Analytical Studies of Fragmented-Spectrum Multi-Level OFDM-CDMA Technique in Cognitive Radio Networks

In this paper, we present a multi-user resource allocation framework using fragmented-spectrum synchronous OFDM-CDMA modulation over a frequency-selective fading channel. In particular, given pre-existing communications in the spectrum where the system is operating, a channel sensing and estimation method is used to obtain information of subcarrier availability. Given this information, some real-valued multi-level orthogonal codes, which are orthogonal codes with values of $\{\pm1,\pm2,\pm3,\pm4, ... \}$, are provided for emerging new users, i.e., cognitive radio users. Additionally, we have obtained a closed form expression for bit error rate of cognitive radio receivers in terms of detection probability of primary users, CR users' sensing time and CR users' signal to noise ratio. Moreover, simulation results obtained in this paper indicate the precision with which the analytical results have been obtained in modeling the aforementioned system.Comment: 6 pages and 3 figure

Numerical modelling of masonry-infilled reinforced concrete frames : model calibration and parametric study

Generally two methods are proposed for analyzing the infilled frames; Micro modelling approach which finite element method is used to take into account local effects in detail and Macro modelling approach which is a very simplified method that takes into account the global behavior of the structure by replacing the infill with diagonal strut. In the present study a numerical analysis is carried out on a one bay one storey reinforced concrete frame with masonry infill under in-plane loading by using finite element modelling through the DIANA software. The numerical model was calibrated based on experimental results and then a parametric study was carried out, taking into account variation of material properties of infill and its height to length ratio. It is concluded that compressive strength and height to length ratio of the masonry infill has dominant role on the in-plane behavior of these types of masonry infilled frames. Increasing the compressive strength of the masonry enhances the lateral strength of the infilled frames while increasing the height to length ratio of the infill panel results in decrease of their lateral strength and initial stiffness.Fundação para a Ciência e a Tecnologia (FCT

Prior in-plane damage on the out-of-plane response of masonry infills

Although the masonry infills are assumed as non-structural elements, their vulnerability during past earthquakes resulted in huge economical costs and life losses. The out-of-plane collapse of the infills is assumed as a common collapse mechanism. One important parameter on the out-of-plane collapse of the infills, is a presence of prior in-plane damage which in the present paper will be studied in detail. In this scope, the main objective of this study is to analyze the out-of-plane experimental behavior of masonry infilled frames that are characteristic of Portuguese buildings and can be seen in other south European countries. In the experimental program, four half-scale specimens were constructed; one reference specimen and three specimens with different prior inplane damage related to the in-plane drifts of 0.3%, 0.5% and 1%. The out-of-plane loading was applied uniformly to the brick infills by means of an airbag to simulate the effect of earthquakes. The results show that presence of prior in-plane damage affects the out-of-plane response of the specimens and a formula was derived to predict the out-of-plane stiffness and resistance of the infills taking into account the effects of prior in-plane damage

Cellular Underwater Wireless Optical CDMA Network: Potentials and Challenges

Underwater wireless optical communications is an emerging solution to the expanding demand for broadband links in oceans and seas. In this paper, a cellular underwater wireless optical code division multiple-access (UW-OCDMA) network is proposed to provide broadband links for commercial and military applications. The optical orthogonal codes (OOC) are employed as signature codes of underwater mobile users. Fundamental key aspects of the network such as its backhaul architecture, its potential applications and its design challenges are presented. In particular, the proposed network is used as infrastructure of centralized, decentralized and relay-assisted underwater sensor networks for high-speed real-time monitoring. Furthermore, a promising underwater localization and positioning scheme based on this cellular network is presented. Finally, probable design challenges such as cell edge coverage, blockage avoidance, power control and increasing the network capacity are addressed.Comment: 11 pages, 10 figure

Out-of-plane response of masonry infilled RC frames: effect of workmanship and opening

Publicado em "Brick and block masonry: trends, innovations and challenges. ISBN 978-1-138-02999-6Out-of-plane response of typical South European masonry infilled frames was investigated by testing three reduced scale specimens to investigate the effect of workmanship and presence of opening on the out-of-plane behaviour. The tests were performed considering an airbag to apply the uniform out-of-plane loading for each mass of the infill and by imposing pre-defined values of displacements in the out-of-plane direction in the control point taken at mid height and mid length of the masonry infill wall. Quasi-static cyclic testing was performed just in one direction to be able to monitor the propagation of the cracks and performance of the interfaces during out-of-plane loading. It was concluded that the workmanship is an important factor that may change the out-of-plane response of the specimen by changing the initial stiffness and lateral strength of the specimen. Another important contribution of the workmanship is the change of the collapse pattern of the infill by formation of twoway arching mechanism or one way arching mechanism. When the upper boundary condition of the infill in contact with RC frame is filled properly with mortar, two way arching mechanism was observed otherwise one-way horizontal arching mechanism was formed which exhibits lower out-of-plane resistance. The specimen with a central opening exhibits lower deformation capacity with respect to the reference wall but any decrease in its lateral strength was not recorded.FCT (Portuguese Foundation for Science and Technology), within ISISE, project UID/ECI/04029/2013Portuguese Foundation of Science and Technology for the funding of the project RetroInf—Development of innovative solutions for seismic retrofitting of masonry infill walls (PTDC/ECM/122347/2010

Experimental evaluation of a constructive system for earthquake resisting masonry enclosure walls

University of Minho is a partner of the INSYSME research project (Innovative Systems for earthquake resistant masonry enclosures in RC buildings), funded by the European Commission. The main aims of this project are to study new systems for masonry infill walls, which combine simplicity with low cost, and to propose recommendations and calculation procedures for their design to seismic actions, filling an existing gap in current regulations. At University of Minho a new construction system for masonry enclosures was developed, being composed of a new commercial unit and vertical steel reinforcement placed in ceramic brick frogs, connected to top and bottom beams. In this paper, the experimental work developed at the University of Minho for validation of the solution proposed for masonry infills is presented and discussed. The experimental validation process of the solution for the masonry enclosure walls was based on in-plane and out-of-plane static cyclic tests. The tests were carried in four specimens built at reduced scale (1:1.5). In order to assess the in-plane behaviour, two specimens have been tested. The first test was done, in a specimen with masonry infill, until maximum drift. In the second test, only reinforcement concrete frame was tested, to access the contribution of masonry infill. For out-of-plane direction two specimens were tested one without reinforcement, and other with reinforcement. The out-of-plane test was carried using an airbag system. In this case only positive direction was considered. In-plane and out-of-plane tests were performed under displacement control according to a load pattern defined based on the FEMA 461 recommendations.FCT -Fuel Cell Technologies Program(606229

Strategies for seismic strengthening of mansonry infilled reinforced concrete frames

Doctoral Thesis Civil EngineeringA vulnerabilidade sísmica de edifícios de betão armado preenchidos com paredes de alvenaria tem vindo a ser constatada durante sismos recentes no sul da Europa, causando um número elevado de mortos e elevados custos de reabilitação ou reconstrução, e justifica a necessidade de estudos detalhados acerca do comportamento sísmico de pórticos de betão armado preenchidos com alvenaria construídos em países do sul da Europa desde 1960. Apesar de existirem vários trabalhos em paredes de enchimento, não existe muita investigação em paredes de enchimento tradicionais do sul da Europa. Assim, os principais objetivos desta tese consistem em: (1) conseguir uma compreensão do comportamento cíclico no plano e fora do plano de paredes de enchimento tradicionais construídas nas últimas décadas em Portugal; (2) analisar o desempenho de diferentes técnicas de reforço com o objetivo de melhorar o comportamento sísmico das paredes de enchimento; (3) analisar os principais parâmetros que influenciam o comportamento de pórticos de betão armado preenchidos com paredes de enchimento a ações no plano. No sentido de atingir os objetivos propostos, foi definido um plano de trabalhos baseado em análise experimental e numérico. O programa experimental foi composto por três fases, nomeadamente: (1) ensaios estáticos cíclicos no plano; (2) ensaios cíclicos para fora do plano; (3) validação experimental de diferentes técnicas de reforço (argamassa de reboco reforçada e conectores metálicos). Para este efeito foram dimensionados pórticos de betão armados com paredes de enchimento à escala reduzida com base num protótipo seleccionado, considerado representativo da construção tradicional nas últimas décadas. Foram ensaiados cinco pórticos sujeitos a ações no plano, nomeadamente um pórtico simples, um pórtico com parede de enchimento até à rotura, e três pórticos preenchidos sujeitos a diferentes níveis de deformação lateral (drift de 0.3%, 0.5% e 1%) com o objetivo de impor diferentes níveis de dano e avaliar o seu efeito no comportamento das paredes de alvenaria sujeitas a ações fora do plano. Seis pórticos preenchidos foram ensaiados a ações para fora do plano para caracterizar a influência da qualidade da mão-de-obra, a presença de aberturas e o dano no plano induzido previamente. Os ensaios para fora do plano foram realizados em controlo de deslocamento e a força foi aplicada através de um airbag. O desempenho do reforço através de argamassa reforçada e a ligação dos panos das paredes duplas através de ligadores metálicos também foi avaliado experimentalmente. Para o reboco armado foram seleccionadas duas malhas de reforço à base de fibras de vidro, sendo uma comercial e outra desenvolvida no departamento de Engenharia Têxtil da Universidade do Minho. Com base nos resultados experimentais foi possível concluir que a presença das paredes de enchimento altera significativamente a rigidez e a resistência quando se compara o comportamento do pórtico simples e preenchido. A mão-de-obra tem um papel importante no comportamento das paredes a ações no plano e fora do plano. Verifica-se também que as paredes de enchimento com mais dano prévio apresentam uma resistência e rigidez mais baixa. O reboco armado melhora consideravelmente o comportamento no plano mas a sua eficiência para acões para fora do plano é muito moderada. O trabalho numérico incluiu a modelação de pórticos preenchidos para ações no plano através de elementos finitos e com base num programa de cálculo comercial. Após a calibração com base em resultados experimentais disponíveis na literatura, foi efetuada uma análise paramétrica com enfoque na avaliação da influência da distribuição aleatória de aberturas no comportamento no plano. Concluiu-se que as paredes de enchimento com uma distribuição de aberturas aleatória podem ser representadas por bielas equivalentes com uma espessura que tenha em consideração a presença de aberturas. Foi feita ainda a calibração de um modelo numérico para a análise de paredes de enchimento a ações para fora do plano.Seismic vulnerability of masonry infilled frames observed during past earthquakes in south Europe, caused death of thousands of people and left huge repair or reconstruction costs, justifies the need of deep study of the seismic behavior of masonry infilled frames constructed in South European Countries since 1960s. In spite of several works have been carried out on masonry infills, there is no much investigation on south European traditional infills. Therefore, the main goals of this thesis are related to (1) better understanding of the cyclic inplane and out-of-plane behavior of traditional brick infills built in the past decades as enclosures in reinforced concrete (rc) buildings; (2) analysis of different strengthening solutions aiming at enhancing their in-plane and out-of-plane behavior; (3) systematic analysis of the main parameters influencing the in-plane behavior of rc frames with brick infills. To accomplish the defined objectives, extensive experimental and numerical analysis were carried out. The experimental campaign was composed of three phases, namely; (1) static cyclic in-plane testing; (2) out-of plane testing; (3) experimental validation of different strengthening solutions (textile reinforced mortar technique and steel ties). Reduced scale rc frames with brick infills were designed based on a selected prototype representative of construction tradition of rc buildings in the last decades. Five reduced scale specimens were tested under in-plane loading, namely one bare frame, one rc frame with brick infill tested until failure and more three specimens subjected to different lateral drifts (0.3%, 0.5% and 1%) to impose distinct levels of damage and to investigate the effect of this damage in their out-of-plane response. Six specimens were tested in the out-of-plane direction to characterize the influence of workmanship, presence of central opening and of existence of prior in-plane damage on the out-of-plane response. The out-of-plane testing was performed under displacement control method by using an airbag. The performance of the textile reinforced mortar applied on the surfaces of the brick infills and of the connection of the leaves of the traditional double leaf walls were also evaluated experimentally. For the textile reinforced mortar technique two different types of meshes were used, namely a commercial textile mesh and a textile mesh that was developed at the university in collaboration with the textile department. It was concluded that presence of infill inside the bare frame could significantly enhance the in-plane stiffness and resistance of bare frame. The workmanship played an important role in the in-plane and out-ofplane behaviour of rc frames with brick infills. It is also found that specimens with higher inplane damage presented lower out-of-plane stiffness and resistance. It was also concluded that TRM technique could enhance the in-plane behaviour of infilled frames but its efficiency on the out-of-plane was very moderate. Numerical modelling of one-bay and one-storey masonry-infilled reinforced concrete frames was performed using commercial software. After the calibration based on experimental results available in literature, a parametric study was carried out focusing on the evaluation of the influence of random distribution of openings in the in-plane behaviour of the infilled frames. It was also concluded that infill panels with any type of opening can be replaced by an equivalent diagonal strut, whose width can be calculated according to the proposed formula, taking into account different types of openings and relative positioning within the masonry infill. Additionally, the calibration of a numerical model for describing the out-of-plane behaviour was also carried out

Out-of-plane strengthening of masonry infills using textile reinforced mortar (TRM) technique

Published online: 29 May 2021The out-of-plane collapse of masonry infills during seismic actions resulted in human life losses and huge repair or reconstruction costs. These problems will result in disturbance of the operational functions of the buildings. The main scope of this research is to analyze the efficiency of different strengthening techniques based on textile reinforced mortar (TRM) technique and using steel connectors in the out-of-plane direction. To accomplish the objectives, four half-scale specimens were tested under uniform out-of-plane loads applied by an airbag to each mass of the infill cyclically. The performance of the textile reinforced mortar technique by using two different meshes was also evaluated experimentally. Besides the protection of the infill from collapsing and protection of human lives, using TRM technique enhances the out-of-plane response of the specimen but its connection to the infill has to be deeply investigated.Fundação para a Ciência e Tecnologia (FCT

Performance of textile reinforced mortar as strengthening solution of masonry infill walls to seismic action

A elevada vulnerabilidade sísmica das paredes de enchimento em alvenaria tem conduzido à necessidade de reforço deste tipo de paredes, utilizando técnicas convencionais ou usando materiais inovadores. Os Fiber reinforced polymers (FRP’s) são utilizados principalmente como materiais inovadores para o reforço de estruturas. Apesar das vantagens associadas ao uso deste tipo de materiais, esta técnica de reforço apresenta algumas desvantagens, como problemas de aderência, mau comportamento à humidade e ao fogo. Uma solução possível para os problemas associados a estes materiais, pode passar pela substituição de agentes ligantes orgânicos para os inorgânicos, tais com argamassas à base de cimento. As interações entre as fibras e a matriz e também as condições de aderência em compósitos cimentícios pode ser melhorado através da utilização de malhas de reforço embebidas na argamassa de reboco, técnica habitualmente designada em língua inglesa por textile reinforced mortar (TRM). Esta técnica é relativamente nova (utilizada desde dos anos 80), tendo sido estudada por vários investigadores em diferentes aplicações. Neste artigo, investiga-se a utilização desta técnica no reforço de paredes de enchimento de alvenaria para ações no plano que simulam a ação sísmica. Foram ensaiados no plano, três provetes à escala reduzida, representativos da construção dos anos 70 em Portugal, um provete de referência, um provete reforçado com uma malha comercial e um provete reforçado com uma malha de reforço desenvolvida para o efeito. Neste caso as malhas de reforço foram desenvolvidas na Universidade do Minho no departamento de engenharia têxtil. A eficácia da técnica desenvolvida foi comparada com soluções comerciais.The high seismic vulnerability of masonry infilled frames have lead to their in-plane and out-of-plane strengthening by means of conventional techniques or by using innovative materials. Fiber reinforced polymers (FRP’s) are mostly used as innovative materials for retrofitting of structures. In spite of many advantages associated with use of FRPs, this retrofitting technique is not problem-free One possible solution to the problems of FRPs could be the replacement of organic binders with inorganic ones such as cement based mortars. Fiber-matrix interactions and also the bond conditions in cementitious composites could be improved if the fibers replaced with textile sheets. This lead to the formation of textile reinforced mortar (TRM) technique. This technique is relatively a new technique (it was started to use in early 1980s) and was studied by few researchers. In this paper, in-plane retrofitting of the infilled frames was investigated by using textile reinforced mortar (TRM) technique. Three half scale specimens which are representative of construction of 1970s in South European countries, were tested in the in-plane direction, a reference specimen, specimen retrofitted by commercial TRM technique and specimen retrofitted with developed TRM technique. In the developed TRM technique the textile meshes were developed and produced in the Textile Department. The effectiveness of the developed technique was compared with commercial solutions