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CONTENTS
Volume 13, Number 4, April 2014
 

Abstract
Ground Granulated Blast Furnace Slag (GGBFS) is widely used as an effective partial cement replacement material. GGBFS inclusion has already been proven to improve several performance characteristics of concrete. GGBFS provides enhanced durability, including high resistance to chloride penetration and protection against alkali silica reaction. In this paper results of an experimental research work on influence of low-reactivity GGBFS (which is largely available in Iran) on the properties of mortars and concretes are reported. In the first stage, influence of GGBFS replacement level and fineness on the compressive strength of mortars was investigated using Taguchi method. The analysis of mean (ANOM) statistical approach was also adopted to develop the optimal conditions. Next, based on the obtained results, concrete mixtures were designed and water penetration, capillary absorption, surface resistivity, and compressive strength tests were carried out on high-strength concrete specimens at different ages up to 90 days. The results indicated that 7-day compressive strength is adversely affected by GGBFS inclusion, while the negative effect is less evident at later ages. Also, it was inferred that use of low-reactivity GGBFS (at moderate levels such as 20% and 30%) can enhance the impermeability of high-strength concrete since 28 days age.

Key Words
GGBFS; high-strength concrete; Taguchi method; mortar; permeability

Address
A. A. Ramezanianpour and A. Kazemian: Concrete Technology and Durability Research Center (CTDRC), Amirkabir University of Technology, Tehran, Iran

A. Kazemian E. Radaei and M.A. Moghaddam: Department of Civil Engineering, Amirkabir University of Technology, Tehran, Iran

H. AzariJafari: Civil Engineering Department, Tabari Institute of Higher Education, Babol, Iran

Abstract
This work incorporates newly introduced Lattice Discrete Particle Model (LDPM) to assess the failure mechanism and strength of hollow concrete blocks. Alongside, a method for the graphical representation of cracked surfaces in the LDPM is outlined. A slightly modified calibration procedure is also suggested and used to estimate required model parameters for a tested concrete sample. Next, the model is verified for a compressively loaded hollow block made of the very same concrete. Finally, four geometries commonly used in the production of hollow concrete blocks are selected, numerically simulated, and their failure properties are explored under concentric and eccentric compressions.

Key Words
concrete block; failure; lattice discrete particle model; graphical representation; calibration

Address
Fatemeh Javidan, Sharif Shahbeyk and Mohammad Safarnejad: Faculty of Civil and Environmental Engineering, Tarbiat Modares University, Jalal Ale Ahmad Highway,
P.O. Box 14115-143, Tehran, Iran


Abstract
This paper summarizes available literature on the optimization of reinforced concrete (RC) beams. The objective of optimization (e.g. minimum cost or weight), the design variables and the constraints considered by different studies vary widely and therefore, different optimization methods have been employed to provide the optimal design of RC beams, whether as isolated structural components or as part of a structural frame. The review of literature suggests that nonlinear deterministic approaches can be efficiently employed to provide optimal design of RC beams, given the small number of variables. This paper also presents spreadsheet implementation of cost optimization of RC beams in the familiar MS Excel environment to illustrate the efficiency of the exhaustive enumeration method for such small discrete search spaces and to promote its use by engineers and researchers. Furthermore, a sensitivity analysis is performed on the contribution of various design parameters to the variability of the overall cost of RC beams.

Key Words
reinforced concrete beam; optimization; discrete search space; exhaustive enumeration; genetic algorithm; spreadsheet implementation; sensitivity analysis

Address
Ima Rahmanian and Solomon Tesfamariam: School of Engineering, The University of British Columbia, Kelowna, BC, Canada

Yves Lucet: Computer Science, The University of British Columbia, Kelowna, BC, Canada

Abstract
Most of the methods presented in the literature to define the target service stresses (Objective Service Stage, OSS) of cable-stayed bridges rarely include the time-dependent phenomena effects. Nevertheless, especially in concrete structures, this assumption might be on the unsafe side because time-dependent phenomena usually modify service stresses. To fill this gap, this paper studies the time-dependent phenomena effects into service stresses of concrete cable-stayed bridges. After illustrating the important role of these phenomena in an asymmetrical cable-stayed bridge without backstay, a new method to include their effects into the OSS is presented. An important issue to be considered in this method is the target time in which the OSS is defined to be achieved. The application of this method to two different structures showed the convenience of defining the OSS to be achieved at early times because that way the envelope of service stresses is reduced.

Key Words
cable-stayed bridge; time-dependent phenomena; creep; shrinkage; concrete; service stresses

Address
Jose Antonio Lozano-Galant: Department of Civil Engineering, University of Castilla-La Mancha, Spain

Jose Turmo: Department of Construction Engineering, Universitat Politècnica de Catalunya, BarcelonaTech, Spain

Abstract
The purpose of this study was to investigate the performance of precast concrete pier cap system. The proposed precast pier cap provides an alternative to current cast-in-place systems, particularly for projects in which a reduced construction time is desired. Five large-scale pier cap specimens were constructed and tested under quasistatic monotonic loading. The computer program, RCAHEST (Reinforced Concrete Analysis in Higher Evaluation System Technology) was used for the analysis of reinforced concrete structures. A bonded tendon element is used based on the finite element method, and can represent the interaction between the tendon and concrete of a prestressed concrete member. A joint element is used in order to predict the inelastic behaviors of segmental joints with a shear key. This study documents the testing of the precast concrete pier cap system under monotonic loading and presents conclusions and design recommendations based on the experimental and analytical findings. Additional full-scale experimental research is needed to refine and confirm design details, especially for actual detailing employed in the field.

Key Words
performance; precast concrete pier cap; construction time; quasistatic; computer program

Address
T.H. Kim: Construction Product Technology Team, Samsung Construction & Trading Corporation, 5th Fl., Daerung Gangnam Tower, 826-20 Yeoksam1-dong, Gangnam-gu, Seoul 135-935, Korea

Y.J. Kim: Civil Engineering Research Team, Daewoo Institute of Construction Technology, 60 Songjuk-dong, Jangan-gu, Suwon-si, Gyeonggi-do, 440-210, Korea

H.M. Shin: School of Civil and Architectural Engineering, Sungkyunkwan University, 300 Cheoncheon-dong, Jangan-gu, Suwon-si, Gyeonggi-do, 440-746, Korea

Abstract
In order to increase the load carrying capacity and/or increase the service life of existing circular reinforced concrete bridge columns, Carbon Fiber Reinforced Polymer (CFRP) composites could be utilized. Transverse wrapping of circular concrete columns with CFRP sheets increases its axial and shear strengths. In addition, it provides good confinement to the concrete column core, which enhances the bending and compressive strength, as well as, ductility. Several experimental and analytical studies have been conducted on CFRP strengthened concrete cylinders/columns. However, there seem to be lack of thorough investigation of the effect of elevated temperatures on the response of CFRP strengthened circular concrete columns. A concrete confinement model that reflects the effects of elevated temperature on the mechanical properties of CFRP composites, and the efficiency of CFRP in strengthened concrete columns is presented. Tensile strength and modulus of CFRP under hot conditions and their effects on the concrete confinement are the primary parameters that were investigated. A modified concrete confinement model is developed and presented.

Key Words
CFRP; circular concrete column; confinement; elevated temperature and humidity

Address
Raizal S.M. Rashid: Department of Civil Engineering, Universiti Putra Malaysia, 43000 Serdang, Selangor Malaysia

Riyad S. Aboutaha: L.C. Smith College of Engineering and Computer Science, 151 Link Hall, Syracuse NY 13244, USA

Abstract
The purpose of this paper is to develop a prediction model for the compressive strength of waste LCD glass applied in concrete by analyzing a series of laboratory test results, which were obtained in our previous study. The hyperbolic function was used to perform the nonlinear-multivariate regression analysis of the compressive strength prediction model with the following parameters: water-binder ratio w/b, curing age t, and waste glass content G. According to the relative regression analysis, the compressive strength prediction model is developed. The calculated results are in accord with the laboratory measured data, which are the concrete compressive strengths of different mix proportions. In addition, a coefficient of determination R2 value between 0.93 and 0.96 and a mean absolute percentage error MAPE between 5.4% and 8.4% were obtained by regression analysis using the predicted compressive analysis value, and the test results are also excellent. Therefore, the predicted results for compressive strength are highly accurate for waste LCD glass applied in concrete. Additionally, this predicted model exhibits a good predictive capacity when employed to calculate the compressive strength of washed glass sand concrete.

Key Words
compressive strength; concrete; prediction model; waste glass; regression

Address
C.C. Wang: Department of Civil Engineering and Geomatics, Cheng Shiu University, Kaohsiung, 833, Taiwan

T.T Chen: Departments of Civil Engineering and Engineering Management, National Quemoy University, 892, Taiwan


H.Y. Wang and Chi Huang: Department of Civil Engineering, National Kaohsiung University of Applied Sciences, Kaohsiung, 807, Taiwan, R.O.C






Abstract
Precast Seismic Structural Systems (PRESSS) provided an iterative procedure for obtaining optimum design of unbonded post-tensioned coupled precast concrete wall systems. Although PRESSS procedure is effective, however, it is lengthy and laborious. The purpose of this research is to employ Artificial Neural Network (ANN) to predict the optimum design parameters for such wall systems while avoiding the demanding iterative process. The developed ANN model is very accurate in predicting the non-dimensional optimum design parameters related to post-tensioning reinforcement area, yield force of shear connectors and ratio of moment resisted by shear connectors to the design moment. The Mean Absolute Percent Error (MAPE) for the test data for these design parameters is around %1 and the correlation coefficient is almost equal to 1.0. The developed ANN model is then used to study the effect of different design parameters on wall behavior. It is observed that the design moment and the concrete strength have the most influence on the wall behavior as compared to other parameters. Several design examples were presented to demonstrate the accuracy and effectiveness of the ANN model.

Key Words
seismic design; precast concrete wall; unbonded post-tensioned; neural network; PRESSS

Address
Jamal A. Abdalla and Rami A. Hawileh: Department of Civil Engineering, American University of Sharjah, UAE

Elias I. Saqan: Department of Civil Engineering, American University in Dubai, UAE


Abstract
In this paper, a four-layer road structure consisting of an edge transverse crack is simulated using three-dimensional finite element method in order to capture the influence of a single-axle wheel load on the crack propagation through the asphalt concrete layer. Different positions of the vehicular load relative to the cracked area are considered in the analyses. Linear elastic fracture mechanics (LEFM) is used for investigating the effect of the traffic load on the behavior of a crack propagating within the asphalt concrete. The results obtained show that the crack front experiences all three modes of deformation i.e. mode I, mode II and mode III, and the corresponding stress intensity factors are highly affected by the crack geometry and the vehicle position. The results also show that for many loading situations, the contribution of shear deformation (due to mode II and mode III loading) is considerable.

Key Words
edge transverse crack; 3D finite element modeling; stress intensity factor; asphalt concrete; traffic load

Address
Majid R. Ayatollahi, Sadjad Pirmohammad and Karo Sedighiani: Fatigue and Fracture Laboratory, Center of Excellence in Experimental Solid Mechanics and Dynamics, School of Mechanical Engineering, Iran University of Science and Technology, Narmak, Tehran, 16846, Iran


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