City Research Online

Abstract

Conventional seismic design of bridges aims to provide to the structure the necessary strength and ductility to withstand seismic forces. However, significant level of damage is expected in these structures, as clearly demonstrated after recent strong earthquakes; this damage is deemed as acceptable by current code provisions. In recent years, the need for alternative design methodologies that can limit structural damage and guarantee post-earthquake serviceability was highlighted. An alternative seismic isolation technique that can combine these concepts is based on the rocking behaviour. The rocking movement is expected to relieve the structure from deformation, stresses and ultimately damage due to the lack of monolithic joints.

The research community has explored the feasibility of rocking isolation in structures that included columns, then frames, and finally bridges. The relatively few real-life applications of rocking isolation in bridge piers and the several simplifications that were adopted to study this behaviour in previous works, motivated the present study to examine this isolation technique in realistic bridge configurations and determine its effectiveness in earthquake-resistant bridges. Therefore, in view of the identified gaps in the literature on bridges with rocking pier isolation, the present study presents (i) simplified analytical tools to predict the longitudinal rocking response of bridges with rocking piers, (ii) proposals of rocking piers with non-conventional shapes in cross-section and in elevation accounting for the concept of accelerated bridge construction, and (iii) a comparative numerical assessment of conventional seismic isolation and rocking pier isolation in bridges, accounting also for the effect of the pier height/slenderness.

In this context, simplified models for predicting the longitudinal response of regular and irregular bridges with rocking piers are presented to expand the initial studies on the corresponding frame models without end supports presented in previous studies. This is done by accounting for all the salient features of a bridge structure in a performance assessment context, and by integrating the dynamic interaction between the structural members. It is shown that the simple frame model without end supports is not capable of predicting the behaviour of a realistic bridge configuration. Additionally, the effect of asymmetry in the height of the piers seems to be negligible in a seismic performance context, although the response parameters vary considerably.

Rocking piers with non-conventional shapes are proposed to enhance the seismic performance of the ‘traditional’ configurations that are usually employed in earthquake-resistant bridges. These proposals build on the inherent advantages that rocking mechanism and accelerated bridge construction offer, thus leading to lighter sections compared to the ‘traditional’ configurations, but leaving open the question of seismic performance due to the fact that the inherent restoring mechanisms are also reduced. The results from several analyses using both single- and multi-frequency ground motions show that rocking piers with relatively light section reduce the rocking amplitudes and protect to higher extent the integrity of the abutment-backfill system than the relatively heavy section that is the one usually adopted in earthquake-resistant bridges.

The comparative numerical assessment of the ‘conventional’ seismic isolation technique and the ‘unconventional’ one based on the rocking mechanism considers a bridge configuration that is expected to be unfavourable for the latter, while several simplifications that were found in previous studies with regard to the analysis of bridges with rocking pier isolation are addressed. It is shown that the rocking alternative improves some aspects of the conventional design, especially in terms of the recentring capability of the entire system. However, considerable flexural strains are found in the rocking piers and this should be considered in the design, while the vertical movement of the rocking piers is detrimental to the flexural response of the superstructure. These effects seem to be less severe in bridges with tall/slender piers compared to those on short/squat members.

Finally, proposals for future research are made with a view to (i) progressively improving and validating the analytical tools presented herein, and (ii) further examining the seismic performance of bridges with rocking pier isolation as well as enhancing the seismic performance of the ‘bare’ configurations that were addressed herein.

Publication Type:	Thesis (Doctoral)
Subjects:	T Technology > TA Engineering (General). Civil engineering (General)
Departments:	Doctoral Theses School of Science & Technology > School of Science & Technology Doctoral Theses School of Science & Technology > Engineering

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