A preliminary study of the strength of non-prismatic columns using fabric formwork

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Abstract

Columns are perhaps the most iconic and emblematic of architectural elements. Their functional and symbolic presence represents both order and control over gravity. In the development of flexible formwork for concrete there are many examples of tectonically interesting columns. One of the first commercially available systems to use fabric as formwork produced circular columns. Research into fabric formed concrete structures has tended to focus on optimum geometries for beams, where the fabric can be shaped to respond to the bending moments leading to expressive, organic looking shapes. Less attention has been given to the influence of form on the strength of axially loaded columns.

This paper presents some preliminary results on the influence of shape on the compressive strength of non-prismatic columns. There appears to have been relatively little research on the strength of non prismatic columns, probably as a consequence of the difficulty in construction of the formwork using conventional planar materials. In this project using flexible textile formwork it is shown that non prismatic columns are straightforward to construct and with no additional complexity compared to cylindrical columns.

A series of structural tests were undertaken on circular columns with diameters that vary along their axis. The columns were constructed carefully to produce non-prismatic geometries that were concave (tapered, from the top) or convex (bulging from the top). In addition prismatic control columns were constructed of constant diameter. All the columns were of the same height and all were designed to use the same volume of concrete. The columns were tested under axial compression to failure at the Engineering Laboratories of the University of Edinburgh.

The results show that the shape of the column has a marked effect on the strength of the columns. The convex columns with increased diameters at mid-point carried the least load and the concave columns with reduced diameters sustained the greatest load approximately 90 - 100% stronger in some cases. The increased load is attributed to the influence that shape has on the development of lateral tensile strains in the columns. Using fabric formwork it is possible to optimise the shape of a column to maximise the compressive strength for a given volume of concrete at no additional cost in the construction process.
Original languageEnglish
Title of host publicationProceedings of the International Society of Flexible Formwork (ISOFF) Symposium 2015, Amsterdam
Place of PublicationDen Haag, Netherlands
PublisherKoninklijk Instituut Van Ingenieurs
Number of pages12
ISBN (Print)9789053630426
Publication statusPublished - 16 Aug 2015

Keywords

  • fabric formwork
  • axial loading
  • structural testing
  • strength
  • non - prismatic
  • column
  • concrete

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