A Modelling Tool for Dynamic Analysis of Masonry Collapse Mechanisms

Abstract eng:
Typical out-of-plane collapse mechanisms for unreinforced masonry structures have been well documented. During assessment, these collapse mechanisms are usually evaluated from a static perspective, in order to determine the ground acceleration which would activate the mechanism. As the structure can resist larger ground motions due to dynamic resistance that increases with the scale of the structure, a multiple of the static acceleration is often used in assessment. Alternatively, the dynamics of these nonlinear collapse mechanisms are approximated by a single-degree-of-freedom linearelastic oscillator. However, there are limitations to the accuracy of this approximation. As an alternative, the equations of motion for potential collapse mechanisms can be solved directly using rocking dynamics. Deriving these equations can be cumbersome and time-consuming, particularly for structures with complicated geometries and mechanisms which may involve multiple elements in the kinematic chain. In this paper, a new tool is presented which uses a digital drawing of a masonry structure in typical CAD software to directly generate the relevant equations of motion for user-defined, or automatically generated, collapse mechanisms. These equations of motion are then solved in Matlab to generate overturning envelopes which predict the response of the structure for a range of pulse-type excitations. The tool is applied to assess potential collapse mechanisms of a typical church in order to prioritise potential intervention measures.

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