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RISS 인기검색어
- 검색키워드
- 저자 : Vahid Saberi (검색결과 4 건)
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Post Tensioned Tendons for Seismic Retrofitting of Weak Bolted T-stub Connections
Vahid Saberi,Mohsen Gerami,Ali Kheyroddin 한국강구조학회 2017 International Journal of Steel Structures Vol.17 No.3
Current design philosophy for conventional steel moment resisting frames (MRFs) in high seismic regions is that the frames should not collapse for major earthquakes. However, significant structural damage and residual drift due to inelastic deformations in beams and columns may cause loss of building occupancy or operation after major earthquakes. On the other hand, Selecting the optimum technique for rehabilitation of existing structures with weak connections has been a challenge for engineers in the recent years. In this study, the authors proposed using post-tensioned tendons for rehabilitation of bolted Tstub connections with weak bolts or weak T-stub flange as well as a technique for changing pinned connections to moment connections. Six corner connection specimens are made and tested under SAC cyclic loading protocol. The results of this study show that this rehabilitation technique not only modifies the cyclic behavior of weak rigid connections and changes simple bolted connections into moment connections, but also it improves the behavior of the rehabilitated connections in a way that their behavior is more desirable than that of the reference rigid connection designed according to AISC. For example, flexural capacity and rotational stiffness of the retrofitted connections are higher than those of the reference connection by 18 and 26% in average respectively. Besides, rehabilitation using post tensioned tendons add self-centering ability to the retrofitted connection that has a major role in preventing permanent deformations in frame and thus, the possibility of using frictional dampers in self-centering frames for increasing the energy absorption capacity is provided. This rehabilitation technique in bolted connection with weak T-stub flange has better cyclic behavior compared to that of a connection with weak bolts, since the T-stub participates in energy absorption and higher energy absorption is reached.
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Hamid Saberi,Vahid Saberi,Ali Kheyroddin,Mohsen Gerami 한국강구조학회 2019 International Journal of Steel Structures Vol.19 No.2
A retrofi t method for bolted end plate connections is the use of haunches. This method needs no change or replacement of connection components. The optimum selection of rehabilitation parameters like thickness or haunch-beam angle is of great importance for designers. Besides, one of the important factors for designers to select this retrofi t method, is the effi ciency of retrofi tting by haunches and the eff ectiveness of retrofi t parameters on behavior of retrofi tted frames in near- and far-fi eld earthquakes. The results of 2D numerical modeling of the frames shows that rehabilitation of the weak end plate connections using haunch improves the seismic behavior of the weak frame relative to the reference frame with connections designed according to AISC code. For example, the roof displacements are reduced by 8% averagely and the maximum story drifts in near and far-fi eld earthquakes are reduced by 22% and 12% in the rehabilitated frames compared to those of the reference frame. The results of 3D substructure numerical models, after verifi cation by experimental results, showed that the increase of haunch thickness from 12 to 18 mm did not signifi cantly increase the moment capacity and initial rotational stiff ness. However, the pinching in moment-rotation hysteresis is decreased. The increase of haunch angle from 30 to 60 resulted in shift of plastic hinge to haunch internal area and 100% reduction of energy absorption and initial rotational stiff ness compared to those of the reference specimen. Since the change of retrofi t method parameters results in change of stiff ness and natural time period of the structure and the aff ecting parameter on structure dynamic behavior is “the ratio between structure main time frequency to earthquake predominant time period”, the selection of the fi rst haunch thickness with an angle of 30 degree toward the beam that satisfy the requirements of FEMA350 will be economic and optimized.
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The electroless plating of Cu-Ni-P alloy onto cotton fabrics
Akbar Khodaparast Haghi,Arezoo Afzali,Vahid Mottaghitalab,Mahmood Saberi Motlagh 한국화학공학회 2010 Korean Journal of Chemical Engineering Vol.27 No.4
The objective of this study is to apply the electroless plating of Cu-Ni-P alloy on cotton fabrics to the preparation of conductive fabrics. The alloy composed of infinit small amount of nickel and phosphorus particle originated from sodium hypophosphite and nickel sulphate respectively as reducing agent and hypophosphite oxidation accelerator. Electroless plating of Cu-Ni-P alloy on cotton fabrics and effect of plating on the physical and mechanical properties of alloy coated fabrics as well as electromagnetic interference (EMI) shielding effectiveness were reported in detail. In this research highly washing and abrasion durable conductive fabrics obtained with supreme shielding effectiveness.
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Clinical and Ultrasonographic Changes of the Breast after Use of Soy Isoflavones
Alipour, Sadaf,Afshar, Somayeh,Moini, Ashraf,Dastjerdi, Marzieh Vahid,Saberi, Azin,Bayani, Leila,Eslami, Bita,Hosseini, Ladan Asian Pacific Journal of Cancer Prevention 2012 Asian Pacific journal of cancer prevention Vol.13 No.12
Background: Phytoestrogens may be an alternative therapy in control of menopausal symptoms but their definite effects on breast tissue must be determined. Our study aimed to define the clinical and ultrasonographic changes of the breast after use of soy isoflavones in menopausal women. Materials and Methods: Menopausal women with hot flashes were randomly grouped as cases and controls and cases received soy isoflavones for 12 weeks. Breast examination (BE) and ultrasonography (US) were done at 0, 6 and 12 weeks. Tenderness and nodularity on BE were graded 1-4 by breast surgeons. Results: There were 30 women in the case and 26 in the control group. The mean age was 51.3 years and the mean age of menopause was 49.2 years. There was no change in the BE and US at 6 weeks in controls. In the case group, 10% had grade 1 tenderness and 13.3% grade 2 tenderness and grade 1 nodularity in BE accompanied with diffuse small cysts in US. At 12 weeks, there was no change in BE and US in the 2 groups. Conclusions: There was no statistically significant difference in the BE of the 2 groups at 6 and 12 weeks (p value=0.36 and 0.41 for nodularity and tenderness respectively) and in the US results. Although the literature contains many facts concerning PEs and the breast, further prospective studies are needed to identify structural breast changes produced by PEs in order to identify the appropriate dosage and indications of use.
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