Structural Style Selection And Connections Bearing Behavior Research For JUNO Central Detector

After the success of Daya Bay experiment, which has measured the neutrinomixing angle theta13accurately for the first time, Jiangmen Underground NeutrinoObservatory (JUNO) focuses on neutrino mass ranking. This is the most forefront issueabout neutrino and has great international repercussions. JUNO central detector is ahyper-scale acrylic ball bearing20,000tons of liquid scintillator, which will outdistanceall the other detectors to be the largest sphere central detector in the world. Security andreliability is very significant for the central detector.After having a research on all sphere central detectors applied in the completedneutrino experiments in the world, this paper gives four kinds of structure scheme:(1)acrylic vessel supported by stainless steel truss;(2) acrylic vessel supported by stainlesssteel tank;(3) acrylic module supported by stainless steel tank;(4) balloon supported bystainless steel tank, in order to ensure the safety and design target of JUNO centraldetector. Comparison of the physical performance, structure system, budget andschedule of four systems, acrylic ball supported by stainless steel truss is considered asa relatively ideal choice as it has following known advantages:(1) Be of reasonablestress distribution and good reliability;(2) Be of good stability;(3) Be of low retaininglight rate;(4) Decrease the cost and minimize the construction period.As the selection of structural scheme is acrylic ball supported by stainless steeltruss, this paper made a preliminary design of stainless steel truss, which is based on theoptimal design of partition pattern of acrylic, the thickness of acrylic ball, etc.Preliminary design of the scheme is completed and verified by finite element analysis(FEA) method using ABAQUS, including calculation under three working conditions,overall buckling analysis, thermal effect analysis, seismic effect analysis and sensitivityanalysis in terms of mesh density, etc. It is proved that the structural scheme is veryfeasible and can be a good alternative choice for JUNO.As the scheme is based on the inspiration of point supported glass curtain wall incivil engineering, there are many choices for the design of local joints. This paperdesigned the local joint connection form of point brace. To make sure the wholeness andreliability of organic glass ball, secondary additional organic glass is added in the jointconnection. Stainless steel fastener with plate lug is pre-buried in the glass to connectwith the brace bar of the stainless steel latticed shell. FEA calculation of limit bearing capacity of the joint was carried out using ABAQUS. And two full-size jointexperiments were done to analyze the limit bearing capacity and destruction form. Theresults of FEA calculation and joint experiments are compared. The conclusion showsthat local joint FEA calculation simulates the joint bearing capacity well. This indicatesthat the form and size of the joint matches the requirements of the JUNO project, whichlays a foundation for further and deeper research.This paper puts focus on structural style selection, global finite element analysis,local joint element analysis and experiments. It is proved that the structural scheme isvery feasible and should be a reasonable offer for central detector.