Research On Compression Behavior Of T-shaped & L-shaped Partially Encased Concrete Composite Stub Columns

Partially Encased Concrete Composite(PEC)columns are a new structural form of steel and concrete,which is a combination of welding a certain number of connectors between welded H-shaped steel flanges and pouring concrete on both sides of webs.It fully plays the respective advantages of concrete and steel,and the overall performance is better than that of traditional steel and concrete structures.Irregular-shaped PEC column is a new type of cross-sectional form of PEC structure,which is highly favored by some global scholars and engineers because it not only gives full play to the characteristics of high load-bearing capacity,superior seismic performance and good fire resistance,but also combining with aesthetic appearance,flexible major-minor axis and good aesthetic characteristics of special-shaped columns.Presently,the structure has been gradually applied in practical projects such as high-rise & super high-rise residential and office buildings in some coastal cities of China.However,the application of T-shaped Partially Encased Concrete Composite(T-PEC)stub columns and L-shaped Partially Encased Concrete Composite(L-PEC)stub columns has hardly been used,owing to the lack of in-depth study on the mechanical properties and failure mechanism of T-PEC &L-PEC stub columns.Therefore,this paper carried out relevant research work through experimental research,numerical simulation and theoretical analysis to further understand the mechanical properties of T-PEC & L-PEC stub columns.The main contents of this paper are as follows:(1)The axial compression tests of 15 irregular-shaped PEC columns(9 T-PEC stub columns and 6 L-PEC stub columns)were designed and conducted.The impact of steel content,bollard spacing,section aspect ratio and concrete strength on the loaddisplacement curves,ultimate load capacity,ductility,initial stiffness and damage modes of axial-loaded T-PEC & L-PEC stub columns were explored respectively.The results indicated that the steel and concrete work well together under axial load.The final damage pattern of the specimen is characterized by crushed concrete and localized bulging of the flange between the ties.(2)The finite element parameter analysis models of axial-loaded T-PEC & L-PEC short columns were established and verified.Based on the verification of the correctness and applicability of the FE models,the effects of material and geometric parameters such as steel strength,bollard spacing,flange width-thickness ratio on the damage mode and axial compression load capacity,etc were carried out in detail,and the development of t whole process curve,force mechanism and contact stress of axial-compression specimens were further analyzed.The results provide a scientific basis for calculating the bearing capacity of specimens under axial load.(3)An experimental study of 15 special-shaped PEC columns(9 T-PEC stub columns and 6 L-PEC stub columns)under eccentric compression was carried out.The effects of many vital parameters such as eccentricity,eccentricity direction and crosssectional height-to-width ratio on the ductility,strength index and the curve of load-strain,etc of the eccentrical-loaded specimens were investigated respectively.The test results show that the damage modes of the specimens are mainly large eccentric damage and small eccentric damage,while the specimens also show different damage modes in different eccentric directions.The eccentricity and eccentricity direction of the specimen has a significant influence on the load-carrying capacity and ductility of the specimen,while the specimens section aspect ratio have less influence on the specimen.(4)According to the eccentrical test components,the FE analysis models of T-PEC& L-PEC stub columns were established.The accuracy and applicability of the models were verified according to test results and damage patterns.The influence of concrete strength,steel strength and flange width-thickness ratio,etc on the damage modes,ductility and eccentrical compressive strength of the special-shaped PEC short columns under eccentric loading was analyzed.Combined with the axial stress of the core concrete and steel,and contact stress of the concrete-steel,the whole process response of the specimens under eccentrical loading was revealed.(5)Based on the test and FE analysis of T-PEC &L-PEC stub columns,the compression performance of the two types of special-shaped PEC short columns was analyzed.In view of the limitations of national codes for calculating the axial capacity of T-PEC & L-PEC short columns,puts forward the calculation method of two types of PEC stub columns under the axial and eccentric compression.The results show that the compression calculation formulas proposed in this paper have good applicability and accuracy,providing a certain scientific basis for the design of PEC columns.