Arch bridge,the basic principle is through a horizontal thrust originally produced by the load of the bending stress to compressive stress or most into compressive stress.And the arch is upward convex surface,surface effect,the maximum principal stress arch bridge vertical direction along the arch bridge,the minimum principal stress is zero.Arches of the difference between the largest parts of the beam is horizontal thrust,if the horizontal thrust and bearing reaction force and resultant force with the load acting on the point and direction just right through the axis of the arch,arch is reasonable arch,that arch is a compressive stress.If they are not overlap,then there is a bending stress. Arch bridge,the basic principle is through a horizontal thrust originally produced by the load of the bending stress to compressive stress or most into compressive stress.And the arch is upward convex surface,surface effect,the maximum principal stress arch bridge vertical direction along the arch bridge,the minimum principal stress is zero.Arches of the difference between the largest parts of the beam is horizontal thrust,if the horizontal thrust and bearing reaction force and resultant force with the load acting on the point and direction just right through the axis of the arch,arch is reasonable arch,that arch is a compressive stress.If they are not overlap,then there is a bending stress.