Issue 9

London Underground has more than 300 riveted bridges, 24 of which are more than 100 years old. Calculations suggested that many bridges had reached or exceeded their fatigue lives. The purpose of the investigation, therefore, was to provide an improved basis for fatigue assessment of riveted bridges. Strain range counting monitors were fixed in succession to four bridges, in order to ascertain the strain ranges that actually occurred in service. Also, parts of a riveted bridge that was to be demolished and replaced were fatigue tested at Imperial College. The laboratory tests on riveted girders, tensile specimens with holes, and rivets in tension, with published data from earlier tests, are used to propose a new stress range/fatigue life relation (S–N curve) for riveted girders, which approximately doubles the life predicted by BS 5400 for a given stress range. Min Xie, BSc, MSc, PhD Imperial College of Science, Technology & Medicine G. T. Bessant, CEng, FICE London Underground Ltd J. C. Chapman, FREng, FCGI, PhD, FIStructE, FICE, FRINA Visiting Professor at Imperial College of Science, Technology & Medicine Professor R. E. Hobbs, DSc, FCGI, PhD, CEng, FIStructE, FICE Imperial College of Science, Technology & Medicine

Research efforts in the assessment of masonry arch bridges have concentrated on the strength of the arch in the span direction. However, experience with these structures indicates that masonry arch bridges more often fail by sliding or overturning of the spandrel walls perpendicular to the roadway centreline, or by the development of longitudinal cracks in the arch barrel and eventual separation of the spandrels from the remainder of the arch barrel. The present paper reports results of a 3-dimensional non-linear finite element (FE) model of an arch bridge that uses a Drucker-Prager material for the fill and a brittle material for the masonry. The model predicts that most truck-loaded stone arch bridges will exhibit a premature failure due to lateral effects rather than a mechanism collapse. The predicted lateral failure modes include local spandrel wall failures, overturning of the spandrel walls, edge failure of the arch barrel, and local punching of the arch. Stone bridges with thin arches or bridges with very low tensile strengths were predicted to be significantly weakened by such lateral effects. T. E. Boothby, PhD, PE, RA Department of Architectural Engineering, Pennsylvania State University, USA B. J. Roberts, Department of Architectural Engineering, Pennsylvania State University, USA Keywords: bridge, masonry, spandrel, cracking, collapse, modelling, research, properties