Based on research studies currently being carried out at Dalian University of Technology, some important aspects for the earthquake safety assessmcnt of concrete dams are reviewed and discussed. First, the rate-depend...Based on research studies currently being carried out at Dalian University of Technology, some important aspects for the earthquake safety assessmcnt of concrete dams are reviewed and discussed. First, the rate-dependent behavior of concrcte subjected to earthquake loading is examined, emphasizing the properties of concrete under cyclic and biaxial loading conditions. Second, a modified four-parameter Hsieh-Ting-Chen viscoplastic consistency model is developed to simulate the rate-dependent behavior of concrete. The earthquake response of a 278m high arch dam is analyzed, and the results show that the strain-rate effects become noticeable in the inelastic range, Third, a more accurate non-smooth Newton algorithm for the solution of three-dimensional frictional contact problems is developed to study the joint opening effects of arch dams during strong earthquakes. Such effects on two nearly 300m high arch dams have been studied. It was found that the canyon shape has great influence on the magnitude and distribution of the joint opening along the dam axis. Fourth, the scaled boundary finite element method presented by Song and Wolf is employed to study the dam-reservoir-foundation interaction effects of concrete dams. Particular emphases were placed on the variation of foundation stiffness and the anisotropic behavior of the foundation material on the dynamic response of concrete dams. Finally, nonlinear modeling of concrete to study the damage evolution of concrete dams during strong earthquakes is discussed. An elastic-damage mechanics approach for damage prediction of concrete gravity dams is described as an example. These findings are helpful in understanding the dynamic behavior of concrete dams and promoting the improvement of seismic safety assessment methods.展开更多
Arch dams suffer time-varying external loadings and harsh environment that harm their physical properties. With the aging of such dams, damage accumulates and concrete degradation inevitably appears. In this paper, a ...Arch dams suffer time-varying external loadings and harsh environment that harm their physical properties. With the aging of such dams, damage accumulates and concrete degradation inevitably appears. In this paper, a model is proposed for simulating concrete degradation with aging because of chemo-mechanical damage. The seismic response of an arch dam with aging effects is analyzed using the proposed model. The results show that the damage caused by the aging of arch dams may result in an increase in tensile cantilever stresses during earthquakes. Meanwhile, the dynamic displacement and joint opening also clearly increase in comparison with those without damage. Thus, the seismic safety of arch dams is reduced by aging effects.展开更多
Temporomandibular disorders (TMD) negatively affect quality of life, causing pain and restricted jaw movements. This study evaluates the effectiveness of Transcutaneous Electrical Nerve Stimulation (TENS) on TMD patie...Temporomandibular disorders (TMD) negatively affect quality of life, causing pain and restricted jaw movements. This study evaluates the effectiveness of Transcutaneous Electrical Nerve Stimulation (TENS) on TMD patients before orthodontic treatment at the Juarez Autonomous University of Tabasco. A quantitative, quasi-experimental study was conducted with 30 patients who met the inclusion criteria: aged 18 to 65 years, with TMJ pain symptoms, diagnosed with temporomandibular disorders using the Helkimo index, and who had provided informed consent for the study. The range of mandibular movement and the Visual Analog Scale (VAS) were measured to record values before therapy. The electrodes of the TENS therapy were positioned on both sides of the jaw in the preauricular area and the masseter muscle, the therapy was administered for 40 minutes, utilizing a frequency of 2 - 4 Hz and a pulse duration of 300 microseconds. Following this, the range of mandibular movement and the VAS were reassessed to evaluate the outcomes., significantly improved maximum mouth opening (37.7 ± 6.4 mm to 44.6 ± 5.88 mm), right laterality (3.86 ± 1.57 mm to 5.43 ± 1.21 mm), left laterality (3.13 ± 1.63 mm to 4.53 ± 1.61 mm), protrusion (4.01 ± 1.7 mm to 5.36 ± 1.32 mm), and pain perception (4.56 ± 2.045 to 2.03 ± 1.5) (P < 0.01). TENS therapy enhances mandibular movement and reduces pain, making it a well-tolerated, non-invasive complementary treatment for TMD.展开更多
基金National Natural Science Foundation of China Under Grant No.50139010
文摘Based on research studies currently being carried out at Dalian University of Technology, some important aspects for the earthquake safety assessmcnt of concrete dams are reviewed and discussed. First, the rate-dependent behavior of concrcte subjected to earthquake loading is examined, emphasizing the properties of concrete under cyclic and biaxial loading conditions. Second, a modified four-parameter Hsieh-Ting-Chen viscoplastic consistency model is developed to simulate the rate-dependent behavior of concrete. The earthquake response of a 278m high arch dam is analyzed, and the results show that the strain-rate effects become noticeable in the inelastic range, Third, a more accurate non-smooth Newton algorithm for the solution of three-dimensional frictional contact problems is developed to study the joint opening effects of arch dams during strong earthquakes. Such effects on two nearly 300m high arch dams have been studied. It was found that the canyon shape has great influence on the magnitude and distribution of the joint opening along the dam axis. Fourth, the scaled boundary finite element method presented by Song and Wolf is employed to study the dam-reservoir-foundation interaction effects of concrete dams. Particular emphases were placed on the variation of foundation stiffness and the anisotropic behavior of the foundation material on the dynamic response of concrete dams. Finally, nonlinear modeling of concrete to study the damage evolution of concrete dams during strong earthquakes is discussed. An elastic-damage mechanics approach for damage prediction of concrete gravity dams is described as an example. These findings are helpful in understanding the dynamic behavior of concrete dams and promoting the improvement of seismic safety assessment methods.
基金supported by the National Natural Science Foundation of China (Grant No. 50779021)the Beijing Natural Science Foundation (Grant No. 8082014)+1 种基金the Scientific Foundation for Returned Overseas Chinese Scholars, Ministry of Educationthe State Key Laboratory of Hydroscience and Engineering, China (Grant No. 2008-TC-2)
文摘Arch dams suffer time-varying external loadings and harsh environment that harm their physical properties. With the aging of such dams, damage accumulates and concrete degradation inevitably appears. In this paper, a model is proposed for simulating concrete degradation with aging because of chemo-mechanical damage. The seismic response of an arch dam with aging effects is analyzed using the proposed model. The results show that the damage caused by the aging of arch dams may result in an increase in tensile cantilever stresses during earthquakes. Meanwhile, the dynamic displacement and joint opening also clearly increase in comparison with those without damage. Thus, the seismic safety of arch dams is reduced by aging effects.
文摘Temporomandibular disorders (TMD) negatively affect quality of life, causing pain and restricted jaw movements. This study evaluates the effectiveness of Transcutaneous Electrical Nerve Stimulation (TENS) on TMD patients before orthodontic treatment at the Juarez Autonomous University of Tabasco. A quantitative, quasi-experimental study was conducted with 30 patients who met the inclusion criteria: aged 18 to 65 years, with TMJ pain symptoms, diagnosed with temporomandibular disorders using the Helkimo index, and who had provided informed consent for the study. The range of mandibular movement and the Visual Analog Scale (VAS) were measured to record values before therapy. The electrodes of the TENS therapy were positioned on both sides of the jaw in the preauricular area and the masseter muscle, the therapy was administered for 40 minutes, utilizing a frequency of 2 - 4 Hz and a pulse duration of 300 microseconds. Following this, the range of mandibular movement and the VAS were reassessed to evaluate the outcomes., significantly improved maximum mouth opening (37.7 ± 6.4 mm to 44.6 ± 5.88 mm), right laterality (3.86 ± 1.57 mm to 5.43 ± 1.21 mm), left laterality (3.13 ± 1.63 mm to 4.53 ± 1.61 mm), protrusion (4.01 ± 1.7 mm to 5.36 ± 1.32 mm), and pain perception (4.56 ± 2.045 to 2.03 ± 1.5) (P < 0.01). TENS therapy enhances mandibular movement and reduces pain, making it a well-tolerated, non-invasive complementary treatment for TMD.
