中空夹层圆钢管混凝土短柱的压弯承载力计算法

Load Bearing Capacity Calculation Method of Circular Concrete-Filled Double Skin Steel Tubular Stub Columns

中空夹层圆钢管混凝土短柱在轴压作用下,混凝土材料受到内外钢管约束处于三向受压状态,其抗压承载力较普通混凝土有较大提升。提升幅度与侧压应力有直接关系,侧压应力大小取决于截面尺寸及其所受轴力。现行设计方法认为同一构件在轴压和纯弯状态下侧压应力大小相同,对于偏压状态下的侧压应力如何考虑未明确说明。对此,引入与轴力相关的侧压应力系数β修正混凝土的本构关系,明确在各种受力状态下如何考虑侧压应力的影响。还提出一种应力积分算法用于计算短柱构件的极限承载力,得到短柱截面的轴力-弯矩(N-M)曲线。最后,提供若干构件在轴压、纯弯和偏压状态下的算例,验证修正后的本构模型和应力积分算法,计算结果与试验结果吻合较好。

When a circular concrete-filled double skin tubular(CFDST) stub column is subjected to compression, the inside concrete is in a tri-axial stressing state due to the confining actions induced by the internal and external steel tubes.Consequentially, the compression strength might be increased, which is directly affected by the lateral confining stress applied on the concrete core.The section sizes and axial force levels are two main factors that have influences on this effect.Current design methods assume the confining stress is the same under the loading actions of pure-bending and axial-compression, but it is not clearly stated how to consider the stress under the eccentric pressure.This research proposes a lateral confining stress coefficient β to revise the concrete constitutive model for a more accurate calculation of the confining actions on concrete.A new stress integration method is proposed in this paper for computing the section capacity of stub columns under the ultimate limited state, and the axial-moment(N-M) strength interaction curve can be accordingly generated.Finally, a few several examples are provided for demonstrating the accuracy of the proposed method.