北京市近60年长期超量开采地下水已经引起了严重的地下水水位下降和大范围地面沉降，截止到2009年最大累计沉降量达到1096 mm ，并以30～60 mm · y -1速率扩展，严重威胁城市规划建设和人民交通安全。相对于传统的水准测量、分层...北京市近60年长期超量开采地下水已经引起了严重的地下水水位下降和大范围地面沉降，截止到2009年最大累计沉降量达到1096 mm ，并以30～60 mm · y -1速率扩展，严重威胁城市规划建设和人民交通安全。相对于传统的水准测量、分层标等地面沉降监测手段，永久散射体干涉测量技术（PS-InSAR）可以快速获取高分辨率的地表形变细节信息。利用PS-InSAR技术和2003年12月-2009年3月Envisat卫星29景ASAR影像监测北京平原区地面沉降发展情况，发现北京平原区沉降漏斗已连成一片，沉降梯度变化较大地区主要分布在北京第四系凹陷区，覆盖面涉及朝阳、昌平、顺义、通州等区县，并有东移外扩趋势，平谷县境内出现新的沉降中心。沉降分布受前门-良乡-顺义、黄庄-高丽营、南口-孙河等主要断层控制，地面沉降与地下水水位变化具有明显相关性，呈现季节性下降（3月-6月）与回弹（11月-3月）趋势，并受弱透水层应力应变本构关系（弹性-塑性-黏弹性）影响。展开更多
This study presents experimental and numerical investigations of simply supported steel reinforced concrete(RC)beams under fire.The temperature field of cross sections,the vertical deflection at mid-span,and specifica...This study presents experimental and numerical investigations of simply supported steel reinforced concrete(RC)beams under fire.The temperature field of cross sections,the vertical deflection at mid-span,and specifically the axial expansion displacement at beam-ends were measured during the fire tests.A novel finite element(FE)model of a RC beam under fire was developed,in which the water loss in the heat transfer analysis and the concrete transient strain in the mechanical analysis were considered.Based on the validated FE model proposed in this study,parametric studies were conducted to investigate the effects of the beam type,the protective layer thickness,and the load ratio on the thermal and mechanical behavior of simply supported RC beams.It was found that greater fire resistance and fire performance of girder beams in comparison to secondary beams contributed to the non-structural reinforcements,which effectively compensated for the reduced tensile capacities of structural reinforcements because of the degradation of the material properties.In addition,the history of normal stress distributions of concrete under fire can be divided into three phases:expansion,stress redistribution and plateau phases.展开更多
文摘北京市近60年长期超量开采地下水已经引起了严重的地下水水位下降和大范围地面沉降，截止到2009年最大累计沉降量达到1096 mm ，并以30～60 mm · y -1速率扩展，严重威胁城市规划建设和人民交通安全。相对于传统的水准测量、分层标等地面沉降监测手段，永久散射体干涉测量技术（PS-InSAR）可以快速获取高分辨率的地表形变细节信息。利用PS-InSAR技术和2003年12月-2009年3月Envisat卫星29景ASAR影像监测北京平原区地面沉降发展情况，发现北京平原区沉降漏斗已连成一片，沉降梯度变化较大地区主要分布在北京第四系凹陷区，覆盖面涉及朝阳、昌平、顺义、通州等区县，并有东移外扩趋势，平谷县境内出现新的沉降中心。沉降分布受前门-良乡-顺义、黄庄-高丽营、南口-孙河等主要断层控制，地面沉降与地下水水位变化具有明显相关性，呈现季节性下降（3月-6月）与回弹（11月-3月）趋势，并受弱透水层应力应变本构关系（弹性-塑性-黏弹性）影响。
基金Project(51578548)supported by the National Natural Science Foundation of ChinaProject(2018JJ3202)supported by the Natural Science Foundation of Hunan Province,ChinaProject(17C0681)supported by the Educational Departmental Science Research of Hunan Province,China
文摘This study presents experimental and numerical investigations of simply supported steel reinforced concrete(RC)beams under fire.The temperature field of cross sections,the vertical deflection at mid-span,and specifically the axial expansion displacement at beam-ends were measured during the fire tests.A novel finite element(FE)model of a RC beam under fire was developed,in which the water loss in the heat transfer analysis and the concrete transient strain in the mechanical analysis were considered.Based on the validated FE model proposed in this study,parametric studies were conducted to investigate the effects of the beam type,the protective layer thickness,and the load ratio on the thermal and mechanical behavior of simply supported RC beams.It was found that greater fire resistance and fire performance of girder beams in comparison to secondary beams contributed to the non-structural reinforcements,which effectively compensated for the reduced tensile capacities of structural reinforcements because of the degradation of the material properties.In addition,the history of normal stress distributions of concrete under fire can be divided into three phases:expansion,stress redistribution and plateau phases.
