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CONTENTS
Volume 11, Number 5, May 2013
 

Abstract
Although shear reinforcement in beams typically consists of steel bars bent in the form of stirrups or hoops, the addition of deformed steel fibres to the concrete has been shown to enhance shear resistance and ductility in reinforced concrete beams. This paper presents a model that can be used to predict the shear strength of fibrous concrete rectangular members without stirrups. The model is an extension of the plasticity-based crack sliding model originally developed for plain concrete beams. The crack sliding model has been improved in order to take into account several aspects: the arch effect for deep beams, the postcracking tensile strength of steel fibre reinforced concrete and its ability to control sliding along shear cracks,and the mitigation of the shear size effect due to presence of fibres. The results obtained by the model have been validated by a large set of experimental tests taken from literature, compared with several models proposed in literature, and numerical analyses are carried out showing the influence of fibres on the beam failure mode.

Key Words
shear; steel fibre reinforced concrete; plasticity; size effect; Kani

Address
Nino Spinella: Department of Civil Engineering, Università di Messina, Messina, Italy

Abstract
Two-dimensional tensile stresses are occurring at the back of the anchorage of the tendons of prestressed concrete bridges. A new method named \"tensile stress region\" for the design of the reinforcement is presented in this paper. The basic idea of this approach is the division of an anchor block into several slices, which are described by the tensile stress region. The orthogonal reinforcing wire mesh can be designed in each slice to resist the tensile stresses. Additionally the sum of the depth of every slice defined by the tensile stress region is used to control the required length of the longitudinal reinforcement bars. An example for the reinforcement design of an anchorage block of an external prestressed concrete bridge is analyzed by means of the new presented method and a finite element model is established to compare the results. Furthermore the influence of the transverse and vertical prestressing on the ordinary reinforcement design is taken into account. The results show that the amount of reinforcement bars at the anchorage block is influenced by the layout of the transverse and the vertical prestressing tendons. Using the

Key Words
end anchorage beam; tensile stress region; slice; slice depth; externally prestressed concrete bridge; reinforcement design

Address
C. Liu and D. Xu: Department of Bridge Engineering, Tongji University, Shanghai, China; B. Jung: Research Training Group 1462; G. Morgenthal: Bauhaus-Universität Weimar, Weimar, Germany 3Modelling and Simulation of Structures, Bauhaus-Universität Weimar, Weimar, Germany

Abstract
A nonlinear finite element analysis of R/C hybrid deep T-beam with web opening subjected to pure torsion is presented. Hexahedral 8-nodes and space truss element were used for modeling concrete and reinforcement. The reinforcement was assumed perfectly bonded to the corresponding nodes of the concrete element. The constitutive relations for concrete and reinforcement are based on the modified field theory and elastic perfectly plastic. The smear crack approach was adopted for modeling the crack. The torque-twist angle relationship curve based on the finite element analysis was compared to the experimental results. The comparison shows that the curve of torque-twist angle predicted by the nonlinear finite element analysis is linear before cracking and close to the experimental result. After cracking, the curve becomes nonlinear and stiffer compared to the experimental result.

Key Words
hybrid deep T-beam; web opening; pure torsion; finite element analysis; smear crack

Address
Ade Lisantono: Department of Civil Engineering, Faculty of Engineering, Universitas Atma Jaya Yogyakarta, Indonesia

Abstract
Large fluctuations in surface strain at the level of steel are expected in reinforced concrete flexural members at a given stage of loading due to the emergent structure (emergence of new crack patterns). This has been identified in developing deterministic constitutive models for finite element applications in Ibrahimbegovic et al. (2010). The aim of this paper is to identify a suitable probability distribution for describing the large deviations at far from equilibrium points due to emergent structures, based on phenomenological, thermodynamic and statistical considerations. Motivated by the investigations reported by Prigogine (1978) and Rubi (2008), distributions with heavy tails (namely, alpha-stable distributions) are proposed for modeling the variations in strain in reinforced concrete flexural members to account for the large fluctuations. The applicability of alpha-stable distributions at or in the neighborhood of far from equilibrium points is examined based on the results obtained from carefully planned experimental investigations, on seven reinforced concrete flexural members. It is found that alpha-stable distribution performs better than normal distribution for modeling the observed surface strains in reinforced concrete flexural members at these points.

Key Words
reinforced concrete; surface strain; cracking; thermodynamics; alpha-stable distribution

Address
K. Balaji Rao, M.B. Anoop, K. Kesavan, S.R. Balasubramanian,
K. Ravisankar and Nagesh R. Iyer: CSIR-Structural Engineering Research Centre, CSIR Campus Taramani, Chennai 600 113, India;

Abstract
When using the conventional finite element method, a great number of grid nodes are necessary to describe the large and uneven temperature gradients in the concrete around cooling pipes when calculating the temperature field of mass concrete with cooling pipes. In this paper, the temperature gradient properties of the concrete around a pipe were studied. A new calculation method was developed based on these properties and an explicit iterative algorithm. With a small number of grid nodes, both the temperature distribution along the cooling pipe and the temperature field of the concrete around the water pipe can be correctly calculated with this new method. In conventional computing models, the cooling pipes are regarded as the third boundary condition when solving a model of concrete with plastic pipes, which is an approximate way. At the same time, the corresponding parameters have to be got by expensive experiments and inversion. But in the proposed method, the boundary condition is described strictly, and thus is more reliable and economical. And numerical examples were used to illustrate that this method is accurate, efficient and applicable to the actual engineering.

Key Words
calculation method; temperature field; mass concrete; cooling pipes; boundary condition

Address
Zhenyang Zhu and Weimin Chen: Hydrochina Huadong Engineering Corporation, Hangzhou 310014, PR China; Sheng Qiang: College of Water conservancy & Hydropower Engineering, Hohai University, Nanjing 210098, PR China

Abstract
As known, concrete classes are described as strength of standard specimens produced and kept in ideal conditions, not including reinforcement and not subjected to any load effect before. Under the circumstances, transforming core strengths to the standard specimen strength is necessary and considering all parameters, affected on the core strength, is inevitable. In fact, effects of the reinforcement and the load history on concrete strength are generally neglected when these mentioned transforms are performing. The main purpose of this paper is investigating the effects of the reinforcement and the load history on the core strength. This investigation is experimentally performed on cores drilled from specimens having different keeping conditions, reinforced, unreinforced, subjected to bending and central pressure in various proportions of failure load during specified periods. Obtained results show that the importance of these effects cannot be neglected.

Key Words
concrete strength in structure; load history; effect of reinforcement; core

Address
Ayşegül Durmuş, Hasan Tahsin Öztürk and Ahmet Durmuş: Faculty of Engineering (Civil), Karadeniz Technical University, Trabzon, Turkey

Abstract
Since the beginning of the 90 s, depending on the growth of the industrial sector in Turkey,factory constructions have been increased. The cost of precast concrete buildings is lower than the steel ones for this reason the precast structural systems are used more. Precast concrete structural elements are mostly as strong as not to have damage in the earthquake but weakness of connections between elements causes unexpected damages of structure during earthquake. When looking at the previous researches, it can be seen that there is a lack of studies about socket type base connections although there were many experimental and analytical studies about the connections of precast structural elements. The aim of this study is to investigate the stress transfer mechanism between column and the socket base wall with finite element method. For the finite element analysis ANSYS software was used. A finite element model was created which is the simulation of experimental research executed by Canha et al. (2009) under vertical and horizontal forces. Results of experimental research and finite element analysis were compared to create a successful simulation of experimental program. After determining the acceptable parameters, models of socket bases were created. Model dimensions were chosen according to square section column sizes 400, 450, 500, 550 and 600 mm which were mostly used in industrial buildings. As a result of this study, stress distribution at center section of the socket base models were observed and it is found that stress distribution affects triangular at the half of socket bottom and top.

Key Words
nonlinear finite element analysis; socket base; contact analysis; ANSYS

Address
Özgür ANIL and Burak UYAROĞLU: Civil Eng. Dept., Gazi University, Maltepe, Ankara, Türkiye, 06570


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