Shear behavior and damage identification of π-shaped demountable connector for composite beam equipped with acoustic emission sensors

To advance rapid assembly methodologies in steel-concrete composite bridges, this study proposes a novel demountable π-shaped shear connector and systematically investigates its structural performance. Two configurations, longitudinal (L-Conn) and transverse (T-Conn) π-shaped connectors, were designed and evaluated via standardized push-out tests to explore failure mechanisms under shear loading. Experimental results demonstrate that concrete-filled configurations achieve comparable ultimate shear capacities (T-Conn: 844 kN; L-Conn: 915 kN), yet exhibit a notable divergence in ultimate displacements (T-Conn: 5.19 mm vs. L-Conn: 8.78 mm). In contrast, unfilled connectors fail prematurely due to internal deformation localization and stress redistribution. Stiffness evolution reveals a nonlinear trend, with transverse configurations exhibiting higher initial stiffness than longitudinal counterparts. A high-precision finite element model, validated against experimental data, replicates critical failure modes and load-slip behavior within 5 % error. Complementary acoustic emission (AE) monitoring equipment captures fracture progression through energy, ring count, amplitude, rise time, and duration parameters. During elastoplastic stage, a surge of high-energy AE signals (energy >10,000 aJ) correlates with bolt yielding and interfacial concrete damage. Statistical analysis identifies weak amplitude-parameter correlations but strong energy-based interdependencies, prompting the development of a cumulative damage model integrating energy-amplitude thresholds for real-time degradation assessment. Theoretical validation confirms alignment with Eurocode 4 (EC4) shear capacity predictions (error <10 %). These findings establish a framework for non-destructive evaluation and structural health monitoring of demountable connectors, directly supporting the design and life-cycle management of modular composite bridges.