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0.021i „ 0.018 ¿§ 0.015 g 0.012 '3 0.009 0.006 0.003 0

1.6 1.8 2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 Input frequency

Figure 13. Drift of Model III with constant input amplitude. 4 CONCLUSIONS

In the previous sections the results of 3 series of tests for a total of over 50 geometry/amplitude/frequency combinations have been presented in terms of global response parameters. From these, it would appear that notwithstanding the discontinuous nature of the masonry fabric, having bricks in simple dry contact, a behaviour that can be described in terms of natural frequencies and resonance can be identified, supported by observations in terms of both amplification and energy dissipation. Constraint conditions at corners are also critical to the behaviour and while they do not seem to influence either the façade portion taking part in the shaking or substantially the natural frequency. However the amplification are substantially reduced especially away form resonance. For frequencies closer to the resonance level, the apparent greater stiffness of the model and the fact that it dissipates less by relative rotation at the corners, means greater overall out of plane deformation at the centre of the façade and hence greater damage in this area.

In summary the behaviour and hence the collapse limits are due to the superposition of an overall motion of the walls panel that can be reduced to beam oscillation horizontally and cantilever oscillation vertically; however to this is superimposed a relative sliding of bricks of subsequent courses and a rotation of some of them around a vertical axis, mainly caused by the staggering. This rotation is initiated at corners and propagates. No relevant rocking of individual bricks was observed. On the basis of these observations a multi-body dynamic model is being developed.

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