The progressive collapse of a structure occurs when local failure of a primary structural component leads to the collapse of adjoining members which in turn leads to further collapse through a chain reaction. Often the total damage is disproportionate to the original cause and is associated with a low probability event. The destruction of the World Trade Centre in 200 I due to aircraft impact is an example. Several studies on progressive collapse, mainly of steel structures, have resulted in changes to analysis and design guidelines. In precast concrete structures, connections play an important part in ensuring the safety of the whole structure. Current design practice is to assume these as pinned or rigid but this cannot be relied upon for safety against progressive collapse. The aim of this thesis is to examine the vulnerability of the behaviour of concrete frames with semi-rigid connections. The numerical responses of precast concrete frames with billet connections were studied. The connection was modelled by zero-length spring elements with rotational stiffness values at the ends of beams. These values were obtained from moment-rotation (M-θ ) relationships. A 3-dimensional finite element model was built and used to develop M-θ ) relationship of precast billet connection. Results demonstrate that rotational stiffness of billet connection (23138kNm/rad) leads to a fixity factor of 0.4 which is significantly different from the current practice of pinned connection. A 5-storey concrete building with different types of connection was analysed for the progression of damage after an accidental action. Linear static and nonlinear dynamic analyses associated with alternative load path method were performed. The collapse potential was assessed through demand capacity ratio, maximum deflection, ductility and rotation demand. Analyses show that precast frame with semi-rigid connections has higher potential than rigid connection, when one internal load-bearing element is damaged. Several parametric studies were conducted to investigate the sensitivity of progressive collapse. Results show that number of floors, location of column failure, connection flexibility and duration of column removal do affect the collapse potential results. Of these, the location of column failure is the most significant and the duration of column failure the least. In addition, the dynamic impact factor for the frame with semi-rigid connections were found to be 35% less than the usual guideline of 2. Finally, a new global damage index is proposed to estimate damage as a function of column location, fixity factor and local damage measure. A good relationship was found between the index, connection rigidity and damage.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:683736 |
| Date | January 2015 |
| Creators | Hashim, Nor Fazilah Mohd |
| Publisher | University of Bristol |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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