Sharif Digital Repository

An experimental research study was carried out to investigate the life-time performance of unbounded Steel Reinforced Elastomeric Bearings (SREB), which are designed and used for service limit state in bridges, subjected to seismic demands. Such behaviour was investigated using 13 full-scale specimens in three phases; (1) effects of long-term service, namely the long term presence of vertical loading at service limit state, on the mechanical properties of the bearings, (2) effects of consecutive shear loading at different amplitude in presence of permanent loading, and (3) post-earthquake behaviour of the bearing against service load conditions. An innovative test setup was utilized in which... 

Reduction of large tensile stresses and cost-efficiency has made unbonded isolators an attractive option as an isolation system. Following this idea and the results obtained by various researchers, it is shown that unbonded steel-reinforced elastomeric bearings (SREBs), which are used and designed for non-seismic actions, have inherently acceptable characteristics in tolerating large shear deformations for a cost-effective isolation system and can provide improved structural performance. However, this capacity is neglected in the design process. The current article presents an experimental program to analyze the mechanical properties of steel-reinforced natural rubber bearings without the... 

Following the idea of using unbonded isolators to eliminate the tensile stress and providing a cost-effective isolation system, recent experimental research has shown ordinary unbonded steel reinforced elastomeric bearings (SREBs) as an attractive option for seismic isolation of highway bridges. The focus of current research work is on the evaluation of the seismic vulnerability of a highway bridge isolated by unbonded SREBs through developing fragility curves of the structure. This assessment considers parameters playing a key role in the isolation system behavior, namely the friction coefficient, as well as the isolator aging effects. In this regard, a typical three-span highway bridge is... 

This paper discusses the necessity of considering the concurrent effects of uniform temperature and earthquake loadings in the design of cable-stayed bridges. This load combination is not foreseen in current design standards such as AASHTO and Eurocode. Three-dimensional finite element models of cable-stayed bridges are employed for nonlinear time history analyses. A load combination is proposed that adds uniform temperature loading to the existing extreme event load combination. The proposed combination is compared with existing extreme event load combination and the changes in forces and displacements are noted. A parametric study is then conducted by varying a number of properties of the... 

Different types of gas reservoir such as Liquid Natural Gas (LNG) are among the strategic infrastructures, and have great importance for any government or their private owners. To keep the tank and its contents safe during earthquakes especially if the contents are of hazardous or flammable materials; using seismic protection systems such as base isolator can be considered as an effective solution. However, the major deficiency of this system can be the large deformation in the isolation level which may lead to the failure of bearing system. In this paper, as a solution, the efficacy of an optimally designed combined vibration control system, the combined laminated rubber isolator and... 

Steel Reinforced Elastomeric Bearings (SREB) are mostly designed and used for providing different supporting conditions under service loads; while recent studies have shown remarkable characteristics which help them as a cost-effective isolation system. However, little investigation has been carried out to indicate the influence of parameters affecting the mechanical properties of the bearings under large shear deformations (i.e., the seismic performance as an isolation system). A comparative parametric study was conducted herein through finite element modeling of SREBs. The implemented model was also verified by experimental test results. The hysteretic behavior was studied in both cases of... 

The electroencephalogram (EEG) is a representative signal containing information about the condition of the brain. The shape of the wave may contain useful information about its state. However, the human observer cannot directly monitor these subtle details. Besides, since bio-signals are highly subjective, the symptoms may appear at random in the time scale. Therefore, the EEG signal parameters, extracted and analyzed using computers, are highly useful in diagnosis. The aim of this work is to compare the different classifiers when applied to EEG data from normal and epileptic subjects. For this purpose an adaptive neural fuzzy network (ANFN) to classify normal and epileptic EEG signals is... 

Adsorption isotherms of H2S, CO2, and CH4 on the Si-CHA zeolite were measured over pressure range of 0-190 kPa and temperatures of 298, 323, and 348 K. Acid gases adsorption isotherms on this type of zeolite are reported for the first time. The isotherms follow a typical Type-I shape according to the Brunauer classification. Both Langmuir and Toth isotherms describe well the adsorption isotherms of methane and acid gases over the experimental conditions tested. At room temperature and pressure of 100 kPa, the amount of CO2 adsorption for Si-CHA zeolite is 29 % greater than that reported elsewhere (van den Bergh et al. J Mem Sci 316:35-45 (2008); Surf Sci Catal 170:1021-1027 (2007)) for the... 

A green and simple synthesis method based on a two-step chemical vapor deposition approach has been developed to synthesize transition metal dichalcogenides flakes. With non-toxic precursor such as transition metal oxides and elemental sulfur, large-area, strong photoluminescent and uniform MoS2 nanoflakes were produced at a relatively low growth temperature (650 °C). Controlling the layer number and morphology was achieved only by precursor concentration without any oxide impurity revealed by SEM, PL and Raman spectroscopy. This method can be used to make wide range of metal chalcogenides such as ZnS, SnS2, PtS2 and PdS2  

A high silica CHA-type membrane was synthesized by the in-situ crystallization method on a disk like α-alumina porous support to separate both acid (H2S, CO2) gases from methane. The membrane showed a permeance of 3.39×10-8mol/m2sPa for pure CO2with CO2/CH4 ideal selectivity of 21.6 at 303K and 100kPa pressure difference across the membrane. The membrane was also tested with N2 and O2 pure gases indicating a small O2/N2 selectivity of 1.2-1.4, which shows that this type of membrane is not suitable for O2/N2 separation. The membrane performance was also analyzed by binary (CO2-CH4) and ternary (H2S-CO2-CH4) gas mixtures, with compositions near the real sour natural gas (CO2: 2.13mol%, H2S:... 

In recent years, there hass been a pronounced emphasis on percutaneous needle steering with the aid of advanced soft tissue modeling techniques. In this work an optical flow based motion estimation method is used to estimate the force applied to the needle by the soft tissue during percutaneous applications. The study considers Finite Element Model (FEM) of the tissue evaluated by the deformation data acquired through the optical flow method. To represent the soft tissue behavior, dynamic FEM with Rayleigh damping and viscoelastic models are used. The method is validated experimentally through offline evaluation of the ultrasonic images of the chicken breast punctured by a needle. The force... 

In this paper, a model-based dynamics equation for the needle movement through the soft tissue is developed. A model-based control scheme which uses the force estimation calculated through the simulated tissue deformation data and the dynamic finite element as the tissue model is proposed. To compare the performance of the proposed controller, a PD controller is also used for the proposed needle dynamics equation. It is shown that even with uncertainty in model parameters; the mode-based controller outperforms the PD controller. Furthermore, although increasing the controller gain improves the performance of PD, but the model-based controller's performance is still superior  

In this paper the dynamics and control of the underactuated flexible needle will be discussed. To evaluate the dynamics of the needle, the study uses Saint Venant-Kirchhoff and finite element method. The model is validated using the experimental data provided in the literature. It is also shown that using iterative decomposition of the dynamics equation the unactuated degree of freedom of the needle tip can be feedback linearized. The effect of the control signal exerted on the tip is projected via iterative decomposition of the dynamics equation. The efficiency of the approach will be next explored through some examples  

In percutaneous applications, needle insertion into soft tissue is considered as a challenging procedure, and hence, it has been the subject of many recent studies. This study considers a model-based dynamics equation to evaluate the needle movement through prostate soft tissue. The proposed model estimates the applied force to the needle using the tissue deformation data and finite element model of the tissue. To address the role of mechanical properties of the soft tissue, an inverse dynamics control method based on sliding mode approach is used to demonstrate system performance in the presence of uncertainties. Furthermore, to deal with inaccurate estimation of mechanical parameters of... 

Needle insertion into the soft tissue has been the subject of many studies during the last decade, while needle control has become a crucial training tool, evaluating surgeon's skills in such critical incision. This study considers a model-based dynamics equation for the needle movement through the soft tissue. In the proposed model, the force distribution along the needle shaft is estimated through the use of tissue deformation data and tissue model. A novel algorithm for the needle control simulation is also proposed based on the developed dynamics equation of the needle movement. To point out the role of mechanical properties of the soft tissue, an inverse dynamics control method is used... 

Although 'Needle steering' is considered a challenge in needle insertion strategies, needle control becomes a crucial training tool for evaluating surgeon's skills in such critical incision. In this study, a model-based dynamics equation for the needle movement through the soft tissue is developed. In the proposed control scheme, the force estimation calculated through the simulated tissue deformation data and the dynamic finite element as the tissue model, is used as the force feedback. To point out the role of mechanical properties of the soft tissue, an inverse dynamics control method is used to demonstrate the system performance in presence of uncertainty in tissue mechanical parameters....