Use of stability coefficients for evaluating the effect in regular steel moment resisting frames

This study introduced and evaluated two stability coefficients that can be used to quantify the P – Δ effect during elastic and inelastic lateral displacement of regular steel moment resisting frames (SMRF). The first coefficient, applicable during elastic lateral displacement, was developed through an analytical process. It was found to be a function of the elastic fundamental period and modal shape of the frame and consequently named the modal-elastic stability coefficient ( θ m e ). The second coefficient was developed through a regression analysis process. In spite of its inelastic domain, this coefficient was found to retain a strong correlation with the elastic fundamental period and modal shape of the frame and consequently named the the modal-inelastic stability coefficient ( θ m i ). This study shows that the combined use of these two coefficients permits the accurate prediction of the load–deformation curve (initial stiffness, strength, and post-yield stiffness) of SMRF affected by the P – Δ phenomenon. Twenty-two SMRF were used for developing and testing the proposed stability coefficients.