Lateral stiffness of pipe support for reciprocating compressor

[Thanit]

As per API 618 minimum stiffness refers axial stiffness in equations: k_eff= 0.66 x n x k_s
and minimum k_s= C_KS x A^0.75 x I^0.25 x f_n,T^1.5(n-1/n)

I would like to know the formula of lateral stiffness.

Is there anybody know the base formula behind these two equations and how to find lateral stiffness of pipe support for reciprocating compressor?