Experimental study and constitutive model of bond-slip behavior of large-diameter inner-threaded SMA cable grid in ECC

Shape Memory Alloy (SMA) and Engineered Cementitious Composite (ECC) are considered ideal materials for seismic strengthening due to their excellent properties. This study designed 23 groups comprising a total of 69 specimens and conducted central pull-out tests to investigate the bond-slip mechanism and bond performance of large-diameter inner-threaded SMA cable grid in ECC, primarily focusing on pull-out failure modes and bond stress. Based on the experimental data, a bond-slip constitutive model and a calculation formula for the critical anchorage length between SMA cable grid and ECC were proposed, along with calculation formulas for peak bond stress and ductile-stage bond stress. The results indicate that the SMA cables exhibit excellent superelastic behavior, with residual strains below 1 %. Two failure modes were identified: cable pull-out and cable fracture failure, with the bond-slip curves comprising six stages. The measured peak bond stresses of the SMA cable grid-ECC interface ranged from about 7.6–11.0 MPa for the2.5 mm cables and up to about 13.6 MPa for the 1.3 mm cables, depending on ECC strength and anchorage length. Compared with the steel cable grid, the SMA cable grid increased the ductile segment length by about 35 %. For an ECC strength of E50 and a 2.5 mm cable, the critical relative anchorage lengths leading to fracture were 27d and 30d for the steel and SMA cable grids, respectively. The proposed bond–slip model and the formulas for peak and ductile bond stress and critical anchorage length were validated against tests and existing codes, providing a basis for engineering practice. • Bond-slip behavior of novel inner-threaded SMA cable grids in ECC is first reported. • A unique six-stage bond-slip curve including a ductile plateau was identified. • Transverse cables significantly enhance ductility by providing effective confinement. • A six-stage constitutive model is proposed to accurately predict the bond behavior. • A practical design formula for the critical anchorage length is developed and validated.