Refined Study On Impact Response And Failure Of Reticulated Shells

At present, space structures are always regarded as landmark of a region. They are of great significance of politics and economy. With the characteristics of flexibility and light-weighted, reticulated shells are one of the most representative space structures,which are used widely. Although impact is an accidental loading, the occurrence of construction work accident caused by impact has gradually increased due to war, terrorist attacks, aircraft crashing, falling objects caused by failure at construction and so on. Especially after 9/11 incident, experts and scholars paid much more attention to the effect of impact on buildings. In 1980 s, a light aircraft crashed into the Sao Paulo Exhibition Center, whose span is 260 m and with the roof of grid structure[1]. It indicated that the large-span structures might be impacted, so the research is realistic, arduous and crucial. However, the research on anti-impact of architectures is relatively backward at home and abroad. There are many problems need to be studied and solved, such as the dynamic constitutive relationship of material, analytical method of dynamic response, mode and mechanism of failure under impact and the impact of aircraft on the reticulated shell. The research to these problems are urgent and have realistic significance. First, the dynamic constitutive and failure model of Q235 B, which is used commonly,were proposed by experiment and numeric analysis. Then, based on Taylor impact test, a contrast test between the two kinds of material model was conducted. The results demonstrated that the corrected J-C model presented in this paper has a good forecasting ability of the deformation and fracture under high strain rate. A qualitative study of elastic impact, which is based on conservation of momentum and energy, is also conducted. The conclusions are that the elastoplasticity and size of the impactors, the roof sheathing and other factors should be taken into account in the numerical model. A numerical model for the study of dynamic response of reticulated shells under impact was established. With this sophisticated numerical model and via extensive parameter analyses, the dynamic response of the roof sheathing-latticed shell was studied systematically. And the failure mode was given; meanwhile, the law of impact failure was concluded. In order to verify the model and conclusions proposed in this paper, a drop impact test of reduced scale model of the reticulated shell is conducted. Finally, simulation analysis of the roof sheathing-latticed shell under aircraft impact is conducted. The comparison of simulated results with the domes, which don’t have roof sheathing, laid a foundation for the study of impact protection. The main work carried out in this paper is shown as following.1. Research on dynamic constitutive and failure mode of steel commonly used in reticulated shellsFocus on different strain rate, temperature and stress, experiments of steel which is commonly used in reticulated shells were carried out. Then the constitutive model of J-C and parameters of failure criterion were calibrated according to the experimental results. The temperature mollification of yield strength and the nonlinear temperature mollification of ductility can’t be described properly with the initial J-C model and failure criterion. The initial model of J-C constitutive and failure mode are modified properly in order to modify the fitting result. And the results are preferable.2. Establishment of the sophisticated numerical model for the reticulated shell under impactBy carrying out the Taylor impact test and using the revised J-C constitutive and the failure model, combined with the piecewise linear constitutive model and constant strain fracture model used before, the numerical simulation and comparison of the Taylor test were conducted. The results demonstrated that the corrected J-C model presented in this paper had a good forecasting ability to the deformation and fracture under high strain rate. Then, the impulse and work of the first elastic impact to the dome was gained by qualitative theoretical derivation. It also finds that the factors would affect the response of the reticulated shell. Based on above, the scheme of parameter analysis was determined. And the sophisticated calculated model for the analysis to the impact response of reticulated shell was established. The model was analysed by ANSYS/LS-DYNA, and it takes the size effect of impactors and material properties into account. Finally, the parameter analysis scheme and the model’s accuracy were verified via the typical examples.3. Impact dynamic response and failure law of reticulated shellBased on the sophisticated numerical model established above, via extensive parameter analysis, studied the impact dynamic response of the roof-sheathing reticulated shell systematically. Combining with the typical examples, three kinds of failure modes of the roof-sheathing reticulated shell were given, and each mode’s characteristic of dynamic response was also analyzed. The maximum response of the reticulated shell and the changing law of failure modes with the change of the impactors’ size were investigated. Furthermore, it indicates that the roof-sheathing has effects on the maximum response and failure modes of the reticulated shell under impact. And the effects are not always favorable. The law of failure for roof-sheathing reticulated shell under impact wers given.4. Drop impact test for reticulated shellThe falling weight tests are carried out on the reduced scale model s of latticed shells with or without roof-sheathing. The test includes measurement to the natural frequency of the model, elastic drop weight test and ruinous test. In order to carry out numerical simulation and calculation, the numeric model for latticed shell under impact was present. Compared the results of simulation and experiment(the comparison of natural frequency, axis stress of the members under elastic impact and so on), the accuracy of the numerical model was verified. The conclusion that roof sheathing did affect the failure mode of reticulated shell under impact is also verified.5. Study on reticulated shell subjected to aircraft impactThe small passengers plane of Challenger Bombardier 850 was chosen as a prototype to establish a model for the research. A numerical model for latticed shell under airplane strike was established according to the model described above. The principles to establish the numerical model for airplanes were determined. Simulation of reticulated shell under four different conditions was conducted. Comparing with the failure mode without roof-sheathing taken into account, the conclusion was that the effect of plane’s wings on the study cannot be neglected. The failure modes are different when the structure is stroked under different conditions. In general, the reticulated shells with roof-sheathing are liable to collapse under impact, which is a kind of terrible accidental action. Deformation of the reticulated shell under impact is affected by the roof sheathing, and sometimes it is disadvantageous. To some extent, this aggravates the collapse or damage of the structure. A fuller theoretical framework for the study on reticulated shell under impact was developed by combining with the contents described above. It laid a foundation for the study on shock-resistance of reticulated shell.