Abstract

Abstract

Most of the maintenance actions in the construction sector are still reactive and sporadic, based on subjective criteria. Usually, maintenance actions are performed when the building already presents unacceptable degradation levels, and the reactive maintenance actions carried out only correct the anomalies observed, not dealing with the causes, thus leading to additional costs and risks for owners. This study establishes a condition-based maintenance model applied to natural stone claddings. This model has a stochastic nature, in order to deal with the complexity of the degradation phenomena. For that purpose, Petri nets are used, providing an efficient tool to model the deterioration process and the maintenance decisions considered for stone claddings. The maintenance model is a full life-cycle model that encompasses: (i) the stochastic assessment of the degradation condition of the stone claddings, and their expected service life; (ii) and the inspections, maintenance and renewal processes. In this study, 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 impact of the different maintenance strategies in the future performance and remaining service life of stone claddings is analysed, also evaluating the economic impact of each maintenance plan.

Abstract

Building inspection systems are a useful tool for surveyors, standardising the collection of information. Thisresearch is framed within the development of a global inspection system based on twelve expert inspection systems for twelve types of building elements used in the envelope of current buildings. Homogenised classification lists replace the use of several records and unify designations used in fieldwork. A homogenised global classification list of repair techniques comprises, in a single component, all the techniques used to repair defects and eliminate their causes for different types of building elements. It includes curative and preventive repairs, as well as planned maintenance works. Well-defined criteria guided the harmonisation process of a large set of repair techniquesin a user-friendly list. For instance, the association of different operations in a single repair technique took into account: similarities between procedures, applicability to one type of building element, solving identical defects and the use of similar repair materials. Considering data from the validation samples of the expert inspection systems, it is observed that techniques "R-A1 Cleaning" in painted façades and "R-A12 Application of a new (adequate) cladding/finishing coat over the existent/replacement" in wall renders are the most commonly prescribed. The provision of a homogenised classification list of repair techniques is expected to improve the quality of information collected on-site and give a comprehensive view of the most relevant repair techniques used in the envelope of current buildings.

Abstract

The New Zealand Building Code is unique in the world in requiring evidence of a minimum durability of 50 years for all structural building elements. This prescriptive durability requirement equally applies to the adhesives used in structural applications such as engineered wood products (EWPs), including glulam, CLT and LVL. Conventional resorcinol-based structural adhesives have a long history of use in New Zealand, providing evidence of their ability to meet stringent durability requirements. Structural adhesives based on polyurethanes (PURs) are used extensively in other parts of the world and are rapidly gaining increasing interest in New Zealand due to their perceived environmental and production advantages. However, without a sufficiently long history of use, and a lack of data around their performance in the preservative treated pine EWPs typically manufactured in New Zealand, it is difficult to provide evidence of long-term durability for PURs in our domestic building industry. In this work, attenuated total reflectance Fourier transform infrared (ATR FTIR) spectroscopy in conjunction with multi-component analysis (chemometrics) was used to understand the changes that accelerated ageing cause in the chemistry of five PUR-based adhesives. The effect of hygrothermal stress was investigated through exposure of samples to accelerated ageing cycles of varying temperatures and humidities for up to 3 years’ duration. Different samples were affected to different extents by each cycle. Spectroscopic data were also used to build predictive models which have the potential to be used in long-term durability assessment. Spectroscopic investigation in conjunction with mechanical testing offers the opportunity to provide a robust, fit-for-purpose test methodology for assessing the long-term durability of PUR-based structural adhesives.

Abstract

Abstract

Abstract

The equivalent frame model takes into account the shear and bending mechanisms that take place in piers and spandrels through plastic hinges. It represents a good compromise between accuracy and computational burden in the analysis of complex masonry walls. For the purposes of dynamic analysis, in addition to the hysteretic behaviour of the plastic hinges, it is also necessary to introduce their degradation of strength and stiffness. This study presents a macroelement model for piers and spandrels in which the bending mechanism is described by two hinges at the ends of the macroelement, and the shear mechanism by a shear link. They are characterized by a hysteretic behaviour with progressive plasticity, described by the Bouc-Wen model, and by degradation of strength and stiffness. Degradation is described through a damage parameter, which governs both strength and stiffness decay, and a flexibility increase parameter, which only governs stiffness reduction. In this way it is possible to independently control both strength and stiffness degradation. The model is applied to simulate experimental tests on panels, highlighting a good agreement with the experimental results.

Abstract

The application of organic coatings is one of the most effective and economic methods to protect concrete structures from deterioration. However, organic coatings are prone to degradation under aggressive environmental actions, so the protective function may loss. While ultraviolet (UV) aging is often blamed for the degradation of organic coatings, water may play a more important role on the interfacial adhesion between the coatings and the substrate. To uncover the effect of water on the degradation performance of coating-substrate system, mortar samples coated with water-borne epoxy resin (WER) were exposed to three assigned environments, i.e., UV radiation, UV/water immersion, and UV/dry-wet cycle, up to 60 days. The surface appearance, chemical structure, wettability, and surface micro-morphology of the aged WER coatings were characterized via image process analysis, attenuated total reflectance flourier transform infrared spectroscopy (ATR–FTIR), static water contact angle, and scanning electronic microscopy (SEM). Results show that the UV/water immersion resulted in severest blistering on the WER-mortar interface, while the UV/wet-dry cycle caused the formation of micro-pinholes on the WER surface. In contrast, the UV radiation did not induce such severe aging. The data implied that water can accelerate the aging of WER-mortar system.

Abstract

Abstract

The current increase in the demand for electric power and the obligation to comply with the regulations associated with reliability and continuity in the supply, have prompted the manufacturers of electrical conductors to focus on designing their products with special care when considering the electrical properties of the materials. The use of XLPE insulated cables in underground transmission lines in 115 kV systems has increased in cities due to urban, environmental and reliability requirements. This is also related to the fact that air networks are exposed to external factors such as lightning, comets, vegetation, animals, etc., which can affect their functioning failures. The fact of using transmission technology with insulated cables gives rise to the need to evaluate the behavior of its components when operating in the long term. To achieve this, it is necessary to implement a procedure that allows analyzing the aging of these elements when operating in load cycles for a certain period of time. Thus, this document presents the development of a prototype that allows conducting the aging test to conductors isolated by XLPE.