Evaluation of Flexural Strength Reduction Factors of Members in Reinforced Concrete Moment Frames

Document Type : Research Article

Authors

1 Department of Civil and Environmental Engineering

2 Civil Engineering Department, Amirkabir University of Technology

Abstract

In this paper, the precise estimation of flexural resistance reduction factors in reinforced concrete beams and columns is investigated, considering the interaction effect of axial force for columns. To determine the reduction factors, 6,750 beams and 3,000 columns with various cross-sectional shapes, including rectangular, T-shaped, and L-shaped beams, as well as rectangular and circular columns, were examined. Different design variables, such as concrete compressive strength, reinforcement yield strength, reinforcement ratio, axial load ratio, and geometric dimensions, were considered for these sections. Random analyses were performed using the Latin hypercube sampling method with 1,000 samples for each section to account for uncertainties related to materials, geometry, and modeling. Additionally, statistical models of modeling uncertainty were updated using experimental data and analysis, and these updated models were employed. The proposed reduction factors for various conditions were calibrated based on reliability indices from the ASCE 7-22 code. The results indicate that, in many cases, particularly for transition and compression-controlled columns, the proposed factors are higher than the prescribed values in the ACI 318-19 code. This increase, especially in the design of gravity columns, can significantly reduce the weight of reinforcement and the volume of concrete (by approximately 40% and 15%, respectively, in an 8-story building), thereby considerably lowering construction costs while maintaining the required safety level. These findings highlight that updating the resistance reduction factors and utilizing variable values based on design characteristics can contribute to more economical and optimized structural designs.

Keywords

Main Subjects

References

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Amirkabir Journal of Civil Engineering
Volume 57, Issue 6
September 2025
Pages 1021-1046

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