Study On Structural Behavior Of Damaged Steel Frame

Many of existing steel structure failure is in fact partial buckling failure caused by overcritical loads in stead of overall instability caused by the ultimate strength. In these situations, most elements of the structure are not intensively damaged and loss the stabilities. To achieve the maximum economic benefit while ensuring the safety, the partial damaged structure should be analyzed with a proper calculation model to guarantee the safe operation and usage requirements. In this thesis, a major theme here is how the partial damaged influences structure’s behavior with the secondary loading. Referred to the damage assessment method in the classical damage mechanic book which considering elastic modulus decrease, the damaged steel frame structure is analyzed from the four levels:material, cross section, element and structure.Firstly, Experimental study on material property variations about damaged steel with standard specimens’ shows that different degrees of damage led to decline of elastic modulus in different way. This conclusion is obtained from the tests of Q235steel. The rule of elastic modulus decreases has been analyzed, and a new calculating method of elastic modulus of damaged steel is studied in this thesis. It can modify the constitutive relation of steel.Secondly, the damage degree of cross section is Analyzed, for example, I-section. Defining K, it’s a ratio of the length of section is not destroyed part to the length of whole section. Categorizing different degrees of damage by K, and, deriving the method for calculating the average elastic modulus of I section which is damaged. According to the stiffness degradation rules defining section damage index D. Analyzing the relationship between D and K, and print D-K curve.Thirdly, the partial damaged element is analyzed by postulating that damaged infinitesimal element is a rotation springs. Under the second load the springs bearing certain bending moment, at the same time, it generates corresponding rotation displacement. The relationship of moment and rotation can be expressed by this model appropriately. The key of this model is the rotational stiffness R, the function of R contains K is obtained.Finally, spring model simulate the damaged part of steel frame, the mechanical property of damaged structure is analyzed, Crafting a program for analyze the damage degree of structure by FORTRAN. Increased generalization of counting methods which is summarizes in this thesis. At the end of this thesis, the numerical example of damaged steel frame is analyzed by using the program. The contrast of damaged structure and intact structure shows the change rules of internal force and deformation. This analysis method can verify the safety performance of the structure, for example, in the numerical example, some story drift is over-limit when structure partial failure.