| Most of the structures in China will undergo freeze-thaw cycle,and their mechanical properties will be affected to varying degrees after experiencing long-term freezing and thawing cycles.Concrete-filled steel tube composite structure,compared with ordinary concrete,its stiffness,strength and stability has been greatly improved,it is this good mechanical performance,so that it is widely used in production practice,and the relevant theoretical research is also rich.However,there are still shortcomings in concrete filled steel tubular composite structure materials,that is,steel is easy to rust,poor corrosion resistance,which will not only lead to the increase of maintenance costs,but also bring hidden dangers in the structure.When concrete-filled steel tube composite structure is subjected to freezethaw cycle for a long time in extreme harsh environment,these shortcomings of steel may cause fatal damage.Therefore,some scholars proposed to study metal tubular concrete composite structure of different materials,such as stainless steel and aluminum alloy materials.Among them,in the construction industry,there have been many successful cases of the application of aluminum alloy concrete composite structure.Aluminum alloy material has many characteristics different from steel,such as corrosion resistance,small weight,and beautiful appearance and so on,But the thermal expansion coefficient of aluminum alloy material and steel tube material is quite different,the former is about twice that of the latter.At present,there are few studies on the mechanical properties of the concrete filled steel tubular and aluminum alloy tube beam-column joints after freezethaw cycle,which limits their application in more fields.In order to study the performance difference between the two kinds of joints after freeze-thaw cycle,the following works were completed in this paper through experiments and theories:1)Frame beam-column joints were chosen as the research objects.Some specimens were made,included five concrete-filled steel tube "beam-column joints" and "push-out specimens",and five concrete-filled aluminum alloy tube "beam-column joints" and "push-out specimens".These specimens were subjected to freeze-thaw cycles of 0 times,100 times,200 times,300 times respectively in the freeze-thaw environment test box.2)The bending moment bearing capacity of pipe concrete joints of the two materials after freeze-thaw cycle was obtained through the experiment,and the bending momentangle curve of these joints was drawn,the causes of the results were explained,and the calculation model of the moment-rotation relationship of the joints range was given within a certain;3)By using the designed "push-out specimens" and pushing-out experiments,the whole process curve of bond-slip between concrete and steel tube and aluminium alloy tube surface after different freeze-thaw cycles was obtained.The strain distribution on the surface of metal tube during pushing-out process was measured,and the bonding between concrete and tube wall was explained;4)The finite element software ABAQUS was used to simulate the static loading process of the joints specimens,and the failure mechanism of the joints was explained The bond-slip process between concrete and metal tube surface was studied by simulating the "push-out specimens". |
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