Abstract: The bar element of failure assessment for the plane frame structure is defined. The normalized end moment and normalized end curvature of the element are introduced. The failure envelope, the state diagram, and the failure index of the failure-assessment bar element are presented. Then the failure envelope, the state diagram, and the failure index of the plane frame structure are initiated. Three structure failure indexes are constructed considering the probability distribution. The weighted average and maximum value are obtained form the distribution of the points in the diagram representing the elements, respectively. As a geometrical scheme, the structure failure assessment which differs from the common damage assessment depending on the physical property variation of the structure is implemented concisely and graphically with these failure indexes. A frame of 3 spans and 6 storeys is analyzed. The failure indexes of the frame are solved for various loads, ratios between stiffness factors of the beams and columns, and division density of the failure-assessment bar element.