Damping Clause Samples

Damping. For all building codes there is an established convention that the “standard” damping factor is 5 % of critical damping (ξ = 0.05, if expressed as a proportion of critical damping). There are many circumstances under which it is necessary to consider other levels of damping, particularly in the case of base isolated buildings or structures with passive energy dissipation devices. Similarly, the use of capacity spectrum and direct-displacement based loss estimation methodologies require a means of modifying the seismic input to different levels of damping. The constraint of elastic response spectra for different levels of damping can be undertaken in different ways. Several empirical ground motion prediction models are available that give spectral ordinates of acceleration or displacement for different levels of damping (▇▇▇▇▇ & ▇▇▇▇▇▇, 2007b; ▇▇▇▇▇▇ & ▇▇▇▇▇▇▇▇, 2008). Direct calculation of the damped acceleration and displacement from the GMPE has a greater degree of accuracy for damping factors for which the ordinates are given. This has important uses for design of higher damped structures. Equivalent linearization procedures, however, require iterative calculation of the effective period and equivalent viscous damping of the structure. Damping at values other than those given in the GMPEs are needed. The most common approach to address this is to calculate the spectrum for the new damping level using a damping modification factor (ε). The damping modification factor may be determined using analytical equations given in existing building codes or published literature. The determination of ε in EN1998-1 and other codes is the focus of this section. Also introduced are other relations to determine ε that have been developed by various authors.