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CONTENTS
Volume 6, Number 5, October 2009
 

Abstract
In the design of concrete columns, it is important to provide some nominal flexural ductility even for structures not subjected to earthquake attack. Currently, the nominal flexural ductility is provided by imposing empirical deemed-to-satisfy rules, which limit the minimum size and maximum spacing of the confining reinforcement. However, these existing empirical rules have the major shortcoming that the actual level of flexural ductility provided is not consistent, being generally lower at higher concrete strength or higher axial load level. Hence, for high-strength concrete columns subjected to high axial loads, these existing rules are unsafe. Herein, the combined effects of concrete strength, axial load level, confining pressure and longitudinal steel ratio on the flexural ductility are evaluated using nonlinear moment-curvature analysis. Based on the numerical results, a new design method that provides a consistent level of nominal flexural ductility by imposing an upper limit to the axial load level or a lower limit to the confining pressure is developed. Lastly, two formulas and one design chart for direct evaluation of the maximum axial load level and minimum confining pressure are produced.

Key Words
columns; confinement; ductility; high-strength concrete.

Address
J. Y. K. Lam: Department of Civil Engineering, The University of Hong Kong, Pokfulam, Hong Kong
J. C. M. Ho: Department of Civil Engineering, The University of Hong Kong, Pokfulam, Hong Kong
A. K. H. Kwan: Department of Civil Engineering, The University of Hong Kong, Pokfulam, Hong Kong

Abstract
In this paper an improved one-dimensional frame element for modelling of reinforced concrete beams and columns subjected to impact is presented. The model is developed in the framework of a flexibility fibre element formulation that ignores the shear effect at material level. However, a simple shear cap is introduced at section level to take account of possible shear failure. The effect of strain rate at the fibre level is taken into account by using the dynamic increase factor (DIF) concept for steel and concrete. The capability of the formulation for estimating the element response history is demonstrated by some numerical examples and it is shown that the developed 1D element has the potential to be used for dynamic analysis of large framed structures subjected to impact of air blast and rigid objects.

Key Words
beam element; flexibility formulation; impact; strain rate; reinforced concrete.

Address
Hamid R. Valipour: Centre for Infrastructure Engineering and Safety(CIES), School of Civil and Environmental Engineering, The University of New South Wales, Sydney 2052, Australia
Luan Huynh: Centre for Infrastructure Engineering and Safety(CIES), School of Civil and Environmental Engineering, The University of New South Wales, Sydney 2052, Australia
Stephen J. Foster: Centre for Infrastructure Engineering and Safety(CIES), School of Civil and Environmental Engineering, The University of New South Wales, Sydney 2052, Australia

Abstract
This paper presents a study of the strength and chloride penetration of blended Portland cement mortar containing ground palm oil fuel ash (POA) and ground river sand (GS). Ordinary Portland cement (OPC) was partially replaced with POA and GS. Compressive strength, rapid chloride penetration test (RCPT) and chloride penetration depth of mortars were determined. The GS only asserted the packing effect and its incorporation reduced the strength and the resistance to chloride penetration of mortar. The POA asserted both packing and pozzolanic effects. The use of the blend of equal portion of POA and GS also produced high strength mortars, save cost and excellent resistance to chloride penetration owing to the synergic effect of the blend of POA and GS. For chloride depth, the mathematical model correlates well with the experimental results. The computer graphics of chloride depth of the ternary blended mortars are also constructed and can be used to aid the understanding and the proportioning of the blended system.

Key Words
palm oil fuel ash; ground river sand; strength; chloride; mortar.

Address
Sumrerng Rukzon: Rajamangala University of Technology Phra Nakhon, Bangkok, Thailand 10300
Prinya Chindaprasirt: Department of Civil Engineering, Faculty of engineering, Khon Kaen University, Khon Kaen, Thailand 40002

Abstract
Short column effect is cause to failure of columns which may result in severe damages or even collapse during earthquakes. The scope of the study is mainly to reveal the effect of short column on the holistic behaviour of the buildings. The nonlinear analysis of 31 different frame buildings containing short column problem are carried out using finite element method. The finite element models were selected by 2 bays and 3 stories. Since the short columns are generally seen in the first storey of the buildings, in the study, they are only constructed in the same storey. The adverse effect of the short column on the response of buildings was shown in terms of the total load factor and displacement capacity of building. The response of buildings in terms of ground storey displacements is presented in figures and discussed. It is revealed that if the window openings are constructed along the bays, the total load capacity is decreased 85% compared with reference model in which all of bays are filled with infill walls.

Key Words
short column effect; RC frame; failure of columns; nonlinear analysis; finite element analysis.

Address
Naci Caglar: Department of Civil Engineering, University of Sakarya, Sakarya 54187, Turkey
Mahir Mutlu: Department of Civil Engineering, University of Sakarya, Sakarya 54187, Turkey

Abstract
Chloride induced corrosion is a concern that governs the durability of concrete structures in marine environments, especially in tidal environments. During the service lives of concrete structures, internal cracks in the concrete cover may appear due to imposed loads, accelerating chloride penetration because of the simultaneous action of environmental and service structural loads. This paper investigated the effects of cyclic flexural loads on chloride diffusion characteristics of plain concretes, and proposed a model to predict the chloride penetration into plain concretes subjected to both tidal environments and different cyclic flexural load levels. Further, a new experiment was performed to verify the model. Results of the model using Finite Difference Method (FDM) showed that the durability of concretes in tidal environments was reduced as cyclic flexural load levels, SR, increased, and the modeling results fitted well with the experimental results.

Key Words
chloride penetration; cyclic flexural load; actual concrete structures; model.

Address
Tran Van Mien: Department of Civil Engineering, Chulalongkorn University, BKK 10330, Thailand
Boonchai Stitmannaithum: Department of Civil Engineering, Chulalongkorn University, BKK 10330, Thailand
Toyoharu Nawa: Graduate School of Engineering, Hokkaido University, Hokkaido 060-8628, Japan


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