7. Assumptions#

Below are a list of assumptions and conventions used by concreteproperties:

7.1. General#

  • Plane sections remain plane (Euler-Bernoulli) i.e. linear strain profile throughout the cross-section

  • For a given depth, the strain in the reinforcement is equal to the strain in the concrete, i.e. there is a perfect bond between concrete and reinforcement

  • Materials that have meshed=False (e.g. SteelBar) are characterised by a constant strain at it’s geometric centroid

  • Stresses in materials are determined from strains by linear interpolation from the corresponding stress-strain profile (linear extrapolation is used where the strains are outside the range of the profile)

  • All moments in service and ultimate analyses (moment-curvature, ultimate bending, moment interaction, biaxial bending, service stress, ultimate stress) are calculated about, or assumed to be about the gross centroid (no material properties applied), unless otherwise specified in the intitialisation of ConcreteSection

  • Moment inputs for elastic stress analysis (cracked and uncracked), are assumed to be taken to be about the geometric centroid (material properties applied)

  • Finite element assumptions and background can be found here

7.2. Cracked Analysis#

  • Concrete is assumed to have zero tensile strength

7.3. Ultimate Analysis#

  • The maximum strain at the extreme concrete compression fibre is assumed to reach a maximum limiting compressive strain, see note in Concrete Ultimate Stress-Strain Profiles

  • The tensile strength of the concrete is assumed to be zero

  • There are no geometric instabilities (e.g. buckling) prior to the cross-section reaching its ultimate strength

  • The stress-strain relationship for concrete may be assumed to be rectangular, trapezoidal, bilinear, parabolic, or any other arbitrary shape that results in the prediction of strength in substantial agreement with the results of comprehensive tests

7.4. Conventions#

  • Compressive stresses are positive, tensile stresses area negative

  • Angles are measured in radians and are positive counter clockwise from the positive x axis

7.5. Prestressed Analysis#

  • All prestressing strands are fully bonded to the concrete

  • Internal actions arising from prestressing forces are automatically included in all analyses