Study On Mechanical Properties Of PBL Shear Connector Groups In Hybrid Structures

Latest research findings on PBL shear connectors were summarized firstly, three batches and twenty-eight groups of large-scale PBL shear connector specimens were designed and tested according to above research, then static properties and deformation behavior of PBL shear connectors were studied deeply, their bearing mechanism was revealed, inner relationship between the shear connector groups and the single connector was clarified, ultimate bearing capacities on PBL shear connector groups in hybrid structures were evaluated precisely, load-transfer laws on PBL shear connector groups were probed, a load-transfer model of PBL shear connector groups suitable for engineering application was presented. Therefore, the study was focus on the following six aspects:(1) In order to obtain the microscopic mechanical characteristics of reinforced concrete dowels and restraints perpendicular to perforated plates, test systems of distributed fiber sensors were adopted to effectively acquire strain distribution characteristics of the core parts of PBL connectors. Based on the theory of Beam of Elastic Foundation and the principle of Modified Conjugated Beam, mechanical behavior and deformation characteristic of perforated rebars were analyzed, theoretical formulation on the yield slip of PBL connectors was suggested. Based on distributed strain measurement of transverse rebars in surrounding concrete and theoretical analysis, the relationship curves between vertical slip and transverse dilation deformation on interfaces of perforates plates were proposed for further study of bearing mechanism. Experimental findings on bearing mechanism of PBL connectors show that dowel action has a slighter contribution to bearing capacities of PBL connectors before yielding of connectors, and the dowel action becomes more and more apparent at later loading stage because of "cable effect" caused by the kink deformation of perforated rebars.(2) Combined the shear-transfer theory on concrete interface with finite element analysis, the shear-friction mechanism on PBL connectors was expounded, and the mechanism is that:cracking of concrete dowels under exterior loading, then transverse dilation deformation between two cracked sliding surfaces is produced by the action of aggregate interlock, it leads to counter activated clamping force caused by confined rebars perpendicular to perforated plates, and greater shear-friction effect is caused by above clamping force in the oval area nearby openings of perforated plates, it constitute bearing capacities of PBL connectors along with the cohesion force on the interface of perforated plate and the dowel force of perforated rebars. Based the analysis of bearing mechanism on PBL connectors in hybrid structures, formulations of ultimate bearing capacity in their fullest theoretical sense were presented. Calculated results show that the formulas have a higher accuracy.(3) Main difference between PBL connectors in hybrid structures and PBL connectors in composite beams comes from significant difference of transverse restraints, so the upper bound index and lower limit index of transverse restraints in PBL connectors were determined on basis of related clauses of shear-friction theory suitable for bearing mechanism analysis of PBL connectors. Based on the strut-and-tie model and local compression theory of concrete, expressions of proper construction and detailed index for PBL connectors were suggested, and the theoretical minimum space of multi-rows PBL connectors to prevent splitting failure of concrete was proposed, above analysis provided theoretical basis for engineering design and application of PBL connectors.(4) Base on nonlinear FEM method, constitution models of the metallic material related on ductile damage and shear damage were introduced, plastic deformation, damage development and failure property of perforated rebars in multi-rows PBL connectors were studied deeply, calculating method on the discount coefficient of "cable effect" and the damage discount coefficient of shear-friction effect were presented, then formulations on the ultimate bearing capacity of PBL connector groups was proposed. Based on a mass of measurement data, calculation formulas on the elastic stiffness of PBL connectors were suggested. Combined with the shear-friction mechanism, the serviceability limit index of PBL connector groups was determined comprehensively. Multi-parameters" constitutive equation of PBL connectors was established on the basis of the Fast Simulation Annealing algorithm.(5) In order to identify the interactive influence among multi-rows and multi-columns PBL connectors, a method of spring analogy on clamping effect of perforated rebars was introduced, formulation of influence radius of a PBL connector were suggested on the basis of the theory of Elastic Foundation Plate. Strain distribution of perforated plates was investigated by the measurement of distributed fiber sensors, it shows that the spatial distribution of perforated plate’s strain along loading direction may be degenerated to two-dimensional strain distribution, and normalized strain of perforated plates along loading direction may be characterized by Lorentz curves. Based on the mathematical properties of Lorentz probability density curves which characterized the normalized strain distribution of PBL connectors, the analytical continuum method was introduced, the fundamental differential equations which can reflect the vertical mechanical characteristics of PBL group specimens were deduced, the iterative algorithm on the load-transfer model of PBL connector groups was presented. Compared to test results, the algorithm proposed above has advantages of convenient calculation, distinct meaning in theory and enough engineering accuracy.(6) In order to simulate the bearing capacity and load-transfer behavior of PBL connectors, Arbitrary Lagrangian-Eulerian (ALE) method and Subcycling Integration Algorithm were introduced, secondary development to extend material properties of concrete was conducted, USDFLD programs were developed to fulfill the effective simulation of the function gradient model on the dilation angle of concrete. Using the above method, properties about the dilation of concrete dowels, progressive damage of perforated rebars and hardening behavior after yielding of PBL connectors were described accurately. Then more detailed parametric selection to FEM analysis of PBL connectors was presented, it provided an experience reference to the numerical analysis of PBL connectors.