# Shear Behavior of Superposed Perfobond Connectors Considering Lateral Constraints
## 5 Conclusions  
In this study, the push-out test results for superposed perfobond connectors were obtained. The effects of lateral constraints on the mechanical properties and load-slip curves of the connectors were studied by varying the diameter of the perforating rebar, the stirrup form, and the concrete strength. In addition, the shapes, areas, and numbers of holes, as well as other parameters, were also investigated. Finally, based on the test results, a model for calculating the shear capacity of multi-hole superposed perfobond connectors was proposed. The main conclusions are as follows:  
(1) The crucial factors determining the lateral constraints on the concrete dowed are the concrete wrapping force, axial force of the perforating rebar, and transverse reinforcement constraints. When the specimen with a large lateral constraint was destroyed, the number of cracks on the concrete slab was larger, but the width was smaller than other specimens.  
(2) The failure mode of perfobond connectors with perfobond rib thicknesses exceeding 9 mm was double-sided shear failure. After the concrete slab was chiseled, the perfobond rib remained intact and exhibited little deformation, the concrete dowed exhibited a comparatively intact shear fracture surface and bending, and shear deformation occurred through the perforating rebar. Furthermore, the stronger the lateral constraints, the more the concrete dowels were prone to forced shear failure.  
(3) The shear capacity of the perfobond connector was determined by the hole area, the concrete strength, the perforating rebar diameter, and the number of holes. The shear stiffness depended on the bearing area of the concrete at the initial loading stage. Hence, it was primarily affected by the hole area and concrete strength.  
(4) The variation trend of the load-slip curve after the peak value mainly depended on the lateral constraints, areas, and numbers of holes. The stronger the lateral constraints, the smaller the hole areas, and the fewer the numbers of holes, the slower the bearing capacity of the connector decreased after reaching the peak value, and the load-holding capacities of the specimens were better. The load-slip curve of the single-hole connector  
Figure 19: Evaluation of the proposed capacity equation [6; 22; 23; 24].  
even showed characteristics consistent with those of inserted perfobond connectors with strong constraints.  
(5) An analytical model based on the double shear failure mechanism is proposed to calculate the shear capacity of the superposed perfobond connectors considering the lateral constraints. The equation considers many factors and can more clearly describe the shear mechanism of connectors. Therefore, the equation is valid to predict the shear capacities of multi-hole connectors.  
(6) In the actual engineering design, when the construction conditions are limited, such as the height of the concrete slab or the hole spacing of the perfobond rib is limited, the lateral constraints of the concrete dowel can be improved by changing the hole shape or increasing the transverse reinforcement in the slab, so as to improve the bearing capacity of the connector.  
Conceptualization, J.G. and Q.S.; methodology, T.L.; software, J.G.; validation, G.M. and J.G.; formal analysis, T.L.; investigation, J.G.; resources, Q.S.; data curation, J.G. and T.L.; writing--original draft preparation, J.G.; writing--review and editing, Q.S.; visualization, G.M. and T.L.; supervision, Q.S.; project administration, Q.S.; funding acquisition, Q.S. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Natural Science Foundation of China, grant number 51878540.  
Not applicable.  
The authors are grateful for the financial support from the National Natural Science Foundation of China (Grant No. 51878540).  
The authors declare no conflict of interest.