Under vertical loading, the movement tendency of sloped roof portal rigid frame is downward deformation of the roof ridge and outward deformation of the roof eaves.The roof panel will resist this deformation trend in the form of a deep beam together with the supporting purlins. In this case, the roof panel is subjected to shear force and acts as the web of the deep beam.And the edge purlin is subjected to axial force and acts as the flange of the deep beam.Obviously, the shear resistance of the roof panel is much greater than its bending resistance.Therefore, the skin effect refers to the resistance effect of the skin plate due to its shear stiffness to the load that causes deformation in the plane of the plate.For the sloped roof portal frame, resistance to vertical load effect of the skin effect depends on the roof slope, the greater the slope of the skin effect is more significant; and resistance to horizontal load effect of the skin effect with the reduction of the slope and increase.It is the skin unit that constitutes the skin effect of the whole structure.The skin unit consists of the skin plate between the two bays, edge members and connectors and intermediate members.The edge members are the two adjacent stiffeners and the edge purlins (ridge and eave purlins), and the intermediate members are the intermediate part purlins.The main performance indicators of the skin effect are strength and stiffness.