| The industrialization of construction in China can not be achieved without the vigorous development of assembled concrete structures.The structural design of the prefabricated joints is the research focus of prefabricated concrete structures,the key to ensure the force transfer between reinforcing bars and the structural performance is reliable connection of reinforcing bars at the connecting nodes.Constraint grout-filled lap connection of steel bar is a common form of vertical reinforcement connection in prefabricated concrete structure.At present,there are some problems in this connection mode,such as complex hole forming technology,overlong lap length,unclear research on the impact of the connection performance,and so on.In order to simplify the holeforming process and shorten the lap length effectively,the prefabricated hole with embedded metal bellows for constraint grout-filled lap connection of steel bar is put forward.The connection technology uses metal bellows to form holes and spiral stirrups are used to strengthen constraints,which simplifies the construction technology and improves the integrity of overlap section to a certain extent.In order to explore the ultimate lap length of this new type of connection and study the influence of different factors on the connection performance,six groups of 18 specimens are designed and manufactured with the parameters of concrete strength,steel bar diameter and lap length,and unidirectional pull-out tests were carried out to record the failure modes,load-displacement curves,stirrup strain curves and crack development of specimens.The main research contents of this paper are as follows: Firstly,the failure modes and crack development of specimens under different influencing factors were studied to accurately grasp the influence of various factors on the connection performance;Secondly,the mechanical models of concrete sections under stress different development state are established,the bearing capacity calculation formula is deduced,and the stress state boundary of each specimen is distinguished;Thirdly,regression analysis of ultimate bond stress is carried out based on test data,and the ultimate lap length is solved by approximate method;Fourthly,the formula for calculating the ultimate lap length is established,and the applicability of the formula is verified by comparing with the results of relevant studies;Finally,the finite element simulation analysis is carried out,and the bond slip between interfaces is considered reasonably in different ways,and the simulation expansion analysis is completed.Research proves that the diameter and lap length of reinforcing bar are the main factors affecting the failure mode of specimens;concrete strength and bellows diameter are important parameters in calculating the ultimate lap length;the finite element analysis method can carry out effective simulation demonstration and expand the analysis work;the test results show that the specimens with 0.7 times of the basic anchorage length have reliable connection performance,the theoretical analysis results show that 0.64 times of the basic anchorage length can realize effective stress transfer between overlapped reinforcement bars.This new connection method is safe and reliable,has great optimization space in hole forming technology and lap length,and has good application prospects. |
