# Study on Load-Slip Curve of a PBL Shear Key at a Steel-Concrete Composite Joint
###### Abstract
The study showed that the essence of the working mechanism of the PBL shear key group is the result of the coordinated deformation of steel, concrete members, and various PBL keys. The study of the PBL shear key group needs a strong basis and method for the study of a single PBL shear key. [PERSON] et al. [9] observed that environmental stress, material strength, plate opening, the penetrating steel bar's size, and other factors influence the ultimate bearing capacity of PBL keys, which can be fitted by linear equations to determine the ultimate bearing capacity of PBL shear keys. [PERSON] [10] studied the breaking characteristics and influencing factors of PBL shear keys in each working stage and proposed the load-slip relation formula of PBL shear keys in the entire process under external load using a normalized treatment coefficient. [PERSON] et al. [11] used finite element analyses and observed that the failure process of PBL shear keys can be divided into three stages: linear, elastic, and plastic. Via the study of the load-displacement relationship of the PBL shear key, it was concluded that the stress mechanism is as follows: The initial concrete expands outward, the PBL shear key slips with the increase in load, and the concrete slips outward with the shear key. [PERSON] [12] designed the static failure tests of 13 groups of 45 specimens based on combinations of parameters such as the diameter of the steel plate's opening, the penetrating steel bar's diameter, the steel plate's thickness, concrete strength, and the number of opening rows. The load-slip relation formulas of single-row shear connectors and double-row shear connectors are fitted. Based on the calculation method of the PBL shear key's bearing capacity proposed by predecessors, it was observed that most calculation formulas are only suitable for push-out specimens with unilateral fixed-end bracings and unidirectional loading, some of which are only based on the fitting results of a large number of test data, and the load-slip calculation formula obtained is only a summary of experience and has no specific theoretical support. Some theoretical calculation formulas are too complex, and the prediction of relevant data requires many complex calculations, even requiring calculations using the help of software. The volume of required engineering operations is substantial, more time-consuming, and laborious. There are currently few experimental studies on the PBL shear key inside the composite joint; thus, it is necessary to seek a simple and reliable calculation theory. In order to provide stronger theoretical support for the theoretical calculation formula of the load-slip relationship of a single PBL shear key, using existing research results, this paper mainly draws lessons from the calculation method of the pile-bearing capacity issued by horizontal load and combines the study of separated ear plate joints in composite truss bridge joints. A theoretical formula suitable for separating the load-slip relationship of a single PBL shear key in the entire loading process of ear plate composite joints is proposed. Because a simplified straight-curved-straight-type load-slip curve is proposed, the critical point between compression yields and the failure of tenon concrete in the shear key is taken as the dividing point of each straight and curved section, which makes the calculation process more convenient; moreover, this provides a convenient design method for the design of PBL shear keys in new composite structure joints.