| Composite action between concrete and reinforcing steel cannot occur without bond. Therefore, the bond performance of reinforcing bars and/or prestressing tendons play a major role in the behavior of reinforced and prestressed concrete structures when subjected to static and dynamic loads. In particular, the bond stress-slip characteristics of reinforcing steel may significantly influence the stiffness, strength, ductility, and safety of structural members and systems. A factor paramount to bond performance is the cracking of concrete and thus its tensile stress-strain behavior. In this regard, emerging materials, such as high performance fiber reinforced cementitious composites (HPFRCCs), can provide promising solutions to enhance bond between reinforcing bars (or strands) and concrete. Unlike conventional concrete, whose tensile strength drops very quickly after first cracking, HPFRCCs show no degradation in post-cracking tensile strength up to large tensile strains, generally in excess of 0.5%.; The main objective of this study was to evaluate the bond behavior of reinforcing bars and prestressing strands embedded in HPFRCC matrices when subjected to monotonic and cyclic loads. Enhancing the bond between bars (or strands) and concrete would lead to: (1) reduction of anchorage (or splice) length in structural elements; (2) reduction or elimination of slippage of bars in beam-column connections; (3) reduction and/or delay of bond deterioration; and (4) overall structural safety.; Three phases of study were conducted to achieve the above objectives. The first phase included extensive experimental pullout tests to evaluate the bond stress-slip response of reinforcing bars and prestressing strands embedded in fiber reinforced cement composites (FRCCS), including tensile softening FRCCs and tensile strain-hardening HPFRCCs. Parameters included: reinforcement type and diameter, reinforcement cover, fiber type, fiber volume fraction, matrix compressive strength, and loading history. The second phase dealt with the bond-slip response of bars passing through HPFRCC beam-column joints subjected to displacement reversals. The third phase focused on the development of local and global bond stress-slip models that depend on the tensile stress-strain behavior of HPFRCC materials. Design recommendations for development (anchorage) length of reinforcing bars and prestressing strands embedded in HPFRCC materials are provided. |
