Vulnérabilité sismique des piles de ponts rectangulaires sous-armées dans l'Est Canadien

Abstract

Under bidirectional earthquake ground motions, the performance of bridges depends on the ability of the columns to withstand large deformations without shear or flexural failures. It has been shown that high level of ductility is ensured if sufficient and adequate confinement is provided in the column section. Modern seismic design codes include specifications to limit the minimal amount of longitudinal reinforcement. The Canadian Standards Association’s code, the CSA-S6, specifies that the area of longitudinal reinforcement shall not be less than 0,8% of the gross section. This limit is aimed to prevent excessive creep and shrinkage cracking. Past and recent researchs indicate that it could be possible to reduce the 0.8% lower limit for longitudinal steel if adequat confinement is provided. The objective of this research is to assess the seismic vulnerability of brige columns with low longitudinal steel ratios located in Eastern Canada. A numerical bridge model was developed with Opensees to carry out the study according to the specifications of the Canadian Highway Bridge Design Code (CSA-S6). A series of response spectrum analysis and nonlinear dynamic time history analysis have been performed to investigate the seismic behavior of bridge columns under bidirectional earthquake ground motions. The orthogonal ground motion components from 1988 M5,7 Saguenay and 1985 M6,5 Nahanni earthquakes were used. For Saguenay, the records from the stations Chicoutimi-Nord, Les Éboulements and Saint-André have been selected and transformed for each soil category of the CNBC-2005. Design Spectra have been used to determine earthquake forces while bidirectional ground motion signals have been used in nonlinear time history analysis to examine the seismic response of the bridge columns. Four columns with 0,31%, 0,56%, 0,83% and 1,08% steel ratios have been design to assess the behavior of bridge columns with low longitudinal steel ratios. The bridge columns were modeled using nonlinear beam column with fiber section to analyse the state of the confined and unconfined concrete, as well as the reinforcing steel fibers. Two fiber hinges have been assigned both at top and bottom of each column as specified in the CSA-S6. Results indicate that the four columns have shown a satisfactory seismic behavior. The determination of ductility reveals that the 0,31% steel ratio column presents significant level of damage. However, the others columns, including the one with 0,56% steel ratio, present moderate damages. The results of this study suggest that the current CSA-S6-06 limit could be reduced from 0,8% to 0,5%.

Date	29 Mar 2012
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	Amar Khaled (Supervisor) & Marie-José Nollet (Co-supervisor)