The deterioration and maintenance model was applied to components of two types of infrastructure: bridges (pre-stressed concrete decks and bearings) and buildings (ceramic claddings). The complete management system was used to analyse a section of a road network. All examples are based on Portuguese data

Anomalies detection in adhesive wall tiling systems by infrared thermography

Tiling systems for building facade coatings are widely used all over the world. Despite very common, mainly due to its aesthetic characteristics, this kind of cladding is characterised by a complex application, given the fact that it is a system in direct contact with a support (the rendered wall) and composed by three different components with specific characteristics and technical requirements: the tiles, the adhesive grout, and the joint grout. This complexity can result in several possible anomalies, as it is the case of detachment, the most common onerous one and probably the most difficult anomaly to early diagnosis in this type of cladding. Infrared thermography is a non-destructive testing method with a broad applicability in buildings’ inspection. The method consists in using a thermal camera that, by detecting thermal radiation, reads thermal variations that can indicate the presence of anomalies. Taking into account this diagnosis method’s potential, it was developed in LNEC a wide study where the results of thermographic surveys on laboratory specimens, exterior panels cladded with tiles with controlled anomalies and case studies of real situations are presented. In order to characterize the claddings behaviour and the anomalies’ detectability using this method, in a first phase eight specimens were studied in laboratory with differences in terms of: colour, thickness, kind of support, finishing and presence of anomaly. In a second phase, four panels divided into two experimental cells, located in LNEC’s campus, aiming to evaluate the diagnostic technique in exterior facades with differences in terms of tiles’ colour and support of application. As a complement of the laboratory surveys (indoors and outdoors) certain features of this kind of cladding were characterized, such as their emittance and reflectance. In order to evaluate infrared thermography’s diagnosis capability in real and unfamiliar situations, two real cases of buildings in Lisbon, cladded with ceramic tiles, were studied. The results obtained in the form of thermal differentials between “normal” and “anomalous” zones in a tiled facade or specimen proved that Infrared Thermography can be a valuable tool to early identification of anomalies, mainly detachments, in this kind of coating systems

Pellet Cladding Mechanical Interactions of Ceramic Claddings Fuels Under Light Water Reactor Conditions

Ceramic materials such as silicon carbide (SiC) are promising candidate materials for nuclear fuel cladding and are of interest as part of a potential accident tolerant fuel design due to its high temperature strength, dimensional stability under irradiation, corrosion resistance, and lower neutron absorption cross-section. It also offers drastically lower hydrogen generation in loss of coolant accidents such as that experienced at Fukushima. With the implementation of SiC material properties to the fuel performance code, FRAPCON, performances of the SiC-clad fuel are compared with the conventional Zircaloy-clad fuel. Due to negligible creep and high stiffness, SiC-clad fuel allows gap closure at higher burnup and insignificant cladding dimensional change. However, severe degradation of SiC thermal conductivity with neutron irradiation will lead to higher fuel temperature with larger fission gas release. High stiffness of SiC has a drawback of accumulating large interfacial pressure upon pellet-cladding mechanical interactions (PCMI). This large stress will eventually reach the flexural strength of SiC, causing failure of SiC cladding instantly in a brittle manner instead of the graceful failure of ductile metallic cladding. The large interfacial pressure causes phenomena that were previously of only marginal significance and thus ignored (such as creep of the fuel) to now have an important role in PCMI. Consideration of the fuel pellet creep and elastic deformation in PCMI models in FRAPCON provide for an improved understanding of the magnitude of accumulated interfacial pressure. Outward swelling of the pellet is retarded by the inward irradiation-induced creep, which then reduces the rate of interfacial pressure buildup. Effect of PCMI can also be reduced and by increasing gap width and cladding thickness. However, increasing gap width and cladding thickness also increases the overall thermal resistance which leads to higher fuel temperature and larger fission gas release. An optimum design is sought considering both thermal and mechanical models of this ceramic cladding with UO2 and advanced high density fuels

Low cost, energy and impact ceramic cladding cooling system by means of evapotranspiration or ‘botijo-effect’.

A new ceramic cladding system was first applied in the house prototype named "SOLARKIT”, representing the University of Seville in the international competition Solar Decathlon Europe 2010, where its effectiveness was registered by thermographs y and the monitoring of the building. Therefore, as a result of this R+D+I experience derived from the search of a low energy and innovative cooling bioclimatic strategy, a new cladding system has been invented and patented. Consequently, the patented invention relates to an external cladding system using tiles made from a porous-ceramic material or similar, named as a façade with “botijo-effect”. Thus, the system can be applied directly as a final cladding or used in external sheets of ventilated façades. Compared to traditional claddings, this system provides de possibility of cooling its surface by means of evapotranspiration generated by supplying water through a network of canaliculi inside the tiles. An estimated superficial cooling power of over 80 W/m² can be considered, plus an 8 to 10ºC cooling effect on the air temperature Its application is particularly interesting at locations with hot-dry climates where there is a high cooling energy demand or where is intended to mitigate the "heat island" effect in urban environments

The aesthetics of gravity

Beyond taste or fashion, there exists a lasting and common consensus for a perception of beauty linked to weight or weightlessness. This essay attempts to develop an understanding of different approaches to the issue of weight and weightlessness in architecture and civil engineering. In complex urban and programmatic settings, however, the question of gravity has to be integrated with many other issues, as exemplified by Albini and HeIg's La Rinascente department store in Rom