The Structural Engineer > Archive > Volume 86 (2008) > Issues > Issue 11 > Refurbishment of St Pancras: justification of cast iron columns
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Refurbishment of St Pancras: justification of cast iron columns

This paper presents the results of an extensive programme of material and full-scale laboratory tests undertaken on existing cast iron columns from St Pancras Railway Station in London.
The original station, which was constructed during the 1860s, has been upgraded to form the international terminus for the Channel Tunnel Rail Link. The existing station is Grade I listed, and is incorporated into the new station scheme.
The current use will impose greater vertical loads and horizontal displacements on the cast iron columns than they previously experienced. A preliminary assessment suggested that it would be prudent to undertake a programme of tests to determine the material properties and understand the structural behaviour under load with more confidence. A total of five columns were made available for full-scale testing to destruction; these were made redundant by the introduction of escalator slots and light wells. In addition, coupons were obtained from columns for material tests.
The coupon tests provided sufficient information to determine a reliable materials model suitable for a non-linear finite element analysis of the columns.
The full-scale tests confirmed that the presence of cast-in features affects the overall structural behaviour of the column. In addition, it confirmed that the 1860s practice of standing columns on padstones with a layer of felt between is an unsatisfactory detail, and can initiate premature failure of the column base.
The results from the material and full-scale tests have been compared. It is concluded that there is consistency between the material and fullscale tests. Back analysis of the full-scale tests using the material model developed from the material tests confirmed that the model is reliable for analysis in the permissible stress domain and gives reasonable assessments of the failure mode and load when lack-of-fit conditions can be properly assessed.

Ian Brooks, BSc(Eng), MSc DIC, CEng, MIStructE, MICE
Associate, Ove Arup & Partners Ltd

Alan Browne, BSc(Eng), CEng, FICE
Associate Director, Ove Arup & Partners Ltd

David Alan Gration, BEng CEng MIMechE
Associate Director, Ove Arup & Partners Ltd

Andrew McNulty, MA, MSc, DIC, CEng, MICE
Associate Director, Ove Arup & Partners Ltd

The authors were seconded to Rail Link Engineering for the work described in this paper.

Author(s): Brooks, Ian;Browne, Alan;Gration, David Alan;McNulty, Andrew

Keywords: st pancras station, london;railway stations;listed structures;cast iron;columns;appraising;testing;compression;stress;strain;behaviour