Relationship between Strain, Curvature, and Drift in Reinforced Concrete Moment Frames in Support of Performance-Based Seismic Design

Through the use of moment-curvature analyses, trends between strain and curvature for rectangular reinforced concrete (RC) sections are explored. Variables in the analyses included section dimensions, axial load ratio (ALR) and longitudinal steel ratio (rho(long)). Curvature-strain relationships that depend on ALR and p(long) are developed from the results. These expressions are subsequently used to develop equations to compute interstoty drift as a function of material strains for RC moment frames. The resultant equations can be used in performance-based design approaches such as direct displacement-based seismic design to compute target drifts and system displacements based on concrete and reinforcing steel strains. The interstory drift equations were correlated against 54 frame building analyses using a fiber-based analysis program. The drift expressions are shown to be accurate to within +/-12% and +/-20% for steel tension and concrete compression strain, respectively. Lastly the implications of the proposed expressions on current code-based drift and ductility limits are explored.