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본 연구에서는 교량구조물의 내진 안전성을 확보하기 위한 내진설계 및 내진 및 면진 교량받침에 대하여 다음과 같이 연구하였다. 먼저 최근에 개정된 내진설계법에 대하여 고찰해보고, 현재 국내외에서 사용되고 있는 내진 및 면진 교량받침에 대한 분석을 통하여, 교량의 내진성 향상을 위하여 설계에 사용되는 국내외의 내진 및 면진 교량받침의 종류 및 기술적특성에 대해 분석평가하였다. 그리고 연속형 도로교량을 모델링하여 면진받침을 사용하여 면진설계된 교량과 일반 교량받침을 사용하여 내진설계 되지않은 일반교량에 대하여 각각 지진하중(EL CENTRO 지진)에 의한 동적수치해석을 수행하여 면진 교량받침의 지진에 대한 저항성 즉 효용성을 분석한 결과, 면진받침을 사용한 교량은 단면력이 전체 교각으로 분산되어 단면력이 감소됨을 알 수 있었다. 따라서 면진설계된 교량의 지진저항성이 효율적임을 알 수 있었다. In this study, recently developed seismic design criterion is analyzed, and the characteristics and applicability of the various special seismic bridge bearings are studied. The dynamic analysis is performed in this study to characterize the hehavior continuous bridge with two different types of bridge bearings(seismically isolated bearings and conventional bearings) under seismic loading condition(EL CENTRO). For the bridges with the seismically isolated bearings, the sectional forces are evenly distributed to entire piers and the total forces are reduced compared with that of the conventional bridges. It means that the bridges with seismically isolated bearing can make a efficient rather than conventional bearings under earthquake loading.
Eventhough the material in the cable-stayed bridge behaves in a linear elastic manner, the overall load-displacement relationships will be nonlinear. An algorithm which consists of the nonlinear stiffness relationships for the cable-stayed bridges is developed. The nonlinearity due to the cable sag is modeled using an equivalent modulus of elasticity. The nonlinearity of the bending member is considered modifying the member stiffness matrix by introducing the concept of stability functions, the geometric nonlinearity is considered recompositing the stiffness matrix caused by the geometric changes in the structure at each loading step. The developed algorithm is used to analyze a cable-stayed bridge of the harp type. The bending moment of the girder, deflections of the girder and tension in cables from the nonlinear analysis are compared with those from linear analysis. The comparison show that the results are in similar pattern, but the nonlinear analysis gives larger values than the linear analysis. The difference between the results from the linear and nonlinear analysis increases as the initial cable tension increases for bending moments of the girder. For deflections of the girder, and the tensions in the cable, it decreases as the initial cable tension increases.
This study proposes a new smart base isolation system that employs Magneto-Rheological Elastomers (MREs), a class of smart materials whose elastic modulus or stiffness can be varied depending on the magnitude of an applied magnetic field. It also evaluates the dynamic performance of the MRE-based isolation system in reducing vibrations in structures subject to various seismic excitations. As controllable stiffness elements, MREs can increase the dynamic control bandwidth of the isolation system, improving its vibration reduction capability. To study the effectiveness of the MRE-based isolation system, this paper compares its dynamic performance in reducing vibration responses of a base-isolated single-story structure (i.e., 2DOF) with that of a conventional base-isolation system. Moreover, two control algorithms (linear quadratic regulator (LQR)-based control and state-switched control) are considered for regulating the stiffness of MREs. The simulation results show that the MRE-based isolation system outperformed the conventional system in suppressing the maximum base drift, acceleration, and displacement of the structure.
This study proposes a new smart base isolation system that employs Magneto-Rheological Elastomers (MREs), a class of smart materials whose elastic modulus or stiffness can be varied depending on the magnitude of an applied magnetic field. It also evaluates the dynamic performance of the MREbased isolation system in reducing vibrations in structures subject to various seismic excitations. As controllable stiffness elements, MREs can increase the dynamic control bandwidth of the isolation system, improving its vibration reduction capability. To study the effectiveness of the MRE-based isolation system, this paper compares its dynamic performance in reducing vibration responses of a base-isolated singlestory structure (i.e., 2DOF) with that of a conventional base-isolation system. Moreover, two control algorithms (linear quadratic regulator (LQR)-based control and state-switched control) are considered for regulating the stiffness of MREs. The simulation results show that the MRE-based isolation system outperformed the conventional system in suppressing the maximum base drift, acceleration, and displacement of the structure.
To determine whether fatty marrow conversion of the proximal femoral metaphysis is related to osteonecrosis of the femoral head, a case-control study was conducted on 42 osteonecrotic hips in 28 patients using Tl-weighted MRls. The 42 hips with osteonecrosis were matched with 84 normal control hips as for gender, age (5-year range), and time of presentation (1-year range). The signal intensities of the proximal femoral metaphysis (SM) and the greater trochanter (ST) were measured in each hip studied. We derived a marrow conversion index (%) using the formula: (SM/ST) x IOO (%). The index was 90.2% (SD, 8.2) in osteonecrotic hips, and 75.1% (SD, 9.1) in matched controls (p = 0.000). By conditional logistic regression, a 5% increase in the index above our control group value of 75% was associated with 3.6 times higher risk for osteonecrosis (95% CI = 1.9-6.7, p = 0.000) and a 10% increase with 12.9 times higher risk (95% CI = 3.7-44.8, p = 0.000). The marrow conversion index, which reflects the ratio of fatty marrow conversion of the proximal femoral metaphysis to that of the greater trochanter measured on Tl-weighted MRI, has a strong association with an increased risk for osteonecrosis.
<P>Maintenance of skeletal muscle function is critical for metabolic health and the disruption of which exacerbates many chronic diseases such as obesity and diabetes. Skeletal muscle responds to exercise or metabolic demands by a fiber-type switch regulated by signaling transcription networks that remains to be fully defined. Here, we report that protein arginine methyltransferase 7 (Prmt7) is a key regulator for skeletal muscle oxidative metabolism. Prmt7 is expressed at the highest levels in skeletal muscle and decreased in skeletal muscles with age or obesity. Prmt7(-/-) muscles exhibit decreased oxidative metabolism with decreased expression of genes involved in muscle oxidative metabolism, including PGC-1 alpha. Consistently, Prmt7(-/-) mice exhibited significantly reduced endurance exercise capacities. Furthermore, Prmt7(-/-) mice exhibit decreased energy expenditure, which might contribute to the exacerbated age-related obesity of Prmt7(-/-) mice. Similarly to Prmt7(-/-) muscles, Prmt7 depletion in myoblasts also reduces PGC-1 alpha expression and PGC-1 alpha-promoter driven reporter activities. Prmt7 regulates PGC-1 alpha expression through interaction with and activation of p38 mitogen-activated protein kinase (p38MAPK), which in turn activates ATF2, an upstream transcriptional activator for PGC-1 alpha. Taken together, Prmt7 is a novel regulator for muscle oxidative metabolism via activation of p38MAPK/ATF2/PGC-1 alpha.</P>
Jeong, Byung-Chul,Lee, Yong-Soo,Park, Yun-Yong,Bae, In-Ho,Kim, Don-Kyu,Koo, Seung-Hoi,Choi, Hong-Ran,Kim, Sun-Hun,Franceschi, Renny T,Koh, Jeong-Tae,Choi, Hueng-Sik American Society for Biochemistry and Molecular Bi 2009 The Journal of biological chemistry Vol.284 No.21
<P>Estrogen receptor-related receptor gamma (ERRgamma/ERR3/NR3B3) is a member of the orphan nuclear receptor with important functions in development and homeostasis. Recently it has been reported that ERRalpha is involved in osteoblast differentiation and bone formation. In the present study we examined the role of ERRgamma in osteoblast differentiation. Here, we showed that ERRgamma is expressed in osteoblast progenitors and primary osteoblasts, and its expression is increased temporarily by BMP2. Overexpression of ERRgamma reduced BMP2-induced alkaline phosphatase activity and osteocalcin production as well as calcified nodule formation, whereas inhibition of ERRgamma expression significantly enhanced BMP2-induced osteogenic differentiation and mineralization, suggesting that endogenous ERRgamma plays an important role in osteoblast differentiation. In addition, ERRgamma significantly repressed Runx2 transactivity on osteocalcin and bone sialoprotein promoters. We also observed that ERRgamma physically interacts with Runx2 in vitro and in vivo and competes with p300 to repress Runx2 transactivity. Notably, intramuscular injection of ERRgamma strongly inhibited BMP2-induced ectopic bone formation in a dose-dependent manner. Taken together, these results suggest that ERRgamma is a novel negative regulator of osteoblast differentiation and bone formation via its regulation of Runx2 transactivity.</P>