Structural Fire Design According to DIN EN 1993-1-2 (Thermal Material Properties)
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 ≤ Θ_{a} < 750 °C:
$$\frac{\u2206\mathrm{l}}{\mathrm{l}}=1.2\xb7{10}^{-5}\xb7{\mathrm{\Theta}}_{\mathrm{a}}0.4\xb7{10}^{-8}\xb7{\mathrm{\Theta}}_{\mathrm{a}}^{2}-2.416\xb7{10}^{-4}$$
At 750 °C ≤ Θ_{a} ≤ 860 °C:
At 860 °C < Θ_{a} ≤ 1,200 °C:
$\frac{\u2206\mathrm{l}}{\mathrm{l}}=2\xb7{10}^{-5}\xb7{\mathrm{\Theta}}_{\mathrm{a}}-6,2\xb7{10}^{-3}$
Image 01 - Thermal expansion of steel
Specific Heat Capacity
The specific heat capacity c_{a} in J/(kgK) is the heat amount required to heat one kilogram of material by one Kelvin.
At 20 °C ≤ Θ_{a} < 600 °C:
$${\mathrm{c}}_{\mathrm{a}}=4257.73\xb7{10}^{-1}\xb7{\mathrm{\Theta}}_{\mathrm{a}}-1.69\xb7{10}^{-3}\xb7{\mathrm{\Theta}}_{\mathrm{a}}^{2}2.22\xb7{10}^{-6}\xb7{\mathrm{\Theta}}_{\mathrm{a}}^{3}$$
At 600 °C ≤ Θ_{a} < 735 °C:
At 735 °C ≤ Θ_{a} < 900 °C:
At 900 °C ≤ Θ_{a} ≤ 1,200 °C:
$${\mathrm{c}}_{\mathrm{a}}=650$$
Image 02 - Specific heat capacity of steel
thermal conductivity
The thermal conductivity λ_{a} in W/(mK) describes the ability to transfer heat energy by means of heat transfer.
At 20 °C ≤ Θ_{a} < 800 °C:
At 800 °C ≤ Θ_{a} ≤ 1,200 °C:
Image 03 - Thermal conductivity of steel
Literature
Author
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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In RF-/STEEL EC3, sets of members are calculated according to the General Method (EN 1993-1-1, Cl. 6.3.4) together with stability analysis. For this, it is necessary to determine the correct support conditions for the equivalent structure with four degrees of freedom.
SHAPE-THIN | Cold-Formed Sections
SHAPE-THIN determines the effective cross-sections according to EN 1993-1-3 and EN 1993-1-5 for cold-formed sections. You can optionally check the geometric conditions for the applicability of the standard specified in EN 1993‑1‑3, Section 5.2.
The effects of local plate buckling are considered according to the method of reduced widths and the possible buckling of stiffeners (instability) is considered for stiffened sections according to EN 1993-1-3, Section 5.5.
As an option, you can perform an iterative calculation to optimize the effective cross-section.
You can display the effective cross-sections graphically.
Read more about designing cold-formed sections with SHAPE-THIN and RF-/STEEL Cold-Formed Sections in this technical article: Design of a Thin-Walled, Cold-Formed C-Section According to EN 1993-1-3.
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- Which cross-sections can I design with the "RF‑/STEEL Cold-Formed Sections" add-on module?
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- Is it possible to use the RF‑/STEEL EC3 add-on module itself to specify the internal forces, for example, from another calculation or program?
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