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CONTENTS
Volume 28, Number 3, September 2021
 

Abstract
Based on differential quadrature method (DQM), a nonlinear vibrational analysis of hybrid multi-scale cylindrical panels has been performed in this article. The mechanical properties of hybrid composites have been formulated within the framework of three-dimensional Mori-Tanaka model taking into consideration the effects of unidirectional oriented fibers and randomly dispersed carbon nanotubes (CNTs). The governing equations for cylindrical panels have been established with respect to thin shell assumptions taking into account geometrical non-linearity. Next, DQM has been used to solve the governing equations for establishing the frequency-deflection curves of the cylindrical panel. It will be exhibited that frequency-deflection curves change by the varying of CNT weight fractions, fiber orientations, fiberglass volume, panel radius and dimension of CNTs.

Key Words
curved panels; cylindrical panel; nanocomposite materials; nonlinear vibrations; shell theory

Address
Jun Liu: School of Economics and Management, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, Jiangsu, China; Hanjing Project Management Co., Ltd, Jinan 250101, Shandong, China
Houli Wang: State Power Investment Group Shandong New Energy Co., Ltd, Jinan 250100, Shandong, China
Hongmei Yin: Shandong Juyuan Project Management Co., Ltd, Jinan 250100, Shandong, China

Abstract
Recently, designing irregular structures has been interested among civil engineers. The existing seismic codes like Iranian one do not present the separated response modification factor for regular and irregular structures. In this study, a procedure is presented to estimate the response modification factor of irregular Reinforced Concrete Moment Resisting Frames (RCMRFs). To do so, firstly, several irregular RCMRFs with various types of irregularity are designed based on the behavior factor of Iranian seismic code. Then, the inter-story drifts of these frames subjected to the proportional seismic ground motions are achieved and evaluated by the acceptance criteria. Secondly, the behavior factors of the aforementioned frames resulting from pushover analysis are acquired and the frames are redesigned based on these behavior factors. After that, the inter-story drifts of redesigned frames are again obtained and it is shown that these frames satisfy the admissible restrictions. In addition, two new relations are presented to acquire the behavior factor and the main period of irregular RCMRFs. Six new irregular RCMRFs are designed using the behavior factors achieved via the proposed relations. The behavior factors and the fundamental periods of these frames, which are computed from pushover and modal analyses respectively, are compared with those achieved via the presented relations. This comparison validates the accuracy of the suggested relations.

Key Words
behavior factor; inter-story drift; irregular structure; reinforce concrete; seismic response

Address
Alireza Habibi: Department of Civil Engineering, Shahed University, Tehran, Iran
Mehdi Izadpanah: Department of Civil Engineering, Kermanshah University of Technology, Kermanshah, Iran
Mohsen Ghasem Fam: Department of Civil Engineering, Kurdistan University, Sanandaj, Iran

Abstract
In this study, the forced vibration analysis of a micro sandwich plate with an isotropic/orthotropic cores and polymeric nanocomposite face sheets is taken into account based on first order shear deformation theory (FSDT). The core of this plate is considered as five isotropic Devineycell materials (H30, H45, H60, H100 and H200) and an orthotropic material, while facesheets layers are as polymeric matrix reinforced by carbon nanotubes under temperature-dependent and hydro material properties on the elastic foundations. The governing equations of motion are derived using the Hamilton's principle and then solved by analytical method. Also, the effects of different parameters such as size dependent, side ratio, volume fraction, various material properties of cores and facesheets and temperature and humidity changes on the dimensionless frequency are investigated. It is shown from the results that the dimensionless frequency for CT is lower than that of for MSGT. Also, it is presented that the least amplitude oscillation is related to the modified strain gradient theory due to higher stiffen. It is illustrated that the dimensionless frequency for Devineycell H200 is highest and lowest for H30. The results of this research can be used in aircraft, automotive, shipbuilding industries and biomedicine.

Key Words
first-order shear deformation theory; forced vibration analysis; isotropic and orthotropic cores; micro sandwich plate

Address
Javad Rajabi and Mehdi Mohammadimehr: Department of Solid Mechanics, Faculty of Mechanical Engineering, University of Kashan, P.O. Box: 87317-53153, Kashan, Iran

Abstract
In reinforced concrete (RC) frames, the applied seismic energy is dissipated through the ductile behavior of RC moment resisting frames. The main elements of the RC frames carry the gravity loads in addition to the seismic loads. Since the RC frames are sensitive to gravity loads, the ductility of the frames is reduced by increasing the gravity loads. Moreover, because of the low stiffness of the RC moment frames, huge member sizes of structural elements are required to control lateral drifts under lateral loading. In addition, the existing RC moment frame buildings with non-ductile characteristics pose a considerable hazard during earthquakes. To solve the mentioned problems, an innovative metallic damper with a shear link (metallic-passive energy damper) was developed in this paper. The proposed damper not only enjoys an easy fabrication and a good seismic performance but also can be easily replaced after a severe earthquake. Since the damper does not carry the gravity loads, replacing the damper does not affect the severability of the building during repairing. The main goal of this study is to confine the plastic deformation in the proposed damper. The numerical results indicated that the proposed damper improved the behavior of the RC frame in elastic and inelastic zones. It enhanced the shear capacity, shear stiffness, energy absorption, and ductility of the RC moment resisting frame. The results indicated that the proposed damper enhances the shear stiffness and the ultimate shear capacity from a minimum of 11% to a maximum of 24% and from a minimum of 11% to a maximum of 48%, respectively. Also, the proposed damper improved the yielding strength from a minimum of 53% to a maximum of 61%. Moreover, the dynamic analysis indicated that the damper improved the behavior of the system in the case of maximum lateral displacement and base shear. Based on the time-history dynamic analysis, dampers in the 5- and 10-story frames are more effective compared to the 15-story frame. This result confirms the suitable performance of the proposed damper. Herein the required equations and the recommendations for the design of the proposed metallic-shear damper have been presented.

Key Words
ductility; metallic damper; moment resisting frame; nonlinear behavior; passive damper; reinforced concrete frame; seismic performance; shear yielding

Address
Ahmad Jabbar Hussain Alshimmeri: Department of Civil Engineering, College of Engineering, University of Baghdad, Baghdad, Iraq
Denise-Penelope N. Kontoni: Department of Civil Engineering, School of Engineering, University of the Peloponnese, GR-26334 Patras, Greece; School of Science and Technology, Hellenic Open University, GR-26335 Patras, Greece
Ali Ghamari: Department of Civil Engineering, Darreh Shahr Branch, Islamic Azad University, Darreh Shahr, Iran

Abstract
Discrete element and experimental approaches were utilized for investigating the effects of non-persistent joint sets on the failure behaviour of concrete under uniaxial compressive test. concrete specimens (100 mmx120 mmx50 mm dimension) were prepared. Tensile strength of concrete was 1 MPa. Two sets of specimens consisting three and five joints were prepared. These joint have two different parallel and intersecting configurations. In samples consisting both of the parallel and intersecting configurations with three joints, the length of larger joint was 6 cm and the lengths of two small joints was 3 cm. In samples consisting both of the parallel and intersecting configurations with five joints, The length of two larger joints were 3 cm and the lengths of three small joints was 2 cm. When the notch number was 3, the angle of larger joints were changed from 0o to 90o by increasing the 30o. When the notch number was 5, the angle of smaller joints were changed from 0o to 90o by increasing the 30o. In intersectiong joint configurations, two joint sets were perpendiqular to eachother. Totally, 16 different models were tested under compression test. Cuncurrent with experimental tests, numerical simulation (Particle flow code in two dimension) were performed on the models comprising non-persistent joint sets. joints configurations were similar to experimental one. the results revealed that the failure procedure was governed mostly by both of the joint configuration. The specimens' compressive strengths were associated with the failure mechanism and fracture pattern of the discontinuities. Furthermore it was shown that the discontinuities' compressive behaviour is caused by the number of the induced tensile cracks incremented by decreasing the joint length. Only some AE hits exist in the initial phase of loading, then AE hits grow rapidly prior to reaching the peak applied stress. Moreover, every stress drop was convoyed by numerous AE hits. Finally, the failure strength and pattern are similar in both approaches of the experimental tests and the numerical simulation.

Key Words
non-persistent joint set; PFC2D; physical test

Address
Mohammad Saeed Amini: Department of Mining Engineering, Amirkabir University of Technology, Tehran, Iran
Vahab Sarfarazi, Nima Babanouri: Department of Mining Engineering, Hamedan University of Technology, Hamedan, Iran

Abstract
The present study investigated experimentally and numerically the behavior of reinforced concrete plates subjected to pure torsion. The main parameters examined were: steel reinforcement ratio or spacing and plate width. A pure torsion test was carried out on nine reinforced concrete plate with different dimensions and reinforcement. A 3D numerical analysis by the finite element method and a torsion theories were adopted for all specimens tested. The finite element results overestimate the cracking torque, accurate of ultimate torque. Skew-bending theory calculate the cracking torque more accurate compared to FE and other theories. Moreover, ACI318-14 building code is unconservative for cracking torque, conservative of ultimate torque.

Key Words
concrete plates; concrete slabs; finite elements; pure torsion; torsion theory

Address
Omer F. Ibraheem and Osama A. Mukhlif: Department of Civil Engineering, University of Tikrit, Tikrit, Iraq

Abstract
The large diameter reinforced concrete drain-pipe were applied in a underground drain-pipe jacking engineering. The inside and outside diameter of the drain-pipe are 3.5 m and 4.2 m respectively. The weight is 26000 kg, and jacking distance is 640 m. The nondestructive testing technology and three-edge bearing test were used to evaluate quality of the two large diameter concrete drain-pipe which selected randomly in engineering. The load-displacement curves and load-strain curves of drain-pipe were obtained, the global and local deformation laws of drain-pipe were analyzed through static test. The finite element model was established by ABAQUS, and the test results and simulation results were compared. The results of comparison show that the displacement of each measuring point increases with increasing load, and both of the two drain-pipe show well overall performance, and the well overall performance was shown in both of the two drain-pipe. The maximum displacement and strain were measured at the top of the drain-pipe, and the cracks are observed at the sidewall and bottom of drain-pipe. The load-displacement curves from simulation results is in well agree with the load-displacement curves from test results. It means that there is a good accuracy of the calculation results with the finite element model, which could be used as the basis for the corresponding research. Cracking load values under three-edge bearing test (the load value when the width of crack reaches 0.20 mm) of the two drain-pipe are 325 kN/m and 324 kN/m, respectively. And both drain-pipe meet the Chinese national standard, which the large diameter reinforced concrete drain-pipe could be used in actual engineering.

Key Words
large diameter reinforced concrete drain-pipe; nondestructive testing technology; numerical simulation; static test; three-edge bearing test

Address
Yanmin Yang, Zhixin Zhang: School of Civil Engineering, Jilin Jianzhu University, Changchun 130118, China
Yongqing Li: Changchun Xinlicheng Reservoir Management Center, Changchun 130000, China
Zesen Ge, Ying Xiong, Xiangkun Meng: School of Civil Engineering, Jilin Jianzhu University, Changchun 130118, China

Abstract
This paper introduces a simple but effective strength reduction factor to directly determine the strength reduction due to the creep deformation of concrete in circular CFT columns. Upon constructing the linearized P-M interaction diagram on the basis of the design procedure introduced in the previous paper or described in the existing design codes, multiplying the introduced strength reduction factor makes it possible to determine the ultimate resisting capacity of CFT columns without a rigorous time-dependent nonlinear analysis. The efficiency and accuracy of the introduced strength reduction factor are verified through comparison of the P-M interaction diagrams determined by the use of the strength reduction factor and those obtained by rigorous nonlinear analysis considering the creep deformation. Numerous additional parametric studies show that the introduced strength reduction factor can effectively be used especially in the preliminary design stage where many trial and error procedures are performed while considering the creep effect in concrete to select a proper section dimension of a CFT column.

Key Words
concrete-filled tube (CFT); time-dependent behavior; creep; nonlinear finite-element analysis; structural design; P-A effect; P-M interaction diagram

Address
SeongHun Kim and Hyo-Gyoung Kwak: Department of Civil and Environmental Engineering, Korea Advanced Institute of Science and Technology, 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea

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