# Study on Shear Performance of Web-Embedded Composite Shear Connector
## 2 Push-Out Test
### Test Process and Failure Pattern  
(1) External failure pattern  
According to the failure mode of each specimen (as shown in Figure 7), the crack failure mechanism of the WECSC is as follows: (1) Vertical cracks appeared on the outer side of the concrete, extending from the bottom to the upper side. Subsequently, the cracks expanded in all directions and continued to expand vertically with a high probability, which was caused by the dilatancy effect of the compressive concrete of the specimen. (2) The cracks in the upper part of the concrete originated at the hole in the steel web and extended along the steel bar axis. (3) Oblique shear cracks appeared inside the concrete slab, generally starting at the position from where the upper row of steel bars ran through and extending diagonally downward from the steel-concrete junction. (4) The front concrete was pulled apart in the vertical direction, and the crack extended upward from the bottom, corresponding to the hole position. (5) With the development of cracks, the concrete front cracks connected with the top cracks or with the inner cracks such that the inner wall of the concrete was split off entirely. When the cracks were on the front, the inside and top three sides of the concrete were connected, network cracks formed, and the inner wall concrete fell off as a sheet piece. The development of major cracks was accompanied by the crushing of the concrete in the cracks, as well as the concrete at the bottom. In addition, concrete cracking and spalling became increasingly evident with an increase in the internal components of the specimens. The change in the diameter of the penetrating rebar mainly affected the crack development in the top concrete. The larger the diameter, the more obvious the crack development along the penetrating rebar and the more obvious the steel-concrete separation phenomenon. Increasing the end bearing  
Figure 6: Specim loading scheme. area resulted in an increase in small cracks outside the concrete; however, it weakened the tendency of crack widening. (2) Internal failure pattern  
(1) Embedded steel web  
As shown in Figure 8, no visible buckling deformation or plastic deformation was observed. The concrete dowel in the P-0 specimen was cut, and a certain amount of concrete broke owing to the absence of a reinforcing bar in the opening hole. The remaining steel plate holes were arranged with penetrating rebars; thus, the concrete in the holes was subjected to the joint action of embedded steel web and penetrating rebars, accompanied by shear damage. (2) Stud  
Shear failure did not occur in any of the studs because the arrangement of the stirrup resulted in the concrete restraining the studs and the reinforcement bore a part of the shear force. Consequently, all studs in the test pieces were bent and deformed at the root. The degree of stud bending in the P-14-S specimen was significantly higher than that in the P-22-S specimen because the penetrating rebar in the P-22-S specimen bore greater shear. The damage patterns of the studs are shown in Figure 9.  
Figure 7: Overall failure mode of P-18-S specimen in static push out test. (**a**) Specimen top; (**b**) specimen face; (**c**) inner side of specimen; (**d**) specimen outer side. Figure 8: Damage pattern of perforated steel plate. (**a**) Steel plate is not buckling; (**b**) concrete dowell cut in the hole; (**c**) no plastic deformation; (**d**) shear failure. Figure 9: Stud failure pattern. (**a**) P-14-S specimen; (**b**) P-22-S specimen. (3) Penetrating rebar  
The failure mode of the penetrating rebars was flexural shear failure along the loading direction instead of shear failure. Furthermore, the degree of bending of the upper bars was higher than that of the lower bars, indicating that the upper bars exhibited higher shear degrees. Because the end-bearing area shared a portion of the shear force, the bending degree of the penetrating rebar in P-18-S# specimen was smaller than that in P-18-S, and the same was true for the other specimens.