Second-Order Analysis

词汇表条目

In the calculation according to the second-order analysis, the equilibrium on a deformed structural system is determined.

The calculation according to the second-order analysis (also: P‑delta) detects the deformation effects due to loading, which affect the distribution of internal forces. Axial forces in the structural system usually lead to an increase of bending moments. In the case of pressure-loaded members, additional moments arise and thus overlinear effects of loads and moments occur. On the other hand, tension forces have a positive effect.

In RFEM and RSTAB, it is possible to calculate load cases and load combinations according to the various methods of analysis (see Figure 01). However, result combinations superimpose the results of the calculated load cases and combinations, so that the method of analysis can only be controlled indirectly.

The calculation according to the second-order analysis examines stability problems, for example buckling. In the RF‑/STEEL EC3 add‑on module, you can also perform the stability analysis considering lateral-torsional (torsional-flexural) buckling. The module extension RF‑/STEEL Warping Torsion allows you to perform the analysis according to the second‑order theory with 7 degrees of freedom (warping torsion).

In the case of steel structures, the second-order analysis must be used if the compression force in a member exceeds 10% of the elastic critical buckling load [4]. For concrete structures, certain limiting slendernesses are governing. Timber structures are usually calculated according to the linear static analysis.

Chapter 7.2.1.1 of the RFEM [1] or RSTAB manual [2] contains further information about the methods of analysis.

In the attached example, a load is analysed according to the linear static analysis and the second-order analysis. A vertical load with a small horizontal load acts on the column head (see Figure 02). The axial force has no influence on the moment distribution My in LC 1. However, the additional moment according to the second-order analysis is clearly recognisable in LC 2. If the load is further increased (or the cross-section is reduced), the program will display a message about the instability.

关键词

second-order analysis deformed system P-delta

目录

[1]   Manual RFEM. (2018). Dlubal Software: Tiefenbach.
[2]   Manual RSTAB. (2013). Tiefenbach: Dlubal Software.
[3]   Roik, K.; Carl, J.; Lindner, J. (1972). Biegetorsionsprobleme gerader dünnwandiger Stäbe. Berlin: Ernst & Sohn.
[4]   Eurocode 3: Design of steel structures - Part 1‑1: General rules and rules for buildings; EN 1993‑1‑1:2010‑12

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RFEM 主程序 RFEM
RFEM 5.xx

主程序

结构设计与有限元­分析软件(FEA)可以用于建立 平面与空间结构模型,适用于由杆件、面、 板、墙、折板、膜、壳、实体以及接触单元等的建模与分析计算。

首个许可价格
3,540.00 USD
RSTAB 主程序
RSTAB 8.xx

主程序

空间结构设计与分析软件,主要用于框架、梁与桁架等空间结构的建模与计算。可以输出内力、变形与制作反力的线性与非线性的计算结果。

首个许可价格
2,550.00 USD
RFEM 钢结构和铝合金结构
RF-STEEL Warping Torsion 5.xx

RF-STEEL EC3/RF-STEEL AISC 扩展模块

弯扭屈曲验算按照二阶效应理论和 7 个自由度进行计算

首个许可价格
850.00 USD
RSTAB 钢结构和铝合金结构
STEEL Warping Torsion 8.xx

STEEL EC3/STEEL AISC 扩展模块

弯扭屈曲验算按照二阶效应理论和 7 个自由度进行计算

首个许可价格
850.00 USD