连续钢-混工字组合梁桥收缩徐变效应研究

以某实际钢-混工字组合连续梁桥工程为背景,结合主梁构造设计了3根小试验梁,用于室内试验加载和有限元模型分析,研究该类结构在长期荷载下的收缩徐变性能。在试验基础上,结合各国规范的收缩徐变计算模型,对结构的收缩徐变效应进行了对比分析。研究结果表明:钢-混工字组合连续梁桥结构跨中截面为收缩徐变效应的最大截面;《公路桥涵设计规范》(JTG D60—2015)的计算结果最为安全可靠;当龄期约为10年时,其跨中挠度值逐渐趋于稳定。但构件的截面最大应力值则仍然在缓慢增长的状态,其增长幅度随着年限增加逐渐减少,但最终其应力值满足结构的正常使用状态要求。

Health monitoring and comparative analysis of time-dependent effect using different prediction models for self-anchored suspension bridge with extra-wide concrete girder

The structural health status of Hunan Road Bridge during its two-year service period from April 2015 to April 2017 was studied based on monitored data.The Hunan Road Bridge is the widest concrete self-anchored suspension bridge in China at present.Its structural changes and safety were evaluated using the health monitoring data,which included deformations,detailed stresses,and vibration characteristics.The influences of the single and dual effects comprising the ambient temperature changes and concrete shrinkage and creep(S&C)were analyzed based on the measured data.The ANSYS beam finite element model was established and validated by the measured bridge completion state.The comparative analyses of the prediction results of long-term concrete S&C effects were conducted using CEB-FIP 90 and B3 prediction models.The age-adjusted effective modulus method was adopted to simulate the aging behavior of concrete.Prestress relaxation was considered in the stepwise calculation.The results show that the transverse deviations of the towers are noteworthy.The spatial effect of the extra-wide girder is significant,as the compressive stress variations at the girder were uneven along the transverse direction.General increase and decrease in the girder compressive stresses were caused by seasonal ambient warming and cooling,respectively.The temperature gradient effects in the main girder were significant.Comparisons with the measured data showed that more accurate prediction results were obtained with the B3 prediction model,which can consider the concrete material parameters,than with the CEB-FIP 90 model.Significant deflection of the midspan girder in the middle region will be caused by the deviations of the cable anchoring positions at the girder ends and tower tops toward the midspan due to concrete S&C.The increase in the compressive stresses at the top plate and decrease in the stresses at the bottom plate at the middle midspan will be significant.The pre-deviations of the towers toward the sidespan and pre-lift of the midspan girder can reduce the adverse influences of concrete S&C on the structural health of the self-anchored suspension bridge with extra-wide concrete girder.

埃及CBD标志塔超高层施工模拟分析

以埃及CBD标志塔超高层项目为背景,针对海外工程施工特点,研究核心筒领先层数对超高层框架-核心筒结构竖向位移的影响,并根据实际施工进度计划,对埃及标志塔进行施工全过程模拟计算,分析得到了埃及标志塔施工过程中,核心筒与外框柱的竖向位移和内力的分布模式与变化规律,以及混凝土收缩-徐变等因素对结构整体受力性能的影响特征,为该工程施工提供了计算数据和控制依据,同时也为了解海外工程结构的施工特点与控制技术提供有益借鉴。

基于混凝土收缩—徐变试验的拼宽结构受力规律研究

研究拼宽结构的应力、应变、位移、基础沉降的时变规律,基于混凝土收缩—徐变试验提出了拼接带材料改进措施,给出了有限元预测模型和实桥监测方法。以1座10×15 m的拼宽PC空心板梁桥为例,通过收缩、徐变试验获得材料的时间关联函数,建立有限元预测模型,根据计算结论提出拼宽结构的监测方案。对PC空心板拼接带的应变、全桥跨中位移、新拼桥基础沉降进行了3年的跟踪监测,结果表明:收缩徐变差对结构应力影响较大,在1年后趋于稳定;掺入钢纤维聚酯纤维能显著减少收缩徐变差。相对收缩和徐变,挠度和沉降的时变特性不明显,对结构的应力影响较小。应变实测数据与有限元预测数据对比结果表明,提出的有限元预测模型能有效预测拼宽结构的应力变化趋势,提出的监测方案、预测方法和受力特性时变规律结论可推广应用于其他拼宽桥,为拼宽结构的理论计算和实桥监测提供参考方案和对比数据。

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.

环境湿度影响下大尺寸结构预应力损失及挠度变化的多场多尺度分析

预应力结构作为桥隧结构的主要构件常服役于高湿或变湿环境,为了研究预应力梁在不同环境湿度下的长期变形发展及长期预应力损失,基于DuCOM-COM3多场多尺度有限元计算程序对不同环境湿度下的预应力混凝土结构进行了有限元分析,并与试验结果进行对比,结果表明:混凝土梁的预应力损失受到环境湿度的影响,环境湿度增大有利于减小构件的长期变形从而减缓预应力结构的预应力损失与长期挠度。这表明基于多尺度微观孔隙结构的材料本构可以考虑孔隙结构的微观变形,通过计算混凝土材料内部的微观行为和水分传输可以得到混凝土结构的力学性能。通过对比试验与计算证明了混凝土结构的多场多尺度分析能分析变化的环境对预应力混凝土结构的长期性能的影响。通过水-热-力学耦合的多场多尺度分析机理,模拟环境湿度为40%、60%以及80%情况下的预应力混凝土梁的预应力损失与长期挠度情况。得出环境湿度大小与收缩、徐变以及长期变形、预应力损失情况之间的关系。