ABSTRACT
U.K. NATIONAL ANNEX 20.1 INTRODUCTION Eurocodes have been written to be applicable to all counties which belong to the European Union. However there is recognition that differences in construction materials and practices as well as climatic conditions leading for example to differences in wind and snow loading exist. In order to accommodate these differences, Eurocode allows each country to adopt ‘nationally determined parameters’. In the U.K., the nationally determined parameters are given in U.K. National Annex (UKNA). In the vast majority of cases the recommendations of Eurocode and UKNA are identical. Only in a small number of cases do they differ. The object of this chapter is to highlight some of these important differences. The reader should refer to the full document for complete details. 20.2 BENDING DESIGN (a) Design compressive strength: fcd =αcc fck/γc. In Eurocode αcc = 1, fcd = fck/γc. In UKNA, αcc = 0.85, fcd = 085fck/γc in flexure and axial loading but may be used in all phenomena. (b) If concrete strength is determined at an age t > 28 days, in Eurocode αcc = 0.85 and in UKNA αcc = 1.0. 20.2.1 Neutral Axis Depth Limitations for Design Using Redistributed Moments Eurocode uses the following equations:
(5.10a)
(5.10b)
Note in equation (5.10b), δ ≥ 0.7 if Class B and Class C reinforcement is used and δ ≥ 0.8 if Class A reinforcement is used. UKNA uses the following equations for fyk ≤ 500 MPa:
828 Reinforced concrete design to EC 2
(5.10a)
(5.10b)
20.3 COVER TO REINFORCEMENT For c min, dur, Eurocode gives values in code Table 4.4N. This is summarised in Chapter 2, section 2.9. UKNA recommends following the values in BS8500-1:2006. 20.4 SHEAR DESIGN The main recommendation in UKNA is that unless tests show otherwise, the shear strength of concrete for fck > 50 MPa may be limited to that of fck = 50 MPa. An additional restriction is that while normally 1 ≤ cot θ ≤ 2.5, if shear co-exists with externally applied tension, then cotθ = 1.25. In Eurocode, ν1 = ν= 0.6(1 − fck/25). In UKNA ν1 = 0.6(1 − fck/25) × (1 – 0.5 cos α) where α = inclination of shear links to the horizontal. If α = 900, ν1 = ν= 0.6(1 − fck/25). 20.4.1 Punching Shear Both in Eurocode and in UKNA, the value of the maximum punching shear stress vRd, max adjacent to the column in is limited to 0.5 ν fcd. However in UKNA it is further required that at the first control perimeter, the shear stress is limited to 2vRd, c. 20.5 LOADING ARRANGEMENT ON CONTINUOUS BEAMS AND SLABS UKNA allows for the following three options: Option 1: Use the Eurocode recommended loading pattern. Option 2: (a) All spans carrying (γG Gk + γQ Qk). (b) Alternate spans carrying (γG Gk + γQ Qk) and other spans carrying γG Gk. The same value of γG should be used throughout the structure.
