A MECHANISTIC APPROACH IN DEFINING INELASTIC ROTATION CAPACITY OF RC COLUMNS

When a reinforced concrete (RC) column is subjected to lateral sway as a result of earthquake action, the large strain demand in the end sections is supported by development of strains in the anchorage.This causes the bars to displace (or slip) relative to the anchoring concrete at the column fixed end(s).The lumped slip causes rigid-body rotation of the column, thereby alleviating partially the column deformation.This reinforcement slip is assumed to occur in the tension bars only and cause the rotation about the neutral axis.Development of flexural yielding and large rotation ductilities in the plastic hinge zones of frame members is synonymous with the spread of bar reinforcement yielding.Yield penetration in the anchored reinforcing bar inside the shear span of the column where it occurs, destroys interfacial bond between bar and concrete and reduces the strain development capacity of the reinforcement.This affects the plastic rotation of the member by increasing the contribution of bar slippage.In order to establish the plastic rotation in a manner consistent with the above definition, this paper uses the explicit solution of the field equations of bond over the shear span of a column.Through this approach, the bar strain distributions and the extent of yield penetration from the yielding cross section towards the shear span are resolved and calculated analytically.By obtaining this solution the aim is to illustrate the true parametric sensitivities of plastic hinge length as a design variable for practical use in seismic assessment of existing structures.Results obtained from the analytical procedures are compared with experimental evidence from tests conducted on reinforced concrete columns under seismic loading reported in the literature.