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CONTENTS
Volume 17, Number 4, April 2016
 

Abstract
The main purpose of this study is to perform optimum cost design of cut and cover RC shallow tunnels using Artificial bee colony and genetic algorithms. For this purpose, mathematical expressions of objective function, design variables and constraints for the design of cut and cover RC shallow tunnels were determined. By using these expressions, optimum cost design of the Trabzon Kalekap

Key Words
optimization; shallow tunnels; genetic algorithm; artificial bee colony algorithm

Address
Hasan Tahsin Öztürk: Karadeniz Technical University, Faculty of Technology, Department of Civil Engineering, Trabzon, Turkey
Erdem Türkeli: Provincial Organization of Ministry of Environment and Urbanization, Ordu, Turkey
Ahmet Durmuş: Nuh Naci Yazgan University, Faculty of Engineering, Department of Civil Engineering, Kayseri, Turkey

Abstract
Dynamic characteristics, named as natural frequencies, damping ratios and mode shapes, affect the dynamic behavior of buildings and they vary depending on the construction stages. It is aimed to present the effects of construction stages on the dynamic characteristics of reinforced concrete (RC) buildings considering theoretical and experimental investigations. For this purpose, a three-storey RC building model with a 1/2 scale was constructed in the laboratory of Civil Engineering Department at Karadeniz Technical University. The modal testing measurements were performed by using Operational Modal Analysis (OMA) method for the bare frame, brick walled and coated cases of the building model. Randomly generated loads by impact hammer were used to vibrate the building model; the responses were measured by uni-axial seismic accelerometers as acceleration. The building

Key Words
construction stages; dynamic characteristics; finite element analysis; modal testing; operational modal analysis; reinforced concrete building

Address
Temel Türker and Alemdar Bayraktar: Karadeniz Technical University, Department of Civil Engineering, 61080, Trabzon,TURKEY

Abstract
This paper aims to model the effects of five different variables which includes: cement content (C), the steel fiber amount (F), the silica fume amount (SF), the superplasticizer (SP), the silica fume amount (SF), and the water to cementitious ratio (w/c) on 28 days flexural toughness of Ultra High Performance Concrete (UHPC) as well as, a study on the variable interactions and correlations by using analyze of variance (ANOVA) and response surface methodology (RSM). The variables were compared by fine aggregate mass. The model will be valid for the mixes with 0.18 to 0.32 w/c ratio, 4 to 8 percent steel fiber, 7 to 13 percent cement, 15 to 30 percent silica fume, and 4 to 8 percent superplasticizer by fine aggregate mass.

Key Words
ultra high performance concrete; response surface method; flexural toughness; central composite methodology

Address
Mohammad A. Mosabepranah and Ozgur Eren: Department of Civil Engineering, Eastern Mediterranean University (EMU), Famagusta, Cyprus

Abstract
In this paper, the flexural strength (ffs) and splitting tensile strength (fsts) of concrete containing different proportions of fly ash have been modeled by using gene expression programming (GEP). Two GEP models called GEP-I and GEP-II are constituted to predict the ffs and fsts values, respectively. In these models, the age of specimen, cement, water, sand, aggregate, superplasticizer and fly ash are used as independent input parameters. GEP-I model is constructed by 292 experimental data and trisected into 170, 86 and 36 data for training, testing and validating sets, respectively. Similarly, GEP-II model is constructed by 278 experimental data and trisected into 142, 70 and 66 data for training, testing and validating sets, respectively. The experimental data used in the validating set of these models are independent from the training and testing sets. The results of the statistical parameters obtained from the models indicate that the proposed empirical models have good prediction and generalization capability.

Key Words
flexural strength; splitting tensile strength; fly ash; genetic programming

Address
Mustafa Saridemir: Department of Civil Engineering, Niğde University, 51240 Niğde, Turkey

Abstract
In this paper, a probabilistic- and finite element-based approach to evaluate and predict the lifetime performance of reinforced concrete (RC) bridges undergoing various maintenance actions is proposed with the time-variant system reliability being utilized as a performance indicator. Depending on their structural state during the degradation process, the classical maintenance actions for RC bridges are firstly categorized into four types: Preventive type I, Preventive type II, Strengthening and Replacement. Preventive type I is used to delay the onset of steel corrosion, Preventive type II can suppress the corrosion process of reinforcing steel, Strengthening is the application of various maintenance materials to improve the structural performance and Replacement is performed to restore the individual components or overall structure to their original conditions. The quantitative influence of these maintenance types on structural performance is investigated and the respective analysis modules are written and inputted into the computer program. Accordingly, the time-variant system reliability can be calculated by the use of Monte Carlo simulations and the updated the program. Finally, an existing RC continuous bridge located in Shanghai, China, is used as an illustrative example and the lifetime structural performance with and without each of the maintenance types are discussed. It is felt that the proposed approach can be applied to various RC bridges with different structural configurations, construction methods and environmental conditions.

Key Words
RC bridges; lifetime performance; degradation process; maintenance actions; time-variant system reliability; finite element;Monte Carlo simulations

Address
Hao Tian: 1Zhejiang Scientific Research Institute of Transport, Hangzhou 310006, China

Fangyuan Li: Department of Bridge Engineering, College of Civil Engineering, Tongji University, Shanghai 200092, China

Abstract
Alkali-activated binder (AAB) is increasingly being considered as an eco-friendly and sustainable alternative to portland cement (PC). The present study evaluates 30 different AAB mixtures containing fly ash and/or slag activated by sodium hydroxide and sodium silicate by correlating their properties from micro to specimen level using regression. A model is developed to predict compressive strength of AAB as a function of volume fractions of microstructural phases (physicochemical properties) and ultrasonic pulse velocity (elastic properties and density). The predicted models are ranked and then compared with the experimental data. The correlations were found to be quite reasonable (R2 = 0.89) for all the mixtures tested and can be used to estimate the compressive strengths for similarAAB mixtures.

Key Words
alkali-activated binder; compressive strength; prediction model

Address
Arkamitra Kar: Department of Civil Engineering, Birla Institute of Technology and Science-Pilani,Hyderabad - 500078, Telangana, India
Indrajit Ray: Department of Civil and Environmental Engineering, Faculty of Engineering, The University of theWest Indies, St Augustine, Trinidad and Tobago
Avinash Unnikrishnan: Department of Civil and Environmental Engineering, Portland State University, Portland, OR 97201, USA
Udaya B. Halabe: Department of Civil and Environmental Engineering, West Virginia University, Morgantown,WV 26506, USA

Abstract
Asphalt pavements are exposed to complex weather conditions and vehicle traffic loads leading to crack initiation and crack propagation in asphalt pavements. This paper presents the impact of weather conditions on fracture toughness of an asphalt concrete, prevalently employed in Ardabil road networks, under tensile (mode I) and shear (mode II) loading. An improved semi-circular bend (SCB) specimen was employed to carry out the fracture experiments. These experiments were performed in two different weather conditions namely fixed and cyclic temperatures. The results showed that consideration of the impact of temperature cycling resulted in decreasing the fracture toughness of asphalt concrete significantly. Furthermore, the fracture toughness was highly affected by loading mode for the both fixed and cyclic temperature conditions studied in this paper. In addition, it was found that the MTS criterion correctly predicts the onset of fracture initiation although this prediction was slightly conservative.

Key Words
fracture toughness; SCB specimen; weather conditions; asphalt concrete; low temperature

Address
Sadjad Pirmohammad and Ahad Kiani: Department of Mechanical Engineering, Faculty of Engineering, University of Mohaghegh Ardabili, Ardabil, Iran

Abstract
Fracture energy is one of the key parameters reveal cracking resistance and fracture toughness of concrete. The main purpose of this study is to determine fracture behavior, mechanical properties and microstructural analysis of high strength basalt fiber reinforced concrete (HSFRC). For this purpose, threepoint bending tests were performed on notched beams produced using HSFRCs with 12mm and 24mm fiber length and 1, 2 and 3 kg/m

Key Words
basalt fiber, high strength concrete, mechanical properties, fracture energy, microstructure

Address
Mehmet E. Arslan: Department of Civil Engineering, Technology Faculty Düzce University, 81620, Turkey


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