IMPAβ: Incremental Modal Pushover Analysis for Bridges

Abstract

In the present study, the incremental modal pushover analysis (IMPA), a pushover-based approach already proposed and applied to buildings by the same authors, was revised and proposed for bridges (IMPAβ). Pushover analysis considers the effects of higher modes on the structural response. Bridges are structurally very different from multi-story buildings, where multimodal pushover (MPA) has been developed and is currently used. In bridges, consideration for higher modes is often necessary: The responses of some structural elements of the bridge (e.g., piers) influence the overall bridge response. Therefore, the failure of these elements can determine the failure of the whole structure, even if they give a small contribution total base shear. Incremental dynamic analysis (IDA) requires input accelerograms for high intensities, which are rare in the databases, while scaling of generated accelerograms with a simple increment of the scaling acceleration is not appropriate. This fact renders IDA, which is by its nature time-consuming, not straightforward. On the contrary, the change of input spectrum required by IMPA is simple. IMPAβ also utilizes a simple complementary method coupled to MPA, to obtain bounds at very high seismic intensities. Finally, the two incremental methods based on static nonlinear and dynamic nonlinear analyses are compared.

Application of the Incremental Modal Analysis for Bridges (IMPAb) Subjected to Near-Fault Ground Motions

“…In general, every pushover procedure considered underestimates the response at the center (Pier 2) and at the flexible side (Pier 3). This result is consistent to what was obtained in [17], applying IMPAb to the same case study for far field events (FF).…”

“…It is assumed that NRHA represents the "correct" response evaluation, even for NF input. The incremental modal pushover analysis for bridges (IMPAb) [17] is carried out and results compared to IDA's. IMPAb requires the execution of several pushover analyses according to two different load patterns: a uniform loading profile (UPA) and a modal pushover analysis (MPA) according to the procedure presented in [15,16].…”

“…The case study selected is a straight bridge with four equal 50 m spans for a total length of 200m ( Figure 2), already used by many authors in previous comparison works since 1990s [ 21] and also to explain the IMPAb in [17]. The deck of the bridge consists of 14m wide pre-cast concrete box girder supported by piers through bearings locked in the transverse direction and, at the abutments, through elastomeric bearings (movement in the longitudinal direction is allowed at the abutments, but transverse displacements are restrained).…”

“…In [15][16][17], the authors of this paper proposed an incremental (in term s of seismic intensity) pushover-based procedure (specifically developed for bridges) named IMPAb, and discussed the validity in case of far field accelerograms (FF). The procedure employs the envelope of a single-run conventional uniform pushover analysis (UPA) and modal pushover analyses (MPA), to determine the seismic demands for each intensity level considered,.…”

“…The main task of this work is to apply IMPAb procedure using a set of near-fault ground motion records as input. In the present paper the same case study of irregular bridge selected in [ 17] was analyzed.…”