Understanding of fire scaling relationships for concrete-filled steel tubes (CFST) columns remains incomplete. Fire resistance research often relies on scaled tests, given the substantial expenses associated with full-scale fire tests. This approach faces theoretical limitations: temperature field similarity dictates elevated heating rates for reduced-scale models, exceeding practical furnace capabilities. This study aims to investigate the relationship between the fire exposure time ratio required to achieve similar fire responses and their size ratio under the same fire exposure conditions. Through a thermo-mechanical sequentially coupled simulation method, a series of geometrically similar CFST columns were designed and subjected to heating according to the ISO-834 standard temperature–time curve. An empirical formula was developed to establish the relationship between the equivalent fire exposure time ratio and the size factor. Key findings reveal that: (1) Elevated temperature profiles and dimensional scaling exert negligible influence on failure mechanisms, with mid-height bulging remaining the predominant failure mode; (2) This investigation develops scaling relationships between fire exposure duration (t) and dimensional size factor (λ) for specified degradation thresholds of load-bearing capacity and axial stiffness. (i) Load-bearing capacity degradation follows <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="43452_2025_1268_Article_IEq1.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="56" /> </InlineMediaObject> <EquationSource Format="TEX">$t\propto {\lambda }^{0.5}$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>t</mi> <mo>∝</mo> <msup> <mrow> <mi>λ</mi> </mrow> <mrow> <mn>0.5</mn> </mrow> </msup> </mrow> </math></EquationSource> </InlineEquation> (pre-40% reduction) and <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="43452_2025_1268_Article_IEq2.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="56" /> </InlineMediaObject> <EquationSource Format="TEX">$t\propto {\lambda }^{1.0}$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>t</mi> <mo>∝</mo> <msup> <mrow> <mi>λ</mi> </mrow> <mrow> <mn>1.0</mn> </mrow> </msup> </mrow> </math></EquationSource> </InlineEquation> (post-40% reduction); (ii) Axial stiffness deterioration scales as <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="43452_2025_1268_Article_IEq2.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="56" /> </InlineMediaObject> <EquationSource Format="TEX">$t\propto {\lambda }^{1.0}$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>t</mi> <mo>∝</mo> <msup> <mrow> <mi>λ</mi> </mrow> <mrow> <mn>1.0</mn> </mrow> </msup> </mrow> </math></EquationSource> </InlineEquation>. (3) After 3600 s of fire exposure, the steel tube in the CFST column reaches 800 °C, rendering its load-bearing capacity negligible and thereby influencing the relationship between the fire exposure time ratio and the size factor. These scaling laws provide critical guidance for scaled fire resistance studies of CFST columns.

Scaling of fire exposure time for axial compression performance of geometrically similar CFST columns

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发表日期：

2025年7月11日

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Liu Jin,
Ningbo Fan,
Renbo Zhang,
Yitao Gao,
Xiuli Du

摘要

Understanding of fire scaling relationships for concrete-filled steel tubes (CFST) columns remains incomplete. Fire resistance research often relies on scaled tests, given the substantial expenses associated with full-scale fire tests. This approach faces theoretical limitations: temperature field similarity dictates elevated heating rates for reduced-scale models, exceeding practical furnace capabilities. This study aims to investigate the relationship between the fire exposure time ratio required to achieve similar fire responses and their size ratio under the same fire exposure conditions. Through a thermo-mechanical sequentially coupled simulation method, a series of geometrically similar CFST columns were designed and subjected to heating according to the ISO-834 standard temperature–time curve. An empirical formula was developed to establish the relationship between the equivalent fire exposure time ratio and the size factor. Key findings reveal that: (1) Elevated temperature profiles and dimensional scaling exert negligible influence on failure mechanisms, with mid-height bulging remaining the predominant failure mode; (2) This investigation develops scaling relationships between fire exposure duration (t) and dimensional size factor (λ) for specified degradation thresholds of load-bearing capacity and axial stiffness. (i) Load-bearing capacity degradation follows $t\propto {\lambda }^{0.5}$ $t \propto λ^{0.5}$ (pre-40% reduction) and $t\propto {\lambda }^{1.0}$ $t \propto λ^{1.0}$ (post-40% reduction); (ii) Axial stiffness deterioration scales as $t\propto {\lambda }^{1.0}$ $t \propto λ^{1.0}$ . (3) After 3600 s of fire exposure, the steel tube in the CFST column reaches 800 °C, rendering its load-bearing capacity negligible and thereby influencing the relationship between the fire exposure time ratio and the size factor. These scaling laws provide critical guidance for scaled fire resistance studies of CFST columns.