Research On The Mechanical Performance Of Concrete-filled Square Steel Tube Stiffened With PBL Under Axial Compression Load

A novel idea of setting PBL stiffeners into section of steel and concrete composite wasproposed. PBL stiffeners may improve the mechanical properties of the interface of steel andconcrete as well as its composite effect. The project “Mechanical behavior and design methodstudy of new type arch with PBL stiffened section of steel-concrete composite” was funded bythe National Natural Science Foundation(51178051). The objective of the study is toinvestigate its mechanical performance, failure modes, its applications in arch bridges withrectangular shape section and its advantages in mechanical properties. The research canprovide the basis for its application in bridge engineering.The research content and research results are as follows:(1) A total of27short columns with various section: rectangular steel-concrete composite,rectangular steel-concrete composite with stiffeners and rectangular steel-concrete compositewith PBL stiffeners were tested in axial compression. Component failure modes,load-displacement curve and load strain curve were analyzed. The results show that: thefailure modes of the rectangular steel-concrete composite columns with PBL stiffeners aresimilar to those of rectangular steel-concrete composite columns with stiffeners, but they aremuch different from those of rectangular steel-concrete composite columns. The reason is thatPBL stiffeners can help steel plates to resist load and transfer the load to concrete effectively,which enhances steel-concrete combination effect. Also, it can enhances constrain effect ofsteel plates on core concrete of the composite section. Bearing capacities of concrete filledsteel tubular and axial compression stiffness are significantly improved by using steelstiffeners or PBL stiffeners.(2)The behavior of short columns subjected to axial loads was analyzed by ANSYS-afinite element software program. A revised stress-strain relationship of core concrete wasproposed. The numerical results show a good agreement with the experimental results.According to the numerical results, we investigated and compared stress distribution ofrectangular steel-concrete composite columns. The results show that hole concretecompressive stress is higher than the rest of the core concrete compressive stress. Also, PBLstiffened core concrete stress distribution is most uneven among all columns; the mechanismof PBL stiffened concrete short columns was analyzed and results show that steel stresses atthe transverse direction of steel plates at the center of columns first increases and thendecreases with the increase of the diameter of hole of the stiffeners. (3)According to the experimental data, universal regression equations of bearing capacityand stiffness for rectangular steel-concrete composite, rectangular steel-concrete compositewith stiffeners and rectangular steel-concrete composite with PBL stiffeners are given andcompared to the equations in related codes. The results from regression equations andexperimental results are in good agreement. Based on the above analyses, we continued to dosensitive analyses for rectangular steel-concrete composite with PBL stiffeners and verify thefeasibility of the calculation method. Finally, a design method was proposed.(4)Five rectangular steel-concrete composite slender columns with PBL stiffeners weretested in axial compression. Before the test, quality of internal fill concrete was tested. Theultrasonic testing results show that: PBL stiffeners are bonded well with concrete, whichmeans a good quality concrete pouring. The test results also show that: the slenderness ratio isa major factor that affects the behavior of slender columns subjected to axial compressionforce. Practical method of calculating for bending stiffness and stability capacity of slendercolumns with PBL stiffeners under axial compression were proposed. The results from thepractical method are in good agreement with the experimental results.(5)We applied PBL stiffeners to a square steel-concrete composite arch bridge and analyzedthe effect of PBL stiffeners on the mechanical properties of the bridges. The results show that:PBL stiffeners can significantly improve the flexural stiffness and ultimate bearing capacity ofarch bridges. The steel ratio of the arch bridge with PBL stiffeners is increased by about30%,while the carrying capacity is increased by about54%. In the ultimate limit state, the load canbe more effectively transferred to the arch rib; thereby the combination effect of steel-concrete is improved.