Coupling model for calculating prestress loss caused by relaxation loss,shrinkage,and creep of concrete

The calculation model for the relaxation loss of concrete mentioned in the Code for Design of Highway Reinforced Concrete and Prestressed Concrete Bridges and Culverts(JTG D62—2004) was modified according to experimental data. Time-varying relaxation loss was considered in the new model. Moreover, prestressed reinforcement with varying lengths(caused by the shrinkage and creep of concrete) might influence the final values and the time-varying function of the forecast relaxation loss. Hence, the effects of concrete shrinkage and creep were considered when calculating prestress loss, which reflected the coupling relation between these effects and relaxation loss in concrete. Hence, the forecast relaxation loss of prestressed reinforcement under the effects of different initial stress levels at any time point can be calculated using the modified model. To simplify the calculation, the integral expression of the model can be changed into an algebraic equation. The accuracy of the result is related to the division of the periods within the ending time of deriving the final value of the relaxation loss of prestressed reinforcement. When the time division is reasonable, result accuracy is high. The modified model works excellently according to the comparison of the test results. The calculation result of the modified model mainly reflects the prestress loss values of prestressed reinforcement at each time point, which confirms that adopting the finding in practical applications is reasonable.

某轨道项目地下超长结构温度作用分析

超长结构的温度应力问题一直备受结构设计关注,结合轨道交通线路穿越某商业综合体形成的超长混凝土结构进行分析,考虑结构施工进度计划的影响,对比了三种不同的收缩当量温差计算方法,将收缩当量温差与最大季节温差叠加后,并考虑徐变应力松弛和刚度折减的最不利温差施加于结构,采用有限元软件MIDAS Gen对其进行温度作用分析,得出温度作用效应在超长结构的分布规律,对类似超长结构设计具有借鉴意义。