The seismic analysis of statically designed tall reinforced concrete buildings using the finite element method
Earthquakes present one of the most devastating hazards on the planet. They threaten the safety of civilians in seismically active regions, and are of extreme concern in applications that demand a high level of safety, i. e. the nuclear industry. However in nearly all cases, the fatalities that occur are as a result of the collapse of man-made structures. Hence the problems facing Civil Engineers who are concerned with seismic mitigation is evident. The dynamic behaviour of their structures must now be accounted for in the design. As our knowledge broadens, structures can, and are being designed to be earthquake resistant. However there are many buildings still standing in seismically active regions which have been designed for static load cases only, or are now of substandard design. Seismic engineering research and application has progressed rapidly over the last few decades, not least in part due to the evolution of computer technology, and our ability to produce computer models which aid us in the design and analysis processes. Hence the research presented focuses on the global behaviour of a typical statically designed tall reinforced concrete building. A literature review has been performed to investigate current mathematical and experimental work which has been carried out with regard to reinforced concrete structures under seismic/cyclic loading. The main point to note from this is that most of the current research has focussed on local behaviour rather than overall global response. The majority of models incorporating global 3D finite element modelling using time history analysis are being created in the Nuclear Industry. After verification work, the ANSYS general purpose finite element computer package has been used to analyse a statically designed 10-storey reinforced concrete building (designed to the rules of BS8110) for static, modal and time-history analyses under a typical (synthetic) earthquake. Certain features have been incorporated in the model with the foresight that these might cause problems under dynamic loading (i. e. softstoreys). The global response of the building has then been investigated, backed up with supporting 'hand' calculations. A 'margins' assessment was carried out mainly on the columns to the requirements of a static code. This enabled the identification of the problematic areas of the building, giving insight into the collapse behaviour and possible areas where design upgrade, attention to workmanship or retrofit may be required. In this process the potential for redistribution and overload capacity of the structure is also demonstrated. In conclusion, a number of suggestions for future work using global response models are made, and the benefits of using the global model approach adopted are discussed in detail. The global response, as opposed to local effects are captured providing insight into the potential for partial or total collapse.