Effectiveness evaluation of positive reinforcement in beam elements of moment-resistant frames subjected to seismic loads

The requirement of minimum positive reinforcement in critical sections located at ends of beams of multistory moment-resistant frames according to chapter 21 of the committee ACI 318 building code is evaluated with the aim to determine its behavior due to gravitational and seismic nature loads. It is noted that the amount of positive reinforcement has direct relation to the capacity of ductility that reinforced concrete sections have to resist negative moments. However, the positive reinforcement has relation to the levels of incursion in the inelastic range, which are not equally distributed according to the level of floor. In accordance with the Park & Ang's damage indices, there is established a greater structural damage concentrated in the lower floor as the minimum requirement of positive reinforcement is increased. In addition, the total damage is greater in the meantime bigger be the amount of minimum positive reinforcement used.