In this paper, a practical design procedure for thin-skinned steel-composite composite panels subjected to axial or flexural loadings is developed. Ignoring the adhesive forces between steel and core concrete, steel skins may be modeled as thin plates resting on tensionless rigid or elastic foundations (concrete material). Sections of steel skin tend to become separated (delaminated) from the core concrete and buckle away from it, while other areas keep contact with the inside material. This phenomenon is named as contact buckling. Based on the governing equations of thin plates in contact area and noncontact area, initial buckling response of thin skins may be obtained. Then it becomes possible to use effective width-based formulas to deduce ultimate strengths of the unilaterally constrained skins. At last, design formulas for section capacity of composite members due to axial and flexural loadings are developed.