To investigate the seismic performance of hollow reinforced concrete （RC） bridge columns of rectangular cross section under constant axial load and cyclically biaxial bending, five specimens were tested. A parametri...To investigate the seismic performance of hollow reinforced concrete （RC） bridge columns of rectangular cross section under constant axial load and cyclically biaxial bending, five specimens were tested. A parametric study is carried out for different axial load ratios, longitudinal reinforcement ratios and lateral reinforcement ratios. The experimental results showed that all tested specimens failed in the flexural failure mode and their ultimate performance was dominated by flexural capacity, which is represented by the rupture/buckling of tensile longitudinal rebars at the bottom of the bridge columns. Biaxial force and displacement hysteresis loops showed significant stiffness and strength degradations, and the pinching effect and coupling interaction effect of both directions severely decrease the structural seismic resistance. However, the measured ductility coefficient varying from 3.5 to 5.7 and the equivalent viscous damping ratio varying from 0.19 and 0.26 can meet the requirements of the seismic design. The hollow RC rectangular bridge columns with configurations of lateral reinforcement in this study have excellent performance under bidirectional earthquake excitations, and may be considered as a substitute for current hollow RC rectangular section configurations described in the Guideline for Seismic Design of Highway Bridges （JTG/T B02-01-2008）. The length of the plastic hinge region was found to approach one sixth of the hollow RC rectangular bridge column height for all specimen columns, and it was much less than those specified in the current JTG/T. Thus, the length of the plastic hinge region is more concentrated for RC rectangular hollow bridge columns.展开更多
According to the rules of UIC515-3, the service loads of the axles are defined, which include some different loads cases as follows： the static loads; the impact loads resulted from running through the rail joints an...According to the rules of UIC515-3, the service loads of the axles are defined, which include some different loads cases as follows： the static loads; the impact loads resulted from running through the rail joints and unevenness rails; the loads through curves and from braking. Through the calculating and analysis, the stress distribution of the hollow axles is obtained for 200 km/h high speed motor trains used in China. At the same time, the fatigue crack growth of hollow axles is studied, and the initial surface cracks of 2 mm depth caused by hard objects strike or the other causes are discussed. On the basis of the linear elastic fracture mechanics theory, the stress intensity factor of the crack of the geometry transition outside the wheel seat is also studied. Associated with fatigue crack propagation equation and the corresponding crack propagation threshold, the crack propagation characteristics under different shapes are calculated. Then the running distances are educed with different shapes propagating to the critical length, and the estimation of the residual lives about hollow axles which are the reference values of examine and repair limit of the hollow axle is given.展开更多
An analytical method is derived for the thermal consolidation of a saturated, porous, hollow cylinder with infinite length. The solutions in Laplace transform space are first obtained and then numerically inverted by ...An analytical method is derived for the thermal consolidation of a saturated, porous, hollow cylinder with infinite length. The solutions in Laplace transform space are first obtained and then numerically inverted by Stehfest method. Two cases of boundary conditions are considered. First, variable thermal loadings are applied on the inner and outer pervious lateral surfaces of the hollow cylinder, and a variable mechanical loading with time is applied on the outer surface;while the displacement of the inner surface remains fixed. Secondly, variable thermal and mechanical loading are applied on the outer pervious surface, and the inner surface remains fixed, impervious and insulated. As two special problems, a solid cylinder with infinite length and a cylindrical cavity in a half-space body are also discussed. Finally, the evolutions of temperature, pore pressure and displacement with time along radial direction are analyzed by a numerical example.展开更多
空心弹是一种具有通孔结构的新型射弹,与相同口径的实心射弹相比,阻力更小,在同等装药量的条件下具有初速高的优点,其入水时呈现复杂的入水流体动力学和弹道特性.文章基于雷诺时均Navier-Stokes方程、VOF(volume of fluid)多相流模型、S...空心弹是一种具有通孔结构的新型射弹,与相同口径的实心射弹相比,阻力更小,在同等装药量的条件下具有初速高的优点,其入水时呈现复杂的入水流体动力学和弹道特性.文章基于雷诺时均Navier-Stokes方程、VOF(volume of fluid)多相流模型、SST(shear stress transfer)k-ω湍流模型、Schnerr-Sauer空化模型、六自由度模型和重叠网格技术对空心弹高速入水进行了数值模拟,研究了入水速度和角度对空心弹入水空泡、空化、载荷和弹道稳定性的影响.将数值计算结果与实验结果进行对照,空泡形态和质心轨迹曲线与实验结果吻合较好,验证了数值模拟方法的可行性.结果表明:空心弹入水速度对空泡的大小和空泡内空化的程度影响较大,随着入水速度越高,空泡也越大,空化越明显,弹体的速度衰减越快,弹道越不稳定,弹体失稳越早;随着入水速度越低,空心弹的阻力和升力系数越小,弹体运动越稳定.入水角度对空泡的大小及弹体的偏转程度有较大影响,入水角度越大,弹体偏转时刻的空泡越大,空泡内的空化越明显,弹体头部的高压区域越小,阻力、升力和力矩系数越小,相同时间内弹体的偏转角越小,弹体姿态越稳定.入水角度越小,弹体的偏转角增加的越快,弹体运动越不稳定.展开更多
基金National Natural Science Foundation of China under Grant No.51178008,No.50908005National Basic Research Program of China under Grant No.2011CB013600+1 种基金the International Cooperative Project of NSFC-JST under Grant No.51021140003a Joint Research Project between the Beijing University of Technology and the University at Buffalo with Partial Support from the U.S.Federal Highway Administration under Contract No.DTFH61-07-C-00020
文摘To investigate the seismic performance of hollow reinforced concrete （RC） bridge columns of rectangular cross section under constant axial load and cyclically biaxial bending, five specimens were tested. A parametric study is carried out for different axial load ratios, longitudinal reinforcement ratios and lateral reinforcement ratios. The experimental results showed that all tested specimens failed in the flexural failure mode and their ultimate performance was dominated by flexural capacity, which is represented by the rupture/buckling of tensile longitudinal rebars at the bottom of the bridge columns. Biaxial force and displacement hysteresis loops showed significant stiffness and strength degradations, and the pinching effect and coupling interaction effect of both directions severely decrease the structural seismic resistance. However, the measured ductility coefficient varying from 3.5 to 5.7 and the equivalent viscous damping ratio varying from 0.19 and 0.26 can meet the requirements of the seismic design. The hollow RC rectangular bridge columns with configurations of lateral reinforcement in this study have excellent performance under bidirectional earthquake excitations, and may be considered as a substitute for current hollow RC rectangular section configurations described in the Guideline for Seismic Design of Highway Bridges （JTG/T B02-01-2008）. The length of the plastic hinge region was found to approach one sixth of the hollow RC rectangular bridge column height for all specimen columns, and it was much less than those specified in the current JTG/T. Thus, the length of the plastic hinge region is more concentrated for RC rectangular hollow bridge columns.
基金National Basic Research and Development Program of China(973 Program,No.2007CB714705).
文摘According to the rules of UIC515-3, the service loads of the axles are defined, which include some different loads cases as follows： the static loads; the impact loads resulted from running through the rail joints and unevenness rails; the loads through curves and from braking. Through the calculating and analysis, the stress distribution of the hollow axles is obtained for 200 km/h high speed motor trains used in China. At the same time, the fatigue crack growth of hollow axles is studied, and the initial surface cracks of 2 mm depth caused by hard objects strike or the other causes are discussed. On the basis of the linear elastic fracture mechanics theory, the stress intensity factor of the crack of the geometry transition outside the wheel seat is also studied. Associated with fatigue crack propagation equation and the corresponding crack propagation threshold, the crack propagation characteristics under different shapes are calculated. Then the running distances are educed with different shapes propagating to the critical length, and the estimation of the residual lives about hollow axles which are the reference values of examine and repair limit of the hollow axle is given.
文摘An analytical method is derived for the thermal consolidation of a saturated, porous, hollow cylinder with infinite length. The solutions in Laplace transform space are first obtained and then numerically inverted by Stehfest method. Two cases of boundary conditions are considered. First, variable thermal loadings are applied on the inner and outer pervious lateral surfaces of the hollow cylinder, and a variable mechanical loading with time is applied on the outer surface;while the displacement of the inner surface remains fixed. Secondly, variable thermal and mechanical loading are applied on the outer pervious surface, and the inner surface remains fixed, impervious and insulated. As two special problems, a solid cylinder with infinite length and a cylindrical cavity in a half-space body are also discussed. Finally, the evolutions of temperature, pore pressure and displacement with time along radial direction are analyzed by a numerical example.
文摘空心弹是一种具有通孔结构的新型射弹,与相同口径的实心射弹相比,阻力更小,在同等装药量的条件下具有初速高的优点,其入水时呈现复杂的入水流体动力学和弹道特性.文章基于雷诺时均Navier-Stokes方程、VOF(volume of fluid)多相流模型、SST(shear stress transfer)k-ω湍流模型、Schnerr-Sauer空化模型、六自由度模型和重叠网格技术对空心弹高速入水进行了数值模拟,研究了入水速度和角度对空心弹入水空泡、空化、载荷和弹道稳定性的影响.将数值计算结果与实验结果进行对照,空泡形态和质心轨迹曲线与实验结果吻合较好,验证了数值模拟方法的可行性.结果表明:空心弹入水速度对空泡的大小和空泡内空化的程度影响较大,随着入水速度越高,空泡也越大,空化越明显,弹体的速度衰减越快,弹道越不稳定,弹体失稳越早;随着入水速度越低,空心弹的阻力和升力系数越小,弹体运动越稳定.入水角度对空泡的大小及弹体的偏转程度有较大影响,入水角度越大,弹体偏转时刻的空泡越大,空泡内的空化越明显,弹体头部的高压区域越小,阻力、升力和力矩系数越小,相同时间内弹体的偏转角越小,弹体姿态越稳定.入水角度越小,弹体的偏转角增加的越快,弹体运动越不稳定.
