Elastically restrained Bernoulli-Euler beams applied to rotary machinery modelling

Facing the lateral vibration problem of a machine rotor as a beam on elastic supports in bending, the authors deal with the free vibration of elastically restrained Bernoulli-Euler beams carrying a finite number of concentrated elements along their length. Based on Rayleigh's quotient, an iterative strategy is developed to find the approximated torsional stiffness coefficients, which allows the reconciliation between the theoretical model results and the experimental ones, obtained through impact tests. The mentioned algorithm treats the vibration of continuous beams under a determined set of boundary and continuity conditions, including different torsional stiffness coefficients and the effect of attached concentrated masses and rotational inertias, not only in the energetic terms of the Rayleigh's quotient but also on the mode shapes, considering the shape functions defined in branches. Several loading cases are examined and examples are given to illustrate the validity of the model and accuracy of the obtained natural frequencies

The effect of incorporating high reflectance pigments in thermal enhanced exterior finishing systems

In the recent years, the concerns on building thermal performance tend to follow the challenges imposed by more demanding building design. The increase of new building materials and technologies with improved thermal characteristics, such as ETICS, thermal mortars and high reflectance coatings, contribute to meet the thermal requirements, by lowering the façade U-value and/or the surface temperature variation. This paper has the objective of evaluating the effect of incorporating high reflectance pigments in organic coatings applied in thermal systems, such as ETICS and thermal rendering. The effect on the thermal behaviour is also discussed by comparing them with a non-insulated system. The solar absorptance and the surface temperature of different façade systems with distinct coatings were measured "in situ". The solar absorptance was measured with a pyranometer with an adapted methodology based on the ASTM E1918 standard. The surface temperature of the specimens was continuously monitored for an extended period enabling a comparison under different climatic conditions. The results showed that the incorporation of high reflectance pigments allowed a significant decrease of the solar absorptance even in darker colours and that the absence of thermal insulation proved to have a significant effect on the surface temperature

A new durability assessment methodology of thermal mortars applied in multilayer rendering systems

The increase of the thermal resistance of building envelopes is a result from the growing demand of energy efficiency. Several new materials and systems emerged in recent years as an answer to that growing need. Thermal mortars applied in thermal rendering systems are an example of how the research community and the building industry try to tackle that challenge. A gap in the durability assessment of thermal rendering systems can however be observed. The existing standardization for the durability assessment of mortars does not allow a consistent evaluation of thermal mortars, especially in multilayer systems. As such, the main goal of the present work consists in proposing a durability assessment methodology of thermal mortars applied as multilayer systems. Accelerated ageing cycles, directly applicable to thermal mortars, were developed through numerical simulation, taking into account material properties, climatic conditions and consequent degradation mechanisms to which the system is subjected. A theoretical methodology for the determination of heat-cold cycles that can represent specific climatic conditions was developed. The implementation of the developed accelerated ageing cycles and the obtained experimental results contributed to the definition of a new durability assessment methodology. This methodology defines the accelerated ageing cycles that should be performed in each climate zone, representative of the main degradation mechanisms. One of the major advantages is the temperature adaption of the accelerated ageing cycles to the climatic conditions. The new methodology contributes to the evaluation of new solutions, during their development stage, and to their adequacy for specific climatic conditions

NIR reflective finishing coatings with nanoparticle inclusion

About 40% of the energy consumption of European countries are attributed to buildings. For the construction sector development, it is necessary to ensure the enhancement of sustainability in buildings, eventually by designing new energy- efficient buildings. To accomplish such goal it is crucial to reduce the amount of solar radiation absorbed by buildings. Several solutions have already been reports in the literature, being the development of coatings with high reflectance of the solar energy for envelope system one of the promising methods to be effective in reducing the thermal gains in buildings. Coatings that contain near-infrared reflective nanomaterials can be applied onto a surface (such as roofs, pavements or, façades) exposed to solar radiation to reducing its radiation absorption. Our study aimed the development of innovative finishing coatings for envelope systems by increasing their solar reflectance through new material formulations with the inclusion of nanoparticles. We studied the reflectance and colour properties by doping a standard black colorant with different types and sizes of nanoparticles (TiO2 in rutile and anatase phase, Al2O3 and CuO), in an acrylic substrate. In particular, such nanoparticles were used with the concentration in the coating being varied (1% to 20%). The results obtained can help formulate new finishing coatings with increased near-infrared reflectance of buildings façades, using, for instance, more than one type of nanoparticles or core-shell structures

Durability of etics incorporating high reflectance pigments in finishing coatings

The increase of the durability of building materials and components presents great importance since it contributes to a more sustainable environment by increasing its service life. The development of new building materials and technologies with improved thermal characteristics, such as ETICS with high reflectance coatings, contributes to meet the thermal requirements defined by the European regulation. However, the importance of the durability assessment of new solutions cannot be understated as it plays a key role in the prevention of future early degradation. This paper has the objective of assessing the durability of ETICS incorporating high reflectance pigments in organic coatings. The solar reflectance can be increased through optimized material formulations with the inclusion of nanoparticles in coatings. If the near-infrared (NIR) solar absorption is reduced, the referred benefits can be achieved even in darker colours. One of the main concerns is the durability of the entire system, but the stability of the darker colours must also be taken into account. As such, relevant parameters solar absorptance, surface temperature and colour were measured in a long-term in-situ experimental campaign, in ETICS specimens with distinct coatings. The effect of the thermal insulation layer, in the referred parameters, was also evaluated, by measuring the effect of the same coatings in samples with traditional substrates. The solar absorptance was measured with a pyranometer with an adapted methodology based on the ASTM E1918 standard. The surface temperature of the samples was continuously monitored for an extended period enabling a comparison of the benefits under different climatic conditions. The colour was determined by the CIELAB colour space, by measuring the L*A*B parameters. The results showed that the incorporation of high reflectance pigments leads to a decrease in the solar absorptance and surface temperature even in darker colours. The pigments also influenced the lightness of the coating, by increasing the L parameter. The potential benefits of these thermal enhanced systems combine an enhanced thermal performance, durability and a higher diversity of aesthetic features

Solar reflectance of ETICS finishing coatings - a comparison of experimental techniques

The solar reflectance has a significant role in the thermal behaviour and surface temperature of ETICS finishing coats. Incomplete information of solar reflectance of ETICS with nanopigments can sometimes difficult their adequate selection. In this work, the solar reflectance of different ETICS finishing coats was measured using two distinct methodologies, and the importance of the adopted procedure was discussed. The experimental methodologies used were: i) the adapted conventional pyranometer technique (non-ASTM E 1918A), which measures the global solar reflectance; and ii) the use of the spectrophotometry, to measure the spectral reflectance. It was verified that the El 918A methodology is more sensitive to environmental conditions than the spectrophotometry procedure. Also, the calculation of solar reflectance with spectrophotometer can be carried out by the 50 or 100 ordinates. However, the surface characteristics, as the concentration of pigments and roughness, affect more the solar reflectance measured with the spectrophotometer than with the pyranometer. It was verified that the nanopigments could improve solar reflectance and change the spectral reflectance. The results showed that, if the procedure is well applied, both methodologies could be used to evaluate the advantages of incorporating nanopigments in facade finishing coatings and also to assess the durability of these materials

Colour degradation of facade coatings - the effect of nanopigments incorporation

The increasing interest in the use of a wide range of colours in buildings, especially dark colours, may lead to the early degradation of the facades, compromising their aesthetic and thermal performance. On the other hand, the incorporation of nanopigments with high reflectance properties can contribute to reducing the absorption of solar radiation. The nanoparticles contribute to increasing the solar reflectance of coatings, decreasing the surface temperature and improving the coating performance. This work evaluates the natural degradation of the colour of finishing coat with nanopigments in ETICS. The colour parameters were evaluated in different ETICS specimens, considering the colour black and red with and without incorporated nanopigments, under natural ageing. The colour measurement was performed according to ISO 1164-4, using a portable spectrophotometer. The results confirmed that the use of nanopigments improved the colour durability, promoting the maintenance of the colours parameters. The total colour difference was lower than the perceptible by the human eyes, even as the lower variation on chroma and hue parameters of the colours with nanopigments. In summary, the incorporation of nanoparticles in finishing coat of ETICS can contribute to increasing their durability and improve their thermal performance without compromising the aesthetic characteristics

Damage detection and quantification using transmissibility

Structures experience various types of loads along their lifetime, which can be either static or dynamic and may be associated to phenomena of corrosion and chemical attack, among others. As a consequence, different types of structural damage can be produced; the deteriorated structure may have its capacity affected, leading to excessive vibration problems or even possible failure. It is very important to develop methods that are able to simultaneously detect the existence of damage and to quantify its extent. In this paper the authors propose a method to detect and quantify structural damage, using response transmissibilities measured along the structure. Some numerical simulations are presented and a comparison is made with results using frequency response functions. Experimental tests are also undertaken to validate the proposed technique. (C) 2011 Elsevier Ltd. All rights reserved

Durability of a New Thermal Aerogel-Based Rendering System under Distinct Accelerated Aging Conditions

The widespread application of innovative thermal enhanced facade solutions requires an adequate durability evaluation. The present work intends to assess the durability of a new aerogel cement-based rendering system through the adaptation of different accelerated aging cycles, such as heating-freezing, freeze-thawing, and heat-cold. Several mechanical properties and also capillary and liquid water absorptions were tested for uncoated and coated specimens. A decrease in the mechanical strength, especially after freeze-thaw cycles, was observed. However, the water action promoted the late hydration of the cement paste contributing to the densification of the matrix and, consequently, the increase of the adhesive strength. Additionally, a decrease in the dynamic modulus of elasticity and an increase in the Poisson's ratio were observed after aging, which indicates a higher capacity of the render to adapt to substrate movements, contributing to a reduction of cracking

Impact of Incorporating NIR Reflective Pigments in Finishing Coatings of ETICS

Near-infrared (NIR) reflective materials are being developed for mitigating building cooling needs. Their use contributes to broadening the range of colours, responding to the urban aesthetic demand without compromising the building performance. Despite the increase in NIR reflective pigments investigation, there is still a knowledge gap in their applicability, impact, and durability in multilayer finishing coatings of External Thermal Insulation Composite Systems (ETICS). Hence, the main goal of this work consists of evaluating the impact of incorporating NIR reflective pigments (NRP) in the solar reflectance of the surface layer of ETICS, without affecting the colour perception, as well as their influence on the colour durability and surface temperature. As such, colour, solar reflectance, and surface temperature were monitored for 2 years in dark-coloured specimens of ETICS, with and without NRP and a primer layer. It was confirmed that the main contribution of NRP is the increase of solar reflectance and, consequently, the decrease in surface temperature, especially for high exterior temperatures (around 30 degrees C). Moreover, these pigments highly increase the NIR reflectance without affecting the visible colour. In addition, they contribute to maintaining the colour characteristics. The application of primer increased the surface temperature, especially for higher exterior temperatures. However, it contributes to a lower colour difference and solar reflectance variation, which is an important achievement for durability purposes