Development of fragility curves for RC bridges subjected to reverse and strike-slip seismic sources

Abstract

This paper presents a probabilistic fragility analysis for two groups of bridges: simply supported and integral bridges. Comparisons are based on the seismic fragility of the bridges subjected to accelerograms of two seismic sources. Three-dimensional finite-element models of the bridges were created for each set of bridge samples, considering the nonlinear behaviour of critical bridge components. When the seismic hazard in the site is controlled by a few seismic sources, it is important to quantify separately the contribution of each fault to the structure vulnerability. In this study, seismic records come from earthquakes that originated in strike-slip and reverse faulting mechanisms. The influence of the earthquake mechanism on the seismic vulnerability of the bridges was analysed by considering the displacement ductility of the piers. An in-depth parametric study was conducted to evaluate the sensitivity of the bridges' seismic responses to variations of structural parameters. The analysis showed that uncertainties related to the presence of lap splices in columns and superstructure type in terms of integral or simply supported spans should be considered in the fragility analysis of the bridge system. Finally, the fragility curves determine the conditional probabilities that a specific structural demand will reach or exceed the structural capacity by considering peak ground acceleration (PGA) and acceleration spectrum intensity (ASI). The results also show that the simply supported bridges perform consistently better from a seismic perspective than integral bridges and focal mechanism of the earthquakes plays an important role in the seismic fragility analysis of highway bridges.

Analysis of an Isolation System with Vertical Spring-viscous Dampers in Horizontal and Vertical Ground Motion

“…However, unstable contact areas occurred around the natural frequencies of the x direction, where the amplitudes are greater than the static deflection. For example, in Figure 7d, resonance occurs near 0.8 Hz of the excitation frequency, because the natural frequency in the x direction is 0.8 Hz, as indicated in Figure 5 and Equation (13). Moreover, as the friction coefficient decreased, the unstable region increased, as illustrated in Figure 8, and as the friction coefficient increased, the unstable region decreased.…”

“…The relationship between f x and f y is determined by the radius of the concave surface R and installation distance ratio α of the spring-damper, as indicated in Equation (13).…”

“…Figure 12 illustrates the T r values of the horizontal and vertical motions for various friction coefficients. The results obtained were for a seismic isolator with f y = 5 Hz, R = 0.6 m, and α = 0.1, where f x was 0.82 Hz for this device, according to Equation (13). In the case of the friction coefficient of µ = 0.005 in Figure 12a, relative motion did not occur, as T r = 1 until the excitation frequency reached 0.51 Hz, following which relative motion occurred.…”

“…Thus, did not change until the excitation frequency reaches 0.71 Hz, as indicated in Figures 13-15. Figure 13 illustrates when was 3, 5, 6, and 7 Hz and was 0.72, 0.82, 0.89, and 0.96 Hz from Equation (13) or Figure 5, respectively. In the case of = 3 Hz, because was 0.71 Hz, which is almost equal to the natural frequency 0.72 Hz, the resonance was suppressed and the maximum was 1.1, which is slightly larger than 1.…”

“…Initial research on the rolling bearing seismic isolation system (RIS) was carried out by Lin and Hone in 1993 [10,11]. Their model consists of a flat plate and cylindrical rolling bearings and is used extensively owing to its protective effect against earthquakes [12,13]. To overcome the disadvantages of re-centering, Tsai [14] constructed an RIS with cylindrical rollers between two V-shaped rolling surfaces and applied these to a bridge structure.…”