| With rapid development of economy,the demand of the speed and quality of construction and developing Green Building is higher and higher.The Concrete composite structure that is with the advantages both of prefabricated concrete structure and Cast-in-situ concrete structure has been the focus in building industry.At present,some kind of prefabricated composite beam we used are not behaving well,such as the U-shaped,the T-shaped,the rectangular.The rectangular is with big weight,the T-shaped is need of template on either side of beam,the U-shaped is with low strength,easy broken during transportation and lots of template supports are needed.So we need a new kind of composite beam to improve the present situation.In addition,because of lots of old buildings’ useful life is coming and to meet the need of development of the Urban Planning.The old buildings must be dismantled and reconstructed.As a result a lot of building waste will come out.This would bring some grave consequences,such as environmental pollution,occupation of land and so on,if we can not treat building waste well.Meanwhile,on account of the large quantities of building,the resource exhaustion is coming.So how to achieve the effective use of the abandoned concrete in new building without reducing the performance of structure to meet the demand of Green Building.It has been the immediate research focus.Based on the research background above,we do the experimental study that adding the Core made by recycled concrete in the U-shaped composite beam to overcome it’s shortcomings,such as low strength,easy broken during transportation and lots of template supports are needed.And to enhance the integrity of the structure by enlarging the composite area of beam-column joint,lower the weight of structure,we made the part at both ends of beam of the Core as step-shaped.At the same time,to make the best use of renewable resources and meet demand of Green Building,we adopted recycled concrete as the material of Cast-in-situ part.By the method above we made the new composite beam-column joint mixed using concrete and recycled concrete.In this research,we made one of the new composite beam-column joint as tested specimen,and four specimens.By doing the model test under static load,we got some experimental results about specimens.For example,the cracking load,the ultimate bearing capacity,the load-deformation curves,the load-strain curves of concrete and rebar and the mechanical characteristic of the composite area of beam-column joint.And we used corresponding theoretical formulas and the finite elements software ABAQUS to do contrastive analysis for the experimental results.We get conclusions as follow.(1)By comparing the theoretical values with measured values of cracking load and ultimate bearing capacity for all of specimens,we put forward that the formulas 1-4 for normal section bending capacity in 6.2.10 part and the formulas for cracking load in 7.2.3 and 7.2.4 part in Code for design of concrete structures(GB 50010-2010)are suitable for the new composite mixed using concrete and recycled concrete,and the result from the formulas is based on the safe.(2)The new tectonic type that making up the prefabricate part by Core and U-shaped,making the part at both ends of beam of the Core as step-shaped and setting the stirrup of beam as the shear connector for composite area of beam has achieved the purpose that improving the bearing capacity and integrality of composite beam.(3)By comparing the ultimate bearing capacity of every specimen,we conclude that by substituting the recycle concrete for concrete as the material of the U-shaped part,the bearing capacity of the whole specimen can be enhanced;adopting recycled concrete as the material of the Core and keeping the percentage that its area of prefabricate part under 30%,the bearing capacity of specimen will not be reduced and will achieve the aim that making the best use of recycled aggregates;comparing with the inclined plane adopting the step-shaped as the shape of the composite area in both ends of beam of the Core is better and can improve the ultimate bearing capacity of specimen.(4)As the structural style of the whole Cast-in-situ concrete specimen and the new composite beam-column joint mixed using concrete and recycled concrete is different,the law of the development of the deflection is similar;in addition,comparing the slope of the load-deformation curves for all of specimens,we found that the new structure style of the new composite beam put forward by us is significant for enhancing the mechanical property and enlarging the applied range.(5)By comparing the displacement ductility of every specimen,we found that by using the structural style and material in the new composite beam put forward in this research,the shortcoming that the ductility of the joint of fabricated structure is improved,the anti-seismic property is enhanced.By researching the length of plastic hinge and rotation capacity,we found that the rotation capacity of plastic of the new composite beam-column joint is close to the whole Cast-in-situ concrete specimen.(6)By comparing the cracks on every specimen,we found that the utilization of steel rebar of new composite beam-column joint mixed using concrete and recycled concrete is the best among the five specimens when the layout of steel rebar of every specimen is same.And for the new composite beam-column joint,the integrality is good,the stress distribution is comparatively homogeneous,on both respects it is better than the existing composite that the composite area in both ends of beam of the Core is inclined plane.(7)By comparing the measured bending rigidity of every specimen,we found that because of the character of compound section of the new composite beam-column joint,it’s bending rigidity is greater than others before cracks coming,then the bending rigidity of every specimen is approximate.And from the statistics of the measured and calculated bending rigidity,we got the modifier formulas for the reduction factor β of bending rigidity that after cracks coming of the new composite beam-column joint,its results coincident with measured data.The modifier formula is as follow.(8)By comparing the step-shaped composite area with inclined plane composite area,we found that the structural with inclined plane composite area at the end of beam is bad for bearing capacity and is not useful for prevent cracks from running on,but the structural with step-shaped composite area at the end of beam is useful for prevent cracks from running on,and its bearing capacity is greater than the former of 7.1%.(9)By comparing the load-deformation curves computed by ABAQUS with the experimental value,we found that there is a little of difference between them,so the new composite beam-column joint put forward by this research can be computed preferably by ABAQUS.From the Mises stress nephogram we found that the law of stress for every specimen is identical to the test.The maximum stress area is on the column of the new composite beam-column joint,so we can enhance the strength of the column to improve the bearing capacity of the whole structure. |
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