Proposed permissible limit state assessment criteria for masonry arch bridges

The Ultimate Limit State (ULS) is commonly used when assessing masonry arch bridges. Traditionally one or more, relatively large, partial factors are applied to the ULS to determine the level of service loading that can be safely applied to a given bridge. However the resulting limit on the live load capacity will sometimes prove conservative, and in other cases non-conservative, depending on the bridge makeup. To address this, an alternative, more discriminating, measure, the ‘Permissible Limit State’ (PLS) has recently been proposed, to be checked in conjunction with the ULS. The PLS is defined as the state which, if not exceeded, will ensure the lifespan of the bridge is not measurably reduced by repeated live loading. In this paper limiting PLS criteria based on both masonry stress range and soil-arch interaction considerations which are simple enough to be included in existing masonry arch bridge analysis software programs are considered and then applied to a bridge cyclically tested in the laboratory.