• Coupled systems mechanics
• /
• v.9 no.4
• /
• pp.359-379
• /
• 2020

Due to susceptibility of bridges in the past earthquakes, vulnerability assessment and strengthening of bridges has gained a particular significance. The objective of the present study is to employ an analytical method for the development of fragility curves, as well as to investigate the effect of strengthening on the RC box-girder bridges. Since fragility curves are used for pre-and post-earthquake planning, this paper has attempted to adopt the most reliable modeling assumptions in order to increase the reliability. Furthermore, to acknowledge the interaction of soil, abutment and pile, the effect of different strengthening methods, such as using steel jacketing and FRP layers, the effect of increase in the bridge pier diameter, and the effect of vertical component of earthquake on the vulnerability of bridges in this study, a three-span RC box-girder bridge was modeled in 9 different cases. Nonlinear dynamic analyses were carried out on the studied bridges subjected to 100 ground motion records via OpenSEES platform. Therefore, the fragility curves were plotted and compared in the four damage states. The results revealed that once the interaction of soil and abutment and the vertical component of the earthquake are accounted for in the calculations, the median fragility is reduced, implying that the bridge becomes more vulnerable. It was also confirmed that steel jackets and FRP layers are suitable methods for pier strengthening which reduces the vulnerability of the bridge.

• Structural Engineering and Mechanics
• /
• v.54 no.2
• /
• pp.257-289
• /
• 2015

Shear connectors are generally used to link the slab and girders together in slab-on-girder bridge structures. Damage of shear connectors in such structures will result in shear slippage between the slab and girders, which significantly reduces the load-carrying capacity of the bridge. Because shear connectors are buried inside the structure, routine visual inspection is not able to detect conditions of shear connectors. A few methods have been proposed in the literature to detect the condition of shear connectors based on vibration measurements. This paper proposes a different dynamic condition assessment approach to identify the damage of shear connectors in slab-on-girder bridge structures based on power spectral density transmissibility (PSDT). PSDT formulates the relationship between the auto-spectral densities of two responses in the frequency domain. It can be used to identify shear connector conditions with or without reference data of the undamaged structure (or the baseline). Measured impact force and acceleration responses from hammer tests are analyzed to obtain the frequency response functions at sensor locations by experimental modal analysis. PSDT from the slab response to the girder response is derived with the obtained frequency response functions. PSDT vectors in the undamaged and damaged states can be compared to identify the damage of shear connectors. When the baseline is not available, as in most practical cases, PSDT vectors from the measured response at a reference sensor to those of the slab and girder in the damaged state can be used to detect the damage of shear connectors. Numerical and experimental studies on a concrete slab supported by two steel girders are conducted to investigate the accuracy and efficiency of the proposed approach. Identification results demonstrate that damages of shear connectors are identified accurately and efficiently with and without the baseline. The proposed method is also used to evaluate the conditions of shear connectors in a real composite bridge with in-field testing data.

• Journal of the Korean GEO-environmental Society
• /
• v.23 no.5
• /
• pp.5-13
• /
• 2022

In this study, dynamic characteristics and liquefaction resistance characteristics of silica sand which is used to simulate sandy layer were conducted using the cyclic triaxial test according to the relative density difference. The difference in liquefaction resistance with the relative density was confirmed through the test results, which the relative density conditions were changed to 40%, 60%, and 80%, and the cyclic resistance ratio (CRR) curve of the silica sand was obtained. In addition, in order to examine the validity of the liquefaction resistance ratio (CRR) curve, artificial silica sand ground was created, and liquefaction potential was evaluated through the simple assessment method and the detailed assessment method, and the safety factors of each were compared.

• Physical Therapy Korea
• /
• v.24 no.1
• /
• pp.30-40
• /
• 2017

Background: Many studies have reported positive results of the various mirror training and virtual reality games in improving dynamic standing balance and posture adjustment in chronic stroke patients. However, no systematic study has been conducted to compare the effects of virtual reality games and the mirror balance training. Objects: The purpose of this study was to compare the effectiveness of Wii balance games and Mirror Self-Balancing Exercises in improving proprioception of knee joint and standing balance of people with chronic stroke. Methods: Twenty patients with chronic stroke volunteered for this study. The subjects were randomly divided into a Wii balance games group and a Mirror Self-Balancing Exercises group with 10 patients in each group. Each training was performed for 30 mins a day for 4 days. In addition to the balance training, 30 mins neuro-developmental-treatment based routine physical therapy was given to both groups. Proprioception was measured using two continuous passive motion devices, and static balance was measured using a Wii balance board. Dynamic balance assessment tools included the Berg Balance Scale, Dynamic Gait Index, and Timed Up-and-Go test. Results: All measured variables before and after the experimental results showed a significant improvement in both groups (p<.05). Only the improvement of the affected knee proprioception appeared to be significantly greater in the Wii balance game group (p<.05). However, other variables did not differ between the groups (p>.05). Conclusion: The findings suggest that both Wii balance games and Mirror Self-Balancing Exercises may be helpful for improving the proprioception of knee joint and the balance of patients with chronic stroke.

• Steel and Composite Structures
• /
• v.41 no.5
• /
• pp.761-773
• /
• 2021

This study presents a 3D non-linear finite element (FE) assessment of dynamic soil-structure interaction (SSI). The numerical investigation has been performed on the time domain through a Finite Element (FE) system, while considering the nonlinear behavior of soil and the multi-directional nature of genuine seismic events. Later, the FE outcomes are analyzed to the recorded in-situ free-field and structural movements, emphasizing the numerical model's great result in duplicating the observed response. In this work, the soil response is simulated using an isotropic hardening elastic-plastic hysteretic model utilizing HSsmall. It is feasible to define the non-linear cycle response from small to large strain amplitudes through this model as well as for the shift in beginning stiffness with depth that happens during cyclic loading. One of the most difficult and unexpected tasks in resolving soil-structure interaction concerns is picking an appropriate ground motion predicted across an earthquake or assessing the geometrical abnormalities in the soil waves. Furthermore, an artificial neural network (ANN) has been utilized to properly forecast the non-linear behavior of soil and its multi-directional character, which demonstrated the accuracy of the ANN based on the RMSE and R² values. The total result of this research demonstrates that complicated dynamic soil-structure interaction processes may be addressed directly by passing the significant simplifications of well-established substructure techniques.

• Advances in aircraft and spacecraft science
• /
• v.2 no.2
• /
• pp.109-124
• /
• 2015

This paper deals with the aerodynamic and aerothermodynamic trade-off analysis of a hypersonic flying test bed. Such vehicle will have to be launched with an expendable launcher and shall re-enter the Earth atmosphere allowing to perform several experiments on critical re-entry phenomena. The demonstrator under study is a re-entry space glider characterized by a relatively simple vehicle architecture able to validate hypersonic aerothermodynamic design database and passenger experiments, including thermal shield and hot structures. A summary review of the aerodynamic characteristics of two flying test bed concepts, compliant with a phase-A design level, has been provided hereinafter. Several design results, based both on engineering approach and computational fluid dynamics, are reported and discussed in the paper.

• The Journal of Korean Physical Therapy
• /
• v.16 no.2
• /
• pp.17-21
• /
• 2004

We need to study about lower extremity alignment because the structure dictates the function of lower extremity. Through lower extremity alignment assessment in static posture, we recognize abnormal structural conditions which could affect dynamic motion such as gait. To evaluate of lower extremity alignment provide so many useful information, but method of measurement is so limited. Therefore, this review will assist understanding for measurement of lower extremity alignment in static posture. From now on study about the objective measurement method must be achieved much more in physical therapy.

• The Journal of Korean Physical Therapy
• /
• v.15 no.1
• /
• pp.1-8
• /
• 2003

We need to study about lower extremity alignment because the structure dictates the function of lower extremity. Through lower extremity alignment assessment in static posture, we recognize abnormal structural conditions which could affect dynamic motion such as gait. To evaluate of lower extremity alignment provide so many useful information, but method of measurement is so limited. Therefore, this review will assist understanding for measurement of lower extremity alignment in static posture. From now on study about the objective measurement method must be achieved much more in physical therapy.

• Smart Structures and Systems
• /
• v.16 no.6
• /
• pp.1049-1068
• /
• 2015

In the paper, the authors propose the application of operational deflection shapes (ODS) for the detection of structural changes in technical objects. The ODS matrix is used to formulate the spatial filter that is further used for damage detection as a classical modal filter (Meirovitch and Baruh 1982, Zhang et al. 1990). The advantage of the approach lies in the fact that no modal analysis is required, even on the reference spatial filter formulation and other components apart from structural ones can be filtered (e.g. harmonics of rotational velocity). The proposed methodology was tested experimentally on a laboratory stand, a frame-like structure, excited from two sources: an impact hammer, which provided a wide-band excitation of all modes, and an electro-dynamic shaker, which simulated a harmonic component in the output spectra. The damage detection capabilities of the proposed method were tested by changing the structural properties of the model and comparing the results with the original ones. The quantitative assessment of damage was performed by employing a damage index (DI) calculation. Comparison of the output of the ODS filter and the classical modal filter is also presented and analyzed in the paper. The closing section of the paper describes the verification of the method on a real structure - a road viaduct.

• Structural Engineering and Mechanics
• /
• v.59 no.4
• /
• pp.703-718
• /
• 2016

Masonry arch bridges present a large segment of Iranian railway bridge stock. The ever increasing trend in traffic requires constant health monitoring of such structures to determine their load carrying capacity and life expectancy. In this respect, the performance of one of the oldest masonry arch bridges of Iranian railway network is assessed through field tests. Having a total of 11 sensors mounted on the bridge, dynamic tests are carried out on the bridge to study the response of bridge to test train, which is consist of two 6-axle locomotives and two 4-axle freight wagons. Finite element model of the bridge is developed and calibrated by comparing experimental and analytical mid-span deflection, and verified by comparing experimental and analytical natural frequencies. Analytical model is then used to assess the possibility of increasing the allowable axle load of the bridge to 25 tons. Fatigue life expectancy of the bridge is also assessed in permissible limit state. Results of F.E. model suggest an adequacy factor of 3.57 for an axle load of 25 tons. Remaining fatigue life of Veresk is also calculated and shown that a 0.2% decrease will be experienced, if the axle load is increased from 20 tons to 25 tons.