Ladder frames are widely used in multi-body flexible structures such as chassis of an automotive vehicle, aircraft and spacecraft frames, robots, and road bridges. The finite element method (FEM) is widely used to determine the modal characteristics of such structures. Any design modification requires regeneration of the new geometry, followed by FE modeling. This involves considerable time and effort. In order to reduce this effort, two different formulations based on binary asymptotic admissible functions (BAAF) are proposed. The results from these two proposed formulations are compared with those from a conventional FE model. A good correlation of the results is observed. In the continuous formulation, the horizontal member of the ladder frame structure is modeled as the Euler-Bernoulli beam, and the vertical members (cross-members) are modeled as an axial bar. The continuous formulation is demonstrated to work very well over a large range of horizontal member to vertical member length ratios. Detailed design curves have been proposed to help make quick decisions in the early design stages of the ladder structure. Further, a discrete formulation is proposed wherein the cross-members of the ladder frame structure are replaced by equivalent lumped masses and springs at the beam-bar interface. The discrete model formulation is computationally efficient since the bar is replaced with discrete elements. A comparison between the continuous model and discrete model was carried out, and guidelines are proposed.