基于动力放大系数与等效单自由度体系的圆中空夹层钢管混凝土抗撞设计方法

Design method for impact resistance of circular concrete-filled double-skin steel tubular members based on dynamic increase factor and equivalent single DoF system

中空夹层钢管混凝土(concrete-filled double-skin steel tubular,CFDST)构件作为超高输电塔、海上平台等重要结构的承重构件,其抗撞性能是设计阶段需考虑的关键问题。因此,在前期试验研究的基础上,采用ABAQUS有限元软件建立了200个圆CFDST柱力学模型,并进行了轴力与撞击耦合作用下的抗撞机理分析,研究了在0~0.7轴压比下不同名义含钢率、空心率、截面直径、材料强度对构件抗撞性能的影响规律;基于动力放大系数和等效单自由度方法提出了构件抗撞承载力计算公式,并预测了撞击作用下构件的跨中动力响应。结果表明:在0~0.7轴压比下,名义含钢率、外径、外钢管强度、撞击速度与撞击质量对构件跨中挠度峰值和撞击力平台值影响显著,空心率与混凝土强度影响较小;提出的简化计算方法能较好地预测圆CFDST构件的抗撞承载力和跨中位移响应。

Concrete-filled double-skin steel tubular(CFDST)members are widely employed as load-bearing members in the ultra-high power transmission tower and offshore platform.The impact resistance of this type of members should be considered in the design stage.Based on the previous test results,in total 200 finite element(FE)models considering the coupling of axial and lateral impact loads were established with the ABAQUS software,and the damage mechanism of impact resistance was analyzed.Then,the parametrical studies were carried out to investigate the influences of key factors,including the nominal steel ratio,hollow ratio,cross-sectional diameter and material strength on the impact resistance of the members for the axial load ratio ranging from 0 to 0.7.Finally,the calculation formula for the impact bearing capacity is proposed and the dynamic response at the mid-span was predicted based on the methods of dynamic increase factor and an equivalent single degree-of-freedom model.In this work,the deflection at the mid-span and the plateau impact force were taken as the key indexes to evaluate the impact resistance.Results indicate that the impact resistance of the circular CFDST columns decreases with the increasing of axial load ratio.Under lateral impact,the CFDST members with the hollow ratio lower than 0.7 exhibit flexural failure.The interaction between the external steel tube and the inner concrete is stronger than that between the inner steel tube and the outer concrete.In addition,the nominal steel ratio,outer diameter of the cross-section,yield strength of the outer tube,impact velocity and impact mass all play significant roles on the maximum deflection at the mid-span and the plateau impact force when the axial load ratio ranges from 0 to 0.7.Effects of hollow ratio and concrete strength are marginal.The proposed calculation methods can reasonably predict the impact bearing capacity and mid-span displacement response of the CFDST members subjected to an impact.