Structural Health Assessment of Composite Steel Beams: Evaluating Pre-Damage and Post-Damage States using Modal Analysis

Background/Objectives: Composite materials, formed by combining two or more distinct substances at the macroscopic level, exhibit enhanced mechanical properties not attainable by individual constituents. In structural engineering, steel composite beams—comprising a steel girder and a reinforced concrete slab connected via shear connectors—serve as a fundamental element in bridge and building construction. This study aims to evaluate the structural health of such composite beams, focusing on their vibrational response before and after sustaining damage under loading conditions. Methods: A composite preflex girder was subjected to a four-point bending test to simulate realistic structural loading. The Vibration-Based Damage Detection Method (VDDM) was applied to capture dynamic changes using accelerometer-based measurements. Modal parameters, especially the natural frequencies, were recorded and analyzed for both undamaged and damaged states to assess the impact of structural degradation. Findings: The results revealed a consistent and measurable decrease in natural frequencies following the induced damage, indicating a significant reduction in structural stiffness. This frequency drop validates the sensitivity of vibrational parameters to internal damage and confirms their suitability for detecting and quantifying deterioration in composite beams. Novelty: This study demonstrates the applicability of the VDDM as a practical, non-destructive tool for real-time structural health monitoring. By applying this method to a full-scale preflex composite beam, the research offers a simplified, cost-effective approach for early damage detection in steel-concrete structures, which is essential for ensuring structural safety and prolonging service life. Keywords: Structural health monitoring, Preflex beam, Natural frequency, Non-destructive testing, Damage detection