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CONTENTS
Volume 11, Number 1, January 2013
 

Abstract
There is an abundance of research on the strengthening of reinforced concrete (RC) structural elements such as beams, columns and slabs with fibre reinforced polymer (FRP) composites. Less research by comparison has been conducted on the strengthening of RC beam-column connections and the majority of such research has been predominantly experimental to date. Few existing experimental studies have reported extensive instrumentation of test specimens which in turn makes understanding the behavior of the connections and especially the contributions made by the FRP difficult to ascertain. In addition, there has been even more limited research on the analytical and numerical modelling of FRP-strengthened connections. In this paper, detailed descriptions of key strategies to model FRP-strengthened RC connections with finite elements are provided. An extensively instrumented and comprehensively documented set of experiments on FRP-strengthened connections is firstly presented and finite element models are then constructed using ANSYS. The study shows that the finite element approach is able to capture the overall behavior of the test specimens including the failure mode as well as the behavior of the FRP which will most importantly lead to a detailed understanding of the FRP and the future development of rational analytical models. The finite element models are, however, unable to model the stiffness of the connections with accuracy in the ultimate load range of response.

Key Words
concrete; connections; fibre reinforced polymers; finite elements; joints; strengthening

Address
Rijun Shrestha: School of Civil and Environmental Engineering, University of Technology Sydney, NSW, Australia; Scott T. Smith: School of Environment, Science and Engineering, Southern Cross University, Lismore NSW 2480, Australia; Bijan Samali: School of Civil and Environmental Engineering, University of Technology Sydney, NSW, Australia

Abstract
High-performance concrete (HPC) usually has higher paste and lower coarse aggregate volumes than normal concrete. The lower aggregate content of HPC can affect the shear capacity of concrete members due to the formation of smooth fractured surfaces and the subsequent development of weak interface shear transfer. Therefore, an experimental investigation was conducted to study the shear strength and cracking behavior of full-scale reinforced beams made with low-cement-content high-performance concrete (LcHPC) as well as conventional HPC. A total of fourteen flexural reinforced concrete (RC) beams without shear reinforcements were tested under a two-point load until shear failure occurred. The primary design variables included the cement content, the shear span to effective depth ratio (a/d), and the tensile steel ratio (w). The results indicate that LcHPC beams show comparable behaviors in crack and ultimate shear strength as compared with conventional HPC beams. Overall, the shear strength of LcHPC beams was found to be larger than that of corresponding HPC beams, particularly for an a/d value of 1.5. In addition, the crack and ultimate shear strength increased as a/d decreased or w increased for both LcHPC beams and HPC beams. This investigation established that LcHPC is recommendable for structural concrete applications.

Key Words
low cement content; high-performance concrete; shear strength; beam

Address
Chao-Wei Tang: Department of Civil Engineering and Engineering Informatics, Cheng Shiu University, No. 840, Chengcing Rd., Niaosong District, Kaohsiung Cinty, Taiwan R.O.C.; Yu-Ping Chen: Graduate Institute of Construction Engineering, Cheng Shiu University, No. 840, Chengcing Rd.,
Niaosong District, Kaohsiung City, Taiwan R.O.C.; How-Ji Chen: Department of Civil Engineering, National Chung-Hsing University, No. 250, Kuo Kuang Road, Taichung, Taiwan; Chung-Ho Huang: Department of Civil Engineering, Dahan Institute of Technology; Tsang-Hao Liu: AU Optronics Corporation

Abstract
The use of ground fly ash in concrete can increase the risk of slump loss due to the drastic surface change of the particles after the grinding treatment and the accelerated reaction compared to the untreated ash. This study is aimed at the early age hydration and time-dependent rheology changes of cement paste containing ground fly ash. An original fly ash is ground into different fineness and the hydration of cement paste containing the ground fly ash is monitored with the ultrasound propagation method. The zeta potentials of the solid particles are measured and the changes of rheological parameters of the cement pastes with time are analyzed with a rheometer. A particle packing model is used to probe packing of the solid particles. The results show that the early age hydration of the paste is strongly promoted by replacing Portland cement with fly ash up to 30 percent (by mass), causing increase of the yield stress of the paste. The viscosity of a paste containing ground fly ash is lower than that containing the untreated ash, which is explained by the denser packing of the solid particles.

Key Words
hydration; ground fly ash; rheology; packing

Address
Wei Chen: State Key Laboratory of Silicate Materials for Architectures, Wuhan University of Technology, Luoshi Road 122, Wuhan, 430070, P.R. China; Hao Huang: School of Materials Science and Engineering, Wuhan University of Technology, Luoshi Road 122, Wuhan, 430070, P.R. China

Abstract
This paper describes earthquake response of the Arhavi Highway Tunnel its geometrical properties, 3D finite element model and the linear time history analyses under a huge ground motion considering soil-structure interaction. The Arhavi Highway Tunnel is one of the tallest tunnels constructed in the Black Sea region of Turkey as part of the Coast Road Project. The tunnel has two tubes and each of them is about 1000 m tall. In the study, lineartime history analyses of the tunnel are performed applying northsouth, east-west and up accelerations components of 1992 Erzincan, Turkey ground motion. In the time history analyses, Rayleigh damping coefficients are calculated using main natural frequency obtained from modal analysis. Element matrices are computed using the Gauss numerical integration technique. The Newmark method is used in the solution of the equation of motion. Because of needed too much memory for the analyses, the first 10 second of the ground motions, which is the most effective duration, is taken into account in calculations. The results obtained 3D finite element model are presented. In addition, the displacement and stress results are observed to be allowable level of the concrete material during the earthquakes.

Key Words
earthquake response; linear time history analysis; highway tunnel; soil-structure interaction; 3D FEM.

Address
Baris SEVİM

Abstract
In this study, the effect of reducing cement by proportional addition of waste powder rubber on the performance of concrete under impact three-point bending loading were investigated experimentally and numerically. Concrete specimens were prepared by adding 5%, 10% and 20 % of rubber powder as filler to the mix and decreasing the same percentage of cement. For each case, three beams of 50 mm

Key Words
rubber powder; cement concrete; compressive strength; impact energy; finite element method

Address
Mustafa Maher Al-Tayeb and B.H. Abu Bakar: School of Civil Engineering, Universiti Sains Malaysia, Engineering Campus, 14300 Nibong Tebal, Penang, Malaysia; Hazizan Md Akil
and Hanafi Ismail: School of Materials & Mineral Resources Engineering, Universiti Sains Malaysia, Engineering Campus, 14300 Nibong Tebal, Penang, Malaysia

Abstract
In this paper, a new approach for cable layout design of pre-stressed concrete slabs is presented. To account the cable profile accurately, it is modelled by B-spline. Using the convex hull property of the Bspline, an efficient algorithm has been developed to obtain the cable layout for pre-stressed concrete slabs. For finite element computations, tendon and concrete are modelled by 3 noded bar and 20 noded brick elements respectively. The cable concrete interactions are precisely accounted using vector calculus formulae. Using the proposed technique a two way prestressed concrete slab has been successfully designed considering several design criteria.

Key Words
pre-stressed concrete; cable layout design; finite element analysis; stress; B-spline

Address
Ahmad Ali Khan and N.Dindorkar: Dept. Civil Engg. MANIT, Bhopal (M.P.), India 462051; K.K.Pathak: CS&PM Group, AMPRI (CSIR), Bhopal (M.P.), India 462064


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