def _M_b_fi_t_Rd(chi_LT_fi, W_y, k_y_theta_com, f_y, gamma_M_fi):
    """
    [Eq. 5.61]
    :param chi_LT_fi: Reduction factor for lateral-torsion buckling in the fire design situation
    :param W_y: Sectional modulus (plastic for class 1 steel)
    :param k_y_theta_com: Reduction factor for yield strength at elevated temperature
    :param f_y: Steel yield strength
    :param gamma_M_fi: Partial safety factor
    :return M_b_fi_t_Rd: The resistant lateral torsion bending moment
    """

    M_b_fi_t_Rd = chi_LT_fi * W_y * k_y_theta_com * f_y / gamma_M_fi

    return M_b_fi_t_Rd