P-d 分析只是用于分析
但是如果要用特点规范进行设计的时候，需要指定参数。
两者不是一回事情，具体的计算长度需要指定。(这个貌似比较烦 )
不知道有什么办法可以让这些计算长度自动计算？
以下是转自bently的一专家的解释，希望大家一起讨论

ust for clarity, the effective lengths are a design issue, and P-Delta is an analysis issue.  So you don't need to worry about effective lengths for a P-Delta analysis, but you will need to consider effective lengths when you get to the design stage, if your design code or standard requires their use.  The alignment charts for braced and unbraced structures are the most common way that i am aware of for determining the K factors for buckling about each axis.

You should be able to use the Ky parameter to specify the K factor for buckling about the local y axis, Kz parameter to specify the K factor for buckling about the local z axis, Ly parameter to specify the length to use when determining KyLy/ry, and Lz parameter to specify the length to use when determining KzLz/rz.  To the best of my knowledge, these design parameters were available in STAAD.Pro 2006.

关于计算长度的回复，bently明确指出，计算长度系数，软件不自动计算，需要人为指定。

Performing a P-Delta analysis does not eliminate the need to assign effective lengths for columns. The P-Delta analysis addresses secondary effects in members due to interstory drift and member deflection. Column effective length factors address column stability/buckling, which is a separate issue. STAAD.Pro does not compute the effective lengths of columns in a frame automatically.

SSDD？

一般情况下，SSDD是可以计算并输出的，可以用于美国规范设计，因为中美规范计算公式是一样的

看新的钢结构规范报审稿，我朝的柱子计算长度系数的计算公式修改了一下下，跟美帝的有所不同了，不是超越方程了，搞得便于手算了。不过结果差别很小：）