Diagnosis of hysteretic dampers used for seismic protection of structures by means ultrasonic measurements

Abstract

Energy dissipation is an innovative strategy for the passive protection of buildings and infrastructures against earthquakes. It entails installing special devices called dampers in a construction. They dissipate most of the energy input by an earthquake, thus keeping the main structure basically undamaged. Among the different types available, the so-called hysteretic dampers are commonly used to dissipate energy through plastic deformations in metallic parts of the device. Several moderate ground motions or even a single severe earthquake would not exhaust the capacity of the dampers, but they do cause damage —namely, plastic deformations in the device. Therefore, continuous or periodic inspections of the damper are required in order to decide upon its eventual replacement. The present work proposes Ultrasonic Testing (UT) as a method to quantify the damage upon hysteretic dampers subjected to cyclic loadings. To this end, several hysteretic dampers made of stainless steel were subjected to different patterns of quasi-static (low-frequency) cyclic loads that caused diverse levels of damage. Each damper underwent UT before and after the cyclic loading. UT parameters related to ultrasound waves including spectral amplitude and spectral energy were properly analyzed at each damage level. Based on these parameters, a UT damage index is put forth. The proposed UT index was then compared with a well-established mechanical damage index, ID, based on decomposing load–displacement curves into the skeleton part and Bauschinger part and computing the corresponding energies. A successful correlation was observed between the mechanical damage index ID and the novel UT index, making the UT technique promising for this particular application. © 2019 Elsevier Ltd