Reduction of Column Yielding During Earthquakes for Reinforced Concrete Frames

An investigation to reduce the number of columns that are vulnerable to yielding in reinforced concrete frames subjected to earthquakes is described. Simple limit analysis is used to demonstrate that a reasonable minimum column-girder strength ratio cannot be defined to eliminate yielding in columns of regular frames. A method is developed for reducing the number of columns vulnerable to yielding by applying a strength reduction factor to the girders in the upper floor levels of the frames. Nonlinear static and dynamic analyses of 16 reinforced concrete frames demonstrate that drift can be reduced by using the suggested girder strength reduction factor. Application is limited by the initial stiffness of the elements because of the increased drift demands in the top portion of the frame and by the allowable reduction in girder strength that will satisfy gravity-load demands