Bond between reinforcement and the adjoining concrete has been extensively studied, and it is confirmed that the use of deformed bars is essential for composite behavior of reinforced concrete (RC) structures. But since bond between the longitudinal bars and concrete results in concentration of damage at a specific localized interval of longitudinal bars where the local buckling occurs, Takiguchi et al. (1976) suggested mitigating this concentration of damage through unbonding of the longitudinal bars from concrete at plastic hinge zone. Kawashima et al. (2001) conducted an experimental study on RC columns reinforced with different lengths of unbonded bars at the plastic hinge zone. It was noticed that the failure of concrete was much less in the unbonded column than standard column, and strain on unbonded bar was less than that on the reinforcement of standard column. Recently, to improve the seismic performance of RC members, it is highlighted in the study of Pandey and Mutsuyoshi (2005) that reducing bond strength between the longitudinal bars and concrete has a favored effect on the failure mode, shear capacity and ductility of RC bridge piers: failure mode at ultimate state is changed from shear to flexural and shear strength and ductility are increased. In the performance-based design approach, the design is primarily focused on meeting a performance objective, which is in line with a desired level of service (Floren et al., 2001, Priestley et al., 2007). For instance, new seismic design philosophies for bridges recommend that important bridges subject to massive earthquakes should be able to sustain the expected maximum lateral force in the inelastic stage with limited damages. To achieve this aim, structure should realize the existence of post-yield stiffness, damage level should be limited, and its permanent deformations (residual deformations) should be smaller than a specified limit; and all these indices are essentially dependent on the composite behavior of RC structures. On the other hand, the studies of Kawashima et al. (2001) & Pandey and Mutsuyoshi (2005) revealed the importance of reducing concrete-to-steel bond to mitigate the concentrated damage in the plastic hinge zone. In the last two decades, civil engineers and designers have attempted to develop and adopt new forms of materials that would assist in the building of stronger, larger, more longer

ABSTRACT Flow field design in PEM fuel cells has an important influence on both the power density and efficiency of fuel cell systems. In order to effectively utilize the active area, flow distribution and current density should be as homogenous as possible. In addition, pressure losses should be minimized. The main objective of this work is to provide a comprehensive study of the flow field characteristics for different parallel flow channel configurations. The investigated channel configurations are parallel with various cross-sectional configurations. For each channel configuration pressure drop, species mass fraction, velocity, and current distributions are numerically predicted. In addition, performance curves are presented and discussed. The predicted performance parameters are compared with the corresponding available experimental data. Based on the computed results the optimum channel design is selected. Detailed results are presented and discussed. The present work would help PEM fuel cell manufacturers, companies and researchers to choose the optimum configuration for their applications and products to achieve the best possible performance.

abstract The performance of Proton exchange membrane fuel cell (PEMFC) has been experimentally investigated. An experimental set-up was designed to study the effects of operating parameters such as cell temperature, gas humidification, and cell operating pressure on the performance of fuel cell. The results indicated that the output power increase with the increase of humidification ratio. Furthermore, an increase of cell pressure results in a significant increase of cell power. The results indicated that increasing of the temperature leads to a decrease of cell power. The results are explained and discussed in more details for different operational parameters.

This paper investigates carbon dioxide enrichment in commercial greenhouses to improve CO2 capture and utilization. The paper develops and numerically solves a mathematical model that simulates the CO2 capturing process through the coupled-non steady- energy and mass species (CO2, H2O) balance equations in the greenhouse components. The model accurately treats the solar radiation transport inside greenhouse. The realistic photosynthesis sub model selected in the present work is a mechanistic one applicable to the commonly planted C3 species. The present model allows strategies for CO2 enrichment and for cooling air inside sealed and ventilated greenhouses. These strategies keep both CO2 concentration and air temperature inside the greenhouse at the required prescribed value within small specified deviation. The validity and accuracy of the present mathematical model were verified through the agreement of its numerical results with the available experimental data in the literature. Numerical predictions of the present model was obtained for a case study to investigate the effects of environmental conditions, CO2 concentration enrichment level, and the cooling method on the cumulative amount of captured CO2 in the greenhouse that describe its performance.