钢管混凝土收缩变形与钢管混凝土拱收缩应力

Shrinkage Deformation of Concrete Filled Steel Tube and Shrinkage Stress of Concrete Filled Steel Tubular Arch

钢管混凝土拱桥在我国桥梁中得到广泛的应用,其管内混凝土收缩产生的收缩应力是结构受力的重要组成部分,收缩应力计算的关键是收缩变形值的确定。以混凝土强度等级和粉煤灰掺量、钢管直径以及含钢率为主要参数,进行11根钢管混凝土构件和2根素混凝土密闭构件的收缩试验。试验结果表明,钢管混凝土的收缩变形,随粉煤灰掺量的增加而下降,随混凝土强度等级的提高而增大,随含钢率的增大而减小,而钢管直径对其影响较小。应用常用的收缩预测模型对试件的收缩预测分析表明,ACI 209R-92模型预测精度较高,可用于粉煤灰掺量不大于20%的钢管混凝土构件;当掺量大于20%时,预测值偏大,可对现模型进行修正;而CEB-FIP MC78和CEB-FIP MC90模型预测结果明显偏小。对钢管混凝土拱桥的收缩应力分析表明,收缩自应力较大,在设计计算中应予以考虑;而收缩次应力较小,在初步设计的应力估算中可以忽略不计。常用的混凝土拱收缩作用的等效降温法,因钢管混凝土拱的收缩变形变化范围大,合理降温值确定难度大,且该法无法计算比重较大的收缩自应力,建议设计计算时不采用该方法。

Concrete filled steel tubular（CFST）arch bridges are widely applied in the bridge engineering in China.Shrinkage stress caused by the shrinkage of core concrete is an important part of structure stress,and the determination of the shrinkage deformation value is the key issue for the calculation of the shrinkage stress.With strength grade of concrete,content of fly ash,and steel tube diameter as well as steel ratio as the main parameters,shrinkage tests on 11 CFST and 2air-tight plain concrete specimens were carried out.Test results showed that the shrinkage deformation of the CFST member decreased with the increase of the content of fly ash and the steel ratio,and increased with the increase of the strength grade of the concrete,while it was little affected by the diameter of the steel tube.Prediction analysis of the shrinkage deformation of the specimens by the common shrinkage prediction models indicated that the ACI 209R-92 model with higher prediction precision can be used to predict the shrinkage of CFST members when the content of fly ash of the core concrete is less than 20%.When the content of fly ash is greater than 20%,correction of the model is required as the prediction value would be higher.The prediction results by CEB-FIP MC90 model and CEB-FIP MC78 model were significantly smaller than the tested ones.Analysis of shrinkage stresses of CFST arch bridges showed that the shrinkage self-stress was large and should be taken into account in design calculation,whereas the secondary shrinkage stress was small and could be ignored in stress estimation during preliminary design.The use of e-quivalent cooling method,commonly used for calculation of shrinkage effect of concrete arch,should be discouraged in the design calculation of shrinkage effect of a CFST arch due to large variation range of shrinkage deformation,difficulty to determine an equivalent cooling value,and inability to calculate the shrinkage selfstress which accounts for a large proportion of the shrinkage stress.