Improved behaviour of concrete-filled-stee-tube columns with external confinement

In high-strength concrete columns, because of the heavy demand of confining steel to restore the column ductility, it is more efficient to provide the confinement in the form of steel tube to form concrete-filled-steel-tube (CFST) column. Comparing with the transverse steel, CFST columns provide a stronger and more uniform confining pressure to the concrete core, and reduce the steel congestion problem for better concrete placing quality. However, a major shortcoming of CFST columns is the imperfect steel-concrete interface bonding at the elastic stage as steel dilates more than concrete in compression. This adversely affects the confinement of the steel tube and decrease the elastic modulus. To resolve the problem, it is proposed in this study to use external steel confinement in the forms of rings and ties to restrict the dilation of steel tube. For verification, a series of uni-axial compression test was performed on some CFST columns to study the effectiveness of external confinement. From the results, it was found that: (1) Both rings and ties improved the stiffness of the CFST columns; (2) The rings improve significantly the axial strength of the CFST columns while the ties did not improve the axial strength; (3) All externally confined CFST columns can reach a strain of at least 20% before failure occurs.postprintThe Australian Earthquake Engineering Society (AEES) 2011 Conference, Barossa Valley, South Australia, 18-20 November 2011. In Proceedings of the AEES Conference, 2011, paper 2

Treatment of non-small cell lung cancer in the era of targeted therapy

Lung cancer, mostly non-small cell carcinoma (NSCLC), is still a major global problem with devastating outcomes. The majority presents at late stages, in which the chance of cure is minimal. With the better understanding of lung cancer biology, there have been several novel targeted approaches against NSCLC. Anti-angiogenesis has been proven to be an important approach in combination with systemic chemotherapy treatment in NSCLC at the first-line setting. The prototypic monoclonal antibody against vascular endothelial growth factor (VEGF), be- vacizumab, is now approved for clinical use in combination with platinum-based chemotherapy in first-line treatment of advanced non-squamous NSCLC, associated with improved response and survival compared with chemotherapy alone. The most notable example of targeted therapy for lung cancer is epidermal growth factor receptor tyrosine kinase inhibitors (EGFR TKI). There have been extensive evidences supporting the superiority of EGFR TKI (like gefitinib or erlotinib) over standard platinum-based doublet chemotherapy in first-line treatment of advanced NSCLC carrying EGFR activating mutations. Almost following the same path as EGFR TKI, a novel target (anaplastic lymphoma kinase, ALK) has been identified recently with a very promising targeted agent (crizotinib) that has already been approved for clinical use in NSCLC carrying ALK rearrangements. Over the past decade, there have been undoubtedly growing armamentaria in the treatment of NSCLC, focusing on personalized and targeted approach.published_or_final_versio

Deformability design of high-performance concrete beams

The use of high-performance materials (HPMs) such as high-strength concrete (HSC) and high-strength steel (HSS) is becoming more popular in the construction of beams and columns of tall buildings. These HPMs not only increase the stiffness and decrease the strength-to-weight ratio, but also provide a more sustainable construction method by minimising the construction materials needed. However, HSC and HSS are more brittle than normal-strength concrete and steel, respectively. Therefore, it will adversely affect the deformability of concrete beams. To evaluate the pros and cons of adopting HPM in beam design, the author will investigate the flexural strength and deformability of concrete beams made of HPMs. The deformability in this study is expressed in normalised rotation capacity and investigated by a parametric study using nonlinear moment-curvature analysis taking into account the degree of reinforcement, confining pressure, concrete and steel yield strength. From the results, it is evident that the deformability of concrete beams increases as the degree of reinforcement decreases or confining pressure increases. However, the effects of concrete and steel yield strength depend on other factors. For practical design purpose, charts and formulas are produced for designing high-performance concrete beams to meet with specified flexural strength and deformability requirement. © 2011 John Wiley & Sons, Ltd.preprin

Ductility design of high-strength concrete beams and columns

High-strength concrete (HSC) is increasingly used for the construction of tall buildings and long span bridges. However, most engineers just focus on how to better utilize the strength potential of HSC and little attention is paid to ensure that the HSC structures would have sufficient ductility. In this regard, it should be noted that the current design codes, which do not provide any guidelines for ductility design, are not applicable to HSC structures. In recent years, the authors have been conducting research on how the use of HSC would affect the flexural ductility of concrete members. Herein, an overall summary of their research is presented. It will be shown that depending on the reinforcement detailing and loading conditions, the ductility of HSC structures is not necessarily lower than that of normal concrete structures. Finally, guidelines for the ductility design of HSC beams and columns, augmented with design formulas and charts, are given.published_or_final_versio

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

Flexural strength and ductility improvement of NSC beams

Open Access JournalIn order to calculate the flexural strength of normal-strength concrete (NSC) beams, the nonlinear actual concrete stress distribution within the compression zone is normally replaced by an equivalent rectangular stress block, with two coefficients of α and β to regulate the intensity and depth of the equivalent stress respectively. For NSC beams design, α and β are usually assumed constant as 0.85 and 0.80 in reinforced concrete (RC) codes. From an earlier investigation of the authors, α is not a constant but significantly affected by flexural strain gradient, and increases with the increasing of strain gradient till a maximum value. It indicates that larger concrete stress can be developed in flexure than that stipulated by design codes. As an extension and application of the authors- previous study, the modified equivalent concrete stress block is used here to produce a series of design charts showing the maximum design limits of flexural strength and ductility of singly- and doubly- NSC beams, through which both strength and ductility design limits are improved by taking into account strain gradient effect.published_or_final_versio

Strain gradient effects on concrete stress-strain curve

The stress–strain characteristic of concrete developed in flexure is one of the essential parameters for the ultimate flexural strength design of reinforced concrete (RC) members. Currently, the stress–strain curve of concrete developed in flexure is obtained by scaling down the uniaxial stress–strain curve. In current RC design codes, it is represented by an equivalent rectangular concrete stress block depending solely on the concrete strength. By comparing the theoretical strength evaluated for the stress block with the measured strength, the authors found that current codes underestimate the actual flexural strength of RC beams and columns by 9% and 19%, respectively. Since the underestimation is different for beams and columns, which are subjected to different strain gradients at ultimate, it is suggested that the maximum concrete stresses developed in flexure should depend also on strain gradient. The effects of strain gradient on the concrete stress developed in flexure were investigated in this work by testing RC columns under concentric and eccentric axial loads or horizontal loads. The concrete stress–strain curves of the eccentrically/horizontally loaded specimens were derived by modifying those of concentrically loaded counterparts based on axial force and moment equilibriums. The results indicate that the maximum concrete stress developed in flexure depends significantly on strain gradient. Formulas were developed to correlate the maximum and equivalent concrete stresses developed in flexure to the strain gradient. Their applicability was verified by comparing the results with measured flexural strengths of RC beams and columns.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