Answer :

Solution :

External tensile load applied to a no preloaded joint transmits entirely to the bolt. The stiffness of a bolted joint without a preload equals the bolt stiffness K_e = K_b. For a preloaded bolted joint, joint stiffness is the sum of bolt & clamped member stiffness k_e = Kb + K_c. Therefore, preloading increases the stiffness of the bolted joints, which also increases the resonant frequency of an assembly.

Note:

However, once a joint is preloaded, increasing the magnitude of the preload can not make a joint stiffer.