Study on Flexural Behavior of High-Strength Reinforced Concrete Columns Confined by Steel Tube

进行了方钢管和圆钢管约束的钢筋混凝土柱的单调受弯性能试验，研究了钢管侧向约束对高强钢筋混凝土柱极限受弯性能的影响。20根试验柱，其中10根采用方钢管约束，其余10根采用圆钢管约束，采用抗压强度为60或100 MPa的高强混凝土，进行了单调弯矩和等轴压组合作用下的试验。试验结果表明，约束高强混凝土柱的弯曲反应和极限性能不仅与钢管壁厚有关，而且与轴向荷载水平有关。在相同壁厚的情况下，圆钢管的约束效果远高于方钢管。最有趣的体验…研究结果表明，在最大弯矩时，约束混凝土截面极限混凝土纤维处的压应变不是现行设计规范所建议的常数，而是几乎与轴压水平无关的随钢管约束程度而增大的变量。与上述试验研究平行进行的是对约束高强混凝土柱的弯曲反应进行了分析研究，提出了一种从理论上评估约束混凝土柱极限弯矩和变形能力的简单实用的方法。基于参数研究的结果，建立了预测约束混凝土极限应变的数学表达式。此外，还提出了两个矩形等效应力块，以简化极限弯矩的计算。对于方钢管约束的柱，提出了一种应力块；对于圆钢管约束的柱，提出了一种应力块。测量结果与理论预测的良好一致性验证了所提出的应力块的有效性。较少

An experimental study of monotonic flexural behavior of reinforced concrete columns confined by square or circular steel tube was conducted to investigate effects of lateral confinement by steel tubes on ultimate flexural properties of the confined high-strength reinforced concrete columns. Twenty test columns, ten of which were confined by square steel tubes and the others by circular steel tubes, were made of high-strength concrete with compressive strength of 60MPa or 100MPa, and all of these columns were tested under combined monotonic bending moment and constant axial compression. Test results indicated that flexural response as well as ultimate properties of a confined high-strength concrete column not only depended upon wall thickness of the steel tube, but the axial load level as well. It has also been shown that confinement effect of circular steel tube was much higher than that of square steel tube when the steel tubes had the same wall thickness. The most interesting experim … More ental result obtained in this study was that the compressive strain at the extreme concrete fiber of the confined concrete section developed at the maximum moment was not a constant as recommended in many current design codes, but a variant increasing as the confinement degree provided by the steel tubes almost regardless of the axial load level.Parallel to the experimental study described above, an analytical study of the flexural response of confined high-strength reinforced concrete columns was carried on to develop a simple and practical method of theoretically evaluating the ultimate moment and deformation capacity of confined concrete column. Based on the results of parametric study, a mathematical expression for predicting the ultimate strain of confined concrete was developed. Furthermore, two rectangular equivalent stress blocks were proposed to simplify the calculation of ultimate moment capacity. One stress block was proposed for columns confined by square steel tube and the other was for columns confined by circular steel tubes. Good agreement between the measured results and the theoretical predictions verified validity of the proposed stress blocks. Less