How long can existing masonry arch bridges continue to carry heavily increased traffic loading? Is there a weight limit for masonry bridges below which no long-term damage will occur to the structure? Can the life expectancy for masonry arch bridges be estimated? The present report attempts to explore some of these questions and suggest a framework to incorporate long-term life-cycle assessment into the thinking process.
While the fatigue behaviour of metals and metallic structures has been widely studied, little information exists on the fatigue behaviour of masonry structures. There are no specific guidelines available to assess the fatigue limit and residual life expectancy of masonry arch bridges.
Similarly to any material, masonry also deteriorates under long-term fatigue loading. The majority of masonry arch bridges were built over 100 years ago and carry far greater traffic loading than they were originally designed for. Although masonry bridges do not generally collapse or suffer visible fatigue damage, they may suffer localised deterioration under long-term service loading. Even if the ultimate capacity is not reached, localised deterioration can lead to changes in the load path and to accelerated deterioration of the overall structure.
Failure under long-term cyclic loading can be different from the failure mode associated with quasi-static loading. While four-hinge mechanism is the typical failure mode under quasi-static loading, multi-ring arches are more likely to fail by ring separation under cyclic loading.
Although available test data is insufficient to quantify the long-term cyclic capacity of the wide range of masonry arch bridges, the report seeks to raise awareness of potential issues associated with long-term cyclic loading and provide a methodology for identifying the remaining service life and residual capacity for masonry arch bridges. Assessing the impact of long-term cyclic loading on masonry arch bridges seeks to identify
- safe long-term loading limits
- expected service life
- likely forms of deterioration over time
- future strengthening needs.