As reported in the literature, structural domains in (110) oriented rhombohedral La1-xSrxMnO3 (LSMO) films on (110) SrTiO3 show a pattern with alternating domain widths and inclined domain walls. An appropriate one-dimensional periodic domain model was developed and the non-uniform strain field in a coherently grown film was calculated by applying the coherency-defect approach. The strain is sharply peaked at the junction of the domain walls and the film/substrate interface. The dependence of the equilibrium domain-width ratio and domain-pattern period on film thickness was determined by minimizing the sum of elastic and domain-wall energies. The proposed domain structure can be formed only in a certain range of the film's crystal-structure data compared to the substrate. Corresponding composition-dependent structure data of LSMO are compiled.