Detailing

The actual process of detailing has not changed dramatically. However, many detailed provisions are different to those that were in BS 8110.

The main reference for detailing is the IStructE Standard Method of Detailing Structural Concrete, 3rd edition, which is named as NCCI in the UK National Annex. Guidance can be found in Chapter 10 (Detailing) of How to Design Concrete Structures using Eurocode 2. The main issues are discussed here.

Cover

The nominal cover should generally be specified by the designer (See: How to Design Concrete Structures using Eurocode 2: Chapter 2, Getting Started). The nominal cover should be shown on the drawings and should refer to the reinforcement nearest to the surface of the concrete e.g. the links in a beam. The cover to the main bar should be at least equal to the size of that bar, plus the allowance for deviations, cdev which is usually 10 mm depending on the quality assurance. In high exposures nominal covers will be greater.

Anchorage and lap lengths

Eurocode 2 introduces a range of factors (1 to 6) for use when calculating the appropriate anchorage and lap lengths. A number of assumptions can be made that enable the Table 2 (below) to be developed for anchorage and lap lengths.

If the conditions noted in the table are not met then reference should be made to Eurocode 2. Lap lengths for unequal size bars may be based on the smaller bar.

The top of sections > 250 mm thick and the top 300 mm of sections deeper than 600 mm are considered to provide poor bond conditions. In these locations, bond strengths are reduced and anchorage and lap lengths are increased accordingly.

Eurocode 2 states that where possible laps in a member should be staggered and not located in areas of high stress. The arrangement of lapped bars should comply with How to Design Concrete Structures using Eurocode 2: Detailing, see Figure 5.

Table 2: Anchorage and lap lengths for concrete class C25/30 (mm) 


 Extract from How to Design Concrete Structures using Eurocode 2: Detailing (page 90, Table 2)

Tension laps

Transverse tensile stresses occur at the ends of lapped bars. Where the diameter, f, of the lapped bars needs to be more than 20 mm diameter transverse bars (i.e. links) should be provided close to the ends of the lapped bars.

Curtailment

Longitudinal reinforcement should be extended beyond the point at which it is no longer required for flexural strength by a distal al which may calculated or conservatively be taken as al = 1.125d (this is known as the ‘shift rule’).  Simplified rules are shown in Figures 8 and 10 below.

Figure 8: Simplified detailing rules for beams

Extract from How to Design Concrete Structures using Eurocode 2: Detailing (Page 92, Figure 8)

Figure 10: Simplified detailing rules for slabs

Extract from How to Design Concrete Structure using Eurocode 2: Detailing (Page 94, Figure 10) 

Punching shear reinforcement

There are detailed rules for punching shear reinforcement.

Detailing minima and maxima

The clauses and values for most detailing minima and maxima are given in Table 1 below:

Table 1 Detailing minima and maxima according to Eurocode 2

Item                                      EC2 Clause / Values

Beams                                   

Main Bars in Tension           

As,min                                       9.2.1.1 (1):    0.26 fctm/fykbd  ³ 0.0013 bd

As,max                                      9.2.1.1 (3):    0.04 bd

Main Bars in Compression

As,max                                      9.2.1.1 (3):    0.04 bd

Spacing of Main Bars           

smin                                         8.2 (2):         dg + 5 mm or f or 20mm

Smax                                         Table 7.2N or Table 7.3N

Links                                      

Asw,min                                     9.2.2 (5):    (0.08 b s Öfck)/fyk

sl,max                                       9.2.2 (6):    0.75 d

st,max                                       9.2.2 (8):    0.75 d £ 600 mm

st,maxcompression                            9.2.1.2 (3)  15f

 Slabs

Main Bars in Tension

As,min                                       9.2.1.1 (1):  0.26 fctm/fykbd  ³ 0.0013 bd

As,max                                      9.2.1.1 (3):  0.04 bd

Secondary Transverse Bars

As,min                                       9.3.1.1 (2): 0.2As for single way slabs

Spacing of Bars                     

smin                                         8.2 (2):    dg + 5 mm or f or 20mm

Smax                                         9.3.1.1 (3): main 3h £ 400 mm

                                                             secondary: 3.5h £ 450 mm

                                                              in places of maximum moment:

                                                                   main:  2h £ 250 mm

                                                                   secondary: 3h £ 400 mm

 Punching shear links

Asw,min                                     9.4.3 (2): Link leg = 0.053sr st Ö(fck)/fyk

Sr                                            9.4.3 (1):    0.75d

St                                            9.4.3 (1):    within 1st control perim.:  1.5d

                                                                      outside 1st control perim.:  2d

Columns                                

Main Bars in Compression

As,min                                       9.5.2 (2):   0.10NEd/fyk £ 0.002bh

As,max                                      9.5.2 (3):   0.04 bh

Links                                      

Min size                                 9.5.3 (1) 0.25f or 6 mm

Scl,tmax                                     9.5.3 (3): generally MIN (20fmin; b;  400 mm)

                                                               but within h of a slab or beam or in lap lengths MIN(12fmin; 0.6b; 240 mm)

                                               9.5.3 (6): No compression bar > 150 mm from a restrained bar

How to Design Concrete Structures using Eurocode 2: Second edition

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