Study On The Axial Compression Mechanical Properties Of Angle Steel-Fiber Reinforced BMSCC Permanent Formwork Short Column

Based on the study of the permanent formwork concrete column,the thin-wall shell is made by the fiber fabric reinforced basic magnesium sulfate cement base composite material（BMSCC）,and embedded in the Angle steel to form a new composite permanent template of the Angle steel-basic magnesium sulfate cement base composite material shell.The Angle steel takes the place of the ordinary longitudinal reinforcement,and the weld plate takes the place of the stirrup between the Angle steel.After the template shell is prefabricated in the steel mill and transported to the construction site,only the internal concrete needs to be poured,which avoids the traditional construction process of steel processing,support mold removal and other complicated steps,shortens the construction period and improves the construction quality.The permanent formwork shell has high temperature resistance,corrosion resistance,good compatibility with concrete,high strength,low cost compared to other high-performance materials,and low alkaline appearance,and is more flat and beautiful.The material ratio,fabrication and axial compressive properties of angle steel-fiber reinforced BMSCC permanent formwork short column are studied.The main research contents and conclusions are as follows:（1）The BMSCC used to make the short-column thin-wall shell was prepared by mixing a certain concentration of magnesium sulfate solution heptahydrate and lightly fired magnesium oxide powder,and then adding an appropriate amount of modifier and sand.This kind of material has high bearing capacity,good toughness and fluidity,and small aggregate particle size,which is suitable for the production of permanent formwork shell.Through the study of a series of physical and mechanical properties,the final selection of Mg O:7H₂O·Mg SO₄:H₂O molar ratio of 7:1:22,mixed with medium sand,cemilar-sand ratio of 1:2.5 as the main cement material for the short column thin-wall shell.（2）Five fiber-reinforced BMSCC composite permanent formwork short columns with built-in Angle steel and three concrete short columns were made.Using the built-in double-layer fiberglass mesh,wet-bonding and Longitudinal rib and other new production methods.The bonding property between precast shell and core concrete and the formation and development of cracks are improved.（3）Five fiber-reinforced BMSCC composite permanent formwork short columns with built-in angles and three reinforced concrete short columns were tested under axial compression and static load to investigate the effects of different Angle steel dosage and plate spacing on the axial compressive properties of composite permanent formwork columns.The results show that,compared with the reinforced concrete short column with longitudinal reinforcement ratio and volumetric hoop ratio,the mechanical properties and specimen ductility of composite permanent formwork short column have been optimized to a certain extent.The short column cracking load of Z1,Z3 and Z5 has increased by 54.85%,71.43%and 54.95%,respectively.The ultimate load was increased by 12.99%,13.39%and 14.12%respectively.And its mechanical properties are improved with the increase of the cross-sectional area of the Angle steel and the decrease of the spacing between the plates.（4）The finite element simulation was carried out for the composite permanent formwork column and reinforced concrete column.The good agreement between the analysis results and field tests indicates that the finite element simulation analysis has certain practical significance.（5）By introducing the reduction coefficient of Angle steel strengthα_s and the reduction coefficient of cement strengthα_c,and considering the influence of Angle steel constraint and permanent formwork on the compressive capacity of composite permanent formwork column,the formula for calculating the axial compressive capacity of angle steel-fiber reinforced BMSCC permanent formwork short column was established.