Parametric equations for design of fire insulation coating thickness of steel columns

Document Type : Original Research

Authors
M. Chaboki 1
A. Aghakouchak 2
1 Ph. D. Student
2 Professor
10.22034/24.4.125
Abstract
This paper investigates the effects of various parameters, including support conditions, the Demand to Capacity Ratio (DCR) of the member under gravitational loads, the section factor (the ratio of perimeter to area), and the fire insulation coating thickness on the fire resistance duration of steel columns under fire effects. To this end, four steel H-shaped columns and four steel tube columns with the height of 4 meters, are subjected to the standard fire curve (ASTM E119) from four sides, and the effects of different parameters are studied. Initially, a heat transfer analysis is carried out on the 2D cross-section of columns with its fire insulation coating in Abaqus software. Then, a nonlinear general static analysis is performed on a 3D steel column model subjected to gravity (concentrated axial) and thermal loading simultaneously.

Results of this study indicate that the columns only expand but do not deform significantly until approximately 250oC. After that, a decrease in the steel strength and stiffness and as a result, a decrease in fire resistance and bearing capacity of the steel column occurs. This is accompanied by an increase in the mid-span horizontal displacement of the column and an increase in the effect of the P-δ bending moment, which results in the column failure at about 500oC to 650oC. The results also show that the fixed or pin support condition on the bottom end of the column does not significantly affect the column failure time under fire effects. In square box columns, the increase in the section thickness increases the fire resistance duration of the steel column. However, increasing the section width does not significantly affect the column failure time. In H-shaped columns, the increase in the flange thickness and the decrease in the column web height increases the column fire resistance duration. On the other hand, the results indicate that the section factor, the initial load level of the member due to gravitational loads, and the fire insulation coating thickness have a significant effect on column failure time to the extent that with the increase in DCR of the member from 0.3 to 0.7, the failure time of the column decreases by about 25 to 35 minutes.

Based on the results of this study, two formulae have been presented to calculate the failure time of protected columns by CAFCO300. The results of these formulae have also been compared to a relationship proposed in Chapter 10 of the Iranian National Building Regulations. It is found that the results of these formulae are fairly similar, when the initial DCR equals 0.7. Therefore, the relationships of the present study provide a more optimal and accurate design of the fire insulation coating thickness, because this load level can only occur in structures that are not designed for lateral loads and are designed only under gravitational loads.

Keywords

Subjects

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Modares Civil Engineering journal
Volume 24, Issue 4
September and October 2024
Pages 125-136