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CONTENTS
Volume 69, Number 4, February25 2019
 

Abstract
The determination of Paris\' law parameters based on crack growth experiments is an important procedure of fatigue life assessment. However, it is a challenging task because it involves various sources of uncertainty. This paper proposes a novel probabilistic method, termed the S-N Paris law (SNPL) method, to quantify the uncertainties underlying the Paris\' law parameters, by finding the best estimates of their statistical parameters from the S-N curve data using a Bayesian approach. Through a series of steps, the SNPL method determines the statistical parameters (e.g., mean and standard deviation) of the Paris\' law parameters that will maximize the likelihood of observing the given S-N data. Because the SNPL method is based on a Bayesian approach, the prior statistical parameters can be updated when additional S-N test data are available. Thus, information on the Paris\' law parameters can be obtained with greater reliability. The proposed method is tested by applying it to S-N curves of 40H steel and 20G steel, and the corresponding analysis results are in good agreement with the experimental observations.

Key Words
Bayesian approach; fatigue crack growth; Paris\' law; statistical parameter; S-N curve

Address
Sreehari Ramachandra Prabhu:
1) School of Urban and Environmental Engineering, Ulsan National Institute of Science and Technology (UNIST),
50 Unist-gil, Eonyang-eup, Ulju-gun, Ulsan 44919, Republic of Korea
2) Department of Civil and Environmental Engineering, University of Waterloo, 200 University Avenue West, Waterloo, ON N2L 3G1, Canada
Young-Joo Lee: School of Urban and Environmental Engineering, Ulsan National Institute of Science and Technology (UNIST), 50 Unist-gil, Eonyang-eup, Ulju-gun, Ulsan 44919, Republic of Korea
Yeun Chul Park: Institute of Construction and Environmental Engineering, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 08826, Republic of Korea

Abstract
A hybrid prestressed segmental concrete (HPSC) girder utilizing low carbon materials was developed in this paper. This paper introduces the hybrid prestressing concept of pre-tensioning the center segment and assembling all segments by post-tensioning, as well as the development process of the low carbon HPSC girder. First, an optimized mix proportion of 60 MPa high strength concrete containing high volume blast furnace slag was developed, then its mechanical properties and durability characteristics were evaluated. Second, the mechanical properties of 2,400 MPa high strength prestressing strands and the transfer length characteristics in pre-tensioned prestressed concrete beams were evaluated. Third, using those low carbon materials and the hybrid prestressing concept, the HPSC girders were manufactured, and their structural performance was evaluated. A 30-m long HPSC girder for highway bridges and a 35-m long HPSC girder for railway bridges were designed, manufactured, and structurally confirmed as having sufficient strength and safety. Finally, five 35-m long HPSC girders were successfully applied to an actual railway bridge for the first time.

Key Words
HPSC girder; 2,400 MPa prestressing strand; low carbon concrete; blast furnace slag; field application

Address
Jun-Mo Yang: Department of Civil Engineering, Keimyung University, 1095 Dalgubeol-daero, Dalseo-gu, Daegu 42601, Republic of Korea
Jin-Kook Kim: Department of Civil Engineering, Seoul National University of Science and Technology, 232 Gongneung-ro, Nowon-gu, Seoul 01811, Republic of Korea

Abstract
More than one longitudinal web stiffener may be economical in the design of plate girders that have considerably high width-to-thickness ratio of webs. In this study, the bend-buckling strength of relatively deep webs with two horizontal lines of flat plate-shaped single-sided stiffeners was numerically investigated. Linear eigenvalue buckling analyses were conducted for specially selected hypothetical models of stiffened web panels, in which top and bottom junctions of a web with flanges were assumed to have simply supported boundary conditions. Major parameters in the analyses were the locations of two longitudinal stiffeners, stress ratios in the web, slenderness ratios and aspect ratios of web panels. Based on the application of assumptions on the combined locations of the two longitudinal web stiffeners, simplified equations were proposed for the bend-buckling coefficients and compared to the case of one longitudinal stiffener. It was found that bend-buckling coefficients can be doubled by adopting two longitudinal stiffeners instead of one longitudinal stiffener. For practical design purposes, additional equations were proposed for the required bending rigidity of the longitudinal stiffeners arranged in two horizontal lines on a web.

Key Words
plate girder; stiffened web; two longitudinal stiffeners; web bend-buckling strength; bending rigidity of stiffener

Address
Byung Jun Kim and Yong Myung Park: Dept. of Civil Engineering, Pusan National University, Busan 46241, Republic of Korea
Kyungsik Kim: Dept. of Civil Engineering, Cheongju University, Cheongju 28503, Republic of Korea
Byung H. Choi: Dept. of Civil Engineering, Hanbat National University, Daejeon 34158, Republic of Korea

Abstract
The present study investigated the reliability-based reinforcement ratio of FRP reinforced concrete structure applying recycled coarse aggregate (RCA) concrete. The statistical characteristics of FRP bars and RCA concrete were investigated from the previous literatures and the mean value and standard deviation were obtained. The statistical data can be regarded as the material uncertainty for configuring the probability distribution model. The target bridge structure is the railway bridge with double T-beam section. The replacement ratios of RCA were 0%, 30%, 50%, and 100%. From the probability distribution analysis, the reliability-based reinforcement ratios of FRP bars were suggested with four cases according to the replacement ratio of RCA. The reinforcement ratio of FRP bars at RCA 100% showed about 17.3% higher than the RCA 0%, where the compressive strength at RCA 100% decreased up to 27.5% than RCA 0%. It was found that the decreased effect of the compressive strength of RAC could be compensated with increase of the reinforcement ratio of FRP bars. This relationship obtained by the reliability analysis can be utilized as the useful information in structural design for FRP bar reinforced concrete structures applying RAC.

Key Words
reliability-based reinforcement ratio; sustainable construction materials; FRP bars; recycled coarse aggregate (RCA); replacement ratio of RCA; design information

Address
Minkwan Ju and Kyoungsoo Park: Department of Civil and Environmental Engineering, Yonsei University, Republic of Korea
Kihong Lee, Ki Yong Ahn and Jongsung Sim: Department of Civil and Environmental Engineering, Hanyang University, Republic of Korea

Abstract
This paper develops a wireless sensor for online fatigue crack detection and failure warning based on crack-induced nonlinear ultrasonic modulation. The wireless sensor consists of packaged piezoelectric (PZT) module, an excitation/sensing module, a data acquisition/processing module, a wireless communication module, and a power supply module. The packaged PZT and the excitation/sensing module generate ultrasonic waves on a structure and capture the response. Based on nonlinear ultrasonic modulation created by a crack, the data acquisition/processing module periodically performs fatigue crack diagnosis and provides failure warning if a component failure is imminent. The outcomes are transmitted to a base through the wireless communication module where two-levels duty cycling media access control (MAC) is implemented. The uniqueness of the paper lies in that 1) the proposed wireless sensor is developed specifically for online fatigue crack detection and failure warning, 2) failure warning as well as crack diagnosis are provided based on crack-induced nonlinear ultrasonic modulation, 3) event-driven operation of the sensor, considering rare extreme events such as earthquakes, is made possible with a power minimization strategy, and 4) the applicability of the wireless sensor to steel welded members is examined through field and laboratory tests. A fatigue crack on a steel welded specimen was successfully detected when the overall width of the crack was around 30 um, and a failure warnings were provided when about 97.6% of the remaining useful fatigue lives were reached. Four wireless sensors were deployed on Yeongjong Grand Bridge in Souht Korea. The wireless sensor consumed 282.95 J for 3 weeks, and the processed results on the sensor were transmitted up to 20 m with over 90% success rate.

Key Words
wireless sensor; fatigue crack detection; nonlinear ultrasonic modulation; failure warning; steel structure; online monitoring

Address
Suyoung Yang, Peipei Liu, Hyung Jin Lim and Hoon Sohn: Department of Civil and Environmental Engineering, Korea Advanced Institute of Science and Technology, 291 Daehak-ro, Yuseong-gu, Daejeon, 34141, Korea
Jinhwan Jung and Yung Yi: Department of Electrical Engineering, Korea Advanced Institute of Science and Technology, 291 Daehak-ro, Yuseong-gu, Daejeon, 34141, Korea
In-hwan Bae: New Airport Hiway Co., Ltd, 1048 Bongsudae-ro, Seo-gu, Incheon, 22694, Korea

Abstract
Buckling is one of the major causes of failure in thin-walled plate members and the presence of cracks with different lengths and locations in such structures may adversely affect this phenomenon. This study focuses on the buckling stability assessment of centrally and non-centrally cracked plates with small-, intermediate-, and large-size cracks, and different aspect ratios as well as support conditions, subjected to uniaxial compression. To this end, numerical models of the cracked plates were created through singular finite element method using a computational code developed in MATLAB. Eigen-buckling analyses were also performed to study the stability behavior of the plates. The numerical results and findings of this research demonstrate the effectiveness of the crack length and location on the buckling capacity of thin plates; however, the degree of efficacy of these parameters in plates with various aspect ratios and support conditions is found to be significantly different. Overall, careful consideration of the aspect ratio, support conditions, and crack parameters in buckling analysis of plates is crucial for efficient stability design and successful application of such thin-walled members.

Key Words
thin-walled structures; plates; crack; buckling; numerical simulation

Address
Sina Saberi and Parham Memarzadeh: Department of Civil Engineering, Najafabad Branch, Islamic Azad University, P.O. Box 85141-43131, Najafabad, Iran
Tadeh Zirakian: Department of Civil Engineering and Construction Management, California State University, Northridge, CA, USA

Abstract
In this study, an alternative solution procedure presented by using variational methods for analysis of shear deformable functionally graded material (FGM) beams with mixed formulation. By using the advantages of Gâteaux differential approaches, a refined complex general functional and boundary conditions which comprises seven independent variables such as displacement, rotation, bending moment and higher-order bending moment, shear force and higher-order shear force, is derived for general thick-thin FGM beams via shear deformation beam theories. The mixed-finite element method (FEM) is employed to obtain a beam element which have a 2-nodes and total fourteen degrees-of-freedoms. A computer program is written to execute the analyses for the present study. The numerical results of analyses obtained for different boundary conditions are presented and compared with results available in the literature.

Key Words
finite element method; high order shear deformation beam theory; functionally graded material beam; static analysis

Address
Emrah Madenci: Department of Civil Engineering, Faculty of Engineering and Architecture, Necmettin Erbakan University, 42140 Konya, Turke

Abstract
This research deals with thermo-electro-mechanical buckling analysis of the sandwich nano-beams with face-sheets made of functionally graded carbon nano-tubes reinforcement composite (FG-CNTRC) based on the nonlocal strain gradient elasticity theory (NSGET) considering various higher-order shear deformation beam theories (HSDBT). The sandwich nano-beam with FG-CNTRC face-sheets is subjected to thermal and electrical loads while is resting on Pasternak\'s foundation. It is assumed that the material properties of the face-sheets change continuously along the thickness direction according to different patterns for CNTs distribution. In order to include coupling of strain and electrical field in equation of motion, the nonlocal non-classical nano-beam model contains piezoelectric effect. The governing equations of motion are derived using Hamilton principle based on HSDBTs and NSGET. The differential quadrature method (DQM) is used to calculate the mechanical buckling loads of sandwich nano-beam as well as critical voltage and temperature rising. After verification with validated reference, comprehensive numerical results are presented to investigate the influence of important parameters such as various HSDBTs, length scale parameter (strain gradient parameter), the nonlocal parameter, the CNTs volume fraction, Pasternak\'s foundation coefficients, various boundary conditions, the CNTs efficiency parameter and geometric dimensions on the buckling behaviors of FG sandwich nano-beam. The numerical results indicate that, the amounts of the mechanical critical load calculated by PSDBT and TSDBT approximately have same values as well as ESDBT and ASDBT. Also, it is worthy noted that buckling load calculated by aforementioned theories is nearly smaller than buckling load estimated by FSDBT. Also, similar aforementioned structure is used to building the nano/micro oscillators.

Key Words
critical buckling load; nonlocal strain gradient theory; high order shear deformation; reinforcement composite

Address
Ali Ghorbanpour Arani, Mahmoud Pourjamshidian and Mohammad Arefi: Department of Solid Mechanics, Faculty of Mechanical Engineering, University of Kashan, 87317-53153, Kashan, Iran
M.R. Ghorbanpour Arani: Electrical Engineering Faculty, Amirkabir University of Technology, Tehran, Iran

Abstract
This paper presents an efficient higher-order nonlocal beam theory for the Critical buckling, of functionally graded (FG) nanobeams with porosities that may possibly occur inside the functionally graded materials (FG) during their fabrication, the nonlocal elastic behavior is described by the differential constitutive model of Eringen. The material properties of (FG) nanobeams with porosities are assumed to vary through the thickness according to a power law. The governing equations of the functionally graded nanobeams with porosities are derived by employing Hamilton\'s principle. Analytical solutions are presented for a simply supported FG nanobeam with porosities. The validity of this theory is studied by comparing some of the present results with other higher-order theories reported in the literature, Illustrative examples are given also to show the effects of porosity volume fraction, and thickness to length ratios on the critical buckling of the FG beams.

Key Words
nanobeam; nonlocal; higher-order; buckling; functionally graded; porosity

Address
Abdelillah Benahmed, Bouazza Fahsi and Abdelnour Benzair: Laboratory de Modelisation et Simulation Multi-echaelle, Département de Physique, Faculte des Science Exactes Universite de Sidi Bel Abbes, Algeria
Mohamed Zidour: Civil Engineering Department, Universite Ibn Khaldoun, BP 78 Zaaroura, 14000 Tiaret, Algeria
Fouad Bourada: Civil Engineering Department, Laboratory of Materials et Hydrology, University of Sidi Bel Abbes,
BP 89 Cite Ben M\'hidi, 22000 Sidi Bel Abbes, Faculty of Technology, Algeria
Abdelouahed Tounsi:
1) Civil Engineering Department, Laboratory of Materials et Hydrology, University of Sidi Bel Abbes,
BP 89 Cite Ben M\'hidi, 22000 Sidi Bel Abbes, Faculty of Technology, Algeria
2) Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals, 31261 Dhahran, Eastern Province, Saudi Arabia

Abstract
Digital image correlation (DIC) is now a popular and extensively used full-field metrology technique. In general, DIC is performed by using a turnkey solution offered by various manufacturers of DIC. In this paper, a simple and economical set-up for DIC is proposed which uses easily accessible digital single-lens reflex (DSLR) camera rather than industrial couple-charged device (CCD) cameras. The paper gives a description of aspects of carrying a DIC experiment which includes experimental set-up, specimen preparation, image acquisition and analysis. The details provided here will be helpful to carry DIC experiments without specialized DIC testing rig. To validate the responses obtained from proposed DIC set-up, tension and fatigue tests on specimens made of IS 2062 Gr. E300 steel are determined. Tensile parameters for a flat specimen and stress intensity factor for an eccentrically-loaded single edge notch tension specimen are evaluated from results of DIC experiment. Results obtained from proposed DIC experiments are compared with those obtained from conventional methods and are found to be in close agreement. It is also noted that the high resolution of DSLR allows the use of proposed approach for fracture characterization which could not be carried out with a typical turnkey DIC solution employing a camera of 2MP resolution.

Key Words
digital image correlation; DSLR; fracture characterization; SIF; tensile properties

Address
Abhishek Kumar and S. Vishnuvardhan:
1) CSIR – Structural Engineering Research Centre, Chennai, India
2) Academy of Scientific and Innovative Research (AcSIR), India
A. Ramachandra Murthy and G. Raghava: CSIR – Structural Engineering Research Centre, Chennai, India


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