Dynamic monitorization of structures with optical sensors

Fiber optical sensors, namely Fiber Bragg gratings, are one the most promising technologies in several sensing systems. This sensing technology could be useful and cost effective in most civil engineering infrastructures. FBG sensors take advantage of the optical fiber properties, such us low transmission losses, immunity to electromagnetic interference, light weight and electrical isolation. But also, since the information is codified in the optical domain, they can be used in hostile environments, where electrical currents of electronic devices might pose a hazard. In this work we proposed the application of optical FBG based accelerometers to monitor two structures: a reinforced concrete building and a steel footbridge. The results show that optical monitoring schemes can be used in structural health monitorization of large structures, being a low cost solution. The two implemented acceleration systems, with different interrogation techniques allow to successfully obtaining the eigenfrequencies of structures with an error, when compared with the value obtained with a reference electronic accelerometer inferior to 0.80 %

Health monitoring of civil engineering infrastructures with optical fiber sensors

Structural health monitoring is a fundamental tool to guaranty the civil infrastructure lifetime. In this paper, the monitoring of an adobe structure with optical fiber sensors is reported. Static and dynamic measurements were made during a destructive test on a full-scale wall, with an optical fiber accelerometer and a network of thirteen multiplexed displacement sensors. The measured values shown a decrease of 47.8 % in the first natural frequency value, between the initial situation (structure undamaged) and after the cyclic test (structure damaged). The results show very good agreement (maximum relative error in terms of structural frequency of 2.08 %) between the results obtained using electronic sensing technology and the optical sensing technology

Structural health monitoring of different geometry structures with optical fiber sensors

In this paper, we describe the structural health monitoring of several structures, with different geometry, materials and behaviors, using optical fiber sensors. Those studies aimed to demonstrate the feasibility of such technologies in structural health monitoring, with all the advantages inherent to the optical fiber technology

Sensor óptico para monitorização do comportamento dinâmico de estruturas

Este trabalho centra-se no desenvolvimento de um sistema, baseado em tecnologia óptica, que permite a identificação das frequências naturais de estruturas especiais de engenharia e que vai de encontro às necessidades de uma monitorização eficaz e de baixo custo. O sistema óptico implementado foi validado através de testes de campo numa ponte pedonal, comparando a resposta medida com a obtida com sensores baseados em tecnologia electrónica. Os resultados alcançados confirmam a viabilidade da solução implementada nas medidas dinâmicas pretendidas para estruturas

A composição arquitectónica no Tractado de Architectura Que Leo o Mestre, e Archit.º matheus do Couto o velho No Anno de 1631

O estudo que aqui apresentamos corresponde à análise das indicações relativas à criação da composição arquitectónica na primeira metade do século XVII, segundo as informações contidas no manuscrito de arquitectura, da lição transmitida pelo Arquitecto Régio e Mestre de Obras Mateus do Couto. Perspectivamos com este estudo criar bases de apoio para clarificar a forma de desenhar arquitectura presente na Tradição Construtiva Portuguesa. Os objectivos finais são contribuir para esclarecer a unidade e composição usados no método da criação arquitectónica das residências nobres em Lisboa, criando dados úteis à sua intervenção de salvaguarda e conservação, e, usar este método de desenho arquitectónico na criação de obra nova.info:eu-repo/semantics/publishedVersio

Sistema óptico de baixo custo para monitorização dinâmica de estruturas

Neste trabalho descreve-se a implementação de um sistema baseado em tecnologia óptica, sendo o elemento sensor uma rede de Bragg (FBG). Pretende-se um sistema de baixo custo que permita a monitorização dinâmica de estruturas, nomeadamente para determinação das suas frequências naturais, com elevada capacidade de multiplexagem, sendo esta uma propriedade intrínseca a dispositivos baseados em FBG’s. O sistema implementado apresenta uma sensibilidade de 0.985 V/G

Chirped polymer optical fiber Bragg grating sensors

We report chirped fiber Bragg gratings (CFBGs) photo-inscribed in undoped PMMA polymer optical fibre (POF) for the first time. The chirped polymer optical fiber Bragg gratings (CPOFBGs) were inscribed using an UV KrF excimer laser operating at 248 nm. The rectangular gauss laser beam was expanded to 25 mm in horizontal direction along the fiber core by a cylindrical lens, giving a total of 25 mm grating length. A 25 mm long chirped phase mask chosen for 1550 nm grating inscription was used. The laser frequency was 1 Hz with an energy of 5 mJ per exposure, exposing few pulses for each grating inscription. The reflection amplitude spectrum evolution of a CPOFBG is investigated as a function of the applied strain and temperature. Also, some results regarding to group delay are collected and discussed. These results pave the way to further developments in different fields, where POFs could present some advantages preferably replacing their silica counterparts

Structural reliability assessment based on optical monitoring system: case study

ABSTRACT Optical systems are recognized to be an important tool for structural health monitoring, especially for real time safety assessment, due to simplified system configuration and low cost when compared to regular systems, namely electrical systems. This work aims to present a case study on structural health monitoring focused on reliability assessment and applying data collected by a simplified optical sensing system. This way, an elevated reinforced concrete water reservoir was instrumented with a bi-axial optical accelerometer and monitored since January 2014. Taking into account acceleration data, the natural frequencies and relative displacements were estimated. The reliability analysis was performed based on generalized extreme values distribution (GEV) and the results were employed to build a forecast of the reliability of the water elevated reservoir for the next 100 years. The results showed that the optical system combined with GEV analysis, implemented in this experimental work, can provide adequate data for structural reliability assessment

Community-based population recovery of overexploited Amazonian wildlife

The Amazon Basin experienced a pervasive process of resource overexploitation during the 20th-century, which induced severe population declines of many iconic vertebrate species. In addition to biodiversity loss and the ecological consequences of defaunation, food security of local communities was relentlessly threatened because wild meat had a historically pivotal role in protein acquisition by local dwellers. Here we discuss the urgent need to regulate subsistence hunting by Amazonian semi-subsistence local communities, which are far removed from the market and information economy. Following positive examples from community-based management of aquatic and terrestrial resources, we advocate that hunting practices, based on modern scientific principles firmly grounded in population ecology, represent a strong window of opportunity to recover viable populations of previously overexploited wildlife

High-quality Phase-Shifted Bragg grating sensor inscribed with only one laser pulse in a polymer optical fiber

We present the first phase-shifted polymer optical fiber Bragg grating sensor inscribed with only one KrF laser pulse. The phase shift defect was created directly during the grating inscription process by placing a very narrow blocking aperture, in the center of the UV beam. One laser pulse with a duration of 15 ns and energy 6.3 mJ is adequate to introduce a refractive index change of 0.69×10-4 in the fiber core. The high-quality produced Bragg grating structure rejects 16.3 dB transmitted power, thus providing 97.6% reflectivity, which is well suited for photonic applications. The transmission notch depth is about 10 dB and very sharp notches of 3 dB width ranging from 14 pm is reported. The temperature, strain, and pressure response of the sensor has been characterized showing promising results in applications that require high-precision measurements. The ability to inscribe these high-quality sensors effectively can significantly reduce their production cost in industry