Keywords: web openings, Porthole Beams, steel design, spreadsheets, VBA, DLL.

Steel beams with multiple openings in the web have become popular in recent years. These were initially restricted to castellated beams and more recently cellular beams. Advances in the production of deeper steel sections, up to 1m in depth, have led to Porthole^TM beams being an economic alternative to cellular beams. The Porthole beam is simply a hot rolled steel section with a customised pattern of openings cut into the web. Cellular beams require regular cutting patterns. With the Porthole beam, the pattern of the openings is much more flexible. Additionally, it is possible to produce customised plate girders, so-called fabricated beams, with individually arranged web penetrations. The Steel Construction Institute (SCI) [1,2] has covered the design of beams with web openings and software is available for cellular beams [3] as well as for fabricated beams [4]. However, existing methods are either based on the restricted patterns required for the fabrication of cellular beams or limited to fabricated beams only. This paper proposes a more general approach to the design of hot rolled I-sections with a number of relatively large web openings. The approach uses a spreadsheet for user input/output and design calculations while interfacing with a bespoke finite element analysis engine (FE engine) for the structural calculations. The paper outlines the advantages of the spreadsheet compared to bespoke software and discusses issues relating to the development of the integrated spreadsheet.

The principle purpose of the software presented in this paper is to support the design of Porthole beams. The graphical user interface (GUI) to the software should allow for simple operation of the software. Whilst the interface is required to be user-friendly and simple, the underlying program has to be capable of performing complex structural calculations. Furthermore, it is important to keep the structure of the software as flexible as possible for subsequent expansion and modification of the program.

In order to meet the above mentioned requirements the software developer is left with a number of options. On the one hand, it is possible to design a bespoke application which usually has to be developed from scratch. This approach involves, among other things, the design of a GUI. It is well known that the development of a GUI can be complex and time-consuming. On the other hand, it is possible to utilise an existing application which provides a GUI that is familiar to the end-user and allows for suitable expansion. This approach makes it possible to produce programs with little overhead in software design.

Microsoft© Excel^TM together with the integrated programming language, Visual Basic for Applications (VBA), has, to a certain extent, proved to be a feasible basis for the development of software. Excel spreadsheets provide a variety of useful and powerful features. VBA expands the capabilities of the spreadsheet by allowing the developer or indeed the user to create custom-made subroutines and functions. For more complex calculations VBA can interface with subroutines written in other programming languages when compiled into the form of a dynamically linked library (DLL).

The proposed Porthole beam design software is basically subdivided into two parts, a customised GUI for user input/output and a pre-written generic FE engine. The GUI is provided by an Excel spreadsheet subdivided into a number of worksheets. The FE engine is made available on demand as a DLL. This structure gives rise to a great deal of flexibility for the development of Excel based software where an FE analysis has to be integrated.

Spreadsheet based software design is an effective approach to create customised applications. An efficient and user-friendly GUI can be developed with little overhead when compared to the development of bespoke applications. By linking the spreadsheet to a generic FE-DLL a useful tool for analysing and designing Porthole beams can be produced. Both, the developer and the end-user benefit from the spreadsheet approach. The end-user has the opportunity to customise the spreadsheet for other purposes or link the spreadsheet to existing spreadsheets which is not as easily done with stand-alone software.

At present user tests are being carried out and extra functionality is being added. The software is available for download at www.barnshaws.com.

1

J.K. Ward, "Design of Composite and Non-Composite Cellular Beams", SCI Publication 100, The Steel Construction Institute, 1990.

2

R.M. Lawson, "Design for openings in the webs of composite beams", CIRA Special Publication 51, SCI Publication 068, 1987.

3

J. Mares, D. Oshatogbe, "CELLBEAM Version 5.0", The Steel Construction Institute (on behalf of Westok Ltd.), 2004.

4

G. Newman et al., "FBEAM Version 3.0", The Steel Construction Institute and Fabsec Ltd., 2004.

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