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Prestressing steel

 
Prestressing Steel General Properties
 
General properties are those properties common to all concrete materials. These properties have labels and values described hereafter:
 
Prestressing Steel General Properties
Name
Material name
 
Type
Prestressing steel
 
E
Elastic modulus
Automatically defined from material library
 
ν
Poisson ratio ()
Default value depends on the active code:
ν = 0.3        Eurocode 2
ν = 0.3        ACI
ν = 0.3        EHE
 
ρ
Density
 
Act. time
Activation time
 
Deact. time
Deactivation time
 
G
Shear modulus. Is calculated using the formula:
 
α
Coefficient of linear thermal expansion
Default value depends on the active code:
α = 1.0E-5 (ºC-1)    Eurocode 2 (Art 3.2.3)  
α = 1.0E-5 (ºC-1)    ACI 318
α = 1.0E-5 (ºC-1)    EHE
 
Damping
Damping properties
 
 
 
Prestressing Steel Specific Material Properties
 
Specific material properties are always available for a particular material, regardless of the code under which the material was defined.
 
Prestressing Specific Steel Properties
μ
Friction coefficient for tendon-sheathing
μ = 0.2 (default value)
k
Unintentional angular displacement per unit of length
k= 0.01 m-1 (default value)
Slip
Anchorage slip
Slip= 0.006 m (default value)
Ε shrink
Concrete shrinkage strain
Slip= 0.0004 m (default value)
ϕ
Creep coefficient for concrete
ϕ = 2.00 m (default value)
Analysis σ-ε diagram
Analysis stress-strain diagram. Each different type of stress-strain diagrams available depends on the code for which the material was defined. Apart from available diagrams supported by the codes, it is possible to define new diagrams by changing the table data.
SAε:  Strain values corresponding to a point of the diagram.
SAσ: Stress values corresponding to a point of the diagram.
 
Design σ-ε diagram
Design stress-strain diagram. Each different type of stress-strain diagrams available depends on the code for which the material was defined. Apart from available diagrams supported by the codes, it is possible to define new diagrams by changing the table data.
SDε:  Strain values corresponding to a point of the diagram.
SDσ: Stress values corresponding to a point of the diagram.
 
ε max
Maximum admissible strain in tension at any point of the section (Point A in the pivot diagram).
Sign criterion: + Tension, - Compression
ε max  0, if ε max = 0, there is no limit
The initial value depends on the active code:
ε max = 0.010    Eurocode
ε max = 0            ACI (there is no limit)
ε max = 0.010   EHE
 
 
 
Prestressing Steel Specific Code Properties
 
There are some properties in CivilFEM that are code dependent. Code dependent properties are described hereafter for prestressing steel materials supported by CivilFEM.
 
Prestressing Steel σ-ε diagrams
Codes
Analysis σ-ε diagram
Design σ-ε diagram
EC2_08,  EC2_91, ITER
Bilinear
BilinearHorizTopBranch
BilinearInclinedTopBranch
EHE-98, EHE-08
Bilinear
Characteristic
Design
ACI318
Bilinear
Bilinear
 
1. Eurocode 2 (Prestressing Steel) Properties
 
For this code, the following properties are considered:
 
Eurocode 2 Prestressing Steel Properties
γs
Partial safety factor (GAMs  0) 
γs = 1.15 (default value)
 
εuk
Characteristic elongation at maximum load
 
fpk
Characteristic tensile stress (fpk  0)
 
fp01k
Characteristic stress that produces a residual strain of 0.1% (fp01  0)
 
ρ60
Relaxation for 1000 hours and 60%fpk
 
ρ70
Relaxation for 1000 hours and 70%fpk
 
ρ80
Relaxation for 1000 hours and 80%fpk
 
Relax. ratio
Long term relaxation/1000 hours relaxation ratio
 
 
Stress Strain Diagram for Structural Analysis
 
The available stress-strain diagrams for Eurocode 2 are the following:
 
 
a)     Definition of the elastic diagram
 
Number of diagram points = 2
 
The sign criterion for the definition of points of the stress-strain diagram is as follows:
 
 
Strain points are the following:
 
 
Stress points are the following:
 
 
b)     Definition of the bilinear diagram
 
Number of diagram points = 3
 
The sign criterion for the definition of points of the stress-strain diagram is as follows:
 
 
Strain points are the following:
 
 
Stress points are the following:
 
 
Stress-Strain Diagrams for Section Analysis
 
The different types of stress-strain diagrams available are:
 
 
a)     Definition of the bilinear diagram with horizontal top branch stress-strain
 
Number of diagram points = 3
 
The sign criterion for the definition of points of the stress-strain diagram is as follows:
 
 
Strain points are the following:
 
 
The corresponding stress points are the following:
 
 
b)     Definition of the bilinear diagram with inclined top branch stress-strain
 
Number of diagram points = 3
 
The sign criterion for the definition of points of the stress-strain diagram is as follows:
 
 
Strain points are the following:
 
 
The corresponding stress points are the following:
 
 
 
2. ACI 318-05 (Prestressing Steel) Properties
 
For this code, the following properties are considered:
 
ACI 318-05 Prestressing Steel Properties
fy
Yield strength
fyd
Design strength
fpu
Tensile strength
fpy
Yield strength
Type
Prestressing steel type:
Low-relaxation
Stress-relieved
 
Relax. Coeff. 1
Relaxation coefficient 1
Relax. Coeff. 2
Relaxation coefficient 2
 
Stress Strain Diagram for Structural Analysis
 
The available stress-strain diagrams for ACI 318-05 are the following:
 
 
a)     Definition of the elastic diagram
 
Number of diagram points = 2
 
The sign criterion for the definition of points of the stress-strain diagram is as follows:
 
 
Strain points are the following:
 
 
Stress points are the following:
 
 
b)     Definition of the bilinear diagram
 
Number of diagram points = 3
 
The sign criterion for the definition of points of the stress-strain diagram is as follows:
 
 
Strain points are the following:
 
Stress points are the following:
 
 
Stress-Strain Diagrams for Section Analysis
 
The different types of stress-strain diagrams available are:
 
 
a)     Definition of the bilinear diagram
 
Number of diagram points = 3
 
The sign criterion for the definition of points of the stress-strain diagram is as follows:
 
 
Strain points are the following:
 
 
The corresponding stress points are the following:
 
 
 
3. EHE (Prestressing Steel) Properties
 
For this code, the following properties are considered:
 
EHE Prestressing Steel Properties
fmax
Characteristic tensile strength (Art.32.2)  fmax  0
 
γs
Strength reduction factor (Art. 15.3)   γs  0
 
εuk
Characteristic elongation at maximum load (Art. 38.2)  (εuk  0)
 
fpk
Characteristic yield stress (Art. 38.6) fpk  0
 
ρ1 60
Relaxation for 100 hours and 60%fmax
 
ρ1 70
Relaxation for 100 hours and 70%fmax
 
ρ1 80
Relaxation for 100 hours and 80%fmax
 
Stress Strain Diagram for Structural Analysis
 
The available stress-strain diagrams for EHE are the following:
 
 
a)     Definition of the elastic diagram
 
Number of diagram points = 2
 
The sign criterion for the definition of points of the stress-strain diagram is as follows:
 
 
Strain points are the following:
 
SAε   (1)= -1.0E-2
SAε   (2)= 1.0E-2
 
Stress points are the following:
 
 
b) Definition of the bilinear diagram
 
Number of diagram points = 4
 
The sign criterion for the definition of points of the stress-strain diagram is as follows:
 
 
Strain points are the following:
 
 
Stress points are the following:
 
 
c)     Definition of the characteristic diagram
 
Number of diagram points = 20
 
The sign criterion for the definition of points of the stress-strain diagram is as follows:
 
 
Strain points are the following (Art 38.5):
 
 
Points from 3 to 20:
 
 
Stress points are the following:
 
 
 
Diagrams for Section Analysis
 
The different types of stress-strain diagrams available are:
 
 
a)     Definition of the design diagram
 
Number of diagram points = 20
 
The sign criterion for the definition of points of the stress-strain diagram is as follows:
 
 
Strain points are the following (Art 38.6):
 
 
Points from 3 to 20:
 
 
Stress points are the following: