Research On The Flexural Performance Of U Type Laminated Beam With Recycled And Self-compacting Concrete

The reinforced concrete superimposed structure combines the advantages of the prefabricated concrete structure and the cast-in-place monolithic concrete structure.It has the characteristics of quick construction and good integrity,and it satisfies the social development requirements for the construction period and construction quality of the construction industry.In line with the trend of industrialization of the building,it conforms to the trend of green building.The prefabricated cross-sections of the composite beams are various,such as U-shaped and rectangular.However,they all have shortcomings.For example,the prefabricated part of U-shaped laminated beam has low strength and is easily destroyed;the prefabricated part of rectangular laminated beam has a larger weight and is not conducive to construction and transportation.Therefore,it needs to be combined with the existing cross-section to improve it.In this study,we added recycled concrete as the core to the prefabricated part of the existing U-shaped laminated beam to increase the rigidity of the prefabricated part of the U-shaped laminated beam.Through a large number of literature inspections,the main research results obtained in the U-shaped core composite beams are the bending performance of U-shaped composite beam columns and columns.At present,there is no research on the mid-span flexural performance of recycled concrete and self-compacting concrete in U-shaped core composite beams.In the area of self-compacting concrete,the cross-section of the U-shaped laminated beam is more complex than the traditional rectangular cast-in-place beam,especially when the U-shaped cross-section is manufactured;there are parts that are difficult to vibrate.In order to ensure the pouring quality of U-shaped laminated beams,the specimens of this study were cast with self-compacting concrete with high flow ability.In the recycling of coarse aggregate,in order to make full use of resources and reduce the pollution to the environment,this study will crush and screen the abandoned concrete and use recycled coarse aggregate to replace part of the natural coarse aggregate in cast-in-place concrete of composite beams.In order to study the mid-span flexural performance of U-core cores with recycled self-compacting laminated composite beams,a total of seven beam specimens were fabricated in this study,including cast-in-situ self-compacting concrete beams RCB,prefabricated heights of 120 mm and 170 mm,respectively.220mm U-shaped laminated beams URCB1,URCB2,URCB3,and ordinary laminated beams PRCB1,PRCB2,PRCB3 with prefabricated heights of 120mm,170mm,220mm,respectively.The static loading model test was carried out to measure the cracking load values,deflections and ultimate bearing capacity of each test piece.The load-deflection curves,the characteristics of the load-strain curve of the steel bar and the concrete were analyzed,and the existing concrete structural design specifications were used.The formulas for the calculation of the ultimate bearing capacity,cracking load,and stiffness of U-shaped belt core regenerated self-compacting concrete composite beams are studied.And ABAQUS finite element software simulation U-shaped belt core regeneration of self-compacting composite beams flexural bending simulation,draw the following conclusions:(1)By comparing and analyzing the calculated values and experimental values of the cracking load and ultimate bearing capacity of each test piece,the calculation formula for the normal section bending bearing capacity in the Code for Design of Concrete Structures(GB50010-2010)is applicable to the U type.Regenerated self-compacting concrete composite beams,and the calculation results are more secure.The bending cracking load of U-shaped reclaimed self-compacting concrete composite beam is similar to that of the ordinary whole-concrete beam,and it is higher than that of the rectangular composite beam.The calculation formula for the bending cracking load of the full-flow bending members in the Code for Design of Concrete Structures(GB50010-2010)is applicable to U-shaped reclaimed self-compacting composite beams with certain safety reserves.(2)Before concrete cracking,the concrete strain along the height of the beam is basically an oblique straight line.All beam specimens including core U-shaped regenerated self-compacting composite beams meet the requirements of the flat section.After the cracking of the concrete,the cracks of the U-shaped recycled self-compacting composite beams developed to the position of the overlapped surface,but did not develop along the overlapped surface,indicating that the new and old concrete can work together well.(3)U-shaped regenerated self-compacting composite concrete beams,ordinary laminated beams,and cast-in-place beam specimens are structurally different,but their flexural development rules are basically the same;in addition,the load-deflection curve is used to crack the specimens.The comparison of the slopes shows that the U-type recycled self-compacting composite beams have better mechanical properties than ordinary composite beams.(4)By comparing and analyzing the displacement and deflection ductility of each test piece,the U-shaped recycled self-compacting composite beams improve the ductility of ordinary composite beams and have good seismic performance.Through comparative analysis of the plastic rotation angles,the plastic rotation angle and deformation capacity of the U-shaped recycled self-compacting concrete composite beams are approximately equal to the level of the entire cast-in-place beam,and are obviously better than those of ordinary rectangular composite beams.(5)By comparing the actual stiffness of each test piece,it is found that the early stiffness of the U-shaped recycled self-compacting composite beams before cracking is similar to the stiffness calculation formula in the Code for Design of Concrete Structures(GB50010-2010),but after cracking the actual stiffness of U-shaped recycled self-compacting composite beams is quite different.Based on the statistics and regression analysis of the actual stiffness and calculated stiffness of the test piece,the correction formula for the reduction coefficient ? of the normal section of the U-shaped regenerated self-compacting concrete composite beams after cracking.(6)The load-deflection curve,stress and strain cloud obtained by ABAQUS simulation of U-shaped regenerated self-compacting composite concrete composite beams is obtained.The simulated values agree well with the experimental values.ABAQUS can be applied to study the flexural behavior of U-shaped recycled self-compacting composite beams.