Issue 78

S. A. Mustafa et alii, Fracture and Structural Integrity, 78 (2026) 298-314; DOI: 10.3221/IGF-ESIS.78.18

performance requirements. Although conventional cast-in-place reinforcement typically requires development lengths considerably larger than the embedment depths investigated in this study, post-installed adhesive anchors are commonly qualified according to ACI 355.4-19, which recommends anchor embedment depths not less than 4Ø and generally not exceeding 20Ø. Accordingly, embedment lengths of 10Ø, 15Ø, and 20Ø were selected within this qualified range to represent short, intermediate, and relatively long anchorage conditions. These values were chosen to investigate the influence of anchorage length on force-transfer mechanisms, failure modes, and the overall cyclic performance of newly implanted RC shear walls. Despite these advancements, most existing research has focused on isolated anchorage behavior or small-scale connection specimens, with relatively few studies addressing the global seismic performance of newly added shear walls connected to existing foundations using implanted reinforcement [6]. Recent research collectively shows that the seismic performance of reinforced concrete shear walls depends strongly on detailing, axial load, and retrofit strategy. Basereh et al. [16] proposed a retrofit for non-ductile RC shear walls using selective base weakening and external unbonded post-tensioning, which shifted behavior from brittle shear–flexure interaction to controlled rocking, reducing residual drift and damage while improving reparability. Bastami et al. [17] found through full-scale cyclic tests that axial load ratio strongly affects stiffness, ductility, and failure mode: moderate axial load improved flexural behavior, while higher axial load reduced ductility and caused compression-controlled failure, and they suggested a modified stiffness backbone model. Further studies stressed on the importance of ductile boundary detailing and improved analytical backbone models to capture stiffness degradation, residual deformation, and brittle failure mechanisms [18, 19]. Anbu et al. [20] showed that in precast ventilated walls, opening size and confinement detailing critically govern cracking, ductility, and energy dissipation. Other alternative retrofit concepts such as rocking walls, self-centering systems, and externally bonded reinforcement were introduced. While these methods offer advantages in repairability and energy dissipation, they may not be practical for many rehabilitation projects due to cost, construction complexity, or architectural constraints. Consequently, there remains a strong need to better understand how conventionally detailed RC shear walls - newly added to existing foundations using post-installed bars perform under realistic cyclic demands [2]. A critical unresolved issue involves the required embedment length of post-installed vertical reinforcement. If embedment is insufficient, premature bond failure and wall-foundation separation may occur; overly conservative embedment requirements, however, may be impractical or excessively costly. Recent analytical and experimental studies underscore the sensitivity of lateral strength, stiffness degradation, ductility, and failure mechanisms to anchorage performance, yet large-scale experimental investigations on newly constructed shear walls remain limited. The present study focused on this gap by experimentally examining the cyclic behavior of RC shear walls newly added to existing foundations using implanted vertical reinforcement with varying development lengths. Prior to this study, the best bonding material and the most effective hole diameter that can be used for implanting the reinforcement bars were investigated via pull-out tests. The investigation of the shear walls focused on lateral capacity, stiffness degradation and ductility, with the aim of providing practical guidance for enhancing its performance in existing RC buildings through the addition of new shear walls. he experimental program was designed to understand how new RC shear walls behave when connected to an existing foundation using post-installed vertical rebars. In this method, holes are drilled into the concrete and the new bars are anchored with a bonding material so forces can be transferred safely between the new and existing elements. Because this connection is so important, the program was carried out in two stages. In the First stage, pull-out tests were used to determine which hole size and adhesive created the most reliable anchorage. Then, using the best combination identified, the second stage was performed using large-scale shear walls with post-installed vertical rebars that were fabricated and subjected to displacement controlled cyclic lateral loading. This method ensured that the anchorage system was strong enough before studying the walls' overall structural behavior. Material properties The materials used for the concrete mix in this study were selected and tested thoroughly to meet the standards set by the Egyptian Code of Practice for the Design and Construction of Concrete Structures (ECP 203). The concrete mix was prepared with a water-Cement ratio of 0.5, and a maximum aggregate size of 10 mm. All specimens used in the experimental program; both the pull-out cylinders and the full-scale shear walls; were constructed using the same carefully selected materials to ensure consistency throughout the study. The designed average compressive strength at the time of T E XPERIMENTAL PROGRAM AND TEST SPECIMENS

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