How can you monitor and sense structural vibrations and dynamics?

1 Why monitor and sense structural vibrations and dynamics?

Monitoring and sensing structural vibrations and dynamics can help you identify and diagnose structural problems, such as cracks, damage, fatigue, resonance, or instability. It can also help you evaluate the effectiveness of structural design, retrofitting, or maintenance. Moreover, it can help you improve the comfort and functionality of the occupants and users of the structure, by reducing noise, vibration, and motion.

2 What are the main sources and types of structural vibrations and dynamics?

Structural vibrations and dynamics can be caused by various sources, such as wind, earthquakes, traffic, machinery, or human activities. Depending on the source, the frequency, amplitude, and duration of the vibrations and dynamics can vary greatly. Free vibrations occur when a structure is disturbed by an initial force and then vibrates at its natural frequency without external forces. On the other hand, forced vibrations happen when a structure is subjected to a continuous or periodic external force that causes it to vibrate at the same frequency as the force. Damped vibrations take place when a structure loses energy due to friction, air resistance, or other factors that reduce its amplitude over time. Finally, resonant vibrations happen when a structure is subjected to a force that matches its natural frequency, leading to large amplitude vibrations that can cause damage or failure.

3 How to measure structural vibrations and dynamics?

There are various methods and instruments to measure structural vibrations and dynamics, depending on the type, scale, and purpose of the measurement. For instance, accelerometers are devices that measure acceleration of a structure or point by converting mechanical motion into an electrical signal. They can be wired or wireless, and attached to or embedded in the structure. Strain gauges measure strain or deformation of a structure by changing electrical resistance when stretched or compressed, and they can be bonded to or embedded in the structure. Displacement sensors measure displacement or movement of a structure by using optical, magnetic, or mechanical methods; they can be contact or non-contact, and fixed or movable. Dynamic testing is a method that applies a known force or excitation to a structure and measures its response in terms of vibration or dynamic properties such as natural frequency, damping ratio, or mode shape; it can be static or dynamic, and use various types of excitations like impact, harmonic, random, or ambient.

4 How to analyze structural vibrations and dynamics?

There are various techniques and software available for analyzing structural vibrations and dynamics, depending on the complexity, accuracy, and objectives of the analysis. Signal processing is a popular technique that processes raw data from measurement devices, such as accelerometers, strain gauges, or displacement sensors, to extract useful information, like frequency, amplitude, phase, or power spectrum. Fourier transform, wavelet transform, or modal analysis are some of the methods used in signal processing. Finite element analysis is another technique that models the structure as a system of discrete elements and solves equations of motion for each element using numerical methods. This method can simulate the behavior of the structure under various loading and boundary conditions and estimate dynamic properties such as natural frequency, damping ratio, or mode shape. Experimental modal analysis is a combination of measurement and analysis of structural vibrations and dynamics to identify modal parameters like natural frequency, damping ratio, or mode shape. This technique can use various types of excitations such as impact, harmonic, random or ambient and uses software like MATLAB, LabVIEW or ME'scope.

5 How to control structural vibrations and dynamics?

When it comes to controlling structural vibrations and dynamics, there are various methods and devices to choose from, depending on the source, type, and effect of the vibrations and dynamics. Passive control is a method that uses the inherent properties of the structure or the materials to reduce or isolate the vibrations and dynamics without requiring external energy or feedback. This could include dampers, isolators, absorbers, or tuned mass dampers. Active control is a method that uses external energy and feedback to apply counteracting forces or displacements to the structure to reduce or cancel the vibrations and dynamics. This could include actuators, sensors, or controllers. Hybrid control combines passive and active control to achieve better performance or efficiency in reducing or canceling the vibrations and dynamics. This could include semi-active dampers, smart materials, or adaptive structures.

6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?