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CONTENTS
Volume 15, Number 1, January 2015
 

Abstract
Many existing reinforced concrete (RC) columns in structures tend to become substandard RC ones due to updated standards or environmental changes. These substandard columns may alter the behaviors of the whole structure and therefore are in urgent need of seismic retrofitting. Owing to their superior advantages, carbon fiber reinforced polymer (CFRP) composites are widely used to retrofit RC columns. The applications mainly focus on various substandard RC columns, but few deals with substandard columns with deteriorated concrete, especially damaged by earthquake. The purpose of this paper is to investigate the seismic behaviors of CFRP reinforced partially deteriorated RC columns and to evaluate the effect of CFRP sheets on them. Six flexure-dominant columns were tested under a constant axial load and transverse cyclic displacements. It is found that the seismic behaviors of partially deteriorated columns can be recovered by wrapping CFRP sheets on them. Numerical analysis is then conducted using finite element methods and verified with experimental results. The effects of the axial load ratio, the ratio of the thickness of CFRP sheet to the column diameter, and the slenderness ratio on the seismic behaviors of CFRP reinforced RC columns are evaluated. Finally, a method is proposed to determine the required thickness of CFRP sheet.

Key Words
substandard RC column; partially deteriorated concrete; seismic behavior; CFRP sheet

Address
Dongxu Hou, Zhimin Wu and Yao Cui: State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology,No.2 Linggong Road, Ganjingzi District, Dalian City, The Peoples

Abstract
The objective of this study is to examine the effect of carbon fiber reinforced polymer (CFRP) on the shear strengths of deep beams with web openings. A total of 18 high-strength concrete deep beams with web openings were tested. Twelve were externally wrapped with four layers of CFRP, six of them strengthened in the horizontal direction and the others in the vertical direction. The parameters of the configuration of CFRP, the sizes of the openings and the locations of the openings were covered in this study. The test results indicates the shear strengths of deep beams with openings sized 60x40 mm were about 16% higher than that with openings sized 68X68 mm. For deep beams with openings sized 60x68 mm. For deep beams with openings sized 60x68 mm. For deep beams with openings sized 60x68 mm. For deep beams with openings sized 60x40 mm, the lower the locations of openings the higher the shear strengths were. The test results also indicate the shear strengths of deep beams with web openings strengthened by CFRP wrapped in the vertical direction can be enhanced by about 10%. However, the shear strengths of deep beams with web openings strengthened by CFRP wrapped in the horizontal direction can only be enhanced by about 6%. The shear strengths of deep beam, with different size and location of web openings and strengthened by different configuration of CFRP can be reasonably predicted by the empirical formulas of Kong and Sharp.

Key Words
deep beams; web openings; shear strengths; carbon fiber reinforced plastics (CFRP)

Address
Wen-Yao Lu, Chun-Liang Chen, Shen-Lung Liu and Ting-Chou Chen: Department of Interior Design, China University of Technology, Taipei 11695, Taiwan, R.O.C.

Hsin-Wan Yu: Department of Civil Engineering, China University of Technology, Taipei 11695, Taiwan, R.O.C.

Abstract
In general, cracks significantly deteriorate the in-situ performance of concrete members and structures, especially in urban metro tunnels that have been embedded in saturated soft soils. The microcapsule self-healing method is a newly developed healing method for repairing cracked concrete. To investigate the optimal microcapsule parameters that will have the best healing effect in concrete, a 3D analytical probability healing model is proposed; it is based on the microcapsule self-healing method\' s healing mechanism, and its purpose is to predict the healing efficiency and healing probability of given cracks. The proposed model comprehensively considers the radius and the volume fraction of microcapsules, the expected healing efficiency, the parameters of cracks, the broken ratio and the healing probability. Furthermore, a simplified probability healing model is proposed to facilitate the calculation. Then, a Monte Carlo test is conducted to verify the proposed 3D analytical probability healing model. Finally, the influences of microcapsules\' parameters on the healing efficiency and the healing probability of the microcapsule self-healing method are examined in light of the proposed probability model.

Key Words
self-healing; microcapsule; crack healing; 3D analytical probability healing model

Address
Hehua Zhu and Zhiguo Yan: State Key Laboratory for Disaster Reduction in Civil Engineering, Tongji University,1239 Siping Road, Shanghai 200092, China

Hehua Zhu, Shuai Zhou, Zhiguo Yan, Woody Ju and Qing Chen: Department of Geotechnical Engineering, Tongji University, 1239 Siping Road, Shanghai 200092, China

Hehua Zhu, Shuai Zhou, Zhiguo Yan and Qing Chen: Key Laboratory of Geotechnical and Underground Engineering of the Ministry of Education, Tongji University, 1239 Siping Road, Shanghai 200092, China

Shuai Zhou and Woody Ju: Department of Civil and Environmental Engineering, University of California, Los Angeles, CA 90095, USA

Abstract
This paper presents a novel harmony search (HS)-based data-driven single input rule modules (SIRMs)-connected fuzzy inference system (FIS) for the prediction of stress in externally prestressed tendon. The proposed method attempts to extract causal relationship of a system from an input-output pairs of data even without knowing the complete physical knowledge of the system. The monotonicity property is then exploited as an additional qualitative information to obtain a meaningful SIRMs-connected FIS model. This method is then validated using results from test data of the literature. Several parameters, such as initial tendon depth to beam ratio; deviators spacing to the initial tendon depth ratio; and distance of a concentrated load from the nearest support to the effective beam span are considered. A computer simulation for estimating the stress increase in externally prestressed tendon, is then reported. The contributions of this paper is two folds; (i) it contributes towards a new monotonicity-preserving data-driven FIS model in fuzzy modeling and (ii) it provides a novel solution for estimating the even without a complete physical knowledge of unbonded tendons.

Key Words
bond reduction coefficient; externally prestressed tendon stress; harmony search; monotonicity index; single input rule modules (SIRMs)-connected fuzzy inference system (FIS)

Address
See Hung Lau and Chee Khoon Ng: Department of Civil Engineering, Faculty of Engineering, Universiti Malaysia Sarawak, 94300 Kota, Samarahan, Sarawak, Malaysia

Kai Meng Tay: Department of Electronic Engineering, Faculty of Engineering, Universiti Malaysia Sarawak,
94300 Kota, Samarahan, Sarawak, Malaysia

Abstract
Following previous studies, the current paper describes the results of an experimental program concerning the repair of reinforced concrete columns by thixotropic pseudo plastic mortar, preformed to analyze and quantify the influence of initial construction damage to the behavior of the repaired element. Five columns (section scale 1:2) were designed according to the minimum requirements of reinforcement of ductility orientated codes\' design with variables the percentages of initial construction damages. All were tested in axial compression with repeated cycles up to failure. For comparison reasons, another one of the same characteristics, yet healthy, was constructed and tested as a reference specimen. A numerical study (Finite Element Analysis) was conducted for further investigation of the behavior of the thixotropic mortar as repair material. The results indicate that: a) surpassing a specific amount of damage, columns even suitably repaired present lower strain capacity, b) finite element analysis present the same way of deboning of the repaired material taking into consideration the buckling of the reinforcement bars.

Key Words
RC columns, construction damages, repair; fiber reinforced thixotropic mortar, finite element analysis

Address
Dimitra V. Achillopoulou, Konstantinia C. Arvanitidou
and Athanasios I. Karabinis: Civil engineering Department, Democritus University of Thrace, Vas. Sofias 12, 67100, Greece

Abstract
In this paper, Artificial Neural Networks (ANN) and Multiple Linear Regression (MLR) models were discussed to determine the compressive strength of clinker mortars cured for 1, 2, 7 and 28 days. In the experimental stage, 1288 mortar samples were produced from 322 different clinker specimens and compressive strength tests were performed on these samples. Chemical properties of the clinker samples were also determined. In the modeling stage, these experimental results were used to construct the models. In the models tricalcium silicate (C3S), dicalcium silicate (C2S), tricalcium aluminate (C3A), tetracalcium alumina ferrite (C4AF), blaine values, specific gravity and age of samples were used as inputs and the compressive strength of clinker samples was used as output. The approximate reasoning ability of the models compared using some statistical parameters. As a result, ANN has shown satisfying relation with experimental results and suggests an alternative approach to evaluate compressive strength estimation of clinker mortars using related inputs. Furthermore MLR model showed a poor ability to predict.

Key Words
clinker; prediction; compressive strength; artificial neural networks; multi linear regression

Address
Ahmet Beycioğlu, Mehmet Emiroğlu and Serkan Subaş

Abstract
Thermal effects are significant loads for assessing concrete dam behaviour during operation. A new methodology to estimate thermal loads on concrete dams taking into account processes which were previously unconsidered, such as: the evaporative cooling, the night radiating cooling or the shades, has been recently reported. The application of this novel approach in combination with a three-dimensional finite element method to solve the heat diffusion equation led to a precise characterization of the thermal field inside the dam. However, that approach may be computationally expensive. This paper proposes the use of a new one-dimensional model based on an explicit finite difference scheme which is improved by means of the reported methodology for computing the heat fluxes through the dam faces. The improved model has been applied to a case study where observations from 21 concrete thermometers and data of climatic variables were available. The results are compared with those from: (a) the original one-dimensional finite difference model, (b) the Stucky-Derron classical one-dimensional analytical solution, and (c) a three-dimensional finite element method. The results of the improved model match well with the observed temperatures, in addition they are similar to those obtained with (c) except in the vicinity of the abutments, although this later is a considerably more complex methodology. The improved model have a better performance than the models (a) and (b), whose results present larger error and bias when compared with the recorded data.

Key Words
thermal analysis; arch dam; finite element method; finite difference scheme

Address
D. Santillán, E. Salete, M.Á. Toledo and A. Granados: Technical University of Madrid, Department of Civil Engineering: Hydraulic and Energy Engineering C/Profesor Aranguren s/n, 28040 Madrid, Spain

Abstract
The process of chloride ingress in saturated concrete was presented by a previous study that used a mathematical model for the same as that concrete. This model is to be studied chloride ion diffusion which is considered as a chemical phenomenon and is to be represented the chloride diffusion process to be a nonlinear partial differential equation (PDE). In this paper, this nonlinear PDE is solved by the Kirchhoff transformation to render into a linear PDE. This linear PDE associated with initial and boundary conditions is also solved by the Laplace transformation to obtain an analytical solution. To verify the serviceability and reliability of this proposed method, the practical application should be supplied. The input parameters were cited from the previous study. The free chloride concentration profiles obtained by the analytical solution of mathematical model for saturated concretes after 24 and 120 hrs of exposure were compared with the previous study. The predicted results obtained from proposed method have a tendency with experimental results obtained by the previous study and trend toward numerical results approximated by finite difference technique.

Key Words
chloride concentration; chloride diffusion; chloride profile; mathematical model; saturated concrete; solution

Address
Wen-Hu Tsao and Nai-Ming Huang: Department of Civil Engineering, China University of Science and Technology, No. 245, Sec. 3,Academia Rd., Nangang Dist.,Taipei, Taiwan 11581, ROC


Ming-Te Liang: Department of Harbor and River Engineering, National Taiwan Ocean University, Keelung,
Taiwan 20224,ROC


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