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

ABSTRACT

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.     

Serviceability of facade claddings

In the present world economic situation, the resources directed to the maintenance of buildings are very limited. Therefore, an increasing concern arises for the planning and prioritization of necessary maintenance works during buildings’ life cycle. The planning of maintenance action is achieved by predicting the moment when construction elements reach degradation levels that exceed acceptable standards. To be able to make such forecasts, crucial developments must be made regarding the methods to predict the serviceability of building materials and components. In this study, 444 facades located in the cities of Lisbon and Almada and the Algarve region (Portugal) are analysed based on in situ visual inspections. The approach proposed can be employed in various scopes of service life prediction and maintenance of constructions. This paper develops a priority hierarchy of maintenance actions for the claddings under analysis. The expertise acquired in buildings’ serviceability is very useful to support decision-making in the development of proactive maintenance strategies. The results reveal accurate outcomes in the correlation with the functionality and degradation parameters of facade claddings. The serviceability of the most common types of facades claddings (render, ceramic and paints) applied in Portugal is analysed.     

残损木柱受力性能退化试验研究与有限元分析

梁、柱等构件存在腐朽等局部残损是现存古建筑木结构的普遍状况,其显著地降低了木结构受力性能。为研究残损木柱受力性能退化规律,采用局部去除腐朽木材的方法模拟木柱上的局部残损,对4根不同残损程度的矩形木柱进行了轴心受压试验,得到了残损木柱的荷载-侧移、荷载-应变关系曲线,分析了残损木柱的破坏模式、承载力及刚度退化规律。试验结果表明,随着残损程度增加,残损木柱逐渐由轴压破坏变为偏压破坏,受压承载力显著降低。采用ABAQUS有限元软件对4种不同残损程度的木柱受压性能进行了模拟分析,模拟结果与试验结果吻合较好。在此基础上,分析了残损区域深度、长度等因素对木柱受力性能退化的影响规律。分析结果表明：随着损伤区域深度的增大,承载力降低幅值随之增大;随着损伤区域长度的增大,承载力降低趋于缓和。     

Probabilistic transition of condition: render facades

The service life of cement-rendered facades is closely related to the environmental conditions to which they are exposed. The probability distribution is determined for the degradation condition of render facades considering different environmental exposures. A sample of 100 render facades was subjected to meticulous fieldwork to determine their condition. The analysis focuses on the environmental factors that most influence the overall degradation of the facades, evaluated through the condition level. Probabilistic models based on Markov chains are developed to predict the evolution of facade deterioration according to exposure to outdoor environmental conditions. The proposed model provides data on the synergy between the degradation agents and the degradation condition of render facades, the average time of permanence in each degradation level, and indications of the effect of degradation on the durability of render that may be applied in the implementation and fine-tuning of maintenance procedures. A better understanding of the durability of render facades allows a more rational management of their maintenance, contributing to a reduction of their life cycle costs. The proposed stochastic model provides information that can be applied in the context of insurance policies, allowing an evaluation of the risk of failure of coatings.     

Development of a tram track degradation prediction model based on the acceleration data

Abstract

Although vibration is considered as one of the important factors in passenger ride comfort, yet it has not been applied for predicting tram track degradation in tram network. Rail track degradation prediction models form an essential part of the rail infrastructure maintenance management systems. Vibration can be measured by acceleration signals. The acceleration signal is derived from the movement of railway vehicles on rail structure. In this study, vehicle acceleration data along with other track structural parameters have been used to predict tram track degradation index which can be considered as a representative of tram track quality. The index used in this study has been developed based on a mixture of tram track geometry deviations of several years. Three types of machine learning models have been employed for creating the prediction models. In this study, Melbourne tram network data have been applied for developing as well as predicting the degradation index. Based on the evaluation results, the proposed random forest regression model made more accurate predictions on track degradation compared to other developed models. The results of this study can help tram track managers to deploy cost-effective maintenance strategies by applying vehicle acceleration data in their decision-making processes.     

Modelling the service life of rendered facades using fuzzy systems

The knowledge of the service life and durability of building components is paramount to sustainable analysis and decision making since it allows a more rational management of the maintenance of building and provides data for life cycle analysis procedures. Nevertheless, predicting the service life of a building or its components is a complex process with which a number of variables are associated. The main difficulties associated with service life prediction are related to the complexity of the degradation phenomena and to the lack of understanding of degradation factors and mechanisms. This paper aims at establishing a model for the service life prediction of rendered facades using a Takagi–Sugeno fuzzy model. The models proposed include the variables that influence the degradation of rendered facades (render age, render type, building height, facade orientation, exposure to damp, and facade protection level). In this study, the degradation condition of 100 case studies located in Portugal is analyzed based only on in situ visual inspections. The proposed models are able to describe appropriately the degradation of rendered facades and to predict the service life of the sample analyzed.     

Protection value and functional service life of heritage timber buildings

ABSTRACT

The development of objective methodologies for the preventive conservation of historic buildings is extremely relevant to mitigate the deterioration of buildings and sites with exceptional cultural value. In this sense, there is a growing need to develop comprehensive, coherent plans to manage, preserve and protect heritage buildings in areas that are extremely susceptible to natural disasters, such as the case of the Pacific coast of South America. Two methodologies are presented in this study to assess the functional service life and protection level of cultural heritage in Chile. This research intends to establish a correlation between the functional performance of heritage buildings and the Chilean code related to the definition of the preservation of historic heritage buildings. This study applies both methodologies to 25 heritage buildings (timber housing) located in the city of Valdivia, Chile. A multiple linear regression analysis is applied in order to rank the influence of the variables used to define the protection level, according to the Chilean standard, in the functionality index of timber heritage constructions. The information obtained in this study is exceptionally relevant for the researchers and stakeholders responsible for the definition and implementation of maintenance programmes in building stocks.     

Housing Recovery Lessons From Chile

Problem, research strategy and findings: The 8.8 magnitude earthquake and subsequent tsunami that struck south-central Chile on February 27, 2010, affected 75% of the country's population and damaged or destroyed 370,000 housing units (about 10% of the housing in six regions). Within six months, the Ministry of Housing and Urban Development published a plan to repair or rebuild 220,000 units of low- and middle-income housing with government assistance within four years. By February 2014, 94% of the housing was complete. The successful rebuilding effort had strong leadership at the national and local levels and used existing programs and institutions. The management staff adapted programs over time to meet the needs of local conditions. When compared with housing recovery programs in other countries, Chile's program stands out, combining national government management with local citizen input. The reconstruction plan also included updated zoning plans, road and infrastructure improvements, heritage recovery, and new master plans for affected cities. Going forward, the earthquake created an opportunity for Chile to use the recovery planning to expand national urban policy and to develop a framework for citizen participation at the local level.

Takeaway for practice: Successful planning in disaster recovery involves strong government leadership and coordination together with the engagement of local government and the participation of citizens.     

Impacts of the shading-type building-integrated photovoltaic claddings on electricity generation and cooling load component through shaded windows

The shading-type building-integrated photovoltaic (BIPV) claddings can act as power generators as well as external shading devices of a building, which reduce the energy consumption of the building. However, there is little information about energy impacts of different tilt angles of the shading-type BIPV claddings. By considering the typical meteorological conditions of Hong Kong, the energy performance of the shading-type BIPV claddings, in terms of the electricity generation and the cooling load reduction, is analyzed in this paper. The optimum tilt angle of PV modules for maximum electricity generation is found to be 20° instead of local latitude. Combining electricity generation and cooling load reduction, it can be concluded that the optimum tilt angles for the first type of the shading-type BIPV claddings vary from 30° to 50°, while the optimum tilt angle for the second type is 0°.     

Timber Supply and Timber Building in a Sussex Parish

Abstract

This paper questions the commonly held view that the quality and number of timber framed houses in a district reflects the local availability of standing timber. A case history is provided from records and standing buildings of the parish of Warminghurst (Sussex). The settlement history and forms of tenure are summarized. It is then shown from written evidence that, while there was much standing timber in the Middle Ages and later, the policy of landlords from the 15th century, if not earlier, was to treat that timber as their private resource and to encourage tenant builders to re-use material from demolished buildings. That evidence is confirmed by a brief examination of houses and farm buildings surviving from the 15th to the early 18th century.     

Application of stress wave propagation technique for condition assessment of timber poles

Abstract

The stress wave propagation technique can be effectively used to assess the condition of timber utility poles. However, reliable detection of damage based on the reflected wave within the time domain is not always possible. Therefore, various signal processing methods such as frequency-domain analysis and time-frequency analysis can be adopted to overcome this problem depending on the application. In this paper, Hilbert–Huang and continuous wavelet transforms are selected as signal processing methods to analyse the reflected wave. The signal is initially subjected to an empirical mode decomposition process prior to the computation of instantaneous frequencies of the decomposed signals using the Hilbert–Huang transformation. The anomalies in the instantaneous frequency plots can be used to identify any damage and its location along the pole. Additionally, the decomposed signals are subjected to a wavelet transformation to further confirm the existence of damage. The combined Hilbert–Huang and continuous wavelet transform technique is applied to the stress wave signal recorded from the in-service poles to assess the accuracy of the proposed method. This method increases the confidence level of defect identification of timber utility poles.     

Suspended timber ground floors: measured heat loss compared with models

ABSTRACT

There are approximately 6.6 million dwellings in the UK built before 1919, predominantly constructed with suspended timber ground floors whose thermal performance has not been extensively investigated. The results are presented from an in-situ heat-flow measuring campaign conducted at 27 locations on a suspended timber ground floor, and the estimated whole-floor U-value compared with modelled results. Findings highlight a significant variability in heat flow, with increased heat loss near the external perimeter. In-situ measured-point U-values ranged from 0.54?±?0.09?Wm^?2 K^?1, when away from the external wall perimeter, to nearly four times as high (2.04?±?0.21?Wm^?2 K^?1) when near the perimeter. The results highlight the fact that observing only a few measurements is likely to bias any attempts to derive a whole-floor U-value, which was estimated to be 1.04?±?0.12?Wm^?2 K^?1 and nearly twice that derived from current models. This raises questions about the validity of using such models in housing stock models to inform retrofit decision-making and space-heating-reduction interventions. If this disparity between models and measurements exists in the wider stock, a reappraisal of the performance of suspended timber ground floors and heat-loss-reduction potential through this element will be required to support the UK’s carbon-emission-reduction targets.     

Effects of the climatic conditions of the southeastern Brazil on degradation the fibers of coir-geotextile: Evaluation of mechanical and structural properties

In tropical countries where rainfall rates are high, and especially in deforested areas in the Atlantic Rainforest and Cerrado in southeastern Brazil, water is the dominant driving force of erosion. The most common method used to restore degraded tropical lands is to plant nursery-raised tree seedlings, but this method is not always practical and a variety of newer reforestation techniques have become available. Biodegradable coir geotextiles combined with native seeds can be used to restore degraded forest areas. The effects of the climatic conditions during a seasonal cycle of rain and drought were evaluated on the structural and mechanical properties of coir geotextile fibers that were treated, or not, with lime. Analyses of the tensile strength of coir fibers showed that after 12 months of exposure untreated fiber had retained 23% and treated fiber 19% of their initial strength. Two principal factors were considered in evaluating the structural properties of the coir fibers after environmental exposure: (i) initial cellulose retention and its stability after lime-treatment; (ii) lignin degradation and/or its loss to the environment. The structural changes seen by thermogravimetry (TGA) and Fourier Transforms in Infrared spectroscopy (FTIR) analyses explained the changes seen in coir mechanical properties. The greater cellulose contents of fiber structures treated with lime explained their greater tensile strength and high Young's modulus measures after the first three months of exposure in local weather conditions. Considering that lime treatment improved coir fiber properties, lime applications are indicated when coir geotextiles are to be used in acidic Brazilian Cerrado soils.     

Ist die Hinterlüftung von Holzfassaden ein Muss?

Nach Durchführung einer großen Schweizer Forschungsinitiative zum Thema “Brandschutz im Holzbau” sind seit 2005 Außenwandbekleidungen aus Holz unter Zuhilfenahme von bestimmten Brandschutzmaßnahmen bis zur Hochhausgrenze (22 m) möglich [1]. Dazu zählen unter anderem auch Außenwandbekleidungen, deren Hinterlüftungsraum geschossweise unterbrochen und oben verschlossen wird. Solche Fassaden weisen brandschutztechnische Vorteile auf, da sie die Brandweiterleitung hinter der Bekleidung reduzieren bzw. verhindern. In diesem Zusammenhang stellte sich die Frage, ob eine Hinterlüftung von Holzfassaden aus bauphysikalischer Sicht überhaupt notwendig ist. Im Rahmen eines Forschungsvorhabens an der Berner Fachhochschule — Architektur, Holz und Bau in Biel/Bienne wurde dieser Frage nachgegangen [2]. Is ventilation of timber façades essential? Following a major Swiss research initiative, “Fire protection in Timber Structures”, exterior timber wall claddings incorporating specific fire protection measures have been permitted up to the high‐rise limit of 22 m since 2005 [1]. This includes exterior wall claddings with a ventilation space that is interrupted and closed off from above at each storey level. Such façades have advantages when it comes to fire protection as they reduce or prevent the spread of fire behind the cladding. This has raised the question of whether the ventilation of timber façades is necessary at all from a building physics perspective. This matter was investigated as part of an Architecture, Timber and Construction research project at Bern University of Applied Sciences [2].     

Electrochemical degradation of perfluorooctanoic acid (PFOA) by Ti/SnO2-Sb, Ti/SnO2-Sb/PbO2 and Ti/SnO2-Sb/MnO2 anodes

Electrochemical decomposition of environmentally persistent perfluorooctanoic acid (PFOA) in aqueous solution was investigated over Ti/SnO₂-Sb, Ti/SnO₂-Sb/PbO₂, and Ti/SnO₂-Sb/MnO₂ anodes. The degradation of PFOA followed pseudo-first-order kinetics. The degradation ratios on Ti/SnO₂-Sb, Ti/SnO₂-Sb/PbO₂, and Ti/SnO₂-Sb/MnO₂ anodes achieved 90.3%, 91.1%, and 31.7%, respectively, after 90 min electrolysis at an initial 100 mg/L PFOA concentration at a constant current density of 10 mA/cm² with a 10 mmol/L NaClO₄ supporting electrolyte solution. The defluorination rates of PFOA on these three anodes were 72.9%, 77.4%, 45.6%, respectively. The main influencing factors on electrochemical decomposition of PFOA over Ti/SnO₂-Sb anode were evaluated, including current density (5-40 mA/cm²), initial pH value (3-11), plate distance (0.5-2.0 cm), and initial concentration (5-500 mg/L). The results indicated that PFOA (100 mL of 100 mg/L) degradation ratio and defluorination ratio achieved 98.8% and 73.9%, respectively, at the optimal conditions after 90 min electrolysis. Under this optimal condition, the degradation rate constant and the degradation half-life were 0.064 min⁻¹ and 10.8 min, respectively. The intermediate products including short-chain perfluorinated carboxylic acids (PFCAs, C₂∼C₆) and perfluorocarbons (C₂∼C₇) were detected by electrospray ionization (ESI) mass spectrum. A possible electrochemical degradation mechanism of PFOA including electron transfer, Kolbe decarboxylation, radical reaction, decomposition, and hydrolysis was proposed. The electrochemical technique could be employed to degrade PFOA from contaminated wastewater as well as to reduce the toxicity of PFOA.     

基于Copula函数的现场暴露混凝土寿命预测方法

针对基础工程中混凝土结构在现场暴露环境下的寿命预测问题,提出了1种基于Copula函数的多退化因素剩余寿命预测方法.先选取质量损失和超声声速作为关键退化因素,针对其不同退化轨迹,对实际采集数据进行退化建模,得到混凝土剩余寿命的边缘分布函数;再通过Copula函数建立各退化因素间的相关关系,将混凝土剩余寿命的边缘分布进行融合,得到其联合分布函数.结果表明:选择质量损失和超声声速这2个退化因素有助于建立混凝土在现场暴露环境下的退化模型,并得到其剩余寿命的边缘分布函数;基于Copula函数预测西宁市现场暴露环境下的混凝土使用寿命约225个月,损伤发展始于第180个月左右.     

Neural networks applied to service life prediction of exterior painted surfaces

Service life prediction is assuming a primary role as it allows a more rational use of scarce resources; its methods are useful for defining preventive maintenance plans, thereby increasing performance and reducing costs. A new mathematical model is presented that uses artificial neural networks to evaluate the service life of painted surfaces. The data on facade degradation were collected from field observations on 160 buildings (220 painted surfaces) in Lisbon, Portugal, examining several degradation agents. In service conditions, the mean estimated service life of exterior painted surfaces is found to be 9.49 years, with a standard deviation of 0.633 years. Detailed factors are identified and incorporated into the model, which account for variations in degradation. Some statistical parameters are used to evaluate the validity and efficiency of the model. The values obtained are consistent with the existing perception relative to the durability of painted coatings. These values can be used to evaluate the economic and environmental performance of painted surfaces throughout their life cycle. The use of this model can optimize inspection and maintenance plans as well as the implementation of inform decisions at the design and construction stages.     

Experimental investigation on radiation heat transfer properties degradation of (black nickel-coated aluminium) solar receiver tube material

In our previous research, we have studied the surface property degradation of the uncoated receiver tubes of solar water heater at elevated temperatures Logesh et al. [2017. “Experimental Investigation on Radiation Heat Transfer Properties Degradation of Aluminium Solar Receiver Tube Material.” International Journal of Ambient Energy 1–6]. In this study, the investigation is extended to property degradation of selective surface, black nickel-coated aluminium material. The selective surface has been investigated for its absorptivity (α) and emissivity (?) changes due to its exposure to sunlight at elevated temperatures. The duration of exposure ranges from 240 to 960?h; the properties are measured at four intervals in the selected range of exposure. The investigation is also carried out to find the temperature dependence nature of the heat transfer properties. The properties are measured at 10 temperature intervals for every period of exposure. The absorptivity (α) is found to be increased for the coated surface than the uncoated, whereas the emissivity (?) gets decreased for the same period of exposure.     

Stochastic Petri net-based modelling of the durability of renderings

In this study, a methodology to model and predict the life-cycle performance of building façades based on Stochastic Petri Nets is proposed. The proposed model evaluates the performance of rendered façades over time, evaluating the uncertainty of the future performance of these coatings. The performance of rendered façades is evaluated based on a discrete qualitative scale composed of five condition levels, established according to the physical and visual degradation of these elements. In this study, the deterioration is modelled considering that the transition times between these condition states can be modelled as a random variable with different distributions. For that purpose, a Stochastic Petri Nets model is used, as a formal framework to describe this problem. The model's validation is based on probabilistic indicators of performance, computed using Monte-Carlo simulation and the probability distribution parameters leading to better fit are defined as those maximizing the likelihood, computed using Genetic Algorithm. In this study, a sample of 99 rendered façades, located in Portugal, is analysed, and the degradation condition of each case study is evaluated through in-situ visual inspections. The model proposed allows evaluating: i) the transition rate between degradation conditions; ii) the probability of belonging to a given degradation condition over time; and iii) the mean time of permanence in each degradation condition. The use of Petri Nets shows to be more accurate than a more traditional approach based on Markov Chains, but also allows developing future research to consider different environmental conditions, maintenance actions or inspections, amongst other aspects of life-cycle analysis of existing assets.