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From BS 8110 to Eurocode 2: what changes for reinforced concrete design

Moving from BS 8110 to EN 1992-1-1: concrete strength, partial factors, loads, bending, shear, deflection, cover and columns compared side by side.

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Two stacks of engineering books and a notebook of hand calculations on a desk
Reading time
5 minutes
Standard
BS 8110 and EN 1992-1-1
Calculator
Beam
Updated
On this page 10 sections
  1. The code family
  2. Concrete strength
  3. Loads
  4. Bending
  5. Shear
  6. Deflection and cracking
  7. Cover
  8. Columns
  9. Notation at a glance
  10. Learning it quickly

Many engineers and lecturers learnt reinforced concrete design with BS 8110, and many Sri Lankan offices still think in it. Eurocode 2 (EN 1992-1-1) works with the same mechanics, but it names things differently, splits the loading into a separate code (EN 1990), and gives some checks in a more general form. This guide sets the two side by side, so that the familiar steps can be found in their new places.

A beam design, BS 8110 step by Eurocode step
  1. Concrete: fcu of the mix → fck of the class (C30/37: 30 MPa)
  2. Loads: 1.4 Gk + 1.6 Qk → 1.35 Gk + 1.5 Qk, or 6.10a and 6.10b
  3. K = M / (b d² fcu) → K = MEd / (b d² fck)
  4. Is K within K'?

    Yes

    1. Lever arm z = d [0.5 + √(0.25 − K / c)] ≤ 0.95 d

    No

    1. Compression steel, or a deeper section
  5. Steel: M / (0.87 fy z) → As,req = MEd / (fyd z)
  6. Shear: vc from a table → VRd,c from 6.2.a, then links take it all
  7. Deflection: span/depth tables → Expressions 7.16a and 7.16b
  8. Cover: a table by grade → cnom = cmin + Δcdev

The code family

BS 8110 was largely self-contained. The Eurocodes are a family:

SubjectBS practiceEurocodes
Basis of design, load combinationsBS 8110-1 section 2EN 1990
Loads (dead, imposed)BS 6399EN 1991-1-1
Concrete designBS 8110-1EN 1992-1-1
National choicesin the codea National Annex to each part

The National Annex matters: values such as or the largest bar spacing can differ between countries. The Sri Lanka National Annex guide lists those that differ in Sri Lanka.

Concrete strength

BS 8110 designates concrete by its cube strength . Eurocode 2 designs with the cylinder strength and names a class by both: C30/37 has = 30 MPa and a cube strength of 37 MPa.

The design strength is then

with and = 0.85 in Sri Lanka (and in the UK), giving the same that appears in many Eurocode textbooks:

EN 1992-1-1 §3.1.6(1)P, Eq. (3.15)
EN 1992-1-1 §2.4.2.4(1), Table 2.1N

Design compressive strength

= 17.00 MPa
EN 1992-1-1 §3.2.7(2), Figure 3.8
EN 1992-1-1 §2.4.2.4(1), Table 2.1N

Design yield strength (horizontal top branch)

Assumption (b) of 3.2.7(2): no strain limit needs checking. Es = 200 GPa (3.2.7(4)).

= 434.8 MPa

Loads

BS 8110 combines dead and imposed loads as . EN 1990 uses (Expression 6.10), or the less favourable of 6.10a and 6.10b. For the beam of the worked example, with = 18.750 kN/m and = 12.00 kN/m:

ExpressionDesign load
BS 811045.45 kN/m
EN 1990, 6.1043.313 kN/m

The Eurocode load is a few per cent lower, but the material factors and the stress block also differ, so the steel areas usually come out close.

Bending

Both codes use a rectangular stress block and the same equilibrium. The differences are in the block:

BS 8110EN 1992-1-1
Depth of the block (up to C50/60)
Stress in the block, with
Steel stress over its partial factor
Ductility limit, from 5.5(4) with the annex's values

The lever arm formula keeps its familiar shape, , with a different constant : 0.9 in BS 8110 with , and 1.134 in the Eurocode form with and .

Shear

BS 8110 compares a shear stress with a concrete stress from a table, and adds links for the difference, with 45° struts. Eurocode 2:

  • gives the concrete's resistance by a formula of a similar shape, with a size factor and the steel ratio (Expression 6.2.a);
  • once links are needed, lets them carry the whole shear, but through struts as flat as about 22° (cot θ = 2.5), so fewer links are needed for the same load;
  • checks the struts against crushing with .

The shear and links guide works through an example.

Deflection and cracking

BS 8110 starts from basic span to effective depth ratios (7 for a cantilever, 20 simply supported, 26 continuous, for rectangular sections) and multiplies them by factors for the tension and compression steel. Eurocode 2 builds the steel ratio and the concrete strength into Expressions 7.16a and 7.16b, multiplied by a factor for the support conditions. Crack control moves from BS 8110's bar spacing rules to Tables 7.2N and 7.3N, which limit the bar size or spacing according to the steel stress. The deflection and cracking guide explains both.

Cover

BS 8110 tabulates nominal cover by exposure condition and concrete grade. Eurocode 2 builds it up from bond, durability (by exposure class and structural class) and an allowance for deviation, . The exposure classes are also new: XC1 to XC4 for carbonation, XD and XS for chlorides, XF for freeze-thaw, XA for chemical attack. See the cover guide.

Columns

BS 8110 calls a braced column short if , and adds a moment for a slender one. Eurocode 2 compares the slenderness with a limit that depends on the axial load, creep, the steel and the end moments, adds geometric imperfections to every column, and gives the second order moment by nominal curvature or nominal stiffness. The column slenderness guide follows an example.

Notation at a glance

BS 8110EN 1992-1-1Meaning
characteristic concrete strength (cube / cylinder)
characteristic yield strength of steel
, , , , design moment, shear, axial force
—, , design resistances
reqsteel area needed
effective length

Learning it quickly

The fastest way to get used to the Eurocode is to design the same member both ways and compare each step. The calculator sets every Eurocode step out with its clause, so you can follow it beside your BS 8110 hand calculation. Open the beam calculator and start with a simply supported beam you already know.