Research On Mechanical Performance Of Under-Column Independent Foundation Assembled With Prefabricated Sheets And By Pre-Compression

In recent years,the research and development of new high-efficiency precast fabricated concrete structure precast members and the research on the connection performance between precast members are in full swing.However,the research on precast as prefabricated foundation is very few compared with the research on column,beam,slab,wall and other concrete members.A small amount of research and application on prefabricated foundation are mostly concentrated in the prefabricated tower crane foundation and the power industry.At present,for low-rise houses in domestic civil buildings,mainly adopt strip foundation,independent foundation under columns and other shallow foundation forms,and basically wet operation,almost all on site pouring construction,assembly foundation can improve the construction efficiency of foundation engineering,reduce labor time,high quality speed up the project progress.In addition,for some special conditions in the region,such as frozen soil,desert and other harsh environment,it is very difficult to pour concrete on site,so the research and development of independent foundation under the prefabricated column is particularly important.For this purpose,a new preloaded prefabricated foundation is proposed,namely the independent foundation under the piece-based preloaded column.ABAQUS software is used to investigate the mechanical properties of the independent foundation under the piece-based preloaded column and the connecting interface from two factors of the preloaded stress level and different interface angles.The details are as follows:(1)The basic technical scheme of the independent foundation under the fragment prefabricated and preloaded assembly column is proposed,and the design process of the prefabricated component is introduced.The characteristic of this foundation is that the joint interface adopts the inclined joint which is different from the traditional vertical joint.In the design of the fragment scheme,the size of the fragment body is determined by considering the conditions such as factory processing and component transportation.Pre-stressed steel strand is used to connect the fragments to form a good working whole.(2)The finite element models of 18 precast and 1 cast-in-place foundation were established by ABAQUS software,and vertical loads were applied to them.The mechanical properties of the independent foundation pieces under the precast and preloaded column were investigated from three aspects: the compressive stress distribution of concrete profile,the stress distribution of ordinary reinforcement and the tensile damage of the bottom surface of the precast foundation.The results show that when the preloading stress reaches more than 4MPa,each block of the precast foundation enters the whole working stage,and the profile compressive stress distribution is uniform.The smaller the Angle of the interface is,the greater the flexural stiffness of the structure is,the smaller the tensile stress value of the ordinary steel bar is,and the whole section through cracks will not be formed on the foundation bottom.(3)By extracting the values of loads changing with the time of analysis step of 18 models and combining with the extracted relative displacement values of interfaces,load-interface slip curves of 18 models are made.The interfaces of fragmented blocks FP2 and FP3 are selected as weak interfaces for force analysis.The results show that:The interface slip value decreases with the increase of the interface preloading stress and increases with the increase of the interface dip Angle.The inflection point with the obvious increase of interface slip is defined as the "starting slip point".The higher the inflection point,the stronger the interface anti-slip ability and the stronger the connection performance.(4)The function curves of the interface dip Angle of the maximum compressive stress at the splicing interface,the maximum stress of ordinary reinforcement and the "sliding force" with the preloading stress are obtained through data fitting,which can be used to evaluate the mechanical performance of the prefabricated foundation.