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CONTENTS
Volume 74, Number 2, April25 2020
 

Abstract
In the finite element modelling of long-span cable-stayed bridges, there are a lot of uncertainties brought about by the complex structural configuration, material behaviour, boundary conditions, structural connections, etc. In order to reduce the discrepancies between the theoretical finite element model and the actual static and dynamic behaviour, updating is indispensable after establishment of the finite element model to provide a reliable baseline version for further analysis. Traditional sensitivity-based updating methods cannot support updating based on static and dynamic measurement data at the same time. The finite element model is required in every optimization iteration which limits the efficiency greatly. A convenient but accurate Kriging surrogate model for updating of the finite element model of cable-stayed bridge is proposed. First, a simple cable-stayed bridge is used to verify the method and the updating results of Kriging model are compared with those using the response surface model. Results show that Kriging model has higher accuracy than the response surface model. Then the method is utilized to update the model of a long-span cable-stayed bridge in Hong Kong. The natural frequencies are extracted using various methods from the ambient data collected by the Wind and Structural Health Monitoring System installed on the bridge. The maximum deflection records at two specific locations in the load test form the updating objective function. Finally, the fatigue lives of the structure at two cross sections are calculated with the finite element models before and after updating considering the mean stress effect. Results are compared with those calculated from the strain gauge data for verification.

Key Words
cable-stayed bridge; fatigue life; health monitoring; mean stress effect; model updating; surrogate model

Address
Jing Zhang and Dong Yang: Department of Civil Engineering, Hefei University of Technology, Hefei, Anhui Province, China
Jing Zhang, Francis T.K. Au and Dong Yang: Department of Civil Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong, China

Abstract
The theories having been developed thus far account for higher-order variation of transverse shear strain through the depth of the beam and satisfy the stress-free boundary conditions on the top and bottom surfaces of the beam. A shear correction factor, therefore, is not required. In this paper, the effect of surface on the axial buckling and free vibration of nanobeams is studied using various refined higher-order shear deformation beam theories. Furthermore, these theories have strong similarities with Euler–Bernoulli beam theory in aspects such as equations of motion, boundary conditions, and expressions of the resultant stress. The equations of motion and boundary conditions were derived from Hamilton's principle. The resultant system of ordinary differential equations was solved analytically. The effects of the nanobeam length-to-thickness ratio, thickness, and modes on the buckling and free vibration of the nanobeams were also investigated. Finally, it was found that the buckling and free vibration behavior of a nanobeam is size-dependent and that surface effects and surface energy produce significant effects by increasing the ratio of surface area to bulk at nano-scale. The results indicated that surface effects influence the buckling and free vibration performance of nanobeams and that increasing the length-to-thickness increases the buckling and free vibration in various higher-order shear deformation beam theories. This study can assist in measuring the mechanical properties of nanobeams accurately and designing nanobeam-based devices and systems.

Key Words
higher-order shear; surface effect; elastic medium; axial bulking; analytical modeling

Address
Omid Rahmani: Structures and New Advanced Materials Laboratory Department of Mechanical Engineering, University of Zanjan, Zanjan, Iran
S. Samane Asemani: Department of Mechanical Engineering, University of Tarbiat Modares, Tehran, Iran

Abstract
Researchers have elaborated several accurate methods to calculate member-end rotations or moments, directly, for bridge-type structures. Recently, the concept of rotation and moment propagation (RMP) has been presented considering bending flexibility, only. Through which, in spite of moment distribution method, all joints are free resulting in rotation and moment emit throughout the structure similar to wave motion. This paper proposes a new set of closed-form equations to calculate member-end rotation or moment, directly, comprising both shear and bending flexibility. Furthermore, the authors program the algorithm of Timoshenko beam theory cooperated with the finite element. Several numerical examples, conducted on the procedures, show that the method is superior in not only the dominant algorithm but also the preciseness of results.

Key Words
bridge-frame; closed-form solution; continuous beam; finite element; Timoshenko beam

Address
Mahmoud-Reza Hosseini-Tabatabaei and Mahmoud R. Mollaeinia: Department of Civil Engineering, University of Zabol, Zabol, Iran,
Mohmmad Rezaiee-Pajand: Department of Civil Engineering, Ferdowsi University of Mashhad, Mashhad, Iran

Abstract
This study aims at evaluating composite moment frame structures (CFS) using wavelet analysis of the displacement behavior of these structures. Five seismic damage mitigation systems' models of 9-story CFS are examined namely, basic (Model 1), reinforced (Model 2), buckling restrained braced (BRB) (Model 3), lead rubber bearing (LRB) (Model 4), and composite (Model 5) moment frames. A novel integration between continuous and discrete wavelet transforms is designed to estimate the wavelet power energy and variance of measurements' behaviors. The behaviors of the designed models are evaluated under influence of four seismic loads to study the dynamic performance of CFS in the frequency domain. The results show the behaviors of models 3 and 5 are lower than other models in terms of displacement and frequency performances. Model 3 has been shown lower performances in terms of energy and variance wavelets along the monitoring time; therefore, Model 3 demonstrates superior performance and low probability of failure under seismic loads. Furthermore, the wavelet variance analysis is shown a powerful tool that can be used to assess the CFS under seismic hazards.

Key Words
composite frame; wavelet; dynamic analysis; seismic

Address
Mosbeh R.Kaloop, Hong Min Son, Hyoung-Bo Sim, Dongwook Kim and Jong Wan Hu: Department of Civil and Environmental Engineering, Incheon National University, Incheon 22012, Korea
Hong Min Son, Jong Wan Hu:Incheon Disaster Prevention Research Center, Incheon National University, Incheon 22012, Korea
Mosbeh R.Kaloop: Public Works and Civil Engineering Department, Mansoura University, Mansoura 35516, Egypt

Abstract
Thin films easily wrinkle under compressive loading due to their small bending stiffness resulting from their tiny thickness. For a thin film deposited on a functionally graded substrate with non–uniform stiffness exponentially changes along the length span in this paper, the uniaxial wrinkling problem is solved analytically in terms of hyper–Bessel functions. For infinite, semi–infinite and finite length systems the wrinkling load and wrinkling wavenumber are determined and compared with those in literature. In comparison with a homogeneous substrate–bounded film in which the wrinkling pattern is uniform along the length span, for a functionally graded substrate–film system the wrinkles accumulate around the softer location of the functionally graded substrate. Therefore, the effective length of the film influenced by the wrinkles decreases, the amplitude of the wrinkles on softer regions of the functionally graded substrate grows and the wrinkling load of the functionally graded substrates with higher softening rate decreases more. The results of the current research are expected to be useful in science and technology of thin films and wrinkling of the structures especially living tissues.

Key Words
thin film; substrate; wrinkling; functionally graded materials; hypergeometric function

Address
Faculty of Mechatronics, Islamic Azad University (Karaj Branch), Karaj, Iran

Abstract
The bi-axial and shear buckling behavior of laminated hypar shells having rhombic planforms are studied for various boundary conditions using the present mathematical model. In the present mathematical model, the variation of transverse shear stresses is represented by a second-order function across the thickness and the cross curvature effect in hypar shells is also included via strain relations. The transverse shear stresses free condition at the shell top and bottom surfaces are also satisfied. In this mathematical model having a realistic second-order distribution of transverse shear strains across the thickness of the shell requires unknown parameters only at the reference plane. For generality in the present analysis, nine nodes curved isoparametric element is used. So far, there exists no solution for the bi-axial and shear buckling problem of laminated composite rhombic (skew) hypar shells. As no result is available for the present problem, the present model is compared with suitable published results (experimental, FEM, analytical and 3D elasticity) and then it is extended to analyze bi-axial and shear buckling of laminated composite rhombic hypar shells. A C0 finite element (FE) coding in FORTRAN is developed to generate many new results for different boundary conditions, skew angles, lamination schemes, etc. It is seen that the dimensionless buckling load of rhombic hypar increases with an increase in c/a ratio (curvature). Between symmetric and anti-symmetric laminations, the symmetric laminates have a relatively higher value of dimensionless buckling load. The dimensionless buckling load of the hypar shell increases with an increase in skew angle.

Key Words
buckling; composite; finite element method; skew hypar shell

Address
Abhay K. Chaubey: Department of Civil Engineering, Koneru Lakshmaiah Education Foundation, Vaddeswaram-522502, India
Shubham Raj, Ajay Kumar: Department of Civil Engineering, National Institute of Technology Patna, Patna-800005, India
Pratik Tiwari: Department of Aerospace Engineering, Indian Institute of Technology Kharagpur, Kharagpur-721302, India
Anupam Chakrabarti: Department of Civil Engineering, Indian Institute of Technology Roorkee, Roorkee-247667, India
K.K. Pathak: Department of Civil Engineering, Indian Institute of Technology (BHU), Varanasi-221005, India

Abstract
Devastating RC structural failures in the past have identified that the behavior of beam-column joints is more critical and significantly governs the global structural response under seismic loading. The congestion of reinforcement at the beam-column joints with other constructional difficulties has escalated the attention required for strengthening RC beam-column joints. In this context, numerous studies have been carried out in the past, which mainly focused on jacketing the joints with different materials. However, there is no comparative study of different approaches used to strengthen RC beam-column joints, from efficiency and cost perspective. This paper presents a detailed investigation carried out to study the various strengthening schemes of exterior RC beam-column joints, viz., steel fiber reinforcement, carbon fiber reinforced polymer (CFRP) strengthening, steel haunch strengthening, and confining joint reinforcement. The effectiveness of each scheme was evaluated experimentally. These specimens were tested under horizontal loading that produced opening moments on the joints and their behavior was studied with emphasis on strength, displacement ductility, stiffness, and failure mechanism. Special attention was given to the study of crack-width.

Key Words
beam-column joint; RC member; strengthening; strength; ductility; stiffness; CFRP

Address
M. Adil Dar: Department of Civil Engineering, Indian Institute Technology Delhi, New Delhi, India
N. Subramanian: Consulting Engineer, Maryland, U.S.A.
3Department of Civil Engineering, National Institute Technology Srinagar, J&K, India

Abstract
The main requirements of modern welded metal structures are the load-carrying capacity (safety), fitness for production, and economy. The primary objective of attaching longitudinal stiffeners is to improve the buckling strength of relatively thin compression panels. This paper gives several comparisons for stiffened plates with different loadings (static, dynamic), different shape of stiffeners (flat, L-shape, trapezoidal), different steel grades, and different welding technologies (SMAW, GMAW, SAW), different costs to show the necessity of a combination of design, fabrication and economic aspects. Safety and fitness for production are guaranteed by fulfilling the design and fabrication constraints. The economy is achieved by minimizing the cost function. It is shown that the optimum sizes depend on the welding technology, the material yield stress, the profile of the stiffeners, the load cycles and the place of the production.

Key Words
stiffened plates; stability; optimum design; static; fatigue loading; cost calculation

Address
Zoltán Virág: Institute of Mining and Geotechnical Engineering, University of Miskolc H-3515 Miskolc, Egyetemváros, Hungary
Károly Járma: Institute of Energy Engineering and Chemical Machinery, University of Miskolc H-3515 Miskolc, Egyetemváros, Hungary

Abstract
The seismic performance and failure modes of the dual system of moment resisting frames and thin steel plate shear walls (TSPSWs) without and with one or two outrigger trusses are studied in this paper. These structural systems were utilized to resist vertical and lateral loads of 40-storey buildings. Detailed Finite element models associated with nonlinear time history analyses were used to examine seismic capacity and plastic mechanism of the buildings. The analyses were performed under increased levels of earthquake intensities. The models with one and two outriggers showed good performance during the maximum considered earthquake (MCE), while the stress of TSPSWs in the model without outrigger reached its ultimate value under this earthquake. The best seismic capacity was in favour of the model with two outriggers, where it is found that increasing the number of outriggers not only gives more reduction in lateral displacement but also reduces stress concentration on thin steel plate shear walls at outrigger floors, which caused the early failure of TSPSWs in model with one outrigger.

Key Words
failure modes; seismic capacity; thin steel plate shear walls; moment resisting frames; outrigger trusses

Address
Structural Engineering Department, Faculty of Engineering, Zagazig University, Zagazig, Sharkia, Egypt

Abstract
The coupled hydro-mechanical loading conditions commonly occur in the geothermal and petroleum engineering projects, which is significantly important influence on the stability of rock masses. In this article, the influence of flaw inclination angle of fracture behaviors in rock-like materials subjected to both mechanical loads and internal hydraulic pressures is experimentally studied using the 3-D X-ray computed tomography combined with 3-D reconstruction techniques. Triaxial compression experiments under confining pressure of 8.0 MPa are first conducted for intact rock-like specimens using a rock mechanics testing system. Four pre-flawed rock-like specimens containing a single open flaw with different inclination angle under the coupled hydro-mechanical loading conditions are carried out. Then, the broken pre-flawed rock-like specimens are analyzed using a 3-D X-ray computed tomography (CT) scanning system. Subsequently, the internal damage behaviors of failed pre-flawed rock-like specimens are evaluated by the 3-D reconstruction techniques, according to the horizontal and vertical cross-sectional CT images. The present experimental does not only focus on the mechanical responses, but also pays attentions to the internal fracture characteristics of rock-like materials under the coupled hydro-mechanical loading conditions. The conclusion remarks are significant for predicting the rock instability in geothermal and unconventional petroleum engineering.

Key Words
hydro-mechanical loading; flaw inclination angle; internal fracture behaviors; rock-like materials; 3-D reconstruction

Address
Miaomiao Kou, Xinrong Liu and Yunteng Wang: School of Civil Engineering, Chongqing University, Chongqing, 400045, China;
Miaomiao Kou: School of Civil Engineering, Qingdao University of Technology, Qingdao, 266033, China;
Miaomiao Kou: Cooperative Innovation Center of Engineering Construction and Safety in Shandong Blue Economic Zone, Qingdao, 266033, China

Abstract
The main purpose of this study is to analyze the effects of external pressure on the vibration and buckling of functionally graded (FG) spherical panels resting of elastic medium. The material characteristics of the FG sphere continuously vary through the thickness direction based on the power-law rule. In accordance with first-order shear deformation shell theory and by the use of Ritz formulation the governing equations are presented. In this regard, the beam functions are applied in two-dimensions for different sets of boundary supports. The Winkler and Pasternak models of elastic foundations are also taken into account. In order to show the validity and applicability of the presented formulation, various comparison studies are given. Furthermore, a diverse range of numerical results is reported to check the impacts of geometrical and material parameters along with external pressure on the vibration and buckling analysis of FG spherical panels.

Key Words
functionally graded materials; spherical panel; vibration; buckling; beam functions

Address
Yan Cao, Xueming Qian, Qingming Fan: School of Mechatronic Engineering and Shaanxi Key Laboratory of Non-Traditional Machining,
Xian Technological University, Xian 710021 China
Farbod Ebrahimi: Young Researchers and Elite Club, Tehran Branch, Islamic Azad University, Tehran, Iran


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