Assessment of material Strain Limits for Defining Different Forms of Plastic Hinge region in Concrete Structures

Abstract

The New Zealand Structural Loading Standard, until its latest revision, was using the structural displacement ductility factor as a measure of the deformation demand of all potential plastic hinges in a structure. In the revised version of New Zealand Structural Loading Standard for Earthquake Actions (NZS 1170.5:2004) the detailing of potential plastic regions is determined according to the local inelastic deformation demand in these regions. The change has been prompted by evidence that the structural ductility factor gives a poor indication of the demand on individual plastic regions. This is a major paradigm shift in international design codes. This new approach has been adopted by the New Zealand Concrete Structures Standard (NZS 3101:2006) which classifies potential plastic regions into three categories (namely ductile, limited ductile and nominally ductile) based upon their inelastic deformation demand which has been specified in terms of material strain limits in the form of curvatures or shear deformations. The values of material strain limits currently used in New Zealand Concrete Standard (NZS 3101:2006) to categorise the plastic regions are based on limited evidence and need a closer revision. This research attempts to obtain more justifiable values of material strain limits through experimental data existing in literature. Moreover, experimental testing is also conducted to compensate for a lack of data in the nominally ductile range of detailing. The experimental work explores the effects of transverse reinforcement arrangement, reinforcing steel grade and plastic hinge type. Together the literature review and experimental work provide a sound basis for re-defining the material strain limits for different plastic regions.