Abstract
In analyzing seismic behaviour of highway bridges constructed on soft soil deposits, it is important to take account of soil-structure interaction effects. In this paper, seismic response of a bridge pier-foundation is investigated based on earthquake acceleration records measured simultaneously on the pier crest and on the ground surface near that bridge. Four motions were used in the analysis, i.e., two were induced by two earthquakes with magnitudes of 7.5 and 6.6, respectively; and two by their aftershocks. In the former two earthquakes, the maximum accelerations were 186 and 438 gals on the ground surface, and 310 and 230 gals on the pier top, respectively. Analyses of frequency characteristics of the motions showed that the predominant frequencies of pier-foundation were always approximately identical with the fundamental natural frequency of the subsoil. Analyses of micro-tremors measured at the sites revealed that the natural frequency of the pier-foundation system is higher than the fundamental natural frequency of the subsoil. Analytical models were formulated to calculate the seismic response of the pier-foundation assuming the subsoil and pier-foundation to be a shear column model with an equivalent linear shear modulus and an elastically supported beam on the subsoil, respectively. Bedrock motions were computed from the measured ground surface motions and then applied to the bedrock of the analytical model. The seismic responses of pier-foundation were thus calculated and compared with the measured records giving a good agreement.
Highlights
In the past, numerous highway bridges have suffered extensive damage due to strong motion earthquakes
In has been well recognized from these evidences that the influences of surrounding subsurface ground are very important for the seismic responses of foundations deeply embedded in the ground, and considerable interest was concentrated on the soil-structure interaction effects of such structures through model experiments and theoretical analyses
This investigation presents the results of observation of seismic motions on a bridge pier and on the ground surface nearby with high accelerations which were measured during four earthquakes, and correlates the pier motions measured with the pier motions analyzed using the ground surface acceleration records
Summary
Numerous highway bridges have suffered extensive damage due to strong motion earthquakes. The wave forms of all the four acceleration records during the A- Earthquake are very simple with one predominant frequency It should be noted here, that the ground motions have a predominant frequency close to the 1.4 Hz they are not the most predominant It can be recognized from these results that the acceleration records of the pier always contained motions rn the range of 1.3 - 1.7 Hz as the most predominant ones in both the longitudinal and transverse directions. It would be deduced from these considerations that the most predominant frequency that is always contained in the motions of the pier is significantly influenced by the lowest natural frequency of the sub-surface ground so that the pier vibrates almost in accordance with the motion of the subsurface ground nearby
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Schedule a callMore From: Bulletin of the New Zealand Society for Earthquake Engineering
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