Eurocodes: Using the Eurocodes for bridge design

 Introduction

Over the years numerous design studies have been carried out to develop and validate the rules in Eurocodes.  These studies involved using the Eurocodes to re-design structures that had already been designed and built to current Highways Agency and British Standards.

The Agency has identified a number of objectives for these studies, including:

Studies Undertaken

The Eurocodes have been used on studies on a number of different bridges including steel/concrete composite, pre-stressed concrete and reinforced concrete.  Studies have been carried out using Eurocodes to design superstructures, substructures and buried structures.   All of the bridges used in the studies had previously been designed to current British Standards and the DMRB.

The studies involved using the Eurocodes to design the structural elements originally designed using British Standards.  This included using the Eurocodes traffic loading model instead of the BS5400/BD37 model.

Some of the studies also involved developing a new Approval in Principle form for the Eurocodes, developing draft specification documents, and a review of European product and execution standards to determine if they will affect the specification.

Principal Findings of Studies

In general the studies have all found that the Eurocodes would make little difference to common forms of bridges and highway structures in terms of member sizes and, compared on a like for like basis, the Eurocodes generally resulted in sectional resistances that were within 10% of the results from the British Standards.  Some notable differences exist, particularly for shear in concrete: for sections without shear links the resistance in accordance with the Eurocodes is slightly lower, reflecting more recent work done in this area; for shear reinforced sections the variable angle truss model in the Eurocodes offers notably higher shear resistance.  Another noteworthy issue is that the Eurocodes treat pre-stressed concrete and reinforced concrete in a consistent manner, rather than the separate treatment as in BS5400-4.  Despite there being little overall difference to the design outcomes in these studies, it should be noted that the Eurocodes do offer greater scope for innovation.

As stated earlier the studies included a preliminary assessment of the impact of Eurocodes on technical approval.  The Eurocodes themselves do not change the role of the Technical Approval Authority (TAA), but will, of course, have an effect on the practices.  There will be obvious effects on the BD2 Approval in Principle (AIP) form, such as the need to change the sections on loading from the current type HA and HB loads to the Eurocodes traffic models, and the need for the Technical Approval Schedule to reference the Eurocodes. An extra appendix will also be needed in which designers record the options and their choices where allowed in the Eurocodes.

The outcomes from the studies also highlighted some common areas of UK practice that are not covered in the Eurocodes.  This informed the work being done to develop additional complementary guidance.  Of particular note is that the Eurocodes do not contain provisions for the distribution of wheel loads through fill, surcharge models, and do not explicitly cover integral bridges.  Guidance on all of these aspects is at an advanced stage of development. The studies also discovered a small number of areas in the Eurocodes where the design provision is not clear.  This is important feedback which will be recorded and reported back to the relevant committee at CEN (the European Committee for Standardisation) for consideration in future Eurocodes maintenance activities.

The studies involved a significant learning curve for the designers, as would be expected.  The designers observed that the Eurocodes are generally more academic, with clauses expressed in a more "mathematical" style than the British Standards.  They also found that although the design principles are generally clear, it is not always obvious how they should be satisfied.  However during the course of studies the designers involved quickly became conversant in the Eurocodes, and found them to be different to use but not necessarily more difficult.

Perhaps the most significant finding of the studies was that it is possible to design common types of highway bridges using the Eurocodes and in some cases they are more logical. This is a reassuring confirmation that Eurocodes can be used, although further training and guidance will be necessary.

Challenges and opportunities

The introduction of Eurocodes presents significant challenges and opportunities to the construction industry.  The potential to open the sector to wider, pan-European competition should lead to greater choice when procuring construction services, and there exists a challenge for the British industry to adapt to a potential increase in competition.  The introduction of the Eurocodes also increases the potential for significant cost savings in pan-European research and resolution of technical issues.

Designers in the UK must be prepared for the introduction of Eurocodes or risk being left behind by their European counterparts.