Types of fire resistance calculation

Three types of calculation are implemented in the program:

• Detailing provisions,

• Simplified method,

• Advanced method.

Detailing provisions

Detailing provisions will be setting in Concrete setup.

There are three type of calculation (adjusted globally in the Concrete > Setup or individually for each beam in the Member Data):

• Automatic,

• From temp. curve,

• Input by user.

Detailing provisions are checked only if the check box Check detailing provisions for fire resistance (Concrete > Setup > Detailing provisions > Fire resistance) is ON.

Detailing provisions are supported only for:

• any load case, combination and class in case of "Automatic" and "Input by user" calculation,

• only for a load case, combination and class with defined Temperature distribution curve in case of "From temp. curve".

Only the check of practical reinforcement is supported.

The value Standard fire resistance R (Fire duration) used for the calculation of values b_min, a_min and h_s,min from tables is defined by:

• the temperature distribution curve for type of calculation "from temp.curve",

• the value in Concrete setup or Member data for other type of calculation.

The value Critical temperature Theta_cr for modification of a_min and b_min is:

• loaded from Concrete setup or Member data for type of calculation = "Input by user",

• loaded from Temperature distribution curve for type of calculation = "from temp. curve",

• calculated according to chapter 5.2(6) for type of calculation = "Automatic" .

Function Check fire resistance-detailing rules is added to Member check > Concrete Fire Resistance check.

Simplified method

This type of calculation is supported only for accidental combinations:

• EN-ULS Accidental – Psi1,

• EN-ULS Accidental – Psi2.

Only Check capacity and Check response functions are supported.

Check capacity and Check response are performed for changed cross-section and materials properties

• changes in cross-section properties:

• • reduced height of section (damaged zone),

  • new eccentricities.

• changes in materials properties of concrete and non-prestressed reinforcement:

• • new stress/strain diagram,

  • thermal expansion coefficient,

  • reduced ultimate limit strain,

  • reduced strength,

  • reduced module of elasticity.

Shear capacity is calculated according to EN 1992-1-1, but with following changes:

• reduced strength f_cd (temperature in centroid of section),

• reduced strength f_ctd (temperature in centroid of section),

• reduced geometry of cross-section,

• reduced strength of stirrups f_sd (the reference temperature is the temperature in the point P (intersection of the branch of a stirrup with the section a–a, where the section a–a is the boundary of the effective tension area calculated according to EN 1992-1-1, chapter 7.3.2 (3)

For members with prestressed reinforcement there are the following simplifications:

• check is performed only for a member that is statically determined (simply supported beam, cantilever). This property can be adjusted in the Member data dialogue,

• all initial stresses are set to zero (We justify this step by the assumption that all stresses relaxed at high temperature - due to accelerated concrete creep and steel relaxation),

• check shear is not supported for members with prestressed reinforcement.

There are four functions under Concrete Fire Resistance Check:

• Check fire resistance response,

• Check fire resistance capacity,

• Prestress check fire resistance response,

• Prestress check fire resistance capacity.

Advanced method

Functionality Physical non-linearity for reinforced concrete must be ON.

The calculation of fire resistance through the physically (and geometrically) nonlinear calculation is not possible for members with prestressed reinforcement.

Three types of calculation are supported (prefire, during fire and post-fire) and depend on the type of a nonlinear combination ("prefire", "during fire" and "post fire").

Only nonlinear combinations can be used.

Practical reinforcement should be manually editing after each calculation.

Prefire calculation – standard physically (and geometrically) nonlinear calculation is carried out without any changes in the member and material properties for nonlinear combinations without a load case of type "Temperature distribution curves"

During fire calculation – standard physically (and geometrically) nonlinear calculation is carried out with changes in the member (reduced cross-section, new eccentricities) and material properties (new stress/strain diagram) for nonlinear combinations with load case of type "Temperature distribution curves"

Post fire calculation – standard physically (and geometrically) nonlinear calculation is carried out with changes in member (reduced cross-section, new eccentricities) and material properties (new stress/strain diagram) for nonlinear combinations without load case of type "Temperature distribution curves".

The results are presented in functions PNL stress/strain and PNL stiffness of service Results.