Damage Identification in Masonry Wall Specimens: Shake Table Studies

Abstract

Abstract Over the past few decades, vibration-based structural health monitoring and damage detection have drawn significant research attentions world-wide. The major motivation for such a research emphasis is the need to develop reliable methods to monitor the performance of structures in real-time. Real-time or continuous monitoring is also beneficial for timely maintenance of structure and to avoid any undesired failure. In this study, the efficiency of a few vibration based damage detection approaches has been investigated for identifying damage in a few wall specimens of brick masonry structures. Masonry is one of the most common and oldest material which is being used for constructing buildings for many years. Like concrete, masonry is also a brittle and highly non-linear material with good compressive but poor tensile strength. In masonry structures, damage generally occurs in distributed fashion and the pattern of cracks is often very complex as compared to steel structures. In addition, damping changes with the level of damage. An experimental study using shake table has been performed on a few half-scale wall-specimens. A suit of ground motions were selected based on Indian Code specified design ground motion spectrum. These motions were then scaled from very low intensity to high intensity by introducing amplitude scale factor with respect to the code specified level. The purpose of varying intensity input was to introduce progressive damage when subjected to the these excitations. In between each scale change, shake table tests with low intensity white-noise motions were performed. The purpose of white noise run in between two consecutive level of excitation was to simulate an ambient vibration condition for system identification. The specimens and the shake table were instrumented with accelerometers and displacement sensors to measure the input and responses. Various vibration-based techniques such as frequency domain decomposition and natural excitation technique (NExT) coupled with Eigen realization algorithm (ERA) techniques have been used for extraction of modal properties. It has been found from the experimental results that damage level can be easily correlated with a few damage identification parameters.