Evaluation of a Modified MPA Procedure Assuming Higher Modes as Elastic to Estimate Seismic Demands

Abstract

The modal pushover analysis (MPA) procedure, which includes the con tributions of all significant modes of vibration, estimates seismic demands much more accurately than current pushover procedures used in structural engineering practice. Outlined in this paper is a modified MPA (MMPA) pro cedure wherein the response contributions of higher vibration modes are computed by assuming the building to be linearly elastic, thus reducing the computational effort. After outlining such a modified procedure, its accuracy is evaluated for a variety of frame buildings and ground motion ensembles. Although it is not necessarily more accurate than the MPA procedure, the MMPA procedure is an attractive alternative for practical application because it leads to a larger estimate of seismic demands, improving the accuracy of the MPA results in some cases (relative to nonlinear response history analy sis) and increasing their conservatism in others. However, such conservatism is unacceptably large for lightly damped systems, with damping significantly less than 5%. Thus the MMPA procedure is not recommended for such sys tems.

Pushover analysis for the seismic response prediction of cable-stayed bridges under multi-directional excitation

“…The modal responses obtained through pushover analysis are combined by means of CQC rule to obtain the inelastic contribution. On the other hand, all the modes between f gov and f max = 25 Hz are considered merely elastic and included by means of response spectrum analysis [12]. This elastic response is combined with the inelastic one obtained previously by employing the SRSS rule.…”

“…This procedure, initially proposed for buildings under one-directional ground shaking and included in FEMA-440 [6], has been improved in order to include the effect of higher modes through spectral analysis, considering their response completely elastic [12]. The modal contribution is finally combined with standard rules like CQC (Complete Quadratic Combination) or SRSS (Square Root of the Sum of Squares), based on elastic superposition principles unable to retain the sign of the modal force distributions, which may introduce errors [13].…”

Analysis in seismic provisions for buildings: past, present and future

“…For more details, see Kreslin and Fajfar (2012) and Fardis et al (2015). Note that a variant of Modal pushover analysis is also based on the assumption that the vibration of the building in higher modes is linearly elastic (Chopra et al 2004).…”

Seismic Response of Rc Bridges Using Generalised Force Vectors

“…Some of the most commonly employed procedures include the N2 Method [1]; Capacity Spectrum Method (CSM) [2,3], Modal Pushover Analysis (MPA) and its variant, the Modified Modal Pushover Analysis (MMPA) [4,5]; Incremental Response Spectrum Analysis (IRSA) [6]; Adaptive Capacity Spectrum Method (ACSM) [7][8][9]; Modified Adaptive Modal Combination Method (M-AMC) [10]; and Multi-Mode Pushover Analysis using Generalized Force Vectors, or Generalized Pushover Analysis (GPA) [11]. All these procedures can be distinguished based on: (i) the use of single-mode based conventional pushover analysis, such as N2 and CSM; (ii) the use of multi-mode based conventional pushover analysis, such as MPA, MMPA, IRSA and GPA; and (iii) the use of multi-mode adaptive pushover analysis, such as ACSM and M-AMC.…”