The Non-linearity And Stability Analysis On Single-layer Spherical Eticulated Shell

With the increasing development and pursuit of space structures, thereticulated shell is widely used abroad and home for lightweight,rationally loaded character, low fabrication cost, novel pattern and thecapacity to form a larger space. However, the stability behavior ofreticulated shells became the most important respect in design for it’slarge span, especially for single-layer spherical reticulated shell.A program for the analysis of the stability of the reticulated shell isestablished in ANSYS which is a finite element analytical program, basedon the previous studies. In the beginning, a example of two-hinge arch islisted, the program is verified and the overall process before and afterbucking of the arch and arch-like structure were analyzed, which providereference for the analysis of the stability of the reticulated shell. Then,model of K8shell which is the most common shell in single-layerspherical reticulated shell is solved and analyzed, the load-displacementcurve of structure is got, which consider initial imperfections, geometric and material non-linearity and other factors, by this method, the strength,stiffness and stability in the whole process will be shown clearly.According to this principle, the nonlinear stability of k8reticulatedshells are studied in different initial imperfections and different loaddistribution, including different sag, different height-to-span ratio,different section area and different constraint conditions of the boundary.By changing parameters, the effect of the factors on buckling modes,stability capability and displacement of nodes of k8reticulated shells canbe got, and concluded as follows:(1) It is necessary to consider initial imperfections in the studies ofelasticity and elastoplasticity of reticulated shells for it is sensitive to theinfluence of initial imperfections(2) For the stability capability is greatly drop and the average of thereduction coefficient of the capability is0.447, it is necessary to considermaterial non-linearity.(3) In the condition of asymmetric load distribution, the asymmetricload coefficient is close to1, it is concluded that asymmetric load distribution have no influence on shell’s stability capability of bothelasticity and elastoplasticity.(4) As to the constraint conditions of the boundary considering theinitialing imperfections, the load-displacement post bucking track issimilar to each other at both all-fixed and all-hinged, the capability of theformer is7.58%larger than the latter, the interval-hinged is smaller thanboth all-fixed and all-hinged. The track will drop faster after the extremepoint with the decrease of the boundary stiffness.(5) The studies of the buckling modes indicated that, the instabilityof idea shells and initialing imperfection shells appears in the main ribsfirstly. The maximum displacements tend to be in the second, third andforth ring from the outside under the condition of ideal shells, but themaximum displacements tend to be in the first, second ring from thecentre for initialing imperfection shells. The size of grid have no obviouseffect on the buckling modes.Moreover, the effect of temperature load on the non-linear stabilityof the k8reticulated shells is also analyzed, the conclusions are as follows:(1)The influence of temperature is generally concentrate upon areasthat are near the boundary, more farer away from the boundary, moreweaker.(2)The stable capability of the k8shells decrease as the negativetemperature differences increase. It is suggested that reticulated shells arenot suitable for being constructing in low temperature. When encountercold season or temperature pelter, we should pay attention to heatpreservation maintenance of the shells.(3)When negative temperature difference is-25℃, The stablecapability decrease by10.7%in contrast of non-temperature difference,When it comes to-65℃, the decreasing range reach37.6%, It proves thatif negative temperature difference achieve a certain extent, the effect ofthe temperature can’t ignore.(4)Neither elasticity nor elastoplasticity, stable capability will cometo a negative value at the beginning of loading with negative temperaturedifference impacting and to a certain extent. In order to counteract this adverse effects, it is advisable to exert force which is upward on keynodes in some way.