Study On The Layered Pouring Size Of Cast-in-Place Composite Beam

With the development of urbanization,high-rise buildings have become an important part of urban construction.In order to meet the functions of commercial and residential purposes,highrise buildings often have conversion floors.The commonly used concrete beams for conversion floors are usually large cross-section and large-volume structure.If large-section beams are cast in one step during the construction process,it is easy to cause excessive load on the supporting system and the underlying structure(the next or up to the first layer of the structure must participate in the support),and at the same time,whether it is the support setting or the heat of hydration,the problems are both downsides.In order to improve these problems,it is an effective way to use layered pouring to form a composite beam.In this paper,with a transfer beam in the project as the background,adopting the method of superimposed pouring,aiming at the selection of the layering method and the layering height,the concrete structure design inspection method was combined with the ANSYS finite element method,and the beams were respectively cast with two-layer and three-layer pouring method.The stress and deformation of the pre-cast part(pre-cast layer)of the beam at different heights were calculated,and the influence of the section size of the beam,the concrete strength grade and the age on the selection of the layer height was studied,and the following conclusions were obtained:(1)The 0.8m×2.1m beam in the original project should adopt the method of two-layer pouring,and the height of the first pouring layer must be above 0.9m;the construction method is to set the formwork and support to cast the first pouring layer.After the first pouring layer reaches 50%strength,the support under the beam is removed,and then the post pouring layer is poured.If the method of three-layer is adopted,the best layering method is to pour 0.7m first,then 0.3～0.7m,and finally pour the remaining part.(2)For the beams in the original project,while comparing with the cast beams,two-layer pouring method has significant effects in supporting settings and improving the heat of hydration;three-layer pouring method can save up to 20% of the support rods compared to two-layer pouring method.(3)The transfer beam in the project adopts the method of two-layer to form a composite beam,and the height of first layer must be greater than 0.4h,and it is appropriate to be close to 0.5h;when the transfer beam satisfies h/b>2.5,h/L>1/6,and the concrete strength is between C35～C50,and the concrete demoulding strength is more than 50% of the 28 d strength,the above conclusions can be used;if it is not within the above range,it needs to be determined separately based on the actual project.