Traditional analyses of gravity secondordereffect for tall concrete structures are basically approximate. This approximate method will bring obvious errors.
A model for simplified secondorder analysis of the double resistance to lateral force system is built on the basis to transform secondordereffect into negative stiffness.
为简化双重抗侧力体系二阶分析，将结构的二阶效应转化为结构的负刚度，从而建立分析模型。
3
Making use of equivalent principle of secondordereffect, the load on middle stories is converted into that at top and the approximate formula for the critical load of the system is suggested.