The building forms part of the Smart City Project in Malta's southern village of Mtarfa and consist of various office and hospitality buildings and are meant to serve as a corporate IT village. The building comprises a 12,000 square metres and is nine storey's in height in total. Retail spaces are to be provided within the bottom floors and office space at every other level.
My main task was to be the lead structural engineering team which consisted of structural engineers, detailers and draughts-men. When designing the structure it was decided that two solutions would be designed/ envisaged at concept stage and that the most adequate solution would be then be chosen and designed. The two solutions consisted of a flat plate system and a beam and slab system. I decided that a list of constraints must be chosen, each with a weighting so that a self assessment matrix system could be developed. This would ensure that a thorough assessment of each of the schemes would be carried out and hence the more adequate scheme would eventually be chosen. The flat plate system was chosen as it is very popular for office buildings as it is quick and easy to construct and also allows easy service distribution.
When carrying out the structural analysis, finite element analysis was used due to the fact that it allowed the entire floor slab to analyzed as a continuous whole rather than analyzing it as a series of strips spanning in both directions. The fact that the structure was structurally indeterminate ensured savings in reinforcement and overall slab depth. The finite element model also allowed for accurate displacements to be computed thus ensuring that the design engineer will be able to obtain a real understanding of how the structure will perform.
The long term deflection of the slab was calculated at various points. The internal columns were not designed to carry any of the lateral loads and therefore acted only as gravity resisting elements. Lateral loads acting on this building were designed to be resisted by the central cores and the external walls. It must be noted that these elements were also designed to carry substantial vertical load too. Although the location of the cores (within the building perimeter) is not perfect it can be considered good structurally. A common problem faced with buildings of irregular plan shape, such as this is the torsional effects of the lateral loads which cause the building to twist (on plan). These torsional moments were calculated and the building was found to behave adequately overall.
As the building was meant to resist both seismic and wind loads it was imperative that the load resisting elements were continuous in nature. PCA opted for a mixture of reinforced concrete and reinforced block work walls. The earthquake and wind loads were analysed using EC 8 and all seismic forces were calculated using the lateral force method of analysis. The structure was designed to act as a ductile structure so that in the case of a severe earthquake any elements would not fail in a brittle manner but rather will fail gradually in order to minimize the loss of lives.
Due to the fact that the bedrock is of good quality and was located reasonably close to the natural ground level, meant that differential settlement was not a cause for concern. Pad foundations were designed beneath the internal columns whilst raft foundations were designed beneath each of the internal cores. Strip footings were designed beneath the internal and external walls.
David Grima, CEng MICE, Member in Malta