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CONTENTS
Volume 84, Number 4, November25 2022
 


Abstract
For the first time, the higher-order shear and normal deformable plate theory (HOSNDPT) is used for the vibration and flutter analyses of the multilayer functionally graded graphene platelets reinforced composite (FG-GPLRC) plates under supersonic airflow. For modeling the supersonic airflow, the linear piston theory is adopted. In HOSNDPT, Legendre polynomials are used to approximate the components of the displacement field in the thickness direction. So, all stress and strain components are encountered. Either uniform or three kinds of non-uniform distribution of graphene platelets (GPLs) into polymer matrix are considered. The Young modulus of the FG-GPLRC plate is estimated by the modified Halpin-Tsai model, while the Poisson ratio and mass density are determined by the rule of mixtures. The Hamilton's principle is used to obtain the governing equations of motion and the associated boundary conditions of the plate. For solving the plate's equations of motion, the Galerkin approach is applied. A comparison for the natural frequencies obtained based on the present investigation and those of three-dimensional elasticity theory shows a very good agreement. The flutter boundaries for FG-GPLRC plates based on HOSNDPT are described and the effects of GPL distribution patterns, the geometrical parameters and the weight fraction of GPLs on the flutter frequencies and flutter aerodynamic pressure of the plate are studied in detail. The obtained results show that by increasing 0.5% of GPLs into polymer matrix, the flutter aerodynamic pressure increases approximately 117%, 145%, 166% and 196% for FG-O, FG-A, UD and FG-X distribution patterns, respectively.

Key Words
functionally graded plate; graphene platelet; higher-order shear and normal deformable plate theory; multilayer; vibration and flutter analyses

Address
Mahdieh Abdollahi, Ali Reza Saidi and Reza Bahaadini: Department of Mechanical Engineering, Shahid Bahonar University of Kerman, Kerman, Iran

Abstract
Thin plates are the most common spatially stressed members in engineering structures that bear out-of-plane loads. Therefore, it is of great significance to study the deformation performance characteristics of thin plates for structural design. By constructing 12 basic displacement and deformation basis vectors of the four-node square thin plate element, a deformation decomposition method based on the complete orthogonal mechanical basis matrix is proposed in this paper. Based on the deformation decomposition method, the deformation properties of the thin plate can be quantitatively analyzed, and the areas dominated by each basic deformation can be visualized. In addition, the method can not only obtain more deformation information of the structure, but also identify macroscopic basic deformations, such as bending, shear and warping deformations. Finally, the deformation properties of the bidirectional thin plates with different sizes of central holes are analyzed, and the changing rules are obtained.

Key Words
central hole; complete orthogonality; deformation decomposition; thin plate; warping deformation

Address
Dongwei Wang, Kaixuan Liang and Panxu Sun: School of Civil Engineering, Zhengzhou University, Zhengzhou, 450001, China

Abstract
The formation of biopolymer-soil matrices mainly depends on biopolymer type and concentration, soil type, pore fluid and phase transfer to influence its strengthening efficiency. In this study, the physical and mechanical properties of sodium alginate (SA) treated kaolinite are investigated through compaction test, thread rolling teat, fall cone test and unconfined compression test with considering biopolymer concentration, curing time, initial water content, mixing method. The results show that the liquid limit slightly decreases from 69.9% to 68.3% at 0.2% SA and then gradually increases to 98.3% at 5% SA. At hydrated condition, the unconfined compressive strength (UCS) of SA treated clay at 0.5%, 1%, 2% and 3% concentrations is 2.57, 4.5, 7.1 and 5.48 times of untreated clay (15.7 kPa) at the same initial water content. In addition, the optimum biopolymer concentration, curing time, mixing method and initial water content can be regarded as 2%, 28 days, room temperature waterdry mixing (RD), 50%-55% to achieve the maximum unconfined compressive strength, which corresponds to the UCS increment of 593%, compared to the maximum UCS of untreated clay (780 kPa).

Key Words
Atterberg limits; initial water content; sodium alginate; unconfined compressive strength

Address
Zhanbo Cheng: School of Engineering, University of Warwick, Coventry CV47AL, UK; School of Civil and Environmental Engineering, Nanyang Technological University, Nanyang 639798, Singapore
Xueyu Geng: School of Engineering, University of Warwick, Coventry CV47AL, UK

Abstract
Aiming to examine different failure patterns in multistory URM walls, two 1/3 scaled three-story and three-bay URM models were designed for the quasi-static loading tests to contrastively investigate the failure processes and characteristics of the multistory URM walls. Two different failure responses were observed with special attention paid to the behavior of spandrelfailure mode. By evaluating the seismic performance and deformation behavior of two test walls, it is demonstrated that spandrels, that haven't been properly designed in some codes, are of great significance in the failure of entire URM walls. Additionally, compared with pier-failure mode, spandrel-failure for multistory URM building is more reasonable and advisable as its effectively participation in energy dissipation and its efficiently improvement on seismic capacity and deformation in the overall structure. Furthermore, the experimental results are beneficial to improve seismic design and optimize reinforcement method of URM buildings.

Key Words
failure mode; quasi-static tests; seismic performance; spandrels; unreinforced masonry (URM)

Address
Ren Xin: School of Civil Engineering, Xi'an University of Architecture and Technology, Xi'an 710055, China
Dengshan Bi: Central Research Institute of Building and Construction Co., Ltd., MCC, Beijing 100088, China
Wei Huang: School of Civil Engineering, Xi'an University of Architecture and Technology, Xi'an 710055, China

Abstract
This paper is aimed at developing an optimization-based Finite Element model updating approach for structural damage identification and quantification. A modal flexibility-based error function is introduced, which uses modal assurance criterion to formulate the updating problem as an optimization problem. Because of the inexplicit input/output relationship between the candidate solutions and the error function's output, a robust and efficient optimization algorithm should be employed to evaluate the solution domain and find the global extremum with high speed and accuracy. This paper proposes a new multi-stage Selective Particle Swarm Optimization (SPSO) algorithm to solve the optimization problem. The proposed multi-stage strategy not only fixes the premature convergence of the original Particle Swarm Optimization (PSO) algorithm, but also increases the speed of the search stage and reduces the corresponding computational costs, without changing or adding extra terms to the algorithm's formulation. Solving the introduced objective function with the proposed multi-stage SPSO leads to a smart feedback-wise and self-adjusting damage detection method, which can effectively assess the health of the structural systems. The performance and precision of the proposed method are verified and benchmarked against the original PSO and some of its most popular variants, including SPSO, DPSO, APSO, and MSPSO. For this purpose, two numerical examples of complex civil engineering structures under different damage patterns are studied. Comparative studies are also carried out to evaluate the performance of the proposed method in the presence of measurement errors. Moreover, the robustness and accuracy of the method are validated by assessing the health of a six-story shear-type building structure tested on a shake table. The obtained results introduced the proposed method as an effective and robust damage detection method even if the first few vibration modes are utilized to form the objective function.

Key Words
damage detection; flexibility matrix; model updating; multi-stage; particle swarm optimization

Address
Bahador Adel Sanjideh: Natural Disasters Prevention Research Center, School of Civil Engineering, Iran University of Science & Technology, Tehran, Iran
Azadeh Ghadimi Hamzehkolaei: Aryan Institute of Science and Technology, Babol, Iran
Ali Zare Hosseinzadeh: Department of Structural Engineering, University of California San Diego, San Diego, CA, USA
Gholamreza Ghodrati Amiri: Natural Disasters Prevention Research Center, School of Civil Engineering, Iran University of Science & Technology, Tehran, Iran

Abstract
In re-assessing the Jacket-type fixed steel structures, the current standards often allow the simplicity of corrosion sections using local buckling or equivalent section approach to applying empirical formulae of frame stress and resistance analyses. However, those approaches can lead to significant errors for non-uniform corroded frames in a specific area, including force distribution, stress, and allowable strength of the tubular section, compared to the actual cases. This paper investigates a suitable approach to determine the actual stress on non-uniform corroded tubular frames under compression through the nonlinear ABAQUS model by considering the effect of large deformation on the frame axis and the frame section. There are 3 scenarios of interest. In the 1st and 2nd scenarios with simple corrosion cases, the stress ratios using the numerical model and theoretical formulae correspond to the calculation of allowable strength reduction ratios in standards. However, scenario 3, which describes non-uniform corroded sections based on survey data, provides considerable differences in results. Therefore, it proves the reliable and effective results when using this method to analyze the resistance of the actual corroded section in the Jacket platforms.

Key Words
ABAQUS program; compression; non-uniform corrosion; numerical models; stress distribution; tubular members

Address
Vu Dan Chinh and Hà Thi Thu Nguyên: Faculty of Coastal and Offshore Engineering, Hanoi University of Civil Engineering, 55 Giai Phong Street, Hai Ba Trung District, Hanoi 100 000, Vietnam

Abstract
Headed bars are often used when there is insufficient space for a straight or curved bar to be fully developed to ensure the transference of forces between steel and concrete in several types of connections between structural members. In such cases, the concrete breakout strength of the headed bars can be a critical point of the design and must be considered appropriately. This paper evaluates the tensile strength of headed bars embedded in reinforced concrete members, failing due to concrete breakout. Four experimental tests on headed bars embedded in slender concrete members are presented and discussed, showing that strength previsions from the design codes can be significantly conservative as they ignore the contribution from the flexural reinforcement. 3D finite element models were developed using Abaqus Unified FEA to simulate the tested specimens, and it was observed that they were able to reproduce the formation of the concrete cone accurately, besides the response and resistance observed in tests. Furthermore, the experimental, numerical, and design code resistances are compared and discussed. A new equation to evaluate the concrete cone strength of the tested headed bars is proposed, which takes into account parameters not explicitly considered in the current design equations.

Key Words
Abaqus; cast-in anchors; concrete breakout strength; finite-element model; headed bars

Address
Paulo F.M. Santana, Patricia C.S. Silva, Luciano M. Bezerra, Marcos H. Oliveira: Department of Civil and Environmental Engineering, University of Brasilia, Brasilia, Federal District, Brazil
Mauricio P. Ferreira: Institute of Technology, Federal University of Para, Belem, Brazil

Abstract
By presetting various reinforcement diameters in topology optimization with the discrete model finite element analysis, an algorithm of bidirectional evolutionary structural optimization of multi-level reinforcement diameter is presented to obtain the optimal reinforcement topologies which describe the degree of stress of different parts. The results of a comparative study on different reinforcement feasible domain demonstrate that the more angle types of reinforcement are arranged in the initial domain, the higher utilization rate of reinforcement of the optimal topology becomes. According to the nonlinear finite element analysis of some deep beam examples, the ones designed with the optimization results have a certain advantage in ultimate bearing capacity, although their failure modes are greatly affected by the reinforcement feasible domain. Furthermore, the bearing capacity can be improved when constructional reinforcements are added in the subsequent design. However the adding would change the relative magnitude of the bearing capacity between the normal and inclined section, or the relative magnitude between the flexural and shear capacity within the inclined section, which affects the failure modes of components. Meanwhile, the adding would reduce the deformation capacity of the components as well. It is suggested that the inclined reinforcement and the constructional reinforcement should be added properly to ensure a desired ductile failure mode for components.

Key Words
flexural and shear resistance of inclined section; multi-level reinforcement diameter BESO; normal section bearing capacity; reinforcement feasible domain; structural optimization design; topological optimization

Address
Hu-zhi Zhang, Peng Luo, Yao-sen Huang: School of Civil Engineering, Hunan University of Science and Technology, Xiangtan 411201, China
Jian Yuan, Jia-dong Liu: College of Civil Engineering, Central South University of Forestry and Technology, Changsha 410004, China


Abstract
This paper presents a new model to obtain the minimum area of the contact surface for rectangular isolated footings, considering that the contact surface works partially to compression (a part of the contact surface of the footing is subjected to compression and the other is not in compression or tension). The methodology is developed by integration to obtain the axial load "P", moment around the X axis "Mx" and moment around the Y axis "My". This document presents the simplified and precise equations of the four possible cases of footing subjected to uniaxial bending and five possible cases of footing subjected to biaxial bending. The current model considers the contact area of the footing that works totally in compression, and other models consider the contact area that works partially under compression and these are developed by very complex iterative processes. Numerical examples are presented to obtain the minimum area of rectangular footings under an axial load and moments in two directions, and the results are compared with those of other authors. The results show that the new model presents smaller areas than the other authors presented.

Key Words
biaxial bending; contact surface works partially to compression; linear pressure distribution of the soil; minimum area; rectangular isolated footings

Address
Victor Bonifacio Vela-Moreno, Arnulfo Luévanos-Rojas, Sandra López-Chavarría, Manuel Medina-Elizondo, Ricardo Sandoval-Rivas and Carmela Martínez-Aguilar: Institute of Multidisciplinary Researches, Autonomous University of Coahuila, Blvd. Revolución No, 151 Ote, CP 27000, Torreón, Coahuila, México


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