Theoretical Study On Rotational Stiffness Of Column-base Joint Of Existing Low-rise Masonry-concrete Added Steel Structure

The masonry-concrete structure has a large proportion in the existing structure,and it is one of the most effective ways to transform the large area of masonry-concrete structure by adopting the steel structure adding-stories reconstruction.The key of existing masonry structure on steel structure adding-stories is the connection of new and old structure——mechanical properties of adding-stories steel column base connection.Aiming at the adding-stories steel column base joint of steel structure,there is no clear provisions of the current national standards or regulations,and no basis for the transformation of the steel structure,which leads to some security risks.This paper was supported by natural science foundation project of Shanxi(2015011062)and Taiyuan University of Technology School team science foundation project(2014TD043),aiming at column-base joint of existing low-rise masonry-concrete structure added steel structure,the theoretical research on Rotational Stiffness was conducted,the main research work and conclusions are as follows:1.Research Based on literature search and project case,in accordance with the present existing specifications and manuals,to construct suitable for steel column-base joint of existing low-rise masonry-concrete structure added steel structure.The axial force of steel column,steel columns,steel column base plate geometry,geometric size,column base anchor arrangement and concrete beam column specifications and the geometric dimensions of the 14 factors as variables for the 240 mm and 370 mm wide concrete girder,designed and completed a total of 42 flat plate type column base joint finite element analysis model.2.Parametric analysis method was conducted by APDL language of finite element software ANSYS,considering the influence of material nonlinearity,geometric nonlinearity and nonlinear contact force of column base,numerical simulation of 42 finite element model of column base joints were conducted,obtained the column base M-? curve of the node models in the influence of the above 14 different factors;comparison of related literature of column base,systematically discusses the 14 factors of column base joint stress distribution,the initial rotational stiffness of node and node limit bearing capacity.3.Aiming at the numerical simulation of the each node analysis of the rotational stiffness value,compared with the existing mature base joint stiffness calculation formula results,the main factors that affect the joint stiffness are the axial force of steel column,the number of anchors,the size of steel column and the diameter of anchor bolt,The design of the ZJ1 series of column base jointlimit rotation at between 4.0E-3~5.0E-3rad,and the angle of column base joint plate and anchor bolt to yield maintained at between 1.0E-3~2.0E-3rad;the stiffness value of the plate type steel column base with two pairs of anchor bolt in the uniform axial compressive stress of 100 MPa is about 0.25-1.97 times as much as the stiffness value of the plate type steel column base with a pair of anchor bolt,and puts forward steel column-base joint of existing low-rise masonry-concrete structure added steel structure design related suggestions.