Performance Analysis Of Damaged Lightweight Steel Structures Under Disaster Loading

Lightweight steel structure is mainly used for monolayer industrial factory building. Because of the characters of light material and relatively large span, there will be stress concentration and large deformation in lightweight steel structure when subjected to storm, heavy snow and other strong disaster loading. For the steel structure, damage is start from the local site, especially for the welding and corrosion sites. These sites often reach the plastic stage and lose effectiveness while the whole structure is in the elastic stage when storm and snowstorm come, which initiates the failure of the whole structure.If we can detect the actual damage through the damage detection technology, then set up the finite element model according to the corresponding physical model and introduce the damage into the whole structure model to realize model updating. The affection of local damage to the whole structure can be got by comparing the performance analysis of damaged structure with the original structure under disaster loading. The project makes sense to the performance analysis of damaged lightweight structures under disaster loading.Facing to the lightweight steel structures with information of damage detection, around the problems of modeling for damaged lightweight steel structures, ultimate performance analysis of damaged lightweight steel structures, the elastic-plastic analysis and fracture analysis of local component. Using finite element software ANSYS to establish multi-scale models which can reflect the local details of lightweight steel structures. Using the method of consistent multi-scale analysis to realize the nonlinear analysis and fracture analysis of local component when the most part of structure is in the elastic stage. Make an accurate performance analysis of damaged lightweight steel structures which reveals the affection of local damage to performance of lightweight steel structures. The work and results of this research are briefly listed as below:1) Through the analysis of damage testing information of the lightweight steel structures, corrosion damage of the main part of structure and the welding crack are common in pratical engineering and have great influence on the performance of lightweight steel structures. Corrosion damage not only leads to the change of material mechanical properties, but also changes the local component section size of corrosion structure. According to the corrosion configuration of local component, corrosion damage can be divided into homogeneous corrosion damage and inhomogeneous corrosion damage.The welding crack in light steel structure is mainly perforative and surface cracks in root of welding and welding heat effect regions of structure center and beam-column joints areas.2) Damage variables were defined to represent the corrosion damage basing on different mathematical models. The structure local homogeneous damage variable which was defined by the reduction of section bending stiffness can primly reflect the degree of local damage of lightweight steel structures, while the damage variable which was defined by the reduction of section area can not reflect that well. The damage variable of inhomogeneous corrosion damage can be defined by the max reduction of section bending stiffness, which neglects the effect of distribution of corrosion pits to the degree of damage.3) Multi-scale models of lightweight steel structures including corrosion damage were established basing on multi-scale finite element modeling strategy. Different scales and types of units were connected by the method of multipoint constraint equations. Responses of the structures without regard for damage and structures with corrosion under snow load were obtained by nonlinear analysis. Corrosion damage of the structure resulted in advanced plastic stage of the local structure, lower bearing capacity of structure and lower plastic deformation capacity of the structure while improved the stress level of local corrosion areas. Material of corrosion areas lost effectiveness in advance because of the stress concentration of corrosion pits, which leads to the failure of the whole structure.4) The variation law of the performance of the corrosion structure under snowstorm with the change of corrosion damage was revealed by comparison of performance of different corrosion structures. It shows that with the increase of corrosion depth, corrosion damage degree increases, the bearing capacity of structure with corrosion damage decreases, and the rate of reduction is faster and faster. The decrease of bearing capacity is proportional to the depth of corrosion pit when corrosion is in a light degree. When the depth of corrosion pit is more than half of the section size, bearing capacity of structure quickly reduces and the rate of reduction is significantly higher than that of the depth of section. The structure bearing capacity changes indeterminately with the increase of corrosion pit radius and surface density change, there are some fluctuations.5) Through the establishment of different types and different length of cracks, which were introduced into the multi-scale model of lightweight steel structures, the change of the fracture capacity of local structure of different welding crack was got by the loading of structure with and without cracks. The results show that the difference between the cracks of different type is reflected in local stress distribution of structure. The increase of crack length improve stress intensity factor of crack tip, which makes crack easier to be unstably propagating. For structures which contain crack in beam-column joint areas under snowstorm, with the increase of crack length, stress level of area of beam-column joints without the area of cracktip decreases with the decrease of plastic zone. The structure loses function when the crack length increases to a certain extent.