Low-Cycle Fatigue Life Estimation Curve for Buckling-Restrained Braces Based on Cumulative Plastic Deformation

Buckling-restrained braces (BRBs) are commonly used as a kind of energy dissipator in structures, which can be quickly replaced after strong earthquakes. However, there is no reasonable and effective damage assessment method to quantitatively analyze the damage degree in a BRB. Since the cumulative plastic deformation (CPD) of a BRB is closely related to its loading history, the CPD can reflect the low-cycle fatigue life of a BRB. In this paper, two CPD curves of BRBs under low-cycle fatigue damage are presented: C-CPD curves under a constant strain amplitude (CSA) loading history and R-CPD curves under a random strain amplitude (RSA) loading history. The solving process and the shape of two curves are given. In the C-CPD curve, the influence of different fatigue parameters on the curve characteristics is thoroughly studied. In the R-CPD curve, the rationality of the maximum plastic strain range (Delta(epsilon pmax)) as the evaluation index of the R-CPD curve is verified through a sensitivity analysis. Finally, a parametric analysis of the R-CPD curve is presented. The analysis results show that the two curves both pass through the zero point and present an obvious characteristic of "increasing then decreasing". The C-CPD curve describes the relationship between Delta epsilon(p)andCPD(c)of BRBs under CSA loading, which can be derived directly from Coffin-Manson curves. Therefore, the C-CPD curve is only influenced by the fatigue parameters. The R-CPD curve describes the relationship between Delta epsilon(pmax)andCPD(c)of BRBs under RSA loading, which is fitted with many IDA results. The R-CPD curve is both greatly influenced by the fatigue parameters, and slightly influenced by the building height, theK(d)/K(f)value and the structure layout. Therefore, the C-CPD curve and the R-CPD curve are inherent curves of BRB. In addition, the sensitivity analysis of the R-CPD curve shows thatCPD(c)is most sensitive to Delta epsilon(pmax), so the Delta epsilon(pmax)is a reliable parameter to reflect the RSA loading history. The two curves provide a theoretical basis for the low-cycle fatigue life evaluation of BRB.