Year

1991

Degree Name

Doctor of Philosophy

Department

Department of Civil and Mining Engineering

Abstract

This study is devoted to the development of a method of analysis for the structural behaviour of masonry arch bridges up to failure under applied loading and support movements.

Masonry arch bridges have been studied for many centuries. Numerous analytical methods have been developed but mainly for the study of the elastic behaviour and ultimate strength of arches. In recent years, the finite element approach has been applied to provide nonlinear analysis of masonry arches but the work was limited to using one dimensional beam elements.

In this thesis, a new approach which embodies the two dimensional nonlinear finite element procedure is introduced for the progressive failure analysis of masonry bridges. Failure criteria normally used for plain concrete are adopted to define the failure of masonry as a material under all biaxial stress states. Nonlinear stress-strain relationships are assumed for masonry in compression and the elastic-brittle constitutive relationship is used when masonry is subjected to tension. The failure criteria together with the adopted constitutive relationship for masonry enable both cracking and crushing of the arch under incremental loading conditions to be analysed simultaneously. A stress redistribution scheme is employed such that results for stress distribution, cracking and crushing at any load level may be traced graphically on a computer. Finally, the iterative procedure produces, for the arch, the failure load and the associated collapse mechanism (if it exists).

The two dimensional effects of the spandrel fill on the arch behaviour are also included in the study. This allows the load dispersion through the spandrel fill from the road level onto the arch rib to be taken into account. Effects of both the resulting vertical and horizontal pressures from the spandrel fill are investigated. In the analysis of multispan masonry arches, the spandrel fill acts as if it is a series of struts which transmit the compressive pressure from one span to another.

The accuracy and reliability of the numerical procedure developed in this thesis are checked using experimental results from several masonry arch bridges tested in the United Kingdom. These include two full-scale models tested at Liverpool University, the bridge at Bridgemill (Bridgemill bridge) near Girvan and the bridge at Bargower (Bargower bridge). The application of the proposed method of analysis is demonstrated on both single span arches and multispan arch bridges under concentrated loads and subjected to support movements.

The structural behaviour of a masonry arch bridge is complex mainly due to the material characteristics and its geometrical shape. A n extensive parametric study on these two aspects is carried out in this thesis. The primary aims of the study are to obtain an insight into the structural performance of masonry arches as well as to provide some useful guidance for the design engineer. The tensile strength of masonry, the strain softening parameter and the dispersion action through the spandrel fill are found to be the significant factors which influence the failure load. It is also observed that for most arches the failure due to crushing of the masonry hardly occurs except for an arch with a thick rib and a short span.

A comparative study on multispan masonry arches indicates that very small support movements could cause seemingly disproportionate distress to the structure. It is also noted that for a "rigid system" - a multispan masonry arch bridge with very short piers or without piers, damage is confined mainly to the spans immediately adjacent to support where movements occur. On the other hand, for a more "flexible" multispan arch viaduct with tall piers, the damage tends to spread to the remote spans as well. In the same study, some explanations are also given for the general causes of cracking damage to the Stanwell Park Viaduct, an eight-span railway bridge in N.S.W., Australia.

The nonlinear finite element program developed as part of this research is easy to use and comparatively efficient in terms of computing time. The graphic output, in particular, is convenient for practical use by the design engineer. The program is capable of analyzing the structural behaviour of all kinds of masonry structures. The analysis carried out from the elastic stage through crack propagation and finally reaching the ultimate state. The failure mechanism if it exists will be identified.

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