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CONTENTS
Volume 10, Number 5, November 2012
 

Abstract
In the recent years, rehabilitation of structures, strengthening and increasing the ductility of them under seismic loads have become so vital that many studies has been carried out on the retrofit of steel and concrete members so far. Bridge piers are very important members concerning rehabilitation, in which the plastic hinging zone is very vulnerable. Pier is usually confined by special stirrups predicted in the design procedure; moreover, fiber-reinforced polymers (FRP) jackets are used after construction to confine the pier. FRP wrapping of the piers is one of the most effective ways of increasing moment and ductility capacity of them, which has a growing application due to its relative advantages. In many earthquake-resistant bridges, reinforced concrete columns have a major defect which could be retrofitted in different ways like using FRP. After rehabilitation, it is important to check the strengthening adequacy by dynamic nonlinear analysis and precise modeling of material properties. If the plastic hinge properties are simplified for the strengthened members, as the simplified properties which FEMA 356 proposes for nonstrengthened members, static nonlinear analysis could be performed more easily. Current paper involves this matter and it is intended to determine the plastic hinge properties for static nonlinear analysis of the FRP-strengthened circular columns.

Key Words
plastic hinge; pushover analysis; finite element model; FRP; Ansys.

Address
Gholamreza Ghodrati Amiri: Center of Excellence for Fundamental Studies in Structural Engineering, School of Civil Engineering, Iran University of Science & Technology, Tehran, Iran; Azadeh Jaberi Jahromi: School of Civil Engineering, Iran University of Science & Technology, Tehran, Iran; Benyamin Mohebi: Department of Civil engineering, Faculty of Engineering, Imam Khomeini International University, Qazvin, Iran

Abstract
Using appropriate raw materials for cement is crucial for providing the required products. Monitoring relationships and analyzing distributions in a cement material quarry are important stages in the process. CaO, one of the substantial chemical components, is included in some raw materials such as limestone and marl; furthermore, appraising spatial assessment of this chemical component is also very critical. In this study, spatial evaluation and monitoring of CaO concentrations in a cement site are considered. For this purpose, two effective regression-based models were applied to a cement quarry located in Turkey. For the assessment, some spatial models were developed and performance comparisons were carried out. The results show that the regression-based spatial modelling is an efficient methodology and it can be employed to evaluate spatially varying relationships in a cement quarry.

Key Words
cement; quarry; regression-based modelling; spatial relationship.

Address
Bulent Tutmez: Department of Mining Engineering, Inonu University, 44280 Malatya, Turkey; Ahmet Dag: Department of Mining Engineering, Cukurova University, 01100 Adana, Turkey

Abstract
This paper presents a study on the behaviour of the joints of segmental concrete bridges with external prestressing, focusing on the structural response of dry non-epoxied joints with shear keys. A Finite Element joint model to study such structures is validated modelling eight concrete panel tests. The most important feature of this model is that it has been validated with experimental tests on concrete panels which were specifically designed to fail in shear. Interface elements are used to reproduce the non linear behaviour of the joint and parameters deduced from the tests are used to define the constitutive law of these elements. This joint model is of great importance because it will permit the development of a structural model that faithfully reproduces the behaviour of these structures under combined flexure and shear and the study of its global behaviour after the opening of the joints. Interesting conclusions about the behaviour of the dry joints, about the contribution of the different mechanisms transferring shear (friction and cohesion) and about the shear stress distribution in the joint have been reached.

Key Words
segmental bridges; castellated joints; shear strength; dry joints; shear keys.

Address
J. Turmo, G. Ramos and A.C. Aparicio: Departament of Construction Engineering. Universitat Politecnica de Catalunya, Barcelona Tech. c/Jordi Girona 1-3, C1, 08034. Barcelona, Spain

Abstract
This paper presents a simplified grid beam model for simulating the nonlinear response of reinforced concrete flat-plate structures. The beam elements are defined with nonlinear behavior for bending moment and torsion. The flexural stiffness and torsional strength of the beam elements are defined based on experimental data to implicitly account for slab two-way bending effects. A failure criterion that considers the interaction between the punching strength and slab flexural behavior is incorporated in the model. The effects of bond-slip of slab reinforcement on connection stiffness are examined. The proposed grid beam model is validated by simulating large-scale tests of slab-column connections subjected to concentric gravity loading and unbalanced moment. This study also determines the critical parameters for a hysteretic model used to simulate flat-plates subjected to cyclic lateral loading.

Key Words
cyclic loading; flat-plate; grid model; hysteretic behavior; punching failure; slab-column connection.

Address
Ying Tian and Aly Said: Department of Civil and Environmental Engineering and Construction, University of Nevada Las Vegas, Las Vegas, USA; Jianwei Chen: College of Civil and Architectural Engineering, Hebei United University, Tangshan, China; Jian Zhao: Department of Civil Engineering and Mechanics, University of Wisconsin-Milwaukee, Milwaukee, USA

Abstract
The capacity design of shear forces is one of the special demands of EC8 by which the ductile behavior of structures is implemented. The aim of capacity design is the formation of plastic hinges without shear failure of the elements. This is achieved by deriving the design shear forces from equilibrium conditions, assuming that plastic hinges, with their possible over-strengths, have been formed in the adjacent joints of the elements. In this equilibrium situation, the parameters (dimensions, material properties, axial forces etc) are random variables. Therefore, the capacity design of shear forces is associated with a probability of non-compliance (probability of failure). In the present study the probability of non-compliance of the shear capacity design in columns is calculated by assuming the basic variables as random variables. Parameters affecting this probability are examined and a modification of the capacity design is proposed, in order to achieve uniformity of the safety level.

Key Words
reliability; shear; capacity design; columns.

Address
George C. Thomos and Constantin G. Trezos: Laboratory of Reinforced Concrete, National Technical University of Athens,
5 Iroon Polytechniou, Zografou, Greece 157 73

Abstract
Silica fume has long been used as a mineral admixture to improve the durability and produce high strength and high performance concrete. And in marine and coastal environments, penetration of chloride ions is one of the main mechanisms causing concrete reinforcement corrosion. In this paper, we proposed a numerical procedure to predict the chloride diffusion in a hydrating silica fume blended concrete. This numerical procedure includes two parts: a hydration model and a chloride diffusion model. The hydration model starts with mix proportions of silica fume blended concrete and considers Portland cement hydration and silica fume reaction respectively. By using the hydration model, the evolution of properties of silica fume blended concrete is predicted as a function of curing age and these properties are adopted as input parameters for the chloride penetration model. Furthermore, based on the modeling of physicochemical processes of diffusion of chloride ion into concrete, the chloride distribution in silica fume blended concrete is evaluated. The prediction results agree well with experiment results of chloride ion concentrations in the hydrating concrete incorporating silica fume.

Key Words
silica fume; chloride; diffusion; simulation; durability.

Address
Xiao-Yong Wang and Ki-Bong Park: Department of Architectural Engineering, College of Engineering, Kangwon National University, Chuncheon, 200-701, Korea; Han-Seung Lee: School of Architecture & Architectural Engineering, Hanyang University, Ansan, 425-791, Korea

Abstract
This paper presents an algorithm for the evaluation of stresses in reinforced concrete sections under service loads. The algorithm is applicable to any section defined by polygonal contours and is based on an analytical integration of the stresses. The nonlinear behaviour of concrete is represented by the parabola-rectangle law used in the Eurocode-2 for the ultimate concrete design. An integrated definition of the strains in concrete and steel is possible by the use of Heaviside functions, similarly to what is done for ultimate section design in Barros et al. (2004). Other constitutive equations for the definition of the stresses in the concrete or steel can be easily incorporated into the code. The examples presented consist in the evaluation of resulting axial load and bending moment in an irregular section and in a section in L shape. The results, for service stresses, can also be plotted in terms of design abacus; a rectangular doubly reinforced section is presented as example.

Key Words
reinforced concrete; serviceability limit state; stress control; analytical solution; design abacus.

Address
Helena F.M. Barros: Institute for Systems Engineering and Computers at Coimbra (INESC Coimbra), Department of Civil Engineering, Faculty of Sciences and Technology University of Coimbra, Portugal; Rogerio A.F. Martins: Engineering Faculty, Lusiada University, V N Famalicao, Portugal


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