English：

The demolishing time of the formwork support frame should take into account the actualstrength of the beam-plate, the load, the span and other factors. On the basis of summarizing theconstruction experience of twice demolition of tall formwork support system, its reliability is verified byfinite element analysis and field monitoring. A new force analysis method of beam-plate support scaffold isadopted, that is, the support frame model is introduced into the building structure design model, so thatthe finite element modeling algorithm of the cooperative force and deformation of the frame body and thebuilding structure is adopted. The joint stiffness of the scaffold joint is set according to the recommendedvalue of the specification, and the calculation is carried out together with the main reinforced concretestructure according to the steel structure design specification. The deformation and axial force changes ofthe beam-plate and the support scaffold during the concrete pouring, curing and formwork demolitionprocess of the 0——28d structure and its support system are simulated. Through numerical calculation andframe monitoring, it is found that the stiffness of beam-plate increases graduallywith the increase ofconcrete age. When the construction speed of each layer is ≥10d / layer and the concrete strength reachesmore than 85% of the design value, the influence of the construction of each layer above the N-layer onthe N-layer can be ignored. For span > 8m or tall formwork support system, can be divided into 14,28dtwice demolition, so as to accelerate the turnover of formwork and steel pipe. The research shows thatwith the increase of concrete age, the force of the scaffold under the-beam plate decreases gradually.When the beam-plate can withstand the upper construction load, the lower scaffold of the beam-platewithdraws from the work, and the strength and deformation of the beam-plate meet the designrequirements,which achieves the purpose of safe construction and cost saving.