Application of direct displacement based design to long span bridges

Abstract

The paper investigates the applicability of current direct displacement based seismic design (DDBD) procedure, developed by Priestley and his coworkers, for straight long span bridges under transverse seismic excitation synchronous to all supports. This category of bridges often possess some additional features such as massive tall piers, highly irregular distribution of mass and stiffness due to unequal superstructure spans and pier heights, large deformation capacity etc. that are absent in short-to-moderate span bridges for which DDBD has extensively been verified. It is shown that DDBD in its current form is unable to capture both displacement and base shear demand when compared with nonlinear dynamic analysis results. Accordingly, a simple mechanics based extension of the current procedure that takes into account the effect of pier mass while computing base shear demand as well as a modal combination rule for estimating displacement demand is proposed and validated using a series of parametric studies. The new procedure also allows engineer to allocate strength at the potential plastic hinge location in more general terms.Keywords Seismic design · Displacement-based approach · Fore-based approach · Long span bridges

Performance-Based Seismic Design and Assessment of Bridges

“…Another study (Adhikari et al 2010) focussed on the difficulties involved in applying DDBD to long-span bridges with tall piers. This study introduced some additional considerations to account for higher mode effects on flexural strength of plastic hinges in the case of long-span concrete bridges with limited ductile piers.…”

Consistency of PPP GPS and strong-motion records: case study of Mw9.0 Tohoku-Oki 2011 earthquake

“…Previous studies have shown the significance of the displacement waveforms for the design of the structure (Panagiotakos and Fardis, 1999;Adhikari et al, 2010;Penucci et al,. 2009;Sadan et al, 2013) and revealed the need of using geodetic techniques and especially GNSS technology.…”

Extension of direct displacement‐based design methodology for bridges to account for higher mode effects

“…This was then followed by the calculation of secant stiffnesses at maximum response (Equation (17)). Design base shears were calculated from Equation (18) and member shear forces from Equation (19). It is noted, that in the case of modal targetdisplacements with different signs, Equation (23) was used in lieu of (19) (see Table A1, Mode 2).…”

“…So far, the vast majority of studies performed on this topic do not consider directly higher mode effects, as a result of the procedure's inherent limitation (because of the equivalent SDOF approach) to structures wherein the fundamental mode dominates the response. In a recent study, Adhikari et al [18] introduced some additional considerations to account for higher mode effects on the flexural strength of plastic hinges in the case of long-span concrete bridges with limited ductile piers. Following the suggestion of Priestley et al [12], Adhikari et al used a response-spectrum analysis, after completion of the DDBD procedure, with two different design spectra (a 5%-damped design spectrum and a design spectrum with damping value obtained from the DDBD procedure) to determine the design responses (elastic and inelastic respectively) at critical locations of the bridge as combinations of several modes.…”