Abstract: Modern large-scale livestock and poultry breeding houses,slaughterhouses,agricultural products processing workshops and other buildings often adopt light-weight steel portal frame structure systems,steel column base often adopts simple exposed column base.This kind of buildings have high indoor humidity and a certain corrosive sometimes,in order to protect the steel column base and improve the durability of the structure,the practice of secondary pouring concrete is often used.Because the pouring concrete is usually plain concrete,the influence of the secondary pouring concrete on the bending capacity,rotational stiffness and ductility is often ignored in the structural analysis and design,which makes the analysis results differ from the actual working conditions to a certain extent,and may bring about waste in design or hidden safety hazards.Therefore,taking the light-weight steel structure of this kind of buildings as the engineering background,considering the three types of pouring concrete thickness of 100 mm,150 mm and 200 mm under the action of axial compression and bending moment,it is found that the pouring concrete can obviously improve the bending capacity and ductility of the column base,and the bigger the thickness is,the bigger the improvement is.At the same time,there is a certain law of increasing the rotational stiffness.Further in the package thickness under the condition of 150 mm,considering the pouring concrete without reinforcement net,add a layer of reinforcement net and add two layers of reinforcement net three scenarios,in pouring concrete section 4 mm and 6 mm outer clad steel of two situations,with the general commercial finite element software simulation,it compared the eight kinds of conditions on the properties of the steel column base mechanical performance,the emphasis was placed on the bending capacity,rotational stiffness and ductility.
The results show that the plastic stress concentration exists in the tensile side and the compression side of the pouring concrete,the lower part of the compression side is more concentrated than the upper part,and the upper part of the tensile side is more concentrated than the lower part.With the increase of the pouring concrete thickness,the bending capacity and ductility coefficient of column base increase more and more.The addition of two kinds of reinforcement net can improve the rotational stiffness to a certain extent,and the effect of laying two layers of reinforcement net is more obvious.Adding a layer of reinforcement net on the top makes the plastic strain area on the top of the pouring concrete smaller.The plastic strain areas of the upper and lower parts of the concrete are reduced by adding two layers of reinforcement net,which indicates that the reinforcement net provides effective constraints on the concrete and can delay the crack development of the pouring concrete.The upper and lower layers of reinforcement net bear a certain tensile stress,especially the upper layer of reinforcement net bear a greater tensile stress.With the addition of outer clad steel,the bending capacity of column base is not significantly improved,but the rotational constraint stiffness of column base is improved to a certain extent.
Therefore,it is suggested that the contribution of secondary pouring concrete to column base bending capacity,rotational stiffness and ductility should be taken into account in mechanical performance analysis of portal frame structure,which can make the design more accurate.If the pouring concrete is thicker,additional reinforcement net or outer clad steel,the rotation constraint of column base should be considered,and the hinged analysis should not be used any more,which can make the structural analysis of portal frame more reasonable.