Abstract

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

For rehabilitation of existing concrete structures, strength and durability related properties of the reinforced element are of high importance. Assessment of these properties of existing structures can be performed by (i) destructive testing of drilled cores and testing the extracted samples in lab environment and (ii) indirect methods by using non- or semi-destructive techniques on site. The use of core-drilling is a time-consuming and labour-intensive method that weakens the existing concrete structure, leaving a lasting impression on it. As an alternative, many different non and semi-destructive techniques are available for the in-situ determination of compressive strength and durability related properties. An experimental program is conducted on concrete slabs of different strength classes intended for various exposure classes (according to EN206), based on a limestone aggregate matrix, which is typically used for Belgian applications. The plates have an age of approximately 5 years, which were also characterized at younger stage (in 2014). Besides destructive core drilling and testing (compressive strength tests, chloride migration testing, and determination of carbonation rate), several non-destructive techniques were selected for this study: the rebound hammer, the ultrasonic pulse velocity tester, the Wenner probe for concrete resistivity and the air permeability tester. Best fit correlations between the output of these different techniques were established. The effect of age (e.g. carbonation) on the established predictive models is being evaluated.

Abstract

Abstract

This contribution is a study of the durability and transport properties of sprayed concrete used in an actual construction site. It considers whether concrete spraying can generate different porosities as the thickness of the sprayed layer increases. The work consisted of a study of the properties of the interior and exterior concrete layers with a particular focus on chloride penetration. A few of the methodologies and techniques used are compressive strength at 28 days, depth of penetration of water under pressure UNE EN 12390-8, boiled absorption and volume of permeable voids ASTM C642, and accelerate chloride penetration NT BUILD 443. Calculated transport property values included absorption (A) and volume of permeable voids (VPV), porosity interconnection, and chloride diffusion coefficient (De). The conclusion obtained is that there are no significant differences between the physical microstructural properties of the interior and exterior sprayed concrete layers, they present a similar porosity, and behave in the same way under a chloride attack when test tubes are completely saturated.

Abstract

Currently, there is still no information regarding the performance of public buildings after their construction and the relationship with the needs for carrying out maintenance activities. This paper presents some of the main anomalies detected in six schools, built between 1997 and 2003 in Lisbon. The analysis of the degradation condition of these schools was based on data obtained through detailed visual inspections, carried out in three distinct periods of their operation phase, 2007, 2013 and 2018. The highest level of severity mainly concerns defects on buildings structure and buildings envelope and results from bad decisions made during design and/or construction. Therefore, there are serious problems related to the premature deterioration of these educational buildings, requiring expensive, complex and unplanned major repairs to achieve their specified design service life. This work highlights the need for greater involvement of school building management entities, in the early stages of the building process, including design, tendering, construction and handover.

Abstract

Due to the inevitable degradation of material properties in structures in daily use, such as stiffness degradation due to cracking in concrete elements, their durability will definitely be influenced, and their serviceability and safety could be in danger. Thus, understanding and identifying the change in the structural parameters provides new approaches to evaluate their durability. Structural system identification by dynamic observability method, which is using subsets of masses, natural frequencies and modal shapes, is a powerful tool to detect the change of structural parameters. Taking into account the presence of noise in the measurement data in real world structures, this method establishes the relative dynamic equation with the error separation items. The equation is solved by error minimization of an objective function combining the measured frequencies and mode shapes through the parameter MAC (Modal Assurance Criterion). Additionally, the algorithms and the steps are introduced based on the dynamic eigenvalue equation, which can fully demonstrate the performance of observability techniques. The present paper provides an example on how to successfully identify structural parameters. Its suitability for practical applications is demonstrated in a large frame structure. The result is a much more accurate identification of the parameters involved in the durability of the structure even in the case of noise-corrupted measurement signals.

Abstract

Abstract

Abstract

The service life of buildings and components is extremely difficult to model and predict, mainly due to the uncertainty and variability associated with the degradation phenomena. These uncertainties are usually related with the intrinsic randomness of natural phenomena, such as the environmental degradation agents. In order to deal with these uncertainties, in this study, a stochastic approach is used, to model the service life of timber claddings. For this purpose, a logistic regression analysis is used to evaluate the probability of timber claddings to reach the end of their service life over time. Moreover, the impact of the environmental exposure conditions (e.g. facades orientation, distance from the ocean, exposure to damp and exposure to wind/rain action), which influence the degradation and service life of timber claddings, is also evaluated. The proposed models are applied to 150 timber claddings, located in Valdivia (South Chile), which have been analysed during an extensive fieldwork survey. The results obtained in this study aid the definition of maintenance plans, in a technically informed manner, in order to promote the conservation of these claddings, which are an important symbol of the local identity of this region, depicting a complexity of cultural values, inherited by Spanish and German colonisations.