Prestressing steel

(See note preceeding 3.2). 3.3.0 Notation (see also 1.6, 1.7)

fp

Tensile strength of prestressing steel

fpk

Characteristic tensile strength of prestressing steel

fp0.1

0.1 % proof-stress of prestressing steel

fp0.1k

Characteristic 0.1 % proof-stress of prestressing steel

(u

Elongation of prestressing steel at maximum load

(uk

Characteristic elongation of prestressing steel at maximum load

3.3.1 General

P(1) This section applies to wires, bars and strands used as prestressing tendons in concrete structures.

P(2) The requirements apply to the product in the condition in which it is delivered.

(3) The methods of production, the specified characteristics, the methods of testing and the methods of attestation of conformity are as defined in EN 10138 and other relevant Standards for prestressing materials.

P(4) Each product shall be clearly identifiable with respect to the classification system in 3.3.2. P(5) Tensile strength (fp), 0,1 % proof stress (fp0,1) and elongation at maximum load (eu) shall all be appropriately specified in relevant Standards, and established by standard tests.

(6) For steels complying with this Code, tensile strength, 0.1 % proof stress, and elongation at maximum load are specified in terms of characteristic values; these values are designated respectively fpk, fp0.1k and euk.

3.3.2 Classification and geometry

P(1) The products (wires, strands and bars) shall be classified according to:

i) Grade, denoting the value of the 0,1 % proof stress (fp0.1k) and the value of the tensile strength (fpk) in N/mm2.

ii) Class, indicating the relaxation behaviour iii) Size iv) Surface characteristics.

P(2) Each consignment shall be accompanied by a certificate containing all the information necessary for its identification with regard to i)-iv) in (1) above and additional information where necessary. P(3) The actual cross sectional area of the products shall not differ from their nominal cross sectional area by more than the limits specified in the relevant standards.

P(4) There shall be no welds in wires and bars. Individual wires of strands may contain staggered welds made only before cold drawing.

P(5) For coiled products, after uncoiling a length of wire or strand lying free on a flat surface, the maximum bow height from a base line of specified length shall be less than the values specified in the relevant standards.

P(6) In this Code, three classes of relaxation are defined (see 3.3.5.2); Class 1: for wires and strands, high relaxation Class 2: for wires and strands, low relaxation Class 3: for bars.

P(7) Where required, surface characteristics of prestressing steel shall comply with EN 10138 or other relevant Standards.

3.3.3 Physical properties

P(1) The following mean values may be assumed:

— coefficient of thermal expansion: 10 x 10-6/°C.

3.3.4 Mechanical properties

3.3.4.1 Strength

P(1) The 0,1 % proof stress (fp o.1k) and the specified value of the tensile strength (fpk) are defined as the characteristic value of the 0,1 % proof load and the characteristic maximum load in axial tension respectively, divided by the nominal cross sectional area.

P(2) The ratio of the actual maximum load to the specified maximum load shall not exceed the values specified in EN 10138 or other relevant Standards.

3.3.4.2 Stress-strain diagram

P(1) Stress-strain diagrams for the products, based on production data, shall be prepared and made available by the producer as an annex to the certificate accompanying the consignment [see 3.3.2(2)].

3.3.4.3 Ductility characteristics

P(1) The products shall have adequate ductility in elongation, as specified in relevant Standards.

(2) Adequate ductility in elongation may be assumed if the products obtain the specified value of the elongation at maximum load ((uk) given in EN 10138 (see Figure 3.3).

Prestressed Steel Stress Strain

P(3) The products shall have adequate ductility in bending.

(4) Adequate ductility in bending may be assumed if the products satisfy the requirements for bendability of the relevant standards.

P(3) The products shall have adequate ductility in bending.

(4) Adequate ductility in bending may be assumed if the products satisfy the requirements for bendability of the relevant standards.

3.3.4.4 Modulus of elasticity

(1) A mean value of 200 kN/mm2 may be assumed for wires and bars. The actual value can range from 195 to 205 kN/mm2, depending on the manufacturing process.

(2) A value of 190 kN/mm2 may be assumed for strand. The actual value can range from 175

to 195 kN/mm2, depending on the manufacturing process. Certificates accompanying the consignment should give the appropriate value.

3.3.4.5 Fatigue

P(1) The products shall have adequate fatigue strength.

(2) For fatigue requirements of prestressing steel, see Part 1E and relevant Standards.

3.3.4.6 Multi-axial stresses

P(1) The behaviour of the products under multi-axial stresses shall be adequate.

(2) Adequate behaviour under multi-axial stresses may be assumed if the products satisfy the requirements specified in the relevant standards.

3.3.5 Technological properties

3.3.5.1 Surface condition

P(1) The products shall be free from defects which could impair their performance as prestressing tendons.

(2) Longitudinal cracks need not be considered as defects if their depth is less than the values specified in EN 10138 or other relevant standards.

3.3.5.2 Relaxation

P(1) The products shall be classified for relaxation purposes, according to the maximum percentages of loss of stress.

3.3.5.3 Susceptibility to stress corrosion

P(1) The products shall have an acceptably low level of susceptibility to stress corrosion.

(2) The level of susceptibility to stress corrosion may be assumed to be acceptably low if the products comply with the criteria specified in relevant Standards.

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Responses

  • ferruccio
    How to find characteristic tensile strength of prestressed steel?
    2 years ago
  • hagosa nasih
    What is mean in prestress tendon st 1570/1770 and fp0.1k?
    1 year ago

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