Flexural strength enhancement of confined reinforced concrete columns

As part of a continuing research study, this paper proposes a new design aid to calculate the actual moment capacity of confined reinforced concrete columns. Up to now the moment capacity of a reinforced concrete column is calculated based on the code's guidelines for an unconfined section. As most reinforced concrete columns contain transverse or confining reinforcement, which will enhance the column moment capacity, the actual moment capacity will be much higher than the unconfined moment capacity. This additional flexural strength will increase the shear force demand in the column, and if it is not accounted for in the design will jeopardise the column to fail in shear. In this study the actual moment capacity of a confined reinforced concrete column is obtained by multiplying the moment capacity calculated using the BS 8110 method with the proposed flexural strength enhancement factor. By using regression analysis, an equation for the flexural strength enhancement factor is derived as the function of all the parameters that have effects on the moment capacity. An example is presented to show the accuracy of the proposed method.published_or_final_versio

Deformability evaluation of high-strength reinforced concrete columns

Plastic hinge length and ultimate curvature are the crucial parameters that enable inelastic deformability (deflection and rotation) of reinforced concrete columns to be evaluated. Prediction of deformability beyond the elastic range is important in the performance-based design of earthquake-resistant structures. Although large numbers of tests have been conducted in the past by numerous researchers on reinforced concrete columns subjected to simultaneous axial load and large inelastic displacement, available design tools that enable rapid evaluation of deformability of reinforced concrete columns are still limited. The situation is even worse for high-strength reinforced concrete columns. The objective of this paper is to investigate plastic hinge length and ultimate curvature for deformability evaluation of high-strength reinforced concrete columns. In connection with this, two equations are proposed in this paper for estimating the plastic hinge length and ultimate curvature of high-strength reinforced concrete columns leading to their deformability evaluation. The proposed equations are used to evaluate the theoretical deflection of other researchers' column test specimens, and it is proven that these theoretical deflections mostly underestimate slightly their respective measured deflections. Therefore, the proposed equations can be used for conservative estimation of high-strength reinforced concrete column deformability at an early design stage without performing the tedious load-deflection analysis. © 2010 Thomas Telford Ltd.published_or_final_versio

Flexural strength and ductility of reinforced concrete beams

In the design of reinforced concrete beams, especially those made of high-strength concrete and those in earthquake-resistant structures, both the flexural strength and ductility need to be considered. From the numerical results obtained in a previous study on the post-peak behaviour and flexural ductility of reinforced concrete beams, the interrelation between the flexural strength and the flexural ductility that could be simultaneously achieved was evaluated and plotted in the form of charts. Using these charts, a new method of beam design called 'concurrent flexural strength and ductility design' that would allow engineers to consider both the strength and ductility requirements at the same time before deciding on whether to use high-strength concrete or add compression reinforcement has been developed. For application to cases in which the concrete grade is prescribed, a simpler method of first determining the limits of steel ratios that would satisfy the ductility requirement and then designing the reinforcement details according to the strength requirement has also been proposed. Examples are presented to illustrate the application of these methods.published_or_final_versio

Minimum flexural ductility design of high-strength concrete beams

In the flexural design of reinforced concrete beams, apart from the provision of adequate strength, it is also necessary to provide a certain minimum level of ductility. Traditionally, this has been done by limiting the tension steel ratio or the neutral axis depth to no more than certain fixed maximum values. However, this would result in a variable level of curvature ductility depending on the concrete grade and the steel yield strength. Of greater concern is that this would lead to a lower level of curvature ductility than has been provided in the past to beams made of conventional materials when high-strength concrete and/or high-strength steel are used. It is proposed herein that instead of limiting the tension steel ratio and the neutral axis depth, it is better to set a fixed minimum to the curvature ductility factor. The maximum values of tension steel ratio and neutral axis depth corresponding to the proposed minimum curvature ductility factor for various concrete grades and steel yield strengths have been evaluated. Based on these maximum values, simplified guidelines for providing minimum flexural ductility have been developed.published_or_final_versio

Minimum flexural ductility design of high-strength concrete beams

In the flexural design of reinforced concrete beams, apart from the provision of adequate strength, it is also necessary to provide a certain minimum level of ductility. Traditionally, this has been done by limiting the tension steel ratio or the neutral axis depth to no more than certain fixed maximum values. However, this would result in a variable level of curvature ductility depending on the concrete grade and the steel yield strength. Of greater concern is that this would lead to a lower level of curvature ductility than has been provided in the past to beams made of conventional materials when high-strength concrete and/or high-strength steel are used. It is proposed herein that instead of limiting the tension steel ratio and the neutral axis depth, it is better to set a fixed minimum to the curvature ductility factor. The maximum values of tension steel ratio and neutral axis depth corresponding to the proposed minimum curvature ductility factor for various concrete grades and steel yield strengths have been evaluated. Based on these maximum values, simplified guidelines for providing minimum flexural ductility have been developed.published_or_final_versio

Equivalent stress block for normal-strength concrete incorporating strain gradient effect

To account for the different behaviours of concrete under uniaxial compression and bending in the flexural strength design of reinforced concrete (RC) members, the stress-strain curve of concrete is normally scaled down so that the adopted maximum concrete stress in flexural members is less than the uniaxial strength. However, it was found from previous experimental research that the use of a smaller maximum concrete stress would underestimate the flexural strength of RC beams and columns. To investigate the effect of strain gradient on the maximum concrete stress developed in flexure, a total of 12 plain concrete and RC inverted T-shaped specimens were fabricated and tested under concentric and eccentric loads separately. The maximum concrete stress developed in the eccentric specimens was determined by modifying the concrete stress-strain curve obtained from the counterpart concentric specimens based on axial force and moment equilibriums. The test results revealed that the maximum concrete stress increases with strain gradient up to a certain maximum value. A formula was developed to correlate the maximum concrete stress to strain gradient. A pair of equivalent rectangular concrete stress block parameters that incorporate the effects of strain gradient was proposed for flexural strength design of RC members. © 2012 Thomas Telford Ltd.published_or_final_versio

Superfluid vs Ferromagnetic Behaviour in a Bose Gas of Spin-1/2 Atoms

We study the thermodynamic phases of a gas of spin-1/2 atoms in the Hartree-Fock approximation. Our main result is that, for repulsive or weakly-attractive inter-component interaction strength, the superfluid and ferromagnetic phase transitions occur at the same temperature. For strongly-attractive inter-component interaction strength, however, the ferromagnetic phase transition occurs at a higher temperature than the superfluid phase transition. We also find that the presence of a condensate acts as an effective magnetic field that polarizes the normal cloud. We finally comment on the validity of the Hartree-Fock approximation in describing different phenomena in this system.Comment: 10 pages, 2 figure

Effects of fermentation time and pH on soursop (Annona muricata) vinegar production towards its chemical compositions

Vinegar is a liquid product that undergoes both alcoholic and acetous fermentation of sugar (carbohydrate) sources. Soursop (Annona muricata) is easily available in Malaysia throughout the year. However, it is also highly perishable and has a short shelf-life. Therefore, in this research, soursop was used in the production of vinegar, to increase its utilisation and reduce wastage. The objectives of this research were to determine the effects of fermentation time and pH on soursop vinegar using a 3 × 5 factorial design and to determine its chemical compositions. It was found that pH and fermentation time showed significant (p0.05). It was evident that the sugar concentration reduces over time and it was inversely proportional to the ethanol and acetic acid concentrations, due to the conversion of sugar to ethanol and subsequently acetic acid. It was found that higher pH (pH5.5) gave significantly (p0.05) effect on ethanol production. There were no significant differences (p>0.05) in vitamin C content in all vinegar samples. Thus, it can be established that at fermentation time of 120 h and pH5.5, more sugar was used and more ethanol and acetic acid were produced

Review: Quality of Life in Lower Limb Peripheral Vascular Surgery

PURPOSE: Vascular intervention studies generally consider patency and limb salvage as primary outcomes. However, quality of life is increasingly considered an important patient-oriented outcome measurement of vascular interventions. Existing literature was analyzed to determine the effect of different treatments on quality of life for patients suffering from either claudication or critical limb ischemia. BASIC METHODS: A review of the literature was undertaken in the Medline library. A search was performed on quality of life in peripheral arterial disease. Results were stratified according to treatment groups. PRINCIPAL FINDINGS: Twenty-one articles described quality of life in approximately 4600 patients suffering from peripheral arterial disease. Invasive treatment generally results in better quality of life scores (at a maximum of 2 years of follow-up), compared with non-invasive treatment. In patients with critical limb ischemia, successful revascularization improves quality of life scores. Only one study reported long-term results. CONCLUSIONS: Increase in quality of life scores can be found for any intervention performed for peripheral arterial disease. However, there is scarce information on long-term quality of life after vascular intervention.info:eu-repo/semantics/publishedVersio