Study On Post-fire Mechanical Properties Of Reticulated Shell Structure Connected By Welded Spherical Joints

The reticulated shell structure is one of the main structural forms of the long-span space structure.Studying the mechanical response of the reticulated shell under fire or after fire plays a significant role in evaluating its safety under corresponding conditions.In this paper,the mechanical properties of hot-rolled steel and butt welds after reheating are studied experimentally,and the mechanical response of the reheating process of the reticulated shell is analyzed.The main research work includes:An experimental investigation was conducted to reveal the post-fire mechanical properties of hot-rolled Q235,Q345,and Q420 steels as well as of cold-formed Q235 steels that underwent different levels of cold working.Specimens were heated to various preselected temperatures up to 1000 °C and subsequently cooled down to ambient temperature via two different methods,namely,air and water cooling.Tensile coupon tests were performed to obtain the post-fire stress–strain curves,elastic moduli,yield strengths,ultimate strengths,and ductility.New predictive equations that incorporated the influences of various cooling methods were developed to evaluate the post-fire mechanical properties of both hot-rolled and cold-formed steels studied.To study post-fire mechanical properties of Butt welds,Q235-E4303 and Q345-E5016 butt welds specimens were heated to different high temperatures between 400°C and 800°C,and then naturally cooled to normal temperatures.Tensile tests were conducted afterwards to obtain the force-displacement curve and relevant mechanical properties(yield strengths,ultimate strengths and ductility).New predictive were developed to evaluate the post-fire mechanical properties of both hot-rolled and cold-formed steels studied.The finite element software ABAQUS was used to study the mechanical response of the single-layer reticulated shell structure under fire and after fire.Based on the practical formula describing the changing rules of air temperature under fire in high-rise or long-span structures proposed by Li,non-linearity of materials as well as geometrical nonlinearity were involved in this paper to study the temperature field distribution,displacement,internal force and forces in the support.The finite element model was established to study the mechanical response of cooling process of the composite dome arch structure of the Chipping Gymnasium.The temperature field distribution and displacement of the structure under fire were analyzed.In addition,bearing forces,the influence of different fire locations and superimposed arch on the mechanical properties of the structure were compared.