## Eurocode Structure Class

1 In order to satisfy the provisions of 4.1.3.3 P(3), these minimum values for cover should be associated with particular concrete qualities, to be determined from Table 3 in ENV 206.

2 For slab elements, a reduction of 5 mm may be made for exposure classes 2—5.

3 A reduction of 5 mm may be made where concrete of strength class C40/50 and above is used for reinforced concrete in exposure classes 2a—5b, and for prestressed concrete in exposure classes 1—5b. However, the minimum cover should never be less than that for Exposure Class 1 in Table 4.2.

4 For exposure class 5c, the use of a protective barrier, to prevent direct contact with the aggressive media, should be provided.

4.1.4 Materials

P(1) Materials shall comply with the requirements of appropriate international or national standards. The choice of materials shall be made, taking account of the environmental conditions including any aggressive actions. These should be considered in conjunction with other factors such as design and detailing, standards of workmanship and construction, and intended maintenance regimes — to produce the required level of performance for the structure throughout its service life.

(2) For concrete the requirements should generally be in accordance with ENV 206. These requirements relate to the constituents and composition of the mix and to the processes involved in mixing, transporting, placing, compacting and curing the concrete in the structure.

(3) For reinforcement, the requirements of 3.2 apply.

(4) For prestressing steel, the requirements of 3.3 apply.

(5) For anchorage devices, the requirements of 3.4 apply. For exposure classes 2 — 5, any anchorage or fixing device which is not fully embedded in the concrete may have to be protected against corrosion by special measures.

(6) Other materials may be used, provided that full account is taken of their effects on design requirements and that there are satisfactory data on their suitability and quality.

### 4.1.5 Construction

P(1) The standard of workmanship on site shall be such as to ensure that the required durability of the structure will be obtained. The combination of materials and procedures used in making, placing and curing the concrete shall be such as to achieve satisfactory resistance to aggressive media for both concrete and steel.

P(2) During construction, adequate measures shall be taken, by means of supervision and quality control, to ensure that the required properties of the materials and standards of workmanship are achieved. (3) The requirements for workmanship are given in chapter 6 and in ENV 206.

4.2 Design data 4.2.1 Concrete

Ec,nom Either the mean value of Ecm (Table 3.2) or the corresponding design value Ecd (Equation 4.1)

Fc Force due to the compression block at a critical section at the ultimate limit state

Fs Force in the tension reinforcement at a critical section at the ultimate limit state k Coefficient used in defining the shape of the stress-strain diagram of concrete

a Reduction factor for concrete compressive strength

Eci Compressive strain in the concrete at the peak stress fc ecu Ultimate compressive strain in the concrete n Ratio for the physical description of the stress-strain diagram for concrete (Equation 4.2

and Figure 4.1)

### 4.2.1.1 General

P(1) Data on material properties in this section are either representative values, corresponding to the relevant strength class of concrete, or are idealizations suitable for design purposes.

If not stated otherwise, the properties with regard to strength shall be represented by their characteristic values (see 3.1.2.2).

P(2) Design data for concrete shall be derived from measured or known properties. These properties shall be determined by means of standard tests.

P(3) Design shall be based on a specified strength class of concrete (see 3.1.2.4).

(4) The applicability of the idealizations and design assumptions of this Code for concrete with strength classes less than C 12/15 or higher than C 50/60 should be investigated.

(5) in the absence of more accurate data or when great accuracy is not required the rules given in the following clauses may be used as a general approximation.

(6) Design data on plain concrete, lightweight concrete, high strength concrete, and concrete subject to steam curing are given separately in relevant Appendices or Parts of this Code. The applicability of the idealizations given in this section should be investigated for those cases.

4.2.1.2 Physical properties a) Density

The density of normal weight concrete may be assumed to be: p = 2 400 kg/m3 for plain (unreinforced) concrete;

p = 2 500 kg/m3 for reinforced or prestressed concrete with normal percentages of reinforcement.

b) Poisson's ratio Section 3.1.2.5.3 applies.

c) Coefficient of thermal expansion Section 3.1.2.5.4 applies.

4.2.1.3 Mechanical properties

4.2.1.3.1 Strength

(1) Characteristic values for defined strength classes of concrete may be taken from Table 3.1 (see 3.1.2.4).

(2) For each strength class of concrete three values of concrete tensile strength are to be distinguished [see 3.1.2.3(4)]. They should be applied appropriately, depending on the problem being considered.

4.2.1.3.2 Modulus of elasticity (1) Section 3.1.2.5.2 applies.

4.2.1.3.3 Stress-strain diagrams

(1) The actual stress-strain diagram of concrete, obtained by experiment as described in 3.1.2.5.1, may be replaced by an idealized diagram.

(2) A distinction is made between diagrams for structural analysis [(3)-(8) below] and those for cross-section design [(9)-(12) below].

a) Diagrams for structural analysis

(3) For non-linear or plastic analysis (see Appendix 2), or for the calculation of second order effects (see Appendix 3), stress-strain diagrams for short-term loads, as shown diagrammatically in Figure 4.1, may be applied. These are characterised by the modulus of elasticity Ec nom, the concrete compressive strength fc, and the strain (ci at the peak stress fc. (Compressive stress and strain both taken as negative).

Figure 4.1 — Schematic stress-strain diagram for structural analysis [4.2.1.3.3(5)-(7)]

ecl ~cu

Figure 4.1 — Schematic stress-strain diagram for structural analysis [4.2.1.3.3(5)-(7)]

(4) For the relevant values of the modulus of elasticity Ec,nom and the compressive strength fc, either

— mean values Ecm (see 3.1.2.5.2) and fcm [see equation (4.3) below]

— design values

are applicable according to the relevant clauses in sections 2.5.3 and 4.3.5. In equation (4.1), Ecm and fc ck refer to the mean values of modulus of elasticity and characteristic strength respectively. Yc is the partial safety factor for concrete (see 2.3.3.2 and A.3.1).

(5) The Bc - (c relationship given in Figure 4.1 for short-term loading, can be expressed by the following function:

= (c/(c1 ((c and (c1 are both < 0) = - 0,0022 (strain of the peak compressive stress fc) = (1.1 Ec,nom) . (c1/fc (fc introduced as - fc)

denotes either the mean value Ecm of the longitudinal modulus of deformation (Table 3.2)

where: n

-Lir> rin or the corresponding design value Ecd (see paragraph (4) above). Equation (4.2) is valid for 0 > (c > (cu where (cu denotes the ultimate strain in the extreme fibre of the concrete in compression.

(6) For a compression zone of rectangular shape, the mean values for (cu related to the concrete strength class are given in Table 4.3.

Table 4.3 — Nominal values of (cu (rectangular sections)

where (cu denotes the ultimate strain in the extreme fibre of the concrete in compression.

(6) For a compression zone of rectangular shape, the mean values for (cu related to the concrete strength class are given in Table 4.3.

Table 4.3 — Nominal values of (cu (rectangular sections)

Strength class |
12/15 |
16/20 |
20/25 |
25/30 |
30/37 |
35/45 |
40/50 |
45/55 |
50/60 |

fcm N/mm2 |
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