Bridge Design to Eurocodes - UK Implementation

22 - 23 November, 2010 Institution of Civil Engineers

Brid Br idge ge Design si gn to Euroc ur ocod ode es - UK Impleme Imp lement nta ation ti on Developm velo pme ent of UK NA for fo r EN1990 Anne Ann ex  A2  A 2 John Jo hn Lane, Rail Safety and Standa tand ards rd s Board B oard

Development of UK NA for EN1990  Annex A2

• Key points from paper • Background summary • Design working life •  Actions outside scope of EN 1991 • Highways Agency studies • RSSB/Network Rail studies • Conclusions

Background to development of UK NA for EN1990 Annex A2 • BS EN 1990 Annex A2 published as an amendment to BS EN 1990 in 2005 • Contains load combination rules, load combination factors (0, 1,2) and partial factors for permanent (G) and variable (Q) actions applicable to bridges •  Also contains requirements for serviceability limit state verification (deformation and vibration limits for example) • Common approach adopted for road, pedestrian and rail bridges i.e. to provide equivalent

Design working life ‘assumed period for which a structure or part of it is to be used for its intended purpose with anticipated maintenance but without major repair being necessary’ • Achieved for persistent and transient design situations through selection of appropriate combination and partial factors •120 years for persistent design situations •Table 3.1, BS EN 1991-1-6 ‘Actions during execution’ recommends return periods for determination of characteristic values of climatic actions (min 50 years for permanent structures)

 Actions beyond the scope of EN 1991 • Design of bridges restricted to actions covered in ‘actions’ parts of EN 1991 • CEN proposes to develop new ‘actions’ parts to address ‘waves and currents’ and ‘atmospheric icing’ • BS EN 1990, clause 1.1(3) anticipates the need to derive characteristic values of ‘actions’, combination factors and partial factors on a project specific basis ‘EN 1990 is applicable for the design of structures where other materials or other actions outside the scope of EN 1991 to EN 1999 are involved.’ • Ship collision is an example where ‘actions’ are developed on project-specific basis • In general, appropriate to use existing standards as

Highways Agency Studies - 1 • Values for  and  derived from reliability studies for typical RC and composite steel/concrete bridges of varying span length and width •  Aim to verify that selected values achieved similar reliability to designs based on ‘actions’ from HA DMRB BD37 •  Average reliability indices of 6.3 for bending and 5.3 for shear are implicit for design to HA DMRB BD37 for loaded lengths > 20 m (much higher for shorter spans)

Highways Agency Studies - 2 Reliability levels for UK NA to BS EN 1990 consistently higher than target reliability of 5.8 for spans up to 50 m 9.5

9   g   n 8.5    i    d   n   e    B 8   r   o    f   x   e    d 7.5   n    I   y    t    i    l 7    i    b   a    i    l   e    R6.5    l   a   u   n   n 6    A

5.5

5

BD37 Compo sit e 3.0m Lane

BD37 Concr ete 3.0m Lane

BD37 Compo sit e 3.65m Lane

BD37 Concr ete 3.65m Lane

NA Concr ete 3.0m & 3.65m Lane

NA Compo sit e 3.0m & 3.65m Lane

Reliability index 5.8

RSSB/Network Rail Studies - 1 • Two separate RSSB research projects ‘T696 Appraisal of Eurocodes for railway loading (2008)’ and ‘T741 Design of railway structures to the structural Eurocodes (2009)’ • T696 extended studies undertaken for Network Rail • T741 extended work of T696 to include consideration of strength and non-traffic action effects, for example, and also included case studies for typical railway bridges • For all studies comparative calculations based on ratio of design load effect to design resistance using deterministic assessments of ‘actions’ and ‘strength. •  Aim to achieve consistent margin of safety compared to BS 5400

RSSB/Network Rail Studies – 2 (T696)

RSSB/Network Rail Studies – 3 (T741)

Z type – filler beam deck

Western box  – steel deck

Filler beam deck

E type – steel cross girders with steel deck plate

Steel / concrete composite deck

Prestressed concrete beam deck

Concluding remarks • The combination factors () and partial factors for permanent actions (G) and variable actions (Q) selected to provide equivalent reliability to that obtained with previous design practice using BS 5400/HA DMRB • Design life is 120 years for persistent design situations and minimum of 50 years for permanent structures for transient design situations • Reduced values of Q factors for wind and thermal actions corresponding to a mean return period equal to the design working life of 50