Research Of Stability Of Cylindrical Steel Silos With Lap Joints

Flat-bottom squat steel silo is a vertical storage container which contained loose material, widely used in agriculture, metallurgy, coal, electricity and many other areas. Steel silos are commonly constructed by welding together a large number of curved steel panels with lap joints. Where the lap runs horizontally around the silo circumference, the lap connection causes a local eccentricity in the line of vertical thrust in the shell wall. This eccentricity induces high local bending stresses, which are detrimental to the stability of the structure. This paper chooses a flat-bottom squat steel silo as the research object to analyze the stability of lap jointed steel silo by comparing with a butt-jointed steel silo.Chinese Code for design of grain steel silos (GB50322-2001) and Eurocode were used to check the design of a silo. The results show that the bulking stress calculated by Chinese code is higher than Eurocode which make provisions for lap joint silo.To analyze the stability of lap jointed steel silo in detail, the paper build the finite element model of lap jointed and butt-jointed steel silo with the use of finite element analysis software ADINA. By stressing loads calculated according to Chinese code for design of grain steel silos, considering two load cases including axial compression only and combined axial compression and internal pressure, this paper do numerical analyses including linear buckling analysis, geometric nonlinear buckling analysis and geometric-material nonlinear buckling analysis. By comparing the results of buckling analysis, the effects of material nonlinearity and lap joint on stability were studied. The results show that negative impact of lap joint on stability is obvious under axial compression only, while considering internal pressure the buckling resistance of lap jointed and butt-jointed silo show little difference.As a kind of thin-wall shell structure, the steel silo is sensitive to geometric imperfection. This paper import consistent mode imperfection to do geometric nonlinear buckling analysis and geometric-material nonlinear buckling analysis, considering two load cases too. By comparing the results of buckling analysis, the effects of material nonlinearity, geometric imperfection and lap joint on stability were studied. When the geometric imperfection amplitude was taken as the bottom plate thickness, the results show that the silo is more sensitive to geometric imperfection under axial compression only than considering internal pressure, the sensitivity to imperfection under axial compression lessen the negative impact of lap joint on stability, when considering internal pressure, geometric imperfection and lap joint reduce the buckling resistance. The deformation of imperfect silo under two load cases is respectively similar to that of linear buckling analysis; it indicates that the deformation of imperfect silo is concerned with geometric imperfection. The results of nonlinear buckling analysis taking different sizes of geometric imperfection show that, under axial compression only, the negative impact of lap joint on stability was lessened with the increasing imperfection amplitude, when considering internal pressure, importing initial imperfection increased that negative impact of lap joint.