Structural Fire Design According to DIN EN 1993-1-2 (Thermal Material Properties)

Technical Article on the Topic Structural Analysis Using Dlubal Software

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Technical Article

Using RF-/STEEL EC3, you can apply nominal temperature‑time curves in RFEM or RSTAB. For this, the standard time-temperature curve (ETK), the external fire curve, and the hydrocarbon fire curve are implemented in the program. Based on these temperature curves, the add‑on module can calculate the temperature in the steel cross‑section and thus perform the fire design using the determined temperatures. This article explains the thermal behaviour of structural steel as this is a direct impact on the calculation of component temperatures in RF‑/STEEL EC3.

The material properties of structural steel are described in EN 1993‑1‑2 [2] by using functions in order to have an accurate value for each property at each temperature.

Thermal Expansion

The thermal expansion Δl/l is a change in geometrical dimensions caused by the temperature change.

At 20 °C ≤ Θa < 750 °C:

Formula 1

ll = 1.2 · 10-5 · Θa  0.4 · 10-8 · Θa2 - 2.416 · 10-4

At 750 °C ≤ Θa ≤ 860 °C:

ll = 1.1 · 10-2

At 860 °C < Θa ≤ 1,200 °C:

Formula 3

ll = 2 · 10-5 · Θa - 6,2 · 10-3

Image 01 - Thermal expansion of steel

Specific Heat Capacity

The specific heat capacity ca in J/(kgK) is the heat amount required to heat one kilogram of material by one Kelvin.

At 20 °C ≤ Θa < 600 °C:

Formula 4

ca = 425  7.73 · 10-1 · Θa - 1.69 · 10-3 · Θa2  2.22 · 10-6 · Θa3

At 600 °C ≤ Θa < 735 °C:

Formula 5

ca = 666  13.002738 - Θa

At 735 °C ≤ Θa < 900 °C:

Formula 6

ca = 545  17.820Θa - 731

At 900 °C ≤ Θa ≤ 1,200 °C:

Formula 7

ca = 650

Image 02 - Specific heat capacity of steel

thermal conductivity

The thermal conductivity λa in W/(mK) describes the ability to transfer heat energy by means of heat transfer.

At 20 °C ≤ Θa < 800 °C:

Formula 8

λa = 54 - 3.3 · 10-2 · Θa

At 800 °C ≤ Θa ≤ 1,200 °C:

Formula 9

λa = 27.3

Image 03 - Thermal conductivity of steel

Literature

[1] Eurocode 3: Design of steel structures - Part 1-1: General rules and rules for buildings; EN 1993-1-1:2005 + AC:2009
[2] Eurocode 3: Design of steel structures - Part 1-2: General rules - Structural fire design; EN 1993‑1‑2:2005 + AC:2009

Author

Dipl.-Ing. (FH) Stefan Frenzel

Dipl.-Ing. (FH) Stefan Frenzel

Product Engineering & Customer Support

Mr. Frenzel is responsible for the development of products for dynamic analysis. He also provides technical support for customers of Dlubal Software.

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  • Updated 20 April 2021

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RFEM
RFEM 5.xx

Main Program

Structural engineering software for finite element analysis (FEA) of planar and spatial structural systems consisting of plates, walls, shells, members (beams), solids and contact elements

Price of First License
3,540.00 USD
RSTAB
RSTAB 8.xx

Main Program

The structural engineering software for design of frame, beam and truss structures, performing linear and nonlinear calculations of internal forces, deformations, and support reactions

Price of First License
2,550.00 USD
RFEM
RF-STEEL EC3 5.xx

Add-on Module

Design of steel members according to Eurocode 3

Price of First License
1,480.00 USD
RSTAB
STEEL EC3 8.xx

Add-on Module

Design of steel members according to Eurocode 3

Price of First License
1,480.00 USD