Degradation process assessment of prestressed concrete continuous bridges in life-cycle

To accurately evaluate the degradation process of prestressed concrete continuous bridges exposed to aggressive environments in life-cycle,a finite element-based approach with respect to the lifetime performance assessment of concrete bridges was proposed.The existing assessment methods were firstly introduced and compared.Some essential mechanics problems involved in the degradation process,such as the deterioration of materials properties,the reduction of sectional areas and the variation of overall structural performance caused by the first two problems,were investigated and solved.A computer program named CBDAS(Concrete Bridge Durability Analysis System) was written to perform the above-metioned approach.Finally,the degradation process of a prestressed concrete continuous bridge under chloride penetration was discussed.The results show that the concrete normal stress for serviceability limit state exceeds the threshold value after 60 a,but the various performance indicators at ultimate limit state are consistently in the allowable level during service life.Therefore,in the case of prestressed concrete bridges,the serviceability limit state is more possible to have durability problems in life-cycle;however,the performance indicators at ultimate limit state can satisfy the requirements.

GDP Now:原理及启示

利用实时有效的宏观经济数据对宏观经济变动进行即时预测,既可以帮助政府做出恰当的经济决策,同时也有助于经济主体制定相应的决策计划。本文对GDP Now的原理与其进一步完善进行了详细阐述,其中原理方面主要包括对GDP13个子项增长率的预测、月度数据序列预测、提取潜在公共因子和对GDP项下进出口、政府投资支出、消费支出和库存投资变化等的预测;改进完善方面则体现在GDP13个子项和动态因子模型上。基于此,本文认为对于我国而言应从数据与预测模型入手,逐渐构建适当的即时预测模型:搭建适当的即时预测指标、提高实时数据的可获得性与透明性以及推进我国即时预测模型开发与完善。