Diameter–embedment depth interaction of post-installed adhesive anchors in low-strength concrete

Abstract

Türkiye lies across multiple tectonic plates, resulting in numerous active fault lines that generate destructive earthquakes. Given the vulnerability of the existing building stock, effective retrofitting is critical. In line with the Türkiye Earthquake Code (TEC 2018) for C25, minimum reinforcement diameters for adhesive-anchored bars were reduced to 16 mm. However, because many existing buildings in Türkiye exhibit low concrete strengths (<10 MPa), this study comprehensively investigates the tensile performance of post-installed adhesive anchors under weak concrete conditions. Monotonic pull-out tests were conducted on 192 specimens utilizing four reinforcement diameters (Ø8, Ø10, Ø12, Ø14) and four embedment depths (8Ø, 10Ø, 12Ø, 14Ø) in concrete blocks with four compressive strengths (f_c) of 4.51, 5.35, 7.77, and 10.45 MPa. The results show that increasing the embedment ratio from 8Ø to 14Ø substantially enhances tensile capacity—by up to 95% for Ø8 bars at 4.51 MPa. Moreover, a multiple linear regression model calibrated using the dataset demonstrated a high coefficient of determination (R² = 0.91), confirming that anchorage performance is primarily governed by geometric parameters rather than material strength. Notably, adequate bond performance is severely limited below 10 MPa, often making failure modes bond-controlled. Based on these findings, it is recommended to evaluate anchorage design on a project-specific basis and avoid standard strengthening interventions in structures with concrete strengths below 10 MPa. In addition, it has been observed that under low concrete strength conditions, the anchor diameter must be reduced to ensure that the expected ductile failure mode via steel bar yielding can be achieved.