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Volume 46, Number 3, February10 2023

This study aims to examine the elastic stiffness properties of Elliptic-Braced Moment Resisting Frame (EBMRF) subjected to lateral loads. Installing the elliptic brace in the middle span of the frames in the facade of a building, as a new lateral bracing system not only it can improve the structural behavior, but it provides sufficient space to consider opening it needed. In this regard, for the first time, an accurate theoretical formulation has been developed in order that the elastic stiffness is investigated in a two-dimensional single-story single-span EBMRF. The concept of strain energy and Castigliano' s theorem were employed to perform the analysis. All influential factors were considered, including axial and shearing loads in addition to the bending moment in the elliptic brace. At the end of the analysis, the elastic lateral stiffness could be calculated using an improved relation through strain energy method based on geometric properties of the employed sections as well as specifications of the utilized materials. For the ease of finite element (FE) modeling and its use in linear design, an equivalent element was developed for the elliptic brace. The proposed relation was verified by different examples using OpenSees software. It was found that there is a negligible difference between elastic stiffness values derived by the developed equations and those of numerical analysis using FE method.

Key Words
Castigliano's theorem; drift; elastic lateral stiffness; elliptic-braced moment frame; Numerical analysis' strain energy

Habib Ghasemi Jouneghani:School of Civil and Environmental Engineering, University of Technology Sydney, NSW, Australia

Nader Fanaie:Department of Civil Engineering, K. N. Toosi University of Technology, Tehran, Iran

Mohammad Talebi Kalaleh:Department of Civil and Environmental Engineering, University of Alberta, Canada

Mina Mortazavi:School of Civil and Environmental Engineering, University of Technology Sydney, NSW, Australia

Localizing damages is an essential task to monitor the health of the structures since they may not be able to operate anymore. Among the damage detection techniques, non-destructive methods are considerably more preferred than destructive methods since damage can be located without affecting the structural integrity. However, these methods have several drawbacks in terms of detecting abilities, time consumption, cost, and hardware or software requirements. Employing artificial intelligence techniques could overcome such issues and could provide a powerful damage detection model if the technique is utilized correctly. In this study, the crack localization in flat and folded plate structures has been conducted by employing a Backpropagated Artificial Neural Network (BPANN). For this purpose, cracks with 18 different dimensions in thin, flat, and folded structures having 15°, 30° 45° and 60° folding angle have been modeled and subjected to free vibration analysis by employing the Classical Plate Theory with Finite Element Method. A Four-nodded quadrilateral element having six degrees of freedom has been considered to represent those structures mathematically. The first ten natural frequencies have been obtained regarding healthy and cracked structures. To localize the crack, the ratios of the frequencies of the cracked flat and folded structures to those of healthy ones have been taken into account. Those ratios have been given to BPANN as the input variables, while the crack locations have been considered as the output variables. A total of 500 crack locations have been regarded within the dataset obtained from the results of the free vibration analysis. To build the best intelligent model, a feature search has been conducted for BAPNN regarding activation function, the number of hidden layers, and the number of hidden neurons. Regarding the analysis results, it is concluded that the BPANN is able to localize the cracks with an average accuracy of 95.12%.

Key Words
crack detection; Finite Element Method; folded plates; machine learning; neural network; vibration

Oguzhan Das:National Defence University, Air NCO Higher Vocational School, Department of Aeronautics Sciences, 35410, Izmir, Türkiye

Can Gonenli:Ege University, Department of Machine Drawing and Construction, 35100, Izmir, Türkiye

Duygu Bagci Das:Ege University, Department of Computer Programming, 35100, Izmir, Türkiye

This investigation presents nonlinear free vibration of a carbon nanotube reinforced composite beam based on the Von Karman nonlinearity and the Euler-Bernoulli beam theory The material properties of the structure is considered as made of a polymeric matrix by reinforced carbon nanotubes according to different material distributions. The governing equations of the nonlinear vibration problem is delivered by using Hamilton's principle and the Galerkin's decomposition technique is utilized to discretize the governing nonlinear partial differential equation to nonlinear ordinary differential equation and then is solved by using of multiple time scale method. The nonlinear natural frequency and the nonlinear free response of the system is obtained with the effect of different patterns of reinforcement.

Key Words
carbon nanotubes; composite beams; geometric nonlinearity; nonlinear vibration

M. Alimoradzadeh:Department of Mechanical Engineering, Najafabad Branch, Islamic Azad University, Najafabad, Iran

Ş.D. Akbaş:Bursa Technical University, Department of Civil Engineering, Mimar Sinan Campus, Y

A thermal-mechanical coupling finite element model of the steel-plate concrete composite (SC) wall is established, taking into account the strain rate effect and variation in mechanical and thermal properties under different temperatures. Verifications of the model against previous fire test and impact test results are carried out. The impact response of the SC wall under elevated temperatures is further investigated. The influences of the fire exposure time on the impact force and displacement histories are discussed. The results show that as the fire exposure time increases, the deflection increases and the impact resistance decreases. A formula is proposed to calculate the reduction of the allowable impact energy considering the fire exposure time.

Key Words
elevated temperature; impact; steel-plate concrete composite wall; thermal-mechanical coupling analysis

Lin Wang:Beihang School, Beihang University, Beijing 100191, China

Weiyi Zhao, Caiwei Liu and Qinghong Pang:Department of Civil Engineering, Qingdao University of Technology, Qingdao 266033, Shandong, China

This paper presents a finite-element analysis (FEA) of aluminum alloy rectangular hollow sections (RHSs) and square hollow sections (SHSs) with circular through-openings under three-point and four-point bending. First, a finite-element model (FEM) was developed and validated against the corresponding test results available in the literature. Next, using the validated FE models, a parametric study comprising 180 FE models was conducted. The cross-section width-to-thickness ratio (b/t) ranged from 2 to 5, the hole size ratio (d/h) ranged from 0.2 to 0.8 and the quantity of holes (n) ranged from 2 to 6, respectively. Third, results obtained from laboratory test and FEA were compared with current design strengths calculated in accordance with the North American Specifications (NAS), the modified direct strength method (DSM) and the modified Continuous strength method (CSM). The comparison shows that the modified CSM are conservative by 15% on average for aluminum alloy RHSs and SHSs with circular through-openings subject to bending. Finally, a new design equation is proposed based on the modified CSM after being validated with results obtained from laboratory test and FEA. The proposed design equation can provide accurate predictions of flexural capacities for aluminum alloy RHSs and SHSs with circular throughopenings.

Key Words
aluminum alloy; Finite-Element Analysis (FEA); Rectangular Hollow Section (RHS); Square Hollow Section (SHS); through-opening

Ran Feng and Tao Yang:School of Civil and Environmental Engineering, Harbin Institute of Technology, Shenzhen, China

Zhenming Chen:1)School of Civil and Environmental Engineering, Harbin Institute of Technology, Shenzhen, China
2)China Construction Science and Industry Corporation LTD, Shenzhen, China

Krishanu Roy:School of Engineering, The University of Waikato, New Zealand

Boshan Chen:Department of Civil Engineering, Tsinghua University, China

James B.P. Lim: School of Engineering, The University of Waikato, New Zealand

In this investigation, an improved integral trigonometric shear deformation theory is employed to examine the vibrational behavior of the functionally graded (FG) sandwich plates resting on visco-Pasternak foundations. The studied structure is modelled with only four unknowns' variables displacements functions. The simplicity of the developed model being in the reduced number of variables which was made with the help of the use of the indeterminate integral in the formulation. The current kinematic takes into consideration the shear deformation effect and does not require any shear correction factors as used in the first shear deformation theory. The equations of motion are determined from Hamilton's principle with including the effect of the reaction of the visco-Pasternak's foundation. A Galerkin technique is proposed to solve the differentials governing equations, which enables one to obtain the semi-analytical solutions of natural frequencies for various clamped and simply supported FG sandwich plates resting on visco-Pasternak foundations. The validity of proposed model is checked with others solutions found in the literature. Parametric studies are performed to illustrate the impact of various parameters as plate dimension, layer thickness ratio, inhomogeneity index, damping coefficient, vibrational mode and elastic foundation on the vibrational behavior of the FG sandwich plates.

Key Words
Galerkin technique; Hamilton's principle; improved integral theory; sandwich-plates; vibrational behavior; Visco-Pasternak foundations

Fatima Bounouara: 1)Département de Génie Civil, Faculté d'Architecture et de Génie Civil, Université des Sciences et de la Technologie d'Oran, BP 1505 El M'naouer, USTO, Oran, Algeria 2)Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Civil Engineering Department, Algeria

Salem Mohammed Aldosari: 1)Enhanced Composite and Structures Centre, School of Aerospace, Transport, and Manufacturing, Cranfield University, Cranfield MK43 0AL, UK 2)National Center for Aviation Technology, King Abdulaziz City for Science and Technology (KACST), Riyadh 11442, Saudi Arabia

Abdelbaki Chikh: 1)Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Civil Engineering Department, Algeria 2)Ibn Khaldoun University, BP 78 Zaaroura, 14000 Tiaret, Algeria

Abdelhakim Kaci:1)Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Civil Engineering Department, Algeria 2)Université Dr. Tahar Moulay, Faculté de Technologie, Département de Génie Civil et Hydraulique, BP 138 Cité En-Nasr 20000 Saida, Algérie

Abdelmoumen Anis Bousahla: Laboratoire de Modélisation et Simulation Multi-échelle, Université de Sidi Bel Abbés, Algeria

Fouad Bourada:1) Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Civil Engineering Department, Algeria 2) Science and Technology Department, Faculty of Science and Technology, Tissemsilt University, Algeria

Abdelouahed Tounsi:1) Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Civil Engineering Department, Algeria 2) YFL (Yonsei Frontier Lab), Yonsei University, Seoul, Korea 3)Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals, 31261 Dhahran, Eastern Province, Saudi Arabia

Kouider Halim Benrahou:1) Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Civil Engineering Department, Algeria 2) Department of Physics, College of Sciences, Princess Nourah bint Abdulrahman University (PNU), P.O. Box 84428, Riyadh 11671, Saudi Arabia

Hind Albalawi: Department of Physics, College of Sciences, Princess Nourah bint Abdulrahman University (PNU), P.O. Box 84428, Riyadh 11671, Saudi Arabia

Abdeldjebbar Tounsi: Industrial Engineering and Sustainable Development Laboratory, University of Relizane, Faculty of Science & Technology, Mechanical Engineering Department, Algeria

Steel is becoming increasingly popular due to its high strength, excellent ductility, great assembly performance, and recyclability. In reality, steel structures serving for a long time in atmospheric, industrial, and marine environments inevitably suffer from corrosion, which significantly decreases the durability and the service life with the exposure time. For the mechanical properties of corroded steel, experimental studies are mainly conducted. The existing numerical analyses only evaluate the mechanical properties based on corroded morphology at the isolated time-in-point, ignoring that this morphology varies continuously with corrosion time. To solve this problem, the relationships between pit depth expectation, standard deviation, and corrosion time are initially constructed based on a large amount of wet-dry cyclic accelerated test data. Successively, based on that, an in-situ pitting evolution method for evaluating the residual tensile strength of corroded steel is proposed. To verify the method, 20 repeated simulations of mass loss rates and mechanical properties are adopted against the test results. Then, numerical analyses are conducted on 135 models of corrosion pits with different aspect ratios and uneven corrosion degree on two corroded surfaces. Results show that the power function with exponents of 1.483 and 1.091 can well describe the increase in pit depth expectation and standard deviation with corrosion time, respectively. The effect of the commonly used pit aspect ratios of 0.10–0.25 on yield strength and ultimate strength is negligible. Besides, pit number ratio a equating to 0.6 is the critical value for the strength degradation. When a is less than 0.6, the pit number increases with a, accelerating the degradation of strength. Otherwise, the strength degradation is weakened. In addition, a power function model is adopted to characterize the degradation of yield strength and ultimate strength with corrosion time, which is revised by initial steel plate thickness.

Key Words
aspect ratio; corrosion time; in-situ pitting evolution; pitting corrosion; tensile strength; uneven corrosion

Yun Zhao, Qi Guo, Zizhong Zhao and Ying Xing:College of Civil Engineering, Taiyuan University of Technology, Taiyuan 030024, China

Xian Wu:Shanxi Fifth Construction Group Co., Ltd., Taiyuan 030013, China

This paper summarised and re-examined the theoretical basis of the commonly used design rule developed by Cochrane in the 1920s to consider staggered bolt holes in tension members, i.e., the s 2 /4g rule. The rule was derived assuming that the term two times the bolt hole diameter (2d0) in Cochrane' s original equation appreciably overestimates the net section area of a staggered bolted connection with a small g/d0 ratio. However, the assumed value of 0.5 for the fractional deduction of a staggered hole underestimates the staggered net section area for small g/d0 ratios. To improve the applicability of the above two assumptions, a modified design equation, which covers a full range of g/d0 ratio, was proposed to accurately predict the staggered net section area and was validated by the existing test data from the literature and numerical data derived from this study. Finally, a reliability analysis of the test and numerical data was conducted, and the results showed that the reliability of the modified design equation for evaluating the net section resistance of staggered bolted connections can be achieved with the partial factor of 1.25.

Key Words
bolted connections; finite element analysis; net section area; parametric study; staggered hole arrangement; theoretical analysis

Xue-Mei Lin and Michael C.H. Yam and Qun He:1)Department of Building and Real Estate, The Hong Kong Polytechnic University, Hong Kong, China
2)Chinese National Engineering Research Centre for Steel Construction (Hong Kong Branch),
The Hong Kong Polytechnic University, Hong Kong, China

Ke Ke:School of Civil Engineering, Chongqing University, Chongqing, China

Binhui Jiang:School of Civil Engineering, Central South University, Changsha, China

The maximum ductility and cumulative ductility of connection joints of Buckling-Restrained Braced Frames (BRBF) are critical to the structural overall performance, which should be matched with the BRB ductility. The two-story and one-span BRBF with a one-third scale was tested under cyclic quasi-static loading, and the top-flange beam splice (TFBS) rotational connections were proposed and adopted in BRBF. The deformation capacity of TFBS connections was observed during the test, and the relationship between structural global ductility and local connection ductility was studied. The rotational capacity of the beam-column connections and the stability performance of the BRBs are highly relevant to the structural overall performance. The hysteretic curves of BRBF are stable and full under large displacement demand imposed up to 2% story drift, and energy is dissipated as the large plastic deformation developed in the structural components. The BRBs acted as fuses and yielded first, and the cumulative plastic ductility (CPD) of BRBs is 972.6 of the second floor and 439.7 of the first floor, indicating the excellent energy dissipation capacity of BRBs. Structural members with good local ductility ensure the large global ductility of BRBF. The ductile capacity and hysteretic behavior of BRBF with TFBS connections were compared with those of BRBF with Reduced Beam Section (RBS) connections in terms of the experimental results.

Key Words
buckling-restrained brace; ductility; energy dissipation capacity; hysteretic performance; top-flange beam splice connection

Mingming Jia and Dagang Lu:1)School of Civil Engineering, Harbin Institute of Technology, 73 Huanghe Road, Nangang District, Harbin 150090, China
2)Key Lab of Structural Dynamic Behavior and Control of the Ministry of Education, 73 Huanghe Road, Nangang District, Harbin Institute of
Technology, Harbin 150090, China
3)Key Lab of Smart Prevention and Mitigation of Civil Engineering Disasters of the Ministry of Industry and Information Technology, Harbin
Institute of Technology, 73 Huanghe Road, Nangang District, Harbin 150090, China

Jinzhou He:School of Civil Engineering, Harbin Institute of Technology, 73 Huanghe Road, Nangang District, Harbin 150090, China

Time domain method and frequency domain method are commonly used in the current fatigue life calculation theory. The time domain method has complicated procedures and needs a large amount of calculation, while the frequency domain method has poor applicability to different materials and different spectrum, and improper selection of spectrum model will lead to large errors. Considering that artificial neural network has strong ability of nonlinear mapping and generalization, this paper applied this technique to random fatigue life prediction, and the effect of average stress was taken into account, thereby achieving more accurate prediction result of random fatigue life.

Key Words
artificial neural network; average stress; frequency domain method; random fatigue; time domain method

Jie Xu and Chongyang Liu:Key Laboratory of Earthquake Engineering Simulation and Seismic Resilience of China
Earthquake Administration (Tianjin University), Tianjin 300350, China

Xingzhi Huang and Yaolei Zhang:School of Civil Engineering, Tianjin University, Tianjin 300350, China

Haibo Zhou and Hehuan Lia:Beijing Construction Engineering Group, Beijing 100055, China

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