Dynamic analysis is the study of the response of a structural system (e.g. a building) subjected to a load changing over time (dynamic loading). The response of the system can be obtained by actual measurements of vibrations on the object or by simulating these vibrations using the Finite Element Method engineering program. Dynamic analysis will ensure not only safety, but also comfort for people. Legal regulations clearly impose the necessity to perform a dynamic analysis for all structural objects within the range of the impact of vibrations (e.g. Standard EN 1990 – Basics of Structural Design, Standard EN 1998-1 Eurocode 8: Design of structures for earthquake resistance).
Buildings are constantly exposed to various types of dynamic impact, the source of which may be both natural phenomena occurring on the earth’s surface (e.g. wind load) and under its surface caused by the movements of the earth’s crust, as well as vibrations caused by human activity, resulting from, among others:
An important aspect of designing buildings is the correct assessment of the impact of vibrations on the building and THE people inside and the selection of an appropriate security technology in order to minimize the undesirable effects caused by dynamic interaction. Dynamic loading constitutes an additional load on the structure, which has to be taken into account when carrying out the strength calculations. The assessment of the impact of vibrations is based on considering their destructive effect on structures and discomfort or even harmfulness to people inside the building. There are two methods of considering the impact of vibrations on any construction object: complete and approximate.
Both the approximate and the complete method should take into account the impact of the forecast / existing vibrations on the building and on the people in it. These are two separate analyzes that should be assessed independently, often using other methods of analysis and other standard scales.
The purpose of dynamic analysis, in general, is to obtain additional stress (loading) on the designed structure and to indicate the areas of the structure with exceeded vibration amplitudes. As a consequence, excessive vibration areas of the structure are often required to be redesigned. The sooner we decide to refer to a specialist (preferably at the construction design stage), the smaller and less costly the changes will be. The graph below presents the methodology of proceeding depending on the investment phase (a designed or an existing building) and the source of vibrations.
In situ vibration measurements ( or forecast) + FEM Model of the structure + determination of inertia forces
In situ vibration measurements ( both the structure and the source of vibration needs to exist) + FEM Model of the structure + standard scales
Both the approximate and the complete method should take into account the impact of the forecast / existing vibrations on the building and on the people inside are two separate analyzes that should be assessed independently, often using other methods of analysis and other standard scales.
1. In situ measurement
Assessment of the harmfulness of vibrations transmitted through the ground on buildings (standard’s scales)
2. FEM analysis (integration of motion equations or determination of inertia forces)
1. In situ measurement
Assessment of the harmfulness of vibrations on people (standard’s scales)
2. FEM analysis (integration of motion equations)
The purpose of dynamic analysis in general is to obtain additional forces loading the designed structure and to indicate the areas of the structure with exceeded vibration amplitudes. As a consequence, excessive vibration areas of the structure are often required to be redesigned. The sooner we decide to seek the help of specialists (preferably at the construction design stage), the smaller and less costly the changes will be. The chart below presents the methodology of proceeding depending on the investment phase (designed or existing building) and the source of vibrations.
