The Safety Assessment Theory Of Plane Bar Structures Based On The Failure Envelope

When a building comes forth disrepair or the hidden trouble because of suffering heavy load or materials deterioration, its damnification state and safety state should be exactly assessed to predict the structure's reliability of the next target life and form the most excellent reinforcement and maintenance strategies. therefor, the notion of structural failure envelope is proposed in this paper, and based on this to execute structure's safety assessment from the geometrical. This method has novel concept, intuitionistic expression and the advantages of visualization for the structural safety state. The related research of this article mainly includes the following:(1) On the failure assessment theory of pure bending, the notion of failure envelope in different levels and the general residual safety index under the axis force and bending moment is proposed, namely: the bar sectional failure envelope and failure approaching indexes, the bar element's failure envelope and failure approaching indexes and the structrue's failure envelope , failure approaching index and residual safety index. The problem of bar element's division density is discussed in this chapter and a frame of 3 spans and 6 storeys is computed as an example.(2) Import coefficient of each members will be calculated from the energy point of view. This part is a special study in order to calculate the general failure approaching index of structure. By mean of removing a single bar can cause a changing rate of structure's external potential energy ,the size of the changing rate is to determine the size of bar's import coefficient. The difference of the bar import coefficients between the proportional loading and non-proportional loading will be discussed. And the bar's import coefficience values of a frame of 3 spans and 6 storeys will be calculated for various loads, various ratios between the stiffness factors of the beams and the columns.(3) Using the theory in this paper, the failure envelope of a few typical structures, such as beams, trusses and composite structures, the general failure approaching index and residual safety index are computed under the commonly used loads. Thereinto, On the beam, the article will analyse and compare the security status of the statically determinate structure, statically indeterminate structure and as the structure's number of the statically indeterminate increased; The truss will compare the security status of different structure forms such as triangular roof trusses, trapezia roof trusses and so on; and the composite structures will compare the different status between statically determinate structure and statically indeterminate structure.(4) The collapse order as the structure destroyed will be studied. It will calculate and analyse a frame of 4 spans and 3 storeys' collapse order under the proportional load and non-proportional load. The method is: given the ratio of load, increasing the load range until the first failure pole appears, calculate the general failure approaching index; and then remove the failure bar, continue to increase the loading range until the second or more poles fail, and then calculated the general failure approaching index value again. Repeat these steps until the general failure approaching index value equal to 1, the structure collapsed completely, record the process, the order of failure bars as a description of the character of structure's collapse or destroy .