Economic Concrete Frame Elements to Eurocode 2
Basis and limitations on use
General
The charts and data in this publication are intended for use with the pre-scheme design of medium-rise multi-storey building frames and structures by experienced engineers who are expected to make judgements as to how the information is used. In producing the charts and data many assumptions have been made. These assumptions are more fully described in Section 7, Derivation of charts and data, and in the charts and data themselves. The charts and data are valid only if these assumptions and restrictions hold true.
Accuracy
The charts and data have been prepared using spreadsheets that produced optimised results based on theoretical overall costs (see Section 7.1.1). Increments of 1 mm depth were used to obtain smooth curves for the charts (nonetheless some manual smoothing was necessary). The use of 1 mm increments is not intended to instil some false sense of accuracy into the figures given. Rather, the user is expected to exercise engineering judgement and round up both loads and depths in line with his or her confidence in the design criteria being used and normal modular sizing. Thus, rather than using a 241 mm thick slab, it is intended that the user would actually choose a 250, 275 or 300 mm thick slab, confident in the knowledge that, provided loads and spans had been accurately assessed, a 241 mm slab would work. Going up to, say, a 300 mm thick slab might add 10% to the overall cost of structure and cladding, but this might be warranted in certain circumstances.
Note: The charted data is almost always close to minimum values, so it should never be rounded down.
Sensitivity
At pre-scheme design, it is unlikely that architectural layouts, finishes, services, and so forth, will have been finalised. Any options considered, indeed any structural scheme designs prepared, should therefore not be too sensitive to minor changes that are inevitable during the design development and construction phases.
Reinforcement densities
The data contain estimates of reinforcement densities (including tendons) for each element. The reinforcement data allow for calculated lap lengths and curtailment (but not wastage).
Estimates for elements may be aggregated to give very preliminary estimates of reinforcement quantities for comparative purposes only. They should be used with great caution (and definitely should not be used for contractual estimates of tonnages).
Many factors beyond the scope of this publication can affect reinforcement quantities on specific projects. These include non-rectangular layouts, large holes, actual covers used in design, detailing preferences (curtailment, laps, wastage), and the many unforeseen complications that inevitably occur. Different methods of analysis alone can account for 15% of reinforcement weight. Choosing to use a 275 mm deep slab rather than the 241 mm depth described above could reduce reinforcement tonnages by 7%.
Therefore, the densities given in the data are derived from simple rectangular layouts, using The Concrete Centre’s interpretation of BS EN 1992
[2, 3]
(as described in Section 7), with allowances for curtailment and laps, but not for wastage.
Columns
The design of columns depends on many criteria. In this publication, only axial loads, and as far as possible moment, have been addressed. The sizes given (especially for perimeter columns) should, therefore, be regarded as tentative until proved by scheme design.
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Basis and limitations on use
General
The charts and data in this publication are intended for use with the pre-scheme design of medium-rise multi-storey building frames and structures by experienced engineers who are expected to make judgements as to how the information is used. In producing the charts and data many assumptions have been made. These assumptions are more fully described in Section 7, Derivation of charts and data, and in the charts and data themselves. The charts and data are valid only if these assumptions and restrictions hold true.
Accuracy
The charts and data have been prepared using spreadsheets that produced optimised results based on theoretical overall costs (see Section 7.1.1). Increments of 1 mm depth were used to obtain smooth curves for the charts (nonetheless some manual smoothing was necessary). The use of 1 mm increments is not intended to instil some false sense of accuracy into the figures given. Rather, the user is expected to exercise engineering judgement and round up both loads and depths in line with his or her confidence in the design criteria being used and normal modular sizing. Thus, rather than using a 241 mm thick slab, it is intended that the user would actually choose a 250, 275 or 300 mm thick slab, confident in the knowledge that, provided loads and spans had been accurately assessed, a 241 mm slab would work. Going up to, say, a 300 mm thick slab might add 10% to the overall cost of structure and cladding, but this might be warranted in certain circumstances.
Note: The charted data is almost always close to minimum values, so it should never be rounded down.
Sensitivity
At pre-scheme design, it is unlikely that architectural layouts, finishes, services, and so forth, will have been finalised. Any options considered, indeed any structural scheme designs prepared, should therefore not be too sensitive to minor changes that are inevitable during the design development and construction phases.
Reinforcement densities
The data contain estimates of reinforcement densities (including tendons) for each element. The reinforcement data allow for calculated lap lengths and curtailment (but not wastage).
Estimates for elements may be aggregated to give very preliminary estimates of reinforcement quantities for comparative purposes only. They should be used with great caution (and definitely should not be used for contractual estimates of tonnages).
Many factors beyond the scope of this publication can affect reinforcement quantities on specific projects. These include non-rectangular layouts, large holes, actual covers used in design, detailing preferences (curtailment, laps, wastage), and the many unforeseen complications that inevitably occur. Different methods of analysis alone can account for 15% of reinforcement weight. Choosing to use a 275 mm deep slab rather than the 241 mm depth described above could reduce reinforcement tonnages by 7%.
Therefore, the densities given in the data are derived from simple rectangular layouts, using The Concrete Centre’s interpretation of BS EN 1992
[2, 3]
(as described in Section 7), with allowances for curtailment and laps, but not for wastage.
Columns
The design of columns depends on many criteria. In this publication, only axial loads, and as far as possible moment, have been addressed. The sizes given (especially for perimeter columns) should, therefore, be regarded as tentative until proved by scheme design.
Download
*
