Mechanical Properties And Optimization Analysis Of New Cold-rolled Sleeve Connector Based On Large Diameter Steel Bars

As an important connection mode of prefabricated structure,reinforced grouting sleeve joint has good mechanical and seismic performance.The technology of nodular cast iron sleeve in domestic market is mature,but the disadvantage of high cost also restricts its application.The new sleeve proposed by zheng yongfeng’s team is made of seamless steel tube cold rolled,which is easy to manufacture and low cost.However,there are few related researches,especially those on the properties of sleeve joint for large diameter steel bars.In this paper,by means of experiment and numerical analysis,the stress mechanism of cold rolling grouting sleeve applied to 32 mm large diameter steel reinforcement is studied and analyzed,and the structural form of the sleeve is optimized.The main results are as follows:1.Two sets of grouting sleeve connectors with different inner and outer diameters were made and unidirectional drawing test was conducted.The results show that the yield strength and ultimate strength of the type A specimen with A wall thickness of 7mm and A grouting material thickness of 15.5mm are 360 kN and 466 kN respectively,which are less than the relevant strength of the reinforcement.The ultimate failure form is the reinforcement pulling out failure,which does not meet the requirements of the specification.The yield strength and ultimate strength of class B specimens with a wall thickness of 9mm and a grouting material thickness of 13 mm are 375 kN and 490 kN respectively.The ultimate failure form is the fracture failure of steel reinforcement,which meets the strength requirements of the grouting sleeve connector in the code.2.According to the two parameters of grouting material thickness and sleeve wall thickness,18 sets of different steel grouting sleeve specimens were simulated and analyzed.The analysis shows that the wall thickness of sleeve and the thickness of grouting material are proportional to the bearing capacity of the specimen.The sleeve and grouting material work together.When the grouting material is insufficient in thickness,the sleeve will bear more force.If the strength or thickness of the sleeve is not enough,the stiffening rib will be deformed,which is not good for the structure.The bearing capacity can be improved by increasing the wall thickness or the groutingmaterial thickness when the grouting sleeve specimen is designed.3.Taking the strain energy of the reinforced grouting sleeve specimen as the objective function and the ultimate strength of the three materials as the state variables,the layout of the sleeve stiffener was optimized and tested.The results show that after optimization,the yield strength of the grouted sleeve increases from 436.0MPa to 466.8 MPa,an increase of 7%.The ultimate strength increased from 580.0MPa to 607.8 MPa,an increase of 5%,which is close to the actually measured tensile strength of reinforcement of 609.0 MPa.At the same time,it is proved that the location of the stiffener will affect the bearing capacity of the grout sleeve to a great extent,and the strain energy as the objective function is reliable.4.After verification,finite element optimization function was used to optimize the sleeve with a wall thickness of 9mm.When the anchoring length was 7.5d,8d,8.5d and 9d respectively,when the deformation section accounted for 65%~70%,the force of the grouting sleeve was more reliable and met the requirements of the specification.