Structural Health Monitoring

An accelerometer is a sensor that measures acceleration — the rate of change of velocity — typically by detecting the displacement of a proof mass relative to its frame. It is the most widely used sensor in earthquake engineering, structural health monitoring, and vibration analysis.

Ambient vibration refers to the low-amplitude, broadband vibration that a structure experiences continuously from environmental sources — wind, traffic, microtremors, and human activity. It is the excitation source used in operational modal analysis (OMA) for identifying structural modal properties without controlled input.

Damage detection is the process of identifying the presence, location, and severity of damage in a structure using measurements of its response or properties. It is the primary objective of structural health monitoring and is applied across a wide range of civil, mechanical, and aerospace systems.

A damage index is a scalar or vector quantity that quantifies the extent of damage in a structure or structural element, typically by comparing a measured or computed response to a reference (undamaged) state. It provides a single measure for assessing severity and supporting decision-making.

The Fast Fourier Transform (FFT) is an efficient algorithm for computing the Discrete Fourier Transform (DFT), which converts a signal from the time domain to the frequency domain. It is the fundamental computational tool for frequency-domain analysis in structural dynamics, SHM, and signal processing.

Model updating is the process of calibrating a numerical model — typically a finite element model — to match measured data from a real structure, usually by adjusting model parameters such as stiffness, mass, or boundary conditions. It is essential for accurate prediction of structural response and for reliable SHM.

Operational Modal Analysis (OMA), also called output-only modal analysis, is the identification of a structure's modal properties (natural frequencies, mode shapes, damping ratios) using only response measurements, without measuring the input excitation. It is the primary modal identification technique for full-scale structures under ambient or operational conditions.

A sensor network is a system of multiple sensors distributed across a structure or site, connected to data acquisition and communication infrastructure, that collectively monitor structural behavior, environmental conditions, or seismic activity. It is the physical foundation of any structural health monitoring system.

Structural Health Monitoring (SHM) is the process of implementing a damage detection and characterization strategy for engineering structures using continuous or periodic measurements. It combines sensing, data acquisition, signal processing, and decision-making to assess the condition of a structure over its lifetime.

System identification is the process of building mathematical models of dynamic systems from measured input-output data. In structural engineering, it is used to identify modal properties, update finite element models, and characterize structural behavior for monitoring and control.