Analysis of masonry arch bridges.

In January 1999, the maximum axle weight increased from IN to 11.5t for theassessmenot f highway bridges and structures. At the samet ime, the maximum vehicleweight also increased from 38t to 44t. Highway authorities are urgently searching for amore refined assessmenmt ethod to predict the behaviour of masonry arch bridges.LUSAS finite element analysis was used to study the behaviour of masonry archbridges. Load versus deflection curves and collapse loads are given for some of the fulland large scale arches previously tested to collapse. A parametric study was alsoperformed to determine the influence of the arch material properties and the loaddispersal angle: the arch tensile strength and the load dispersal angle were found tohave the most significant influence on the collapse load predictions.Repeatability tests were carried out by building three nominally identical large scalearch bridges in the laboratory and testing them to collapse. The first, second and thirdarches collapsed at 2lkNm', 16kNm', and 25kNm 1 respectively. Finite elementanalysis predicted a range of 18kNm' to 39kNm 1 for the same arches. This led to anexamination of a statistical, risk based, approach to bridge assessment.Two novel risk assessment programs were developed by integrating Monte Carlosimulation with the MEXE and the mechanism methods. Statistical information aboutthe predicted collapse load and allowable axle load is given. These risk assessmenttools are offered for incorporation within routine assessmenmt ethods. Their principalbenefit lies in providing engineers with a feel for the reliability of their analyses.A modification has been made to the mechanism method by considering archdeflection. A mechanism prediction is accurate only when all the forces and theirpositions are accurately located. The modified mechanism method was used to analysesome of the full scale arch bridges, previously tested to collapse, which revealed thatarch deflections had a significant influence on the collapse load prediction