In the current work, using the method of gluing in combination with the method of initial parameters, we derive a strict closed linear theory for a regular spatial girder of orthogonal structure, an elementary cell of which has the shape of a rectangular parallelepiped with one diagonal column at each of its faces. The theory derived is a discrete analogue to the spatial theory of elasticity, within the frames of which we present the alternative statements of problems in the node displacements and in the initial loads of columns. We demonstrate the theory application by the example of a composite column without internal nodes of finite, infinite, and semi-infinite length. For all of these cases, we obtain the exact analytical solutions. We also present the results of calculations for some particular problems.