Seismic vulnerability of reinforced concrete knee joints under reversed cyclic loading

Reinforced concrete beam–column knee joints are generally located at the roof level of moment-resisting frame structures. Knee joints undergo significantly different closing and opening actions under seismic excitations. The complex and vulnerable behaviour of knee joints makes them considerably different from conventional exterior and interior joints. To understand this complexity, three full-scale knee joint specimens were subjected to varying closing and opening joint shear stresses produced from the variation of relative closing and opening moment capacities. Peak opening-to-closing joint shear stress ratios of 0·5, 0·6 and 0·8 were achieved for the three specimens. In addition, the effect of anchorage of longitudinal and joint transverse reinforcement was studied in terms of the enhancement of peak joint closing and opening shear stresses. This paper presents a detailed discussion on the effect of closing and opening actions on the overall joint performance of knee joints subjected to reversed cyclic loading.