竖向荷载下弹性支承直墙拱反弯点理论分析

在工程实践中,直墙拱应用较多。由于拱脚位移的存在,合理假设拱脚约束为转角约束、竖向约束和水平弹性约束,应用力法推导出了在弯矩、剪力和轴力共同作用下直墙拱沿弧长的弯矩公式。研究了竖向均布荷载、竖向三角形荷载和竖向集中力荷载作用下,直墙拱沿弧长的弯矩分布及反弯点形成的规律;发现在3种荷载作用下,使得拱脚弯矩为零时的圆心角依次减小。取弹簧支座刚度为等效的下端固支、上端允许水平位移的直墙的抗推刚度,得出了随着直墙高度增加,圆弧拱拱顶弯矩增大而拱脚弯矩减小的变化规律。在直墙拱的设计中,建议选取合适的直墙高度和使得圆弧拱拱脚弯矩为零的圆心角大小,从而有利于提高结构抗弯承载力及拱脚抗剪承载力。     

湖南旱地土壤对铵离子的矿物固定与固定态铵释放的动力学研究

采用振荡平衡法和好气培养-间歇淋洗法研究了湖南省主要旱地土壤对添加铵离子的矿物学固定和土壤固定态铵释放的动力学特性。结果表明,供试土壤对添加铵离子的矿物固定速度很快,反应12小时后基本上达到了最大固定量;而土壤固定态铵的释放则非常缓慢,反应42天后仍未达到最大释放量。这一动力学特征有利于土壤对溶液中NH4+的保持,防止NH4+的环境污染,有效地为作物供氮和提高氮肥利用率。一级动力学方程能较好地拟合供试土壤对铵离子的矿物学固定的动力学资料,一级动力学方程和抛物扩散率方程均能较好地拟合供试土壤固定态铵释放的动力学资料,表现为相关系数r值较高,标准误SE值较低。     

浅谈桥梁整体顶升技术

桥梁整体顶升技术的关键在于保证其上部结构的整体性同步顶升,本文从施工方法、操作要点、注意事项等几方面介绍了桥梁同步顶升技术,可供业内人员参考。     

济南建邦黄河公路大桥主桥斜拉桥辅助墩顶超重主梁施工控制措施

济南建邦黄河大桥主桥是一座三塔、双索面的预应力混凝土梁斜拉桥,跨度布置为53.5＋56.5＋2×300＋56.5＋53.5m,中塔处为塔梁墩固结。主梁采用前支点挂篮进行施工,边跨合龙段位于过渡墩与辅助墩之间,中边跨合龙有一定难度。墩助墩顶主梁较重,施工难度大,本文主要介绍了该桥辅助墩顶超重主梁施工的方法及控制的措施。     

库布齐沙漠流动沙丘与固定沙丘沙物质粒径分析的研究

通过采样分析对库布齐沙漠流动沙丘与固定沙丘沙粒径进行测定,对两类沙丘的沙物质粒径进行对比,分析沙粒的粒级变化规律.结果表明:实验区沙粒的粒径主要集中在0.25～0.05mm范围内,约占总含量的95%左右;固定沙丘地表和流动沙丘0.25mm沙...     

固定态铵的含量及中国某些耕地土壤NH4+的固定能力

Fixed ammonium contents and NH4^ fixation capacities of some representative cultivated solis collected from 16 provinces of China were studied.Results showed that the contents of fixed ammonium in soils ranged from 35 to 573 mg N kg^-1,with an average of 198mg Nkg^-1.The content of fixed ammonium correlated very significantly with mica content for tropical and subtropical soils,whereas this was not the case for soils in the temperate zone.At the end of K-exhausting experiment the fixed ammonium content increased in most soils studied.However,it decreased in smom temperate soils.Generally,fixation of added NH4^ could not be found either before or after K-exhausting experiment for highly weathered soils,including tropical soils and soils derived from granite-gneiss or Quaternary red clays in the subtropic zone,while for most soils in the Yangtze River dalta the NH4^ fixation capacity was rather high and increased significantly in the K-exhausted soils.     

固定顶储罐液下喷射泡沫灭火技术

与液上喷射泡沫灭火系统的相比，液下喷射泡沫灭火系统具有安全可靠，灭火速度快，省投资等优点，但却存在单阀易渗漏问题。针对这一问题，提出了通过在单向阀和控制阀之间增设爆破片，或在灭火系统泡沫喷口处设置泡沫带以及改善单向阀密封性能等解决办法。     

尤溪口闽江多跨悬索桥

本文简述尤溪口闽江多跨悬索桥的主要结构、施工安装及其工作原理。     

拱形屋面空旷建筑基础的实用设计

拱形屋面结构单层空旷建筑的基础偏心距较大，用常规设计方法基础面积过大，使这种结构在实际工程中的应用受到限制。分析了这种结构的受力特点，针对我国的工程实际，提出了改进基础设计的几种方法：1)加大基础自重，利用基础梁把墙体的重力传给基础；2)采用复合基础，将条形基础和独立基础浇筑成整体，使条形基础承担部分弯矩和剪力；3)风荷载较小且没有吊车时采用偏心基础，相当于预先给基础施加适当的反向弯矩。工程实例表明，与常规设计相比，采用复合基础设计的独立基础底面积较小，降低了基础高度，混凝土体积减小约30％。降低了工程造价，方便基础施工。     

Fixed Ammonium Content and Maximum Capacity of Ammonium Fixation in Major Types of Tillage Soils in Hunan Province, China

In order to understand the status of fixed ammonium, fixed ammonium content, maximum capacity of ammonium fixation, and their influencing factors in major types of tillage soils of Hunan Province, China, were studied with sampling on fields, and laboratory incubation and determination. The main results are summarized as follows: (1) Content of fixed ammonium in the tested soils varies greatly with soil use pattern and the nature of parent material. For the paddy soils, it ranges from 135.4 ± 57.4 to 412.8 ± 32.4 mg kg⁻¹, with 304.7 ± 96.7 mg kg⁻¹ in average; while it ranges from 59.4 to 435.7 mg kg⁻¹, with 230.1 ± 89.2 mg kg⁻¹ in average for the upland soils. The soils developed from limnic material and slate had higher fixed ammonium content than the soils developed from granite. The percentage of fixed ammonium to total N in the upland soils is always higher than that in the paddy soils. It ranges from 6.1 ± 3.6% to 16.6 ± 4.6%, with 14.0% ± 5.1% in average for the paddy soils and it amounted to 5.8 ± 2.0% to 40.1 ± 17.8%, with 23.5 ± 14.2% in average for upland soils. (2) The maximum capacity of ammonium fixation has the same trend with the fixed ammonium content in the tested soils. For all the tested soils, the percentage of recently fixed ammonium to maximum capacity of ammonium fixation is always bellow 20% and it may be due to the fact that the soils have high fertility and high saturation of ammonium-fixing site. (3) The clay content and clay composition in the tested soils are the two important factors influencing their fixed ammonium content and maximum capacity of ammonium fixation. The results showed that hydrous mica is the main 2:1 type clay mineral in <0.02 mm clay of the paddy soils, and its content in 0.02–0.002 mm clay is much higher than that in <0.002 mm clay of the soils. The statistical analysis showed that both the fixed ammonium content and the maximum capacity of ammonium fixation of the paddy soils were positively correlated with the total 2:1 type clay mineral content and hydrous mica content in <0.02 mm clay and 0.02–0.002 mm clay at the significant level of P_0.01 or P_0.05, respectively, but not correlated with the total 2:1 type clay mineral content and hydrous mica content in <0.002 mm clay significantly. It demonstrated that the ammonium-fixing matrix of the tested soils mainly exists in the 0.02-0.002 mm clay. The above-mentioned results showed that fixed ammonium is a major form of N in the tillage soils in Hunan Province, China. It would play an important role in N nutrition of crops, especially for upland crops, and deserve to be further researched.