contribution factor

[DODO]

В приведенном ниже контексте (европейский стандарт) непонятен термин contribution factor. Помогите его перевести. Пжоалуйста !

The linear thermal transmittance of the joints (ψ) for the calculation of thermal transmittance U according to Equation (A.26) shall be determined according to EN ISO 10211-2 and given per metre length of panel.
Alternatively the linear thermal transmittance contribution factor of the joints (fjoint) shall be obtained from Table A.3 for steel faces according to the generic type of joint (see Figures A.17 to A.21) and used to determine the thermal transmittance U in accordance with Equation (A.28).