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CONTENTS
Volume 9, Number 3, February 2012
 

Abstract
This paper presents numerical studies of stiff fiber pullout behaviors of fiber reinforced cementitious composites based on a progressive damage model. The ongoing debonding process is simulated. Interfacial stress distribution for different load levels is analyzed. A parametric study, including bond strength and the homogeneity index on the pullout behaviors is carried out. The numerical results indicate that the bond stress decreases gradually from loaded end to embedded end along fiber-cement interface. The debonding initially starts from loaded end and propagates to embedded end as load increasing. The embedded length and bond strength affect the load-loaded end displacement curves significantly. The numerical results have a general agreement with the experimental investigation.

Key Words
pullout behavior; fiber reinforced composites; debonding; damage; numerical simulation.

Address
Xu Chang, Ya-Juan Chen, Hai-Xiao Lin: College of Civil Engineering, Henan Polytechnic University, Jiaozuo City, Henan Province, 454000, People

Abstract
The hydration of cement contributes to the performance characteristics of concrete, such as strength and durability. In order to improve the utilization efficiency of cement and its early properties, the particle size distribution (PSD) of cement varies considerably, and the effects of the particle size distribution of cement on the hydration process should be considered. In order to evaluate effects of PSD separately, experiments testing the isothermal heat generated during the hydration of cements with different particle size distributions but the same chemical composition have been carried out. The measurable hydration depth for cement hydration was proposed and deduced based on the experimental results, and a PSD hydration model was developed in this paper for simulating the effects of particle size distribution on the hydration process of cement. First, a reference hydration rate was derived from the isothermal heat generated by the hydration of ordinary Portland cement. Then, the model was extended to take into account the effect of water-to-cement ratio, hereinafter which was referred to as PSD hydration model. Finally, the PSD hydration model was applied to simulate experiments measuring the isothermal heat generated by the hydration of cement with different particle size distributions at different water-to-cement ratios. This showed that the PSD hydration model had simulated the effects of particle size distribution and water-to-cement ratio on the hydration process of cement with satisfactory accuracy.

Key Words
PSD hydration model; particle size distribution; measurable hydration depth; reference hydration rate; isothermal hydration heat generation.

Address
Changjiu Chen and Xuehui An: State Key Laboratory of Hydro science and Engineering, Tsinghua University, 100084 Beijing, China

Abstract
This paper presents the investigation of the stochastic responses of seismically isolated bridges subjected to spatially varying earthquake ground motions including incoherence, wave-passage and site-response effects. The incoherence effect is examined by considering Harichandran and Vanmarcke coherency model. The effect of the wave-passage is dealt with various wave velocities in the response analysis. Homogeneous firm, medium and soft soil conditions are selected for considering the siteresponse effect where the bridge supports are constructed. The ground motion is described by filtered white noise and applied to each support points. For seismic isolation of the bridge, single and double concave friction pendulum bearings are used. Due to presence of friction on the concave surfaces of the isolation systems, the equation of motion of is non-linear. The non-linear equation of motion is solved by using equivalent linearization technique of non-linear stochastic analyses. Solutions obtained from the stochastic analyses of non-isolated and isolated bridges to spatially varying earthquake ground motions compared with each other for the special cases of the ground motion model. It is concluded that friction pendulum systems having single and double concave surfaces have important effects on the stochastic responses of bridges to spatially varying earthquake ground motions.

Key Words
seismic isolation; highway bridge; spatially varying ground motions; stochastic analysis; equivalent linearization technique.

Address
Sevket Ates: Department of Civil Engineering, Karadeniz Technical University, Trabzon, 61080, Turkey

Abstract
This article employs Support Vector Machine (SVM) for determination of fracture parameters critical stress intensity factor (Ksic) and the critical crack tip opening displacement (CTODc) of concrete. SVM that is firmly based on the theory of statistical learning theory, uses regression technique by introducing

Key Words
concrete; fracture mechanics; support vector machine; sensitivity analysis; artificial neural network; two-parameter model.

Address
Pijush Samui: Centre for Disaster Mitigation and Management. VIT University, Vellore-632014, Tamilnadu, India

Dookie Kim: Department of Civil Engineering, Kunsan National University, Kunsan, Jeonbuk, South Korea

Abstract
A theoretical model for shear strength evaluation of fibrous concrete beams reinforced with stirrups is proposed. The formulation is founded on the theory of plasticity and the stress field concepts, generalizing a known plastic model for calculating the bearing capacity of reinforced concrete beams, to the case of fibrous concrete. The beneficial effect of steel fibres is estimated taking into account the residual tensile strength of fibrous concrete, by modifying an analytical constitutive law which presents a plastic plateau as a post-peak branch. Around fifty results of experimental tests carried out on steel fibrous concrete beams available in the literature were collected, and a comparison of shear strength estimation provided by other semi-empirical models is performed, proving that the numerical values obtained with the proposed model are in very good agreement with the experimental results.

Key Words
eurocode 2; shear; steel fibre reinforced concrete; stirrup; design.

Address
Piero Colajanni, Antonino Recupero and Nino Spinella: Department of Civil Engineering, University of Messina, Messina, Italy


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