VCFPB Base Isolation And Prestressed Tendon Construction Research For LNG Storage Tank

With the development of world industrialization progress, LNG storage tank has become the lifeline engineering, plays a more important role, and is developing towards large-scale. LNG storage tanks also appears some problems to be solved, the development process of LNG storage tank has been restricted, the design and construction is put forward some new challenges, and has become a hot research topic in recent years.In this paper, the mechanical properties of tank-shell structure is studied by using model test, numerical simulation and theoretical analysis, the following significant conclusions are drawed as follows:(1)LNG storage tank simplified mechanical model is proposed by considering the outer tank and expanded perlite, it is noted that higher order sloshing modal mass plays a significant impact on base shear and sloshing wave height.(2)A bidirectional variable curvature friction pendulum system is proposed, is constructed of holder plate, metal slide, PTFE plate, slider, slider cavity and stopper plate, the following mainly issue is analyzed.For the interaction between slider and slide surface of VCFPB under design average pressure ① PTFE plate is conducive to force uniform, by selecting reasonable 2r value and reducing sharp corners at both ends of PTFE plate, PTFE plate can reduce the stress concentration by increasing thickness of PTFE plate, and it is conducive reasonable force of PTFE plate; ②Abauqs numerical simulation results also have the same conclusion, and the slider and slide surface separates only in the individual position, when 2r is 180mm and 200mm.The VCFPB force-displacement hysteresis model under design average pressure, Abaqus numerical simulation results show that generally speaking the force displacement hysteretic curves are in good agreement with the theoretical model, there is a great deal of difference in the design displacement between hysteretic model and theoretical model, convex arc hysteretic model is slightly different from theory model by sliding the design of displacement to the balance position, and the bigger the 2r, the greater difference.(3)VCFPB hysteresis curve is symmetrical, stable, full, regular, together with good energy dissipation capacity, and it is in accordance with the theory of hysteresis model, VCFPB can meet the design requirements; sliding friction coefficient changes large, with the surface pressure, sliding velocity larger, and the slider small size, and hysteretic model of the bearing is presented based on unidirectional experimental results, unidirectional hysteretic model is in good agreement with bidirectional variable curvature friction pendulum bearing hysteresis curve.(4)Resonance phenomenon of VCFPB storage tank occurs under long-period ground motions, base shear reaches design value, its damping rate value decreases, sloshing height damping rate values increase significantly, in particular, when full tank under the action of Kobe and Mexican, there is a greater displacement of isolation layer, it is easy to slide out of the chute, the corresponding hardening period or limiting device is set on the both ends of VCFPB.(5)The impact of vertical ground motion on force - displacement hysteretic curves and isolation periods of friction pendulum system is analyzed, and necessity of vertical ground motion on LNG storage tank is pointed out by numerical example.(6)The change law of displacement with considering stress loss time-varying caused by shrinkage and creep of concrete and stress relaxation of prestressed tendon is consistent with that of field measurement displacement, considering concrete shrinkage and creep and stress loss of prestressed tendons, and it is more close to the actual measured displacement, prestress loss caused by stress relaxation of prestressed tendons is less affected by the deformation of containment vessel, but prestressed loss caused by the concrete shrinkage and creep can not be ignored, there is no interaction between the two. Time varying mechanics analysis taken concrete shrinkage, concrete creep and its prestress loss into consideration is carried out during the prestressed construction of containment vessel.