I have been involved in numerous projects across Europe where we are trying to sell structural steel to markets where it is not necessarily the material of choice. Unfortunately, when working in other European countries it soon becomes evident that life is not as straightforward as was intended by the architects of the single market.
When selecting any structural framing material, the design efficiency, availability, ease of supply and increasingly, the surety of cost must all be considered. The advent of tariffs and quotas has made steelwork availability an issue but also the importance of bias by a design team towards the material that they know best is an important consideration. Experience on some of our projects has also highlighted that for some, the overall use and interpretation of Eurocode 3 is another problem.
Designers lacking in structural steelwork experience generally take a very proscriptive view of the design code rules often leading to delay and confusion. Steel is steel; we are all using the same design code and there should be greater consistency across borders. The Eurocodes replaced numerous national standards with National Annexes and Nationally Determined Parameters (NDPs) developed to smooth the transition. Over time there should have been greater acceptance of the basic rules and a reduced reliance on NDPs, but this doesn’t seem to be the case in practice which acts as a particular disadvantage for steelwork.
A search of the European Commission website shows that at present, Eurocode 3 has 6 parts which are then subdivided, resulting in 20 separate documents and another 3 if you require composite design. All can contain NDPs which change recommended design values and thereby alter calculated design resistances. For comparison, reinforced concrete design has four main parts and structural timber gets by with three.
Overall, the structural Eurocodes contain 1573 NDPs with 437 belonging to structural steel and another 55 to composite construction; roughly a third of the overall total. Eurocode 2 for reinforced concrete only achieves a poor third place with 231 NDPs.
Within Eurocode 3, material safety factors are typically subject to NDP. This can result in the same column section being more likely to buckle in one country than another. Even something as simple as the tabulated steel yield strength used to design this column has to be verified by National Annex as the product standards for the materials we purchase have differing values to those in the text. This amount of variance cannot help our sector and the need to simplify the process should be self-evident.
The EC website states that harmonisation should only diverge where geographical or climatic conditions or specified levels of protection make that necessary. Variations due to climate or geography are understandable but the protection consideration results in even the basic load combinations in Eurocode 1 changing within different jurisdictions. The safety factor for Dead Loading can be 1.15, 1.25 or 1.35 but for some, this factor together with the imposed loading also vary with Execution Class despite the use of a common execution standard.
Structural safety is paramount but, the question has to be asked “if a structure was designed using only the recommended values given in the Eurocodes would it be unsafe”? Geographical implications on the applied loading are noted but the answer in terms of member resistance has to be no. The structural Eurocodes are calibrated design standards that have been developed to produce statistically safe results. It should be acceptable to use the recommended values to design structures anywhere in Europe with NDPs only being accepted where greater structural efficiency can be demonstrated.
Many practicing engineers are not academics, both ease of use and general understanding should be an important consideration when writing any design standard. In my view, the number of individual documents and sheer quantity of NDPs within Eurocode 3 counter ease of use and reinforce resistance by some designers to structural steelwork. Going forward, a simpler approach for all would be to allow more of the recommended values in the pursuit of greater harmony.
Chris Durand
BCSA President
In pursuit of harmony
I have been involved in numerous projects across Europe where we are trying to sell structural steel to markets where it is not necessarily the material of choice. Unfortunately, when working in other European countries it soon becomes evident that life is not as straightforward as was intended by the architects of the single market.
When selecting any structural framing material, the design efficiency, availability, ease of supply and increasingly, the surety of cost must all be considered. The advent of tariffs and quotas has made steelwork availability an issue but also the importance of bias by a design team towards the material that they know best is an important consideration. Experience on some of our projects has also highlighted that for some, the overall use and interpretation of Eurocode 3 is another problem.
Designers lacking in structural steelwork experience generally take a very proscriptive view of the design code rules often leading to delay and confusion. Steel is steel; we are all using the same design code and there should be greater consistency across borders. The Eurocodes replaced numerous national standards with National Annexes and Nationally Determined Parameters (NDPs) developed to smooth the transition. Over time there should have been greater acceptance of the basic rules and a reduced reliance on NDPs, but this doesn’t seem to be the case in practice which acts as a particular disadvantage for steelwork.
A search of the European Commission website shows that at present, Eurocode 3 has 6 parts which are then subdivided, resulting in 20 separate documents and another 3 if you require composite design. All can contain NDPs which change recommended design values and thereby alter calculated design resistances. For comparison, reinforced concrete design has four main parts and structural timber gets by with three.
Overall, the structural Eurocodes contain 1573 NDPs with 437 belonging to structural steel and another 55 to composite construction; roughly a third of the overall total. Eurocode 2 for reinforced concrete only achieves a poor third place with 231 NDPs.
Within Eurocode 3, material safety factors are typically subject to NDP. This can result in the same column section being more likely to buckle in one country than another. Even something as simple as the tabulated steel yield strength used to design this column has to be verified by National Annex as the product standards for the materials we purchase have differing values to those in the text. This amount of variance cannot help our sector and the need to simplify the process should be self-evident.
The EC website states that harmonisation should only diverge where geographical or climatic conditions or specified levels of protection make that necessary. Variations due to climate or geography are understandable but the protection consideration results in even the basic load combinations in Eurocode 1 changing within different jurisdictions. The safety factor for Dead Loading can be 1.15, 1.25 or 1.35 but for some, this factor together with the imposed loading also vary with Execution Class despite the use of a common execution standard.
Structural safety is paramount but, the question has to be asked “if a structure was designed using only the recommended values given in the Eurocodes would it be unsafe”? Geographical implications on the applied loading are noted but the answer in terms of member resistance has to be no. The structural Eurocodes are calibrated design standards that have been developed to produce statistically safe results. It should be acceptable to use the recommended values to design structures anywhere in Europe with NDPs only being accepted where greater structural efficiency can be demonstrated.
Many practicing engineers are not academics, both ease of use and general understanding should be an important consideration when writing any design standard. In my view, the number of individual documents and sheer quantity of NDPs within Eurocode 3 counter ease of use and reinforce resistance by some designers to structural steelwork. Going forward, a simpler approach for all would be to allow more of the recommended values in the pursuit of greater harmony.
Chris Durand
BCSA President