Top-Bar Effect in Self-Compacting Concrete Elements

Self-compacting concrete (SCC) can be considered as one of the most revolutionary innovations in the worldwide concrete construction industry and is rapidly gaining acceptance as a potential replacement for normal concrete (NC). Due to its rheological characteristics, fresh SCC has the ability to flow under its own weight and adequately fill highly congested concrete members without the need of external compaction. The modified composition of SCC, compared to NC, may have consequences on the hardened concrete properties. One of the most important issues is the steel-to-concrete bond, which for NC has been observed to be significantly affected by the concrete depth under the horizontal bars of deep elements, a phenomenon called "top-bar effect". Design codes usually confront this bond reduction by applying a correction factor. The present paper examines the occurrence of top-bar effect in SCC columns with transverse reinforcement bars in various heights by performing pull-out tests to estimate the anchorage capacity of reinforcement bars, in terms of the bond stress curve as a function of slip.