Journal of Concrete Structures and Materials

Journal of Concrete Structures and Materials

The Effect of Concrete Characteristic Strength on the Reliability of the Weak Beam – Strong Column Phenomenon

Document Type : Original Article

Authors
Mohammad Javad Fadaee Fathabadi 1
Hamidreza Azizzadeh Forouzi 2
1 Professor, Civil Engineering Department, Faculty of Engineering, Shahid Bahonar University of Kerman
2 Ph. D. Candidate, Civil Engineering Department, Faculty of Engineering, Shahid Bahonar University of Kerman,
10.30478/jcsm.2026.540669.1401
Abstract
The reliability analysis of the "Weak Beam-Strong Column" phenomenon is recognized as a critical subject in the design of earthquake-resistant structures. Investigation on the "Weak Beam-Strong Column" phenomenon indicates that this principle depends on multiple parameters including geometric properties of the members and their physical characteristics. For reinforced concrete frames, the parameters include geometric properties such as beam and column dimensions, reinforcement area, and reinforcement placement in the sections (concerning effective depth), as well as physical properties including elastic modulus of the materials and material strengths.

The specific subject of this paper is the reliability analysis of the "Weak Beam-Strong Column" condition. In structural design, reliability refers to the probability of a structure maintaining its expected performance under stochastic conditions. For the "Weak Beam-Strong Column" phenomenon, this reliability can serve as an indicator of structural behavior under dynamic effects such as earthquakes or other loadings.

In this study, through probabilistic modeling and by defining a probability function for concrete compressive strength – derived from the governing moment equilibrium equations – the probability of fulfilling this condition under variations in concrete compressive strength has been investigated.

The results emphasize that material uncertainties in construction cannot be ignored in component design. This principle is recognized as fundamental in modern codes such as FEMA guidelines. However, a key limitation of this research is its exclusive focus on concrete compressive strength without consideration of other stochastic parameters such as steel tensile strength variability, cross-sectional geometric variations, or material fatigue effects.

These findings could facilitate the development of reliability-based design guidelines that incorporate inherent material uncertainties in calculations. The outcome may optimize both structural safety and economic efficiency.
Keywords
Structural reliability
Weak beam - strong column
Concrete compressive strength
Normal probability distribution
Uncertainty
Subjects
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  • Receive Date 30 September 2025
  • Revise Date 20 November 2025
  • Accept Date 06 May 2026