Pseudo-spectral acceleration

Pseudo-spectral acceleration

Consider a quantity A for a SDOF system

Let A/g be called base shear coefficient or lateral force coefficient. It is used in building codes to represent the coefficient by which structural weight is multiplied to obtain the base shear. A is the peak pseudo-acceleration. A pseudo-acceleration response spectrum is a plot of A as functions of T_n.

The parameters have certain characteristics that are of practical interest. The pseudo-spectral velocity S_pv is close to spectral velocity S_v for short period structures and is almost equal to the intermediate periods but is different for long period structures. A comparison of the NS component of the Northridge earthquakes is made in Fig. 17.14 for spectral velocity and spectral acceleration for Ï‚ = 0.05. For zero damping, pseudo-spectral acceleration is identical to spectral acceleration S_a. However, for damping other than zero these two are slightly different. Nevertheless, for damping levels encountered in most engineering applications the two may be considered to be practically equal.

Evaluation of spectral displacement S_d by the use of Eq. 17.9a after numerical integration of Eq. 17.2 is to be carried out to obtain the time history response u(t). The corresponding pseudo-spectral velocity S_pv and pseudo-spectral acceleration S_pa can readily be established from Eq. 17.19 and 17.21.