### Abstract

In Eurocode 3, Part 1.2 (ENV 1993-1-2 1993) simple
calculation models are given by which the load-bearing
capacity can be determined for different structures at
elevated temperatures. These simple models are restricted
to steel sections where the first order theory in global
plastic analysis may be used. Eurocode 3, Part 1.2 gives
no simple calculation method for a class 4 cross-section
but does mention that the steel temperature of a class 4
cross-section should be below 350 °C, otherwise a general
calculation method should be used. If the temperature is
limited to 350 °C the insulation thickness increases,
making structures of class 4 cross-sections uneconomical.
The aim of this study is to find a simple calculation
method for calculating the fire resistance of certain
structures that may fail by local buckling. A series of
fire tests was carried out for cold-formed rectangular
hollow sections (RHS 200 x 200 x 5 and RHS 150 x 100 x 3)
of structural steel S355. Both concentric and eccentric
compression tests were performed. The fire tests were
transient-state tests (heating rate 10 *C per minute
under constant load) on unprotected specimens.
A proposition for a simple calculation method is
submitted. According to the proposition the effective
width at elevated temperatures may be determined with the
same formulae as at normal temperature, but the yield
strength and the modulus of elasticity must be reduced.
The yield strength of steel is determined corresponding
the 0.2% proof strain at elevated temperatures. The
stress-strain relationship and the modulus of elasticity
at elevated temperatures are determined according to
Eurocode 3, Part 1.2. The effects of actions during fire
exposure may be deduced from the properties determined at
normal temperature, using the reduction factor. With the
typical value of the reduction factor, the end
temperature according to load-bearing capacity calculated
with a proof strain of 0.2% is clearly above 350 °C for
rectangular hollow sections RHS 200 x 200 x 5 and RHS 150
x 100 x 3.
The fire tests were analysed with the finite element
method (FEM). Both geometrical and material non-linearity
were included and the used stress-strain relationship at
elevated temperatures was as determined in Eurocode 3,
Part 1.2.

Original language | English |
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Place of Publication | Espoo |

Publisher | VTT Technical Research Centre of Finland |

Number of pages | 81 |

ISBN (Print) | 951-38-4827-2 |

Publication status | Published - 1995 |

MoE publication type | Not Eligible |

### Publication series

Series | VTT Tiedotteita - Meddelanden - Research Notes |
---|---|

Number | 1672 |

ISSN | 1235-0605 |

### Keywords

- buckling
- construction materials
- hollow sections
- steels
- steel structures
- calculations
- methods
- fire resistance
- compressing
- tests
- temperature

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## Cite this

Ala-Outinen, T., & Myllymäki, J. (1995).

*The local buckling of RHS members at elevated temperatures*. VTT Technical Research Centre of Finland. VTT Tiedotteita - Meddelanden - Research Notes, No. 1672