Comparison of LRFD and ASD for Pre-Fabricated Gable Frame Design

Naser Katanbafnezhad, Alan Hoback

American Journal of Engineering Research (AJER), vol. 9(5), 2020, pp. 120-134.


Pre-fabricated gable frames with tapered members of varying angles were designed for six locations using both Allowable Stress Design (ASD) and Load and Resistance Factor Design (LRFD). The locations were chosen to represent a range of local loading conditions as found in ASCE's Minimum Design Loads. Roof angles varied from 10 to 45 degrees and spans varied from 20 to 200 feet. The results demonstrate significant differences in the economies of ASD and LRFD. Each design basis had scenarios from one location to the next where it was more economical. The biggest differences were for steep roofs in areas with high wind. The differences were up to 30% with LRFD generally being favored. The biggest variations were LRFD gave up to 30% less stress in some situations, and ASD gave 10% less in others.

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1. Kaehler, R. C., White, D. W., & Kim, Y. D.: Frame design using web-tapered members. American Institute of Steel Construction. Design Guide 25, (2011).
2. Ftoeder, C. W.: Comparison of LRFD and allowable stress design methods for steel structures, (1990).
3. Salmon, C. G., & Johnson, J. E.: Steel Structures: Design and Behavior. 4th Edition, (1997)
4. Ellingwood, B., MacGregor, J. G., Galambos, T. V., & Cornell, C. A.: Probability based load criteria: load factors and load combinations. Journal of the Structural Division, 108(5), 978-997, (1982).
5. American Society of Civil Engineers: ASCE 7-16- Minimum design loads and associated criteria for buildings and other structures, (2016).
6. American Institute of Steel Construction: Specification for Structural Steel Buildings, ANSI/AISC 360-16, Chicago, IL, (2017).
7. Forero, N., Hernandez, J., Gordillo, G.: Development of a monitoring system for a PV solar plant. Energy Conversion and Management 47(15-16), 2329-2336 (2006).
8. Jorge, A., Guerreiro, J., Pereira, P., Martins, J., Gomes, L.: Energy Consumption Monitoring System for Large Complexes. In: Camarinha-Matos, L.M., Pereira, P., Ribeiro, L. (eds.) DoCEIS 2010. IFIP AICT, vol. 314, pp. 22-24. Springer, Heidelberg (2010).