Journal of Steel & Structure

Journal of Steel & Structure

Evaluation of the Collapse Probability of Knee-Braced Reinforced Concrete Frames under Near-Fault Pulse-Type Earthquakes Using the FEMA P-695 Method

Document Type : Original Article

Authors
Alireza Rafatfar
Navid Siahpolo
ACECR Institute of Higher Educatio
10.22034/jss.2025.553884.1011
Abstract
This study presents a comprehensive seismic performance evaluation of reinforced concrete frames equipped with knee braces (RC-KBF) following the FEMA P-695 guidelines. The primary aim is to assess the collapse probability of these frames under severe near-fault earthquakes, particularly focusing on pulse-type ground motions, and to investigate their nonlinear dynamic behavior. Two-dimensional models of RC frames with varying span lengths and numbers of stories were developed based on the Iranian National Building Code (Chapters 9 and 10) and the fourth edition of Standard 2800, using ETABS software. Incremental nonlinear dynamic analyses were then conducted in PERFORM 3D to extract key parameters such as median spectral acceleration at collapse and collapse margin ratio (CMR). Comparative results indicate that pulse-type ground motions cause approximately an 18% increase in median spectral acceleration and a 17% increase in the CMR compared to records without pulses, indicating the severe impact of near-fault pulse effects. Most models met the minimum acceptance criteria specified in FEMA P-695, with only one model failing due to insufficient ductility. The findings underscore the effectiveness of knee braces as a viable seismic retrofit alternative to traditional systems in reinforced concrete frames, especially in regions vulnerable to near-fault earthquakes. Moreover, the study highlights the unique challenges posed by pulse-type records and provides both qualitative and quantitative insight into seismic behavior enhancements achieved by knee-braced systems.
Keywords
RC-KBF (Reinforced Concrete Knee-Braced Frame)
FEMAP-695 Collapse Evaluation
Near-Fault Earthquake
Median Spectral Acceleration at Collapse
Fragility Curves
Subjects
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  • Receive Date 17 October 2025
  • Revise Date 17 November 2025
  • Accept Date 30 December 2025
  • First Publish Date 30 December 2025
  • Publish Date 23 September 2025