Flexural Capacity Calculation Method for Pre-Damaged RC Beam–Column Joints Strengthened with High-Strength Steel Strand Mesh-Reinforced ECC

Abstract

Pre-existing damage in reinforced concrete (RC) beam–column joints may induce strain incompatibility between the original member and subsequently applied strengthening layers, limiting the applicability of conventional flexural-capacity models. This study experimentally and analytically investigates pre-damaged RC beam–column joints strengthened with high-strength steel strand wire mesh-reinforced engineered cementitious composite (HSSWM–ECC). Eight specimens were tested to evaluate the effects of pre-damage level, steel strand spacing, and axial compression ratio on beam-end flexural behavior. HSSWM–ECC effectively suppressed crack localization and concrete spalling, and all strengthened specimens ultimately exhibited beam-end flexural failure while the columns and joint cores remained largely intact. Compared with the unstrengthened specimen, the peak load increased by 39.24–63.88%. Reducing the strand spacing from 70 to 30 mm increased the peak load by 8.86%, whereas the higher pre-damage level caused an 11.28% reduction relative to the undamaged strengthened specimen. Within the investigated axial compression ratio range of 0.2–0.4, the difference in peak load remained below 3.64%, whereas increasing axial compression was associated with more pronounced post-peak strength degradation. Based on sectional force equilibrium and the plane-section assumption, an analytical model was developed by incorporating damage-induced strain lag and the contribution of the wrap-around side strengthening layers. The predicted capacities of the seven strengthened specimens agreed well with the experimental results, with deviations within 7%. The proposed model provides a rational approach for evaluating the beam-end flexural capacity of pre-damaged RC beam–column joints strengthened with HSSWM–ECC within the investigated parameter range and flexure-dominated failure mode.