223 research outputs found
Strengthening of High Strength Reinforced Concrete Slabs with CFRP Laminates
No full textA Master of Science thesis in Civil Engineering by Hasan Saleh Mahmoud entitled, "Strengthening of High Strength Reinforced Concrete Slabs with CFRP Laminates," submitted in May 2016. Thesis advisor is Dr. Rami Hawileh and thesis co-advisor is Dr. Jamal El-Din Abdalla. Soft and hard copy available.During the last few decades, engineers and researchers used high-strength concrete to cast reinforced concrete (RC) structures. Accordingly, the dead weight of buildings and structures were reduced significantly, which allowed engineers to construct higher and larger buildings. Reinforced concrete slabs are the largest structural members in buildings. This research aims to reduce the thickness of RC slabs using high-strength concrete strengthened with carbon reinforced polymers (CFRP) laminates in flexural. In this study the behavior of 100 mm thick RC slabs with different concrete compressive strengths of 40, 70, and 100 MPa was inspected. A total of 54 RC slab specimens were cast and tested under two-point loading until failure. The specimens were divided into three groups having different flexural steel reinforcement ratios of 0.45, 1.00, and 1.79%, respectively. Each group of specimens was strengthened with one and two layers of CFRP sheets, which were externally attached to the soffit of the RC slabs, to enhance their flexural capacity. The test results indicated an increase in the load-carrying capacity of the strengthened slabs in the range between 12 to 378 %. It was also observed that the highest contribution was for those specimens with low reinforcement ratio, in which their control specimens failed by tensile membrane action. The mid-span deflection response curves and load-carrying capacity of the slabs were also predicted with a good level of accuracy using the design guidelines of ACI 440-2R-08. In conclusion, strengthening of high-strength thin RC slabs with CFRP laminates is a valid choice to enhance their flexural behavior, with a minimal increase in their dead load, due to the lightweight of the CFRP laminates.College of EngineeringDepartment of Civil EngineeringMaster of Science in Civil Engineering (MSCE
Recommended from our members
Performance of suction caisson anchors in normally consolidated clay
No full texttextAs the demand on energy rapidly increases, oil companies extend their search for
oil and gas into deeper waters in which floating structures are most economical. These
structures are tied at the seafloor with anchors that can sustain loads from waves, storms,
and currents. Suction caissons are anchors that utilize the large water pressure in
deepwater during anchor installation, making it an efficient and economic alternative to
driven piles. In places all over the world, suction caissons are widely used as foundation
anchors in normally consolidated and lightly overconsolidated clays for a variety of
deepwater structures. Suction caissons in offshore applications are subjected to a wide
range of loading conditions. Loads are vertical in tension leg platforms, inclined in taut
mooring systems, and mostly horizontal in catenary systems. However, the load capacity
of suction caissons is not well defined. Several analytical and numerical models have
been published to estimate the capacity of suction caisson, but very little experimental
data is available to support such models.
Laboratory tests were conducted in an experimental facility specially built to
study the behavior of suction caissons under axial, horizontal, and inclined loading
conditions. The experiments were performed using two 4-inch diameter prototype
caissons inserted to a depth of 32 inches in normally consolidated kaolinite. The tested
prototypes are representative of caisson geometries commonly used in mooring systems
for deep offshore locations having soft seafloor sediments. The first prototype caisson
had a padeye bar along its lower half to allow for horizontal and inclined loading below
mudline. The second prototype caisson was built from two thin tubes forming a doublewalled
caisson capable of providing separate measurements of the components of axial
capacity. Instrumentation was used to measure loads, displacements, tilt, and pore water
pressure for loads ranging from horizontal to vertical. In most tests, the caissons were
inserted into the test bed soil half way using deadweight followed by suction insertion to
full penetration. In some axial loading tests, the caisson was inserted by deadweight to
full penetration for comparison. The caisson was loaded rapidly after allowing for
sufficient setup time. Tests were also conducted with partial setup times to examine the
effect of setup on the axial capacity. The caisson top cap was sealed in all horizontal and
inclined tests, while axial loading tests were conducted with sealed and vented top caps.
Caisson response during insertion, setup, and loading is presented. Measured
capacities are compared with analytical and numerical predictions. The axial capacity of
the caisson was the same whether the caisson was installed using deadweight or suction.
In case of axial loading with a sealed top cap, the limit equilibrium parameters
αexternal and Nc were calculated to be 0.8 and 15, respectively. The external side friction
measured from tests with a vented top cap was higher than from tests with a sealed top
cap. In case of axial loading with a vented top cap, the limit equilibrium parameters
αexternal and αinternal were 0.85 and 0.5, respectively. The external side friction during
pullout of the caisson was observed to increase with setup time until the external excess
pore pressures were practically dissipated, while the end bearing resistance was not
affected by the setup time. Results from horizontal loading tests indicate that maximum
capacity is achieved when the caisson is loaded at a depth between two-thirds and threequarter
of the embedment depth. The failure mechanism and the generated excess pore
pressures depend on the position of the load application. Displacements measured in
inclined loading tests were predominantly horizontal for loading angles less than 20°
from horizontal and were predominantly vertical for loading angles above 30°. Good
comparison was found between measured capacities and predictions from a plasticity
model.Civil, Architectural, and Environmental Engineerin
BNP versus NTproBNP pour le diagnostic de l'insuffisance cardiaque chez le sujet âgé
No full textPrérequis: La valeur diagnostique du BNP est bien établie pour le diagnostic d'une dyspnée aux urgences dans une population jeune/Nous savons que les valeurs de BNP et de NTproBNP doivent être interprétées en fonction de plusieurs paramètres notamment l'âge , le sexe et la fonction rénale. Cependant peu d'études ont été réalisées chez le sujet âgé et la valeur diagnostique du BNP et du NTproBNP n'a pas été évaluée dans cette population où la prévalence de l'insuffisance rénale est élevée. Matériels et méthodes: Nous avons inclus 103 patients consécutifs de plus de 75 ans admis aux urgences pour dyspnée aiguë. Les taux plasmatiques de BNP (Biosite R) et de NTproBNP (Roche diagnostic R) ont été mesurés à l'admission en plus du bilan biologique standard et les paramètres de l'examen clinique initial ont été notés. Un premier diagnostic étiologique a été établi aux urgences puis le diagnostic de consensus de la dyspnée a ensuite été établi par deux cardiologues indépendants qui avaient accès à tous les éléments cliniques et para cliniques excepté le dosage des peptides natriurétiques. Résultats : 61 femmes et 42 hommes ont été inclus avec une moyenne d'âge de 84,9+- 6,2 ans. Le diagnostic final d'insuffisance cardiaque a été retenu chez 47 patients (46%), l'embolie pulmonaire était retrouvée chez 6 patients (6%), une exacerbation aiguë d'une insuffisance respiratoire chronique dans 49 cas (48%). Chez 8% des sujets, la dyspnée a été considérée d'origine mixte pulmonaire et cardiaque. 21 patients ont été orientés en Pneumologie, 30 en Cardiologie, 19 en médecine interne. 10 patients n'ont pas été hospitalisés incluant 4 patients dont le taux de BNP était très supérieur au seuil diagnostique retenu de 300 pg/ml. La fonction rénale était fréquemment altérée avec une créatininémie moyenne à 105+-40umol/l (50-287). L'aire sous la courbe ROC pour le BNP et pour le NTproBNP en tant que marqueurs de l'insuffisance cardiaque sont identiques avec respectivement 0,79 (IC: 0,70-0,88) et 0,80 (IC: 0,71-0,89). Un taux plasmatique de BNP de 300 pg/ml a une sensibilité et une spécificité similaire pour le diagnostic d'insuffisance cardiaque qu'un taux plasmatique de 1500 pg/ml de NTproBNP. Un seuil de BNP de 200 pg/ml a une très bonne VPN (84%) pour l'exclusion de l'insuffisance cardiaque aux urgences. Conclusions : Le BNP et le NTproBNP sont utiles pour le diagnostic de l'insuffisance cardiaque chez le sujet âgé et les deux peptides semblent avoir une valeur diagnostique similaire malgré une altération de la fonction rénale fréquemment retrouvée dans cette population. La valeur seuil diagnostique de 300 pg/ml pour le BNP et 1500 pg/ml pour le NTproBNP peuvent être retenues.PARIS7-Villemin (751102101) / SudocPARIS-BIUM (751062103) / SudocSudocFranceF
Theoretical and experimental study of absorption and absorption/diffusion refrigerating machines using ammonia as a refrigerant: simulation under steady-state and dynamic regimes and experimental characterization of a pilot
No full textASPEN-Plus se utilizó para llevar a cabo investigaciones en régimen estacionario sobre una máquina comercial de refrigeración de absorción de 3 toneladas (10 kW de capacidad de refrigeración) accionada con gas natural y un refrigerador de difusión-absorción (DAR) de pequeña potencia (7.5 W de capacidad de refrigeración).Antes de iniciar las simulaciones, se selecciona entre los nueve modelos implementados en la librería de ASPEN-Plus, el modelo adecuado para estimar las propiedades termodinámicas del fluido de trabajo amoníaco/agua en amplios rangos de temperatura (273,16 ≤ T ≤ 613,15 K) y de presión (0 < P ≤ 210 bar). Se ha demostrado que la ecuación de estado de Peng-Robinson-Boston-Mathias (PR-BM) es la más adecuada para el par de trabajo amoníaco/agua en los intervalos de temperatura y presión típicos en las máquinas de refrigeración de absorción. Los modelos de simulación desarrollados en ASPEN-Plus para las máquinas de refrigeración de absorción, reproducen y predicen bastante bien los resultados experimentales.
Los primeros ensayos experimentales del refrigerador comercial de difusión-absorción (DAR) han mostrado que se requiere un suministro de calor al generador superior a 35W para garantizar el funcionamiento de la máquina y su estabilidad. Además, todas las características esenciales del refrigerador han sido determinadas experimentalmente, especialmente los coeficientes globales de transferencia de calor de la cámara refrigerada y el evaporador, las cuales son(UA)_cab=0.554 WK^(-1) and (UA)_int=0.3 WK^(-1), respectivamente. El mejor rendimiento del refrigerador ha sido obtenido experimentalmente con una fuente de alimentación eléctrica de 46W y una temperatura del generador de 167°C. Se ha encontrado que el COP de la máquina es de 0.159. Las predicciones de los modelos ASPEN-Plus del DAR han mostrado una buena concordancia con los datos experimentales.
Por último, un modelo dinámico de caja negra ha sido desarrollado para el refrigerador de difusión-absorción (DAR) en el entorno de Matlab Simulink®. Se ha encontrado que la función de transferencia de primer orden con retardo describe correctamente la relación entre la potencia de accionamiento en el generador y la capacidad de refrigeración.ASPEN-Plus was used to carry out steady-state investigations on a commercial 3-ton gas-fired absorption chiller (10 kW cooling capacity) and a small capacity (7.5W cooling capacity) diffusion-absorption refrigerator (DAR). Before starting the simulations, the adequate thermodynamic properties model for the ammonia/water fluid mixture over wider ranges of temperature (273.16 ≤ T ≤ 613.15 K) and pressure (0 < P ≤ 210 bar) was selected among nine candidates from the ASPEN-Plus model library. It was found that the Peng-Robinson-Boston-Mathias equation of state (PR-BM) is the most suitable for the ammonia/water working pair in the temperature and pressure ranges encountered in absorption refrigerating machines. The ASPEN-Plus simulation models developed for the absorption chiller were able to reproduce and predict quite well the experimental findings.
First experimental tests on the commercial diffusion-absorption refrigerator showed that a heat supply of greater than 35 W in the generator is required to ensure the functioning of the machine and its stability. Further, all the essential features of the refrigerator were determined experimentally, especially the overall heat transfer coefficients of the refrigerated room cabinet and the evaporator, which were (UA)_cab=0.554 WK^(-1) and (UA)_int=0.3 WK^(-1), respectively. The best performance of the refrigerator was reached experimentally with an electric power supply of 46 W and a generator temperature of 167°C. The machine COP was found to be 0.159. The predictions of the ASPEN-Plus models of the DAR showed good agreement with the experimental data.
Finally, a dynamic black-box model was developed for the diffusion-absorption refrigerator (DAR) using Matlab Simulink® environment. It was found that a first order transfer function with delay describes correctly the relationship between the power input to the generator and the cooling capacity. The unsteady-state behavior of the refrigerator predicted by the black-box developed agreed well with the experimental data
Active fault-tolerant control for switched systems with time delay
No full textLink to a related website: http://vuir.vu.edu.au/7209/1/ACSP-09-0185.pdf, Open Access via UnpaywallThis paper focuses on the problem of active fault-tolerant control for switched systems with time delay. By utilizing the fault diagnosis observer, an adaptive fault estimate algorithm is proposed, which can estimate the fault signal fast and exactly. Meanwhile, a delay-dependent criterion is obtained with the purpose of reducing the conservatism of the adaptive observer design. Based on the fault estimation information, an observer-based fault-tolerant controller is designed to guarantee the stability of the closed-loop system. In terms of linear matrix inequality, sufficient conditions are derived for the existence of the adaptive observer and fault-tolerant controller. Finally, a numerical example is included to illustrate the efficiency of the proposed approach.Dongsheng Du, Bin Jiang, and Peng Sh
Predicting Global Solar Radiation Using Recurrent Neural Networks and Climatological Parameters
No full textSeveral meteorological parameters were used for the
prediction of monthly average daily global solar radiation on
horizontal using recurrent neural networks (RNNs). Climatological
data and measures, mainly air temperature, humidity, sunshine
duration, and wind speed between 1995 and 2007 were used to design
and validate a feed forward and recurrent neural network based
prediction systems. In this paper we present our reference system
based on a feed-forward multilayer perceptron (MLP) as well as the
proposed approach based on an RNN model. The obtained results
were promising and comparable to those obtained by other existing
empirical and neural models. The experimental results showed the
advantage of RNNs over simple MLPs when we deal with time series
solar radiation predictions based on daily climatological data
Observer-based H∞ control for systems with repeated scalar nonlinearities and multiple packet losses
No full textThis paper is concerned with the H∞ control problem for a class of systems with repeated scalar nonlinearities and multiple missing measurements. The nonlinear system is described by a discrete-time state equation involving a repeated scalar nonlinearity, which typically appears in recurrent neural networks. The measurement missing phenomenon is assumed to occur, simultaneously, in the communication channels from the sensor to the controller and from the controller to the actuator, where the missing probability for each sensor/actuator is governed by an individual random variable satisfying a certain probabilistic distribution in the interval [0 1]. Attention is focused on the analysis and design of an observer-based feedback controller such that the closed-loop control system is stochastically stable and preserves a guaranteed H∞ performance. Sufficient conditions are obtained for the existence of admissible controllers. It is shown that the controller design problem under consideration is solvable if certain linear matrix inequalities (LMIs) are feasible. Three examples are provided to illustrate the effectiveness of the developed theoretical result
Distributing increased Nile water yield
No full textPresented at River basin management to meet competing needs: proceedings from the USCID conference on shared rivers held on October 21-31, 1998 in Park City, Utah.The River Nile is one of the longest rivers in the world. It is shared by ten countries, all in varying states of development. Numerous studies indicate Nile water resources are not fully utilized. In fact, the Nile Basin's riparian countries utilize less than 50% of the river's total water resources. Cooperation amongst these countries has been recently encouraged to decrease river water losses and increase the water yield. In this study, expected water yield increase (losses saved) is divided amongst the riparian countries based upon each country's ''water index". These indices are developed using several parameters that characterize/individualize each country, including its present available water resources and average water per capita as well as its population, average income, future water demand and the dependence of the country's income on agriculture and other resources. It was found that the most critical and difficult aspects of developing such indices is interlinking economic, social, institutional and environmental factors. All considered, the water index has a substantial and potentially equitable effect when estimating each country's share of the increased water yield
- …
