圆钢管混凝土受弯构件中性层偏移规律及承载力研究

Study on neutral layer migration law and flexural capacity about the concrete filled circular steel tubular flexural members

对4个圆钢管混凝土受弯构件进行了试验研究。结果表明:当荷载约为0.7Pu时,纵向应变沿截面高度分布基本符合平截面假定;当钢管跨中受拉区应变约为1 500~2 000με时,钢管屈服;随套箍系数的增加,S-M曲线中性层偏移线整体下移且分为2个阶段,即近水平段、线性偏移段。试验结果还表明:随套箍系数的增加,中性层偏移速率先快后慢;S-Φ曲线具有线性段和塑性段,速率转折点约在Φ=30 mm附近。在中性层偏移规律的基础上,推导出了圆钢管混凝土受弯构件的承载力计算公式,计算结果与试验结果吻合良好。

Four concrete filled circular steel tubular flexural members were experimentally studyed. The results show that when the load is about 0. 7 times the ultimate load bearing capacity, the steel tube longitudinal strain distribution along the depth of cross-section obeys the plain section assumption. When the steel middle span tensile zone strain is about 1 500 - 2 000 με, the steel yields. With the increase of coefficient of confinement effect, neutral layer offset line moves down as a whole and can be classified into two stages, that is horizontal and linear offset. Experimental results also show that with the increase of coefficient of confinement effect, offset speed of the neutral layer is fast first and slow after. The S-Ф curve has a linear and plastic stage and the rate of turning point is around Ф = 30 mm. On the basis of the neutral layer offset rule, the calculation formula of bearing capacity of the concrete filled circular steel tubular flexural members is deduced, and the predicted results agree well with those of tests.