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- 검색키워드
- 저자 : Ashtari, Payam (검색결과 15 건)
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Experimental and numerical study on innovative seismic T-Resisting Frame (TRF)
Payam Ashtari,Helia Barzegar Sedigh,Farzaneh Hamedi 국제구조공학회 2016 Structural Engineering and Mechanics, An Int'l Jou Vol.60 No.2
In common structural systems, there are some limitations to provide adequate lateral stiffness, high ductility, and architectural openings simultaneously. Consequently, the concept of T-Resisting Frame (TRF) has been introduced to improve the performance of structures. In this study, Configuration of TRF is a Vertical I-shaped Plate Girder (V.P.G) which is placed in the middle of the span and connected to side columns by two Horizontal Plate Girders (H.P.Gs) at each story level. System performance is improved by utilizing rigid connections in link beams (H.P.Gs). Plastic deformation leads to tension field action in H.P.Gs and causes energy dissipation in TRF; therefore, V.P.G. High plastic deformation in web of TRF’s members affects the ductility of system. Moreover, in order to prevent shear buckling in web of TRF’s members and improve overall performance of the system, appropriate criteria for placement of web stiffeners are presented in this study. In addition, an experimental study is conducted by applying cyclic loading and using finite element models. As a result, hysteresis curves indicate adequate lateral stiffness, stable hysteretic behavior, and high ductility factor of 6.73.
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Nouri, Farshid,Ashtari, Payam Techno-Press 2015 Wind and Structures, An International Journal (WAS Vol.20 No.4
In this paper, a novel methodology is proposed to obtain optimum location of outriggers. The method utilizes genetic algorithm (GA) for shape and size optimization of outrigger-braced tall structures. In spite of previous studies (simplified methods), current study is based on exact modeling of the structure in a computer program developed on Matlab in conjunction with OpenSees. In addition to that, exact wind loading distribution is calculated in accordance with ASCE 7-10. This is novel since in previous studies wind loading distributions were assumed to be uniform or triangular. Also, a new penalty coefficient is proposed which is suitable for optimization of tall buildings. Newly proposed penalty coefficient improves the performance of GA and results in a faster convergence. Optimum location and number of outriggers is investigated. Also, contribution of factors like central core and outrigger rigidity is assessed by analyzing several design examples. According to the results of analysis, exact wind load distribution and modeling of all structural elements, yields optimum designs which are in contrast of simplified methods results. For taller frames significant increase of wind pressure changes the optimum location of outriggers obtained by simplified methods. Ratio of optimum location to the height of the structure for minimizing weight and satisfying serviceability constraints is not a fixed value. Ratio highly depends on height of the structure, core and outriggers stiffness and lateral wind loading distribution.
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Mohammad Yassami,Payam Ashtari 대한토목학회 2015 KSCE JOURNAL OF CIVIL ENGINEERING Vol.19 No.5
In this paper, Artificial Bee Colony (ABC) algorithm, fuzzy logic and Simple Genetics (GA) are used for stiffness optimization of steel frames with rigid or semi-rigid connections. In the genetic algorithm, uniform crossover operator is employed and also, binary coding is used to achieve better convergence. Behavior of steel frames depends highly on beam to column connections. Here, beam to column connections are assumed to be semi-rigid or rigid. Linear analysis and design has been used for steel frame structures. Matlab program has been utilized for the process of optimization in combination with OpenSees software for frame analysis. Beams and columns sections are selected from a standard set of steel sections such as American Institute of Steel Construction (AISC) wideflange (W) shapes. Displacement and stress constraints are imposed on the frame. Frye and Morris polynomial model is used for semi-rigid connection. Also, the proposed algorithm considers a fitness function using appropriate balancing factors which leads to a faster convergence. Three different design examples with various types of connections are presented to demonstrate the efficiency and robustness of the proposed approach. The results show that the fuzzy genetic algorithm and artificial bee colony results in lighter structures consuming less computation time compared to simple genetic algorithm.
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Evaluation of Seismic Performance Factors for High-Rise Steel Structures with Diagrid System
Morteza Sohrabi-Haghighat,Payam Ashtari 대한토목학회 2019 KSCE JOURNAL OF CIVIL ENGINEERING Vol.23 No.11
Diagrid system is a new tubular structural system in tall buildings which requires seismic performance factors (R, Ω0, Cd) for seismic design according to the loading and design codes. By considering the fact that the current codes do not include these factors, this paper aims to evaluate them based on the FEMA P695 methodology. For this purpose, five archetypes have been developed in a way that the structure story heights and span lengths are respectively equal to 4 and 6 meters; this makes the diagonal angles equal to 53.13 degrees. The response modification coefficient (R-factor) of the archetypes was calculated by the Uang method through iteration in analysis and design in OpenSees and ETABS software, respectively. Two types of analysis were carried out: non-linear static analysis (pushover analysis) and non-linear incremental dynamic analysis (IDA); the first evaluates ductility, μT, and over-strength factors, Ω, and the second evaluates “collapse margin ratio (CMR)”. At the end, computed “adjusted collapse margin ratio (ACMR)” was controlled by acceptable values of ACMR in the FEMA P695. Based on the results, the values of R-factor, over-strength factor, Ω0, and deflection amplification factor, Cd, are proposed to be 2.5, 2.0 and 2.5, respectively.
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Farshid Nouri,Payam Ashtari 한국풍공학회 2015 Wind and Structures, An International Journal (WAS Vol.20 No.4
In this paper, a novel methodology is proposed to obtain optimum location of outriggers. Themethod utilizes genetic algorithm (GA) for shape and size optimization of outrigger-braced tall structures. Inspite of previous studies (simplified methods), current study is based on exact modeling of the structure in acomputer program developed on Matlab in conjunction with OpenSees. In addition to that, exact windloading distribution is calculated in accordance with ASCE 7-10. This is novel since in previous studieswind loading distributions were assumed to be uniform or triangular. Also, a new penalty coefficient isproposed which is suitable for optimization of tall buildings .Newly proposed penalty coefficient improvesthe performance of GA and results in a faster convergence. Optimum location and number of outriggers isinvestigated. Also, contribution of factors like central core and outrigger rigidity is assessed by analyzingseveral design examples. According to the results of analysis, exact wind load distribution and modeling ofall structural elements, yields optimum designs which are in contrast of simplified methods results. For tallerframes significant increase of wind pressure changes the optimum location of outriggers obtained bysimplified methods. Ratio of optimum location to the height of the structure for minimizing weight andsatisfying serviceability constraints is not a fixed value. Ratio highly depends on height of the structure, coreand outriggers stiffness and lateral wind loading distribution.
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New development of artificial record generation by wavelet theory
Amiri, G. Ghodrati,Ashtari, P.,Rahami, H. Techno-Press 2006 Structural Engineering and Mechanics, An Int'l Jou Vol.22 No.2
Nowadays it is very necessary to generate artificial accelerograms because of lack of adequate earthquake records and vast usage of time-history dynamic analysis to calculate responses of structures. According to the lack of natural records, the best choice is to use proper artificial earthquake records for the specified design zone. These records should be generated in a way that would contain seismic properties of a vast area and therefore could be applied as design records. The main objective of this paper is to present a new method based on wavelet theory to generate more artificial earthquake records, which are compatible with target spectrum. Wavelets are able to decompose time series to several levels that each level covers a specific range of frequencies. If an accelerogram is transformed by Fourier transform to frequency domain, then wavelets are considered as a transform in time-scale domain which frequency has been changed to scale in the recent domain. Since wavelet theory separates each signal, it is able to generate so many artificial records having the same target spectrum.
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An analytical model for shear links in eccentrically braced frames
Saeed Erfani,Amir Ashtari 국제구조공학회 2016 Steel and Composite Structures, An International J Vol.22 No.3
When an eccentrically braced frame (EBF) is subjected to severe earthquakes, the links experience inelastic deformations while beams outside of the link, braces and columns are designed to remain elastic. To perform reliable inelastic analyses of EBFs sufficient analytical model which can accurately predict the inelastic performance of the links is needed. It is said in the literature that available analytical models for shear links generally predict very well the maximum shear forces and deformations from experiments on shear links, but may underestimate the intermediary values. In this study it is shown that available analytical models do not predict very well the maximum shear forces and deformations too. In this study an analytical model which can accurately predict both maximum and intermediary values of shear force and deformation is proposed. The model parameters are established based on test results from several experiments on shear links. Comparison of available test results with the hysteresis curves obtained using the proposed analytical model established the accuracy of the model. The proposed model is recommended to be used to perform inelastic analyses of EBFs.
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Mehran Razvani Habibabadi,Fereshteh Ashtari,Iman Raeisi 사단법인약침학회 2021 Journal of Acupuncture & Meridian Studies Vol.14 No.2
Background: Migraine is a very common neurobiological headache disorder caused by an increased irritability of the central nervous system. Acupuncture as a complementary medicine has been suggested as one of the treatments for migraine headaches; however, the findings are conflicting. Objectives: Therefore, the aim of this study was to evaluate the effect of acupuncture with auricular semi-permanent (ASP) needles on migraine headaches. Methods: In this single-blind randomized controlled trial, 80 patients with migraine were selected and divided into two groups. The intervention group was treated with auricular ASP needles in the active points of the ear, and the control group only received routine treatments. Pain score, frequency of migraine headaches, duration of headaches, severity of nausea and vomiting, and patient satisfaction were compared between the two groups for four weeks after the intervention. Results: Our results showed that the level of pain (4.72 ± 2.53, 2.13 ± 1.76 times) and the frequency of migraine headaches (8.98 ± 8.58 hours) from the second week after the intervention in the ASP group were much lower than those in the control group (p < 0.05). However, pain incidence and ear inflammation in the ASP group were negligible and did not differ significantly from those in the control group (p > 0.05). Conclusion: Auricular acupuncture could be considered as a promising complementary therapy along with other standard migraine therapies for the prevention and treatment of migraine headaches.
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