Effect of column flexural capacities and axial loads on bond behavior of interior beam-column joints: Fid-Bau Portal

Effect of column flexural capacities and axial loads on bond behavior of interior beam-column joints

Gan, Dan / Li, Hongpeng / Zhou, Zheng / Zhou, Xuhong

Abstract The bond behavior of longitudinal beam bars passing through the joint zone is affected by the column flexural capacity, while there is a paucity of research results; in addition, the bond behavior can be improved by the axial compressive load, while the upper limit of the axial load was still not clear due to lack of experimental researches with high axial load ratios (larger than 0.6). In this investigation, the hysteretic behavior of 8 interior joints with 600 MPa high-strength longitudinal beam reinforcing bars was compared and analyzed in detail. Four joints adopted the concrete-filled steel tubular column with continuous steel tube, namely CFSTJ specimens; and the other four joints, i.e., their counterparts, adopted the concrete-filled steel tubular column with discontinuous steel tube, namely TRCJ specimens. The discontinuous column steel tube led to different column flexural capacities and axial load ratios. The test results showed that all specimens exhibited good hysteretic behavior before 5% drift, and the bond behavior of CFSTJ specimens was better than that of their counterpart TRCJ specimens. Combining these observations with available test data of reinforced concrete (RC) interior joints in the literature, the effect of column flexural capacities and axial loads on the bond behavior was then further analyzed and quantified. Finally, based on provisions in NZS 3101 and EN 1998–1, more accurate design equations were proposed by considering the depth of column compression zone and limiting the axial load ratio.

Highlights • The reduced column flexural capacities caused by the discontinuous steel tubes led to the reduced depth of the concrete compression zone above the longitudinal beam bars in joint zone, thus resulting in worse bond behavior. • The larger axial load improved the bond behavior, while the excessively large axial load led to higher compressive stresses in the joint concrete and thus weakened the bond behavior. • The modified equations for NZS 3101 and EN 1998–1 were proposed by considering the depth of column compression zone and limiting the axial load ratio. The predicted results were conservative and more accurate.