Cyclic load capacity and endurance limit of multi-ring masonry arches

A series of large-scale tests have been carried out at the University of Salford on multiring masonry arches to assess their endurance limit and cyclic load capacity. Multi-ring arches represent a significant proportion of the UK bridge stock most of which is over 100 years old. Due to the increasing weight of road and rail traffic their life expectancy and capacity under cyclic loading needs to be predicted. Although there have been a number of small and large scale tests carried out on masonry arches, most of them have been under static loading. There has been however very little work done on load capacity under cyclic loading. The present work entails a series of 3m span two-ring and 5m three-ring brickwork arch tests under cyclic loading at various load levels until failure. The number of load cycles, damage propagation and failure modes have been recorded and recommendations to an endurance limit of such arches have been considered. A few tests under static loading have also been carried out for comparison. While the classical mode of failure of arches under static loading is the four-hingemechanism, all arches within the present test series under cyclic loading have failed by ring separation over the middle section of the arch. Cyclic loading therefore influences the mode of failure. Some theoretical approaches describing the causes of failures have been discussed. C. Melbourne, A.K. Tomor and J. Wang 2 1 BACKGROUND AND CONTEXT There are over 40000 masonry arch bridges in the UK which are being called upon to carry ever increasing levels of loading and increasing volumes of traffic. It is imperative that the bridge stock is not adversely affected by these changes in the loading regime and that appropriate assessment and repair and strengthening techniques are available. Over the past 10 years there has been an extensive programme of research in the UK and abroad which considered various aspects of masonry arch behaviour. One of the conclusions has been the identification of ring separation (delamination) in multi-ring brickwork arch bridges as a major source of concern because its presence reduces the load carrying capacity of the bridge. However, all the experimental work to date has been under monotonic loading conditions and there is a fear that under cyclic loading these phenomena may be aggravated by the incremental deterioration of the brickwork. The current research reported herein addresses some of the issues and offers some guidance. 2 MATERIAL PROPERTIES Class “A” Engineering bricks (215 x 102.5 x 65mm) were used throughout the tests with an average compressive strength of 154N/mm and density of 23.7 kN/m. 1:2:9 (cement:lime:sand) mortar was used with an average compressive strength of 1.7N/mm and density of 15.5 kN/m3. The average compressive strength of the brickwork was 25N/mm and the density 20 kN/m.