26 October 2012
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(NB Technical Guidance Note Level 1, No. 18 contained within this issue was updated in October 2016. For the updated article, see the individual article entry for this issue.)
The development of gas fields in a highly seismic zone in the Caspian Sea required an innovative offshore platform. Arup were the detailed designers of a self-installing gravity based structure (GBS) to meet this demand – the first such platform to be commissioned in the region. Arup became involved after an elastic analysis based prescriptive design approach predicted the platform to have inadequate capacity to withstand signifiant seismic events. The Arup team adopted a performance based approach, in combination with advanced non-linear analyses, to demonstrate the suitability of the design for use in this location. Non-linear time history soil-structure interaction finie element analyses were used to demonstrate that the GBS platform satisfied the peformance requirements of ISO 19901-21. In addition, the performance based approach provided the client with an improved understanding of the likely response of the structure to a real earthquake and a greater ability to manage the risks associated with the facility.
This paper presents advances in funicular tile vaulting, made possible through innovation in form finding, falsework systems and construction methods. A full-scale prototype has been realised with the application of new research in the following areas: newly developed structural design tools based on Thrust Network Analysis (TNA), which allow one to generate novel shapes for funicular (compression-only) structures; an efficient digitally fabricated cardboard falsework system, which provides accurate description of a complex reference surface in space; and adaptations of traditional tile vaulting techniques, which have introduced strategies for generating continuous tiling patterns, non-uniform vault thickening, and construction sequencing for structural stability. The methods described in this paper, as applied for the design and construction of the prototype vault, have offered new insights to the challenges of new funicular form for masonry and have paved the way for future research and applications.
As winter draws closer in the UK, Structural-Safety’s Alastair Soane cites several examples of recent weather-induced structural damage.