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Abstract Background/Introduction <p>A large proportion of India’s steel railway bridges are over a century old, operating under rising axle loads and increasing traffic density. These aging riveted structures are highly vulnerable to fatigue deterioration, especially when subjected to variable-amplitude railway loading. Existing studies rarely analyse multi-kilometre, dual-deck rail-cum-road bridges or quantify the sensitivity of fatigue predictions to stress-band selection.</p> Purpose <p>This study evaluates the remaining fatigue life of a historic double-decker steel truss rail-cum-road bridge (106.68 m major spans; &gt;1,026 m total length; constructed in 1887) and quantifies how different stress-band strategies (SB, SB5, SB10, SB15) influence per-vehicle-passage damage (PVPD) and life predictions under future railway loading scenarios.</p> Methods <p>Material characterization of extracted steel coupons established yield (356.6 MPa), ultimate tensile strength (519.3 MPa), and elongation (12.1%). A calibrated finite-element model of the major span was developed in STAAD.Pro, reproducing field-measured mid-span deflections with &lt;3% error. High-cycle fatigue analysis was performed using axle-by-axle loading for 10,100 train-loading combinations across three load classes (CC+8+2T, 25T, 32.5T) and three speeds (V1 ≤ 50 km/h, V2 = 75 km/h, V3 = 100 km/h). Stress histories of eight critical members were processed using ASTM E1049-85 rainflow counting, and fatigue damage was computed using the stress-life (S-N) method with Palmgren-Miner’s rule. PVPD for each train type was obtained from these damage calculations and used to assemble cumulative damage under projected traffic scenarios.</p> Results <p>Among all analysed cases, stringer 2508 consistently experienced the highest stress demand, followed by diagonal L6M7 and X-beam 2638. For the stringer, remaining fatigue life reduced from 65.6 years (CC+8+2T, V1) to 26.5 years (32.5T, V3). Stress-band selection caused large variations: PVPD differed by up to 173% and remaining-life estimates by up to 52% between SB and SB15. PVPD variation followed a log-logistic model, whereas remaining-life variation followed a generalized-logistic model. Member criticality rankings remained invariant across speeds, load classes, and all stress-band choices.</p> Conclusions <p>Fatigue life predictions for long-span steel railway bridges are highly sensitive to stress-band selection. The significant PVPD and remaining-life variations across SB5, SB10, and SB15 highlight the need for explicit reporting of stress-band effects in fatigue assessments. The findings provide a rigorous basis for maintenance planning and long-term preservation of legacy steel rail-cum-road bridges under evolving traffic and axle-load conditions.</p>

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Statistical Fatigue Life Forecasting of Steel rail-cum-road Bridge with Impact of Stress Band Selection on Damage Accumulation and Residual Life

  • 期刊论文

  • 发表日期：

    2025年12月8日

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  • Sudhir Babu Patel,
  • Krishna Kant Pathak,
  • Ishan Jha

摘要

Abstract Background/Introduction

A large proportion of India’s steel railway bridges are over a century old, operating under rising axle loads and increasing traffic density. These aging riveted structures are highly vulnerable to fatigue deterioration, especially when subjected to variable-amplitude railway loading. Existing studies rarely analyse multi-kilometre, dual-deck rail-cum-road bridges or quantify the sensitivity of fatigue predictions to stress-band selection.

Purpose

This study evaluates the remaining fatigue life of a historic double-decker steel truss rail-cum-road bridge (106.68 m major spans; >1,026 m total length; constructed in 1887) and quantifies how different stress-band strategies (SB, SB5, SB10, SB15) influence per-vehicle-passage damage (PVPD) and life predictions under future railway loading scenarios.

Methods

Material characterization of extracted steel coupons established yield (356.6 MPa), ultimate tensile strength (519.3 MPa), and elongation (12.1%). A calibrated finite-element model of the major span was developed in STAAD.Pro, reproducing field-measured mid-span deflections with <3% error. High-cycle fatigue analysis was performed using axle-by-axle loading for 10,100 train-loading combinations across three load classes (CC+8+2T, 25T, 32.5T) and three speeds (V1 ≤ 50 km/h, V2 = 75 km/h, V3 = 100 km/h). Stress histories of eight critical members were processed using ASTM E1049-85 rainflow counting, and fatigue damage was computed using the stress-life (S-N) method with Palmgren-Miner’s rule. PVPD for each train type was obtained from these damage calculations and used to assemble cumulative damage under projected traffic scenarios.

Results

Among all analysed cases, stringer 2508 consistently experienced the highest stress demand, followed by diagonal L6M7 and X-beam 2638. For the stringer, remaining fatigue life reduced from 65.6 years (CC+8+2T, V1) to 26.5 years (32.5T, V3). Stress-band selection caused large variations: PVPD differed by up to 173% and remaining-life estimates by up to 52% between SB and SB15. PVPD variation followed a log-logistic model, whereas remaining-life variation followed a generalized-logistic model. Member criticality rankings remained invariant across speeds, load classes, and all stress-band choices.

Conclusions

Fatigue life predictions for long-span steel railway bridges are highly sensitive to stress-band selection. The significant PVPD and remaining-life variations across SB5, SB10, and SB15 highlight the need for explicit reporting of stress-band effects in fatigue assessments. The findings provide a rigorous basis for maintenance planning and long-term preservation of legacy steel rail-cum-road bridges under evolving traffic and axle-load conditions.