1,720,992 research outputs found
Prediction of Maritime Pine Boards Modulus of Elasticity by Means of Sonic Testing on Green Timber
Full text linkTimber buildings are experiencing a rapid diffusion due to their good performance and their sustainability; however, some steps of structural timber production process, such as drying, are energy-intensive and environmentally impactful, and many wood species are also affected by low yield. Therefore, it would be important to determine the quality of the green material, that is, in wet condition, before undergoing the most impactful and expensive production steps. This paper describes a research aimed at quantifying the variation of the dynamic modulus of elasticity MoEdyn, which is commonly used for structural timber mechanical grading, from wet to dry condition in Sardinian maritime pine boards to be used for the production of laminated timber, and to examine the relationship between wet and dry MoEdyn. The MoEdyn was determined from measurements of the velocity of sonic waves propagating through the boards. The results show that the dry MoEdyn can be estimated starting from boards sonic testing in the wet condition, so providing a basis for implementing Sardinian maritime pine pre-grading in order to obtain the reduction of manufacturing costs, the abatement of environmental impact, and the increase of structural grade yield
Direct and semi-direct ultrasonic testing for quality control of FRC-concrete adhesion
Full text linkExternally bonded Fiber Reinforced Composite (FRC) materials, such as Fiber Reinforced Polymers (FRP) and Fiber Reinforced Cementitious Matrix (FRCM), have been increasingly used over the last decades for retrofitting existing structural elements due to their excellent mechanical and physical properties. However, the effectiveness of the reinforcement depends on the quality of the adhesion between the reinforcement and its substrate. The present paper reports the results of an experimental campaign in which the Ultrasonic Pulse Velocity (UPV) testing has been applied to detect the presence of adhesion defects at the interface FRC-concrete. UPV has been carried out on concrete specimens strengthened with different types of FRC. Some inclusions have been specifically placed at the interface between the reinforcement and the concrete to simulate adhesion defects. UPV has been applied both in the direct and in the semi-direct mode, to simulate different realistic on-site situations, including the possible inaccessibility of some parts of the element to check. Results show that UPV, applied by means of both direct and semi-direct modes, allows to identify the presence of adhesion defects, and evoke the possibility of discriminating between different defects
Concrete Defects Sizing by Means of Ultrasonic Velocity Maps
Full text linkThe paper illustrates the results of an experimental test which intends to check the efficacy of ultrasonic testing (UT) in detecting anomalies inside concrete elements. For this purpose, UT has been carried out on a small concrete wall having different defects deliberately settled inside the wall during casting. A grid of several measurements points has been arranged on the wall surfaces and for each point the ultrasonic signal has been acquired after passing through the thickness of the wall and the propagation velocity V has been extracted and analyzed. A graphic representation of V distribution has been implemented by a map where each pixel identifies one measurement point and is representative of its neighborhood. This map highlights areas with different velocity values, and allows to visually detect areas having particularly low velocity. The matching between the low-velocity areas and the artificial defects has been analyzed, and the level of accuracy of the V map in detecting and sizing the concrete inner defects has been discussed with reference to different spacing of the grid points. Finally, some considerations regarding the choice of the most suitable measurements grid have been addressed
Fragility curves for RC structure under blast load considering the influence of seismic demand
Full text linkThe complex characteristics of explosion load as well as its increasingly high frequency in the civil environment highlight the need to develop models representing the behavior of structures under blast load. This work presents a probabilistic study of the performance of framed reinforced concrete buildings designed according to the current Italian NTC18 and European EC8 technical standards. First, a simplified single degree of freedom model representing the structural system under blast load has been developed. Then, a probabilistic approach based on Monte Carlo simulation analysis highlighted the influence of seismic demand on the behavior of Reinforced Concrete RC buildings subjected to blast load
Reinforcement of maritime pine cross-laminated timber panels by means of natural flax fibers
Full text linkThe present paper shows the first results of an ongoing research aimed at studying the potentiality of the combination of laminated timber and natural fibers to obtain high-performance structural elements. The experimentation conducted has involved a set of Cross Laminated Timber (CLT) panels made of maritime pine grown in Sardinia (Italy) and externally reinforced with natural flax fibers fabrics. A bending test program has been carried out on two CLT layouts, three-layers and five-layers panels, for a total of 34 specimens. Three-layers panels have been tested with single and double strip of flax fibers aiming to evaluate any difference in the rupture mechanism, capacity and stiffness. The proposed technique allows a straightforward application on the intrados of the panel, aimed at increasing its capacity and stiffness. Results show that in case of three-layers panels a significant increment of load-carrying capacity and stiffness has been achieved, whilst for five-layers panels the effectiveness of the reinforcement is negligible. Variations in the failure mechanisms of reinforced panels have been discussed
FEM models for elastic parameters identification of cross laminated marittime pine panels
No full textThis paper explores the potential of Finite Element (FE) models to complement traditional static and dynamic experimental procedures aimed at elastic parameter identification in the specific case of Cross Laminated Timber (CLT). These timber products are characterized by several elastic constants due to the almost orthotropic mechanical behaviour of timber in combination with the lamination arrangement. This paper refers to an ongoing research programme investigating the possibilities of productive exploitation of a specific Sardinian Maritime Pine (Pinus Pinaster) species. With this respect, FE models have been employed in order to investigate the sensitivity of material parameters in CLT panels deformation, to check their performance with respect to widely used analytical models and to anticipate the results of experimental tests. In particular, the role of rolling shear modulus has confirmed to be a crucial property, governing the overall shear deformation response, but on the other hand being not yet easy to measure. The FE model calibration has finally showed that the investigated material presents some suitable properties for CLT; in fact, though characterized by low elastic modulus (MOE) and flexural strength, it provides a quite high value of rolling shear modulus
Application of infrared thermography in civil engineering: Limits and drawbacks
Full text linkInfrared thermography (IRT) is an effective diagnostic methodology for existing buildings monitoring, whose efficiency is however affected by the operator’s technical knowledge. This paper presents experimental research aimed at evaluating the accuracy of IRT temperature measurements with respect to the incorrect setting of five input parameters required to be set by the operator: emissivity, reflected apparent temperature, ambient temperature, relative humidity, and distance. The goal was to highlight how their accurate evaluation and setting affects the thermographic survey and the post-processing stage. To this end, IRT experimental investigations were carried out on materials characterized by different emissivity and surface roughness, such as concrete, granite and steel. The experimentation outcome has pointed out the factors that most affect the temperature measurement error and allowed to quantify the error on the temperature measurements deriving from the incorrect setting of these parameters during the acquisition phase of the thermogram
Policy design for climate change mitigation and adaptation in sheep farming: Insights from a study of the knowledge transfer chain
Full text linkLow innovation adoption rates in agriculture have spurred intense research on farmers’ attitudes and motivations. Little attention has been paid to attitudes of other important actors in the knowledge transfer chain. Evidence indeed suggests that adoption rarely happens at the farm level, but requires the right inputs from science and extension services. Divergent attitudes among actors in the knowledge transfer chain may hence contribute to low adoption rates by transferring insufficient, outdated, irrelevant and/or incorrect information. This study is an investigation on attitudes towards climate change mitigation and adaptation of three classes of actors: sheep farmers, researchers involved in fields related to sheep farming and extension officers from private companies and public agencies. The investigation is based on data collected through self-administered questionnaires submitted to 165 participants to agricultural field days in Sardinia (Italy). The sample consists of sheep farmers (37,5%), researchers (16,4%), extension officers (32,1%) and other agricultural workers or students (14 %). In order to assess differences in attitude and identify the sources of attitudinal divergence, the study adopts Kolmogorov – Smirnov (KS) equality-of-distribution tests and Partial-least square structural equation modelling (PLS-SEM). Comparing and contrasting attitudes towards several topics related to GHG emission mitigation and adaptation to climate change reveal that researchers and extension officers have different attitudes towards innovation for mitigating GHG, that in turn depend on different information and beliefs on the causes and effects of climate change. This context is less than optimal to promote adoption of climate change mitigation or adaptation strategies. Climate change science and policy design need to recognise the complexity of knowledge transmission and the multiplicity of attitudes and beliefs that inform and affect the process. To mitigate the impact of diverging attitudes and beliefs among researchers and extension officers tailored communication strategies should avoid controversial issues and focus on benefits of innovation on farm efficiency. In turn, this would build trust and cooperation among all the actors in the knowledge transfer chain. Only when cooperation is assured, one could be confident that the information delivered to farmers is scientifically sound, relevant, value-neutral and useful in changing farmers' behaviour
Seismic Analysis of Historical Urban Walls: Application to the Volterra Case Study
Full text linkSeveral Italian cities are characterized by the presence of centuries-old historic walls, which have a cultural heritage value and, due to their structural role as a retaining wall, often influence the safety of adjacent buildings and infrastructure. Ancient urban walls are increasingly subject to instability and collapse phenomena, because the greater frequency of extreme meteoric events aggravates the static condition of the walls and of the wall–soil system. Since the seismic risk in the contexts in which the historical urban walls are located is often medium-high, it is advisable to evaluate the influence of soil moisture on the seismic response of the soil–structure system. In this paper, the seismic vulnerability of historical urban walls was examined through considering scenarios of both dry and wet soil, in order to evaluate the seismic response of the structure as a function of soil imbibition. Seismic vulnerability analyses were carried out on the case study of the historical urban masonry walls of Volterra (Italy), which have been affected by two major collapses in the last ten years. Seismic vulnerability was assessed by means of the limit equilibrium method and the finite element method, and through adopting proper soil imbibition models. The results highlight which sections of the walls are at greater seismic risk due to the presence of soil moisture, as well as the influence of soil imbibition on the structural safety and failure mechanism
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