Integrating Structural Uncertainty into Demand and Capacity Factored Design: A Case Study of Existing Moment-Resisting Steel Structures

Motaghed, Sasan; Barzian, Vahid

doi:10.22034/IJRRS.2026.9.1.4

Integrating Structural Uncertainty into Demand and Capacity Factored Design: A Case Study of Existing Moment-Resisting Steel Structures

Document Type : Original Research Article

Authors

Sasan Motaghed ¹

Vahid Barzian ²

¹ Department of Civil Engineering, Faculty of Civil engineering and architecture, Shahid Chamran University of Ahvaz, Ahvaz, Iran

² Faculty of Engineering, Behbahan Khatam Alanbia University of Technology, Behbahan, Iran

10.22034/IJRRS.2026.9.1.4

Abstract

Quantitative assessment of seismic performance is vital for establishing the safety and reliability of structural systems, especially in high-hazard regions. This study employs the probabilistic Demand Capacity Factored Design (DCFD) framework, integrating structural uncertainty, to evaluate the seismic safety of 12 medium-ductility steel moment-resisting frames designed according to the third (ASD) and fourth (LRFD) editions of the Iranian seismic code (Standard No. 2800) and the Iranian National Building Codes. The frames, varying in height (3, 5, and 8 stories) and bay count (3 and 5 bays), represent typical residential buildings modeled in OpenSees and subjected to Incremental Dynamic Analysis (IDA) using 20 carefully selected ground motion records. Key uncertainties in demand and capacity are explicitly quantified following FEMA guidelines. Seismic performance is evaluated at Life Safety (LS, 10% APE in 50 years) and Collapse Prevention (CP, 2% APE in 50 years) levels. Results demonstrate that structures designed per the fourth code edition consistently achieve superior seismic performance and higher reliability indices than those designed per the third edition, owing to more robust drift limits and response modification factors. At the CP level, all frames meet safety objectives, while at the LS level, taller and more complex frames require fourth edition provisions to ensure reliability targets. These findings highlight the effectiveness of the DCFD framework, combined with IDA, for comprehensive, uncertainty-aware seismic safety assessment and underscore the enhanced protective capacity of updated code provisions for steel moment-resisting frames in high-risk seismic zones.

Keywords

Demand and Capacity Factored Design (DCFD)

Incremental Dynamic Analysis (IDA)

Intermediate Steel Moment Resisting Frame

Ductility

Subjects

Case Studies Related to Reliability, Risk and Safety

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