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CONTENTS
Volume 79, Number 6, September25 2021
 


Abstract
In the present paper, wave propagation behavior of porous temperature-dependent functionally graded curved beams within the thermal environment is analyzed for the first time. A recently-developed method is utilized which considers the reciprocal effect of mass density and Young's modulus in order to explore the influence of porosity. Three different types of temperature variation (uniform temperature change (UTC), linear temperature change (LTC), sinusoidal temperature change (STC)) are employed to study the effect of various thermal loads. Euler-Bernoulli beam theory, also known as classic beam theory is implemented in order to derive kinetic and kinematic relations, and then Hamilton's principle is used to obtain governing equations of porous functionally graded curved beams. The obtained governing equations are analytically solved. Eventually, the influences of various parameters such as wave number, porosity coefficient, various types of temperature change and power index are covered and indicated in a set of illustrations.

Key Words
Euler-Bernoulli beam theory; porosity-dependent method; thermal environment; wave propagation analysis

Address
Xinli Xu: Structural Vibration Control Group, Qingdao University of Technology, Qingdao 266033, China
Chunwei Zhang: Structural Vibration Control Group, Qingdao University of Technology, Qingdao 266033, China; School of Civil Engineering, Qingdao University of Technology, No.11 Fushun Road, Shibei District, Qingdao City, 266033, China
Farayi Musharavati: Department of Mechanical and Industrial Engineering, Qatar University, P.O. Box 2713, Doha, Qatar
Tamer A. Sebaey: Engineering Management Department, College of Engineering, Prince Sultan University, Riyadh, Saudi Arabia; Mechanical Design and Production Department, Faculty of Engineering, Zagazig University, P.O. Box 44519, Zagazig, Sharkia, Egypt
Afrasyab Khan: Institute of Engineering and Technology, Department of Hydraulics and Hydraulic and Pneumatic Systems, South Ural State University, Lenin Prospect 76, Chelyabinsk, 454080, Russian Federation

Abstract
In the present paper, an analysis of elastic stability for mosquito fascicle with the elastic foundation is investigated by the variational iteration method. A mathematical model is established for the mosquito fascicle for the associated clamped and free boundary conditions. Results attained expert the stability condition of mosquito fascicle for given parameters. Design guidelines for the dynamically stable microneedle are developed and critically debated. A uniform homogeneous mosquito fascicle is considered to be restrained by labium along its length. The restraint considered in this work is an elastic foundation model by labium, and it is of great interest to bioengineering and foundation engineers. An analytical solution is not a simple procedure since the equations are highly nonlinear. This study presents the application of the variational iteration method for obtaining exact solutions for continuously restrained mosquito fascicle. The research proves that the variational iteration method is a very efficient and promising approach to understand the probing behavior of mosquitoes and the process of penetration.

Key Words
biomimetics; instability analysis; microneedle; Mosquito mouthparts

Address
Naser Alkenani: Department of Biological Sciences, Faculty of Science, King Abdulaziz University, Jeddah 21589, Saudi Arabia
S.R. Mahmoud: GRC Department, Faculty of Applied Studies, King Abdulaziz University, Jeddah, Saudi Arabia
Ahmed M. Metwally: Mathematics and Theoretical Physics Department, NRC, AEA, Inshas, P.O.13759, Cairo, Egypt
Afaf S. Alwabli: Department of Biological Sciences, Rabigh College of Science and Arts, King Abdulaziz University, Jeddah, Saudi Arabia
Habeeb M. Al-Solami: Department of Biological Sciences, Faculty of Science, King Abdulaziz University, Jeddah 21589, Saudi Arabia

Abstract
This paper proposes an improved variational mode decomposition (IVMD) algorithm for structural modal parameter estimation based on non-stationary responses. In this improved VMD, the mean envelope entropy (MEE) and particle swarm optimization (PSO) are first employed to determine the optimal decomposition parameters for the subsequent VMD analysis. Then the VMD algorithm is used to decompose the non-stationary data into a number of intrinsic mode functions (IMFs). After obtaining the IMFs based on the IVMD, structural modal parameters such as natural frequencies and damping ratios of civil structures can be determined by using Natural Excitation Technique (NExT) and Direct Interpolating approach (DI). The feasibility and accuracy of the proposed procedure are evaluated by both numerical and full-scale examples. The natural frequencies and damping ratios are successfully identified from the vibration responses with high noise and nonstationary characteristics. The results of this study illustrate that the proposed procedure provides a powerful approach to identify the modal parameters of civil structures using non-stationary responses.

Key Words
damping ratios; improved variational mode decomposition; modal parameter estimation; natural frequencies; non-stationary

Address
Lun-hai Zhi, Feng Hu, Chunfeng Zhao and Jingfeng Wang: College of Civil Engineering, Hefei University of Technology, Hefei 230009, China

Abstract
It is necessary to identify structures with unknown mass and unknown seismic excitations simultaneously, but very limited methods have been proposed. In this paper, an algorithm is proposed to identify structural element mass, stiffness, and seismic excitations using only partial absolute structural responses of chain-like systems. In the first stage, the identification of structural element stiffness-mass coupled coefficients and unknown seismic excitations is conducted based on the generalized extended Kalman filter with unknown input (GEKF-UI) developed by the authors. In the second stage, these coupled coefficients are decoupled by cluster analysis and the least squares estimation (LSE) to obtain structural element stiffness and mass changes. The effectiveness of the proposed algorithm is numerically investigated using a four-story frame structure under three scenarios of changed conditions. Moreover, experimental validation by the shaking table test of a shear structure under two scenarios is also performed to identify structures and seismic excitations simultaneously.

Key Words
extended Kalman filter; partial absolute measurement; seismic excitation; structural identification; unknown input; unknown mass

Address
Hao Qiu, Jinshan Huang and Zhupeng Zheng: Department of Civil Engineering, Xiamen University, Xiamen 361005, China

Abstract
In this paper, the porosity distribution of functionally graded porous (FGP) beams are optimized using the genetic algorithm to achieve the maximum ratio of the normalized buckling load to the beam's weight. The analytical forms for critical buckling loads of the FGP beams under different end conditions are determined analytically using principle virtual work based on the Euler and Timoshenko beam theories. The effects of Nano Graphene Platelets (NGPs) on the critical buckling load of the nanocomposite FGP beams are also taken into account. The sensitivity analyses show that porosity will reduce the buckling load-to-weight ratio of porous beams to conventional beams in some cases. Based on the optimization results, the optimum distribution of the porosity and NGPs' volume fraction are proposed for several porosity coefficients. The obtained results indicate that the optimum distribution for porosity has a symmetric sandwich-like shape while the optimum distribution for NGPs' volume fraction is uniform.

Key Words
buckling strength; functionally graded porous beams; nanographene plate reinforcement; optimization; porosity distribution

Address
Mojtaba Farrokh and Mohammad Taheripur: Advanced Structures Research Lab., K. N. Toosi University of Technology, P.O. Box 16765-3381, Tehran, Iran

Abstract
The history of modern humanity is developing towards making the technological equipment used as small as possible to facilitate human life. From this perspective, it is expected that electromechanical systems should be reduced to a size suitable for the requirements of the era. Therefore, dimensionless motion analysis of beams on the devices such as electronics, optics, etc., is of great significance. In this study, the linear and nonlinear vibration of nanobeams, which are frequently used in nanostructures, are focused on. Scenarios have been created about the vibration of nanobeams on the magnetic field and elastic foundation. In addition to these, the boundary conditions (BC) of nanobeams having clamped-clamped and simple-simple support situations are investigated. Nonlinear and linear natural frequencies of nanobeams are found, and the results are presented in tables and graphs. When the results are examined, decreases the vibration amplitudes with the increase of magnetic field and the elastic foundation coefficient. Higher frequency values and correction terms were obtained in clamped-clamped support conditions due to the structure's stiffening.

Key Words
magnetic force effect; multiple scale methods; nanobeam; nonlinear elastic foundation; nonlocal elasticity theory

Address
Burak E. Yapanmiş: Aliağa Vocational and Training School, Ege University, Siteler Mah. İnönü Bulvari, İzmir, Turkey
Necla Toğun: Department of Mechanical Engineering, Gaziantep University, Üniversite Bulvari Şehitkamil - Gaziantep, Turkey
Süleyman M. Bağdatli, Şevki Akkoca: Department of Mechanical Engineering, Manisa Celal Bayar University, Şehit Prof. Dr. İlhan Varank Yerleşkesi, Manisa, Turkey

Abstract
This study presents overviews of a first proposed Hidden boundary one-way Rib precast concrete Slab, so-called HRS. In order to investigate bending behaviors of the novel structural system, three specimens manufactured in factory are tested by corresponding static loading protocol experiments. Four-points bending tests in both cases of the presence and absence of topping concrete slabs are performed. Results of the experiment scrutinize how each structural component such as rebars, topping concretes, strand wires can affect the bending behavior of HRS. As regards the main originality of this paper, approximate equations showing flexural strengths for a partially prestressed concrete flagged section, like HRS, are proposed in accordance with several current global and local design standards such as ACI 318, EN: Eurocode 2, PCI, AASHTO 2002, KCI 2012 and CSA A.23. Moreover, this study provides another predicting approach using finite element analysis of MIDAS FEA for analytical performances of specimens. Through these experimental and analytical results, the general characteristic of HRS may be observed and studied for realization in the field of prestressed precast concrete industries for construction.

Key Words
bending behavior; bi-tensional prestress; finite element analysis; hidden boundary; one-way rib slab; precast slab

Address
Phan Anh Nguyen: Department of Architectural Engineering, Sejong University, Seoul 05006, Republic of Korea
Jeonghoi Kim, Jonghwan Oh, Youngshik Park: Technical Research Institute, IS Dongseo, Seoul 06071, Republic of Korea
Dongkyu Lee: Department of Architectural Engineering, Sejong University, Seoul 05006, Republic of Korea

Abstract
Reinforced concrete (RC) square columns are vulnerable to sudden dynamic impact loadings such as the vehicle crash to the bridges of highway or seaway, rock fall, the collision of masses with the effect of flood and landslide. In this experimental study RC square columns strengthened with and without CFRP strip subjected to sudden low velocity lateral impact loading were investigated. Drop-hammer testing machine was used to apply the impact loading to RC square columns. The test specimens were manufactured with square cross sections with 1/3 geometric scale. In scope of the study, 6 test specimens were manufactured and tested. The main variables considered in the study were the application point of impact loading, and CFRP strip spacing. A 9.0 kg mass was allowed to fall freely from a height of 1.0 m to apply the impact loading on the columns. During the impact tests, accelerations, impact force, column mid-point displacements and CFRP strip strains measurements were taken. The general behavior of test specimens, collapse mechanisms, acceleration, displacement, impact load and strain time relationships were interpreted, and the load displacement relationships were obtained. The data from the experimental study was used to investigate the effect of variables on the impact performances of RC columns. It has been observed that the strengthening method applied to reinforced concrete columns, which are designed with insufficient shear strength, insufficient shear reinforcement and produced with low strength concrete, using CFRP strips significantly improves the behavior of the columns under the effect of sudden dynamic impact loading and increases their performance. As a result of the increase in the hardness and rigidity of the specimens strengthened by wrapping with CFRP strips, the accelerations due to the impact loading increased, the displacements decreased and the number of shear cracks formed decreased and the damage was limited. Moreover, the finite element analyses of tested specimens were performed using ABAQUS software to further investigate the impact behavior.

Key Words
ABAQUS; CFRP; free drop test; impact load; RC column

Address
Omer Mercimek: Department of Civil Engineering, Ankara Yildirim Beyazit University, Ankara, Turkey
Ozgur Anil: Department of Civil Engineering, Gazi University, Ankara, Turkey
Rahim Ghoroubi: Department of Civil Engineering, Çankaya University, Ankara, Turkey
Shaimaa Sakin: Department of Civil Engineering, Al_ Mustansiriya University, Baghdad, Iraq
Tolga Yilmaz: Department of Civil Engineering, Konya Teknik University, Konya, Turkey

Abstract
In low-rise unreinforced masonry (URM) buildings, structural design is generally performed considering the load effects induced by seismic forces as well as the vertical loads. However, there might be cases where the additional or unforeseen loads may be encountered during the lifespan of these buildings. The loads that are induced from the addition of a new storey during the service life is a good example for these additional loads. Since the reconstruction licenses and building height limits specified by the local authorities may vary in life cycle of the structures, it is important to decide the addition of a storey to an existing building considering the structural safety concerns. In this study, an existing low-rise URM building is modelled with added stories (subsequently planned after its construction), and numerical analyses are carried out considering the extra loads of this additional stories. The aim of this study is to assess the earthquake performance of the structures considering this unforeseen situation which was not considered in the original structural design. The suitability of the initial structural design project to the existing building was examined by the site investigations. The results of the analytical analysis were compared with the seismic code requirements, and the seismic performance level of the building is estimated. The study is intended to be useful in determining the path to be followed for the determination of the seismic capacity if existing buildings are exposed to such additional loads. The findings of this study could be used to design local and global retrofitting works. Especially, for the typologies underwent such interventions, solutions that reduce earthquake demands by providing high lateral strength and rigidity could be considered. It is believed that the outcomes obtained with respect to the evaluation of this case study could be generalized to a wide variety of such template buildings and extrapolated for a wide masonry building type.

Key Words
earthquake performance; intervention; seismic risk; story addition; URM buildings

Address
Neritan Shkodrani: Department of Civil Engineering, Polytechnic University of Tirana, Albania
Huseyin Bilgin: Department of Civil Engineering, EPOKA University, Tirana, Albania

Abstract
Seismic design criteria based on performance of structures have recently been adopted by practicing engineers in response to destructive earthquakes. A simple but efficient structural-analysis tool capable of predicting both strength and ductility is needed to analyze reinforced concrete (RC) structures subjected to such events. Hence, a three-dimensional lattice model is developed in this study to analyze torsions in high-strength RC beams. Optimization techniques for determining optimal variables in each lattice model are introduced. Pure torsion tests of RC beams were performed to use to propose a threedimensional lattice model. The experimental test results of pure torsion on RC beam specimens were used to compare with numerical results obtained using the proposed model. Then, the proposed model was also compared to 3D solid model in commercial finite element analysis program, ABAQUS. Correlation studies between the numerical and experimental results confirm that the proposed model is well capable of representing salient features of the experimental results. Furthermore, the proposed model provides better predicted displacement corresponding to peak load. than the result from ABAQUS.

Key Words
non-linear analysis; three-dimensional lattice model; torsional analysis

Address
Yeongseok Jeong, Minho Kwon and Jinsup Kim: Department of Civil Engineering, Gyeongsang National University, Jinju 52828, South Korea


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