Impact of the reinforcement layout on the load capacity of reinforced concrete half-joints

Abstract

A reinforced concrete half-joint beam has a complex geometry that includes both a locally disturbed nib region and a full depth section. While this configuration simplifies the design and construction procedures, half joint structures rely on the internal steel reinforcement to transfer force from the nib into the bulk of the beam. When assessing existing reinforced concrete half-joints, engineers can be confronted with internal reinforcement layouts that do not correspond to the as-designed drawings and/or do not comply with current design practice. Bars may be missing or the location, percentage and spacing of the steel reinforcing bars may be non-compliant.

To provide a better understanding of the contribution of the internal steel reinforcing bars found in a typical half joint detail, an experimental test program on full-scale half-joint beams was undertaken. Four different scenarios were tested to identify the impact of specific reinforcing bars. A reference specimen was designed in accordance with existing practice. The reference beam, and beams with either missing diagonal reinforcement, missing horizontal reinforcement or a reduced amount of shear reinforcement were tested.

All the beams exhibited nib failures with the exception of the beam where the shear reinforcement was reduced. In this case, the failure mode changed from a nib failure to a full-depth failure. The results indicated that if certain bars are missing the overall load bearing capacity of a half-joint could be approximately 40% lower than that of a properly designed detail, but that a redistribution of forces was noted.