[Univ of Cambridge] [Dept of Engineering]

Collapse of Masonry Structures

J A Ochsendorf


This dissertation examines the collapse of masonry structures in response to large support displacements and horizontal ground accelerations.  There are two main classes of masonry structure:  arches that thrust, and supporting elements, such as walls and buttresses, which resist the thrust.  This dissertation analyses the safety of arches and buttresses and identifies the resulting collapse mechanisms due to support displacements or horizontal accelerations.  In particular, this research investigates the stability of a masonry arch supported on buttresses and the conditions necessary for collapse to occur.  Engineers are frequently asked to determine the safety of masonry structures that have been severely distorted over the years, often due to subsidence or other long-term movements in the foundations, and this dissertation provides guidance in the assessment of such structures.

The resistance of masonry buttresses to high-level horizontal loads is examined.  In the case of failure due to overturning, a facture will develop in the masonry, significantly reducing the resistance of the buttress.  The capacity is further reduced by outward leaning of the buttresses, a common source of distress for masonry structures due to movements in the supporting foundations.  Based on these considerations, new measures of safety are proposed for buttresses under horizontal loading.

Outward leaning of the buttresses increases the span of the arch or vault.  Spreading supports will cause large deformations in the arch, which increase the horizontal thrust of the arch and may lead to collapse.  In addition, lateral ground accelerations can cause the collapse of arches.  The influence of seismic action can be approximated to first order by equivalent static analysis to determine the initial collapse mechanism.  These problems are analysed for circular masonry arches, and the collapse conditions are identified for various geometries.

The findings are combined to investigate the stability of the masonry arch supported on buttresses.  The safety of the system is examined by studying the influence of imposed displacements.  As the buttresses lean, the thrust of the vault increases and the resistance of the buttress decreases.  The collapse mechanisms are identified for both the static case of leaning buttresses and the dynamic case of horizontal acceleration.  This analysis illustrates that the arch will collapse and the buttresses will remain standing in most cases.

Based on these considerations, new methods are proposed for assessing the safety of masonry structures and determining the influence of future movements on the stability of existing masonry structures.

[Cambridge University | CUED | Structures Group | Geotechnical Group]

This page is maintained by rcb@eng.cam.ac.uk (last update 10 November 2003)