Numerical Modelling & Analysis

General

Overview of Challenges

In the last half century, much effort has been devoted to developing rational methods for conducting the seismic analysis of nonstructural building components. The hope was to develop rational analytical methods that could be used in specific seismic design situations. Unfortunately, except for very simple nonstructural building components, none of these proposed seismic analysis methods have found their way into industry standards and seismic provisions. There are many reasons for this situation:

Dynamic analysis considering the interaction between structural and nonstructural components in a building requires the development of numerical models with a very large number of degrees-of-freedom and elements, the properties of which have not been well established.
Differences in the order of magnitude of the properties of structural and nonstructural components often make numerical models ill-suited to the traditional modal analysis procedure. Step-by-step time-history dynamic analysis is often required to accurately capture the interaction between structural and nonstructural components in a building. The integration time-step must be carefully selected in order to capture the wide frequency range of properties in the combined structural/nonstructural system.
The natural frequencies of nonstructural components can coincide (be in tune) with one or more natural frequencies of the structure. This gives rise to closely spaced modes in the coupled dynamic system that introduces highly correlated modal responses.
The nature of the coupled equations of motion produces feedback between the motions of nonstructural components and those of the main structure. This feedback tends to reduce the dynamic response of heavy nonstructural components that are in tune with the main structure.
The large differences between the damping characteristics of the nonstructural components and structural system introduce non-classical damping modes, even if the two subsystems are individually classically damped. This results in complex-valued frequencies and mode shapes, for which modal superposition is not applicable.
Nonstructural components can be connected at multiple points in the structure and can be influenced by multiple support excitations.
The structural system and the nonstructural components are typically not selected and designed at the same time in a construction project, making a combined analysis difficult from a scheduling point of view.

One consequence of the limitations mentioned above is that there is currently no guidance in seismic design provisions on how to consider interactions between primary structural and secondary nonstructural systems. In the vast majority of practical design situations, decoupled analyses are conducted using a “cascading” approach. In this approach, the dynamic properties and the floor responses of the primary structure are estimated without considering the interaction with the nonstructural component. The structural response at the attachment level is then considered as the input motion for the estimation of the response of the nonstructural component. One of the most popular of these cascading methods is the Floor Response Spectrum (FRS) method.

General

Overview of Challenges

Studies related to different non-structural element typologies