基于应力比值法的张弦结构动力放大系数研究

Research on dynamic magnification factor of string structures based on stress ratio method

在结构连续倒塌分析中,可通过荷载动力放大系数将静力荷载进行放大,从而间接模拟结构的动力响应。目前国内外相关文献中关于动力放大系数取值的观点不同。对于空间结构,杆件失效后剩余结构容易出现塑性;塑性程度对动力放大系数影响较大,使得动力放大系数具有不确定性。提出采用应力比值法研究张弦结构的动力放大系数,其过程为:在设计荷载组合下控制结构不同的平均应力比值,得到不同构件截面大小的结构模型,然后对这些模型进行动力放大系数的分析。为了充分研究动力放大响应,分别定义了弹性位移动力放大系数、弹塑性动力放大系数和荷载动力放大系数。分析结果表明:对于张弦结构,弹性动力放大系数最大不超过2.0;由于塑性的发展,弹塑性动力放大系数有可能超过2.0。荷载动力放大系数取2.0比较保守;建议索破坏时荷载动力放大系数取1.6~1.8,其他重要构件破坏时荷载动力放大系数取1.3~1.5。

In the progressive collapse analysis,the dynamic response can be obtained by magnifying the static load with the dynamic magnification factor. However,the values of the dynamic magnification factor are in some dispute.For the space structures,plastic area appears easily in the remaining structure when one member fails. Dynamic magnification factor would vary and become indefinite for the degree of plasticity. Stress ratio method was put forward to determine dynamic magnification factor of string structures. The structural models with different cross-sections were obtained by controlling average stress ratios under the design load. Then the models were studied to get dynamic magnification factor. Three kinds of dynamic amplification factors were defined in order to fully study dynamic amplification response: one was elastic displacement dynamic magnification factor,the second was elasto-plastic displacement dynamic magnification factor and the third was load dynamic magnification factor. The results show that for string structures,the maximum elastic displacement dynamic magnification factor is smaller than 2. 0,and the maximum elasto-plastic displacement dynamic magnification factor may be larger than 2. 0 because of the development of plastic area. Moreover,if the value of load dynamic magnification factor is assumed to be 2. 0,it is conservative. It is suggested that the load dynamic magnification factor should be 1. 6-1. 8 under the cable failure and 1. 3-1. 5 under the failure of other important elements.