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CONTENTS
Volume 15, Number 6, December 2013
 

Abstract
Generally the required strength and stiffness of an I-shaped beam to the box-shaped column connection is achieved if continuity plates are welded to the column flanges from all sides. However, welding the forth edge of a continuity plate to the column flange may not be easily done and is normally accompanied by remarkable difficulties. This study was aimed to propose an alternative for box columns with continuity plates to diminish such problems. For this purpose a double-web I-shaped column was proposed. In this case the strength and rotational stiffness of the connection was provided by nearing the column webs to each other. Finite element studies on about 120 beam-column connections showed that the optimum proportion of the distance between two column webs and the width of the column flange (parameter β) was a function of the ratio of the beam flange width to the column flange width (parameter α). Hence, based on the finite element results, an equation was proposed to estimate the optimum value of parameter β in terms of parameter α to achieve the highest connection performance. Results also showed that the strength and ductility of post-Northridge connections of such columns are in average 12.5 % and 54% respectively higher than those of box-shaped columns with ordinary continuity plates. Therefore, a double-web I-shaped column of optimum arrangement might be a proper replacement for a box column with continuity plates when beams are rigidly attached to it.

Key Words
strength; ductility; moment resisting connections; box columns; continuity plates

Address
(1) Hamed Saffari: Department of Civil Engineering, Shahid Bahonar University of Kerman, Kerman, Iran;
(2) Amir A. Hedayat: Department of Civil Engineering, Kerman Branch, Islamic Azad University, Kerman, Iran;
(3) Nasrin Soltani Goharrizi: Department of Civil Engineering, Yazd Branch, Islamic Azad University, Yazd, Iran.

Abstract
CFRP strips are widely used nowadays for repair/strengthening or capacity increase purposes. Sharp bending at the ends of the CFRP strips is frequently encountered at these applications. In this study, Reinforced Concrete (RC) beam specimens that were produced with 10 MPa compression strength concrete were strengthened by using bonded CFRP strips with end anchorages to tension region. The parameters that were investigated in this study are the width of the strip, the number of applied fan anchorages and whether additional layer of CFRP patch is used or not at the strip ends. Specimens were strengthened with 100 mm wide CFRP strips with one or two anchorages at the ends. In addition CFRP patch with two and three anchorages at the ends were tested for investigating the effect of the patches. Specimens that were strengthened with three anchorages at the ends with patches were repeated with 60 and 80 mm wide CFRP strips. The most successful result was obtained from the specimen that was strengthened with 80 mm wide CFRP strips with 3 end anchorages and patches among the others at the experimental program. The numbers of anchorages that were applied to ends of CFRP strips were more effective than the width of the CFRP strips onto strength and stiffness of the specimens. Due to limited space at the ends of the strips at most three anchorages could be applied.

Key Words
RC beams; CFRP; fan type anchorages; strengthening

Address
M. Emin KARA and Mustafa YAŞA: Aksaray University, Civil Engineering Department, Aksaray, Turkey.

Abstract
Concrete filled steel tubular members (CFST) become a popular choice for modern building construction due to their numerous structural benefits and at the same time aging of those structures and member deterioration are often reported. Therefore, actions like implement of new materials and strengthening techniques become essential to combat this problem. The application of carbon fibre reinforced polymer (CFRP) with concrete structures has been widely reported whereas researches related to strengthening of steel structures using fibre reinforced polymer (FRP) have been limited. The main objective of this study is to experimentally investigate the suitability of CFRP to strengthening of CFST members under flexure. There were three wrapping schemes such as Full wrapping at the bottom (fibre bonded throughout entire length of beam), U-wrapping (fibre bonded at the bottom throughout entire length and extended upto neutral axis) and Partial wrapping (fibre bonded in between loading points at the bottom) introduced. Beams strengthened by U-wrapping exhibited more enhancements in moment carrying capacity and stiffness compared to the beams strengthened by other wrapping schemes. The beams of partial wrapping exhibited delamination of fibre and were failed even before attaining the ultimate load of control beam. The test results showed that the presence of CFRP in the outer limits was significantly enhanced the moment carrying capacity and stiffness of the beam. Also, a non linear finite element model was developed using the software ANSYS 12.0 to validate the analytical results such as load-deformation and the corresponding failure modes.

Key Words
CFST members; CFRP fabrics; strengthening; flexure; externally bonded

Address
(1) M.C. Sundarraja: Thiagarajar College of Engineering, Madurai, Tamilnadu, INDIA;
(2) G. Ganesh Prabhu: Sethu Institute of Technology, Virudhunagar, Tamilnadu, INDIA.

Abstract
The objective of the study is to predict the moment anchorage capacity of the concrete filled steel box (CFSB) as footing by using the 3D finite element program CAMUI developed by authors' laboratory. The steel box is filled with concrete and concrete filled steel tube (CFT) column is inserted in the box. Numerical simulation of the experimental specimens was carried out after introducing the new constitutive model for post peak behavior of concrete in compression under confinement. The experimental program was conducted to verify the reliability of the simulation results by the FE program. The simulated peak loads agree reasonably with the experimental ones and was controlled by concrete crushing near the column. After confirming the reliability of the FEM simulation, effects of different parameters on the moment anchorage capacity of concrete filled steel box footing were clarified by conducting numerically parametric study.

Key Words
concrete filled steel box footing; 3D FEM analysis; moment capacity; parametric analysis

Address
(1) Muhammad Aun Bashir: Civil Engineering Department, Imam Muhammad ibn Saud Islamic University, Riyadh, KSA, Pakistan;
(2) Hitoshi Furuuchi and Tamon Ueda: Division of Engineering and Policy for Sustainable Environment, Faculty of Engineering, Hokkaido University, Kita 13 Nishi 8, Kita-ku, Sapporo, Japan;
(3) Nauman Bashir: Lecturer COMSATS, Sahiwal Campus, Pakistan.

Abstract
This paper introduces new specimens of Steel-Carbon Fibre Reinforced Polymer composite developed in accordance with standard test method and definition for mechanical testing of steel (ASTM—A370). The main purpose of this research is to study the behaviour of steel-CFRP composite specimen under uniaxial tension to use it in beams in lieu of traditional steel bar reinforcement. Eighteen specimens were prepared and divided into six groups, depending upon the number of the layers of CFRP. Uniaxial tensile tests were conducted to determine yield strength and ultimate strength of specimens. Test results showed that the stress-strain curve of the composite specimen was bilinear prior to the fracture of CFRP laminate. The tested composite specimens displayed a large difference in strength with remarkable ductility. The ultimate load for Steel-Carbon Fibre Reinforced Polymer composite specimens was found using the model proposed by Wu et al. (2010) and nonlinear FE analysis. The ultimate loads obtained from FE analysis are found to be in good agreement with experimental ones. However, ultimate loads obtained applying Wu model are significantly different from experimental/ F E ones. This suggested modification of Wu model. Modified Wu's model which gives a better estimate for the ultimate load of Steel-Carbon Fibre Reinforced Polymer (SCFRP) composite specimen is presented in this paper.

Key Words
CFRP laminate; steel strip; tensile load; modified model; specimen

Address
(1) Faris A. Uriayer: Department of Civil Engineering, Jamia Millia Islamia, New Delhi, India (on Leave from Kufa Universit, Iraq);
(2) Mehtab Alam: Department of Civil Engineering, Faculty of Engineering and Technology, Jamia Millia Islamia, New Delhi, India.

Abstract
This paper presents experimental investigations of the fundamental behavior of concrete filled steel tube (CFT) beam-columns under fire loading. A total of thirteen specimens were tested to determine the axial force-moment-curvature-temperature behavior of CFT beam-columns. The experimental approach involved the use of: (a) innovative heating and control equipment to apply thermal loading and (b) digital image correlation with close-range photogrammetry to measure the deformations (e.g., curvature) of the heated region. Each specimen was sequentially subjected to: (i) constant axial loading; (ii) thermal loading in the expected plastic hinge region following the ASTM E119 temperature-time T-t curve; and (iii) monotonically increasing flexural loading. The effects of various parameters on the strength and stiffness of CFT beam-columns were evaluated. The parameters considered were the steel tube width, width-tothickness ratio, concrete strength, maximum surface temperature of the steel tube, and the axial load level on the composite CFT section. The experimental results provide knowledge of the fundamental behavior of composite CFT beam-columns, and can be used to calibrate analytical models or macro finite element models developed for predicting behavior of CFT members and frames under fire loading.

Key Words
fire; columns; composite; experiments; temperature

Address
(1) Amit H. Varma: School of Civil Engineering, Purdue University, 550 Stadium Mall Drive West Lafayette, Indiana 47907, USA;
(2) Sangdo Hong: Indiana Department of Transportation, West Lafayette, Indiana, USA;
(3) Lisa Choe: National Institute of Standards and Technology, Gaithersburg, Maryland, USA.

Abstract
The behaviour of steel column at elevated temperature is significantly different than that at ambient temperature due to its changes in the mechanical properties with temperature. Reported literature suggests that steel column may become vulnerable when exposed to fire condition, since its strength and capacity decrease rapidly with temperature. The present study aims at investigating the lateral load resistance of non-insulated steel columns under fire exposure through finite element analysis. The studied parameters include moment-rotation behaviour, lateral load-deflection behaviour, stiffness and ductility of columns at different axial load levels. It was observed that when the temperature of the column was increased, there was a significant reduction in the lateral load and moment capacity of the non-insulated steel columns. Moreover, it was noted that the stiffness and ductility of steel columns decreased sharply with the increase in temperature, especially for temperatures above 400°C. In addition, the lateral load capacity and the moment capacity of columns were plotted against fire exposure time, which revealed that in fire conditions, the non-insulated steel columns experience substantial reduction in lateral load resistance within 15 minutes of fire exposure.

Key Words
HSS steel column; elevated temperature; moment-rotation; lateral load-deflection; axial capacity

Address
(1) M. Shahria Alam, A.H.M. Muntasir Billah and Ahmad Rteil: School of Engineering, The University of British Columbia, Kelowna, BC V1V1V7, Canada;
(2) Shahriar Quayyum: Department of Civil, Construction, & Env Engineering, North Carolina State University, Raleigh, NC 27695-7908, USA;
(3) Mahmud Ashraf: School of Engineering and IT, The University of New South Wales, Canberra, ACT 2600, Australia;
(4) A.N.M. Rafi: IES Associates Windsor, ON, N8Y 4Y6, Canada.


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