kruip – BuildSoft Support https://support.buildsoft.eu BuildSoft Support Thu, 25 Jan 2024 08:29:14 +0000 en-US hourly 1 https://wordpress.org/?v=6.2.11 What is kdef (creep timber)? https://support.buildsoft.eu/knowledge-base/what-is-kdef/ Wed, 28 Jun 2017 13:29:18 +0000 http://buildsoftsupport.com/?post_type=ht_kb&p=1282 The stiffness properties of timber depend on the timber type (solid, glued, …) and the climatic conditions (temperature, moisture variations). The effect is taken into account by the factor kdef.

According to Eurocode

  • Values for kdef are given in EN 1995-1-1 Table 3.2.
  • kdef is used to calculate the final mean values of the stiffness properties according to EN 1995-1-1 §2.4.1.
Design values Mean values Final mean values

    \[ E_d=\frac{E_m_e_a_n}{\gamma_m} \]

    \[ E_m_e_a_n \]

    \[ E_m_e_a_n_._f_i_n=\frac{E_m_e_a_n}{1+\Psi_2 k_d_e_f} \]

    \[ G_d=\frac{G_m_e_a_n}{\gamma_m} \]

    \[ G_m_e_a_n \]

    \[ G_m_e_a_n_._f_i_n=\frac{G_m_e_a_n}{1+\Psi_2 k_d_e_f} \]

 

In Diamonds

  • The values for kdef are implemented in the material library of Diamonds.

  • When you check the option ‘Take creep into account’ after clicking , the final mean value for Young’s modulus E_m_e_a_n_._f_i_n will be used. \Psi_2 is set equal to 1.

 

Note: PowerFrame cannot take kdef into account. Only Diamonds can.

]]> Why are there 2 creep factors? https://support.buildsoft.eu/knowledge-base/why-are-there-2-creep-factors/ https://support.buildsoft.eu/knowledge-base/why-are-there-2-creep-factors/#respond Mon, 03 Apr 2017 07:00:24 +0000 http://buildsoftsupport.com/?post_type=ht_kb&p=550 In Diamonds (and ConCrete) you will see two creep factors \varphi:

  • Creep factor for stress limit \varphi_{stresses}:  this factor is taken into account when checking the steel and concrete stresses in SLS. \varphi_{stresses} is calculated so that the ratio

        \[ \frac{E_s}{E_{c,\infty}} = \frac{E_s}{\frac{E_{c,28}}{1+\varphi_{stresses}}} = 15 \]

        \[ \varphi_{stresses} = \frac{15 \cdot E_{c,28}}{E_s} -1 \]

    For concrete C25/30 this becomes

        \[ \varphi_{stresses} = \frac{15 \cdot 30472N/mm^2}{200 000N/mm^2} - 1 = 1.285 \]

  • Creep factor for deformation \varphi_{deformation}:  this factor is taken into account when calculating the cracked deformation (only if you opted to calculate with creep). \varphi_{deformation} is determined from EN 1992-1-1 Fig. 3.1, \varphi_{deformation}=2 is a ‘standard’ value.

If the creep factor for stresses \varphi_{stresses} would be 2, there is a less probability to ever have to add additional reinforcement because the concrete stresses decrease at increasing creep factor. This would lead to discussions about not calculating sufficient reinforcement.

So to be on the safe side, we need different creep factors for stresses and deformation.

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