# Imperfection concept¶

## Introduction¶

This document provides a short introduction to the general stability approach based on imperfections and second order analysis, which is allowed according to EN 1993-1-1. This tutorial will focus only on the imperfection problem, but not on the design of elements. Design topics are described in other tutorials such as Portal Frame. A simple steel frame is analysed in this tutorial.

This project is fully done using Graphical User Interface (GUI). However, it could be completely reproduced via text input - CADINP language. The intention of this tutorial is to guide you through a simple single-span frame example and introduce the general work-flow for imperfections in SOFiSTiK.

Hint

This tutorial is based on EN 1993-1-1 and EN 1993-1-5.

Tip

If you click on the figure it will show up in original size.

For more details see Imperfection Concept - Theoretical Background

### Objectives¶

• Run linear analysis

• Run second order analysis

## Project Description¶

### Geometry¶

A simple one-span steel frame is presented. The frames are on a 5 m spacing. The frame height is 5000 mm with a span of 6000 mm.

### Materials¶

Number

Notes

1

S 355 (EN 10025-2)

tf < 16 mm, thus fy = 355 MPa

### Cross-sections¶

Number

Title

Notes

1

HEA 200

For whole frame

Number

Title

Action

1

Self-weight

G (Permanent)

Automatically generated

2

G (Permanent)

1.0 kN/m2

3

Imposed

Q (Variable)

2.0 kN/m2

4

W (Variable)

1.0 kN/m2

5

W (Variable)

1.0 kN/m2

11

Imperfection

IMP (Imperfection)

Sway 1/200, bow 1/200 (stress-free)

Number

Title

Permanent

Accompanying Variable

1001

1.35·LC1+1.35·LC2+1.50·LC3+0.9·LC4+1.0·IMP

1.35

Imposed 1.5

Wind 1.5 · 0.6

1002

1.35·LC1+1.35·LC2+1.50·LC3+0.9·LC5-1.0·IMP

1.35

Imposed 1.5

Wind 1.5 · 0.6

1003

1.35·LC1+1.35·LC2+1.05·LC3+1.5·LC4+1.0·IMP

1.35

Wind 1.5

Imposed 1.5·0.7

1004

1.35·LC1+1.35·LC2+1.05·LC3+1.5·LC4-1.0·IMP

1.35

Wind 1.5

Imposed 1.5·0.7

## Step-by-Step¶

### Materials and cross-sections¶

Title: Materials and cross-sections | Quality: 1080p HD | Captions: English

Title: Generate loads inside SOFiPLUS | Quality: 1080p HD | Captions: English

A loadcase Imperfection is defined with TYPE IMP. The loadcases of this type allow the use of imperfection loads for the definition of loadcase combinations for the analysis according to the second (third) order theory. It is meaningless to use imperfection loadcases for a linear analysis of single loadcases with ASE or STAR2 and to superimpose these linear loadcases with MAXIMA, as imperfection alone does not create any additional effects, unless a second order analysis is performed. For imperfections the program is capable to handle a cubic function distribution directly for a single beam.
The same is valid for text input. If a linear analysis has been chosen with SYST PROB LINE and all loadcases are chosen with LC NO ALL, the solver will ignore the imperfection loadcases.