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CONTENTS
Volume 60, Number 6, December25 2016
 

Abstract
The common prospect in diminishing mine-blast vibration is decreasing vibration with increasing distance. This paper indicates that, contrary to the general expectancy, vibration waves change their forms when they are travelling through the low velocity layer like coal and so-called guided waves moving the vibration waves to longer distances without decreasing their amplitudes. The reason for this unexpected vibration increase is the formation of guided waves in the coal bed which has low density and low seismic velocity with respect to the neighboring layers. The amplitudes of these guided waves, that are capable of traveling long distances depending on the seam thickness, are several times higher than that of the usual vibration waves. This phenomenon can many complaints from the residential areas very far away from the blasting sites. Thus, this unexpected behavior of the coal beds in the surface coal mines should also be considered in vibration minimization studies. This study developed a model to predict the effects of guided waves on the propagation ways of blast-induced vibrations. Therefore, vibration mitigation studies considering the nearby buildings can be focused on these target places.

Key Words
surface coal mine; blast vibrations; guided waves; evanescent waves; coal bed

Address
Guzin G. Uyar: Department of Mining Engineering, Hacettepe University, Faculty of Engineering, 06800 Beytepe, Ankara, Turkey
Ezel Babayigit: General Directorate of Turkish Coal Company, Ankara, Turkey

Abstract
A compression to tensile load transforming (CTT) device was developed to determine indirect tensile strength of concrete material. Before CTT test, Particle flow code was used for the determination of the standard dimension of physical samples. Four numerical models with different dimensions were made and were subjected to tensile loading. The geometry of the model with ideal failure pattern was selected for physical sample preparation. A concrete slab with dimensions of 15x19x6 cm and a hole at its center was prepared and subjected to tensile loading using this special loading device. The ratio of hole diameter to sample width was 0.5. The samples were made from a mixture of water, fine sand and cement with a ratio of 1-0.5-1, respectively. A 30-ton hydraulic jack with a load cell applied compressive loading to CTT with the compressive pressure rate of 0.02 MPa per second. The compressive loading was converted to tensile stress on the sample because of the overall test design. A numerical modeling was also done to analyze the effect of the hole diameter on stress concentrations of the hole side along its horizontal axis to provide a suitable criterion for determining the real tensile strength of concrete. Concurrent with indirect tensile test, the Brazilian test was performed to compare the results from two methods and also to perform numerical calibration. The numerical modeling shows that the models have tensile failure in the sides of the hole along the horizontal axis before any failure under shear loading. Also the stress concentration at the edge of the hole was 1.4 times more than the applied stress registered by the machine. Experimental Results showed that, the indirect tensile strength was clearly lower than the Brazilian test strength.

Key Words
compression to tensile load convertor; tensile strength of concrete

Address
Hadi Haeri: Young Researchers and Elite Club, Bafgh Branch, Islamic Azad University, Bafgh, Iran
Vahab Sarfarazi: Department of Mining Engineering, Hamedan University of Technology, Hamedan, Iran
Ahmadreza Hedayat: Department of Civil and Environmental Engineering, Colorado School of Mines, Golden, Colorado 80401, USA

Abstract
Modern performance-based design methods require ways to determine the factual behavior of structures subjected to earthquakes. Drift ratio demands are important measures of structural and/or nonstructural damage of the structures in performance-based design. In this study, global drift ratio and interstory drift ratio demands, obtained by nonlinear time history analysis of three generic RC frames using code-compatible ground motion record sets, are statistically evaluated. Several ground motion record sets compatible with elastic design spectra defined for the local soil classes in Turkish Earthquake Code are used for the analyses. Variation of the drift ratio demands obtained from ground motion records in the sets and difference between the mean of drift ratio demands calculated for ground motion sets are evaluated. The results of the study indicate that i) variation of maximum drift ratio demands in the sets were high; ii) different drift ratio demands are calculated using different ground motion record sets although they are compatible with the same design spectra; iii) the effect of variability due to random causes on the total variability of drift ratio demands is much larger than the effect of variability due to differences between the mean of ground motion record sets; iv) global and interstory drift ratio demands obtained for different ground motion record sets can be accepted as simply random samples of the same population at %95 confidence level. The results are valid for all the generic frames and local soil classes considered in this study.

Key Words
drift ratio demands; ground motion record sets; nonlinear time history; statistical evaluation

Address
Ali Haydar Kayhan and Ahmet Demir: Department of Civil Engineering, Pamukkale University, Denizli, Turkey

Abstract
Stainless steel wire mesh (SSWM) is an alternative material for strengthening of structural elements similar to fiber reinforced polymer (FRP). Finite element (FE) method based Numerical investigation for evaluation of axial strength of SSWM strengthened plain cement concrete (PCC) and reinforced cement concrete (RCC) columns is presented in this paper. PCC columns of 200 mm diameter with height 400 mm, 800 mm and 1200 mm and RCC columns of diameter 200 mm with height of 1200 mm with different number of SSWM wraps are considered for study. The effect of concrete grade, height of column and number of wraps on axial strength is studied using finite element based software ABAQUS. The results of numerical simulation are compared with experimental study and design guidelines specified by ACI 440.2R-08 and CNR-DT 200/2004. As per numerical analysis, an increase in axial capacity of 15.69% to 153.95% and 52.39% to 109.06% is observed for PCC and RCC columns respectively with different number of SSWM wraps.

Key Words
stainless steel wire mesh; axial strength; finite element method; wrap; circular columns

Address
Varinder Kumar: Department of Civil Engineering, Nirma University, Ahmedabad, India
P.V. Patel: Department of Civil Engineering, Institute of Technology, Nirma University, Ahmedabad, India

Abstract
The connector is the most important part of a composite beam and promotes a composite action between a steel beam and concrete slab. This paper presents the experiment results for three large-scale beams with a newly puzzle shape of crestbond. The behavior of this connector in a composite beam was investigated, and the results were correlated with those obtained from push-out-test specimens. Four-pointbending load testing was carried out on steel-concrete composite beam models to consider the effects of the concrete strength, number of transverse rebars in the crestbond, and width of the concrete slab. Then, the deflection, ultimate load, and strains of the concrete, steel beam, and crestbond; the relative slip between the steel beam and the concrete slab at the end of the beams; and the failure mechanism were observed. The results showed that the general behavior of a steel-concrete composite beam using the newly puzzle shape of crestbond shear connectors was similar to that of a steel-concrete composite beam using conventional shear connectors. These newly puzzle shape of crestbond shear connectors can be used as shear connectors, and should be considered for application in composite bridges, which have a large number of steel beams.

Key Words
crestbond rib shear connector; concrete-steel composite beam; composite behavior; loading test; shear resistance formula

Address
Van Phuoc Nhan Le, Duc Vinh Bui: Department of Civil Engineering, Ho Chi Minh City University of Technology, 268 Ly Thuong Kiet Street, Ward 14, District 10, Ho Chi Minh City, Vietnam
Thi Hai Vinh Chu: Faculity of Civil Engineering, MienTrung University of Civil Engineering ,24 Nguyen Du Street, Ward 7, Tuy Hoa City, Phu Yen,Vietnam
In-Tae Kim, Duy Kien Dao: Department of Civil Engineering, Pusan National University, 30 Jangjoen-dong, Geumjeong-gu,Busan 609-735, Korea
Jin-Hee Ahn: Department of Civil Engineering, Gyeongnam National University of Science and Technology, Korea 30 Donghin-Ro, Jinju, Gyeongnam 660-758, South Korea

Abstract
Considerable part of reinforced concrete building has suffered from destructive earthquakes in Turkey. This situation makes necessary to determine nonlinear behavior and seismic performance of existing RC buildings. Inelastic response of buildings to static and dynamic actions should be determined by considering both flexural plastic hinges and brittle shear hinges. However, shear capacities of members are generally neglected due to time saving issues and convergence problems and only flexural response of buildings are considered in performance assessment studies. On the other hand, recent earthquakes showed that the performance of older buildings is mostly controlled by shear capacities of members rather than flexure. Demand estimation is as important as capacity estimation for the reliable performance prediction in existing RC buildings. Demand estimation methods based on strength reduction factor (R), ductility (u), and period (T) parameters (R-u-T) and damping dependent demand formulations are widely discussed and studied by various researchers. Adopted form of R-u-T based demand estimation method presented in Eurocode 8 and Turkish Earthquake Code-2007 and damping based Capacity Spectrum Method presented in ATC-40 document are the typical examples of these two different approaches. In this study, eight different existing RC buildings, constructed before and after Turkish Earthquake Code-1998, are selected. Capacity curves of selected buildings are obtained with and without considering the brittle shear capacities of members. Seismic drift demands occurred in buildings are determined by using both R-u-T and damping based estimation methods. Results have shown that not only capacity estimation methods but also demand estimation approaches affect the performance of buildings notably. It is concluded that including or excluding the shear capacity of members in nonlinear modeling of existing buildings significantly affects the strength and deformation capacities and hence the performance of buildings.

Key Words
pushover analysis; reinforced concrete buildings; seismic demand; capacity spectrum method

Address
Mehmet Palanci: Department of Civil Engineering, Istanbul Arel University, Istanbul, 34537, Turkey
Ali Kalkan and Sevket Murat Senel: Department of Civil Engineering, Pamukkale University, Denizli, 20000, Turkey

Abstract
Based on Vlasov\'s torsional theory of open thin-walled members and the nonlinear constitutive relations of materials, a nonlinear analysis model to predict response of open thin-walled RC members subjected to pure torsion is proposed in the current study. The variation of the circulatory torsional stiffness and warping torsional stiffness over the entire loading process and the impact of warping shear deformation on the torsion-induced rotation of the member are considered in the formulation. The torque equilibrium differential equation is then solved by Runge-Kutta method. The proposed nonlinear model is then applied to predict the behavior of five U-shaped thin-walled RC members under pure torsion. Four of them were tested in an earlier experimental study by the authors and the testing data of the fifth one were reported in an existing literature. Results show that the analytical predictions based on the proposed model agree well with the experimental data of all five specimens. This clearly shows the validity of the proposed nonlinear model analyzing behavior of U-shaped thin-walled RC members under pure torsion.

Key Words
U-shaped RC members; thin-walled members; warping torsion; nonlinear stiffness; warping shear deformation

Address
Shenggang Chen, Quanquan Guo: Department of Civil Engineering, Beihang University, Beijing, 100191, China
Yinghua Ye, Bo Diao: Department of Civil Engineering, Beihang University, Beijing, 100191, China; State Key Laboratory of Subtropical Building Science South China University of Technology, Guangzhou, 510641, China
Shaohong Cheng: Department of Civil and Environmental Engineering, University of Windsor, Windsor, Ontario N9B 3P4, Canada

Abstract
Components manufactured from composite materials are frequently subjected to superimposed mechanical and thermal loadings during their operating service. Both types of loadings may cause fracture and failure of composite structures. When composite cross-ply laminates of type [0m / 90n]s are subjected to uni-axial tensile loading, different types of damage are set-up and developed such as matrix cracking: transverse and longitudinal cracks, delamination between disoriented layers and broken fibers. The development of these modes of damage can be detrimental for the stiffness of the laminates. From the experimental point of view, transverse cracking is known as the first mode of damage. In this regard, the objective of the present paper is to investigate the effect of transverse cracking in cross-ply laminate under thermo-mechanical degradation. A Finite Element (FE) simulation of damage evolution in composite crossply laminates of type [0m / 90n]s subjected to uni-axial tensile loading is carried out. The effect of transverse cracking on the cross-ply laminate strength under thermo-mechanical degradation is investigated numerically. The results obtained by prediction of the numerical model developed in this investigation demonstrate the influence of the transverse cracking on the bearing capacity and resistance to damage as well as its effects on the variation of the mechanical properties such as Young\'s modulus, Poisson\'s ratio and coefficient of thermal expansion. The results obtained are in good agreement with those predicted by the Shear-lag analytical model as well as with the obtained experimental results available in the literature.

Key Words
cross-ply laminate; thermo-mechanical properties; Shear-lag analysis; transverse cracking; finite element method (FEM)

Address
Berriah Abdelatif, Megueni Abdelkader and Lousdad Abdelkader: Laboratory of Mechanics of Structures and Solids (LMSS), Faculty of Technology -Department of Mechanical Engineering University Djilali Liabes of Sidi Bel Abbes, B.P 89 Cité Ben M\'Hidi, Sidi Bel- Abbes 22000, Algeria

Abstract
In this paper, an electromechanical integrated harmonic piezodrive system is proposed. The operating principle of the drive system is introduced. The equation of the relationship between the displacements of the flexible ring and the rotating angle of the rotor is deduced. Using the equation, the displacements of the flexible ring for the drive system and their changes along with the system parameters are investigated. The results show that the displacements of the flexible ring changes periodically along with the rotation of the vibrator; there are abrupt changes in the displacements of the flexible ring at some points where there are abrupt changes in the number of the mesh teeth pair; the length of the flexible ring, the excitation voltage, and the speed ratio have obvious effects on the displacements of the flexible ring. The results are useful for the design of the drive system.

Key Words
electromechanical integrated; piezodrive; flexible ring; Displacement; harmonic drive; movable tooth

Address
Lizhong Xu, Huaiyong Li and Chong Li: Mechanical Engineering Institute, Yanshan University, Qinhuangdao 066004, China

Abstract
Global sensitivity analysis (GSA) has been widely used to investigate the sensitivity of the model output with respect to its input parameters. In this paper a new single-solution search optimization algorithm is developed based on the GSA, and applied to the size optimization of truss structures. In this method the search space of the optimization is determined using the sensitivity indicator of variables. Unlike the common meta-heuristic algorithms, where all the variables are simultaneously changed in the optimization process, in this approach the sensitive variables of solution are iteratively changed more rapidly than the less sensitive ones in the search space. Comparisons of the present results with those of some previous population-based meta-heuristic algorithms demonstrate its capability, especially for decreasing the number of fitness functions evaluations, in solving the presented benchmark problems.

Key Words
global sensitivity analysis; meta-heuristic; single-solution; sensitivity indicator; truss structures

Address
A. Kaveh: Centre of Excellence for Fundamental Studies in Structural Engineering, Iran University of Science and Technology, Tehran, Iran
V.R. Mahdavi: School of Civil Engineering, Iran University of Science and Technology, Narmak, Tehran-16, Iran


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