Spreadsheets enable examination of all structural options

Spreadsheets enable examination of all structural options

Minson, Andrew

Spreadsheets are an important tool for the structural engineer. They are an ideal medium for investigation and comparison of a wide range of concrete structural options and elements quickly and efficiently. Two products from The Concrete Centre allow the engineer to fully utilise the power of spreadsheets.

Concept.xls is a sophisticated new spreadsheet for the conceptual design of reinforced concrete frames which enables the comparison and determination of the optimum structural solution. It assists with concrete frame choice, member sizes and reinforcement estimates. Concept provides an extremely fast way of choosing between different concrete frame options for a scheme design. It can be used for time and cost comparisons and gives initial member sizing, quantities of formwork, reinforcement and concrete; all useful information when making a choice of frame. The optimised solution takes full account of the interaction between frame, cladding and foundation costs in addition to frame construction time.

Program advantages

Data from the publication Economic Concrete Frame Elements is used for member sizing. Spans up to 12m (16m for wide beams) are catered for. Information such as the number of bays, spans and load is simply entered. Cost and time data, and many of the base assumptions may be changed. The program sizes up and compares conceptual designs to BS 8110(1)for 13 forms of reinforced concrete frame construction, then ranks them in order of total or construction cost.

Concept will automatically choose the best cost-optimised scheme from the following forms of reinforced concrete frame, or allow the user to investigate their preferred options:

* Flat slab

* One-way slab

* One-way slab, wide beam

* Two-way slab

* Two-way slab, wide beam

* Ribbed slab

* Ribbed slab, wide beam

* Waffle slab, no beams

Optimisation accounts for foundation, materials, and cladding and, optionally, the cost of time to construct. Thirteen different floor options are investigated, ranging from flat slabs to one- and two-way slabs, and ribbed and waffle slabs. High-efficiency wide beams are also an option when relevant. As it is spreadsheet based, much of the program’s work and data is available for inspection, avoiding the ‘black box’ scenario.

Detailed design optimised

The engineer can then proceed with verification and detailed design in the normal way. Alternatively, the automatic choice can be over-ridden, allowing alternative solutions to be investigated. Printed outputs include floor plans, sections, isometric stick diagrams, cost comparisons and material quantities. A construction cost summary can also be produced, based on default rates for construction costs or those put in by the user. Once the structural frame has been determined the engineer can then use the RC-Spreadsheets for detailed design.

Since their release in 2000, the RC-Spreadsheets have proved to be enormously popular. An updated Version 2.x introducing new spreadsheets to BS 8110 and to the more finalised EN 1992-1-1 (Eurocode 2(2)) and with an overarching spreadsheet has now been published by The Concrete Centre. Use of the spreadsheets promises to speed up the concrete design process by allowing swift prediction of accurate reinforcement quantities and easy examination of alternatives. Their use could also result in significant concrete frame cost savings.

Accurate design calculations

For the experienced engineer, the RC-Spreadsheets allow the rapid production of clear and accurate design calculations. For post-graduates and new engineers they encourage understanding of concrete design and help the gaining of experience by studying ‘what if scenarios. The individual user is able to answer their own questions by chasing through the cells to understand the logic used. Cells within each spreadsheet can be interrogated and can have their formulae checked and values traced.

Concluding remarks

Version 2.x introduces four new spreadsheets to the BS 8110 suite. Three of these cover the rigorous design and analysis of one-way slabs, ribbed slabs and beams. The fourth new BS 8110 spreadsheet is RC43 Wide Beams analysis and design, which allows both top and bottom steel to consist of different size bars. RCCenSS looks at the axial shortening of columns according to prEN1992. In addition to a new over-arching menu spreadsheet, 2.x contains updated versions of the previously issued 24 spreadsheets. It also allows for future integration of spreadsheets to prEN 1992, Eurocode 2, as and when they become available.

* Concept.xls is available on CD or as a free trial download from www.concretecentre.com. PC-Spreadsheets Version 2.x may also be downloaded for trial and examination. However, for commercial use there is a registration fee of £50 plus VAT for each product. Access to any updates is available only to registered users.

References:

1. BRITISH STANDARDS INSTITUTION. BS 8110-1:1997. Structural use of concrete. Code of practice for design and construction. London.

2. COMITÉ EUROPEEN DE NORMALISATION. prEN 1992-1-2 Eurocode 2: Design of concrete structures – Part 1.2: General rules – Structural fire design, Brussels, 2002.

ANDREW MINSON, HEAD OF FRAMED BUILDINGS,, THE CONCRETE CENTRE

Copyright The Concrete Society 2004

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