Effect of Beam Growth on Reinforced Concrete Frames

Abstract

In well-designed reinforced concrete frames subjected to earthquake shaking, flexural yielding and cracking occur at the ends of the beams as they undergo large lateral displacements. As the cracks form, the horizontal distance between column centerlines increases. This is known as “beam growth” and it causes an increase in member demands that is not generally taken into account in analysis used for building design. This paper describes the mechanism of beam growth, observations of it from previous experimental studies, the development and calibration of analytical models considering and ignoring beam growth, and static and dynamic inelastic frame analyses to quantify beam growth effects. Changes in beam axial forces, beam flexural strength, and column moments and shears are quantified for several frame configurations. It is shown that the column demand due to beam growth tends to be greatest at the first story level and this demand tends to be most severe in frames with deep beams and with many bays. For the four-, eight-, and ten-bay frames used in the study, pushover analyses showed increases in column shear demands due to beam growth of 52, 76, and 86%, respectively. Dynamic loading to design-level earthquake records caused a 23% increase in the four-bay reference frame.