Proposal of A Non Linear Static Analysis Procedure for Bridges: The Incremental Modal Pushover Analysis for Bridges (IMPAβ)

Abstract

A large number of bridges are designed and built without considering seismic actions and, differently from buildings, there are currently no comprehensive guidelines to evaluate existing bridges without performing, as in the well known incremental dynamic analysis (IDA), complex non linear dynamic analyses (RHA). Bridges are structurally very different from building but, at the same time, are sensitive to higher modes as well as many multi-storey buildings that inspired innovative pushover procedures such as the well known modal pushover analysis (MPA). In the present study the incremental modal pushover analysis (IMPA), a pushover based approach already proposed and applied on buildings by the same authors, is revised and proposed for bridges (IMPA). IMPA accounts for the effects of higher modes in order to accurately estimate the seismic response of bridges; the effect of higher modes is considered by introducing a suitable number of modes to ensure the participation of a predefined total effective modal mass. The efficiency of the proposed method is demonstrated by conducting a study on two bridges, one regular and one irregular, and the IDA analysis is employed as reference solution. Numerical results indicate good accuracy of the proposed method in assessing the seismic response and a very good accuracy if compared to other available pushover procedures available in the literature. Keywords:Non-linear static (Pushover) analysis, modal pushover, Non-linear time-history analysis, incremental analysis, bridges, assessment of bridges, seismic response of bridges.Preprints (www.preprints.org) | NOT PEER-REVIEWED | Posted: 16 February 2020

IMPAβ: Incremental Modal Pushover Analysis for Bridges

“…According to the capacity spectrum method (ATC 40 [20]), the base shear forces and the corresponding displacements (being V bn − u rn the pushover curve of the multi-degree of freedom) were converted to ADRS format, using the following relationships (being Sa and Sd the spectral accelerations and spectral displacements of an equivalent single degree of freedom (SDOF) system):…”

“…In the Eurocode 8, a pushover procedure based on the N2 is proposed to assess the seismic behavior of regular buildings, and only few specifications for bridges are reported in parts one and two. In FEMA 356 [19], ATC 40 [20] and Caltrans [21], adopting the CSM, NSA is proposed, but the contribution of higher modes is not considered, and the procedure for bridges is not detailed (e.g., there is no discussion on the monitoring point selection for bridges).…”

“…Figure20. Irregular bridge-deck displacements derived by performing nonlinear dynamic analysis and pushover analysis according to the approaches considered (PGA from 0.175 to 0.7 g).…”