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Faculty of Civil Engineering, University of Belgrade, Belgrade, Serbia
Faculty of Civil Engineering, University of Belgrade, Belgrade, Serbia
In practice, consideration of fire protection for structural elements mainly occurs after the adopted dimensions of sections. However, this procedure leads to not the most cost-effective solution in general. To find the optimal solution, it is necessary to apply one of the optimization methods. The presented optimization of purlins RHS cross-section is performed with nonlinear programming available in widely used program Excel. The objective function is defined as producing the purlin at a minimal price, considering the price of steel, work, and fire-resistant paint. Limits are introduced to ensure the cross-section satisfies the ultimate limit state for permanent and transient load situations, as well as in case of fire. Besides the ultimate limit states, the limits are defined for serviceability limit states and for cross-sectional geometry. Optimization analysis for different ISO 834 fire durations is followed by a result comparison. It provides an overview of cross-sectional parameters that most influence the bearing capacity in case of fire. It is concluded that by increasing the exposure time to fire, the optimal solution becomes a section with a smaller perimeter, larger surface area, and a thicker layer of fire-resistant coating.
The first author thanks the Ministry of Science, Technological Development and Innovation of the Republic of Serbia for financial support via a Ph.D. student stipend. The second author thanks the Ministry of Education, Science, and Technological Development, Republic of Serbia, through Project 200092.
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