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

为探讨钢管侧向约束对受约束高强钢筋混凝土柱极限抗弯性能的影响，对方形钢管和圆形钢管约束下钢筋混凝土柱的单调抗弯性能进行了试验研究。采用抗压强度分别为60MPa和100MPa的高强混凝土制作20根试验柱，其中10根为方钢管约束柱，10根为圆钢管约束柱，试验柱均在单调弯矩和恒轴压联合作用下进行试验。试验结果表明，约束型高强混凝土柱的抗弯响应和极限性能不仅与钢管壁厚有关，还与轴向荷载水平有关。在相同壁厚的情况下，圆钢管的约束效应远高于方钢管。本研究更重要的结果是，受约束混凝土截面在最大弯矩处的极限混凝土纤维压应变并不是当前许多设计规范所建议的恒定值，而是随钢管提供的约束程度而增加的变量，几乎与轴向荷载水平无关。在上述试验研究的基础上，对受约束高强钢筋混凝土柱的受弯响应进行了分析研究，提出了一种简单实用的受约束混凝土柱极限弯矩和变形能力的理论计算方法。在参数化研究结果的基础上，建立了约束混凝土极限应变预测的数学表达式。提出了两个矩形等效应力块，简化了极限弯矩承载力的计算。提出了方形钢管约束柱和圆形钢管约束柱的应力块。实测结果与理论预测吻合较好，验证了所提应力块的有效性。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