大跨度桥梁强震动数字监测系统的研制

主跨1 196 m的龙江特大桥是我国第一座位于高烈度地震区的大跨度悬索桥,频繁的地震活动对大桥结构安全构成严重威胁。大桥建设时建立了健康监测系统,其中包含多个结构地震反应观测点,随后布设了场地强震动观测系统,这是对大桥地震响应观测的进一步补充和完善。本文详细介绍场地强震动观测系统的设计方案、系统构成、通信方式等。该系统获取的观测结果,可为龙江大桥在地震作用下结构健康诊断提供依据,为大桥结构地震响应分析提供可靠的地震动输入,有助于了解大桥结构在地震动作用下的反应特征, 提高大跨桥梁的抗震设计水平。     

226Ra distribution in the Antarctic Ocean

²²⁶Ra data on eleven vertical profiles taken during the GEOSECS program from the Antarctic Ocean and its vicinity in both the Atlantic and the Pacific are presented. Replicate measurements were made on each sample using the Rn-emanation method. The precision (1 σ) based on triplicate analyses averages about ±2.5%. Waters all around the Antarctic continent below 2 km depth appear to exhibit a uniform²²⁶Ra concentration of 21.5 ± 1dpm/100kg, except perhaps locally such as the Ross Sea and the Drake Passage where small variations may be present. Higher in the water column, the²²⁶Ra contents decrease toward the surface with gradients which vary as a function of the influence exerted by the Antarctic Convergence. Across this oceanic front, a north-to-south increase of²²⁶Ra occurs (the increase being the largest near the surface: from 8 to 18 dpm/100 kg), reflecting the combining effect of deep-water upwelling and meridional water mixing. The core layer of the Antarctic Intermediate Water contains about 14 dpm/100 kg of²²⁶Ra and that of the Circumpolar Intermediate Water (O₂ minimum and local T maximum) about 18 dpm/100 kg. To a first approximation,²²⁶Ra covaries with Si in the circumpolar waters.     

Not vegetation itself but mis-revegetation reduces water resources

Increasing greening of planet Earth to slow down the rise of atmospheric CO2 concentrations is certainly desirable;however, its consequences on water resources are less affirmative and thus are a matter of wide concern. China, as the largest and most successful country of the world in terms of artificial revegetation, is naturally the focus of the concerns and warnings. Based on previous studies, we analyzed the mechanism for the effects of climate and watershed characteristics on water resources,explained various hydrological results and phenomena, and considered the ways in which water consumption by artificial revegetation projects can be reduced. Moreover, some guidelines are suggested for artificial revegetation at watershed scale with consideration of water resource sustainability. The findings of this study highlight the need for more top-down approaches when studying the mechanism of "forest and water".     

2018年海峡MS6.2地震社会影响调查与分析

以2018年台湾海峡M_S6.2地震造成的社会影响作为主要调查内容,选取了福建省东山县普通群众作为调查对象,从震时人的感觉、灾时应急避险情况、社会心理、防震减灾及地震预警知识普及情况等方面进行调查研究,目的是了解东山县居民地震应急避险情况及防震减灾知识普及程度等,为今后有针对性的做好防震减灾宣传,提升社会公众抵御地震灾害能力提供一定的参考。      

A climatic dataset of ocean vertical turbulent mixing coefficient based on real energy sources

Using data on wind stress, significant height of combined wind waves and swell, potential temperature, salinity and seawater velocity, as well as objectively-analyzed in situ temperature and salinity, we established a global ocean dataset of calculated wind- and tide-induced vertical turbulent mixing coefficients. We then examined energy conservation of ocean vertical mixing from the point of view of ocean wind energy inputs, gravitational potential energy change due to mixing (with and without artificially limiting themixing coefficient), and K-theory vertical turbulent parameterization schemes regardless of energy inputs. Our research showed that calculating the mixing coefficient with average data and artificial limiting the mixing coefficient can cause a remarkable lack of energy conservation, with energy losses of up to 90% and changes in the energy oscillation period. The data also show that wind can introduce a huge amount of energy into the upper layers of the Southern Ocean, and that tidesdo so in regions around underwater mountains. We argue that it is necessary to take wind and tidal energy inputs into account forlong-term ocean climate numerical simulations. We believe that using this ocean vertical turbulent mixing coefficient climatic dataset is a fast and efficient method to maintain the ocean energy balance in ocean modeling research.     

Seismic performance and global ductility of RC frames rehabilitated with retrofitted joints by CFRP laminates

This paper presents a new FRP retrofi tting scheme to strengthen local beam-column joints in reinforced concrete(RC) frames.The new retrofi tting scheme was proposed following a preliminary study of four different existing retrofi tting schemes.A numerical simulation was conducted to evaluate the effectiveness of FRP-strengthened reinforced concrete frames by bridging behavior of local joints to the whole structure.Local confi nement effects due to varying retrofi tting schemes in the joints were simulated in the frame model.The seismic behavior factor was used to evaluate the seismic performance of the strengthened RC frames.The results demonstrated that the new proposed retrofi tting scheme was robust and promising,and fi nite element analysis appropriately captured the strength and global ductility of the frame due to upgrading of the local joints.     

Regional gravity field modeling using free-positioned point masses

A two-step free-positioned point mass method is used for regional gravity field modeling together with the remove-compute-restore (RCR) technique. The Quasi-Newton algorithm (L-BFGS-B) is implemented to solve the nonlinear problem with bound constraints in the first step, while in the second step the magnitudes of the point masses are re-adjusted with known positions in the least-squares sense. In order to reach a good representation of the gravity field, a number of parameter sets have to be defined carefully before the computations. The effects of four important parameter sets (depth limits, number of point masses, original/reduced basis functions and optimization directions) are investigated for regional gravity field modeling based on two numerical test cases with synthetic and real data. The results show that the selection of the initial depth and depth limits is of most importance. The number of point masses for obtaining a good fit is affected by the data distribution, while a dependency on the data variability (signal variation) is negligible. Long-wavelength errors in the predicted height anomalies can be reduced significantly by using reduced basis functions, and the radial-direction optimization proves to be stable and reliable for regular and irregular data scenarios. If the parameter sets are defined properly, the solutions are similar to the ones computed by least-squares collocation (LSC), but require fewer unknowns than LSC.     

Depth Distribution of Moho Discontinuity Beneath Beijing and Its Adjacent Area

Based on the method of "two-dimensional depth structure of the crust" proposed by Horiuchi et al., about 5000 arrival times of 303 local shallow earthquakes recorded by the Beijing Seismographic Network from 1990 ~ 1993 are used to investigate the depth distribution of Moho discontinuity beneath Beijing and its adjacent area. We simultaneously determined the hypocenter parameters and P- and S-wave station corrections. The data of the North China Network were also investigated. The results are as follows: (1) The depth distribution of Moho discontinuity becomes shallower from the northwest to the southeast, i.e., in Zhangjiakou area, the Moho discontinuity is located at a depth range from 40~42 km. In the Beijing area, it is 36~39 km. However, at the eastern and southeastern part of this area, it is only 28-30 km and 30~32 km, respectively. (2) Beneath the Tangshan area, there is another elliptic interface shallower than the Moho discontinuity. Separately, its major and minor axis is approximately along     

渤海及邻近地区各主要断块近期地震活动分析

渤海及邻近地区是我国东部地震较活跃的地区之一,历史上曾发生过多次强震,现今小震活动也较活跃.因该区域主要处在郯庐断裂带和燕渤断裂带上,且这两大断裂带在渤海内交汇,故造成该区域地震活动频发.本文主要是分析了该地区近期地震活动的空间、时间和强度3个方面,总结了地震活动的空间、时间和强度的特征.为本地区地震灾害的防御,减灾等方面工作提供依据.     

打桩对周围建筑物振动影响的研究与实例分析

研究了打桩过程中土层质点振动速度的监测方法,打桩振动对周围建筑物影响程度的评价标准,并结合工程实例探讨了有关因素对检测结果的影响,及施工中应采取的相应减振措施。