Experimental Study On Axial Compression Stability Of Modular Assembled Four-column Spliced Composite Columns

Manufactured steel modular frames are a highly integrated structural form,with the advantages of practical construction,green environmental protection,and high standardization of components.However,the existing modular fabricated steel frame will make the form of "column-column separation" at the middle column,which leads to the lack of constraints among the modular columns,the difficulty of cooperative force between the modular columns,poor vertical bearing capacity and so on.At the same time,the module is dense and the space is narrow at the position of the middle column,therefore,setting up the composite column at this position is more tedious.In this paper,we present a modularly assembled composite column with four spliced columns.In order to investigate the axial compressive mechanical properties of four-column spliced composite columns,in this paper,the axial compression tests and finite element simulation analysis of full-scale modular assembled composite columns are performed.The method for the design of the overall stable load carrying capacity of spliced composite columns with four columns is advanced.The main research results of this paper are as follows:(1)We propose a fully bolted modular assembled four-column composite column,which is composed of a core tube,an outer plate and a column module.Four full-scale members were tested in axial compression,and the mechanical properties of the composite columns under axial compressive loading were compared and analyzed.It has been shown that when the composite plate spacing is small and the slenderness ratio is large,the failure modes of four-column spliced composite columns are primarily global buckling,and composite columns have a clear overall bending strain;When the plate spacing is large and the slenderness ratio is low,in the composite spine failure mode,local buckling failure occurs at the mid-span ventral wall,and there is no obvious flexural deformity.After the test is complete,the core tube and outer plate can effectively enhance the cooperative force between the four column modules,connectors such as the central tube of each specimen have no obvious strain and can be reused and the detachability of the composite column is satisfactory.(2)We establish a finite element simulation model for the axial compressive stability of four-column spliced composite columns by considering initial geometric imperfections and residual stress.The failure mode,axial load-displacement curve,midspan load-displacement curve and load-rotation curve of each composite column are studied.This demonstrates that the finite element simulation method established in this paper can accurately reflect the axial compressive mechanical properties of composite columns spliced with four columns.(3)Based on verification of model accuracy,effects of parameters such as plate spacings,we analyze the core height and initial geometric defects on the axial compressive stability of composite columns,and the design advice was given.When the spacing of the embellishment plate is greater than 550 mm,the spacing of the embellishment plate has an obvious influence on the stable load bearing capacity of the combined column,it is recommended that350mm-550 mm be taken as a reasonable design value for the spacing of the embellishment plate of the four-pillar spliced combined column;The height of the core cylinder can improve the stable load bearing capacity of the combined column to a certain extent,when the column is longer than 3.9m,it is recommended that a core cylinder of 140 mm high and above be used for design;When the geometric initial defects are L/1000 and below,the geometric initial defects have less influence on the axial compressive mechanical properties of the combined column,and the initial defects of the combined column should be strictly controlled within L/1000.(4)In this paper,we calculate and analyze the overall stability coefficients of 108 composite columns spliced into four columns with different strength grades.According to different steel strength grades,by fitting stability coefficient curves appropriate for composite columns with four spines,and the method of calculating the stability load carrying capacity is advanced and compared with steel structure design codes from various countries.This approach provides a reliable and reasonable design method for the engineering application of composite columns with four-column splicing.