In order to investigate the fatigue performance of orthotropic anisotropic steel bridge decks,this study realizes the simulation of the welding process through elastic-plastic finite element theory,thermal-structural ...In order to investigate the fatigue performance of orthotropic anisotropic steel bridge decks,this study realizes the simulation of the welding process through elastic-plastic finite element theory,thermal-structural sequential coupling,and the birth-death element method.The simulated welding residual stresses are introduced into the multiscale finite element model of the bridge as the initial stress.Furthermore,the study explores the impact of residual stress on crack propagation in the fatigue-vulnerable components of the corroded steel box girder.The results indicate that fatigue cracks at the weld toe of the top deck,the weld root of the top deck,and the opening of the transverse diaphragm will not propagate under the action of a standard vehicle load.However,the inclusion of residual stress leads to the propagation of these cracks.When considering residual stress,the fatigue crack propagation paths at the weld toe of the transverse diaphragm and the U-rib weld toe align with those observed in actual bridges.In the absence of residual stress,the cracks at the toe of the transverse diaphragm with a 15%mass loss rate are categorized as type I cracks.Conversely,when residual stress is considered,these cracks become I-II composite cracks.Residual stress significantly alters the cumulative energy release rate of the three fracturemodes.Therefore,incorporating the influence of residual stress is essential when assessing the fatigue performance of corroded steel box girders in long-span bridges.展开更多
A series of fundamental experimental investigation was conducted in order to examine the effect of PWHT by sheet-type ceramic heater on the residual stress, deformation and compressive behavior of non-stiffened welded...A series of fundamental experimental investigation was conducted in order to examine the effect of PWHT by sheet-type ceramic heater on the residual stress, deformation and compressive behavior of non-stiffened welded box columns. The sheet-type ceramic heater was able to control the required temperature history for PWHT with high accuracy. The welding-induced tensile and compressive residual stresses of the specimens were reduced by 90% and 76% respectively with PWHT. Besides, PWHT could reduce the welding-induced out-of-plane deformation by 22%. It was revealed that the PWHT specimens had a slight higher stiffness than the As-welded specimens when applying monotonic static compressive load on both As-welded and PWHT specimens. They could also enhance the ultimate compressive load capacity about 32% of that of the As-welded specimens. The effectiveness of PWHT with the sheet-type ceramic heater could be confirmed.展开更多
针对D2Det(Towards High Quality Object Detection and Instance Segmentation)面对尺度变化目标和小目标的检测效果不佳并且参数量较大的问题,基于D2Det提出一种尺度自适应的目标检测模型G-SAD2Det。首先在数据预处理阶段引入数据增...针对D2Det(Towards High Quality Object Detection and Instance Segmentation)面对尺度变化目标和小目标的检测效果不佳并且参数量较大的问题,基于D2Det提出一种尺度自适应的目标检测模型G-SAD2Det。首先在数据预处理阶段引入数据增强算法CutOut和Mosaic,使模型应对复杂场景时有较好的鲁棒性;其次改进特征提取网络ResNet,在每个残差块内构建多尺度特征提取结构,从细粒度层面上更好地提取目标特征,同时在网络结构上添加可切换的全局上下文语义特征提取模块,通过不同池化层来增强显著性特征和全局上下文语义信息;然后改进候选框生成模块,采用自主定位目标中心区域指导候选框的生成,增强算法对尺度变换目标的自适应能力;最后通过Ghost卷积替换普通卷积降低网络的参数量和计算量。使用VOC数据集和COCO子数据集验证算法的有效性,G-SAD2Det比D2Det在两个数据集上的mAP@0.5分别提升了3.6%和4.9%;模型参数量减少了27.42%,计算量减少了35.96%,证明改进后的算法在提高了精度的同时也减少了计算量。展开更多
基金supported by a grant from the Key Technologies Research and Development Program(No.2021YFF0602005)Jiangsu Key Research and Development Plan(Nos.BE2022129,BE2022134)the Fundamental Research Funds for the Central Universities(Nos.2242022k30031,2242022k30033),which are gratefully acknowledged.
文摘In order to investigate the fatigue performance of orthotropic anisotropic steel bridge decks,this study realizes the simulation of the welding process through elastic-plastic finite element theory,thermal-structural sequential coupling,and the birth-death element method.The simulated welding residual stresses are introduced into the multiscale finite element model of the bridge as the initial stress.Furthermore,the study explores the impact of residual stress on crack propagation in the fatigue-vulnerable components of the corroded steel box girder.The results indicate that fatigue cracks at the weld toe of the top deck,the weld root of the top deck,and the opening of the transverse diaphragm will not propagate under the action of a standard vehicle load.However,the inclusion of residual stress leads to the propagation of these cracks.When considering residual stress,the fatigue crack propagation paths at the weld toe of the transverse diaphragm and the U-rib weld toe align with those observed in actual bridges.In the absence of residual stress,the cracks at the toe of the transverse diaphragm with a 15%mass loss rate are categorized as type I cracks.Conversely,when residual stress is considered,these cracks become I-II composite cracks.Residual stress significantly alters the cumulative energy release rate of the three fracturemodes.Therefore,incorporating the influence of residual stress is essential when assessing the fatigue performance of corroded steel box girders in long-span bridges.
文摘A series of fundamental experimental investigation was conducted in order to examine the effect of PWHT by sheet-type ceramic heater on the residual stress, deformation and compressive behavior of non-stiffened welded box columns. The sheet-type ceramic heater was able to control the required temperature history for PWHT with high accuracy. The welding-induced tensile and compressive residual stresses of the specimens were reduced by 90% and 76% respectively with PWHT. Besides, PWHT could reduce the welding-induced out-of-plane deformation by 22%. It was revealed that the PWHT specimens had a slight higher stiffness than the As-welded specimens when applying monotonic static compressive load on both As-welded and PWHT specimens. They could also enhance the ultimate compressive load capacity about 32% of that of the As-welded specimens. The effectiveness of PWHT with the sheet-type ceramic heater could be confirmed.
文摘针对D2Det(Towards High Quality Object Detection and Instance Segmentation)面对尺度变化目标和小目标的检测效果不佳并且参数量较大的问题,基于D2Det提出一种尺度自适应的目标检测模型G-SAD2Det。首先在数据预处理阶段引入数据增强算法CutOut和Mosaic,使模型应对复杂场景时有较好的鲁棒性;其次改进特征提取网络ResNet,在每个残差块内构建多尺度特征提取结构,从细粒度层面上更好地提取目标特征,同时在网络结构上添加可切换的全局上下文语义特征提取模块,通过不同池化层来增强显著性特征和全局上下文语义信息;然后改进候选框生成模块,采用自主定位目标中心区域指导候选框的生成,增强算法对尺度变换目标的自适应能力;最后通过Ghost卷积替换普通卷积降低网络的参数量和计算量。使用VOC数据集和COCO子数据集验证算法的有效性,G-SAD2Det比D2Det在两个数据集上的mAP@0.5分别提升了3.6%和4.9%;模型参数量减少了27.42%,计算量减少了35.96%,证明改进后的算法在提高了精度的同时也减少了计算量。
