Research On Wind Resistance Of Screw Joints Used In Light-weight Steel Roof

As an important component of light-weight steel roof cladding, screw joints are very sensitive to the winds because of their construction furthers, such as the sheets are light, thin and soft, connection is weak and so on. According to a large body of site surveys of wind-induced damages, screw joints that used in the light-weight steel roof claddings often suffer the wind-induced static as well as fatigue damages and lead to damage of the whole roof systems, thus cause great economical loss. However, few researches have been done with respect to the damages of such screw joints that used in the light-weight steel roof. Consequently, it is necessary to study this kind of joints comprehensively. Selecting the screw joints in the light-weight steel roof cladding as the objective, this thesis studied the static and fatigue performances of screw joints under wind loadings based on the numerical and experimental method. Then an estimation method was further proposed to evaluate wind-induced fatigue damages and estimate the fatigue life of the screw joints.The detailed research contents are as following:(1) Based on the finite element software ABAQUS, a non-linear numerical model of light-weight steel roof cladding was created and the studies of how the thickness of plate, yield strength as well as the plate types influence static wind resistance of screw joints were performed. By fitting the numerical results of the parameter analysis, the design formula of vertical bearing capacity of screw joints were obtained considering different thickness of plate in the light-weight steel roof cladding. Furthermore, this obtained design formula can also be used as a reference when performing the wind resistant design of light-weight steel roof cladding.(2) Based on the experimental method, constant amplitude cyclic loading fatigue test of screw joints was performed. During the test, the fatigue crack growth and the changes of displacement amplitude of the screw joint were observed and summarized under different level of cyclic loading. In the light of the local deformation, crack initiation as well as the growth state of the joint from the test, fatigue damages of the joint were classified and the relationship between damage types and the cyclic loading amplitude were further confirmed in the meanwhile. By analyzing the strain data from the test, it can be concluded that time history curve of the strain can be used to describe the deformations as well as the crack growth of the areas near the screw joint efficiently.(3) According to the statistical estimation theory, semi-log fatigue life curve, say, bearing capacity ranges versus Logarithmic cyclic number S-lgNf curve was obtained by performing regression analysis of the experimental data from constant amplitude cyclic loading fatigue test of screw joints. In the light of the elastic-plastic time-history analysis of double-span roof cladding model and fatigue curve of the screw joints, a general method was proposed to evaluate wind-induced fatigue damage of screw joints. In order to check the validation of the proposed method mentioned above, a case study was also done and the results showed that this method can be used as an efficient and simple tool to predict the wind-induced fatigue of screw joints in the light-weight steel roof system.