Combined Lower and Upper Bound Plastic Analysis: Better than the Sum of its Parts

摘要

Studies have shown that current bridge assessments are often overly conservative. In particular,rnengineers often use elastic analysis to predict the load at which a concrete slab bridge will fail inrnflexure and thus may grossly underestimate its ultimate capacity. This leads to bridges beingrnunnecessarily strengthened or even rebuilt, creating wasteful expense and unsustainable use ofrnresources.rnUpper bound plastic 'yield line' analysis is sometimes used to perform less conservativerncalculations, but it is difficult to apply to cases with complex geometry and engineers are oftenrnconcerned that the result may an unsafe overestimate of the collapse load. Modern computationalrnmethods enable automated lower bound analysis, which has been found to give good results but isrnstill not guaranteed to be accurate. This paper introduces the concept of 'combined lower and upperrnbound plastic analysis', in which the results of a lower bound analysis assist in generating an upperrnbound solution. The resulting close upper and lower bounds on the plastic collapse load prove thatrnthe maximum deviation from the theoretical exact solution is small.