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CONTENTS
Volume 20, Number 3, September 2017
 

Abstract
This study aims to develop a signal processing scheme to accurately predict the thickness of concrete slab using air-coupled impact-echo. Air-coupled impact-echo has been applied to concrete non-destructive tests (NDT); however, it is often difficult to obtain thickness mode frequency due to noise components. Furthermore, apparent velocity in concrete is a usually unknown parameter in the field and the thickness of the concrete slab often cannot be accurately measured. This study proposes a signal processing scheme using guided wave analysis, wherein dispersion curves are drawn in both frequency-wave number (f-k) and phase velocity-frequency (V_cp-f) domains. The theoretical and experimental results demonstrate that thickness mode frequency and apparent velocity in concrete are clearly obtained from the f-k and V_cp-f domains, respectively. The proposed method has great potential with regard to the application of air-coupled impact-echo in the field.

Key Words
concrete; concrete technology; non-destructive tests (NDT); structural health monitoring (SHM); structural safety

Address
Hajin Choi and Hoda Azari: Federal Highway Administration, 6300 Georgetown Pike, McLean, Virginia, 22101, USA

Abstract
An experimental investigation is carried out on the failure mechanism of foam concrete with cold formed steel double C-Channels embedment. The foam concrete is made of cement and fly ash with a compressive strength between 9 and 24 MPa with different densities. Forty-eight tests have been carried out in four groups of specimens with various embedment depths of the steel in the concrete. Four modes of failure are observed, which include the independent failure of the C-Channels with and without a concrete block inside the channel as well as the combined failure of the two channels, and the failure of the extrusion block. A theoretical model has been developed to understand the failure process. The peak compressive force applied onto the C-Channels that causes failure is calculated. It is concluded that the failure involves independent slippage between two C-Channels, and the steel and the foam concrete blocks inside the C-Channels. A method to calculate the peak force is also developed based on the test results. The calculations also show that the shear strength of the foam concrete is about 8% of the compressive strength with a coefficient of 0.4 between the steel and concrete.

Key Words
bond-slip; C-Channel; cold formed steel; foam concrete; fly ash

Address
Dianzhong Liu and Fayu Wang: School of Civil Engineering, Jilin Jianzhu University, No.5088 Xincheng Avenue, Jingyue Economic Development Zone, Changchun, Jilin, CN 130118, People

Abstract
Grouting is an operation often carried out to consolidate and seal the rock mass in dam sites and tunnels. One of the important parameters in this operation is grouting pressure. In this paper, analytical models used to estimate pressure are investigated. To validate these models, grouting data obtained from Seymareh and Aghbolagh dams were used. Calculations showed that P-3 model from Groundy and P-25 model obtained from the results of grouting in Iran yield the most accurate predictions of the pressure and measurement errors compared to the real values in P-25 model in this dams are 12 and 14.33 Percent and in p-3 model are 12.25 and 16.66 respectively. Also, SPSS software was applied to define the optimum relation for pressure estimation. The results showed a high correlation between the pressure with the depth of the section, the amount of water take, rock quality degree and grout volume, so that the square of the multiple correlation coefficient among the parameters in this dams were 0.932 and 0.864, respectively. This indicates that regression results can be used to predict the amount of pressure. Eventually, the relationship between the parameters was obtained with the correlation coefficient equal to 0.916 based on the data from both dams generally and shows that there is a desirable correlation between the parameters. The outputs of the program led to the multiple linear regression equation of P=0.403 Depth+0.013 RQD+0.011 LU–0.109 V+0.31 that can be used in estimating the pressure.

Key Words
grouting; analytical and statistical modeling; pressure

Address
Hassan Bakhshandeh Amnieh: School of Mining, College of Engineering, University of Tehran, Iran
Majid Masoudi: Department of Mining Engineering, Faculty of Engineering, University of Kashan, Iran
Mohammdamin Karbala: Mining Eng., Amirkabir Univ. of Tech (Tehran Polytechnic), Rahsazi & Omran Iran Cons. Co., Iran

Abstract
he aim of this study is to investigate the effect of the bond strength of self-compacting mortars (SCMS) produced from ground pumice powder (GPP) as a mineral additive. In this scope, six series of mortars including control mix were prepared that consist of 7%, 12%, 17%, 22% and 27% of ground pumice powder by weight of cement. A total of 54 specimens of 40x40x160 mm were produced and cured at the age of 3, 28 and 90-day for compressive and tensile strength tests and 18 specimens of 150x150x150 mm mortar were prepared and cured at 28 days for bond strength tests. Flexural tensile strength and compressive strength of 40x40x160 mm specimens were measured at the curing age of 7, 28 and 90-day. Mini V-funnel flow time and mini slump flow diameter tests were also conducted to obtain rheological properties. As a result of the study, it was observed that the SCMs containing 12% of GPP has the highest bond strength as compared to control and GPP mortars. Compressive strength slightly increased up to 12% of GPP.

Key Words
self-compacting mortar; ground pumice powder; bond strength; fresh properties; mechanical properties

Address
Mehmet Karataş and M. Veysel Sastim: Department of Civil Engineering, Firat University, 23100, Elazig, Turkey
Ahmet Benli: Department of Civil Engineering, Bingol University, 12100, Bingol, Turkey

Abstract
Tests on the fracture behavior of CFRP-concrete composite bonded interfaces have been extensively carried out. In this study, a progressive damage model is employed to simulate the fracture behaviors. The crack nucleation, propagation and more other details can be captured by these models. The numerical results indicate the fracture patterns seem to depend on the relative magnitudes of the interface cohesive strength and concrete tensile strength. The fracture pattern transits from the predominated adhesive-concrete interface debonding to the dominated concrete cohesive cracking as the interface cohesive strength changes from lower than concrete tensile strength to higher than that. The numerical results have an agreement with the experimental results.

Key Words
fracture behavior; CFRP composite; concrete; damage

Address
Hai X. Lin, Jian Y. Lu and Bing Xu: College of Civil Engineering, Henan Polytechnic University, Jiaozuo City, Henan Province, 454000, People

Abstract
A CFD software was used to simulate free surface flow of SCC in the T-Box test. In total, seven simulations were developed to study the effect of rheological parameters on the non-restricted flow performance of SCC in both horizontal and vertical directions. Different suspending fluids having five plastic viscosity values between 10 and 50 Pa.s, three yield stress values between 14 and 75 Pa, one density of 2500 kg/m3, and one shear elasticity modulus of 100 Pa were considered for suspension of 178 spherical particles of 20-mm diameter and 2500 kg/m3 density. The results of the simulations are found to correlate well to changes in rheological parameters of the suspending fluid. Plastic viscosity was shown to be the most dominant parameter affecting flowability and dynamic stability compared to the yield stress. A new approach was proposed to evaluate performability of SCC based on a trade-off between flowability and dynamic stability.

Key Words
dynamic stability; flowability; performability; self-consolidating concrete; T-Box test

Address
Masoud Hosseinpoor and Ammar Yahia: Department of Civil Engineering, Université de Sherbrooke, 2500 boul. de l\'Université, Sherbrooke, Québec, Canada
Kamal H. Khayat: Department of Civil, Architectural and Environmental Engineering, Missouri University of Science and Technology, 224 Engineering Research Lab, Rolla, MO, USA

Abstract
This paper investigates the utilization of waste tyre crumb rubber as the fine aggregate in precast concrete Paving block (PCPB). PCPB\'s are generally preferred for city roads, pedestrian crosswalk, parking lots and bus terminals. The main aim of this paper is to evaluate the mechanical properties of wet cast PCPB containing waste tyre crumb rubber. The mechanical properties were investigated using a density, compressive strength, split tensile strength and flexural strength tests at 7, 28 56 days according to the IS 15688:2006 and EN1338. The wet cast method was followed for producing PCPB samples. The fine aggregate (river sand) was replaced with waste tyre crumb in percentage of 5%, 10%, 15%, 20% and 25% by volume. All the test results were compared with the conventional PCPB (Without rubber). The test results indicate its feasibility for incorporating waste tyre crumb rubber in the production of PCPB by the wet cast method.

Key Words
paving block; wet casting; crumb rubber; compressive strength; split tensile strength; flexural strength

Address
R. Bharathi Murugan: Department of Civil Engineering, Kalasalingam University, Krishnankoil, Tamil Nadu, 626 126, India
C. Natarajan: Department of Civil Engineering, National Institute of Technology, Tiruchirappali, Tamil Nadu, 620 015, India

Abstract
Studying the structural behavior of prestressed segmented girders is quite important due to the large use this type of solution in viaducts and bridges. Thus, this work presents a nonlinear three-dimensional structural analysis of an externally prestressed segmented concrete girder through the Finite Element Method (FEM), using a customized ANSYS platform, version 14.5. Aiming the minimization of the computational effort by using the lowest number of finite elements, a new viscoelastoplastic material model has been implemented for the structural concrete with the UPF customization tool of ANSYS, adding new subroutines, written in FORTRAN programming language, to the main program. This model takes into consideration the cracking of concrete in its formulation, being based on fib Model Code 2010, which uses Ottosen rupture surface as the rupture criterion. By implementing this new material model, it was possible to use the three-dimensional 20-node quadratic element SOLID186 to model the concrete. Upon validation of the model, an externally prestressed segmented box concrete girder that was originally lab tested by Aparicio et al. (2002) has been computationally simulated. In the discretization of the structure, in addition to element SOLID186 for the concrete, unidimensional element LINK180 has been used to model the prestressing tendons, as well as contact elements CONTA174 and TARGE170 to simulate the dry joints along the segmented girder. Stresses in the concrete and in the prestressing tendons are assessed, as well as joint openings and load versus deflection diagrams. A comparison between numerical and experimental data is also presented, showing a good agreement.

Key Words
prestressed concrete; segmented girder; contact elements; ANSYS; USERMAT

Address
Paula M. Lazzari:
1) Infrastructure Engineering Graduate Program, Federal University of Santa Catarina, 2700 Dr. João Colin St, 89218-000, Joinville, SC, Brazil
2) Civil Engineering Graduate Program, Federal University of Rio Grande do Sul, 99 Oswaldo Aranha Ave, 90035-190, Porto Alegre, RS, Brazil
Américo Campos Filho, Bruna M. Lazzari and Alexandre R. Pacheco: Civil Engineering Graduate Program, Federal University of Rio Grande do Sul, 99 Oswaldo Aranha Ave, 90035-190, Porto Alegre, RS, Brazil

Abstract
A new simple and practical strut-and-tie model (STM) for predicting the shear strength of RC pile caps is proposed in this paper. Two approaches are adopted to take into account the concrete softening effect. In the first approach, a concrete efficiency factor based on compression field theory is employed to determine the effective strength of a concrete strut, assumed to control the shear strength of the whole member. The second adopted Kupfer and Gerstle\'s biaxial failure criterion of concrete to derive the simple nominal shear strength of pile caps containing the interaction between strut and tie capacity. The validation of these two methods is investigated using 110 RC pile cap test results and other STMs available in the literature. It was found that the failure criterion approach appears to provide more accurate and consistent predictions, and hence is chosen to be the proposed STM. Finally, the predictions of the proposed STM are also compared with those obtained by using seven other STMs from codes of practice and the literature, and were found to give better accuracy and consistency.

Key Words
pile caps; discontinuity region; strut-and-tie model; shear strength

Address
Panatchai Chetchotisak: Department of Civil Engineering, Rajamangala University of Technology Isan, Khon Kaen Campus, Khon Kaen 40000, Thailand
Sukit Yindeesuk: Department of Highways, Ministry of Transport, Bangkok 10400, Thailand
Jaruek Teerawong: Department of Civil Engineering, Khon Kaen University, Khon Kaen 40002, Thailand

Abstract
Dynamic behaviours of reinforced concrete (RC) bending beams subjected to monotonic loading with different loading rates were studied. A dynamic experiment was carried out with the electro-hydraulic servo system manufactured by MTS (Mechanical Testing and Simulation) Systems Corporation to study the effect of loading rates on the mechanical behaviours of RC beams. The monotonic displacement control loading, with loading rates of 0.1 mm/s, 0.5 mm/s, 1 mm/s, 5 mm/s and 10 mm/s, was imposed. According to the test results, the effects of loading rates on the failure model and load-displacement curve of RC beams were investigated. The influences of loading rates on the cracking, ultimate, yield and failure strengths and displacements, ductility and dissipated energy capability of RC beams were studied. Then, the three-dimensional finite element models of RC beams, with the rate-dependent DP (Drucker-Prager) model of concrete and three rate-dependent model of steel reinforcement, were described and verified using the experimental results. Finally, the dynamic mechanical behaviours and deformation behaviours of the numerical results were compared with those of the experimental results.

Key Words
reinforced concrete (RC) beam; loading rate; strength; deformation; ductility; numerical simulation

Address
Shiyun Xiao and Jianbo Li: State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, China
Yi-Lung Mo: Department of Civil and Environmental Engineering, University of Houston, USA

Abstract
This paper presents an efficient membrane finite element for the cyclic inelastic response analysis of RC structures under complex plane stress states including shear. The model strikes a balance between accuracy and numerical efficiency to meet the challenge of shear wall simulations in earthquake engineering practice. The concrete material model at the integration points of the finite element is based on damage plasticity with two damage parameters. All reinforcing bars with the same orientation are represented by an embedded orthotropic steel layer based on uniaxial stress-strain relation, so that the dowel and bond-slip effect of the reinforcing steel are presently neglected in the interest of computational efficiency. The model is validated with significant experimental results of the cyclic response of RC panels with uniform stress states.

Key Words
reinforced concrete panel; reinforced concrete membrane; inelastic cyclic analysis; finite element analysis

Address
Lepoldo Tesser: Géodynamique & Structure, 106, Avenue Marx Dormoy, 82120, Montrouge, France
Diego A. Talledo: Department of Architecture Construction Conservation (DACC), University IUAV of Venice, Campus Terese, Dorsoduro 2206, 30123, Venice, Italy

Abstract
Seismic response of the concrete column covered by nanofiber reinforced polymer (NFRP) layer is investigated. The concrete column is studied in this paper. The column is modeled using sinusoidal shear deformation beam theory (SSDT). Mori-Tanaka model is used for obtaining the effective material properties of the NFRP layer considering agglomeration effects. Using the nonlinear strain-displacement relations, stress-strain relations and Hamilton\'s principle, the motion equations are derived. Harmonic differential quadrature method (HDQM) along with Newmark method is utilized to obtain the dynamic response of the structure. The effects of different parameters such as NFRP layer, geometrical parameters of column, volume fraction and agglomeration of nanofibers and boundary conditions on the dynamic response of the structure are shown. The results indicated that applied NFRP layer decreases the maximum dynamic displacement of the structure. In addition, using nanofibersas reinforcement leads a reduction in the maximum dynamic displacement of the structure.

Key Words
seismic response; NFRP layer; SSDT; HDQM; newmark method

Address
Mohsen Motezaker: Department of Civil Engineering, School of Science and Engineering, Sharif University of Technology, International Campus, Kish Island, Iran
Reza Kolahchi: Department of Civil Engineering, Meymeh Branch, Islamic Azad University, Meymeh, Iran


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