Pedro Lima Gaspar

Limit States and Service Life of Cement Renders on Façades

The research presented in this paper is related to the durability of cement renders on facades, based on fieldwork data relative to the condition and extent of degradation of 100 facades of residential buildings in Portugal. Deterioration paths are obtained for staining, cracking, and detachment that show the loss of performance of the facade over time until a critical minimum acceptance level is reached, which is considered an estimated durability limit. These degradation patterns are analyzed individually to confirm whether any of three types of defects can effectively be considered limit states for the durability of cement renders on facades. The combined effect of all the defects that occur is also modeled as a single degradation path, and the expected service life is quantified. The results confirm that detachment constitutes a limit state of cement-rendered facades because it directly affects the physical durability of renders. Staining and cracking alone do not generally tend to signal the end of t...

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.

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Statistical modelling of the service life prediction of painted surfaces

Service life prediction assumes a primary role as it allows a more rational use of construction elements. This constitutes a useful tool in the definition of preventive maintenance plans providing an increase in performance. The main objective of this research is the development of a statistical methodology for the service life prediction of external painted surfaces. This research is based on field data collected via a survey of the state of deterioration of in-service buildings. The degradation is defined by a number of factors that together contribute to the deterioration of painted surfaces thus ending their service life. In this study a mathematical model was defined using a multiple linear regression analysis and this enables the coatings deterioration over time to be expressed as a function of various degradation factors. 220 painted coatings were inspected in 160 buildings of varying construction types. Analytical tools were devised to monitor the performance of paint coatings on walls and estimate their service life. This study contributes to the automation of the maintenance of painted facades, allowing a more rational management of the maintenance of buildings, converted into economic and performance gains.

Fuzzy Systems in the Service-Life Prediction of Exterior Natural Stone Claddings

AbstractBuildings and their elements are designed to be used for a certain period of time (their service life), fulfilling all requirements for which they were designed without excessive maintenance costs. However, buildings begin to deteriorate because the instant they are put into use, they begin to show a progressive loss of performance until they become obsolete, having deteriorated beyond minimal acceptable levels or having failed to meet economic expectations. Nowadays, mostly for economic and environmental reasons, there is a growing concern about the durability and service life of buildings. This paper discusses the service life prediction of natural stone claddings using a Takagi-Sugeno fuzzy model. The models proposed include variables that influence the degradation of the claddings analyzed. To obtain the models proposed, samples of 140 and 203 facades were subjected to meticulous field work to determine their condition. The service life of the samples was also evaluated and the influence of th...

Stochastic Approach to the Factor Method: Durability of Rendered Façades

AbstractThe degradation of building materials occurs as a stochastic phenomenon. Service life prediction methods are usually divided into deterministic, stochastic, and engineering methods. Deterministic models are simpler and easier to use, but are unable to capture the random nature of the degradation phenomena. On the other hand, stochastic models are more complex but very efficient in dealing with the uncertainty associated with a building’s performance. In this study, a stochastic approach to the factor method is proposed to predict the service life of rendered facades. The model proposed is based on a survey of the degradation state of 85 rendered facades located in Portugal. The factors that affect the durability of this type of coating are identified and translated into probability distributions. This analysis leads to coherent values, revealing that facades on buildings built with adequate design measures are more durable; facades exposed to adverse environmental conditions are more prone to degr...

Probabilistic Analysis of the Degradation Evolution of Stone Wall Cladding Directly Adhered to the Substrate

AbstractEnvironmental factors directly affect a building’s performance and durability. They are particularly detrimental in the case of building envelope materials and systems because these tend to exhibit a large exposed area and relatively narrow thickness. Therefore, tools are needed to model degradation and provide an insight into its occurrence and its relationship with the environmental factors that have the worst effect. In this paper, the degradation of stone wall cladding directly adhered to the substrate is estimated based on the evaluation of the characteristics of 140 wall cladding systems inspected in Lisbon, Portugal. Because it is a complex phenomenon, a probabilistic analysis is developed using multinomial logistic regression. The analysis focuses on the environmental factors that most influence the overall degradation of the facades (condition level). Probabilistic patterns are thus obtained for the evolution over time of each condition level according to their exposure level to outdoor e...

Service Life and Durability of Assemblies

This chapter intends to establish the first approach to the service life prediction methods applied to facades claddings, with three main objectives: i) perform an extensive survey regarding the concepts related with the service life and durability of building components, the methodologies and standardization related to this matter; ii) define the information collected during the field-work, to assess the physical and visual characterization and quantify the degradation condition of the claddings analysed; iii) the characterization of the samples collected during the fieldwork.

Statistical Modelling of Service Life Prediction of Exterior Painted Surfaces

The degradation of building materials is a complex phenomenon, which starts as soon as construction is concluded, evolves over time, and contributes to end the service life of buildings. In fact, even for identical sets of initial conditions, degradation mechanisms and performance requirements, there are many possible outcomes with different levels of probability. Because of their great exposure to external actions and their role in the protection of masonry, wall coatings on facades are one the elements most subjected to degradation. Painting plays an important role as external coating finishing, nationally and internationally, and is the most frequently used coating in Portugal. In this study an approach to evaluate the service life of exterior surface of painted walls is proposed, based on the evaluation of the degradation state of 220 facades surveyed in the Lisbon area, in Portugal. The influence of the various characteristics of the painted surfaces and of their surroundings on their durability is also analysed. For that purpose, four methodologies are used: (i) deterministic methods; (ii) factorial methods; (iii) stochastic methods; and (iv) computational models. These mathematical models are established to estimate the degradation level of this type of coating and their service life. The predictive ability of the models is examined and some recommendations are made, concerning the advantages and limitations of the models proposed.

Comparative Analysis of Service Life Prediction Methods

In this chapter, a comparative analysis of the different proposed models is performed. First the predictive ability of each model is evaluated through the comparison between the values obtained by each model and the data collected in field work, corresponding to the real degradation condition of the facades analysed. In a second step of the analysis, the sensitivity and specificity of each model is evaluated based on ROC curves, to analyse the accuracy of each model to correctly classify the case studies that may have reached the end of their service life. Once the predictive accuracy and the classification capabilities of each model are evaluated, a multi-criteria analysis is performed. This multi-criteria analysis encompasses different criteria that should be taken into account by different stakeholders to choose the best model for a specific application. A sensitivity analysis is performed in order to analyse the best model for distinct decision-making profiles. Based on these analyses, some recommendations are made, referring the advantages and limitations of the models analysed and thus allowing a more rational and informed selection of a service life prediction model as far as the purpose of the model and the profile of the planner and the perspective of the user are concerned.