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CONTENTS
Volume 16, Number 2, August 2015
 

Abstract
It is generally accepted that, in the interest of safety, it is essential to provide a minimum level of flexural ductility, which will allow energy dissipation and moment redistribution as required. If one wishes to be uniformly conservative across all of the design variables, curvature ductility and moment redistribution factor should be calculated using a probabilistic method, as is the case for other design parameters in reinforced concrete mechanics. In this study, simple expressions are derived for the evaluation of curvature ductility and moment redistribution factor, based on the concept of demand and capacity rotation. Probabilistic models are then derived for both the curvature ductility and the moment redistribution factor, by means of central limit theorem and through taking advantage of the specific behaviour of moment redistribution factor as a function of curvature ductility and plastic hinge length. The Monte Carlo Simulation (MCS) method is used to check and verify the results of the proposed method. Although some minor simplifications are made in the proposed method, there is a very good agreement between the MCS and the proposed method. The proposed method could be used in any future probabilistic evaluation of curvature ductility and moment redistribution factors.

Key Words
RC beams; curvature ductility; moment redistribution; reliability; monte carlo simulation

Address
Hassan Baji and Hamid Reza Ronagh : School of Civil Engineering, The University of Queensland, Australia

Abstract
This paper presents results of biaxial compressive tests and strength criterion on two replacement percentages of recycled coarse aggregate (RPRCA) by mass for plain structural recycled aggregate concrete (RAC) at all kinds of stress ratios. The failure mode characteristic of specimens and the direction of the cracks were observed and described. The two principally static strengths in the corresponding stress state were measured. The influence of the stress ratios on the biaxial strengths of RAC was also analyzed. The experimental results showed that the ratios of the biaxial compressive strength 3f to the corresponding uniaxial compressive strength for the two RAC are higher than that of the conventional concrete (CC), and dependent on the replacement percentages of recycled coarse aggregate, stress states and stress ratios; however, the differences of tensile-compressive ratios for the two RAC and CC are smaller. On this basis, a new failure criterion with the stress ratios is proposed for plain RAC under biaxial compressive stress states. It provides the experimental and theoretical foundations for strength analysis of RAC structures subject to complex loads.

Key Words
recycled aggregate concrete (RAC); replacement percentages of recycled coarse aggregate by mass; stress ratios; biaxial compressive strengths; failure criterion

Address
Zhen-Jun He, Gan-Wen Liu,Chang-Yang Zhou and Zhang Jia-Xing : College of Civil Engineering, North China University of Technology, Beijing 100144, PR China
Zhen-Jun He and Wan-Lin Cao : College of Architecture and Civil Engineering, Beijing University of Technology,Beijing 100022, PR China

Abstract
Self-compacting concrete (SCC) can be placed and compacted under its own weight with little or no compaction. It is cohesive enough to be handled without segregation or bleeding. Modifications in the mix design of SCC may significantly influence the material\'s mechanical properties. Therefore, it is vital to investigate whether all the assumed hypotheses about conventional concrete (CC) are also valid for SCC structures. The aim in this paper is to develop analytical models for flexural cracking that describe in appropriate detail the observed cracking behaviour of the reinforced concrete flexural one way slabs tested. The crack width and crack spacing calculation procedures outlined in five international codes, namely Eurocode 2 (1991), CEB-FIP (1990), ACI318-99 (1999), Eurocode 2 (2004), and fib-Model Code (2010), are presented and crack widths and crack spacing are accordingly calculated. Then, the results are compared with the proposed analytical models and the measured experimental values, and discussed in detail.

Key Words
self-compacting concrete; crack width; crack spacing; flexural cracking; time-dependent cracking; analytical models

Address
Farhad Aslani : Centre for Infrastructure Engineering and Safety, School of Civil and Environmental Engineering, University of New South Wales, Australia
Shami Nejadi : School of Civil and Environmental Engineering, University of Technology Sydney, Australia
Bijan Samali : Institute for Infrastructure Engineering, University of Western Sydney, Australia

Abstract
In this study, nominal moment-axial load interaction diagrams, moment-curvature relationships, and ductility of rectangular hybrid beam-column concrete sections are analyzed using the modified Hognestad concrete model. The hybrid columns are primarily reinforced with steel bars with additional Glass Fiber Reinforced Polymer (GFRP) control bars. Parameters investigated include amount, pattern, location, and material properties of concrete, steel, and GFRP. The study was implemented using a user defined comprehensive MATLAB simulation model to find an efficient hybrid section design maximizing strength and ductility. Generating lower bond stresses than steel bars at the concrete interface, auxiliary GFRP bars minimize damage in the concrete core of beam-column sections. Their usage prevents excessive yielding of the core longitudinal bars during frequent moderate cyclic deformations, which leads to significant damage in the foundations of bridges or beam-column spliced sections where repair is difficult and expensive. Analytical results from this study shows that hybrid steel-GFRP composite concrete sections where GFRP is used as auxiliary bars show adequate ductility with a significant increase in strength. Results also compare different design parameters reaching a number of design recommendations for the proposed hybrid section.

Key Words
beam-column; GFRP; interaction diagram; ductility; moment-curvature

Address
Rafic G. El-Helou and Riyad S. Aboutaha : Civil and Environmental Engineering, Syracuse University, Syracuse, New York, USA

Abstract
This study established the standard recommended values and expansion fracture threshold values for the content of steel slag in controlled low-strength materials (CLSM) to ensure the appropriate use of steel slag aggregates and the prevention of abnormal expansion. The steel slags used in this study included basic oxygen furnace (BOF) slag and desulfurization slag (DS), which replaced 5-50% of natural river sand by weight in cement mixtures. The steel slag mortars were tested by high-temperature (100 celcius) curing for 96 h and autoclave expansion. The results showed that the effects of the steel slag content varied based on the free lime (f-CaO) content. No more than 30% of the natural river sand should be replaced with steel slag to avoid fracture failure. The expansion fracture threshold value was 0.10%, above which there was a risk of potential failure. Based on the scanning electron microscopy (SEM) analysis, the high-temperature catalysis resulted in the immediate extrusion of peripheral hydration products from the calcium hydroxide crystals, leading to a local stress concentration and, eventually, deformation and cracking.

Key Words
high-temperature catalysis; basic oxygen furnace slag; desulfurization slag; controlled low-strength materials; volume stability behavior

Address
Wen-Ten Kuo and Chun-Ya Shu : Department of Civil Engineering, National Kaohsiung University of Applied Sciences, No. 415,
Chien-Kung Rd., Sanmin District, Kaohsiung 80778, Taiwan, R.O.C.

Abstract
This paper reports the results of an experimental study on the compressive strength and the stress-strain curve (SSC) of recycled fine glass aggregate concrete with different replacement percentages of recycled fine glass aggregate. The results show that the recycled fine glass aggregate contents have significant impact on the workability, compressive strength, the elastic modulus, the peak and the ultimate strains of recycled fine glass aggregate concrete. Analytical expressions for the stress–strain relationship of recycled fine glass aggregate concrete are given, which can satisfactorily describe the effect of the recycled fine glass aggregate on the SSC.

Key Words
recycled fine glass aggregate; concrete; mechanical properties; stress-strain curve; uniaxial loading

Address
Jiong-Feng Liang, Ze-Ping Yang, Ping-Hua Yi and Jian-Bao Wang : College of Architecture Engineering, East China Institute of Technology, Nanchang 330013, China
Jiong-Feng Liang : Guangxi Key Laboratory of Disaster Prevention and Structural Safety, Guangxi University,
Nanning 530004, China

Abstract
FormWorks-Plus is a generalized public domain user-friendly preprocessor developed to facilitate the process of creating finite element models for structural analysis programs. The lack of a graphical user interface in most academic analysis programs forces users to input the structural model information into the standard text files, which is a time-consuming and error-prone process. FormWorks-Plus enables engineers to conveniently set up the finite element model in a graphical environment, eliminating the problems associated with conventional input text files and improving the user\'s perception of the application. In this paper, a brief overview of the FormWorks-Plus structure is presented, followed by a detailed explanation of the main features of the program. In addition, demonstration is made of the application of FormWorks-Plus in combination with VecTor programs, advanced nonlinear analysis tools for reinforced concrete structures. Finally, aspects relating to the modelling and analysis of three case studies are discussed: a reinforced concrete beam-column joint, a steel-concrete composite shear wall, and a SFRC shear panel. The unique mixed-type frame-membrane modelling procedure implemented in FormWorks-Plus can address the limitations associated with most frame type analyses.

Key Words
graphical user interface; finite element method; computer aided simulation; computer applications; structural models; nonlinear analysis

Address
Vahid Sadeghian and Frank Vecchio : Department of Civil Engineering, University of Toronto, 35 St. George St.,
Toronto, ON, Canada M5S 1A4

Abstract
Employing discrete elements for considering bond-slip effects in reinforced concrete structures is very time consuming. In this study, a new modified embedded element method is used to consider the bond-slip phenomenon in structural behavior of reinforced concrete structures. A comprehensive parametric study of RC slabs is performed to determine influence of different variables on structural behavior. The parametric study includes a set of simple models accompanied with complex models such as multi-storey buildings. The procedure includes the decrease in the effective stiffness of steel bar in the layered model. Validation of the proposed model with existing experimental results demonstrates that the model is capable of considering the bond-slip effects in embedded elements. Results demonstrate the significant effect of bond-slip on total behavior of structural members. Concrete characteristic strengths, steel yield stress, bar diameter, concrete coverage and reinforcement ratios are the parameters considered in the parametric study. Results revealed that the overall behavior of slab is significantly affected by bar diameter compared with other parameters. Variation of steel yield stress has insignificant impact in static response of RC slabs; however, its effect in cyclic behavior is important.

Key Words
modified embedded element; RC slab; parametric study; static loading; cyclic loading

Address
S.S. Mousavi and M. Dehestani : Faculty of Civil Engineering, Babol Noshirvani University of Technology, Babol, Iran

Abstract
The present paper aims at developing a method to accommodate multi-surface concrete plasticity from the point of view of a consistency concept applied to general tangent operators. The idea is based on a Taylor series expansion of the actual effective stress at the stress point corresponding to the previous accumulated true stresses plus the current increment values, initially taken to be elastic. The proposed algorithm can be generalized for any multi-surface criteria combination and has been tested here for typical cement-based materials. A few examples of application are presented to demonstrate the effectiveness of the multi-surface technique as used to a combination of Rankine and Drucker-Prager yield criteria.

Key Words
finite element method; multi-surface plasticity; tangent operators; cement-based materials; concrete

Address
Ana Beatriz C.G. Silva, Jose Claudio F. Telles,
Eduardo M.R. Fairbairn and Fernando Luiz B. Ribeiro : Laboratory of Structures and Materials, Civil Engineering Programme, Federal University of Rio de
Janeiro, Centro de Tecnologia, Ilha do Fundão, CEP 21945-970, Rio de Janeiro, Brazil

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