定点式布设光纤在隧道结构健康监测中的预拉应变损失研究

基于布里渊光频域分析(BOFDA)的分布式光纤监测技术已在岩土工程领域得到初步应用。应变监测结果显示:将光纤进行预拉布设后,随着时间的推移,光纤预拉段会产生一定的应变损失。应变损失的产生主要是由光纤的疲劳特性所造成的。显然,光纤因疲劳产生的应变损失对于工程监测是极其不利的,在实际监测中需要将其剔除。针对分布式光纤监测技术,选取HY料新型紧套应变光纤、聚氨酯紧套光纤2种应变光纤,在实验室进行了点固定式预拉布设(10 000×10-6),并进行了8个月的应变损失监测。对比分析2种光纤的预拉应变损失的差异,获得了光纤应变损失随时间的变化规律,以及预拉状态下的光纤在温度和湿度升高状态下应变损失的速率变化。研究了运用分布式光纤监测技术进行隧道变形监测的点固定式预拉布设方法,可为工程应用提供理论基础和施工指导。

Coupling model for calculating prestress loss caused by relaxation loss,shrinkage,and creep of concrete

The calculation model for the relaxation loss of concrete mentioned in the Code for Design of Highway Reinforced Concrete and Prestressed Concrete Bridges and Culverts(JTG D62—2004) was modified according to experimental data. Time-varying relaxation loss was considered in the new model. Moreover, prestressed reinforcement with varying lengths(caused by the shrinkage and creep of concrete) might influence the final values and the time-varying function of the forecast relaxation loss. Hence, the effects of concrete shrinkage and creep were considered when calculating prestress loss, which reflected the coupling relation between these effects and relaxation loss in concrete. Hence, the forecast relaxation loss of prestressed reinforcement under the effects of different initial stress levels at any time point can be calculated using the modified model. To simplify the calculation, the integral expression of the model can be changed into an algebraic equation. The accuracy of the result is related to the division of the periods within the ending time of deriving the final value of the relaxation loss of prestressed reinforcement. When the time division is reasonable, result accuracy is high. The modified model works excellently according to the comparison of the test results. The calculation result of the modified model mainly reflects the prestress loss values of prestressed reinforcement at each time point, which confirms that adopting the finding in practical applications is reasonable.

Properties of failure mode and thermal damage for limestone at high temperature

The mechanical properties of limestone such as the stress-strain curve, the variable characteristics of peak strength and the modulus of elasticity of limestone were studied under the action of temperatures ranging from room temperature to 800 °C.Our results show that:1) the temperature has not clear effect on the mechanical properties of limestone from room temperature to 600 °C.However, the mechanical properties of limestone deteriorate rapidly when the temperature is above 600 °C.In this case, the peak stress and modulus of elasticity decrease rapidly.When the temperature reaches 800 °C, the entire process, showing the stress-strain curve is displayed indicating an obvious state of plastic-deformation;2) the failure mode of limestone shows the breakdown of tensile strength from room temperature to 600 °C, as well as the compress shearing damage over 600 °C;3) combining our test results with the concept of thermal damage, a thermal damage equation was derived.

氯化钠侵蚀混凝土力学性能的试验研究

为研究NaCl环境下混凝土力学性能的退化规律,采用实验室加速腐蚀的试验方法,利用质量分数分别为10%和20%的NaCl溶液对C30混凝土试件进行侵蚀,对腐蚀后混凝土进行了抗拉和抗压力学性能测试。采用强度退化率和应变能损失率为损伤指标,对不同腐蚀程度混凝土力学性能的退化进行分析。结果表明,强度退化率和应变能损失率可以很好地反映混凝土的受腐蚀程度。在腐蚀作用初期,两者略有降低;随着腐蚀时间的延长和腐蚀液质量分数的增加,两者逐渐增加。

Numerical analysis of magnetization AC losses in high-temperature superconducting slabs subjected to uniform strains

High-temperature superconductors in superconductor apparatuses are subjected to mechanical strains under operating conditions.These strains cause the degradation of the critical current densities and influence AC losses in the superconductors.Based on the dynamic process of thermomagnetic interaction,we report the results of numerical analysis of AC losses in an infinite high-temperature superconducting slab subjected to a uniform in-plane strain in an alternating external magnetic field parallel to the sample surface.The numerical analysis shows the details of electromagnetic phenomena in the slab and the dependences of AC loss on various external parameters including the uniform strain in the slab and the amplitude and frequency of the external magnetic field.In this paper,we find that whether the magnetic field fully penetrates the superconductor is the key factor that influences the features of AC loss.When the magnetic field cannot fully penetrate the superconductor,the loss rises with increasing strain or decreasing frequency.When the magnetic field can fully penetrate the superconductor,the feature is just opposite.We also analyze the effects of periodic strain on AC loss.It is interesting to find that when the periodic strain frequency equals the external magnetic field frequency,the AC loss reaches the maximum,regardless if the magnetic field fully penetrates the superconductor or not.

Melanopsin-expressing retinal ganglion cell loss and behavioral analysis in the Thy1-CFP-DBA/2J mouse model of glaucoma

In this study, the role of melanopsin-expressing retinal ganglion cells （mRGCs） in the glaucoma-induced depressive behavioral response pattern was investigated. The CFP-D2 transgenic glaucoma animal model from five age groups was used in this study. Immunohistochemical labeling, quantitative analysis of mRGC morphology, open field test （OFT）, and statistical analysis were used. In comparison with C57 BL/6 mice, the age-matched CFP-D2 mice had significantly elevated intraocular pressure （lOP）. We observed parallel morphological changes in the retina, including a reduction in the density of cyan fluorescent protein- （CFP） expressing cells （cells mm^-2 at 2 months of age, 1309±26; 14 months, 878±30, P〈0.001）, mRGCs （2 months, 48_＋3; 14 months, 19±4, P〈0.001）, Brn3b-expressing RGCs （2 months, 1283±80; 14 months, 950±31, P〈0.001）, Brn-3b expressing mRGCs （5 months, 50.17%±5.5%; 14 months, 12.61%±3.8%, P〈0.001）, and reduction in the dendritic field size of mRGCs （mm^2 at 2 months, 0.077±0.015; 14 months, 0.065±0.015, P〈0.05）. CFP-D2 mice had hyperactive locomotor activity patterns based on OFT findings of the total distance traveled, number of entries into the center, and time spent in the center of the testing apparatus. The glaucoma induced hyperactive response pattern could be associated with dysfunctional mRGCs, most likely Brn-3b-positive mRGCs in CFP-D2 mice.