Re-evaluating Integral Abutment Bridge Design Practices after Three Decades of Standards in Ontario

Abstract
In 1993, the Ministry of Transportation in Ontario (MTO) released ‘Integral Abutment Bridges’, a report which documented 16 bridges constructed with integral abutments in Ontario. The report explained the theory of their design and proposed standard details. This document and the 1996 update which followed, set the stage for over 300 integral abutment bridges (hereafter IABs) built on provincial highways in Ontario since that time. Over the last three decades, extensive research, field trials and international experience has been gained and an update to the guideline is overdue. While standards benefit design engineers and constructors, they can be an impediment to progress and improvement. There is potential to improve detailing and expand the range of superstructure and foundation types which can be incorporated into integral bridges.

This paper reflects on the design theory, the code requirements which have evolved with time and influenced the design details, and the field behaviour in service observed through visual observation and structural monitoring. Despite widespread use, there is still significant variation in the approach taken by design engineers and inconsistency in design assumptions. What is the appropriate earth pressure to assume in design, and how does it compare to actual pressures observed through site measurements? Is frost protection necessary? What types of foundations are appropriate for integral bridges and how flexible do foundations need to be? How should connections be detailed to ensure appropriate force transfer between girders and abutment wall, and between the abutment wall and piles? Working towards an update of the report, this paper reflects on challenges, presents examples which fall outside of the existing standard details, and attempts to answer these questions.