Deformations of reinforced concrete members at yielding and ultimate

Abstract

A database of more than 1000 tests (mainly cyclic) on specimens representative of various types of reinforced concrete (RC) members (beams, columns, and walls) is used to develop expressions for the deformations of RC members at yielding or failure (at ultimate), in terms of member geometric and mechanical characteristics. Expressions for the yield and the ultimate curvature based on the plane-section assumption provide good average agreement with test results, but with large scatter. The same applies to models for the ultimate drift or chord-rotation capacity based on curvatures and the concept of plastic hinge length. Semi-empirical models for the drift or chord-rotation at member yielding provide good average agreement with test results, but with considerable scatter. Their predictions and the associated test results point to effective secant stiffness at yielding around 20% of that of the uncracked gross section. An empirical expression is also developed for the ultimate drift or chord rotation in terms of: steel ductility; bar pull-out from the anchorage zone; load cycling; ratios of tension; compression; confinement or diagonal reinforcement; axial load ratio; V = N/Agfc′; shear-span ratio; and concrete strength. This expression is characterized by less scatter than alternatives with a more fundamental basis, and applies over a very wide range of parameter values for all types of RC members used in earthquake-resistant structures, including beams or columns with conventional or diagonal reinforcement and shear walls.