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Numerical simulation of seismic collapse mechanisms of vertically irregular steel high-rise buildings Reza Ramezani Azghandi a, Hamzeh Shakib a,⁎, Maedeh Zakersalehi b a Tarbiat Modares University, Tehran, Iran b Niroo Research Institute, Tehran, Iran a b s t r a c t The effect ofmass and stiffness vertical irregularities on the collapse mechanismand resistance of steel high-rise structures is investigated using 3-D numerical simulations. Simulations are carried out utilizing a verified modelling approach in which the collapse processes of a regular and four irregular structures are studied under 11 earthquake records. It is indicated that the utilized finite element model, related considerations and calibrations present a reliable and efficient technique for collapse simulation. The findings showthat vertical irregularities adversely affect the collapse resistance and mechanism of steel high-rise buildings. Especially, mass vertical irregularity with concentration in the lower half of the structure is the most vulnerable one; while the stiffness irregularity with distribution in the top and bottom parts of the structure is the least affecting one. Studying the simultaneous effect of frequency content and vertical irregularities shows that, generally, records with wide frequency content mostly reduce the collapse resistance of the structure and have no significant effect on the collapsemechanismof irregular structures in comparisonwith regular structure;while records with medium frequency content are most effective on the collapse mechanism. منبع 10.1016@j.jcsr.2019.105914.pdf

Finite element evaluation of ultimate capacity of strip footing: assessment using various constitutive models and sensitivity analysis Abstract Finite element method can be used for computing bearing capacity of shallow foundation with irregular geometry resting on variable subsoil. It is necessary to quantify the parameters affecting the ultimate capacity of footing. This paper presents the results of finite element (FE) analysis of the ultimate failure load of a rough base rigid strip footing resting on c-ϕ soil. The soil is assumed as linear elastic perfectly plastic with Mohr–Coulomb failure criterion and non-associative flow rule. Sensitivity analysis is carried out to examine the ultimate capacity of strip footing considering the strength parameters (c′, ϕ′, and ψ), width of strip footing (B), unit weight of soil (γ), surcharge (q) at the base level of footing, and the deformation parameters (E and ν) as the variables. The study also examines the effect of different material models on the ultimate capacity of the strip footing. The material models considered are Mohr–Coulomb (MC) model, Hardening Soil (HS) model, Hardening Soil model with small-strain stiffness (HSsmall), and Soft Soil (SS) mode-l. It is found from the results of FE analysis that the ultimate load of the strip footing is dependent on the strength parameters, width of footing, unit weight of soil, and surcharge at the base level of the footing. The ultimate capacity is independent of the deformation parameters and will remain almost same corresponding to the material models like MC, HS, HSsmall, and SS. The FE results are compared with the analytical solutions of Terzaghi and Meyerhof. Based on the study, a few suggestions are given in regard to the FE analysis of geotechnical stability problems to obtain the quick results. منبع @civilbest - capacity of strip footing.pdf

The Effect of Shifting Natural Frequency on the Reduction of Vortex Induced Vibrations of Marine Risers Younes Komachi1, Said Mazaheri2*, Mohammad Reza Tabeshpour3 1 Ph.D. Student, National Institute for Oceanography; y_komachi@yahoo.com 2* Corresponding author: Assistant Professor, National Institute for Oceanography; said.mazaheri@inio.ac.ir 3Assistant Professor, Mechanical Engineering Department, Center of Excellence in Hydrodynamics and Dynamics of Marine Vehicles, Sharif University of Technology, Tehran, Iran; tabeshpour@sharif.edu ABSTRACT Many procedures suggest for reduction of responses of riser to Vortex Induced Vibrations (VIV). Natural frequencies of marine risers is an important parameter that can affect the responses of riser to VIV. Change of riser properties such as top tension and bending stiffness can alter natural frequencies. In this study effects of riser specifications on the responses and fatigue damage of marine risers were investigated analytically and numerically. For numerically analysis 2D wake-structure coupled model is used for modeling of VIV of riser in two directions of Cross Flow (CF) and In Line (IL). The wake dynamics, including IL and CF vibrations, is represented using a pair of non-linear Van der Pol equations that solved using modified Euler method. The Palmgren–Miner Rule is used for evaluation of fatigue damage. Riser of Amir-Kabir semisubmersible placed in Caspian sea is used for case study. Because VIV is self-limiting, it is showed that lower modes have lower curvature, that in some cases this is lead to lesser stress and also fatigue damage. The results show that for tension dominant modes of vibration, natural frequencies was increased with top tension and for a certain Strouhal frequency, dominant modes of vibration was reduced which leads to reduction of stress and fatigue damage. The results show that stress and fatigue damage increased with module of elasticity of riser and reduction of this leads to reducing of stress and fatigue damage. Therefore suitable procedure for reduction of VIV responses of riser should be selected based on the current velocity. دانلود منبع Tabeshpour_The effect of shifting.pdf

SEISMIC BEHAVIOR OF BURIED PIPELINES SUBJECTED TO NORMAL FAULT MOTION ABSTRACT: The one of the critical elements in infrastructure of today's modern cities that cover large geographic distances is Network of buried pipelines. That is why they face a variety of natural hazards due to permanent ground replacements or wave emissions. Reports suggest that the main cause of damage to these lines is not seismic vibrations but large and permanent ground deformations are major causes of infrastructures' demolition. Most recent studies are related to lines crossing the strike-slip faults, and only a few researchers have tried to study the behavior of structures against the normal fault. This article discusses the behavior and response of structures and infrastructures against the movements of normal faults using the finite elements method. In this study, the interaction between soil-soil and soil-pipe has been considered in modeling terms. منبع دانلود SEISMIC BEHAVIOR OF.pdf

Free vibration analysisof soft-core composite-faced sandwich plates using three-dimensional finite element method Mohammad Mahdi Kheirikhah; Hasan Aghabarati; Pooneh Khosravi In this paper, natural frequencies of the sandwich plates with soft flexible core and composite face sheets are obtained. Three-Dimensional (3D) finite element method (FEM) is used for constructing and analyzing of the sandwich plates to obtain their natural frequencies. Continuity conditions for transverse shear stresses at the interfaces as well as transverse flexibility and transverse normal strain and stress of the core are considered.The effects of plate dimensions such as aspect ratio and thickness ratio are studied. Also, different boundary conditions such as all edges clamped (CCCC), all edges simply supported (SSSS) and combined boundary conditions including (CFCF)are applied to the sandwich plates. Comparison of the present results in special case with those of the accurate plate theories confirms the accuracy of the proposedmodel. منبع دانلود JSEG491443558600.pdf

Slope Stability Analysis by Shear Strength Reduction Method. Farshidfar N., Nayeri A. J. Civil Eng. Urban., 5(1): 35-37, 2015; pii:S22520430150008-5 Abstract This research uses the shear strength reduction method to study soil slopes stability. In this method shear strength is considered to be reduced as less as failure occurs. It uses Plaxis, which is capable of calculating deformations rates and safety factors by gaining geometry data of a problem and soil specifications and using the finite element method (FEM). The analysis is performed at both static and pseudo-static modes. The effects of different parameters on slopes stability are shown by performing several analyses. Finally, the analyses performed by this method are compared with the ones obtained by finite difference method (FDM). Keywords: Finite Differential Method, Finite Element Method, Limit Equilibrium Method, Shear Strength Reduction, Soil slopes, Plaxis, Pseudo-Static. [Full text-PDF] منبع: [Hidden Content] J. Civil Eng. Urban., 5 (1) 35-37, 2015.pdf

Experimental and numerical study of unstiffened steel plate shear wall structures Meng Wang a,⁎, Yongjiu Shi b, Jian Xu c,Weiguo Yang a, Yixin Li b a School of Civil Engineering, Beijing Jiaotong University, Beijing 100044, China b Department of Civil Engineering, Tsinghua University, Beijing 100084, China c China Southwest Architectural Design and Research Institute Corp. LTD, Chengdu 610081, China a r t i c l e i n f o a b s t r a c t Article history: Received 13 March 2015 Accepted 6 May 2015 Available online 20 June 2015 Keywords: Unstiffened thin steel plate shear wall structure Hysteretic behavior Energy dissipation capacity Ductility Finite element method (FEM) Column stiffness In order to investigate the seismic behaviors of unstiffened thin steel plate shear wall structure, tests of four three-story unstiffened steel plate shear wall specimens under cyclic loads were carried out. Parameters of the specimens included height-to-thickness ratio, span-to-height ratio and middle brace. The carrying capacity, hysteretic behavior, degraded characteristics, ductility, failuremodes, energy dissipation capacity were analyzed and compared deeply. Besides, the nonlinear finite element method of shear wall structure was also established, which was verified by test results. Finally, the effect of column stiffness on load-carrying capacity was studied. The practical requirements of in-plane and out-of-plane stiffness of edge column were suggested. The experimental and numerical results showed that: this kind structure exhibits high strength, good energy dissipation capacity, and good ductility (the ductility coefficients are more than 3.0). When the inter-story drift angle reaches 1/50, the strength degradation is no more than 5%, indicating that the structure has good seismic behaviors. The span-to-height ratio has little effect on load-carrying capacity, while slightly affects the initial stiffness and ductility. The effect of height-to-thickness ratio (thickness) on load-carrying capacity is relatively larger than other factors. The middle braces do not improve the behaviors of structures. The stiffness of edge column has great effect on lateral load-carrying capacity of shearwall structures. The value of column stiffness index could bewithin 2.0–2.5 to achieve the sufficient constraints and economical benefit. 1-s2.0-S0143974X15001406-main.pdf

Seismic behaviors of steel plate shear wall structures with construction details and materials Wang Meng a,⁎, YangWeiguo a, Shi Yongjiub, Xu Jian c a School of Civil Engineering, Beijing Jiaotong University, Beijing 100044, China b Department of Civil Engineering, Tsinghua University, Beijing 100084, China c China Southwest Architectural Design and Research Institute Corp. Ltd, Chengdu 610081, China a r t i c l e i n f o a b s t r a c t Article history: Received 3 May 2014 Accepted 8 January 2015 Available online 23 February 2015 Keywords: Steel plate shear wall structure Structural construction detail Low yield point steel T type stiffened ribs Finite element method (FEM) Hysteretic behavior In order to have a systematic and comprehensive comparison of seismic behaviors of steel plate shear wall structures with different construction details, a numerical method was proposed, which was proved accurately to predict the performance of structures with published quasi-static tests. Then, eight typical steel shear wall models with different structural construction details were established. Also an advanced stiffened low yield point steel plate shear wall was proposed to avoid excessive out-of-plane deformation. The seismic behaviors of above nine shear wall models were fully compared and analyzed, and key issues, such as energy-dissipating capacity, ductility, out-of-plane deformation and the effect of tension field on the columns were discussed in depth. The results showed that: in high-intensity seismic area, load-carrying capacity, hysteretic behaviors, failure modes, seismic ductility and economic performance should be taken into account comprehensively to choose the appropriate form of steel plate shear wall structure; the proposed low yield point steel plate shear wall with T type stiffened ribs could most effectively improve the energy dissipation capacity and ductility, and lessen the impact of tension field on the columns, besides, it had better load-carrying capacity and smallest out-of-plane deformation. This method provided a good way for improving the seismic behaviors of steel shear wall structures. 1-s2.0-S0143974X15000097-main.pdf

Strengthening of Steel Slab-On-Girder Bridges by Increasing Torsional Stiffness, Case Study: Karkhe Bridge Original Article, B32 Gharighoran A, Rafizadeh A. Journal. Civil Eng. Urban. 2(5): 182-186. 2012. ABSTRACT:A field investigation is conducted to strengthening of Karkhe Bridge with type of steel slab-girder in Khouzestan, Iran that it was damaged due to unusual loading and had been extra vibration. In the first, two types of truck are assigned that one of them has loading of Iranian code (40-ton-truck), and other has unusual loading (90-ton-truck) that used in field for transportation of materials. In the next step, this bridge is analyzed by finite element method under these two types of loading, and load distribution factors for different modes are determined. According to these factors, flexural and torsional moment and also displacements of bridge are calculated. In order to strengthening of bridge, fin sections are used to increasing the flexural stiffness for girders, and lateral bracings are used to increasing the torsional stiffness. Finally, results of analysis after strengthening of structure are compared with results before strengthening, that it shows improving in distribution of load between girders and decrease of displacements for bridge deck. Keywords:Steel Bridge, Slab-on-girder, Torsional stiffness, Unusual load, Finite element method منبع: [Hidden Content] دانلود: [Hidden Content] JCEU---B 32 182-186.pdf