Impact resistance of masonry walls : |b materials characterisation and numeric modelling.

Structural masonry may often be required to resist out-of-plane dynamic loading. This loading may have been applied using an explosive means (e.g. a bomb blast or gas explosion) or, in the case of a masonry parapet, by a vehicle impact. So far, the dynamic response of masonry materials and structures has received little attention in the literature. The aim of the work described in this thesis is to: (i) investigate the dynamic tensile bond characteristics of masonry and (ii) develop a finite element methodology to investigate the response of masonry walls subject to out-of-plane car-like impacts.
A series of laboratory tests on masonry joints subject to dynamic tensile loading have been carried out using specially designed Split Hopkinson Pressure Bar apparatus. Results showed an apparent dynamic enhancement when specimens were loaded at strain rates of approximately 1 S-l. Finite element modelling has been used to support a conjecture that this effect is probably caused by the inherent variability at the brick-mortar interface and is not a genuine material characteristic per se.
A masonry specific interface model suitable for modelling both brickwork and blockwork walls has been implemented in LS-DYNA, a three-dimensional non-linear explicit finite element program. The model was validated against results from a series of unreinforced walls tested previously in the laboratory. Results showed the proposed modelling strategy was in general able to predict the dynamic response of full-scale masonry walls with reasonable accuracy. However, a parametric study showed wall response was highly dependent on small changes in loading impulse, base friction, fracture energy, joint failure stress and angle of dilatancy.
The masonry specific interface model was also used to simulate the behaviour of reinforced walls. Results showed that the model was able to predict the correct failure mode and approximate peak displacement for some but not all of the walls. Furthermore, the model correctly predicted that the inclusion of diagonal bar reinforcement in a weakly mortared wall prevented punching failure behind the point of impact.