Propagation of local instabilities in braced domes.

The present research deals with the propagation of local instabilities in braced domes. Nodal snap-through and member snap are the main local instabilities occurring in braced domes. Both the nodal snap-through and member snap have dynamic characteristics and neglecting their dynamic effects may lead to an unrealistic estimation of behaviour. When a local nodal snap-through occurs in single-layer braced domes and a member snap occurs in double-layer braced domes, kinetic energy is released in a local region of the dome. If the dome is capable of absorbing the kinetic energy released, the instability will not propagate and will remain contained. However, if the dome is unable to absorb the sudden release of kinetic energy, progressive collapse of the structure will occur. The main objective of the present study is to develop a procedure for modelling the propagation phenomenon taking into consideration the kinetic energy released. The material in the Thesis is presented as follows: Chapter 1 gives an introduction to the phenomenon of the propagation of local instabilities in braced domes. Chapter 2 contains a literature survey. In Chapter 3a procedure is proposed to investigate the dynamic propagation of local nodal snap-through in single-layer braced domes. The key point in the proposed procedure is that the effects of kinetic energy, released during the snap-through phenomenon, are represented by initial velocities at the nodes at which snap-through has occurred. In order to evaluate the accuracy and validity of the proposed procedure, two single-layer braced domes were fabricated and tested to collapse. The experimental results presented in Chapter 4 show the reliability of the proposed procedure. In order to obtain some insight regarding the behaviour of single-layer braced domes during the snap-through phenomenon, a parametric study has been undertaken and the results are presented in Chapter 5. Based on the results of the experimental work and parametric study, some design recommendations are put forward to prevent the occurrence of the propagation phenomenon. In Chapter 6 the concept of member snap is outlined. A procedure is also proposed to investigate the dynamic propagation of member snap in double-layer braced domes. The last Chapter contains the conclusions and some suggestions for future investigations.